Preparation of Macromonomers by Copolymerization ofMethyl Acrylate Dimer Involving � Fragmentation

TAKAHIRO HARADA, PER B. ZETTERLUND, BUNICHIRO YAMADA

Department of Applied and Bioapplied Chemistry, Graduate School of Engineering, Osaka City University,Osaka 558-8585, Japan

Received 27 January 2003; accepted 9 June 2003

ABSTRACT: The unsaturated dimer of methyl acrylate [CH2AC(CO2CH3)CH2CH2-CO2CH3, or MAD] was copolymerized with various monomers to prepare copolymersbearing the �-unsaturated end group [CH2AC(CO2CH3)CH2O] arising from � frag-mentation of the MAD propagating radical. Copolymerizations of MAD with cyclohexyland n-butyl acrylate resulted in copolymers with �-unsaturated end groups, and in-creasing the temperature up to 180 °C resulted in an increase in the rate of � frag-mentation of MAD radicals relative to propagation. Only a small amount of unsatur-ated end groups was introduced by copolymerization with ethyl methacrylate (EMA),and the EMA content in the copolymer increased with temperature. These findingscould be explained by the reversible addition of the poly(EMA) radical to MAD. Thecopolymerization with ethyl �-ethyl acrylate (EEA) did yield a copolymer containingunsaturated end groups with MAD units as part of the main chain, although the sterichindrance of the ethyl group suppressed homopropagation and crosspropagation ofEEA, resulting in low polymerization rates. Therefore, the copolymerization of MADwith acrylic esters at high temperatures was noted as a convenient route for obtainingacrylate–MAD copolymers bearing unsaturated end groups at the � end (macromono-mer). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 597–607, 2004Keywords: radical polymerization; fragmentation; end group; macromonomers; co-polymerization

INTRODUCTION

Radical polymerization is a typical chain reactionthat involves propagating radicals as chain carri-ers and consists of elementary reactions such asinitiation, propagation, termination, and chaintransfer.1 Resonance, polar, and steric factors ofthe substituent bound to the carbon–carbon dou-ble bond of the monomer influence the polymer-izability. In the case of �-alkylacrylic ester, sub-stituents larger than the ethyl group actually pre-vent polymerization because of steric hindrance

against propagation.2–5 However, methyl �-(2-carbomethoxyethyl)acrylate, an unsaturateddimer of methyl acrylate (MAD) bearing the large�-carbomethoxyethyl group, polymerizes fasterthan methyl methacrylate (MMA). The propaga-tion and termination rate constants for MADhave been estimated to be kp � 19 L/mol s and kt

� 5.1 � 105 L/mol s, respectively, based on elec-tron spin resonance (ESR) quantification of thepropagating radical,6 and kp � 28.4 L/mol s hasbeen estimated by gel permeation chromatogra-phy (GPC) analysis of a polymer obtained bypulsed-laser polymerization at 60 °C.7 A compar-ison with the rate constants for MMA (kp � 510L/mol s and kt � 4.2 � 107 L/mol s at 60 °C8)reveals that steric hindrance of the 2-carbome-thoxyethyl group as an � substituent suppresses

Correspondence to: B. Yamada (E-mail: yamada@a-chem.eng.osaka-cu.ac.jp)Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 597–607 (2004)© 2003 Wiley Periodicals, Inc.

597

propagation and termination simultaneously.The suppression of termination is more signifi-cant than that of propagation, and the favorablebalance of slow propagation and slow terminationallows polymer formation by steric-hindrance-as-sisted polymerization.9

Some �-(substituted methyl)acrylate esters[CH2AC(CO2R)CH2X] with labile COX bonds atthe allylic position function as addition–fragmenta-tion chain transfer (AFCT) agents when X isBr,10–13 SR,14,15 or SO2Ar.16 The addition of a prop-agating radical to the double bond of an AFCTagent followed by rapid � fragmentation of the ad-duct radical leads to the formation of a small radicaland polymer bearing the 2-carbomethoxy-2-prope-nyl group [CH2AC(CO2CH3)CH2O] as the �-endgroup. The molecular weight decreases efficiently,and the end groups are introduced almost quanti-tatively if AFCT is sufficiently fast.10,17,18 The prop-agating radicals of MAD undergo both propagationand � fragmentation simultaneously as a result ofslow propagation due to steric congestion aroundthe radical center.6 The frequency of � fragmenta-tion relative to propagation increases with an in-crease in temperature because the activation en-ergy of � fragmentation (unimolecular reaction) ishigher than that of propagation (bimolecular reac-tion).6

