Abstract
Dependent on the mode of preparation, 2-hydroxyethyl methacrylate (HEMA) can at low temperatures acquire either vitreous or crystalline states. On heating γ-irradiated vitreous HEMA, polymerization starts immediately after transition of the system from the vitreous state to that of a supercooled liquid ( T g = 177 K). This provides conditions for growth of polymer chains and suppression of bimolecular termination of active growing centres. Polymerization of radiated crystalline HEMA occurs at higher temperatures in the monomer melting region. At equal dosages of preliminary radiation, the transformation depth for the crystalline sample is considerably lower than that for the vitreous sample; this effect is due to different molecular mobilities in heated crystalline and vitreous samples. In HEMA post-polymerization, the very early transformation stages yielded an insoluble cross-linked polymer. This paper discusses the possible mechanism of cross-linking during polymerization of monomers of the HEMA type as a result of detachment of hydrogen from the carbon atom in the glycol group.
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