Syntheses of UV-curable hyperbranched polysiloxanes and studies on their photo-curing behavior

UV-curable hyperbranched polysiloxanes were synthesized via hydrolysis of γ-methacryloxypropyltriraethyloxysilane (A-174) by controlling the amount of water. Macromolecular structures of the polymers obtained were characterized and confirmed by FT-IR, ¹H-NMR spectra and multi-angle laser light scattering technology (MALLS). The results indicated that the hyperbranched polysiloxanes carrying a large amount of functional vinyl groups could be cured under UV-irradiation. Their photo-initiated curing kinetics were studied by isothermal differential photo calorimeter (DPC) test. It was found that both the polymerization rate and the ultimate conversion first increased and then decreased with the increase in the molecular weight of the polymer and the photoinitiator concentration. The increase in UV-light intensity can lead to increase of both the polymerization rate and the ultimate conversion, and particularly, the polymerization rate is proportional to the square root of light intensity. Although elevated temperature can indeed improve the polymerization rate and the ultimate conversion, the effect of temperature on polymerization rate is not prominent. The total exponent of the photo-polymerization of the polymer 3 # is about 3, and the apparent activation energy is 16.9 kj/mol, calculated from an autocatalytic model.