The influence of AFCT on copolymerization hasbeen analyzed on the basis of the copolymer com-position, molecular weight, and end-group con-tent. The copolymer of styrene (St) with MMAprepared in the presence of methyl �-(bromom-ethyl)acrylate (MBMA) showed 1H NMR reso-nance due to the unsaturated �-end groups boundto the respective monomer units.17 In the case ofthe copolymerization of methyl �-(chloromethyl)-acrylate with MMA, the chloromethyl acrylatefunctioned as a monomer and an AFCT agentsimultaneously, forming the copolymer bearingthe �-chloro and the �-propenyl end groups.18

Although MAD has drawn attention as a polymer-izable AFCT agent, its efficiency as an AFCTagent is considerably lower than that of MBMA.MAD has the advantage of the resulting polymerbeing free of halogens, but the rate of fragmenta-tion of the MAD radical is not high enough for itto be a useful AFCT agent.

Recently, we have found that the �-propenylend group is as reactive as common monomersand that the polymers bearing the unsaturatedend group can be copolymerizable macromono-mers.19 Therefore, macromonomer preparation byAFCT has attracted considerable attention as a

means of preparing radically copolymerizablemacromonomer by radical polymerization.

This article deals with an investigation of theeffects of temperature and various comonomers inMAD copolymerization with the aim of accom-plishing the efficient introduction of the unsatur-ated end group. Temperatures as high as 180 °Cwere employed to facilitate AFCT, and the struc-tures of the copolymers were examined with 1HNMR spectroscopy.

EXPERIMENTAL

Materials

MAD was prepared as reported20 and was iso-lated by distillation under reduced pressure (bp� 80 °C at 3.5 mmHg). The purity and structureof the product were confirmed by 1H NMR spec-troscopy. Ethyl �-ethyl acrylate (EEA) was syn-thesized according to the Mannich reaction of eth-ylmalonic acid monoethyl ester.4 Cyclohexyl acry-late (CHA), n-butyl acrylate (nBA), ethylmethacrylate (EMA), and St were commerciallyavailable and were distilled under reduced pres-sure. Dimethyl 2,2�-azobis(isobutyrate) (MAIB)and 2,2�-azobis(2,4,4-trimethylpentane) (ATMP)were recrystallized from n-hexane. tert-Butyl per-oxide (TBP) was commercially available. Dicumylwas prepared by a mixture of TBP and cumenebeing stirred for 30 h at 130 °C, and the productwas recrystallized from methanol.21

Polymerization Procedure

All polymerizations and copolymerizations werecarried out in glass tubes sealed in vacuo. Afterpolymerization, the contents of each tube werepoured into a large amount of n-hexane [poly-(MAD) and copolymers with CHA, nBA, EMA andEEA] and aqueous methanol (copolymer with St),and the precipitated polymeric product was iso-lated by decantation. The copolymer compositionswere calculated from the intensity ratios of the 1HNMR resonances characteristic of the respectivemonomer units. The monomer reactivity ratios (r1and r2) were evaluated by a nonlinear least-squares procedure.22

GPC and NMR Spectroscopy

The number-average molecular weights (Mn’s) andweight-average molecular weights (Mw’s) of poly-

598 HARADA, ZETTERLUND, AND YAMADA

mers were determined with a Tosoh 8020 serieshigh-performance liquid chromatograph equippedwith columns for GPC packed with TSKgelG5000HHR, MultiporeHXL-M, and GMHHR-L con-nected in that order at 40 °C. Tetrahydrofuran wasused as an eluent, and standard polystyrenes wereemployed for calibration. The 1H NMR spectra wererecorded on a JEOL JNM-A400. Deuteriochloro-form and tetramethylsilane were used as the sol-vent and internal standard, respectively.

RESULTS AND DISCUSSION

Homopolymerization of MAD

Propagating radicals of MAD (MAD�) are involvedin propagation to extend the main chain, in �fragmentation to form the unsaturated endgroup, and in bimolecular termination, as shownin Scheme 1.

