PolymerChemistry

PAPER

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Departement de chimie and Centre de reche

Faculte des sciences et de genie, Universite La

Canada G1V 0A6. E-mail: josee.brisson@chm

418 656 3536

† Electronic supplementary informationcalculations using NMR, and a table shand relative intensities. See DOI: 10.1039/

Cite this: Polym. Chem., 2014, 5, 2548

Received 23rd August 2013Accepted 19th December 2013

DOI: 10.1039/c3py01138k

www.rsc.org/polymers

2548 | Polym. Chem., 2014, 5, 2548–2

Crystallization control of etherethersulfonecopolymers by regular insertion of an allylfunctionality†

Adrien Faye, Mikael Leduc and Josee Brisson*

Acyclic diene metathesis (ADMET) polymerisation and nucleophilic aromatic substitution polycondensation

are used to synthesize alternating copolymers based on polyetherethersulfone (PEES) blocks. ADMET

results in incorporation of trans-allyl groups with more than 94 to 98% selectivity. The resulting polymers

have a Mw of up to 13 600 g mol�1 and low dispersity (Đ ¼ 1.1 to 1.4). Polycondensation, on the other

hand, allows incorporation of either cis- or trans-allyl groups depending on the starting monomers.

Molecular weights in the same range are obtained, but with much larger dispersity (up to 2.3), as

expected. Characterization by differential scanning calorimetry and wide angle X-ray diffraction shows

that incorporation of the cis group completely suppresses crystallization, whereas that of the trans group

results in semi-crystalline polymers. Crystallinity is lost post-melting, but can be restored using

appropriate solvent treatments. The crystal form changes with the length of the etherethersulfone (EES)

group indicating that, when the repeat unit is small (containing a 4-ring etherethersulfone (EES) block),

the allyl function is incorporated into the crystallographic repeat, whereas when the EES segment

increases to eight rings, the allyl group is excluded from the crystal phase. Post-functionalization of the

allyl group is demonstrated by using hydrogenation. The resulting polymer adopts a different crystal

form for the 4-ring block, but the same crystal form for the 8-ring block, confirming the dependence on

the block length for incorporation into the crystallographic repeat unit.

Poly(ethersulfones) (PES) and poly(etherethersulfones) (PEES)show outstanding thermal, chemical and radiative perfor-mances and are found in many applications.1 Modulation ofproperties such as hydrophobicity,2 amphiphilicity,3 glasstransition temperature4 or morphology via self-organization5

through random or block copolymerization has been proposedto improve their properties and tailor these to specicapplications.

Little attention has been given to one specic morphologicalfeature, which markedly inuences the resulting polymerproperties: crystallinity. This is due to the fact that, in spite oftheir regular structure, polyethersulfones are generally consid-ered as being amorphous. Although they are oen slightlycrystalline as synthesized, melting during processing destroysthis crystallinity, and annealing does not allow us to restore it.This is an unusual feature for such a regular homopolymer,partly attributed to an abnormally narrow interval between Tg

rche sur les materiaux avances (CERMA),

val, 1045 Avenue de la Medecine, Quebec,

.ulaval.ca; Fax: +1 418 656 7916; Tel: +1

(ESI) available: NMR spectra and Mn

owing X-ray diffraction peak positionsc3py01138k

560

and Tm.6 However, long-term crystallization occurs, and as theinitially amorphous polymer slowly crystallizes, voids andcracks may appear due to morphology reorganizations, therebycontributing to premature failure.

Control of semi-rigid polymer crystallization through theintroduction of regularly inserted spacers has been the object ofattention in our group. Previous work has shown that intro-duction of exible aliphatic chains of six to eight methyleneunits did not decrease the crystallinity of poly(para-phenyleneterephthalamides)7 (PPTA) and poly(etheretherketones)8

(PEEK), and that single crystals could be obtained, the exiblespacers being segregated at the crystal surface and acting as foldsites. A crystallizable rigid block of one and a half repeat unitwas found sufficient for the resulting crystal structure to be thesame as that of the parent rigid homopolymer in PPTA-basedcopolymers,7 in agreement with the previously proposed valueof one repeat unit.9 Below this minimum requirement, thecrystallographic repeat unit will correspond to a combination ofunits forming a new homopolymer with a crystal structuredifferent from that of parent units.

In this work, two aims were sought: rstly, synthesis of PEEScontaining post-functionalizable groups was targeted. Thesewill allow ne-tuning of various properties of the resultingpolymers while minimizing synthetic efforts. Various applica-tions may in this way be targeted, but in the present work, only

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the proof of concept will be made. Secondly, as a demonstrationof the ability to modify polymer properties through incorpora-tion of an allyl spacer, modulation of the PEES ability to crys-tallize was selected. The cis and trans isomers of the allyl groupoffer the possibility of investigating whether the grouppromotes chain folding, either by pre-orientation of chains inan antiparallel fashion or alternatively by favoring regularalignment along the chain direction. In this respect, such asystem can bring a different light on the possible mechanism ofpolymer crystallization.

In the present work, two different synthesis approaches wereused: acyclic diene metathesis polymerization or ADMET for itslow polydispersities and nucleophilic aromatic substitutionpolycondensation, which allowed synthesis of cis- or trans-allylcopolymers by changing the spacer inserted between rigidblocks. A rigid ethersulfone block of four aromatic rings wasrst studied, and preliminary work on eight-ring blocks will alsobe reported. In both cases, results are discussed in terms of theability of the allyl group to either inhibit or promote crystalli-zation, the effect of dispersity and the number of repeat units inthe regular block. A few post-synthesis modications weremade, to illustrate the concept of property changes throughpost-functionalization.

Experimental sectionInstrumentation

Nuclear magnetic resonance (NMR) spectroscopy measure-ments were performed in CDCl3 or dimethyl sulfoxide-d6solutions on a Bruker AMX 400 MHz at room temperature.

Size exclusion chromatography (SEC) was carried out on asystem composed of a 515 HPLC pump, two Agilent PL-GelMixed B-LS columns and a UV detector Model 441 coupled to aLASER Dawn DSP photometer. Monodisperse poly(styrene)standards were used for calibration and chloroform (CHCl3) aseluent at a ow rate of 1.0 mLmin�1. The sample concentrationwas 0.175 mg mL�1. Chromatograms were analyzed with theASTRA soware version 4.70.07.

Thermogravimetric analyses (TGA) were performed on aMettler TGA/SDTA851e/SF/1100 �C equipped with an MT1balance, under a nitrogen atmosphere.

