KINETIC-STUDY OF THE PHOTOINITIATED POLYMERIZATION OF A LIQUID-CRYSTALLINE DIACRYLATE MONOMER BY DSC IN THE ISOTHERMAL MODE

The photoinitiated polymerization of the liquid crystalline (LC) diacrylate monomer 1,4-(-2-methyl phenylene)-bis[4-(6-acryloyloxy-hexamethyleneoxy)benzoate] with T(k,n) = 85-degrees-C and T(i) = 118-degrees-C, was studied by d.s.c. at various temperatures under different conditions. In the crystalline state there is a low polymerization rate which increases on approaching T(k,n). In the LC state the initial rate is temperature independent up to 10-20-degrees-C above T(i) signifying that a better monomer ordering in the LC state does not appear to affect the rate. Rate invariance on elevation of temperature may be the consequence of a compensation of propagation rate increase by termination rate increase. At still higher temperatures the rate drops probably due to depropagation. The 0.65 order in photoinitiator (= 2,2-dimethoxy-2-phenylacetophenone) points to the presence of a first-order termination mode besides the usual second-order mode. The results on temperature dependence were compared with those of a LC monoacrylate monomer, 4-acryloyloxyhexamethyleneoxybenzoic acid.