Preparation And Characterization Of Phenylpolysiloxane With Regularly Alternating Structure

Phenylpolysiloxane has been widely used in aerospace,electronic and electrical fields and other high-tech fields due to its excellent high and low temperature resistance,radiation resistance,flame retardancy and high refractive index.So far,most of the reported phenylpolysiloxane materials are random or block copolymers,which are usually prepared by ring opening copolymerization of cyclic siloxanes.However,it is believed that more ordered microstructure of phenylpolysiloxane,such as regularly alternating structure,should render a better combination of the two components in performance and thus could obtain novel materials with unique properties.Therefore,in this thesis,Piers-Rubinsztajn reactions?P-R reaction?of methylphenyldialkoxysilane?Me Ph Si?OR?₂?or diphenyldialkoxysilane?Ph₂Si?OR?₂?with hydrogen terminated siloxane oligomers under the catalysis of B?C₆F₅?₃were carried out and novel polysiloxanes with different phenyl contents were successfully prepared.The effects of catalyst amount,feed ratio,reaction temperature and solvents on the preparation of the copolymer were studied.The phenyl content and sequence distribution of the copolymer were analyzed in detail by ¹H NMR and ²⁹Si NMR.The results showed that the efficient preparation of phenylpolysiloxane could be achieved by P-R reaction at room temperature with catalyst loadings of 0.02-0.08mol%?relative to=Si?OR?₂?.Good controllability of the phenyl content of the copolymer was demonstrated by ¹H NMR analyses.The molecular weight of the product was not only influenced by the feeding ratio,but also related to the feeding mode and feeding rate.The sequence structure of the copolymers was primarily dependent on the steric hindrance of the two raw materials,which was distinctly different from the products obtained by ring opening copolymerization.In most cases,the redistribution between Si?H and Si?OR groups was the mainly detectable side reactions.Using the P-R reaction between Ph₂Si?OR?₂?R was methyl or ethyl group?and hydrogen terminated siloxane oligomers,the efficient preparation of phenyl-polysiloxane with alternating structure could be achieved.The molecular weight of polycondensation products tended to follow Poisson distribution.In the P-R reaction,Ph₂Si O units exhibited higher stability than Me Ph Si O units,since there was no appreciable cleavage of Si-Ph bond occurring in the former.Polysiloxane with phenyl contents up to 50%could be prepared by the reaction of Ph₂Si?OR?₂and Ph₂Si?OSi Me₂H?₂.The product was a semi-crystalline material with exactly alternating structure.Terpolymers with regularly alternating structure could be obtained by the reaction of Ph₂Si?OR?₂with Me Ph Si?OSi Me₂H?₂.The catalyst amount and the feed ratio had no obvious influence on the sequence distribution of the copolymers.The effect of reaction temperature and reaction solvent on the sequence distribution of the copolymers was fairly weak.The regularity of the alternating structure of the copolymers decreased with the structure of the starting dialkoxysilane in the following order:Ph₂Si?OEt?₂ > Ph₂Si?OMe?₂ > MePhSi?OEt?₂ > MePhSi?OPrⁿ?₂ >MePhSi?OMe?₂ >> MePhSi?OPrⁱ?₂.Desired results could also be obtained via bulk polycondensation,which was very beneficial for industrial application.