Glass transition Tg and melting temperatures Tm weredetermined as the midpoint of the transitions using a differ-ential scanning calorimeter (DSC) Mettler DSC823e apparatusunder a nitrogen atmosphere. The scan rate was 10 �C min�1

and liquid nitrogen was used for cooling purposes. In somecases, cooling rates down to 1 �C min�1 were used, and theselected samples were also annealed between Tg and Tm1 for 15minutes to 24 hours. In all cases, the STARe soware version9.30 was used for data acquisition and processing. The degree ofcrystallinity was estimated by DSC using the following equation:

cDSC ¼ DHm

DHom

� 100 (1)

where DHm is the melt enthalpy, determined as the area underthe melt endotherm, and DHo

m is the melt enthalpy of acompletely crystalline sample. For the polymers synthesized in

This journal is © The Royal Society of Chemistry 2014

this work, as the value of this constant was not known, as a rstapproximation the value of 130 kJ g�1 for a polymer with asimilar chemical structure, poly(etheretherketone), wasused.10

Crystallinity was studied by wide angle X-ray scattering(WAXS), using a Bruker diffractometer equipped with a Kris-talloex 760 generator, a 3-circle goniometer and a Hi-Star areadetector. The generator produced graphite monochromatizedcopper radiation (Cu Ka ¼ 1.54178 A) at 40 kV and 40 mA.Diffraction diagrams were recorded in the transmission mode.Crystallinity cX-ray was estimated from the following equation:

cX-ray ¼Icryst

Itotal� 100 (2)

where Itotal is the total integrated intensity of the diffractioncurve and Icryst is the intensity of the crystalline peaks, deter-mined by integrating the diffraction curve aer subtraction ofthe amorphous halo of a representative amorphous polymer.

Molecular models were built using HyperChem Pro 6.0(Hypercube, Inc), energies minimized using the block diagonalNewton–Raphson method until a root mean square gradient of0.1 kcal A�1 mol�1 was reached, and the force eld usedwas MM+.

Materials

Bis(4-uorophenyl) sulfone (99%), 4-methoxyphenol (99%),allyl iodide (98%), boron tribromide (BBr3, 99.9%), N,N-dime-thylacetamide (DMAc, 99+%), N-methyl pyrrolidone (NMP),Grubbs 2nd generation catalyst (G2), Hoveyda–Grubbs catalyst(HG) and palladium 10 wt% on activated carbon were allsupplied by Sigma Aldrich and used without any purication.Anhydrous acetone (C3H6O, 99.7%), tetrahydrofuran (THF) anddimethylsulfoxide (DMSO) were purchased from Fisher Scien-tic and used directly. Dichloromethane (CH2Cl2, FisherScientic, 99.9%) was dried by stirring with CaH2 and thendistilled prior to use. Anhydrous potassium carbonate (K2CO3,99%) was supplied by EMD.

Synthesis of monomers

4,40-Bis(4-methoxyphenoxy) diphenyl sulfone (MPDS). Around bottom ask (25 mL) was charged with 10.002 g (39.340mmol) of bis(4-uorophenyl) sulfone, 9.767 g (78.680 mmol) of4-methoxyphenol and 11.962 g (86.548 mmol) of potassiumcarbonate. To this mixture was added 40 mL of DMAc and theresulting solution was stirred and heated to 180 �C over thecourse of 4 hours using an oil bath, as shown in Scheme 1. Thereaction mixture was allowed to cool and precipitated into a 1 MHCl aqueous solution, ltered and washed with a saturatedNaCl aqueous solution three times to remove DMAc andpotassium carbonate.5 The white solid was dried in vacuo at60 �C for 8 hours (15.2 g, 32.8 mmol, 83%).

1H-NMR 400 MHz (CDCl3, r.t.): d 7.82 (d, 4H, 3J ¼ 8.94 Hz,4J ¼ 2.50 Hz), 7.26 (CHCl3), 6.97 (d, 4H, 3J ¼ 8.94 Hz, 4J ¼ 2.50Hz), 6.94 (d, 4H, 3J¼ 8.94 Hz, 4J¼ 2.50 Hz), 6.90 (d, 4H, 3J¼ 8.94Hz, 4J¼ 2.50 Hz), 3.82 (s, 6H), 1.56 (H2O) ppm; 13C-NMR (CDCl3,

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Scheme 1 Synthesis of monomer precursors: (a) APDS (4-ring) precursor and (b) HPSPPDS (8-ring) precursor.

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r.t.): d 162.7, 156.8, 147.9, 134.9, 129.5, 121.7, 116.8, 115.1,55.5 ppm.

4,40-Bis(4-hydroxyphenoxy) diphenyl sulfone (HPDS). Asadapted from by Hayakawa et al.,5 a round bottom ask (25 mL)containing a magnetic stirrer was charged with 8.001 g (17.300mmol) of 4,40-bis(4-methoxyphenoxy) diphenyl sulfone (MPDS).To this mixture was added 20 mL of dichloromethane, and theresulting solution was treated dropwise with 13.1 mL(138 mmol) of boron tribromide under completely dry condi-tions and under nitrogen. The solution was stirred for 1 hour at0 �C, an additional 5 hours at room temperature and thenpoured into cold water (500 mL). The precipitate was lteredand recrystallized from dichloromethane to purify it beforebeing dried in vacuo at 60 �C for 8 hours (7.513 g, 17.29 mmol,99.96%).

1H NMR 400 MHz ((CD3)2SO, r.t.): d 9.52 (s, 2H), 7.84 (d, 4H,3J ¼ 8.94 Hz, 4J ¼ 2.14 Hz), 6.99 (d, 4H, 3J ¼ 8.94 Hz, 4J ¼ 2.14Hz), 6.94 (d, 4H, 3J¼ 8.94 Hz, 4J¼ 2.14 Hz), 6.80 (d, 4H, 3J¼ 8.94Hz, 4J ¼ 2.14 Hz), 5.76 (CH2Cl2), 3.34 (H2O), 2.50 (DMSO) ppm;13C-NMR (CDCl3, r.t.): d 163.0, 155.2, 146.4, 134.9, 130.1, 122.3,117.1, 116.9 ppm.

4,40-Bis(4-allyloxyphenoxy) diphenyl sulfone (APDS). Anhy-drous K2CO3 was added to a solution of 4,40-bis(4-hydroxy-phenoxy) diphenyl sulfone (HPDS) (4.518 g, 10.400 mmol) and18-crown-6 (0.566 g, 2.142 mmol) in acetone (20 mL). Thereaction mixture was stirred at room temperature for 2 hoursunder a nitrogen atmosphere, treated with allyl iodide (2.0 mL,

2550 | Polym. Chem., 2014, 5, 2548–2560

21 mmol) and heated at 60 �C for 6 hours using an oil bath. Thereaction mixture was cooled to room temperature, quenchedwith aqueous NaCl, and concentrated under reduced pressure.The crude product was diluted with dichloromethane andextracted with H2O. The organic layer was dried over MgSO4 andltered, and the solvent was evaporated. The white solidwas ltered and dried in vacuo at 60 �C for 8 hours (2.9 g,5.6 mmol, 54%).