The rates of propagation and fragmentationare given by eqs 1 and 2, respectively:

Rp � kp[MAD�][MAD] (1)

Rf � kf[MAD�] (2)

where kp and kf denote the rate constants forpropagation and fragmentation, respectively. Ifthe �-end groups are formed exclusively by � frag-mentation of the MAD radicals, the formed poly-mer has the following structure:

The ratio of the content of MAD units in thepolymer to the content of the �-unsaturated endgroups is given by eq 3 is based on the assumptionthat the �-unsaturated end groups do not un-dergo further reactions. The intensity ratio of the1H NMR resonances assigned to the olefinic pro-tons of the end group to those assigned to themethoxy protons of the MAD units was employedto evaluate the [MAD unit]/[CH2AC group] ra-tio:6

[MAD unit][CH2AC] �

kp[MAD�][MAD]kf[MAD�] �

kp[MAD]kf

(3)

Table 1 shows Mn as determined by GPC andcalculated from the content of the unsaturatedend groups quantified by 1H NMR spectroscopyon the basis of the polymer structure previouslyshown. The Mw/Mn values were in the range of1.18–1.89. It should be kept in mind that the GPCmolecular weights (polystyrene equivalents) maybe somewhat underestimated because of reac-tions of the unsaturated end group introduced byfragmentation, which lead to branched struc-tures:

The kp/kf values over the temperature range of60–180 °C, estimated with eq 3, decreased mark-edly with an increase in temperature. The accel-eration of � fragmentation relative to propagation

Scheme 1

COPOLYMERIZATION OF METHYL ACRYLATE DIMER 599

was, therefore, confirmed in conformity with theresults for up to 100 °C in our previous article.6

The decrease in the value of kp/kf with increasingtemperature was, as expected, accompanied by adecrease in Mn. However, slow propagation due tothe temperature being near the ceiling tempera-ture (Tc)

6 might also have contributed to the ob-served decrease in Mn. The efficiency of the intro-duction of the unsaturated end groups can beassessed by examination of the quantityMn(GPC)/Mn(NMR), which approaches unity asthe efficiency increases; it rose from 0.40 to 0.71

as the temperature was increased from 60 to 180°C.

Copolymerization of MAD at 60 °C

Copolymerizations of MAD (M2) with CHA, nBA,EMA, EEA, and St (M1) were carried out at 60 °C,and typical results are listed in Table 2. MADunits were mainly incorporated into the mainchain, and only small amounts of MAD units wereintroduced as end groups, as shown by the valuesof [MAD unit]/[CH2AC]. No unsaturated end

Table 1. Polymerization of MAD in Benzene ([MAD] � 2.0 mol/L)

Temperature(°C)

Time(min)

Conversion(%)

Mn

(GPC)[MAD unit][CH2AC]

Mn

(NMR)Mn(GPC)Mn(NMR)

kp/kf

(L/mol)

60a 30 3.1 10,400 163 28,200 0.40 81.9100b 60 6.0 3,200 31 5,600 0.56 17.8130c 10 1.6 2,300 21 3,500 0.65 10.3180d 10 0.8 1,500 12 2,100 0.71 6.0

a [MAIB] � 0.01 mol/L.b [ATMP] � 0.01 mol/L.c [TBP] � 0.01 mol/L.d [Dicumyl] � 0.01 mol/L.

Table 2. Copolymerization of MAD with M1 in Benzene at 60 °Ca

M1

[M1] inComonomer

(mol %)Conversion

(%)

Copolymer

[M1](mol %)

[MAD unit][CH2AC] [Pn(MAD)�1]b

Mn � 10�4

(GPC)cMn(GPC)Mn(NMR)

d

CHA 10 0.72 7.7 102 1.3 0.3550 2.0 42.0 174 3.7 0.4670 3.5 63.0 360 5.3 0.44

nBA 10 1.4 8.2 202 1.4 0.3750 3.1 40.9 226 2.4 0.4170 4.8 58.6 276 4.0 0.42

EMA 10 2.6 19.1 276 1.6 0.2850 3.6 70.8 357 2.8 0.1770 5.1 83.4 —e 3.8 —

EEA 10 16.2 10.0 72 0.80 0.3850 4.1 41.5 80 0.47 0.3270 0.80 54.6 114 0.49 0.21

St 10 1.2 23.7 —f 1.2 —50 1.5 60.7 —f 1.2 —70 1.7 72.8 —f 1.3 —

a [M1] � [MAD] � 2.0 mol/L; [MAIB] � 0.01 mol/L.b Pn(MAD) denotes the number of MAD units per chain.c Mn of copolymer measured by GPC.d Mn(NMR) calculated from [MAD unit]/[CH2AC] and copolymer composition.e The CH2AC content was too low for the calculation of [MAD unit]/[CH2AC].f No unsaturated end groups detected by 1H NMR spectroscopy.

