Thermo-mechanical behavior and specific volume of highly crosslinked networks based on glycerol dimethacrylate and its derivatives

Three substituent derivatives of glycerol dimethacrylate (GDMA) i.e., acetyloxypropyl dimethacrylate (Acet-GDMA), acryloyloxy-hydroxypropyl methacrylate (GMMA), and acetyloxy-acryloyloxypropyl methacrylate (Acet-GMMA) as well as GDMA were prepared and UV-homopolymerized in the presence of 2,2-dimethoxy-2-phenyloacetophenone. The obtained homopolymers were subjected to dynamic mechanical studies and the deflections versus temperature measurements (HDT) were performed. The content of unreacted double bonds, glass transition temperatures (T (g)) as well as degree of inhomogeneity have been examined in all studied systems. Also, expansivity was measured in the function of temperature and the effect of a substituent group on the network properties was investigated. The results show that the hydroxyl-containing networks are characterized by much lower T (g) and higher degree of heterogeneity than those devoid of hydroxyls. When homopolymerized, hydroxyl-free dimethacrylates disclosed untypical deflection pattern which suggests that at higher temperatures the decrease in stiffness is compensated or even overrated by the increase in the specific volume. Expansivity measurements revealed twice as large volume increase of the acetylated polymers as opposed to their hydroxyl-containing analogs. Following these findings, a mechanism of thermally induced polymer swelling was proposed.