纳米TiO_2粒子静电吸附引发剂及其原位锚固丙烯酸丁酯聚合

ELECTROSTATIC ABSORPTION OF AZO INITIATOR ONTO TiO_2 PARTICLES AND in situ ANCHORING POLYMERIZATION OF BUTYL ACRYLATE FROM MODIFIED TiO_2

调节体系酸碱度使分散于水分散液中的纳米TiO2粒子表面带负电,进而通过静电作用高效稳定吸附上偶氮盐类引发剂2,2′-偶氮二异丁脒二氯化氢(AIBA).实验发现引发剂在TiO2粒子表面的静电吸附存在一个稳定吸附上限,其值在pH=10的体系中为0.084mmol/g(相对于TiO2的量).进一步通过原位乳液聚合在TiO2粒子表面就地引发丙烯酸丁酯(BA)的锚固聚合,制备得到了PBA/TiO2复合乳胶.对聚合动力学和聚合产物的观察发现,吸附引发剂在其中起到重大作用,只有当引发剂用量略低于稳定吸附上限时,反应过程稳定性和聚合产物分散性才较好.此时聚合反应阻聚期短、反应速率快、单体转化率高、实验重现性好.热重分析(TGA)和红外光谱分析(FTIR)结合抽提实验证实,通过原位乳液聚合可在TiO2粒子表面锚固上13.5%的不可抽提PBA聚合物.动态激光粒度分析(DLS)发现,原位锚固改性对TiO2粒子软团聚体具有稳定的解团聚作用,可有效提高纳米TiO2粒子在体系中的分散性和分散稳定性.这一化学改性作用与超声分散所带来的物理性的可逆解软团聚作用有着本质区别.

Azo initiator 2,2＇-azobis （isobutyramidine） dihydrochloride （AIBA） can be stably absorbed onto TiO2 particles by electrostatic action. The adsorbed AIBA can initiate the in situ anchoring of butyl acrylate from TiO2 particles surface, and thus poly（butyl acrylate）/TiO2 composite latex particles （PBA/TiO2 ） were prepared via in situ emulsion polymerization. It was found from centrifugation experiment and UV measurement that there was an upper limit of AIBA adsorbed on TiO2 particles surface, and its value was 0.084 mmol/g（relatived to the amount of TiO2 ） in pH = 10 system. The adsorption of AIBA played a more important role both in polymerization behavior and in polymerization product. Only when the addition amount of AIBA was slightly less than the upper adsorption limit, the inhibition period was shorter, the polymerization rate and the monomer conversion were higher and the reaction stability were and the product stability were perfect. It was further proved by thermogravimetric analysis （TGA） and infrared spectrometry （FTIR） with soxhlet extraction experiment of PBA/TiO2 composite particles that 13.5% nonextraction poly （butyl acrylate ） were anchored on TiO2 particles surface. It was also found from dynamic light scattering （DLS） that part of TiO2 soft-aggregation had been disaggregated stably, and both the dispersion and dispersion stability of TiO2 particles in latex can be significantly improved because of the anchoring modification of TiO2 by PBA. This action resulted from anchoring modification, in essence, was different from the reversible disaggregation action of ultrasonication treatment onto TiO2 soft-aggregation. Thus, this study is favourable for maintaining the good dispersion and dispersion stability of nanoscale inorganic particles in organic matrix during its application in the fields of coatings, painting, plastics, rubber, textile, and cosmetic.