600 HARADA, ZETTERLUND, AND YAMADA

groups could be detected in the copolymer with St.The rate of polymerization was considerablylower for the copolymerization involving EEAthan for those involving the other monomers; thecopolymerizations with CHA, nBA, EMA, and Stwere carried out for 10 min to 1 h, whereas 6 hwas employed as the reaction time for the EEAcopolymerizations.

Table 3 shows the monomer reactivity ratios(r1 and r2) and the crosspropagation rate con-stants (k12 and k21). The r1 and r2 values forMAD–CHA copolymerization are similar to thosefor MAD–nBA copolymerization. The k12 and k21values indicate that the acrylate radicals rapidlyadd to MAD, whereas the additions of MAD rad-icals to the acrylates are much slower in confor-mity with the considerable steric hindrance dueto the � substituent of the MAD radical. The k21values (rate constants for the addition of MAD

radicals to monomers) are similar to kp of MAD,regardless of M1. The suppression of homopropa-gation and crosspropagation of MAD radicals is arequirement for efficient � fragmentation of MADradicals. Although 1/r1 (equal to k12/k11) is lessthan unity for the copolymerization with EMA,indicating a lower reactivity of MAD than EMAtoward the poly(EMA) radical, the value of 1/r1 forthe copolymerization with EEA is the largest forall the monomers investigated. However, the rateconstant for the addition of poly(EEA) radicals toMAD, k12 � 26.9 L/mol s, is considerably smallerthan that of poly(EMA), k12 � 405 L/mol s, be-cause of the more severe steric hindrance due tothe �-ethyl group of EEA.

The propagating radical of MAD is involved inadditions to M1 and MAD (M2), in fragmentationto form the unsaturated end group, and in bimo-lecular termination, as shown in Scheme 2. The

Table 3. Monomer Reactivity Ratios for the Copolymerization of MAD (M2) in Benzene at 60°C

M1 r1 r2

k11

(L/mol s)ak12

(L/mol s)bk21

(L/mol s)bkf

(s�1)

CHA 0.68 1.28 30,400c 44,700 15 0.23nBA 0.52 1.26 33,900d 65,200 15 0.22EMA 2.32 0.42 940e 405 45 0.12EEA 0.32 0.96 8.6f 26.9 20 0.42St 0.86 0.28 328g 381 68 —

a Propagation rate constant of M1 at 60°C.b k22 � 19 L/mol s at 60°C;6 k12 � k11/r1; k21 � k22/r2.c Reference 22.d Reference 23.e Reference 24.f Reference 5.g Reference 25.

Scheme 2

COPOLYMERIZATION OF METHYL ACRYLATE DIMER 601

ratio of the content of MAD units in the polymerchain to the content of the �-unsaturated endgroups in a copolymerization can be expressed asfollows:18

[MAD unit][CH2AC] �

k22[MAD�][MAD] � k21[MAD�][M1]kf[MAD�]

(4)

[MAD unit][CH2AC][MAD] �

k22

kf�

k21[M1]kf[MAD] (5)

It was assumed that the effects of the penultimateunit on propagation and fragmentation could beneglected, and so k22 is equal to kp for MAD. They-intercept yields k22/kf, and the slope corre-sponds to k21/kf. It follows that the value of r2 canbe obtained in a somewhat indirect manner fromeq 5. However, this method is expected to give aless accurate estimate of r2 than copolymer com-position analysis, and it is not pursued furtherhere. Figure 1 shows plots according to eq 5 forcopolymerizations of MAD at 60 °C; [MAD unit]/[CH2AC] was determined by 1H NMR spectros-copy. The fraction of MAD radicals that undergopropagation, as opposed to fragmentation, in-creases with decreasing molar fraction of MAD inthe monomer feed.

The kf values for the MAD radical calculatedfrom k22/kf and k22 (Table 3) are smaller thanthose of the radical from the unsaturated dimer ofMMA at 60 °C (�1 � 103 s�1) by three orders ofmagnitude.27 The difference in the kf values canbe explained by the different structures of the

radicals expelled from the radical of the MMAdimer and MAD radical: a tertiary carbon-cen-tered radical from the former and a primary car-bon-centered radical from the latter. The kf val-ues all lie within the narrow range of 0.12–0.42s�1 (Table 3), and this suggests that the value ofkf is only marginally affected by the nature of thepenultimate unit. The copolymerizations withCHA and nBA resulted in the same kf value.Alternatively, the kf value may be obtained fromk21/kf (the slope) and k21 (from r2 and kp for MAD).The results obtained with this method are similarto those listed in Table 3 (evaluated from k22/kfand kp for MAD).

