Studies on Glass XIII. Glass Formation by a Hydrocarbon Polymer

Polyisobutylene, with an average molecular weight of about 4900, is at room temperature a highly viscous liquid. When cooled, it has been found to form a glass, with the same transitions in thermal properties characteristic in the vitrification of substances of low molecular weight. The heat capacity of polyisobutylene has been measured from 118°K to 295°K. It increases by 32 percent between 192°K and 202°K. The thermal expansion coefficient of polyisobutylene has been measured from 160°K to 300°K. It increases by 200 percent between 185°K and 205°K. The mean temperature of transition corresponds to a viscosity of about 1013 poises, in agreement with a rule observed generally for glass-forming materials. The factors on which the transition temperature depends are discussed.