纳米SiO_2/含氟丙烯酸酯共聚物复合乳液的制备与性能及聚合动力学研究

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

采用原位聚合法制备纳米SiO2/含氟丙烯酸酯共聚物复合乳液,研究了其聚合反应动力学,并通过红外光谱(IR)、透射电子显微镜(TEM)、热失重(TGA)等方法表征所得产物的结构及形态、乳胶膜的耐热性能和表面性能.研究结果显示,聚合反应的表观活化能为83.15 kJ/mol,纳米SiO2/含氟丙烯酸酯共聚物复合粒子呈现出明显的核壳结构,纳米SiO2粒子的引入不仅改善了聚合物的耐热性能,也在一定程度上提高了乳胶膜的抗水性.对膜表面自由能的组成分析表明,与一般含氟乳胶膜的表面自由能的情况相反,该乳胶膜的表面能是由较大的极性部分和较小的色散部分组成.

Perfluorinated polymers are of high scientific and technological interest owing to their uniquecharacteristics. 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 mechanicalstrength 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-nBA-co-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 Stǎber procedure, followed by modification via addition of γ-methacryloxy propyhrimethoxysilane （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-nBA-co-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 （MMA-co-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 MPS-grafted silica with a low grafted density was introduced,had been investigated in details. The results can be summarized as follows： Rp ∝ [ FA]^0.25 [SiO2 ]^0.31 [I]^0.66 [E]^0.757 while [SiO2] 〈 8.9 × 10^-2 mol·L^-1, and Rp ∝ [FA]^0.25 [SiO2 ]^-133 [I]^0.66 [E]^0.757 while [SiO2 ] 〉 8.9 × 10^-2 mol· L^-1 . The overall activation energy of the polymerization was calculated to be 83.15 kJ/ mol ,