The Research On Core-shell Modifiers Toughening Ploy(Methyl Methacrylate) Resins

Polymethyl methacrylate (PMMA) resins usually comprise the polymethyl methacrylate homopolymer and the compolymers containing predominantly methyl methacrylate but with small amounts of methyl or ethyl acrylate, acrylonitrile or styrene comonomers added for improved toughness. PMMA resins are rigid, amorphous polymers particularly noted for their exceptional clarity and UV resistance, and therefore wildly used for making household appliances, electronic products, medical devices and automobile, etc. Due to the poor toughness and notch sensitivity, the research on toughening receives much concern, in which adopting core-shell modifiers toughening PMMA resins is one of the most important method. The strategy of PMMA resins toughened by core-shell modifiers show more complexity than other amorphous polymer, which demands modifiers not only promote more fracture energy absorption in the process of toughened blends fracture, which highen the mechanical properties, but refractive index of modifiers match with PMMA resins to maintain better optical property of matrix resins. Both weatherable modifiers with polybutyl acrylate (PBA) rubber phase and non-weatherable modifier with polybutadiene (PB) rubber phase can toughen PMMA resins effectively, but transmittance of blends decreases markly for mismatch of refractive index of PBA and PB with PMMA resins. So combined St with PBA or PB to match refractive index of modifiers with matrix resins can prepare toughening blends with high light transmittance.In this paper, preformed modifiers with controllable structure and proterties were synthesized. The influence of modifiers structure, cross-linking density of rubber phase, and the variance of interface property between modifiers and matrix on PMMA resins toughening were investigated. The main research works and conclusions are as follows:1. The relationship between reaction rate and initior concentration was investigated in the process of constant rate period of P(BA-co-St) emulsion polymerization, and the results showed that the relationship of reaction rate and initior concentration was Rp∞I0.44. The diameter of P(BA-co-St) rubber particles increased according to grow-out manner. Two layers acrylic impact modifiers (AIM), which was composed of BA-St copolymer rubber core and PMMA outer shell, and three layer modifiers with PS or PMMA inner core, BA or BA-St copolymer interface layer and PMMA external shell were synthsized by emulsion polymerization. The influence of AIM structure on PMMA toughess was investigated, and results showed that the optimum diameter of rubber particle of two layers AIMs was269nm, which led to maxium impact strength, fracture energy and stress intensity factor (Kmax) of AIM/PMMA blends, and crack propagating energy (Uprop) reached maxium when rubber particle diameter of AIM was351nm. The transmittance of blends decreased with the increament of rubber particles diameter, whereas the haze increased. The blends with three layers AIM had higher Kmax than those blends with two layers AIM, which indicated that the deformation of rubber phase of three layers AIM was benificial to hinder the generation of crack in the process of blends fracture. Morphology analysis of deformation zone of three layers AIM toughening PMMA blends showed that the AIM with BA-St copolymer as interface rubber layer generated evident cavitation, and the AIM with PBA as interface rubber layer arised matrix crazing, which can be attributing to the influence of rubber phase property on toughening mechanism.2. The influence of rubber phase cross-linking density of AIM on PMMA toughening was studied. It was shown that Kmax, Uprop and Izod impact strength of AIM/PMMA blends reached maximum when appropriate rubber cross-linking density was adopted. Morphology analysis of impact fracture surface showed that deformation mechanism of AIM/PMMA blends was local matrix shear yielding initiated by rubber particles cavitation. The rubber of AIM with appropriate cross-linking density was beneficial to form intensive voids and initiated local shear yielding of PMMA matrix nearby modifiers effectively in impact test.3. Blends of PMMA, AIM with carboxylic acid group and methyl methacrylate-glycidyl methacrylate-methacrylate copolymer were prepared by melt blending. Maxium torque and equilibrium torque of blends in the process of melt blending increased with the increase of carboxylic acid group content in the shell of AIM increament, and impact strength and Kmax of blends enhanced accordingly, but the optical propertie of blends was not affected. It indicated that the reaction of carboxylic acid group of modifiers and epoxy group of matrix resin increased interfacial cohesion of two phases, which led to not only the cohension increament of mixture melt but also more rubber particles cavitation and promoted massive yielding of maxtrix resins in the process of fracture deformation.4. Methyl methacrylate-butadiene-styrene copolymers (MBS), which were used as no-whetherable modifiers in PMMA toughening, were synthsized by emulsion polymerization. The variance of diameter of SBR, which was rubber phase of MBS modifiers, with emulsifier content was studied, and result showed that the diameter of SBR particles decreased with the increase of emulsifier content in emulsion polymerization. Three kinds of MBS core-shell modifier, synthesized by seeded-emulsion polymerization by changing St and MMA addition sequence, can disperse uniformly in MS resins. MBS prepared by grafting St and MMA mixture on SBR can strengthen interfacial adhesion between modifiers and matrix, and the blend showed higher notched-Izod impact strength and transmittance. It indicated that better interfacial property highen the mechanical and optical properties.In this work, on the premise of maintaining PMMA resins outstanding optical properties, the toughening of PMMA was solved successfully. High preformance blends, which transmittance was88.6%and impact strength increased four times than pure PMMA resins, were prepared. The mechanical properties of blends had exceeded general-purpose toughening resins, such as HIPS, and can fulfilled practice demand.