Thermal Degradation of Poly(Allyl Methacrylate) by Mass Spectroscopy and TGA

Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Journal of Macromolecular Sciencew, Part A: Pure and Applied Chemistry, 43:1569–1581, 2006 Copyright # Taylor & Francis Group, LLC ISSN 1060-1325 print/1520-5738 online DOI: 10.1080/10601320600896900 Thermal Degradation of Poly(Allyl Methacrylate) by Mass Spectroscopy and TGA ˘ ˙ ˙ TUGBA KANTAV VARDARELI, SELDA KESKIN, ˙ USANMAZ AND ALI Department of Chemistry and Polymer Science and Technology, Middle East Technical University, Ankara, Turkey Allyl methacrylate, AMA was polymerized in CCl4 solution by a,a 0 -azoisobutyronitrile at 508C. The thermal degradation mechanism of PAMA was characterized by MS, TGA-FT-IR and FT-IR-ATR methods. The mass spectrum and TGA thermogram showed two stage degradation. The first stage of degradation was mostly linkage type degradation for the fragmentation of pendant allyl groups at 225– 3508C. In the second stage, at 395– 5158C, the degradation is random scission and depolymerization types. This was also supported by direct thermal pyrolysis of polymer under vacuum. The degradation fragments of MS and TGA were in agreement. In the degradation process, monomer degraded further to CO, CO2, allyl and ether groups. No strong monomer peak was observed in mass spectrum. Keywords allyl methacrylate, mass spectroscopy, TGA, thermal degradation, FT-IR Introduction The polymerization of allyl methacrylate, AMA by different polymerization methods have been reported (1 – 14). In most of the published works, the possible cyclopolymerization to give lactones are discussed. The solubility of polymer is attributed to the linear nature of the polymer chain. Thus, the insolubility of polymer is suggested to be due to the crosslinking with allyl groups. However, in our previous work (15) it was shown that the insolubility of PAMA is mostly related to the molecular weight but partially to crosslinking. Even at very high conversions, only 1 –2% of allyl groups are involved in cyclization and/ or crosslinking. This was also reported by bromination of pendant allyl groups in linear polymer (1, 2). The degradation of PAMA and its copolymer were studied by Zulfigar et al. (12 –14) using TGA, TVA, DTA and GC-MS methods. They have collected the degradation fragments and characterize them by FT-IR after separation of fragments by condensation. The main pyrolysis products were related to the nature of polymer chain. Received March 2006; Accepted April 2006. Address correspondence to Ali Usanmaz, Department of Chemistry and Polymer Science and Technology, Middle East Technical University, Ankara, Turkey. Tel.: 90-312-2103225; Fax: 90312-2101280; E-mail: usanmaz@metu.edu.tr 1569 Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   1570 T. K. Vardarelı, S. Keskın, and A. Usanmaz In the previous work (15), the polymerization mechanism of AMA under different conditions was studied. The polymer chain structure was investigated by different methods such as FT-IR, NMR, DSC, TGA and ESCA. In this study, thermal degradation of PAMA was carried out by MS, TGA in situ FT-IR