Thermal properties and TGA–FTIR studies of polyacrylic and polymethacrylic acid doped with metal...

Thermal properties and TGA±FTIR studies of polyacrylicand polymethacrylic acid doped with metal clusters

Galo CaÂ rdenasa,*, Carla MunÄ oza, HernaÂ n Carbachob

aDepartamento de PolõÂmeros, Facultad de Ciencias QuõÂmicas, Universidad de ConcepcioÂn, Casilla 160-C, ConcepcioÂn, ChilebDepartamento de QuõÂmica AnalõÂtica e InorgaÂnica, Facultad de Ciencias QuõÂmicas, Universidad de ConcepcioÂn, Casilla 160-C,

ConcepcioÂn, Chile

Received 18 March 1999; received in revised form 12 July 1999; accepted 15 July 1999

Abstract

Polyacrylic (PAA) and polymethacrylic acid (PMAA) doped with metal clusters were prepared by radicalpolymerization. The colloids were obtained by cocondensation of the metals and acrylic acid at 77 K using severalmetals such as Au, Ag, Pd, Cu, Bi, Sn, Sb, Ge, Ga, In, Cd and Zn. The presence of the metal clusters avoids theformation of larger molecular weight polymers. A complete study of the thermal degradation between 50 and 5508Chas been carried out, and the decomposition temperatures (TD) are obtained from the second derivative. In PAA,the highest TD corresponds to the undoped polymer, 5468C, but in PMMA, the Pd doped polymer increases theTD2 from 467 to 4698C for the lowest molecular weight. In fact, the TD of the highest molecular weight polymer

increases 278C the same as PAA-Ge. FTIR spectroscopy of the gases from TGA indicate that the product has beenevolved during the experiment (60 min) with PAA, while the ®rst gas evolved between 20 and 30 min and then from37 to 45 min for PMMA shows that during the ®rst decomposition mainly MAA is found. During the second

decomposition besides the characteristic bands for MAA some alkenes are observed. # 2000 Elsevier Science Ltd.All rights reserved.

1. Introduction

Some polymers and copolymers do function as highwater absorbents and have very good properties forwater retention. Products with high a�nity for water

are frequently de®ned as hydrogels [1,2].The polyacrylate derived from acrylic acid (AA) has

raised as an important absorbent, the advantage ofAA is cheap and easy to polymerize to products of

high molecular weight [3].A suspension polymerization process for polyacrylate

absorbents, which used a combination of hydrophobic

silica and a copolymer of AA and lauryl methacrylate

as the suspension agents has been used [4].Our interest becomes in the study and comparison

between polyacrylic and polymethacrylic homopoly-

mers with those doped with metal clusters. Several in-vestigations on their thermal degradation [5] using thethermogravimetric and infrared analysis (TGA±FTIR)

have been carried out [6]. These polymers degradebasically in two stages. In the polymethacrylic acid(PMAA), a transformation in methacrylic anhydride

was observed by producing another decomposition bysubsequent heating. The degradations occurred at 200and 4008C approximately.Due to the clusters incorporation no swelling was

observed for polyacrylic acid (PAA).

European Polymer Journal 36 (2000) 1091±1099

0014-3057/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PII: S0014-3057(99 )00187-1

* Corresponding author. Fax: +56-41-245974.

2. Experimental

2.1. Colloid synthesis

The metal-acrylic acid colloids were prepared bycocondensation of the metal with the monomer at 77

K using a metal atom reactor [7,8]. Di�erent currentintensities between the electrodes were used dependingupon the metal used and the vacuum. The metals

under study were Pd, Cu, Ag and Au.

