A new approach for measuring the rate of pyrolysis of cross-linked polymers: evaluation of degradation rate constants for cross-linked PMMA

• Published in: Polymer degradation and stability 1998-01, Vol.62 (1), p.67-71
• Main Authors: Bate, David M., Lehrle, Roy S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical reactions and properties; Degradation; Exact sciences and technology; Organic polymers; Physicochemistry of polymers
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/S0141-3910(97)00262-0

Low molecular weight samples of PMMA have previously been observed to degrade at 400 °C via scission-initiated chain unzip in which the majority of the molecules depropagate to the end and are effectively terminated in this way. It was considered by the authors that if a cross-link were present within the PMMA molecule the unzip may be halted and the overall rate of degradation of the PMMA sample thereby reduced. In the present work, samples of cross-linked low molecular weight PMMA have been prepared by free radical polymerisation using azo-bis-isobutyronitrile as an initiator, carbon tetrachloride as a transfer agent and ethylene glycol dimethacrylate as a cross-linking agent. The rate of evolution of MMA monomer from these polymers has been measured and compared with equivalent samples prepared without a cross-linking agent. The samples have all been prepared in situ on the filament subsequently used for pyrolysis. This novel approach has not yet been previously reported, and is the ideal approach for studying the kinetics of intractable cross-linked material. It has been found that cross-linking low molecular weight PMMA does inhibit the rate of evolution of MMA monomer at 400 °C. An explanation of this may be attributed to cross-link units in the chain impeding the unzipping reaction.