1H-NMR 400MHz (CDCl3, r.t.): d 7.82 (dd, 4H, J¼ 9.02 Hz, J¼2.00 Hz), 7.26 (CHCl3), 6.96 (dd, 4H, 3J ¼ 9.27 Hz, 4J ¼ 2.50 Hz),6.94 (dd, 4H, 3J ¼ 9.02 Hz, 4J ¼ 2.00 Hz), 6.91 (dd, 4H, 3J ¼ 9.27Hz, 4J¼ 2.50 Hz), 6.01 (m, 2H, 3Jtrans¼ 17.28 Hz, 3Jcis¼ 10.51 Hz,3J¼ 5.30 Hz), 5.40 (ddd, 2H, 3Jtrans ¼ 17.28 Hz, 4J¼ 3.15 Hz, 2J¼1.60 Hz), 5.29 (ddd, 2H, 3Jcis ¼ 10.51 Hz, 4J ¼ 2.82 Hz, 2J ¼ 1.39Hz), 4.53 (dt, 4H, 3J ¼ 5.30 Hz, 4J ¼ 3.05 Hz, 4J ¼ 1.55 Hz), 1.56(H2O) ppm; 13C-NMR (CDCl3, r.t.): d 162.7, 155.9, 148.1, 135.0,133.0, 129.6, 121.7, 117.9, 116.9, 116.0, 69.2 ppm.

4-Fluoro-40-hydroxy diphenyl sulfone (FHDS). A roundbottom ask (25 mL) containing a magnetic stirrer was chargedwith 15.001 g (59.000 mmol) of bis(4-uorophenyl sulfone)(FPS) and 2 eq. of aqueous KOH 7.0 M (16.9 mL, 118 mmol). Tothis mixture was added 20 mL of DMSO and the resultingsolution was heated to 75 �C for 20 hours using an oil bath, asshown in Scheme 1b. The reaction mixture was allowed to cool,poured dropwise into 50 mL of water and washed 3 times with100 mL of toluene. The aqueous phase was recovered and thenacidied with 100 mL of HCl 8 M. The solution was stirred for

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5 minutes and then ltered. The white product obtained (13.1 g,51.9 mmol, 88%) was dried at 60 �C under vacuum for 8 hours.

1H-NMR 400 MHz ((CD3)2SO, r.t.): d 10.65 (s, 1H), 7.93 (d, 1H,3J ¼ 8.85 Hz, 4J ¼ 2.04 Hz), 7.75 (d, 1H, 3J ¼ 8.85 Hz, 4J ¼ 2.04Hz), 7.40 (d, 1H, 3J¼ 8.85 Hz, 4J¼ 2.04 Hz), 6.90 (d, 1H, 3J¼ 8.85Hz, 4J ¼ 2.04 Hz), 3.33 (H2O), 2.50 (DMSO) ppm; 13C-NMR 400MHz ((CD3)2SO, r.t.): d 165.6, 163.1, 138.5, 130.4, 129.9, 129.8,129.7, 129.2, 116.0 ppm.

4-Fluoro-40-methoxy diphenyl sulfone (FMDS). A roundbottom ask (25 mL) containing a magnetic stirrer was chargedwith 3.279 g (13.00 mmol) of 4-uoro-40-hydroxy diphenylsulfone (FHDS), 1.845 g (13.00 mmol) of iodomethane and 2.156g (15.60 mmol) of potassium carbonate. To this mixture wasadded 20 mL of DMAc and the resulting solution was heated to75 �C for 20 hours using an oil bath (Scheme 1b). The reactionmixture was allowed to cool and precipitated dropwise into 150mL of aqueous KOH 1M. The solution was stirred for 5 minutesand then ltered. The white product obtained was dissolved indichloromethane and ltered, and the solvent was evaporatedunder reduced pressure. The product was dried at 60� undervacuum for 8 hours (3.400 g, 12.77 mmol, 98%). 1H-NMR 400MHz (CDCl3, r.t.): d 7.90 (d, 1H, 3J ¼ 8.89 Hz, 4J ¼ 2.13 Hz), 7.84(d, 1H, 3J¼ 8.89 Hz, 4J¼ 2.13 Hz), 7.26 (CHCl3), 7.12 (d, 1H, 3J¼8.89 Hz, 4J ¼ 2.13 Hz), 6.95 (d, 1H, 3J ¼ 8.89 Hz, 4J ¼ 2.13 Hz),3.83 (s, 3H), 1.56 (H2O) ppm; 13C-NMR 400 MHz (CDCl3, r.t.): d166.3, 163.8, 138.3, 132.8, 129.9, 129.7, 116.4, 116.2, 114.5, 55.58ppm.

4,40-Bis(4-(4-(4-methoxyphenylsulfonyl) phenoxy)pentoxy)di-phenylsulfone (MPSPPDS). A round bottom ask (25 mL) con-taining a magnetic stirrer was charged with 0.800 g (1.84 mmol)of 4,40-bis(4-hydroxyphenoxy) diphenyl sulfone (MPDS), 0.980 g(3.68 mmol) of 4-uoro-40-methoxy diphenyl sulfone (FMDS)and 0.560 g (4.05 mmol) of potassium carbonate. To thismixture was added 30 mL of DMAc and the resulting solutionwas heated to 180 �C over the course of 20 hours using an oilbath. The reaction mixture was allowed to cool and precipitatedinto a 1 M aqueous HCl solution, ltered and washed with asaturated NaCl aqueous solution three times to remove DMAcand potassium carbonate. The white solid was dried in vacuo at60 �C for 8 hours (1.62 g, 1.75 mmol, 95%).

1H-NMR 400 MHz (CDCl3, r.t.): d 7.87 (d, 4H, 3J ¼ 8.80 Hz),7.85 (d, 4H, 3J ¼ 8.80 Hz), 7.26 (CHCl3), 7.05 (s, 8H), 7.01 (d, 4H,3J ¼ 8.80 Hz), 7.00 (d, 4H, 3J ¼ 8.80 Hz), 6.95 (d, 4H, 3J ¼ 8.80Hz), 3.84 (s, 6H) ppm; 13C-NMR 400 MHz (CDCl3, r.t.): d 163.2,161.7, 161.4, 151.8, 151.6, 136.2, 135.6, 133.3, 129.7, 129.6,121.9, 121.8, 117.5, 114.4, 55.58 ppm.

4,40-Bis(4-(4-(4-hydroxyphenylsulfonyl)phenoxy)phenoxy)diphenyl sulfone (HPSPPDS). A round bottom ask (25 mL)containing a magnetic stirrer was charged with 2.966 g (3.200mmol) of 4,40-bis(4-(4-(4-methoxyphenylsulfonyl)phenoxy)phe-noxy) diphenyl sulfone (MPSPPDS). To this mixture was added20 mL of dichloromethane and the resulting solution wastreated dropwise with 3.9 mL (42 mmol) of boron tribromideunder the same conditions (synthesis and subsequent workup)as described for HPDS (2.25 g, 2.50 mmol, 78%). 1H-NMR 400MHz ((CD3)2SO, r.t.): d 10.6 (s, 2H), 7.91 (d, 4H, 3J ¼ 8.89 Hz),7.86 (d, 4H, 3J ¼ 8.89 Hz), 7.73 (d, 4H, 3J ¼ 8.89 Hz), 7.20 (s,

This journal is © The Royal Society of Chemistry 2014

8H), 7.12 (d, 4H, 3J ¼ 8.89 Hz), 7.10 (d, 4H, 3J ¼ 8.89 Hz), 6.89(d, 4H, 3J ¼ 8.89 Hz), 3.33 (H2O), 2.50 (DMSO) ppm; 13C-NMR400 MHz ((CD3)2SO, r.t.): d 161.9, 161.5, 161.1, 151.4, 151.2,136.1, 135.2, 131.1, 129.8, 129.7, 129.5, 122.3, 122.2, 117.7,116.1 ppm.