and thermal pyrolysis residual by FT-IR-ATR. This should give us the detailed chain structure and the thermal properties of the polymer. Experimental Materials Allyl methacrylate, AMA (Aldrich) was purified by distillation. a,a0 -Azoisobutyronitrile, ¨ AIBN (Merck), carbontetrachloride (Merck), methanol (Riedel-de Haen) and toluene (Merck) were all spectroscopic grade and used without further purification. Polymer Characterization The FT-IR spectra were taken on a Bruker Vertex 70 ATR-FT-IR Spectrometer using KBr pellets. TGA in situ FT-IR thermogram was taken on a Perkin-Elmer Pyris 1 TGA and spectrum 1 FT-IR Spectrometer under nitrogen gas atmosphere in a temperature range of 30 –8008C with a heating rate of 58C/min. The mass spectrometer was a Balzers QMG 311 quadrupole with an electron impact of 70 eV. The scan rate of heating was 108C/min starting at 258C. The instrumental control and data acquisition was carried out by computer. Procedure For the polymerization, 2 ml (15 mmol) AMA, 5 mg (0.03 mmol) AIBN, and 4 ml CCl4 were placed in a Pyrex tube, which was degassed via three freeze-pump-thaw cycles on a high vacuum system. The tube under vacuum was sealed by flame and placed in a constant temperature oil bath at 508C for the desired period. It was then broken open, the polymer precipitated by excess methanol, filtered and dried under vacuum to constant weight. The soluble fraction was extracted with toluene. The results for the kinetic and mechanism of polymerization are given in another publication (15). For thermal pyrolysis, the polymer sample was heated at (a) 280 and (b) 3508C in an evacuated test tube. The FT-IR of residual polymer, after removal of volatile degraded fragments, was recorded. Results and Discussion The thermal degradation of PAMA was carried out by direct thermal pyrolysis, MS and TGA in situ FT-IR. The FT-IR spectrum of residual samples of PAMA after pyrolysis at (a) 280 and (b) 3508C are given in Figure 1. The allyl peaks (Figure 1a) observed at 3084.5, 1648.1 and 931.9 cm21 almost disappeared after thermal treatment at 3508C as shown in Figure 1b. Thus, at about 3508C, the linkage degradation of side groups in the polymer chain is maximized with the possible formation of anhydride and end group cyclization to lactones (Scheme 3). The details of fragmentation are obtained from mass spectra and TGA thermogram. Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Degradation of Poly(Allyl Methacrylate) 1571 Figure 1. The FT-IR spectrum of residual samples of PAMA after pyrolysis at (a) 2808C and (b) 3508C. Mass Spectral Investigation The mass spectra of (a) insoluble (b) soluble PAMA are given in Figure 2. The fragmentation in each of the thermograms show two regions at about 225– 3508C and 395 –5158C. Figure 2. Mass thermogram scanning of (a) insoluble and (b) soluble PAMA. T. K. Vardarelı, S. Keskın, and A. Usanmaz Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   1572 Figure 3. Fragments of insoluble PAMA obtained at (a) 1428C, (b) 3358C and, (c) 4428C Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Degradation of Poly(Allyl Methacrylate) 1573 Table 1 The relative