The microstructure of copolymer chains

the system stability of miniemulsion copolymerization and the free radical copolymerization were influenced by the hydrolysis degree of miniemulsion copolymerization of γ-methacryloxypropyltrimethoxysilane (MPS) and styrene (St) was investigated in terms of the ratio of MPS and St

the pH value of medium

the surfactant amount

the type and amount of initiators.The hydrolysis degree was calculated from the methanol concentration during the process of reaction which could be followed by the gas chromatography.Because of the weak dependence on the type of initiators but strong dependence on the surfactant amount of the hydrolysis degree

the interfaces of mini-droplets and latexes were considered as the main locus of the hydrolysis reactions.The amount of hydrolyzed MPS increased with the increase of the ratio of MPS and St

but the final hydrolysis degree was independent of this ratio.The hydrolysis rate was accelerated by either decrease or increase of medium’s pH value.However

compared to the formation of gels under acidic condition in conventional emulsion polymerization

the reaction system was stable

and the final product was stable in the miniemulsion mode which was attributed to the partition of the most of hydrolyzed MPS molecules at the interface of the droplets or particles as a result of the large surface area of droplets or particles in the miniemulsion system.Consequently

the condensation reactions in aqueous phase which were regarded as the main reason of gel product formation decreased corresponding to the decrease of the amount of hydrolyzed MPS in aqueous phase.The hydrolysis degree increased with the increase of surfactant amount as a result of the decrease of the droplets size which in turn increased the surface area of droplets.In the system initiated by KPS

as the polymerization proceeded

the pH value of the medium would decrease because of the formation of acidic groups as a result of the decomposition of KPS.Therefore

with the increase of the amount of initiator the hydrolysis degree increased.The condensation reactions were followed by the 29Si solidstate NMR.Under neutral conditions

the condensation reactions were suppressed effectively even with 1∶1 ratio of MPS and St.The condensation reactions could not be avoided at an acidic pH values

but it could be minimized at a basic pH attested by the presence of a signal at δ =-43 corresponding to silicon atoms belonging to noncondensed MPS.Because the condensation reaction rate was slower under the acidic condition than that under the basic condition

the T2 species

the intermediate resultant of condensation

dominated in the final product under acidic condition

while the T3 species did in the final product under the basic condition.Compared to the emulsion polymerization

the hydrolysis and condensation reactions were more easily controlled in miniemulsion polymerization because of its droplet nucleation mechanism and little mass transfer between droplets which could reduce the contacting opportunity of MPS molecules and water.