Radiation‐induced cationic polymerization of β‐pinene

The radiation‐induced polymerization of β‐pinene carried out in bulk at ca. 25°C has been studied for different methods of monomer drying. It has been confirmed that the polymerization is sensitive to adventitious moisture and that substantial polymer yields (ca. 10% conversion per Mrad) can only be obtained under extremely dry conditions. Complete inhibition of the reaction by added tripropylamine corroborates the view that the polymerization is cationic. About half of the polymer formed is insoluble in the monomer. The number‐average molecular weights for the soluble poly(β‐pinene) fraction have been measured by vapor pressure osmometry and are in the narrow range from 1700 to 2400 with little or no dependence on the degree of monomer conversion to polymer, at least up to 80%. The results are compared with literature reports on the polymerization of β‐pinene by catalytic initiators.