ABSTRACT:The effects of three series of self-synthesized poly(methyl methacrylate) (PMMA)-based low-profile additives (LPAs), including PMMA, poly(methyl methacrylateco-butyl acrylate), and poly(methyl methacrylate-co-butyl acrylate-co-maleic anhydride), with different chemical structures and MWs on the miscibility, cured-sample morphology, curing kinetics, and glass-transition temperatures for styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems were investigated by group contribution methods, scanning electron microscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis, respectively. Before curing at room temperature, the degree of phase separation for the ST/UP/LPA systems was generally explainable by the calculated polarity difference per unit volume between the UP resin and LPA. During curing at 110°C, the compatibility of the ST/UP/LPA systems, as revealed by cured-sample morphology, was judged from the relative magnitude of the DSC peak reaction rate and the broadness of the peak. On the basis of Takayanagi's mechanical models, the effects of LPA on the final cure conversion and the glass-transition temperature in the major continuous phase of ST-crosslinked polyester for the ST/UP/LPA systems was also examined.
ABSTRACT:The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)-block-PMMA as low-profile additives (LPAs) on the volume shrinkage characteristics and internal pigmentability for low-shrink unsaturated polyester (UP) resins during curing at 110°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerization with polymeric peroxides as initiators. Depending on the LPA composition and molecular weight, the reactive LPAs led to a considerable volume reduction or even to a volume expansion after the curing of styrene (ST)/UP/LPA ternary systems; this was attributed mainly to the expansion effects of the LPAs on the STcrosslinked polyester microgel structures caused by the reduction in the cyclization reaction of the UP resin during curing as well as to the repulsive forces between the chain segments of UP and LPAs within the microgel structures. The experimental results were explained by an integrated approach of measurements for the static phase characteristics of the ST/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation with differential scanning calorimetry, scanning electron microscopy, optical microscopy, and image analysis. With the aid of the Takayanagi mechanical model, the factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts were also explored.
ABSTRACT:The effects of reactive poly(vinyl acetate)-block-poly(methyl methacrylate) (PVAc-b-PMMA) and poly-(vinyl acetate)-block-polystyrene (PVAc-b-PS) as low-profile additives (LPA) on the volume shrinkage characteristics and internal pigmentability for low-shrink unsaturated polyester resins (UP) during the cure at 30°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerizations, using polymeric peroxides (PPO) as initiators. Depending on the LPA composition and molecular weight, the reactive LPA could lead to a reduction of cyclization reaction for UP resin during the cure, and would be favorable for the decrease of intrinsic polymerization shrinkage after the cure. The experimental results have been explained by an integrated approach of measurements for the static phase characteristics of the styrene (ST)/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), optical microscopy (OM), and image analysis. Based on the Takayanagi mechanical model, factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts have been explored.
ABSTRACT:The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)-block-poly(methyl methacrylate) (PVAc-b-PMMA) as low-profile additives (LPAs) on the glass-transition temperature and mechanical properties of low-shrink unsaturated polyester resin (UP) were investigated by an integrated approach of determining static phase characteristics, reaction kinetics, cured sample morphology, and property measurements. The factors that, according to Takayanagi mechanical models, control the glass-transition temperature in each phase region of the cured samples, as identified by both the thermally stimulated currents method and dynamic mechanical analysis, and the mechanical properties are discussed.
ABSTRACT:The effects of three series of self-synthesized poly(methyl methacrylate) (PMMA)-based low-profile additives (LPAs), including PMMA, poly(methyl methacrylateco-butyl acrylate), and poly(methyl methacrylate-co-butyl acrylate-co-maleic anhydride) with different chemical structures and MWs on the volume shrinkage characteristics and internal pigmentability for low-shrink unsaturated polyester (UP) resins during curing were investigated by an integrated approach of static phase characteristics of the ternary styrene (ST)/UP/LPA system, reaction kinetics, cured-sample morphology, microvoid formation, and property measurements. The relative volume fraction of microvoids generated during the cure was controlled by the stiffness of the UP resin used, the compatibility of the uncured ST/UP/LPA systems, and the glass-transition temperature of the LPAs used. On the basis of the Takayanagi mechanical model, the LPA mechanism on volume shrinkage control, which accounted for phase separation and microvoid formation, and factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts are discussed.
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