Compatibilization of thermoplastic/silicone blends.

摘要

The melt blending of thermoplastic resins with silicones may offer beneficial property improvements. To achieve these benefits when the dispersed phase concentration is high (>20%), the blend morphology must be stabilized to prevent coalescence. Specifically, this thesis compares poly(styrene) (PS)/poly(dimethylsiloxane) (PDMS) blends stabilized with pre-made versus in situ reactively formed PS-PDMS block copolymers.;The high PS/PDMS immiscibility, comparatively low PDMS viscosity and limited quantities of model polymers required a small (<1 g), intense mixer. The dispersion of two blend systems, PS/poly(propylene) (PP) and PS/PDMS, was improved in a cup and rotor mixer (~0.5 g) by simply adding three steel balls. The PS/PP morphology was similar to that in larger mixers such as internal batch mixers and twin-screw extruders. The addition of the balls may have introduced elongational flows, higher shear rates and a wider range of deformation rates needed for effective particle break-up.;Model reactive PS and PDMS polymers were synthesized by anionic polymerization in order to more easily detect copolymer formation with gel permeation chromatography (GPC). Electron microscopy (scanning and transmission) was then used to observe the effect of reaction on morphology. In agreement with earlier work in other systems, the amine-anhydride reaction was much more effective in producing stable, small PDMS particles in PS compared to the carboxylic acid/epoxy or amine/epoxy reactions. The effectiveness of the amine/anhydride reaction was also suggested by the improved PDMS dispersion into commercial poly(caprolactam) (PA6) when the PDMS possessed pendant anhydride groups.;Pre-made symmetric PS-PDMS diblocks, were added to PS/PDMS blends. Instead of localizing at the interface, the block copolymer preferred to form micelles. The diffusion of block copolymer also limited the block copolymer's ability to reach the interface. The particle size was affected by the PS/PDMS viscosity ratio. When the viscosities were nearly matched, stable sub-micron dispersions of 20% PDMS in PS could be achieved using as little as 1% diblock. The improved dispersion may be attributed to better deformation of the phases or to changes in the interfacial tension as the molecular weight of the homopolymers or diblocks was varied.