KINETIC MEASUREMENTS BY MICROPYROLYSIS GLC - THERMAL DEGRADATION OF POLYMETHYLMETHACRYLATE POSSESSING LAURYL-MERCAPTYL END GROUPS

A sample of polymethylmethacrylate possessing lauryl-mercaptyl end groups has been fractionated by gel permeation chromatography, and measurements of the thermal degradation of the fractions have been performed by micro-pyrolysis-gas-liquid-chromatography. The rates of pyrolysis were measured between 330°C and 463°C by a resistive heating technique incorporating initial boost; between 450°C and 510°C heating by induction ('Curie-point') was attempted. Changes in mechanism with temperature have been deduced from: (a) Trends in specific reaction rate with initial molecular weight at different temperatures, (b) Inflections in the Arrhenius plots for the different fractions, and (c) Trends in molecular weight with conversion, for both fractionated and unfractionated samples. End-initiation is the predominant mechanism at low temperatures, but random scission becomes more important at higher temperatures. The predominating termination process also depends upon temperature; above 400°C the majority of chains unzip to the end provided the initial molecular weight is not too high, but at the lower temperatures termination occurs by a first order process during the unzip. © 1969.