Anionic dispersion copolymerization of styrene and 1,3-butadiene.
The anionic dispersion copolymn. of styrene and butadiene was investigated. The suitability of the lower alkanes butane and pentane as dispersing media was tested. Only pentane turned out to be suited for the synthesis of non-aggregated polymer particles. Following block copolymn. expts., the active chain ends were found to be homogeneously distributed over the whole particle vol. by TEM anal. of OsO4 treated polymer probes. This result contradicts the opinion of Kim et al. [Korea Polym J 7 (1999) 64] who suppose a location of the active centers only at the surface of the polymer particles. Polymer particle aggregation in the synthesis of poly(styrene-b-butadiene) and poly(styrene-b-butadiene-b-styrene) di- and triblock copolymers can be attributed during the early part of butadiene polymn. to the well known assocn. of growing lithium chain ends from sepd. polymer. Later on, at higher butadiene conversions, an entanglement of longer polymer chains causes agglomeration, too. The most important parameter to obtain a stable poly(styrene-b-butadiene)lithium dispersion is the mol. mass of the poly(butadiene) block. The upper limit was evaluated to be 8000 g/mol. For tech. applications, this means a max. of 5 wt% of poly(butadiene) for a total mol. mass of 150,000 g/mol.
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