Block copolymer formation during sequential polymerization

Sequential Polymerization. The sigmoidal reaction curves, which indicate a tendency for the molecular weight to increase during the course of the reaction, and other considerations led to the suggestion that the polymerizing chains had long lifetimes (9), similar to the chains in a living polymerization. If this is the case, sequential addition of different monomers would lead to block copolymer formation. To check this hypothesis, PMDS and HMDS were polymerized sequentially with suflScient time between additions for the first monomer to be consumed. In one experiment, PMDS was the first monomer, and in another experiment, HMDS was the first. In... 

The synthesis of poly(St-h-IB-h-St) triblock copolymer has been accomplished by many research groups [195-201]. The synthesis invariably involved sequential monomer addition using a difunctional initiator in conjunction with TiCU in a moderately polar solvent mixture at low (—70 to —90°C) temperatures. As already mentioned at the synthesis of poly(IB-f)-St) it is important to add St at 100% IB conversion. The selection of the solvent is also critical, coupled product that forms in intermolecular alkylation during St polymerization cannot be avoided when the solvent is a poor solvent (e.g., hexanes/MeCl 60/40 (v/v)) for polystyrene [202]. The formation of coupled product is slower in wBuCl or in MeChx/MeCl 60/40 (v/v) solvent mixture however, to obtain block copolymers essentially free of coupled product it is necessary to stop the polymerization of St before completion. Detailed morphological and physical properties of poly(St-h-IB-h-St) triblock copolymer have been reported [199, 203-206]. The two step sequential monomer addition method has also been employed to obtain poly(p-chlorostyrene-f)-IB- )-p-chlorostyrene) [68, 207], poly(indene-f)-IB- )-indene) [208], poly(p-tert-butylstyrene-f)-IB-h-p-tert-butylstyrene) [209], poly((indene-co-p-methylstyrene)-h-IB-f)-(indene-co-p-methylstyrene)) [210], poly(p-MeSt-f)-IB- )-p-MeSt) [202], and poly(styryl-POSS-i -IB-h-styryl-POSS) (POSS=polyhedral oligomeric silsequioxane) [211] copolymers. 

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