Copolymer synthesis

ADMET polymerization of poly(allyl-co-etherethersulfone)(PA-4EES). The APDS monomer (0.500 g, 0.971 mmol) was dis-solved in dichloromethane in a two-neck ask. The catalyst (G2or HG, 1–6.0 mol%) was then added and the reaction mixturewas stirred and heated at 40 �C using an oil bath under acontinuous, low nitrogen ow for one day. Subsequently, ethylvinyl ether (0.4 mL) was added to quench the reaction. Theobtained product was dissolved in dichloromethane andprecipitated by slowly dropping the solution into cold meth-anol, ltering off the solvent and washing the powder withacetone. To remove ruthenium, the polymer was dissolvedagain in dichloromethane and then washed three times with100 mL of a 0.224 M aqueous solution of sodium dieth-yldithiocarbamate trihydrate. The product was nally driedin vacuo at 60 �C overnight. The resulting polymers are desig-nated PA-4EES, where A stands for the allyl group polymerizedduring the ADMET reaction, and 4 corresponds to the numberof rings in the rigid ethersulfone monomer.

Polycondensation of PTA-4EES, PTCA-4EES, PTA-8EES andPCA-8EES polymers. A round bottom ask (25 mL) containing amagnetic stirrer was charged with 1.216 g (8.800 mmol) ofanhydrous K2CO3, 1.738 g (4.000 mmol) of the 4-ring monomerHPDS or 3.596 g (4.000 mmol) of the 8-ring monomer HPSPPDSand 0.500 g (4.000 mmol) of either (Z)-1,4-dichlorobut-2-ene(Z-DCB) or (E)-1,4-dichlorobut-2-ene (E-DCB). To this mixturewas added 10 mL of DMAc and the resulting solution washeated between 70 �C and 120 �C for one to two days using an oilbath. The reaction mixture was allowed to cool and precipitatedinto a 1 M HCl aqueous solution. The polymer was ltered anddried, redissolved in DMAc, and again precipitated to ensuresalt removal. The resulting polymers are abbreviated PTA-xEESfor the E-DCB synthesis with an x-ring monomer and PCA-xEESfor the Z-DCB synthesis.

Polycondensation of the PAE-4EES polymer. A round bottomask (25 mL) containing a magnetic stirrer was charged with0.869 g (2.000 mmol) of 4,40-bis(4-hydroxyphenoxy) diphenylsulfone (MPDS), 0.030 g (0.093 mmol) of tetrabutylammoniumbromide (TBAB) and 6mL of NaOH 1M. Themixture was stirreduntil everything was dissolved. To this solution was added 0.306g (2.000 mmol) of fumaryl chloride, and the mixture was stirredrigorously at room temperature for 4 hours. The supernatantaqueous layer was decanted and the mixture was then pouredinto hot water (200 mL) containing a few drops of concentratedhydrochloric acid. The crude product (0.850 g, 98%) wascollected by ltration, washed with reuxing methanol, anddried at 80 �C under vacuum overnight.

Hydrogenation to obtain PAH-4EES and PAH-8EES. In asolution of PTA-xEES (0.240 g) in dichloromethane (20 mL) wasadded 10 wt% palladium on activated carbon (0.080 g) while

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stirring at ambient temperature. The mixture was purged withhydrogen to replace the air in the ask and then stirred under ahydrogen atmosphere for 3 hours. The palladium activatedcarbon was ltered off, and the solvent was removed underreduced pressure to give the hydrogenated polymer with a 99%yield. The resulting polymers are abbreviated PAH-xEES, whereH stands for the hydrogenation of the allyl group. The sameabbreviation is used for polymers prepared by using the ADMETmonomers, the cis-containing or the trans-containing mono-mers, as these will yield the same polymer, the only differencebeing the average molecular weights and polydispersities,which remain, within experimental error, the same as thestarting polymer.

Halogenation to obtain PACl-4EES and PABr-4EES. A roundbottom ask (25 mL) containing a magnetic stirrer was chargedwith 0.375 g of PCA-4EES in dichloromethane (20 mL). Themixture was purged with argon and then stirred under a chlo-rine atmosphere for 3 hours. The solvent was removed underreduced pressure to give the chlorinated polymer with a 99%yield. The resulting polymer is abbreviated PACl-4EES, where Clstands for the chlorine of the allyl group.

A round bottom ask (25 mL) containing a magnetic stirrerwas charged with 0.600 g of PCA-4EES in dichloromethane(15 mL). To this solution was added dropwise, under vigorousstirring, bromine (0.036 mL, 0.815 mmol) in 2 mL of CH2Cl2, asadapted from ref. 11. The mixture was allowed to react for 2hours and then poured into water. The precipitated product wasltered and washed with ether. The brominated polymer, PABr-4EES, was obtained with a yield of 99.5%.

Recrystallization of polymers. Solvent recrystallisation wasperformed by dissolving 5 mg of a polymer in 5 mL of a solventor solvent mixture, and the solution was poured into a smallPetri dish and covered. For low boiling-point solvents (THF,CH2Cl2), samples were placed at 4 �C until evaporationoccurred. For samples with higher boiling points, evaporationwas performed at room temperature.

Results and discussionSynthesis of polymers

PA-4EES polymer obtained by ADMET polymerization.ADMET was used to polymerize a diallyl-terminated 4-ringmacromonomer obtained, as depicted in Schemes 1 and 2. The4-ring block corresponds to an etherethersulfoneether moiety,or EESE, but by analogy with the 8-ring monomer, it was chosento use the EES abbreviation for this polymer, this being thesequence common to both copolymers. The resulting copoly-mers are lm-forming, but lm brittleness was an indicator oflowmolecular weight. This was conrmed by NMR spectroscopyand SEC, as reported in Table 1. SEC determination of molec-ular weight is relatively straightforward, although the use ofpoly(styrene) standards can induce a systematic error onmolecular weights. NMR was therefore also used to quantifymolecular weights. Representative NMR spectra are presentedin Fig. 1. Three small-intensity signals appearing between 4.0and 6.3 ppm are related to terminal allyl groups, and decreasein intensity until they disappear into the background noise with

2552 | Polym. Chem., 2014, 5, 2548–2560

increasing molecular weight. To better visualize the attributionof these small-intensity peaks, in Fig. 1b is reported a close-upview of this spectral region, along with that of an allylatedmonomer. Protons appearing at the chain end are denoted by‘EG’ for the end-group, whether these appear as the polymerend-group or at the terminal position of the monomer. Peak fEGis a multiplet in the monomer and the copolymer, whereas peakf is a singlet next to this multiplet. A very small intensity peak isalso observable for the f protons of the cis fraction of the transcopolymer. Likewise, the e region presents a doublet for theend-groups and a singlet for hydrogen atoms in the main chain,and a small ‘cis’ peak is also observed. Spectra were used tocalculate number-average molecular weights Mn, as reported inTable 1 (see ESI† for details on Mn calculation), along withvalues obtained by SEC. As shown by SEC and as expected,ADMET polymers have low dispersity.