abundances of the peaks and their fragments for insoluble PAMA fraction 1428C m/z I/I0 15 18 26 27 28 31 35 39 41 44 45 55 57 69 77 81 87 91 95 97 107 111 117 121 123 125 126 0.11 0.65 0.24 0.49 0.33 0.08 0.07 4.80 7.07 1.78 0.32 0.56 0.70 6.14 0.30 1.53 0.22 5.84 0.25 0.49 0.06 1.87 0.15 0.25 0.17 0.19 0.10 133 137 139 149 153 159 167 171 0.04 0.08 0.08 0.12 0.06 0.04 0.07 0.22 185 195 203 209 0.03 — 0.24 0.03 Fragments CH3 H2O CN, C2H2 C2H3 CO CH3O Cl C3H3 C3H5 CO2 CHO2 C3H3O C3H5O C4H5O C6H5 C4HO2 C4H7O2 C6H5N C5H3O2 C5H5O2 C6H3O2 C6H7O2 CCl3 C7H5O2 C7H7O2 C7H9O2 C7H10O2 (AMA) C8H5O2 C6H5O3 C6H7O3 C9H5O2 C9H9O2 C7H11O4 C8H7O4 C9H17O2N, C8H11O4 C9H13O4 C11H15O3 C12H13O2N C11H13O4 3358C I/I0 1.05 0.57 2.93 6.48 3.70 1.39 0.96 60.26 100 12.31 1.77 6.21 7.69 97.79 1.01 24.42 2.76 0.87 1.29 4.61 0.95 19.94 0.17 0.71 0.65 1.49 1.09 0.16 0.22 0.41 0.16 0.32 0.08 0.06 0.25 0.05 0.04 0.21 0.04 Fragments CH3 H2O CN, C2H2 C2H3 CO CH3O Cl C3H3 C3H5 CO2 CHO2 C3H3O C3H5O C4H5O C6H5 C4HO2 C4H7O2 C6H5N C5H3O2 C5H5O2 C6H3O2 C6H7O2 CCl3 C7H5O2 C7H7O2 C7H9O2 C7H10O2 (AMA) C8H5O2 C6H5O3 C6H7O3 C9H5O2 C9H9O2 C7H11O4 C8H7O4 C9H17O2N, C8H11O4 C9H13O4 C11H15O3 C12H13O2N C11H13O4 4428C I/I0 1.05 1.12 2.15 11.64 7.46 1.46 0.33 32.36 58.43 17.39 8.11 48.86 12.74 56.46 26.19 48.31 6.25 47.72 48.08 15.65 48.82 18.50 15.21 43.47 33.40 14.29 6.87 28.70 16.65 10.22 19.59 12.06 25.63 15.90 18.41 13.85 12.45 10.58 11.57 Fragments CH3 H 2O CN, C2H2 C2H3 CO CH3O Cl C3H3 C3H5 CO2 CHO2 C3H3O C3H5O C4H5O C6H5 C4HO2 C4H7O2 C6H5N C5H3O2 C5H5O2 C6H3O2 C6H7O2 CCl3 C7H5O2 C7H7O2 C7H9O2 C7H10O2 (AMA) C8H5O2 C6H5O3 C6H7O3 C9H5O2 C9H9O2 C7H11O4 C8H7O4 C9H17O2N, C8H11O4 C9H13O4 C11H15O3 C12H13O2N C11H13O4 (continued ) Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   1574 T. K. Vardarelı, S. Keskın, and A. Usanmaz Table 1 Continued 1428C m/z I/I0 Fragments 219 233 0.03 0.06 252 0.02 269 276 287 293 301 319 332 345 352 358 365 377 0.10 0.09 0.07 0.03 0.02 0.05 0.10 0.08 0.11 0.07 0.03 0.13 378 0.10 397 2.54 422 0.02 616 — 718 — 798 — C12H11O4 C14H19O2N, C14H16O4 C14H20O4 (dimer) C14H21O5 C15H16O6 C14H23O6 C17H25O5 C15H25O6 C18H23O5 C18H20O6 C19H21O6 C19H28O6 C20H22O6 C20H29O6 C15H14Cl3 O 4N C21H30O6 (trimer) C16H22Cl3 O 4N C22H30O8 (tetramer) C34H48O10 (pentamer) C40H46O12 (hexamer) C43H58O14 (heptamer) 3358C I/I0 0.03 0.07 0.03 0.09 0.09 0.07 0.03 0.05 0.04 0.10 0.09 0.09 0.09 0.03 0.10 0.09 1.97 — — — — Fragments C12H11O4 C14H19O2N, C14H16O4 C14H19O4 (dimer) C14H21O5 C15H16O6 C14H23O6 C17H25O5 C15H25O6 C18H23O5 C18H20O6 C19H21O6 C19H28O6 C20H22O6 C20H29O6 C15H14Cl3 O4N C21H30O6 (trimer) C16H22Cl3 O4N C22H30O8 (tetramer) C34H48O10 (pentamer) C40H46O12 (hexamer) C43H58O14 (heptamer) 4428C I/I0 8.43 7.76 6.96 5.18 4.16 4.50 4.33 3.96 3.02 2.43 2.44 2.26 2.22 2.27 2.07 2.04 3.53 1.40 0.25 0.07 0.04 Fragments C12H11O4 C14H19O2N, C14H16O4 C14H19O4 (dimer) C14H21O5 C15H16O6 C14H23O6 C17H25O5 C15H25O6 C18H23O5 C18H20O6 C19H21O6 C19H28O6 C20H22O6 C20H29O6 C15H14Cl3 O4N C21H30O6 (trimer) C16H22Cl3 O4N C22H30O8 (tetramer) C34H48O10 (pentamer) C40H46O12 (hexamer) C43H58O14 (heptamer) The first peak is broader and mostly due to the linkage breaking