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 acrylate monomers as reactive diluents: ethylhexylacrylate, hexanediol diacrylate, 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 glass transition temperature (T_g) and the functionality of the reactive diluent do not affect the onset value of the glass transition temperature of the network. Nevertheless, the main mechanical relaxation, denoted α, associated with the glass transition temperature becomes broader 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 the amount of the diacrylate monomer leads to an increase in the equilibrium and storage moduli in the rubbery state and to a decrease in the amplitude of the α relaxation. © 1996 John Wiley & Sons, Inc.