Menashe Tahan

Alkali metal alkoxide derivatives of starch and dextrin as initiators of graft polymerization of methacrylonitrile

Abstract The anionic graft polymerizations of methacrylonitrile on starch in dimethylsulphoxide, initiated by the lithium and sodium alkoxide derivatives, were studied; the results were compared with those previously obtained with the corresponding potassium alkoxide. With lithium the results were not highly reproducible, but with sodium the results were reproducible as seen from the balance of monomer and starch at the end of the polymerization. The yields of pure graft polymer were in the order K > Na > Li; lower alkoxide concentrations were required for attaining full conversion and optimal yields in the case of the potassium alkoxide. The graft polymerization of MAN on the potassium alkoxide derivative of dextrin was studied; the effects of alkoxide and monomer concentrations as well as of temperature were examined. Comparison of the results with those obtained previously with starch indicate that the type of the carbohydrate backbone does not effect the graft polymerization to a significant extent.

Anionic graft polymerization of acrylonitrile on starch and dextrin

Abstract In order to evaluate the anionic grafting reaction for monomers which are prone to chain transfer termination, a study was made of the graft polymerization of acrylonitrile on the potassium alkoxide derivative of starch and dextrin in dimethylsulphoxide. The effects of monomer and alkoxide concentration were investigated. Very high conversions of monomer were obtained even at low alkoxide concentrations. The grafting was accompanied by extensive homopolymerization due to chain transfer to monomer, the extent of which increased with increasing monomer concentration. The yields of graft polymer were low; they were much lower than those obtained with methacrylonitrile which has no α-hydrogen atom for chain transfer.

Observations on the effect of solvents on the anionic polymerization of methyl methacrylate by butyllithium

Abstract The anionic polymerization of methylmethacrylate by n-butyllithium in toluene was investigated in the presence of the following Lewis bases: diethylamine, pyridine, α-picoline, triethylamine, dioxane and tetrahydrofuran. Up to [Lewisbase]/[BuLi] ⋍2 the weight-average molecular weights, M w , decreased to a minimum which did not change with further increase of Lewis base concentration. With diethylamine, pyridine and α-picoline a new N-Li catalyst was formed, which initiated polymerization. Accordingly the polymers contained amino end groups which were titrated by perchloric acid. Thus the M n of the polymers were calculated and were found to increase with the [Lewis Base]/[Buli] ratio. The distribution of the molecular weights, as measured by M w ; M n was high, as previously found with butyllithium, and this decreased with increase of the Lewis base concentration. The M w and M n values were correlated by the presence of low polymer fractions besides high ones, the proportion of the former being very high. The effect of increasing Lewis base concentration was to decrease the proportion of the low polymer fraction (with a corresponding increase in the high fraction) and the DP n of the high polymer fraction, thus leading to the narrower molecular weight distribution observed. The fraction of the catalyst which was lost in side reaction also increased. These observations were correlated with solvation effects which decreased the fraction of low polymer formed due to factors such as “pseudotermination” of short chain polymers.