of pendant allyl groups. The intensity of the second peak is higher, which shows the main polymer chain scissoring and/or depolymerization followed by fragmentation at this temperature range. The small difference between the two thermograms (Figures 2a and 2b) are in peak shape and peak positions. Especially, the first peak area in the soluble PAMA (Figure 2b) is larger because oligomers and cyclic adducts are extracted into this fraction. They are degraded mostly at this temperature range. The second peak area (Figure 2a) is larger and extends to higher temperatures for insoluble PAMA due to some oligomers and cyclic adducts degraded at this stage. The broad peak at 25 –1258C in both spectra corresponds to the impurities (residual monomer and solvent, etc). Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Degradation of Poly(Allyl Methacrylate) 1575 Scheme 1. Degradation of allyl group of PAMA. The detailed fragmentation at (a) 142, (b) 335 and (c) 4428C for insoluble PAMA is given in Figure 3. The relative abundances of the peaks and their fragments are given in Table 1. In Figure 3a, the temperature is 1428C (11.7 min in Figure 2a). There is no apparent degradation peak at 11.7 min. Therefore, the peaks observed (Figure 3a) are due to the fragmentation of residual monomer and other possible oligomers that formed during the polymerization. The monomer peak at 126 is very weak in the spectrum showing the predominant monomer fragmentation. The residual monomer is degraded to give the main peaks at 27, 30, 41, 57, 69, and 111 (Table 1), similar to the reported fragments by Zulfigar et al. (12–14). The fragmentation of monomer is shown in Scheme 1. The peak at 397 corresponds to a cyclic oligomer containing AIBN and CCl4 fragments as in Scheme 2. The observed weak peaks at 398, 399 and 400 are in agreement to the isotopes of Cl. The fragmentation of this product gives weak peaks at 377, 233, 203 and 171 (Table 1). The presence of Cl and N is also shown (15) in the ESCA spectrum of PAMA. The thermal fragmentation at 3358C is given in Figure 3b and the results are tabulated in Table 1. The basic thermal behavior of the polymer at this stage of degradation is mainly formation of anhydride and end group cyclization as also shown by FT-IR spectrum Scheme 2. Cylic oligomer formed during polymerization of AMA. Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   1576 T. K. Vardarelı, S. Keskın, and A. Usanmaz (Figure 1) of residual sample after direct thermal pyrolysis. Therefore, the anhydride formation and/or cyclization to lactones are shown in Scheme 3. The fragmentation at 4428C for insoluble PAMA is similar to that at 3358C, with increasing number of fragments. These are mostly main chain degradation products. The mass spectrum for the soluble fraction of PAMA is given in Figure 2b. The observed m/z at (a) 309 (b) 405 and (c) 4418C is given in Figure 4 and the m/z data at three different temperatures are tabulated in Table 2. The fragment abundance is maximum at 3358C for the insoluble fraction of PAMA (Figure 3b) and that of the soluble fraction is 3098C (Figure 4a). The two thermograms are quite