GAMMA-RAY POLYMERIZATION OF MESOGENIC DIACRYLATES IN THE CRYSTALLINE,LIQUID-CRYSTALLINE AND LIQUID-STATE - A KINETIC-STUDY

A kinetic study of the gamma-ray polymerization of three mesogenic dia crylates, 4,4'-bis(3-acryloyloxypropoxy)biphenyl (DAPB), 4,4'-bis(6-ac ryloyloxyhexyloxy)biphenyl (DAHB) and 4,4'-bis(11-acryloyloxyundecylox y)biphenyl (DAUB), is presented. All compounds were studied on their p olymerizability in the crystalline state. It was found that they can b e completely polymerized though the reaction rates are very different and increase with increasing length of the alkylene spacer unit. Up to moderate conversion, solid-state polymerization is comparable with th at of acrylamide and follows a t(2) rate law. DAPB was chosen for a de tailed kinetic study of the in-source and post-polymerization in the c rystalline, liquid crystalline and liquid phase. In-source polymerizat ion is complete in the various phases though reaction rates and curve shapes of dose vs. conversion curves are very different. Possible orig ins such as enhanced molecular diffusion at elevated temperatures are discussed. X-ray studies indicate that a well-ordered polymer can be o btained from polymerization in a smectic phase, while polymers obtaine d from a crystalline or melt phase are considerably less ordered. Post -polymerization was studied as a function of the radiation dose and th e temperature of the subsequent annealing process. II was found that t he limiting conversion increases with increasing radiation dose and te mperature of the annealing process, but the polymerization is always i ncomplete. Even post-polymerization in the melt phase does nor exceed 55 percent conversion. The post-polymerization behaviour is comparable with that of acrylamide and can be described by a linear relation bet ween conversion and annealing time t.