| A series of p-substituted methyl (alpha)-phenylacrylates having -Cl, -H, -CH(,3), and -OCH(,3) as substituents was synthesized and polymerized anionically. These polymers were degraded thermally and the weight loss was measured by dynamic thermogravimetric analysis at a constant heating rate of 20(DEGREES)C/minute. The activation energies of decomposition were estimated from the thermograms by the ratio method and correlations were attempted with Hammett's substituent constants for the purpose of establishing the role of substituent effects in the thermal decomposition of these polymers.;The polymers were found to degrade by unzipping following random initiation, yielding monomers as an exclusive degradation product. Such mechanisms of degradation were not influenced by the introduction of the substituents.;The apparent overall activation energies of decomposition of polymers were found to be complicated by the influence of the substitutents on the relative contributions of initiation, depolymerization and termination energies. However, it was possible to estimate activation energies of 59, 62, 75, and 75 Kcal/mole for p-CH(,3), -H, -Cl, and -OCH(,3) substituted polymers, respectively. No quantitative linear correlation was found between these activation energies and Hammett's (sigma) or (sigma)('+) values; but they were shown to exhibit a distinct trend with values of (sigma)(,R). A similar trend was also observed in decomposition temperatures determined by thermogravimetry and differential scanning calorimetry. Significantly, the ability of the substituent to stabilize the depolymerizing free radical was shown to be the controlling factor in determining the ease of degradation of the polymer.;The polymerizability and stereoregularity of polymers were found to vary with the polar character of the substituents. |