similar with changes in the relative abundance of fragments. TGA Investigation The TGA thermogram for the insoluble fraction of PAMA was reported before (15) and for soluble fraction, it is given in Figure 5 in the temperature range of 30– 8008C. The degradation of insoluble fraction showed two-stage degradation (15) with second stage peak being more intense. The thermogram for soluble fraction showed three degradation stages. The reduction in the weight of polymer started above 1008C became sharper after 2008C and showed a break in the change of slope at 3008C. The slope of the thermogram curve between 200 – 3008C is sharp indicating the Scheme 3. Degradation of PAMA with formation of anhydride and lactons. 1577 Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Degradation of Poly(Allyl Methacrylate) Figure 4. Fragments of soluble PAMA obtained at (a) 3098C (b) 4058C and (c) 4418C depolymerization mechanism. However, it was shown from the mass spectrum that the monomer does not come out as a fragment, but is fragmented into its components. Thus, in TGA analysis, the polymer is depolymerized to give monomer which is immediately degraded to its fragments. They are observed in FT-IR (Figure 6) Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   1578 T. K. Vardarelı, S. Keskın, and A. Usanmaz Table 2 The relative abundances of the peaks and their fragments for soluble PAMA fraction 3098C m/z I/I0 15 18 26 27 28 29 31 35 39 41 44 45 55 57 69 77 81 87 91 95 97 107 111 117 121 123 125 126 1.21 0.33 2.97 6.94 3.28 5.46 1.29 0.10 60.63 100 6.93 1.45 5.94 9.41 99.09 0.85 27.22 3.14 0.69 1.10 5.62 0.82 23.35 0.19 0.52 0.50 1.66 1.15 133 137 139 149 153 159 167 171 0.30 0.29 0.28 0.62 0.21 0.06 0.31 0.11 185 195 203 0.16 0.11 0.06 Fragments CH3 H 2O CN, C2H2 C2H3 CO C2H5, CHO CH3O Cl C3H3 C3H5 CO2 CHO2 C3H3O C3H5O C4H5O C6H5 C4HO2 C4H7O2 C6H5N C5H3O2 C5H5O2 C6H3O2 C6H7O2 CCl3 C7H5O2 C7H7O2 C7H9O2 C7H10O2 (AMA) C8H5O2 C6H5O3 C6H7O3 C9H5O2 C9H9O2 C7H11O4 C8H7O4 C9H17O2N, C8H11O4 C9H13O4 C11H15O3 C12H13O2N 4058C I/I0 0.57 0.72 1.17 4.56 3.77 4.12 0.59 0.13 17.36 27.25 13.78 2.59 10.49 4.12 19.47 3.53 8.78 1.49 5.39 6.10 2.54 5.13 4.00 1.07 3.75 3.50 1.95 1.18 1.41 1.07 1.05 1.71 0.75 0.76 1.42 0.46 0.39 0.40 0.35 Fragments CH3 H 2O CN, C2H2 C2H3 CO C2H5, CHO CH3O Cl C3H3 C3H5 CO2 CHO2 C3H3O C3H5O C4H5O C6H5 C4HO2 C4H7O2 C6H5N C5H3O2 C5H5O2 C6H3O2 C6H7O2 CCl3 C7H5O2 C7H7O2 C7H9O2 C7H10O2 (AMA) C8H5O2 C6H5O3 C6H7O3 C9H5O2 C9H9O2 C7H11O4 C8H7O4 C9H17O2N, C8H11O4 C9H13O4 C11H15O3 C12H13O2N 4418C I/I0 0.98 1.68 1.61 10.25 7.09 10.97 1.15 0.04 21.48 40.91 15.84 6.56 38.24 10.71 33.03 18.66 33.65 4.32 33.60 34.00 10.67 34.28 10.36 10.26 29.92 23.58 9.17 4.38 18.31 10.66 6.67 12.62 7.34 15.64 10.20 10.27 7.85 7.44 6.71 Fragments CH3 H 2O CN, C2H2 C2H3 CO C2H5, CHO CH3O Cl C3H3 C3H5 CO2 CHO2 C3H3O C3H5O C4H5O C6H5 C4HO2 C4H7O2 C6H5N C5H3O2 C5H5O2 C6H3O2 C6H7O2 CCl3 C7H5O2 C7H7O2 C7H9O2 C7H10O2 (AMA) C8H5O2 C6H5O3 C6H7O3 C9H5O2 C9H9O2 C7H11O4 C8H7O4 C9H17O2N, C8H11O4 C9H13O4 C11H15O3 C12H13O2N (continued ) Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Degradation of Poly(Allyl Methacrylate) 1579 Table 2 Continued 