As inverstigating the influence of monomers and photoinitiator in the polymerization rate of photopolymerization by using IR spectroscopy, photopolymerizations initiated by ultraviolet radiation are characterized by the presence of an autoacceleration in the polymerization rate as the reaction proceeds. The conversion for the end of the autoacceleration varies considerably depending on the monomer and reaction condition which determines coil size and viscosity. In UV curable systems, the autoacceleration begins at only a few percent conversion and continues to 40% in HEA solution and 60% conversion in EHA solution. The polymerization ate in HEA solution increased as follow; DMHA > HCPK > DMPA and could be explained by the interaction between the initiating radical and HEA monomer and the size of the photodissociated radical of initiator. But the tendency of autoacceleration in EHA solution is almost independent on initiator.