DYNAMIC-MECHANICAL PROPERTIES OF UV-CURABLE POLYURETHANE ACRYLATE WITH VARIOUS REACTIVE DILUENTS

UV-curable polyurethane acrylate (PUA) based on polycaprolactone and m -tetramethylxylene diisocyanate were considered with different acrylat e monomers as reactive diluents: ethylhexylacrylate, hexanediol diacry late, and isobornyl acrylate. The effect of the chemical structure and functionality of the reactive diluent (33 wt %) on their thermal and mechanical properties were investigated. The synthetized PUA networks are homogeneous from a thermodynamical point of view. The initial glas s transition temperature (T-g) and the functionality of the reactive d iluent do not affect the onset value of the glass transition temperatu re of the network. Nevertheless, the main mechanical relaxation, denot ed alpha, associated with the glass transition temperature becomes bro ader as the T-g of the homopolymer of the considered reactive diluent becomes higher than the T-g of the PU soft segments. The increase of t he amount of the diacrylate monomer leads to an increase in the equili brium and storage moduli in the rubbery state and to a decrease in the amplitude of the alpha relaxation. (C) 1996 John Wiley & Sons, Inc.