SynopsisA soluble monomer [methyl acrylate (MA)] and an insoluble monomer [butyl methacrylate (BMA)] were grafted onto cellulose by three types of ceric salts under both oxygen-free conditions and in the presence of oxygen. For comparison, Ce(IV) consumption during cellulose oxidation was also determined under similar reaction conditions. Slightly more Ce(1V) was consumed during cellulose oxidation in the presence of oxygen. During graft copolymerization of MA under oxygen-free conditions, the consumption of Ce(1V) was much lower than during cellulose oxidation regardless of the type of ceric salt employed. The opposite was observed in the presence of oxygen: much more Ce(1V) was consumed during grafting than during cellulose oxidation. The consumption of Ce(1V) in the graft copolymerization of BMA by ceric sulfate was nearly independent of reaction conditions and it was approximately the same as in cellulose oxidation. In the reaction initiated by ceric ammonium nitrate under oxygen-free conditions, less Ce(1V) was once again used up during grafting than during cellulose oxidation. However, the difference was much smaller than in the case of MA.
Experiments carried out by Graczyk and Hornof
SynopsisStyrene was grafted onto dissolving pulp by the cellulose xanthate-Fez+ -HzOZ system. Reaction parameters were found to have strong influence on conversion to both copolymer and total polymer, as well as on the dependence of polymerization on stirring. The formation of polymer was almost completely inhibited by pure oxygen, while air only slowed down the reaction. Under inert atmosphere, the effect of agitator speed was found to be strongly dependent on monomer and substrate concentration as well as on the concentration of emulsifier. The location of the maximum on the conversion vs. agitator speed curve was strongly affected by the shape of the stirrer. The presence of emulsifier had a relatively small effect on copolymer formation in the case of acrylamide, a water-soluble monomer. Also the effect of stirring was less marked in the case of acrylamide. In all the systems investigated, the conversion to copolymer and total polymer was found to drop rapidly above a certain limiting agitator speed. The latter was different and characteristic for each system. No polymer formation was observed beyond lo00 rpm regardless of all other reaction conditions.
SynopsisDissolving pulp was grafted with several monomers ranging from hydrophilic (dimethylaminoethyl methacrylate) to hydrophobic (styrene). The conversion of these monomers to polymer and copolymer was investigated in dependence on the number of revolutions of the agitator. The formation of grafted copolymer was found to be strongly influenced by stirring. For all the monomers employed, almost no copolymer was formed above 400 rpm. The formation of homopolymer was also severely reduced at higher stirring speeds. For some monomers, a maximum was obtained at about 200-300 rpm with both copolymer and homopolymer yields dropping off sharply at both lower and higher stirring speeds. The position of this maximum was affected by the size of the reactor. The behavior displayed by the xanthate-Fez+-Hz02, Fe2+-Hz02, and ceric ion initiation systems was very similar. Also, monomer solubility in water seemed to have little importance in determining the general behavior.
Methyl acrylate was grafted onto dissolving pulp by ceric ion in aqueous sulfuric acid under oxygen-free argon. At a low Ce(1V) concentration (up to 1 mmol/L), the rate of polymerization (Rp) is proportional to [Ce] 0 . 5 [MA] ' [cellulose] '. At higher concentrations of ceric ion (1-20 mmolfL), R p is proportional to [Ce] [MI 1.5 [cellulose] '. The mechanism of grafting is consistent with a kinetic scheme involving initiation by primary radicals and termination by growing polymer radicals. Above 20 mmol/L of ceric salt, the data are consistent with the linear termination mode.
SYNOPSISDimethyltitanocene, in conjunction with a wide variety of compounds containing Si -H bonds, is an excellent catalyst for the polymerization of acetylene to give free standing films. Polymerizations of acetylene in a variety of siloxane and silane matrices using this catalyst system are described. The polyacetylenes produced with a [ -(Me-SiHO -) 3 -(Me,Si),,-], random copolymer showed very similar properties to those previously produced by Naarman et al. with a Shirakawa-type catalyst in a polydimethylsiloxane matrix. Ring, or chain, poly(methylhydrosi1oxanes) with higher proportions of -(MeSiHO) -undergo redistribution in the course of acetylene polymerization to give polyacetylene embedded in an insoluble polysiloxane glass. Polyacetylene produced in a poly(phenylsi1ane) matrix yielded a 2-component material from which the polysilane could not be solvent extracted. The electrical conductivity of iodine doped samples of this material is somewhat lower than that of the pure polyacetylene, but its mechanical properties and its resistance to degradative oxidation are superior to those of either of the pure component polymers.
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