The thermal degradation of poly(allyl methacrylate)

fo/wnrr 0 De,qrodurion und Srahi/if.v St (lYY6) 1996 Prmted Published in Northern Ireland. XY-Y3 Science All Limited rights reserved 0141-3Y10/9~/$15.tx) 0141-3910(95)00237-5 ELSEVIER by Elsevier The thermal degradation of poly(ally1 methacrylate) Shagufta Zulfiqar, Asifa Piracha & Khalid Masud Department of Chemistry, (Received Quaid-i-&am 1 November University. Islarnabad, 1995: accepted 22 November Pakistan 1995) The thermal degradation of poly(allyl methacrylate) has been investigated using thermal volatilisation analysis (TVA), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The main pyrolysis products have been identified and the characteristics of the reactions deduced and discussed. Mechanisms have been proposed to account for the products formed. @ 1996 Published by Elsevier Science Limited 1 INTRODUCTION 2.1 Polymerisation The polymerisation of ally1 methacrylate has been studied previously. This polymerisation takes place mainly through the methacrylate groups. ’ The dielectric properties and thermal stability of cross linked copolymers of ally1 methacrylate and methyl methacrylate have also been examined.2.3 The thermal stability of the poly(ally1 methacrylate) and the processes involved in its thermal breakdown however, have not been studied previously. The present investigation is a detailed study of the thermal degradation and the volatile products formed during the thermal degradation of poly(ally1 methacrylate). Poly (ally1 methacrylate) was prepared by bulk polymerisation of the monomer under vacuum at 60°C with 0.05% w/v AIBN as initiator. The extent of polymerisation was indicated by the reduction in total volume and increase in viscosity content. The polymer was precipitated in methanol, purified by reprecipitation in methanol from acetone solution and dried in a vacuum oven at room temperature for 48 h. The number average molecular weight was 16 000. 2.2 Degradation studies Experimental methods include thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA) and thermal volatilisation analysis (TV,A).4.5 The products of degradation were separated by TVA into non-condensable gases, condensable gases and liquids, cold ring fraction (CRF) (products volatile at degradation temperature but not at ambient temperature) and residue. The noncondensable gases were identified by means of an on-line mass spectrometer. The condensable gas/liquid fraction was further separated by subambient TVA (SATVA)h into several frac- 2 EXPERIMENTAL Ally1 methacrylate (AMA) (Aldrich) was washed twice with 5% aqueous sodium hydroxide to remove inhibitor, washed thoroughly with distilled water, and dried over anhydrous calcium chloride. It was degassed and distilled on a high vacuum line, only the middle portion being used. a,a-Azobisisobutyronitrile (AIBN) (E-Merck) was recrystallised from absolute methanol and dried under vacuum at room temperature. 89 90 S. Zulfiqar tions: the more volatile fractions were examined as gases by FTIR spectroscopy and mass spectrometry (MS) and the less volatile liquid fraction was further examined by GC-MS. The CRF was studied by FTIR spectroscopy. 3 RESULTS AND DISCUSSION et al. 1.0 0.5- 01 The TVA behaviour of PAMA is illustrated in Fig. l(a) which .shows that breakdown occurs in two steps, with rate maxima at 276°C and 409°C. In the first stage of degradation only 0°C and -45°C traces show a response which implies that relatively high boiling products are being evolved which may be the monomer ally1 methacrylate. In the second stage of degradation the separation of O”C, -4_5”C, -75”C, -100°C and -196°C traces indicate the presence of products of various volatilities including non-condensable gases. TG, DTG and DTA curves for PAMA are shown in Fig. 2. The polymer is thermally stable up to about 210°C and two stage break-down is confirmed. The first stage accounts for about 100 I 1 0 I 3 I I 10 I 20 Time 30 1 1 350 i I I I 400 soo 600 Temp. OC c I 100 I 200 I 300 I 1 1 500 I LOO I 600 “C (dynamic NZ, 35% of weight loss. Overall weight loss for PAMA is about 98% at 500°C. The DTG behaviour parallels the TVA behaviour by showing D,,,,, at 270°C and DmaxZ 420°C. The at activation energies for the thermal degradation were calculated using Horowitz’s’ method and found to be 12.67 and 31.4 Kcal/mol, respectively. The DTA curve for PAMA shows two endotherms, the first at 290°C and the second at 418.9”C. The DTA data are consistent with the TG, DTG and TVA results. 40 400 600 300 Fig. 2. TG, DTG and DTA curves for PAMA 10°C min ‘). (mtnl 300 1 500 200 Temp. 3.1 Characterisation I I LOO I loo Temp. (b) 250 300 DTG 1 200 200 Temp.% L 0 I I 1 0 I 450 “C Fig. 1. (a) TVA curves (vacuum, 1O”Cmin ‘) for PAMA. -75°C: ---, -100°C: p, 0°C: ” ., -45°C; ---, _._ -196°C. (b) SATVA curve for separation of cbndensable volatile degradation products of PAMA. of volatile products The SATVA trace for warm-up from - 196 to 0°C of the condensable volatile product fraction from degradation in the TVA apparatus up to 500°C is shown in Fig. l(b). The condensable gaseous products and liquid fraction were examined by FTIR and MS. The results are presented in Table 1. The first SATVA peak was mainly due to carbon dioxide together with small amounts of propene and dimethyl ketene. The Thermal degradation of poly(ally1 methacrylate) Table 1. Product assignments SATVA peak (1) Product for the SATVA name separation of Fig. l(b) _~~____~~~--~--IR (cm MS (m/z) ‘) Isobutene Dimethylketene 2170, 2140. (2) Acrolein 3030,2780,2700 2630, 1700. 1410 1150. 980. 920 (3) 44, 28, 16, 27 42, 41, 39, 27 3702,2360, 688 3130, 2980, 2970, 1665, 1470,1380,990,910 3090, 2950. 1660, 890 Diallylether Carbon dioxide Propene Ally1 methacrylate 41, 56, 39. 28. 27, 55. 27, 56, 25, 55. 28. 26. 29, IX 41. 54, 27. 41. 39. 52. 2940, 1720. 1640, 1450, 1410, 1370, 1320, 1300, 1160, 1010, 990 940, Xl0 39. 42. 69. 56, 57. X3 9X 69. 7X Xl. 101 126 second small peak was due to acrolein. The third peak comprised mainly the monomer and diallylether. The liquid fraction, at the third peak was subjected to GC-MS for further investigation. The GC-MS (with peak assignments) chromatogram of the liquid fraction from the degradation of PAMA to 500°C under normal TVA conditions is shown in Fig. 3. fragments. The CRF spectrum shows additional peaks, however, at 1019, 1764 and 1805cm-‘, which are typical of a six-membered ring at structure.X A new C=O peak appears 1709 cm--’ with its overtone above 3200 cm- ’ and a band at 1165 cm-‘, suggesting the formation of ketone in the vicinity of an aliphatic unsaturation. 3.2 Analysis 3.3 Non-condensables of the cold ring fraction (CRF) The CRF which resulted from degradation of the PAMA to 500°C under TVA conditions was examined by FTIR spectroscopy and is compared with undegraded PAMA in Fig. 4. In most respects these spectra are similar, indicating that the CRF consists essentially of polymer chain Scan R.T.