PREPARATION AND GLASS-TRANSITION TEMPERATURES OF ELASTOMERIC POLYHIPEMATERIALS

Highly porous elastomeric PolyHIPE materials have been prepared by pol ymerisation of the continuous phase of high internal phase emulsions ( HIPEs) containing styrene, divinylbenzene and varying amounts of eithe r 2-ethylhexyl acrylate or the corresponding methacrylate monomer. The glass transition temperatures of the resulting copolymers were invest igated by differential scanning calorimetry (DSC). For each series, T- g was found to vary non-linearly with copolymer composition. By consid eration of the comonomer unit sequencing along the polymer backbone, a s deduced from reactivity ratios, the relationship between T-g and com position in each case has been qualitatively explained. Comparison bet ween experimental results and values calculated using an entropic appr oach have been made. It is thought that the (meth)acrylate comonomers reduce the overall T-g by three mechanisms: by introducing large amoun ts of free volume, due to their bulky side groups; by providing a much higher degree of flexibility to the polymer chains; and by reducing t he proportion of adjacent styrene units, which display particularly un favourable steric interactions.