Copolymerization efficient

Preliminary experiments have shown that a polystyrene macromonomer (1, R = Ph) copolymerizes efficiently witli ethyl acrylate. 

This approach was shown to yield block copolymers but its efficiency was not quantified, although it was apparent that it was subject to side reactions which left a significant quantity of the starting polymeric material as the homopolymer. The reaction could possibly involve disproportionation between two molecules of the transient silver adduct (reaction 6) in competition with the uni-molecular decomposition into radicals as shown above. It is difficult to distinguish between the last two alternatives kinetically since both are bimolecular, and both would be reduced if the rate of reaction between the silver salt and the polystyrene lead adduct were retarded, with a consequent increase in copolymerization efficiency. 

The chemical nature of the packing has the largest influence on the retention of molecules and a big impact on the efficiency of the separation itself. The chemical and physical properties of the sorbent are determined by the choice of the comonomers for the copolymerization. The type of the copolymerization process employed by the synthetic chemist introduces the macroporous structure into the sorbent and determines the surface topology (accessibility, resolution) and the surface chemistry of the packing (4). 

Two parameters such as percentage of grafting (%G) and grafting efficiency are usually determined as functions of different variables that influence graft copolymerization. Percent grafting is usually determined from the increase in weight of the backbone polymer after grafting after complete removal of the homopolymer. It is expressed as follows ... 

The use of l3C-labeled initiators in assessing the kinetics and efficiency of initiation2 14,32 60,84 requires that the polymer end groups, residual initiator, and various initiator-derived byproducts should each give rise to discrete signals in the NMR spectrum. So far this method has been demonstrated for homo- and copolymerizations of S and MMA prepared with AIBN-a-L C3 AIBMc-a-13C or HlKi-carbonyl- C/BVQ-rmg- C (1 1) as initiator. 

Thiols react more rapidly with nucleophilic radicals than with electrophilic radicals. They have very large Ctr with S and VAc, but near ideal transfer constants (C - 1.0) with acrylic monomers (Table 6.2). Aromatic thiols have higher C,r than aliphatic thiols but also give more retardation. This is a consequence of the poor reinitiation efficiency shown by the phenylthiyl radical. The substitution pattern of the alkanethiol appears to have only a small (<2-fokl) effect on the transfer constant. Studies on the reactions of small alkyl radicals with thiols indicate that the rate of the transfer reaction is accelerated in polar solvents and, in particular, water.5 Similar trends arc observed for transfer to 1 in S polymerization with Clr = 1.4 in benzene 3.6 in CUT and 6.1 in 5% aqueous CifiCN.1 In copolymerizations, the thiyl radicals react preferentially with electron-rich monomers (Section 3.4.3.2). 

Anionic polymerization of pivalolactone with the polystyrene anion produced only homopolymer mixtures, but the polystyrene carboxylate anion was able to give a block copolymer336. The block efficiency depends on catalyst ratio and conversion because the initiation step is slow compared with propagation337. Tough and elastic films were obtained by graft copolymerization or block copolymerization of pivalolactone onto elastomers containing tetrabutylammonium carboxylate groups338,339. ... 

Radio-chemical graft copolymerization with good efficiency on halogenated polyolefins has been carried out by contacting the substrate with monomer (styrene) vapor [158,159]. Interpenetrating polymer network (IPN) could be made by grafting the monomers on preirradiated substrates... 

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