Clemens Auschra

Poly(styrene-b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly(styrene-co-acrylonitrile) and poly(2,6-dimethyl-1,4-phenylene ether): 1. Location of block copolymers in ternary blends — compatibilization versus micelle formation

Abstract The compatibilizing effect of the symmetric narrowly distributed block copolymer poly(styrene- b -methyl methacrylate) (P(S- b -MMA)) in blends of high-molecular-weight poly(styrene- co -acrylonitrile) containing 20 wt% (PSAN20) or 43 wt% acrylonitrile (PSAN43) with poly(2,6-dimethyl-1,4-phenylene ether) (PPE) was investigated by dynamic mechanical spectroscopy and transmission electron microscopy. In blends with the PSAN43, P(S- b -MMA) forms spherical micelles in the PPE phase with no dispersing efficiency. In contrast to this, for blends with PSAN20, the block copolymer is located at the phase boundary, causing an extremely fine dispersion of the components. Depending on the location of P(S- b -MMA), the PPE glass transition is altered by the PS blocks to different degrees. Even for block copolymer concentrations as high as 20 wt%, in ternary blends with PSAN20 and PPE no micelles could be detected. The results suggest that A/B blends compatibilized with a C-D block copolymer, in which the copolymer components show an exothermic heat of mixing with the bulk phases A/B, are superior to systems A/A-B/B with respect to emulsifying efficiency. Owing to the high tendency of the block copolymer to locate at the phase boundary, micelles do not compete at concentrations of practical interest.

Synthesis of block copolymers with poly(methyl methacrylate): P(B-b-MMA), P(EB-b-MMA), P(S-b-B-b-MMA) and P(S-b-EB-b-MMA)

SummaryWell-defined diblock copolymers poly(butadiene-b-methyl methacrylate) (=P(B-b-MMA)) and triblock copolymers poly(styrene-b-butadiene-b-methyl methacrylate) (=P(S-b-B-b-MMA)) have been prepared by sequential anionic polymerization in THF. The synthesis of P(B-b-MMA) and P(S-b-B-b-MMA) was most efficient in the presence of lithium alkoxides. By this method side reactions are suppressed and the polymerization can be performed at higher temperatures. The resulting triblock copolymers have narrow molecular weight distribution. The 1,2-PB midblock was quantitatively hydrogenated with tosylhydrazide to enhance thermal stability. Alternatively the hydrogenation can be performed at elevated pressure using hydrogen and Wilkinson-catalyst in butanone. Heterogeneous catalyst systems based on Palladium did not yield quantitative hydrogenation.

Poly(styrene-b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly(styrene-co-acrylonitrile) and poly(2,6-dimethyl-1,4-phenylene ether): 2. Influence of concentration and molecular weight of symmetric block copolymers

Abstract The influence of the molecular weight of the symmetric block copolymer poly(styrene- b -methyl methacrylate) (P(S- b -MMA)) in blends with high-molecular-weight poly(styrene- co -acrylonitrile) (PSAN) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE) is investigated by dynamic mechanical analysis and transmission electron microscopy. Total molecular weights of the block copolymers vary from 16 up to 275 kg mol −1 . Independent of molecular weight, all block copolymers locate to the interface with strong dispersing efficiency. The different block copolymers also showed approximately the same emulsifying efficiency. The degree of segmental mixing of the blocks with the respective phases is evaluated from the glass transition behaviour. A qualitative model is developed to relate the observed glass transition behaviour to the segmental distribution. In blends with large block copolymers, polystyrene blocks and PPE are rather uniformly mixed. The degree of mechanical coupling of the phases increases with the block copolymer molecular weight. The favourable enthalpic interaction between the blocks and the blend components is a major factor determining the phase behaviour. In contrast to this, the molecular weight of PPE showed little influence on blend behaviour.

Thermal stability of poly(styrene-b-methyl methacrylate) and poly(styrene-b-ethylene-co-1-butene-b-methyl methacrylate)

SummaryThe thermal stability of poly(styrene-b-methyl methacrylate) diblock copolymers (= P(S-b-MMA)) and poly(styrene-b-ethylene-co-1-butene-b-methyl methacrylate) triblock copolymers (=P(S-b-EB-b-MMA)) was investigated. Well-defined high molecular weight block copolymers with narrow molecular weight distribution (MWD) were molded at different temperatures in vacuum and the alteration of the MWD was sensitively monitored by gel permeation chromatography (GPC). Up to 240°C P(S-b-MMA) shows almost no broadening of the MWD. At higher temperatures low molecular weight polystyrene-rich portions are formed. The number average molecular weight (Mn) is strongly reduced. P(S-b-EB-b-MMA) triblock copolymers show broadening of the MWD to higher and lower molecular weights at elevated temperatures, probably caused by chain scission and linking reactions of the EB block. Mn remains approximately constant. Up to 240°C the broadening of the MWD is not very pronounced. In comparison to unhydrogenated P(S-b-B-b-MMA) triblock copolymers, the thermal stability of P(S-b-EB-b-MMA) is greatly enhanced.