The copolymerization of MAD (M2) with St(M1) yielded copolymers consisting of both mono-mer units, as shown Table 2. However, no 1HNMR resonance assigned to the protons of theunsaturated end group was detected, and thisindicated that the crosspropagation was expectedto be much faster than the fragmentation in

Figure 2. Plots of [MAD unit]/[CH2AC group][MAD]versus [M1]/[MAD] for copolymerization of MAD with(—) CHA and (–) nBA in benzene at (F,E) 100, (■,�)130, and (Œ,‚) 180 °C.

Table 4. Monomer Reactivity Ratios for theCopolymerization of MAD with Acrylic Esters (M1) inBenzene at High Temperaturesa

M1

100 °Cb 130 °Cc 180 °Cd

r1 r2 r1 r2 r1 r2

CHA 0.66 1.00 0.70 0.90 0.67 0.72nBA 0.54 1.01 0.62 0.87 0.55 0.69

a [M1] � [MAD] � 2.0 mol/L.b [ATMP] � 0.01 mol/L.c [TBP] � 0.01 mol/L.d [Dicumyl] � 0.01 mol/L.Figure 1. Plots of [MAD unit]/[CH2AC group][MAD]

versus [M1]/[MAD] for (E) MAD polymerization andcopolymerizations of MAD with (Œ) CHA, (�) nBA, (F)EMA, and (‚) EEA (M1) in benzene at 60 °C ([M1]� [MAD] � 2.0 mol/L).

602 HARADA, ZETTERLUND, AND YAMADA

Scheme 2. An alternative explanation may bethat the unsaturated groups are consumed by theaddition of polystyrene radicals.11

Copolymerization of MAD with Acrylic Esters atHigh Temperatures

The copolymerizations of MAD (M2) with acrylicesters (M1) were carried out in the temperaturerange of 100–180 °C to accelerate the fragmenta-tion with respect to propagation. All the copoly-merizations proceeded smoothly. The monomerreactivity ratios (Table 4), as determined from thecopolymer compositions, were slightly affected bythe temperature. Although the r1 values re-mained almost constant, the r2 values decreasedfrom greater than unity at 60 °C to less than unityat 180 °C. These findings suggest that the in-crease in the rate of homopropagation of MADwith temperature is suppressed at high tempera-tures as Tc is approached.6

Figure 2 shows plots according to eq 5. Thevalue of k22/kf obtained from the y intercept de-creased significantly with an increase in temper-ature: k22/kf � 82–85 L/mol at 60 °C and k22/kf� 6.2–6.6 L/mol at 180 °C for the copolymeriza-tions with nBA and CHA. The values of k21/kfobtained from the slopes also decreased with in-creasing temperature. The kf value of the copoly-merization with nBA at 180 °C (80.7 s�1) wascalculated from k22/kf of this study and k22 � 501L/mol s for MAD, calculated with the reportedArrhenius equation.7 This kf value, which is al-

most the same as that for the unsaturated dimerof MMA at 60 °C, is sufficiently large for theefficient introduction of the unsaturated endgroup.26 It is suggested that the acceleration offragmentation is more significant than that ofpropagation following a temperature increase,causing a decrease in the value of k22/kf. If thecopolymerization temperature is close to or aboveTc of MAD, k22/kf would decrease further as aresult of a lower apparent k22. It is well-knownthat backbiting and intermolecular hydrogen ab-straction result in macromonomer formation inacrylate polymerizations at elevated tempera-tures.27 Although it cannot be excluded that thesepathways contribute somewhat to the formation

Figure 3. Arrhenius plots for the competition be-tween fragmentation and propagation in (E) the ho-mopolymerization of MAD and copolymerizations ofMAD with (Œ) CHA and (�) nBA.

