Degradable Polymers Prepared from Alkyl Sorbates and Oxygen under Atmospheric Conditions and Precise Evaluation of Their Thermal Properties

Abstract

We report here the alternating copolymers of diene monomers with oxygen as a new class of degradable polymer with great potential. The alternating copolymers of alkyl sorbates with oxygen are efficiently prepared without decomposition under atmospheric conditions in the presence of an azo initiator. The produced alternating copolymers exothermically decompose upon heating in a similar mechanism irrespective of the kind of the ester alkyl group of the sorbates; i.e., the methyl, ethyl, octadecyl, and trifluoroethyl esters. The initial and maximum decomposition temperatures (Tinit and Tmax) are determined by differential thermal analysis (DTA) and thermogravimetric analysis (TG) in a nitrogen stream: Tinit = 106–112 °C (DTA), Tmax = 147–152 °C (DTA) or 144–148 °C (TG). The TG curves obtained at a different heating rate are kinetically analyzed to evaluate an activation energy for decomposition by several methods. The decomposition rate constants, as well as overall activation energy, for the polymeric peroxide obtained from methyl sorbate are also precisely determined during the isothermal decomposition in a temperature range of 80–120 °C by two different methods; Ea = 86.7 and 84.7 kJ mol-1 on the basis of the weight loss of the polymer monitored by TG analysis, and the change in the molecular weight of the polymer determined by gel permeation chromatography, respectively. It has been revealed that the thermal cleavage of the peroxy linkage and the subsequent successive β-scission produce fumaraldehyde monoester and acetaldehyde during the thermal decomposition of the alternating copolymers as the polymeric peroxides.