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Colloid Polym Sci (2009) 287:259268
DOI 10.1007/s00396-008-1982-z
ORIGINAL CONTRIBUTION
Synthesis of styrenebutadiene rubber latex via miniemulsion copolymerization
Maria-Verena Kohnle & Ulrich Ziener &
Katharina Landfester
Received: 24 July 2008 /Revised: 3 December 2008 /Accepted: 3 December 2008 / Published online: 8 January 2009 # Springer-Verlag 2009
Abstract High-butadiene-level styrenebutadiene rubber latexes up to high solid-contents are synthesized using the miniemulsion process. It is shown that the miniemulsion polymerization approach offers an efficient heterophase route synthesizing styrenebutadiene copolymer latexes with flexible copolymer composition and narrow size distribution of the resulting latex particles. Secondary nucleation was successfully prevented by using a hydro-phobic initiator. Due to the nanoreactor situation, even at high conversions, a low crosslinking degree and, therefore, low gel contents are obtained. The microstructure of the polymers obtained in miniemulsion is independent of the synthesis parameters, especially the temperature. The molecular weight can be easily adjusted by the application of transfer agents while the insoluble gel content is substantially reduced. An up-scaling of the procedure is easily possible.
Keywords Miniemulsion . Butadiene . Copolymers . Latex
Introduction
The homopolymer polybutadiene (PB) and copolymers consisting of butadiene and styrene are some of the most relevant technical rubbers. They can be synthesized radically or anionically in solution or industrially in most cases by heterophase polymerization, mostly emulsion
polymerization. The type and condition of polymerization determine the resulting microstructures of the polymers. Anionic polymerization of butadiene using n-butyl or sec-butyl lithium as initiator leads typically to microstructures with a composition of 35% 1,4 cis, 55% 1,4 trans, and 10% 1,2 units. However, PB and styrenebutadiene rubber (SBR) latexes are usually produced via typical radical emulsion polymerization processes. Here, two major processes differing in reaction temperature are employed (cold rubber and hot rubber process). The cold rubber polymerization is performed at 5 C using redox initiator systems. A chain transfer agent, such as a mercaptane, is added to control the molecular weight distribution; therefore, the typically high molecular weights in emulsion polymerization can be suppressed. For hot rubber polymerization, potassium persulfate is the most commonly used initiator at temperatures of about 70 C. The microstructure composition of cold and hot rubber SBR latexes (with 23.5% styrene) is usually described as a statistical copolymer. Cold rubber typically displays a microstructure...