Molecular weights of 2000 g mol�1 were rst obtained. Inorder to increase the molecular weight, the amount and thenature of the catalyst, reaction temperature and reaction timewere varied,12 but the highest molecular weight achieved was arelatively low value of Mw of 8700 g mol�1 for 6% catalyst at40 �C for 24 hours using the Hoveyda–Grubbs catalyst. It isproposed in the literature that molecular weight can be limited,for this type of polymer due to a coordination bond occurringbetween the active center of the catalyst, i.e. ruthenium, and thesulfone group13 or the ether oxygen during the formation of ametallacyclobutane intermediate,14 thus disabling the catalyst.This phenomenon has been termed the “negative neighboringgroup effect”.15 Tindall et al.14 proposed that the optimumconditions for ADMET chemistry occur by positioning thefunctional group at least two methylene units distant from themetathesizing olen within the monomer unit. To add amethylene group between the allyl double bond and the etheroxygen was considered, but as this would probably decrease theglass transition temperature and degradation temperature ofthe resulting polymer, this was not pursued.

Polycondensation yielded slightly higher molecular weightswith the cis-monomer, which were found to be optimal for a reac-tion temperature of 120 �C, as reported in Table 1. For a reactiontemperature up to 150 �C, the molecular weight was relatively lowand no conversion of cis to trans allyl or trans to cis could bedetected. The use of higher temperatures resulted in highermolecular weights especially of the cis-allyl copolymers. Neverthe-less, the low reactivity of the hydroxyl group and high numberof termination reactions limited the obtained molar weight.

A second factor that may have contributed to obtaining lowmolecular weights is crystallinity. Crystalline polymers tend tobe less soluble than their amorphous counterparts, and as thepolymer crystallizes during polymerization, precipitation canoccur, and chain growth then stops, which leads to lowmolecular weights.16 This would also explain why temperaturehas a much more marked effect for the cis-allyl copolymers thanfor the more crystalline trans-allyl copolymers.

In order to further improve molecular weights, an additionalreaction was performed using an acid chloride terminated allylspacer instead of a chloride terminated spacer in order toreplace the ether linkage between the EES block and the allyl

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Scheme 2 Polymerization reactions: (a) acyclic dienemetathesis polymerization (ADMET) of the APDSmonomer, (b) polycondensation of HPDSwith (Z) and (E)-1,4-dichlorobut-2-ene, (c) polycondensation of HPSPPDS with (Z) and (E)-1,4-dichlorobut-2-ene and (d) polycondensation withfumaryl chloride to insert ester linkages.

Table 1 Molecular weights and dispersity of polymers synthesized by ADMET and polycondensationa

Polymers Reaction conditionsMn (NMR),g mol�1

Mn (SEC),g mol�1

Mw (SEC),g mol�1 Đ

PA-4EES G2, 1 mol% CH2Cl2, 24 h, 40 �C 2000 3300 3600 1.1PA-4EES G2, 6 mol% CH2Cl2, 24 h, 40 �C — 4900 6400 1.3PA-4EES HG, 1 mol% CH2Cl2, 24 h, 40 �C 2200 3600 4000 1.1PA-4EES HG, 6 mol% CH2Cl2, 24 h, 40 �C — 6200 8700 1.4PTA-4EES DMAc, 24 h, 70 �C — 2600 4600 1.8PTA-4EES DMAc, 48 h, 90 �C — 4100 5700 1.4PTA-4EES DMAc, 48 h, 120 �C — 900 1500 1.7PTA-4EES DMAc, 48 h, 150 �C — 900 1200 1.3PCA-4EES DMAc, 24 h, 70 �C — 4900 8500 1.7PCA-4EES DMAc, 48 h, 90 �C — 4700 7400 1.6PCA-4EES DMAc, 48 h, 120 �C — 8400 13 600 1.6PCA-4EES DMAc, 48 h, 150 �C — 1200 1900 1.6PTA-8EES DMAc, 24 h, 70 �C — 1700 1900 1.1PCA-8EES DMAc, 24 h, 70 �C — 1800 4100 2.3PAE-4EES CH2Cl2, 4 h, 20 �C 7700 38 000 4.9

a G2: Grubbs second generation catalyst, HG: Hoveyda–Grubbs catalyst.

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Fig. 1 1H-NMR spectrum of the representative monomer and poly-mers obtained by ADMET: (a) PA-4EES, Mn ¼ 2200 g mol�1 and (b)enlargement showing end-groups for PA-4EES with two differentmolecular weights and for the monomer.

Table 2 Proton chemical shifts (d) of the allyl group in cis- and trans-poly(etherethersulfones) obtained by polycondensation and byADMET (major configuration trans)

Polymers d (e) (ppm) d (f) (ppm)

PA-4EES 4.584 6.104PTA-4EES 4.580 6.097PCA-4EES 4.666 5.949

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spacer by an ester linkage, as shown in Scheme 2d. Due to thehigher reactivity of this group, reactions could be performed atroom temperature, and higher molecular weights were ach-ieved, as reported in Table 1. This polymer is a better candidatefor eventual applications, but exhibits a lower solubility and amuch higher polydispersity, thus making the ether-linkedcopolymers more interesting subjects for fundamental studieson crystallization.

PTA-xEES and PCA-xEES polymers obtained by poly-condensation. To know whether the polymer synthesized byADMET was in a cis or trans conguration, FTIR spectroscopy isnormally used. In the present case, overlap of ethersulfonevibration bands made such an attribution less straightforward.Therefore, it was decided to rely on NMR peak positions of allylprotons to determine this conguration. To have representativeNMR spectra with which comparisons could be made, poly-condensation reactions were performed to synthesize copoly-mers having the same chemical structure but with either cis ortrans allyl bonds, as shown in Scheme 2b. This approach furtherhas the advantage of yielding the desired allyl conformation bychoosing the right monomer, but does increase the resultingdispersity. Molecular weights and polydispersities of thesecopolymers were determined by SEC and reported in Table 1.

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The obtained copolymers are in the same range of molecularweights as those obtained by ADMET, but have much larger Đvalues, as expected.

NMR peak positions for the cis- and trans-allyl isomers aredifferent, allowing easy determination of isomers present, asreported in Table 2. In the trans copolymer spectrum, a smallpeak, which represents 10% of the total signal, is present at theposition of the cis isomer. This cis isomer is due to the presenceof 10% cis form in the initial E-DCB monomer (see Fig. S4 of theESI†), purication of the trans isomer being extremely difficult.This small portion therefore remains in the polymer.

Comparison of peak positions of PTA-4EES, PCA-4EES andPA-4EES polymers is reported in Table 2, and shows a matchbetween the ADMET polymer, abbreviated PA-4EES, and thetrans isomer (PTA-4EES). Inspection of the NMR spectra in Fig. 1shows that, in the ADMET polymer, from 1 to 6% of the cis formis present, which is less than that in the polycondensationpolymer, for which up to 10% cis isomer was present due totheir presence in the starting monomer. A very high stereo-selectivity is therefore achieved with both the Grubbs 2nd

generation and the Hoveyda–Grubbs catalysts for this polymer,along with a low dispersity, and with molecular weightscomparable to those of step-growth polycondensation, althoughmodest.

