Understanding Structure-Property Relationships for Impact Polystyrene



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The understanding of impact polystyrene structure-property relations was previously limited to ex situ analysis. Developing in situ analysis methods for morphology development and interfacial tension characterization would enhance fundamental understanding of the multi-component, multi-phase impact polystyrene system and would facilitate development of online analysis tools to improve product quality and process control. Diffusing wave spectroscopy measurements and analysis coupled with microfluidic capillary viscometry was verified as a quantitatively accurate tool using polystyrene standards and prepared solutions of well-characterized impact polystyrene samples. The diffusing wave spectroscopy analysis and microfluidic capillary viscometer were then extended as in situ tools to monitor polymerizing systems and thereby follow morphology development. Ex situ rheological methods were then employed on post-phase inversion samples to extract interfacial tension using well-established quantitative rheological models. Polymerizations were conducted at 80 °C for 6 hours with 5 wt% total polybutadiene, styrene-butadiene copolymer concentration varied between 5-15 wt% of the polybutadiene. Bulk viscosity behavior was measured at 50 °C ranging in shear rate from 100 s-1 to 1000 s-1. The effect of block copolymer and random copolymer compatibilizers on controlling the structure and viscoelasticity of impact polystyrene was investigated using these in situ tools. Styrene-butadiene copolymers contained approximately 30 wt% styrene present as a tapered diblock, majority styrene blocks in a triblock, or tapered segments in a second triblock. Structure and viscoelastic behavior during polymerization indicated the effectiveness of block copolymers as compatibilizing agents and provide a quantitative mechanism to control the structure of impact polystyrene. The copolymer compatibilization effect was quantified by rheological methods. Adaptations to capture the complete viscoelastic relaxation time have been proposed and observation of behavior at phase inversion of the impact polystyrene system is recommended for future study. Use of the microfluidic capillary viscometer coupled with the diffusing wave spectroscopy analysis was demonstrated for in situ use on the impact polystyrene polymerizing system, but is readily applicable to other multiphase systems where morphology development and characterizing shear dependent viscosity behavior during processing is beneficial. Principals demonstrated in this work can be extended readily to online process control and quality analysis by the adaptations proposed.



Polystyrene, Diffusing wave spectroscopy, Microfluidic viscometer, Palierne, Interfacial tension, Morphology, Styrene-butadiene copolymer