Polystyrene stereochemistry forms

HIPS) is produced commercially by the emulsion polymerization of styrene monomer containing dispersed particles of polybutadiene or styrene-butadiene (SBR) latex. The resulting product consists of a glassy polystyrene matrix in which small domains of polybutadiene are dispersed. The impact strength of HIPS depends on the size, concentration, and distribution of the polybutadiene particles. It is influenced by the stereochemistry of polybutadiene, with low vinyl contents and 36% d5-l,4-polybutadiene providing optimal properties. Copolymers of styrene and maleic anhydride exhibit improved heat distortion temperature, while its copolymer with acrylonitrile, SAN — typically 76% styrene, 24% acrylonitrile — shows enhanced strength and chemical resistance. The improvement in the properties of polystyrene in the form of acrylonitrile-butadiene-styrene terpolymer (ABS) is discussed in Section VILA. 

Impact polystyrene is produced commercially by dispersing small particles of butadiene rubber in styrene monomer. This is followed by mass prepolymerization of styrene and completion of the polymerization either in mass or in aqueous suspension. During prepolymerization, styrene starts to polymerize by itself, forming droplets of polystyrene with phase separation. When nearly equal phase volumes are obtained, phase inversion occurs, and the droplets of polystyrene become the continuous phase in which the rubber particles are dispersed. The impact strength increases with rubber particle size and concentration, while gloss and rigidity are decreasing. The stereochemistry of the polybutadiene has a... 

As an extension of this work, the same authors have used polystyrene-supported proline as a recyclable catalyst in the Morita-Baylis-Hillman reaction of a range of aryl aldehydes with methyl or ethyl vinyl ketone. These reactions were performed in the presence of imidazole and provided a series of Morita-Baylis-Hillman adducts in moderate to high yields (17 88%) combined with high enantioselectivities of up to 95% ee (Scheme 2.55). This study represented the first example of supported proline as heterogeneous catalyst for the Morita-Baylis-Hillman reaction. In addition, Zhou et al. reported that these reactions could be eatalysed by combinations of L-proline with chiral tertiary amines derived from various readily available chiral sources, such as L-proline or (5)-a-phenylethylamine. In these conditions, the Morita-Baylis-Hillman adducts were obtained in reasonable chemical yields (34-97%) and low to good enantioselectivities (12 83% ee). In this study, it was demonstrated that the proline stereochemistry was the sole factor to determine the eonfiguration of the newly formed chiral centre. 

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