2.2. Typical polymerization

A mixture of the colloid Ag-acrylic acid (10 cm3)and water (10 cm3) were placed in four polymerization¯asks with 0.1, 0.25, 0.5 and 1.0 mol% of benzoyl per-oxide (BPO). The ¯ask tubes were sealed and placed in

an isothermal bath at 558C for 1 h under nitrogen at-mosphere. The content of each ¯ask was quenched in100 cm3 in petroleum ether. The polymers obtained

were ®ltered o� and dried under vacuum at 10ÿ3 Torrfor 48 h at 408C. The yield of polymers was measuredand their molecular weight determined by viscosity in

dioxane at 308C using an Ostwald viscometer. Fromthe intrinsic viscosity and Mark±Houwink equation

[9], the molecular weight was obtained. K = 76� 10ÿ3

cm3/g and a = 0.5 [10]. This is an approximate valuedue to the metal doped polymers.

2.3. Thermogravimetric analyses

A Perkin±Elmer Model TGA-7 Thermogravimetric

system with a microprocessor driven temperature con-trol unit and a TA data station was used. The mass ofthe samples was generally in the range of 3±5 mg. The

sample pan was placed on the balance and the tem-perature raised from 25 to 5508C at a heating rate of108C/min. The mass of the sample pan was continu-ously recorded as a function of temperature.

2.4. TGA±FTIR

Experiments were performed using a Nicolet Magna

550 System consisting of a Fourier Transform InfraredSpectrophotometer with a detector (set at 4 cmÿ1 res-olution) coupled to a Perkin±Elmer TGA-7. TGA

Table 1

Decomposition temperatures and activation energy of doped PAAa

Polymer TD 1b (8C) Ea 1c (kJ) TD 2 (8C) Ea 2 (kJ) TD 3 (8C) Ea 3 (kJ)

PAA-1 ± ± 293 28 412 13

PAA-4 283 37 423 8 546 11

Au-PAA-1 ± ± 280 39 408 10

Au-PAA-4 11 39 285 17 433 6

Ag-PAA-1 152 17 313 9 ± ±

Ag-PAA-4 116 7 317 7 ± ±

Pd-PAA-1 101 9 326 6 475 7

Pd-PAA-4 192 6 291 3 398 2

Sb-PAA-1 ± ± ± ± 404 7

Sb-PAA-4 ± ± 290 8 426 5

Sn-PAA-1 ± ± 273 10 420 6

Sn-PAA-4 147 8 279 7 407 3

Bi-PAA-1 ± ± 273 15 426 6

Bi-PAA-4 152 23 296 19 423 11

Ge-PAA-1 178 11 290 12 540 3

Ge-PAA-4 143 10 314 9 535 5

Ga-PAA-4 150 15 342 10 543 3

In-PAA-1 ± ± 312 13 426 8

In-PAA-4 ± ± 319 13 547 4

Cu-PAA-1 282 9 426 5 508 4

Cu-PAA-4 ± ± 255 12 365 5

Cd-PAA-1 300 19 427 9 492 8

Cd-PAA-4 ± ± 292 14 418 8

Zn-PAA-1 317 17 443 9 501 10

Zn-PAA-4 153 19 317 11 501 10

a PAA: polyacrylic acid.b TD 1, TD 2 and TD 3 correspond to the decomposition temperatures in the ®rst, second and third stages, respectively.c Ea 1, Ea 2 and Ea 3 correspond to the activation energies of the ®rst, second and third stages, respectively.

G. CaÂrdenas et al. / European Polymer Journal 36 (2000) 1091±10991092

sample weights in these studies ranged from 8±10 mg.Under a nitrogen purge, a heating rate of 108C/minwas used to scan from 25 to 5508C. The heated linewhich transferred the evolved gases from the TGA to

the FTIR spectrometer was maintained at 2408C.

3. Results and discussion

The syntheses and thermal properties of PAA andPMAA containing metal clusters have been recentlyreported [11±13]. These polymers have a wide range of

molecular weight, thermal stabilities and colorsdepending on the metal.The modi®ed PAA and PMAA were prepared using

the process shown below.