Polymers were synthesized using two ethersulfone blocks:the 4-ring block in polymers abbreviated PTA-4EES and PCA-4EES but which, as mentioned above, have a EESE block, andthe 8-ring block in PTA-8EES and PCA-8EES, which have aESEESEES block.

Post-polymerization reactions

Hydrogenation of the allyl double bond allowed us to obtainPAH-4EES and PAH-8EES copolymers withmore than 99% yield,thus demonstrating that the double bond remains highlyaccessible for future reactions, as expected. All copolymerssynthesized were hydrogenated post-reaction. A total absence ofpeaks related to the allylic function is noted in NMR spectros-copy (see Fig.S11c of the ESI†). Removing the double bondresults in the presence of a tetramethylene aliphatic spacer.This imparts additional exibility to the polymer, but may notbe sufficient to favor crystallization via chain folding, since evenwhen taking into account adjacent ether groups, this chainlength is small as compared to the minimum ve to eight bondrequirement estimated for most polymers.17–20

However, changing this segment will allow us to verifywhether the allylic group is incorporated into the crystallo-graphic unit, as changing from an allylic group to an aliphatic

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chain should provide enough structural variation to inducechanges in unit cell dimensions, conformation and packing,and should therefore result in observable changes in the X-raydiffraction diagram, as will be discussed later.

To further illustrate the possible modications of allylmodications, chlorination and bromination reactions wereperformed on PCA-4EES.These reactions were chosen for theirhigh yields, and hydrogen atom groups were replaced by chlo-rine or bromine atoms in a 99% yield in both cases, as deter-mined by proton NMR spectroscopy (spectra are reported inthe ESI†).

Fig. 3 Differential scanning calorimetry: (a) heating and cooling scansfor PA-4EES and (b) first heating scan for representative polymers.

Thermal properties of the copolymers

Thermogravimetric analysis (TGA). Polymers obtained byADMET and by step-growth polycondensation were character-ized by thermogravimetric analysis (TGA) to investigate theirthermal resistance, one of the assets of PES and PEES. As shownin Fig. 2, degradation starts around 370 �C, with a slightly betterthermal resistance for the cis polymers. For the 8-ring polymer,a second degradation step occurs around 550 �C, slightly abovethe poly(ethersulfone) homopolymer degradation temperature,which is around 400 �C.21 A decrease in degradation onsettemperature as compared to PES was expected due to theaddition of the exible, aliphatic containing allyl moiety in thepolymer chain.21 This loss in thermal stability is however in partcounterbalanced by the possibility of post-functionalizing theallyl group.

Differential scanning calorimetry (DSC). As one of the aimsof this work was to tune crystallinity by incorporating a spaceralong the PEES chain, differential scanning calorimetrybecomes a method of choice to investigate these polymers. Asmentioned in the Introduction, the temperature differencebetween Tg and Tm has been proposed to be one of the mainfactors inhibiting crystallization of poly(ethersulfones). DSCcan further determine the effect of thermal history oncrystallinity.

Several heating and cooling scans were performed, at aconstant speed of 10 �C min�1. Heating, cooling and reheatingscans of one of the polymers, PA-4EES, are reported in Fig. 3a.During the rst heating scan, two endotherm peaks appear,

Fig. 2 Thermal stability of representative 4-ring and 8-ring polymersas determined by thermogravimetry.

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corresponding to a double melting behaviour, consistent withthe presence of a crystalline phase. It was difficult to detect theglass transition during this rst scan, indicating a high crys-tallinity. During the cooling scan, a glass transition is clearlyobserved, but no crystallization peak is observed. In the secondheating scan, the glass transition still appears, and no meltingpeaks are observed. This is in agreement with the reportedbehaviour of poly(ethersulfones), which do not crystallizereadily aer melting.

Fig. 3b reports the rst heating scan of polymers synthesizedin this work. The same general behaviour was observed for alltrans-containing polymers (PA-4EES, PTA-4EES, PTA-8EES), inthe presence of a single or double melting peak in the rst scanand only a glass transition in subsequent scans, to which isoen superimposed a relaxation peak. NMR analysis of the

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PTA-4EES copolymer post-melting shows that the allyl group isstill in its trans form, thus eliminating the possibility that theincapacity to recrystallize aer melting is related to heat-induced isomerization of the allyl group. (NMR spectra arereported in the ESI.†) In some cases, a peak may be observed,but as on the second scan, this is replaced at the same positionby a glass transition, it is interpreted as a relaxation peaksuperimposed to the glass transition and not as a melt endo-therm (PAH-4EES and PCA-4EES). Only PA-4EES shows a doubleendothermic peak, which will be discussed separately.

In order to induce crystallization for initially amorphouspolymers, or to restore them aer melting for initially crystal-line polymers, various annealing treatments between Tg and Tm(at temperatures varying from 110 to 125 �C) were performed forup to 24 hours. Cooling down to 1� min�1 was also tested fromthe melt. In all cases, polymers remained completely amor-phous, in keeping with the usual PES and PEES thermalbehaviour. This clearly indicates that the incorporation of anallyl group does not increase crystallization speed enough toallow annealing-induced crystallization.

The exact position of the glass transition and melt endo-therms are reported in Table 3. The glass transition temperaturevaries slightly with the content of cis isomer (Tg decreases fromPC4-EES to PTA-4EES to PA-EES, which contains the leastpercentage of cis groups), which is attributed to a higher sterichindrance in the cis isomer. PTA-8EES stands out as being thelowest molecular weight polymer synthesized, which explainsthe observed Tg lower by approximately 20�. Upon hydrogena-tion of the allyl group, the glass transition endotherms shi to alower temperature, in agreement with a higher chain mobility.Upon chlorination and bromination of the allyl group, hinderedmobility due to the size of the substituents results in a return ofthe Tg to the value observed for the allyl copolymer. In othersynthesized copolymers, no notable effect of molecular weightwas observed on either Tg or melting point. In the 4EES series,the highest Tg was observed for the ester-linked PAE-4EES. Thevalue is higher by 5 to 10 degrees only, and this increase could

Table 3 Thermal properties and degree of crystallinity c ofcopolymers

Mw �103 g mol�1

Tg,�C

Tm1,�C

Tm2,�C

DHm,J g�1

cDSC(%)

cX-ray (%)

In.a Rec.a

PA-4EES 6.8 98 133 159 39.5 30 25 37PA-4EES 8.7 94 130 152 36.2 28 25 37PTA-4EES 4.1 108 140 — 28.2 22 23 28PCA-4EES 7.5 115 — — — 0 0 0PCA-4EES 13.6 115 — — — 0 0 0PAE-4EES 38 122 179 — 8.03 6 12 18PAH-4EES 7.5 105 137 — 10.1 8 18 25PCA-8EES 4.1 136 — — — 0 0 0PABr-4EES 14.1 112 127 — 5.88 5 5 —PACl-4EES 13.9 120 — — — — — —PTA-8EES 1.9 84 156 — 36.0 28 37 42PAH-8EES 4.1 115 — — — 0 0 50

a In.: initial, as synthesized, Rec.: recrystallized in a mixture of CH2Cl2and benzoyl alcohol.

