SUMMARY: Copolymers of styrene and ethyl acrylate are prepared by radical polymerization and analysed with respect to microstructure by means of nuclear magnetic resonance. Using 13 C NMR, the compositional styrene-and ethyl acrylate-centered triads can be determined and compared to theoretical values. Good agreement between experimental and calculated triad concentrations are obtained for styrene-rich copolymers. Ethyl acrylate-rich copolymers exhibit significant deviations from the calculated values in particular for the ethyl acrylate homotriads. Using on-line coupled SEC-1 H NMR, the chemical composition across the molar mass axis can be monitored. It is found that ethyl acrylate-rich copolymers exhibit a broader molar mass and chemical composition distribution than styrene-rich copolymers. The results indicate that the block character of the copolymers with respect to ethyl acrylate units increases with increasing molar mass.

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Atactic polypropylene (PP) is an amorphous short-chained by-product of isotactic polypropylene (iPP). Due to its enhanced solubility, PP is a suited model polymer for kinetic studies of iPP melt reactions. The maleination of PP via radical grafting at high temperatures was investigated. Since maleic anhydride (MAA) produces discoloring oligomers, PP was grafted with a mixture of MAA and a-methylstyrene (MS). Advantageous is that MS cannot homopolymerize at high temperatures and that MAA and MS tend to copolymerize alternatingly (to colorless products). The kinetics of the grafting process is complicated by a phase separation of PP and [MAA+MS] that is caused by the special attractions between the two monomers. As a result, two grafted PP products are obtained, of which the major is only slightly but the minor is heavily grafted. The latter graft copolymer, which is probably created in the interfaces between phase domains, carries one MAAMS graft per PP back bone chain, approximately with three MAA and five MS units. ZUS AMMENFASSUNG: Ataktisches Polypropylen (PP) ist ein amorphes, kurzkettiges Nebenprodukt des isotaktischen Polypropylens (iPP). Wegen seiner erhohten Loslichkeit ist PP ein gunstiges Modellpolymeres fur Studien der Kinetik von iPP-Schmelzereaktionen. Untersucht wurde die Maleinierung von PP durch radikalische Pfropfung in der Schmelze. Da Maleinsaureanhydrid (MAA) verfiirbende Oligomere bildet, wurde PP mit einer Mischung aus MAA und a-Methylstyrol (MS) gepfropft. Von Vorteil ist, dal3 MS bei hohen Temperaturen nicht homopolymerisieren kann und dal3 MAA und MS praktisch alternierende, farblose Copolymere liefern. Die Kinetik des Pfropfprozesses kompliziert sich durch eine Phasenseparation von PP und [MAA+MS], die bei hoheren Monomerkonzentrationen auftritt und von speziellen Wechselwirkungen zwischen den beiden Monomeren ausgelost wird. Deswegen werden zwei gepfropfte PP-Produkte gebildet, ein wenig gepfropftes Hauptprodukt und ein hochgepfropftes Nebenprodukt. Dieses entsteht vermutlich in den Phasengrenzflachen. Es tragt pro PP-Kette einen MAWS-Ast, der ungefahr aus drei MAA-und funf MS-Bausteinen besteht.

Copolymers of styrene and ethyl acrylate are prepared by radical copolymerization and analysed with respect to chemical composition distribution. By gradient HPLC using a reversed stationary phase and tetrahydrofuran-acetonitrile as the mobile phase, the copolymers are separated with respect to chemical composition in the order of increasing styrene content. For the samples under investigation, the molar mass does not affect the separation. Quantitative information on the chemical heterogeneity is obtained by calibrating the chromatographic system with chemically narrow-distributed low-conversion copolymers. In agreement with the theory it is found that for high-conversion samples the chemical heterogeneity increases with increasing content of ethyl acrylate in the copolymer. The HPLC separation mechanism is discussed in terms of precipitation and adsorption effects.