PAA homopolymer decomposed in two stages at

2938C (TD1) for the ®rst one and 4128C for the second

(TD2) corresponding to the highest molecular weight

polymer (0.1 mol% initiator), while the lowest molecu-

lar weight sample showed three decompositions at 283,

423 and 5458C (1 mol% BPO), respectively (see Table

1).

The presence of the metal clusters in the PAA in

fraction 1 decreased the TD for Au, Ag and Sb mostly

due to their lower reactivity. The other metal clusters

behaved di�erently showing a small increase of the TD.

But for fraction 4, the TD decreased due to the smaller

polymer chain. The most relevant case is the PAA

doped with Cu decreasing to 3648C due to the metal

redox potential, a mixture of Cu and Cu2+ clusters in

the PAA was observed (see Table 1). The Pd-PAA is

Table 2

Decomposition temperatures and activation energies of doped PMAA

Polymer TD 1 (8C) Ea 1 (kJ) TD 2 (8C) Ea 2 (kJ) TD 3 (8C) Ea 3 (kJ)

PMAA-1a ± ± 234 13 433 22

PMAA-4b 183 21 260 11 467 31

Au-PMAA-1 ± ± 228 25 441 39

Au-PMAA-4 123 28 451 30 ± ±

Ag-PMAA-1 60 9 249 4 433 20

Ag-PMAA-4 ± ± 246 11 461 31

Pd-PMAA-1 ± ± 247 21 450 20

Pd-PMAA-4 ± ± 258 31 469 41

Sb-PMAA-1 ± ± 251 11 422 18

Sb-PMAA-4 ± ± 251 9 455 34

Sn-PMAA-1 ± ± 251 36 433 27

Sn-PMAA-4 127 59 248 35 453 37

Bi-PMAA-1 ± ± 267 15 434 21

Bi-PMAA-4 ± ± 258 22 452 52

a Fraction 1 corresponds to polymethacrylic acid fraction 1, highest molecular weight.b Fraction 2 corresponds to polymethacrylic acid fraction 4, lowest molecular weight.

G. CaÂrdenas et al. / European Polymer Journal 36 (2000) 1091±1099 1093

quite interesting specially due to increases of TD in

fraction 1, being the highest doping cluster.

The activation energy of the decomposition tempera-

tures for PAA is changed by the presence of the high-

est e�ect of the metal clusters in the Au-PAA (38 kJ).

Also, in fraction 4, it increases the Ea to 17 kJ. In both

cases, a 10 kJ increase due to their higher redox poten-

tial was obtained.

For PMAA homopolymer, the higher TD was 4338Cfor fraction 1 and 4678C for fraction 4, respectively

(see Table 2).

Another important factor is the amount of metal in-

corporated into the polymers. Table 3 summarizes the

PAA where Pd doping is the highest (13.3% w/w) in

fraction 1. However, in fraction 4 most of the metals

were incorporated in a range between 0.32 and 2.42%

w/w. The Bi clusters incorporation of 8.37% is also

consistent with the increases in TD of these polymers.

The two main decomposition curves in most of the

thermograms for PAA are due to the decomposition of

the carboxylate and then the hydrocarbonaceous

chain. More details will be done in the TGA±FTIR

analysis.

The lower metal clusters incorporation in PMAA is

probably due to the steric e�ect of the methyl group,

because the clusters are located in the carboxylic part

of the macromolecule. This observation was detected

by IR.

Similar amount of metal clusters incorporated has

been previously reported [14,15]. However, in PMAA-

Bi the highest doped polymer (8.37% w/w) and Ge the

lowest (0.24% w/w) are found in fraction 1. On the

other hand, fraction 4 exhibits a lower metal incorpor-

ation ranging from 0.19 to 1.01% w/w. Table 4 sum-

marizes these results.

Also, the stability of the polymers should be di�er-

ent, depending on the cluster.

