ANIONIC-POLYMERIZATION OF MONOMERS CONTAINING FUNCTIONAL-GROUPS .6. ANIONIC BLOCK COPOLYMERIZATION OF STYRENE DERIVATIVES PARASUBSTITUTED WITH ELECTRON-WITHDRAWING GROUPS

The anionic block copolymerizations between six styrene derivatives para-substituted with electron-withdrawing groups and four conventional comonomers (isoprene, styrene, 2-vinylpyridine (2VP), and tert-butyl methacrylate (tBMA)) were mainly carried out with oligo(alpha-methylstyryl)dipotassium in tetrahydrofuran (THF) at -78-degrees-C by sequential addition of two monomers. The six styrene monomers employed were N,N-diethyl-4-vinylbenzamide (1),N-(4-vinylbenzylidene)cyclohexylamine (2), 2-(vinylphenyl)-4,4-dimethyl-2-oxazoline (3), tert-butyl 4-vinylbenzoate (4), NN-diethyl-4-vinylbenzenesulfonamide (5), and 4-cyanostyrene (6). From the analyses of the copolymerization products, the results of crossover reactions were classified into four categories as follows: (a) successful synthesis of a block copolymer with a narrow molecular weight distribution and a controlled segment composition, (b) synthesis of a block copolymer having a relatively broad molecular weight distribution, (c) examples proceeding with a low initiation efficiency and/or including some side reactions at the second-stage polymerization, and (d) no polymerization at the second stage. From the results, higher reactivities of 1-6 and lower nucleophilicities of their living polymers have been demonstrated, compared with those of styrene and living polystyrene. Both of these characteristic features may be accounted for by the strong electron-withdrawing effects of the substituents of 1-6. For example, the polymerizations of 1-6 were initiated with the low nucleophilic living polymers derived from 2VP and tBMA. By contrast, the living polymers derived from 1-6 were ineffective in initiating further polymerizations of isoprene and styrene. Thus, the anionic polymerizability of 1-6 can be evaluated as being between those of 2VP and alkyl methacrylates. The reactivity ranking of 1-6 can also be estimated from the chemical shifts of the vinyl beta-carbons for these para-substituted styrenes in the C-13 NMR spectra, which is consistent with the present copolymerization results.