Radical Grafting

In order to take into consideration the effects of diverged reactivities of graft radicals, we divided reacting sites into several parts, and kinetic parameters for respective regions were determined as follows. Over-all grafting rate is given by... 

Figure 1. Kinetic parameters for grafting of styrene onto pre-irradiated cellulose acetate films at 50°C from a styrene/MeOH (1/1) solution. Key GR, average growth rate of graft radical PR, average termination probability DA, initiation rate of grafting. (Adapted from Figure 6 of Ref. 2.)...

Slow growth rates of graft radicals indicate that effective concentrations of monomer around active ends of graft radicals are quite low. The rate-determining step would be the diffusion of monomer molecules within and around the surface of microcrystals. Hence, it would be reasonable to assume that growth rate of graft radicals within crystalline parts is much slower than those located outside throughout reactions. 

Termination. The presence of small reactive radical species such as the methyl radical produced by fragmentation of the DCP initiator means that there may be a range of termination routes available. The bimolecular termination of graft radicals on different chains may result in a crosslink unless they disproportionate. The termination of the primary backbone radicals, R, will be competitive with monomer addition at low concentrations of M2 and again produce a crosslink. The possible competing crosslinking reactions are shown in Scheme 1.40. 

The graft copolymer products, poly(met)acrylates branched to polyester-suUbnes, can be produced next way [200]. Firstly, the polyestersulfone is being chlormethylenized by monochlordimethyl ester. The product is used as macrostarter for the graft radical polymerization of methylmethacrylate (I), methylacrylate (II) and butylacrylate (III) in dimethylformamide according to the mechanism of transferring of atoms under die influence of the catalytical system FeCyisophthalic acid. The branched copolymer with I has only one glassing temperature while copolymer with II and III has three. 

FIGURE 104 Graft radical polymerization of cellulose with monomers, using an ionizing agent (hv). After the initial reaction with a monomer (M), propagation ensues. 

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