The combined TGA±FTIR for simultaneous

measurements has been a technique that o�ers detailed

analysis of the thermal properties of synthetic polymers

[16±22]. This technique has been used to distinguish

Table 4

Metal analysis of doped PMMAa

Polymer % Metal

(1)b (4)c

PMAA-Au 0.28 0.21

PMAA-Ag 5.70 0.19

PMAA-Pd 2.41 0.19

PMAA-Sb 2.00 0.74

PMAA-Sn 6.00 1.01

PMAA-Bi 8.37 0.21

PMAA-Ga 1.90 0.17

PMAA-Ge 0.24 0.35

PMAA-In 1.79 0.38

PMAA-Cu 2.89 0.62

PMAA-Cd 3.33 0.34

PMAA-Zn 2.80 0.37

a PMAA: polymethacrylic acid.b Fraction (1) corresponds to the highest molecular weight.c Fraction (4) corresponds to the lowest molecular weight.

Table 3

Metal analysis of doped PAAa

Polymer % Metal

(1)b (4)c

PAA-Au 0.57 1.87

PAA-Ag 1.15 1.30

PAA-Pd 13.30 1.92

PAA-Sb 2.73 0.94

PAA-Sn 1.19 2.42

PAA-Bi 0.22 0.22

PAA-Ga 3.49 2.12

PAA-Ge 1.21 0.32

PAA-In 0.72 0.45

PAA-Cu 3.20 0.56

PAA-Cd 0.55 1.70

PAA-Zn 3.38 0.81

a PAA: polyacrylic acid.b Fraction (1) corresponds to the highest molecular weight.c Fraction (4) corresponds to the lowest molecular weight.

Table 5

FTIR bands of doped PAAa

Polymer nO±H

(cmÿ1)nC±H

(cmÿ1)nC1O

(cmÿ1)nC±O

(cmÿ1)

PAA 3435 2925 1744 1228

PAA-Au 3429 2929 1717 1280

PAA-Ag 3459 2961 1752 1227

PAA-Pd 3455 2936 1716 1234

PAA-Cu 3441 2933 1718 1248

a PAA: polyacrylic acid.

Table 6

FTIR bands of ®rst TGA decomposition of PAAa

Polymer nO±H (cmÿ1) nC1C (cmÿ1) nC1O (cmÿ1)

PAA 3735 2316 1693

PAA-Au 3748 2355 1693

PAA-Ag 3748 2355 1699

PAA-Pd 3739 ± 1696

PAA-Cu 3748 2322 1699

a PAA: Polyacrylic acid.


Fig. 1. Gram±Schmidt of (a) polyacrylic acid and (b) polymethacrylic acid.


homopolymers, copolymers, and to determine compo-

sition of copolymers of ethylene and vinyl acetate [19].

It is not obvious that a single reaction mechanism will

dominate the degradation of a copolymer. In our case,

it is possible to distinguish the degradation of the PAA

and PMAA.

The analysis of the evolved gases in the TGA±FTIR

shows that PAA decomposes in monomers slowly,

however, PMAA shows two important decompositions

at 24 and 43 min, respectively (Fig. 1).

The TGA±FTIR of the highest molecular weight

range for PAA homopolymer (Fig. 2) and polymers

doped with Au, Ag, and Pd were analyzed (Fig. 3, Fig.

4, Fig. 5).

The analysis of fraction 1 corresponding to the high-

est molecular weight polymers was carried out.

The PAA shows the highest shift band in nC±O due

to the Au doping (52 cmÿ1). In the nC1O a 27 cmÿ1

shift was observed. On the other hand, the nO±H shift

was also observed. The PAA doped with silver shows

a 24 cmÿ1 shifted. The shift of the carbonylic band is

due to the metal interaction. Table 5 summarizes the

data.

During the decomposition the gases were analyzed

Fig. 2. TGA±FTIR polyacrylic acid data recorded between 9 and 29 min of decomposition.

Table 7

FTIR bands of second TGA decomposition of PAAa

Polymer nO±H (cmÿ1) nC1C (cmÿ1) nC1O (cmÿ1)

PAA 3741 2309 1692

PAA-Au 3761 2349 1693

PAA-Ag 3745 2358 1697

PAA-Pd 3746 ± 1703

PAA-Cu 3735 2316 1693

a PAA: polyacrylic acid.

