Strengthening And Toughening Effect Of Untreated Nanosilica On PMMA By The Electrostatic Interaction

Nanosilica is one of the important filler materials of rubber, plastic and coatingbecause of its excellent performances. However, the surfaces of nanosilica particlesare usually hydrophilic and unstable. This could result in the agglomeration ofnanosilica particles in the polymer, and further lead to a poor performance of thecomposite, which hinders the applications of nanosilica to some extent. Surfacetreatment of nanosilica is recommended to improve the dispersion of nanosilica inpolymer matrix, which however makes the preparation process more complicate.In this paper, methyl methacrylate （MMA） was selected as the matrix, andcopolymerized with a small amount of cationic comonomer2-（methacryloyloxy）ethyltrimethyl ammonium chloride （DMC） and dimethyl diallyl ammonium chloride（DMDAAC） respectively. Simultaneously the positively charged copolymer couldelectrostatically adsorb untreated nanosilica particles which are negatively charged toprepare the nanocomposite microspheres by in situ suspension copolymerization, andfurther to fabricate the nanocomposite. Prepared nanocomposite microspheres werecharacterized by1H-NMR, the electrostatic interaction between copolymer matrix andnanosilica particles was verified by Zeta potential and FT-IR, the effects of cationiccomonomer and nanosilica on the microsphere morphology and molecular weight ofPMMA were investigated by SEM and GPC, and the mechanical property ofnanocomposite was studied in detail.The results indicated that，PMMA based positively charged copolymers weresuccessfully synthesized despite of the presence of nanosilica, the presence of cationiccomonomer had scarcely effect and the presence of nanosilica had slightly effect onboth the microsphere morphology and molecular weight of PMMA, it was confirmedthat a strong electrostatic interaction existed between the P（MMA-co-DMC）copolymer and nanosilica, and a weak electrostatic interaction existed between theP（MMA-co-DMDAAC） copolymer and nanosilica. When the content of DMC andnanosilica was10vol%and1.0wt%respectively, the tensile and flexural strength ofP（MMA-co-DMC）/SiO₂improved by20.7%and140.7%. When the content ofDMDAAC and nanosilica was7.5vol%and1.0wt%respectively, the tensile strengthof P（MMA-co-DMDAAC）/SiO₂improved by18.5%, and when the content was5vol%and1.0wt%respectively, the flexural strength improved by63.4%.