Table 5. Mn and Mw/Mn for Copolymers of MAD with Acrylic Esters at Different Temperaturesa

M1

Temperature(°C)

[M1] inCopolymer

(mol %)Mn � 10�3

(GPC)bPn(MAD)c

Pn(M1)Mn � 10�3

(NMR)Mn(GPC)Mn(NMR)

[MAD unit][CH2AC]

[Pn(MAD) � 1]

CHA 60d 23.9 41.4 75/25 93.6 0.44 201100c 27.2 6.8 20/8 10.9 0.62 48130f 29.7 4.3 17/8 6.7 0.64 27180g 33.7 2.6 10/6 3.8 0.70 15

nBA 60d 23.3 40.4 71/29 97.3 0.42 215100e 26.5 7.2 31/15 11.2 0.64 51130f 29.7 4.1 17/10 6.2 0.66 28180g 32.1 2.5 10/6 3.4 0.74 15

a [M1] � 0.6 mol/L; [MAD] � 1.4 mol/L.b Mw/Mn � 1.28–1.81.c Ratio of the number of MAD units to M1 units per chain.d [MAIB] � 0.01 mol/L.e [ATMP] � 0.01 mol/L.f [TBP] � 0.01 mol/L.g [Dicumyl] � 0.01 mol/L.

COPOLYMERIZATION OF METHYL ACRYLATE DIMER 603

of unsaturated end groups, the excellent linearityobserved in the plots of eq 5 indicate that frag-mentation of the MAD adduct radicals, uponwhich eq 5 is based, is indeed the main pathwayto unsaturated end groups (Fig. 2).

Table 5 shows the results of GPC analysis ofthe copolymer, indicating that Mn decreased withan increase in temperature and confirming theacceleration of fragmentation with respect to ho-mopropagation. No significant change was ob-served in Mw/Mn. The Mn(GPC)/Mn(NMR) valuefor the copolymerization of MAD with acrylic es-ter rose from 0.40 to 0.70 as the temperature wasincreased from 60 to 180 °C (i.e., a higher effi-ciency of end-group introduction at a higher tem-perature). A small amount of the copolymer with-out unsaturated end groups would be formed as aresult of bimolecular termination involvingmainly acrylate-terminated radicals. It is note-worthy that homopolymerizations (Table 1) andcopolymerizations of MAD with CHA and nBA([M1]/[MAD] � 0.6/1.4 mol/mol) at 180 °C resultedin almost the same Mn(GPC)/Mn(NMR) values,but the Mn’s of the copolymers are higher than for

the homopolymers. However, as already pointedout, the Mn(GPC)/Mn(NMR) value might not be aquantitative measure of the end-group introduc-tion because of GPC error caused by branchingand the use of polystyrene standards.

The Arrhenius plots of k22/kf according to eq 6and kp/kf for the homopolymerization of MAD aredepicted in Figure 3. Differences in the activationenergies (Ef � E22 or Ef � Ep) and the ratio of thefrequency factors (Af /A22 or Af /Ap) were evaluated.

lnk22

kf� ln

A22

Af�

Ef � E22

RT (6)

The linear relationships for the copolymerizationsand homopolymerizations of MAD almost overlap

Figure 4. Comonomer–copolymer compositioncurves for the copolymerization of MAD with EMA inbenzene at (E) 60, (Œ) 100, and (�) 130 °C ([MAD]� [EMA] � 2.0 mol/L).

Table 6. Arrhenius Parameters for the Propagationand Fragmentation of MAD Radicals inHomopolymerization and Copolymerization

PolymerizationEf � E22

(kJ/mol)Af /A22

(mol/L)

Copolymerization with CHA 26.2 1.97 � 102

Copolymerization with nBA 27.4 2.71 � 102

Homopolymerization of MAD 27.3a 2.89 � 102b

a Ef � Ep (kJ/mol).b Af /Ap (mol/L).

Table 7. Introduction of Unsaturated End Groups by the Copolymerization of MAD (M2) with EMA and EEA(M1) in Benzenea

M1

Temperature(°C)

[MAD] inCopolymer

(mol %) r1 r2 r1r2

Mn � 10�4

(GPC)Mn � 10�4

(NMR)Mn(GPC)Mn(NMR)

EMA 60b 29.2 2.32 0.42 0.97 2.79 16.0 0.17EMA 100c 19.5 4.93 0.41 2.02 6.32 63.5 0.10EMA 130d 12.4 9.72 0.47 4.57 3.28 —e —e

EEA 60b 58.6 0.32 0.96 0.31 0.47 1.40 0.34

a [MAD] � 1.0 mol/L; [M1] � 1.0 mol/L.b [MAIB] � 0.01 mol/L.c [ATMP] � 0.01 mol/L.d [TBP] � 0.01 mol/L.e No end groups detected by 1H NMR.

