Phase transitions of poly(oligo(ethylene glycol) methyl ether methacrylate)-water systems

The phase diagrams for poly (oligo (ethylene glycol) methyl ether methacrylate) (POEGMA) hydrogels with varying side chain lengths over broad temperature and composition ranges are shown for the first time. It is also shown that the ability of water to crystallize is strictly correlated with the occurrence of a volume phase transition in hydrogels, as both phenomena require the continuous water pathways in the system. A discontinuity in the water phase appears above w(p) = 0.83 for PMEO(2)MA and w(p) = 0.56 for other POEGMAs. In contrast to PMEO(2)MA, POEGMA hydmgels with longer oligoether chains are characterized by two distinct regimes for the glass transition as a function of polymer content. It was also confirmed that crystallization of the polymer network can be observed for POEGMA networks with suitably long oligoether chain lengths, namely, n >= 7. Moreover, the range of the polymer crystalline phase occurrence was found to increase with the length of the oligoether chain.