| Abstract: | Precipitation of poly(methyl methacrylate) (PMMA) from dimethyl sulfoxide solution by addition of water as a precipitant was studied in the presence of a well-characterized graft copolymer of poly(vinyl alcohol) (PVA). The graft copolymer which had been prepared by a radiation method and freed from PMMA and PVA homopolymers had one PMMA branch whose length was nearly equal to that of the PVA backbone. Even when such an amount of water was added to PMMA solution as to cause all the PMMA to precipitate from the solution, the precipitation was prevented by the presence of relatively small amounts of the graft copolymer. With decreasing molecular weight of PMMA, the effect of protection became more pronounced. When the precipitation was prevented, the solution was transformed into a stable emulsion. The mechanism of protection against precipitation was discussed on the basis of the results obtained and electron microscopic photographs of the emulsion particles. It was concluded that the particles of the precipitated homopolymer were covered by a monolayer of the graft copolymer, resulting in prevention of coagulation. |
