Radiation crosslinking of poly(vinyl chloride) enhanced by a tetrafunctional coagent

Irradiations were carried out with mixtures of poly(vinyl chloride) and a solvent capable of preventing the polymer from discoloration, such as tetrahydrofuran or cyclohexanone, both in the absence and in the presence of a tetrafunctional monomer (ethyleneglycol dimethacrylate) acting as a coagent for enhanced crosslinking. Comparison of the results enabled formulation of a reaction scheme based on an early depletion of the free coagent molecules via polymerization. In the early stages, the PVC macromolecules, whenever dissociated into free radicals, initiate a chain addition of coagent molecules resulting in the formation of complex macromolecules with a number of pendant CC groups. All the latter macromolecules, because of their high susceptibility to radical attack, grow rapidly and eventually become part of the gel portion. In the late stages, radical addition to pendant CC groups in the gel network still occurs effectively but the addition steps are very few and there may be only one such step before radical deactivation. Hence, there is small consumption of double bonds; further, the PVC macromolecules, once homolytically dissociated, are directly incorporated into the gel. An interesting consequence is that no crosslinked macromolecules remain in the sol portion. The influence of the solvent is discussed.