STUDY OF NANO-SILICA/FLUORINATED ACRYLATE COPOLYMER HYBRID EMULSION AND THE POLYMERIZATION KINETICS

Abstract

Perfluorinated polymers are of high scientific and technological interest owing to their unique characteristics.However,their utilization is limited due to their poor cohesiveness,film-forming properties and high cost.When perfluorinated polymers are incorporated with polyacrylate,remarkable properties are exhibited with higher performance price ratio;that is,oil and water repellency of the former is unmitigated while the mechanical strength and cohesiveness of the latter are retained.As an inexpensive functional component,incorporated silica can shield polymeric matrix from the UV,while reinforcement and improved thermal stability are achieved,as well as better rinse-resistance,perdurability and self-cleanness effects. In this paper,nano-silica and poly(MMA-co-nBAco-FA) were combined with covalent bonds.Not only extraordinary properties derived from each individual component were retained,but also a more intimate cooperation was provided between the twos,through an environment-friendly method. At first,the monodisperse silica was prepared in ethanol according to the well-known Stber procedure,followed by modification via addition of γ-methacryloxy propyltrimethoxysilane(MPS).Then,the nano-silica/poly(MMA-co-nBA-co-FA) hybrid emulsion was prepared via in-situ emulsion polymerization in the presence of MPS-grafted silica. The chemical compositions and morphologies of both nano-silica and silica/poly(MMA-co-nBA-co-FA) nanocomposites(NPs) were characterized by Fourier-transform infrared(FT-IR) spectrometry and transmission electron microscopy(TEM),respectively.From TEM images,it was obvious that uniform spherical nano-silica was obtained,with average diameter of 20 nm.FT-IR effectively proved the occurrence of MPS-grafting reaction.According to the amount of MPS added,the MPS-grafted density of nano-silica was determinated as 0.1716 μmol/m~2. Off-centre core-shell structures of silica/poly(MMA-co-nBA-co-FA) NPs were confirmed by TEM images.Approximately 50% of NPs had more than one single core due to the congregating of smaller particles when the diameters of the core were not larger than 100 nm.Under a low MPS-grafted density,not all of monomers were polymerized and connected with MPS on the grafted silica,and most of the polymer chains were twisted and absorbed around the core particles,followed by copolymerization with polymer layer copolymerized with MPS,resulted in an off-centre core-shell structure ultimately. Thermal stability of silica/poly(MMA-co-nBAco-FA) NPs was studied via thermal gravimetric analysis(TGA).The results showed that higher initiative decompose temperature was achieved with more nano-silica incorporated,which implicated the successful encapsulation of silica into NPs,as well as enhanced thermal stability. The surface properties of the latex films produced from silica/poly(MMAco-nBA-co-FA) NPs were also investigated by contact angle method and water absorption measurements.Obviously,the incorporation of silica and FA contributed to degressive surface-free energy,with a minimum value of 9.8 mN/m.Similarly,water absorption ratio decreased with increasing contents of nano-silica and FA.What worth noting was the abnormal polar and disperse component of surface-free energy,which might be attributed to nano-silica's incorporation and distribution while film-forming.Besides these,the kinetics of in situ emulsion polymerization,in which MPSgrafted silica with a low grafted density was introduced,had been investigated in details.The results can be summarized as follows: R_p∝~(0.25)[SiO_2]~(0.31)[I]~(0.66)~(0.757) while [SiO_2]8.9×10~-2 mol·L~-1,and R_p∝~(0.25)[SiO_2]~(-1.33)[I]~(0.66)[E]~(0.757) while [SiO_2]8.9×10~-2 mol·L~-1.The overall activation energy of the polymerization was calculated to be 83.15 kJ/mol.