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be attributed to the combined effects of chain rigidication bythe ester linkage and to the higher molecular weight of thiscopolymer. Tg also varies with relative proportion of EES, thissegment being more rigid than the ally spacer. The observedglass transition temperatures are smaller by approximately 70�

to 100 �C than those of PES (for which values of 205 (ref. 22) to230 �C (ref. 23) have been reported) or of PEES (210 �C valuereported by Kitipichai et al.).24

The melting points of the synthesized copolymers are alsonotably different from that of PES for which Johnson et al.indicate a value of 310 �C for PES.21 The highest value obtainedin this work was 179 �C for ester-linked PAE-4EES, againattributed to the higher chain rigidity and molecular weight ofthis polymer. For the ether linked copolymers, the highestmelting point observed is the second melting point of PA-4EES.More importantly, the difference between Tg and Tm remainswell below the usual 100 degrees value observed for mostpolymers, with values of 32 to 36 �C for the 4-ring ether-linkedblock copolymers, 57 �C for the ester-linked 4-ring copolymerand 72 �C for the ether-linked 8-ring block copolymer. It istherefore a lower temperature difference than that of PES,which is between 80 to 100 �C, in agreement with their inabilityto crystallize upon annealing. Therefore, this factor can beinvoked to explain the lack of crystallization upon annealing,although other factors must be at play to explain the observeddifferences from one polymer to another as synthesized.

Unfortunately, since little is known about the crystal struc-ture of PES or PEES, no melt enthalpy of the pure crystal formhas been reported. It is therefore not possible to determineaccurate crystallinity using DSC-measured melt enthalpy.Nevertheless, if supposing a value equal to that of poly-(etheretherketone), which are chemically similar but for whichthe crystal structure is different,25 crystallinity was estimatedand is reported in Table 3. Values obtained vary between 0 to28% for the polymers as synthesized.

X-ray diffraction. X-ray diffraction was performed to inves-tigate the crystallinity of the synthesized copolymers and tocompare their crystalline form. In order to have accurateinformation on the peak position, and to eliminate changesassociated with the use of different solvents or temperatures,samples were recrystallized. Annealing was not useful in thiscase, as demonstrated by DSC experiments. Only one methodhas been published for recrystallizing PES polymers, by slowevaporation of methylene chloride solutions at low tempera-tures.26 In the present work, various solvent systems were testedfor PA-4EES. For CH2Cl2 and THF, crystallization was conductedat cold temperature in order to obtain slow evaporation,following the work of Blackadder et al.26 For solvents whichnaturally evaporate slowly, this was not found necessary. X-raydiffraction diagrams of samples which yielded high crystallin-ities are reported in Fig. 4.

Whereas for the PA-4EES copolymer only a slight crystallinitywas observed in CH2Cl2, marked crystallinity could be obtainedby using THF, DMAc or NMP. Polymorphism may be present, asthe diffraction diagrams obtained in NMP present an additionalmedium-intensity reection near 47 �C. The best crystallinitywas obtained for a mixture of methylene chloride containing

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Fig. 4 X-ray diffraction diagrams of PA-4EES as recrystallized byevaporation from various solvents.

Fig. 5 X-ray diffraction diagrams of EES-containing copolymers: (a) assynthesized and (b) after recrystallization by evaporation fromdichloromethane–benzyl alcohol solutions.

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10% benzoyl alcohol with 7 reections clearly observed in the 20to 30 �C range, and several lower intensity reections observableat higher angles. This solvent system was subsequently used forall polymers synthesized in this work.

In Fig. 5a are reported the X-ray diffraction diagrams of theas-synthesized polymers, along with that of a low molecularweight PES (Mw ¼ 1600 g mol�1, Đ ¼ 1.15) previously synthe-sized in our group.25 The PES homopolymer is amorphous, buthas a relatively narrow peak width, which may indicate partialorganization in the amorphous phase. Diagrams correspondingto completely amorphous polymers with larger peak width areobtained for the cis-allyl polymers, PCA-4EES and PCA-8EES aswell as one of the two hydrogenated polymers, PAH-8EES.

All other polymers show a superposition of discrete diffrac-tion peaks over the amorphous halo. Trans-allyl poly-condensation PTA-4EES and ADMET PA-4EES copolymers sharethe same diffraction peak positions, and similar relativeintensities of the diffraction peaks as compared to the amor-phous halo, indicating similar crystallinities and conrmingthe DSC results. This similarity also conrms the NMR resultsshowing that PA-4EES comprises almost exclusively trans-allylgroups. Crystallinity can be sensitive to the solvent used, whichis not the same in both synthesis methods, but no markedeffects were found in this case. Upon hydrogenation (PAH-4EES), the diffraction diagram changes in terms of peak posi-tions and relative intensities, indicating that a new crystallineform is observed. This new form is closer to that of PTA-8EES, asthe most intense peaks are at the same position and relativeintensities are similar, which may indicate that a similar

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conformation and packing is adopted. Upon chlorination, nodiscrete diffraction peaks appear, but the ‘amorphous’ peak isvery narrow, much narrower than that of PES, a sign that amesophase with partial pre-ordering is probably present. Uponbromination, on the other hand, a few discrete diffraction peaksare observed, but the crystallinity as-synthesized is low, inagreement with DSC results. Various factors are most probably

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Fig. 6 Molecular models of chain folding due to allyl groups: (a) chainfold models and (b) extended chain conformation, showing deviationfrom linearity.

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at play and affect crystallization, which may include rigidity,steric hindrance, and electrostatic interactions, and whichaffect crystallization in an unpredictable way, the bulkier group(Br) not resulting in the lowest crystallinity. Finally, the 8-ringhydrogenated polymer is completely amorphous as synthesized.

From these observations, a tendency emerges: cis groupsincorporation along the main chain suppress crystallization ofthe as-synthesized polymer, whereas trans-groups promote it.Changes in the dispersity do not affect crystallinity as observedby X-ray diffraction, as demonstrated by the comparison of PA-4EES and PTA-4EES diffraction diagrams.

Once the polymers are recrystallized in a slowly evaporatingsolvent, higher crystallinities are obtained, and these allowbetter measurements of peak position and relative intensities,which are reported in the ESI.† Only two polymers remainamorphous, the two cis-containing polymers, as seen in Fig. 5b,which indicates that the cis group is more effective at sup-pressing crystallinity than the 4-carbon aliphatic chain. In thisgure is not reported PES, as this polymer does not have thesame crystal form and peak positions as the PEES-basedcopolymers of the present work (see ESI† for a detailed list ofpeak positions), and this diagram, which has been previouslyreported in the literature, would add little to the discussionhere. All other polymers are crystalline to various degrees. Thedegree of crystallinity cX-ray was calculated from the relativeintensities of the amorphous and crystalline peaks in X-raydiffraction and is reported in Table 3. In all cases, the benzylalcohol/CH2Cl2 solvent increases crystallinity.

The most impressive increase in crystallinity is noted forPAH-8EES, which did not crystallize upon synthesis, butbecomes the most crystalline polymer (50% crystallinity) aersolvent treatment.

