Effect of structure on the glass transition temperatures of linear and crosslinked poly(isobornylacrylate‐co‐isobutylacrylate)

A series of linear acrylic copolymers based on Isobornyl acrylate (IBOA) and isobutyl acrylate (IsoBA) were elaborated by radical photopolymerization. In addition, several photochemically crosslinked poly(IBOA‐co‐IsoBA) were prepared by introducing small amounts of 1,6‐hexanedioldiacrylate as crosslinking agent. The evolution of the glass transition temperature was determined experimentally by differential scanning calorimetry as a function of composition for both linear and crosslinked poly(IBOA‐co‐IsoBA), yielding Tg values ranging from (~249) to (~315 K). Theoretical modeling was performed applying Fox, Gordon‐Taylor and Couchman‐Karasz models by simple calculations using experimental data, leading to only fair agreement between theoretical and experimental values, or by applying fitting procedures involving one or two adjustable parameters. Likewise, the Kwei model, known to take into account hydrogen bonding interactions between monomers, could not describe well the evolution of Tg, indicating the existence of other factors influencing Tg. Finally, a thermodynamic approach based on entropy considerations allowed to attribute an explanation of the evolution of Tg.