Styrene copolymers, internal crosslinking

The internal cross-linking of styrene copolymers is dealt with in the chapter of R. N. Haward, B. M. Parker and E. F. T. White, who prepared a copolymer of styrene and hydroxyethyl methacrylate and crosslinked the copolymer with hexamethylene diisocyanate. 

To study the internal crosslinking of styrene-hydroxy ethyl methacrylate copolymers, it was necessary to prepare a range of well characterized materials containing only low concentrations of hydroxyethyl methacrylate. To ensure that the copolymers were of uniform composition, only low monomer conversions were used so that the composition of the monomer mixtures did not change appreciably during the reaction. Low polymerization temperatures were used to obtain high molecular weight copolymers. 

TseUos et al. [1997] have compatibilized PO/styrene copolymer blends through crosslinked copolymer formation between PO alcohol groups and anhydride groups on styrene copolymer. Specifically, 50 parts EVAl (1.6-7.5% VAl) was mixed with 50 parts SMA (8.4-14.7 mol% MA) in an internal mixer at 200°C. The blends were characterized by torque rheometry, FTIR, DSC, TGA, selective solvent extraction, and mechanical properties as a function of mole ratio alcohol to anhydride. Blend properties were compared to those with EVAc in place of EVAl. 

In the first one, the two materials are blended on a rubber mill or in an internal mixer. Blending of the two materials can also be achieved by combining emulsion latexes of the two materials together and then coagulating the mixture. Peroxide must be added to the blends in order to achieve some crosslinking of the elastomer to attain optimum properties. A wide range of blends are made by this technique with various properties. Most common commercial blends of ABS resins may contain 70 parts of styrene-acrylonitrile copolymer (70/30) and 40 parts of butadiene-nitrile rubber (65/35). 

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