604 HARADA, ZETTERLUND, AND YAMADA

(see also Table 6). The activation energy and fre-quency factor for the unimolecular reactions aregreater than for bimolecular reactions when thereaction rates are comparable.28 The Arrheniusparameters for fragmentation are, as anticipated,greater than those for propagation in homopoly-merizations and copolymerizations of MAD. Co-polymerization with acrylic ester does not influ-ence the fragmentation of the MAD radicals; theefficiency of the introduction of unsaturated endgroups was as high as during the homopolymer-ization of MAD. The similarity of the Arrheniusplots of kp/kf and k22/kf strongly suggests that

macromonomer formation via backbiting and in-termolecular hydrogen abstraction in the acrylatecopolymerizations has a very limited effect on theresults. The copolymerization of MAD withacrylic ester at high temperatures is, therefore,an efficient method for the preparation of mac-romonomers.

Copolymerization of MAD with EMA and EEA atHigh Temperatures

Table 7 shows the monomer reactivity ratios forthe copolymerization with EMA at high tempera-tures. Unlike the copolymerizations with acrylicesters, for which r1 and r2 were only marginallyaffected by temperature (Table 4), the composi-tion curves for the copolymerization of MAD withEMA exhibited a marked temperature depen-dence (Fig. 4). The content of MAD in the copoly-mer decreased with an increase in temperature.Furthermore, the r1r2 values are greater thanunity, except at 60 °C. The Mn value of the copol-ymer obtained at 100 or 130 °C is higher than at60 °C, depending on the comonomer composition(Fig. 5). This tendency cannot be explained by amore significant acceleration of fragmentationthan propagation at high temperature.

The 1H NMR resonances due to the unsatur-ated end groups at 5.63 and 6.39 ppm could not bedetected at 60 and 100 °C without extreme mag-

Figure 5. Mn for MAD–EMA copolymers prepared inbenzene at (E) 60, (Œ) 100, and (�) 130 °C ([MAD]� [EMA] � 2.0 mol/L).

Figure 6. 1H NMR spectrum of the MAD–EMA copolymer (Mn � 63,000) prepared inbenzene at 100 °C ([EMA] � 1.0 mol/L, [MAD] � 1.0 mol/L, [ATMP] � 0.01 mol/L).

COPOLYMERIZATION OF METHYL ACRYLATE DIMER 605

nification, and this confirmed a very low contentin the MAD–EMA copolymer (Fig. 6). No unsat-urated end groups were detected at 130 °C. TheMn(GPC)/Mn(NMR) values are lower than thoseof the homopolymerization of MAD (Table 7). Theresults in Table 7 and Figures 5 and 6 suggestthat MAD radicals bearing the EMA penultimateunit tend to expel MAD by cleavage of the COCbond at a as opposed to b (Scheme 3). The EMAradical formed would rapidly add to MAD or EMAto extend the polymer chain. Similar competitivecleavage has been reported for the adduct radicalof the dimer of MMA.26

The copolymerization of EEA at 60 °C indi-cated that EEA is a suitable monomer for theefficient introduction of the propenyl end group athigh temperatures; the Mn(GPC)/Mn(NMR) val-ues were as high as those for the acrylate copoly-merizations (Tables 5 and 7), and this is consis-tent with the slow crosspropagation expectedfrom a low k21 value (Table 3). However, the lowTc value of EEA4 prevented copolymer formationat higher temperatures.

CONCLUSIONS

Copolymerizations of MAD with CHA and nBA ac-companied by � fragmentation of the MAD radicalyielded copolymers with unsaturated �-end groups.The values of k22/kf and Mn of the copolymer de-creased with an increase in temperature. Copoly-merization with EMA resulted in the introductionof only a small amount of unsaturated end groups(considerably less than for CHA and nBA), and thecontent of MAD units in the copolymers decreasedwith an increase in temperature. The copolymeriza-tion of MAD with EEA did not give any polymericproducts at higher temperatures. No unsaturatedend groups were detected in the copolymer with St.Among the monomers examined, acrylic esterscould be employed to prepare macromonomers bycopolymerization with MAD at high temperatures.The efficiency of the end-group introduction into thecopolymer was confirmed to be as high as thatduring the homopolymerization of MAD becauseof significant steric hindrance arising from the

Table 8. Summary of Macromonomer Formation by the Homopolymerization and Copolymerization of MAD

M1 Incorporation of MAD Units (M2) Mn(GPC)/Mn(NMR)