In all cases, peak positions before and aer recrystallizationremain the same, and so do relative intensities, althoughchanges occur related to the presence of an important amor-phous halo in poorly crystallized samples. More signicantly,peak widths decrease due to the improvement in crystal phaseperfection and in crystallite size, allowing for a better peakresolution.

As before recrystallization, ADMET PA-4EES and poly-condensation trans copolymer PTA-4EES have almost superim-posable diffraction diagrams, indicating that the decrease indispersity does not affect noticeably crystallization for thismolecular weight range.

In terms of crystal form, various distinct diagrams areobserved. PTA-4EES and PTA-8EES have a completely differentdiffraction diagram. Neither corresponds to a known form ofPES, but unfortunately comparison to PEES could not be made,no X-ray diffraction diagram ever having been obtained to thebest of our knowledge for this polymer.

Observation of a different crystalline form for the 4-ringpolymer can be due to incorporation of the trans-allyl group intothe crystallographic repeat unit, the polymer thus behaving as adifferent homopolymer, due to the length of the regular blockEES which is very short. This is conrmed by comparing withthe diffraction diagrams of the hydrogenated, chlorinated andbrominated copolymers, which are markedly different,

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reecting different crystallographic repeat units and/or pack-ings. On the other hand, the PTA-8EES and its hydrogenatedcounterpart have the same structure, peak positions and rela-tive intensities matching, indicating in this case that the allylgroup and the aliphatic chain are excluded from the crystallo-graphic repeat unit and are therefore segregated in the inter-lamellar region.

The 4-carbon segment of hydrogenated polymers increasesthe exibility of the chain and entropy of the system, andbecomes a better position for chain folds and reorganization tooccur, thus favoring crystallization. On the other hand, trans-allyl also favors crystallization. Chlorination and brominationresult in intermediate crystallization, thus indicating thatpacking may be disrupted by steric hindrance. Molecularmodels were built to verify whether cis and trans allyl groupscould both lead to chain folding, and representative examplesare shown in Fig. 6. Models built show that both the cis andtrans groups can lead to chain folding. In both cases, thenumber of conformations leading to such chain folds is limited,and a very narrow window of torsion angles must be adopted,limiting the probability for folding to occur in such a close-packed way. Energies of the trans- and cis-isomer folds aresimilar (6.8 kcal mol�1 for the lowest energy fold built for the cisisomer, and 6.4 for the trans isomer), but result in small

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interplanar ring distances (from 3.7 to 5.3 A approximately),restricting these chain folds to crystal structures that allow suchclose packing. As various pieces of evidence point to the exis-tence of a helical conformation for PES25 and PEES, such foldsmay not t the required geometry for the adopted crystalstructures. On the other hand, cis- and trans-allyl groups alsoaffect relative chain alignment, as depicted in Fig. 6b: due totheir geometry and to unfavorable H/H contacts, cisconformers do not allow a coplanar segment to form, and chainbifurcation ensues, which may be a reason why this groupinhibits crystallization. On the other hand, trans segments canform extended conformations, thus favoring chain alignment,leading to the occurrence of pre-crystalline aggregates whichmay be precursors to the crystalline phase, in agreement withthe theories proposed by Allegra and Meille27 and by Strobl.28

Finally, the more rigid PAE-4EES copolymer shows a goodcrystallinity, thereby indicating that the addition of a rigidsegment next to the EES block favors crystallization.

Double melting behaviour. PA-4EES is the only polymer inthis study to exhibit a double melting behaviour, which is initself surprising, as PTA-4EES is structurally very similar, withhowever a higher dispersity and approximately 4% more ciscontent. Changes in relative endotherm intensity of the twopeaks have been noted from one synthesis to another, as shown

Fig. 7 Investigation of the double melting behaviour of PA-4EES: (a)representative DSC scans of PA-4EES and (b) X-ray diffractiondiagrams as synthesized and after annealing between Tm1 and Tm2 andrapid quenching.

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in Fig. 7a. These could not be associated with any specicsynthesis conditions or measured properties, and are attributedto random variations during precipitation conditions.

The double melting behaviour is common to many semi-crystalline polymers, and may be caused by the melting of asecondary structure within the spherulite,29 or to phenomenasuch as metastable crystals, secondary crystallization, occur-rence of crystal populations with different crystal forms, shapes,sizes or perfection.30–35 In order to determine what this doublemelting endotherm corresponded to in the present case,samples were heated between Tm1 and Tm2 and then quenched,and the resulting samples were analyzed by X-ray diffraction, asillustrated in Fig. 7b. Under these conditions, the amorphoushalo has grown considerably in intensity, denoting partialmelting of the samples. Diffraction peaks remain, as rstglance, at the same position as the initial sample. However, therelative intensities of the peaks vary in the 15 to 22� region.Further, the shoulder at 21.5� shis to 21.0� and becomes aclearly distinct peak and a new, weak intensity peak appears at37.5�. These changes indicate that a slightly different crystalform is present. Further work will be necessary to ascertainwhether this crystal form was present before partial melting butwent undetected due to the similarity in peak positions, orwhether a change in the crystal form occurs during partialmelting.

Conclusions

In this work, the objective was to synthesize PEES with an allylgroup regularly inserted in its backbone, and to obtain copoly-mers which could crystallize and which could be subjected topost-functionalization reactions, allowing a rapid and straight-forward change in properties. Two synthetic pathways wereused: ADMET polymerization using a Grubbs second generationcatalyst or a Hoveyda–Grubbs catalyst, and traditional step-growth polycondensation.

Regular trans-allyl containing semi-crystalline PEES-basedcopolymers of moderate molecular weight and low dispersitywere synthesized by ADMET. Polycondensation was used toobtain cis-allyl and trans-allyl copolymers of relatively lowmolecular weights, but higher polydispersities. Even highermolecular weights but also polydispersity were obtained byreplacing the ether linkage between the EES and allyl groups byan ester linkage. Post-modication was demonstrated by usinghydrogenation, chlorination and bromination reactions, whichoccured with more than 99% yield.

Modulation of crystallization upon design of the chainsequence by regularly inserting allyl groups was demonstrated.Crystallinity could be totally suppressed by using cis-allylgroups, whereas incorporation of trans-allyl groups regularlyinserted along the main chain favors crystallization. The 4-ringEES allyl block was too short for the crystal structure of PEES tobe adopted, and instead insertion of the trans-allyl group in thecrystallographic repeat unit occurs, as demonstrated by thechange in diffraction diagram upon hydrogenating this poly-mer. This is in agreement with a non-trans conformation ofethersulfone polymers, as proposed previously,25 which may

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require more than a single repeat unit for a helix conformationto be adopted. Changes in the allylic spacer therefore allowpartial control of crystallization of this polymer, and furthermodulations will be attempted in future work by attachingvarious groups at the allyl position, thus investigating the effectof steric hindrance or of specic interactions.

Acknowledgements

The authors wish to acknowledge the nancial support ofNSERC (National Research Council of Canada). Help fromPierre Audet (NMR spectroscopy) and Rodica Plesu (SEC, DSC)of the Departement de chimie, Universite Laval is also gratefullyacknowledged.

Notes and references

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