3098C m/z I/I0 209 219 233 0.09 0.03 0.05 252 0.04 269 287 301 319 332 345 352 358 365 378 0.03 0.04 0.02 0.01 0.04 0.02 0.04 0.01 0.02 0.01 397 0.26 422 — 624 — 748 — 800 — Fragments C11H13O4 C12H11O4 C14H19O2N, C14H16O4 C14H20O4 (dimer) C14H21O5 C14H23O6 C15H25O6 C18H23O5 C18H20O6 C19H21O6 C19H28O6 C20H22O6 C20H29O6 C21H30O6 (trimer) C16H22Cl3 O 4N C22H30O8 (tetramer) C35H44O10 (pentamer) C42H52O12 (hexamer) C43H60O14 (heptamer) 4058C I/I0 0.29 0.23 0.15 0.09 0.07 0.05 0.04 0.06 0.06 0.04 0.02 0.03 0.03 0.02 0.24 — 0.01 — — Fragments C11H13O4 C12H11O4 C14H19O2N, C14H16O4 C14H19O4 (dimer) C14H21O5 C14H23O6 C15H25O6 C18H23O5 C18H20O6 C19H21O6 C19H28O6 C20H22O6 C20H29O6 C21H30O6 (trimer) C16H22Cl3 O 4N C22H30O8 (tetramer) C35H44O10 (pentamer) C42H52O12 (hexamer) C43H60O14 (heptamer) 4418C I/I0 6.78 5.29 4.40 2.57 3.15 2.60 2.24 1.75 1.39 1.39 1.15 1.24 1.26 1.11 1.08 0.98 0.04 0.04 0.01 Fragments C11H13O4 C12H11O4 C14H19O2N, C14H16O4 C14H19O4 (dimer) C14H21O5 C14H23O6 C15H25O6 C18H23O5 C18H20O6 C19H21O6 C19H28O6 C20H22O6 C20H29O6 C21H30O6 (trimer) C16H22Cl3 O 4N C22H30O8 (tetramer) C35H44O10 (pentamer) C42H52O12 (hexamer) C43H60O14 (heptamer) connected to TGA. At 2258C, FT-IR spectrum (Figure 6a) showed the fragments corresponding to –CH2 at 2900 –3000 cm21; allyl groups at 3084.5, 1648.1 and 931.9 cm21; CO, CO2 and CN at 2200 –2300 cm21; carbonyl corresponding to ester anhydride, and lactones at 1720– 1850 cm21; ether and ester at 1100– 1300 cm21. Further temperature treatment (Figure 6b, 3908C) gives similar fragmentation with increase of peak intensity for CO, CO2 and CN and peak broadening of carbonyl group. This can be due to the anhydride and lactones formation which fragmented according to Scheme 3 to give more CO and CO2. At 5808C (Figure 6c) the emission of CO and CO2 is almost completed and the most important fragments are ether or ester type. At this stage, the emissions of OH and NH groups are also noticeable and the complete fragmentation reaches to about 97%. Therefore, the degradation is almost completed at about 6008C. Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   1580 T. K. Vardarelı, S. Keskın, and A. Usanmaz Figure 5. TGA thermogram of soluble fraction of PAMA. Figure 6. FT-IR spectrum of degraded PAMA fragments from TGA at (a) 2258C, (b) 3908C, and (c) 5808C. Downloaded  By:  [TÜBİTAK  EKUAL]  At:  12:07  18  April  2008   Degradation of Poly(Allyl Methacrylate) 1581 Conclusions The degradation of PAMA was studied by MS and TGA. The mechanism of degradation was clarified by analysis of fragments degraded from polymer at different temperatures. Degradation of the polymer chain is generally a depolymerization type. However, the depolymerized monomer is readily degraded further to give its fragments. Generally, in mass spectrum the monomer peak is the main peak for the polymer degradation. In the case of PAMA, the monomer peak is very weak in the spectrum. The main fragmentation is the pendant allyl group breakage. This also indicates that the cyclopolymerization as suggested in the literature (4, 5, 8) has not taken place. 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