None Homopolymerization 0.71 (180 °C)nBA r1 � constant, r2 decreases with

increasing temperature0.74 at [nBA] � 0.6 mol/L and

[MAD] � 1.4 mol/L (180 °C)CHA r1 � constant, r2 decreases with

increasing temperature0.70 at [CHA] � 0.6 mol/L and

[MAD] � 1.4 mol/L (180°C)EMA Decreases with increasing temperature

[reversible addition of poly(EMA)radical to MAD]

Extremely low (130 °C)

EEA r1 and r2 � 1 Low Tc of EEA preventedcopolymerizations at hightemperatures

St r1 and r2 � 1 No end groups detected at 60 °C

Scheme 3

606 HARADA, ZETTERLUND, AND YAMADA

CH2CH2CO2CH3 group bound to the �-carbon ofthe MAD radical (Table 8).

REFERENCES AND NOTES

1. Yamada, B.; Zetterlund, P. B. Handbook of RadicalPolymerization; Wiley: New York, 2002; Chapter 3.

2. Cheng, J. S.; Yamada, B.; Otsu, T. J Polym Sci PartA: Polym Chem 1991, 29, 1837.

3. Chikanishi, K.; Tsuruta, T. Makromol Chem 1965,81, 198.

4. Penelle, J.; Collet, J.; Rufflard, G. J Polym Sci PartA: Polym Chem 1993, 31, 2407.

5. Kobatake, S.; Yamada, B. Polym J 1996, 28, 535.6. Kobatake, S.; Yamada, B. J Polym Sci Part A:

Polym Chem 1996, 4, 95.7. Tanaka, K.; Yamada, B.; Fellows, C. M.; Gilbert,

R. G.; Davis, T. P.; Yee, L. H.; Smith, G. B.; Rees,M. T. L.; Russell, G. T. J Polym Sci Part A: PolymChem 2001, 39, 3902.

8. Carswell, T. G.; Hill, D. J. T.; Londero, D. I.;O’Donnel, J. H.; Pomery, P. J.; Winzor, C. L. Poly-mer 1992, 33, 137.

9. Yamada, B.; Kobatake, S. Prog Polym Sci 1994, 19,1089.

10. Yamada, B.; Kobatake, S. Polym J 1992, 24, 281.11. Kobatake, S.; Yamada, B.; Aoki, S. Polym Bull

1993, 31, 263.12. Bon, S. A. F.; Morsley, S. R.; Waterson, C.; Haddle-

ton, D. M. Macromolecules 2000, 33, 5819.

13. Meijs, G. F.; Rizzardo, E.; Thang, S. H. Polym Bull1990, 24, 501.

14. Meijs, G. F.; Rizzardo, E.; Thang, S. H. Macromol-ecules 1988, 21, 3122.

15. Rizzardo, E.; Chong, Y. K.; Evans, R. A.; Moad, G.;Thang, S. H. Macromol Symp 1996, 111, 1.

16. Sato, T.; Seno, M.; Kobayashi, M.; Kohno, T.;Tanaka, H. Eur Polym J 1995, 31, 29.

17. Kobatake, S.; Yamada, B.; Aoki, S. Macromol ChemPhys 1994, 195, 581.

18. Kobatake, S.; Yamada, B.; Aoki, S. Macromolecules1993, 26, 5099.

19. Yamada, B.; Oku, F.; Harada, T. J Polym Sci PartA: Polym Chem, in press.

20. Trumbo, D. L.; Zander, R. A. J Polym Sci Part A:Polym Chem 1991, 29, 1053.

21. Raley, J. H.; Rust, F. F.; Vaughan, W. E. J AmChem Soc 1948, 70, 88.

22. Tanaka, K.; Yamada, B. Polym J 2002, 34, 692.23. Beuermann, S.; Paquet, D. A., Jr.; McMinn, J. H.;

Hutchinson, R. A. Macromolecules 1996, 29, 4206.24. Hutchinson, R. A.; Paquet, D. A., Jr.; McMinn,

J. H.; Fuller, R. E. Macromolecules 1995, 28, 4023.25. Yamada, B.; Kageoka, M.; Otsu, T. Polym Bull

1992, 29, 385.26. Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H.

Macromolecules 1996, 29, 7717.27. Chiefari, J.; Jeffrey, J.; Mayadunne, R. T. A.; Moad,

G.; Rizzardo, E.; Thang, S. H. Macromolecules1999, 32, 7700.

28. Fossey, J.; Lefort, D. J.; Sorba, J. Free Radicals inOrganic Chemistry; Wiley: Chichester, England,1995; p 148.

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