Study Of Siloxane-modified Polyacrylate Miniemulsion Preparation Technics

Siloxane-modified polyacrylate polymers attracted wide attention due to its properties of weather resistance, film forming, mechanical properties from acrylic polymers, and water resistance, temperature resistance, air permeability from organosilicone. In this research, silicone-acrylic miniemulsion is synthesized via miniemulsion polymerization. The monomers are 3-Methacryloxypropyltrimethoxysilane (MEMO), Methyl Trimethoxysilane (MTMS), Methyl Methacrylate (MMA), and n-Butyl Acrylate (BA). According to study of the siloxane-modified polyacrylate miniemulsion preparation technics, we can synthesize silicone-acrylic miniemulsion that is rich in silicone, high in solid content, with high stability, small particle size and narrow size distribution.The major siloxane monomer is MTMS, which proportion is 26.57 wt%. With the relatively low price of MTMS, the product comes with reasonable organosilicone content at a lower cost. The basic formula and process of silicone-acrylic miniemulsion is optimized according to our research on initiator content, emulsifier ratio, stabilizer choice, stabilizer content, and solid content. We notice that increasing solid content while the system is rich in silicone will affect the stability of miniemulsion, the particle size and its distribution. So we design two kinds of siloxane-containing acrylic copolymers in order to increase the stability of emulsion. With its relatively low molecular weight, we could add it as costabilizer to the miniemulsion polymerization system for increasing its stability. Also, the molecular chain is similar to the structure of polymerization monomers, so it can improve the compatibility of organosilicone and acrylate. Besides, the molecular chain contains reactive hydrolysable siloxane groups, which are able to connect with other siloxane on chemical bond.The CCTP-P, which is synthesized via catalytic chain transfer polymerization, contains double bond at its chain end, which can conduct radial polymerization with active monomers. When applying CCTP-P to the miniemulsion polymerization system with CA as stabilizer, the diameter of silicone-acrylic miniemulsion particle is as low as 88 nm, and its PDI is as low as 0.213. When applying to the miniemulsion polymerization system with HD as stabilizer. diameter of silicone-acrylic miniemulsion particle is not changed obviously, the PDI is decreased a little, while the stability of miniemulsion is not as good.Applying the low-molecular-weight and narrow-distribution ATRP-P synthesized via reverse atom transfer radical polymerization to silicone-acrylic miniemulsion with HD as stabilizer, when decrease the content of HD, the miniemulsion system is still with good stability comparing when CCTP-P is applied. When the content of siloxane in ATRP-P increased, the silicone-acrylic miniemulsion particle is smaller, the distribution of which is narrower, and its stability is higher. Besides, the content of costabilizer has an optimum value of 1wt% (with 1wt% HD), so that we get the optimum formula of this silicone-acrylic miniemulsion polymerization, which m(monomers)/m(H20) is 9:11 (solid content is about 45%) and siloxane monomers mass fraction is 30.61wt%. With the optimized formula and process, the particle size of silicone-acrylic miniemulsion is as low as 62 nm in diameter, the PDI is as low as 0.081. The miniemulsion can stay stable even after 30 days, and it also has good dilution stability and mechanical stability. When applying this formula and process to different organosilicone monomers, we could adjust the hydrolysis and emulsification time to improve the applicability. At the end of this research, we look into the stability effect of siloxane-containing acrylic copolymers in monomer miniemulsion. In the monomer miniemulsion with CA as stabilizer, introducing costabilizer ATRP-P can effectively decrease particle size, narrow its distribution and increase its stability. When the siloxane content in ATRP-P is increasing, the effect is more significant. This effect also happens in the system of different monomers, which proves that siloxane-containing acrylic copolymers ATRP-P contributes to the reduction of Ostwald ripening, inhibit the diffusion of monomers, and increase the stability of miniemulsion.