Table 8

FTIR bands of doped PMAAa

Polymer nO±H

(cmÿ1)nC±H

(cmÿ1)nC1O

(cmÿ1)nC±O

(cmÿ1)

PMAA 3418 3000 1700 1272

PMAA-Au 3420 3000 1700 1272

PMAA-Ag 3433 3001 1702 1272

PMAA-Pd 3416 3000 1700 1274

PMAA-Cu 3395 2999 1700 1275

a PMAA: polymethacrylic acid.


for the two main decompositions. Tables 6 and 7 sum-marize the nOH, nC1C and nC1O: The most relevantinformation is the presence of alkenes during the de-

composition of PAA doped with metal cluster. ThenC1O appears almost at the same region but at lowerwavelength, than the homopolymer. However, the nOH

shows bands near 3700 cmÿ1 with almost 300 cmÿ1

from the normal maximum absorption peak.The PMAA exhibits a great in¯uence due to metal

clusters. In Table 8, we can see the most signi®cantvalue for PMAA-Cu (23 cmÿ1). No di�erence wasobserved in the nC1O: This is probably due to clusters

interaction with the oxygen from the hydroxylic

instead of the carbonylic group of the macromolecule.But during the thermal decomposition in the ®rst de-composition the most relevant bands corresponded to

nOH and nC1O groups, these values are in the normalregion due to the absence of metal clusters (see Table9).

However, during the second decomposition ofPMAA besides the nOH and nC1O, the nC1C showed athermal dehydrogenation of the hydrocarbon chain

catalyzed by the metal clusters (see Table 10).

Fig. 3. TGA±FTIR of polyacrylic acid doped with Au clusters, data recorded between 35 and 54 min of decomposition.

Table 9

FTIR bands of ®rst decomposition of PMAAa

Polymer nO±H (cmÿ1) nC1O (cmÿ1) nC±O (cmÿ1)

PMAA 3582 1766 1120

PMAA-Au 3576 1759 1136

PMAA-Ag 3576 1766 1129

PMAA-Pd 3748 1746 ±

PMAA-Cu 3589 1759 1129


Table 10

FTIR bands of second decomposition of PMAAc

Polymer nO±H

(cmÿ1)nC1C

(cmÿ1)nC1O

(cmÿ1)nC±O

(cmÿ1)

PMAA 3589 2349 1766 1116

PMAA-Au 3741 2362 1752 1129

PMAA-Ag 3735 2356 1786 1123

PMAA-Pd 3741 ± 1739 ±

PMAA-Cu 3741 2369 1765 1129



Fig. 4. TGA±FTIR of polyacrylic acid doped with Ag clusters, data recorded between 35 and 54 min of decomposition.

Fig. 5. TGA±FTIR of polyacrylic acid doped with Pd clusters, data recorded between 35 and 54 min of decomposition.


4. Conclusions

The incorporation of metal clusters was observed

and ranged from 0.22 to 13.3% for PAA and from0.17 to 8.37% for PMAA. The viscosity molecularweights are approximated due to the assumption

that they are similar to the undoped polymers.The infrared spectrum shows the presence of the

characteristic groups in the polymer (C1O, C±O and

O±H) corresponding to PAA and PMAA. During thedecompositon of PAA some alkenes were observed dueto the dehydrogenation produced by the metal clusters.Some bands shift in C1O bands were observed due to

the presence of metal clusters.

Acknowledgements

The authors would like to thank the ®nancial sup-port of FONDECYT (Grant 1960621). Also, the Ther-

mal Analysis Laboratories of the Faculty of ChemistrySciences and Electron Microscopy facilities fromDireccioÂ n de InvestigacioÂ n. C. MunÄ oz is grateful forthe award of the scholarship from FONDECYT.

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