Grafting efficiency, vinyl graft copolymerization

For low radiation doses, peroxides accumulate almost linearly with dose. However, after a certain dose has been reached, their concentration tends to level off. This conclusion can be derived from the observed change in the rate of graft copolymerization initiated by polymers subjected to increasing doses of preirradiation in air. Figure 2 illustrates this effect in the case of grafting acrylonitrile onto polyethylene (2). The drop in the yield of peroxide production presumably results from the efficient radiation-induced decomposition of these peroxides. Peroxides are known to decompose under free radical attack, and selective destruction of peroxides under irradiation has been established experimentally (8). This decomposition can become autocatalytic, and sometimes the concentration of peroxides may reach a maximum at a certain dose and decrease on further irradiation. Such an effect was observed in the case of poly (vinyl chloride). Figure 3 shows the influence of preirradiation dose on the grafting ratio obtained with poly (vinyl chlo-... 

As the initiator concentration increased in the graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate), the total conversion increased, but the per cent grafting and the graft efficiency decreased (Table 2) (4). The number of monomer units of trunk polymer per polystyrene branch decreased from 104 to 42. Accordingly, the number of branches per trunk polymer increases with increasing initiator cgncentration, even if the graft efficiency becomes lower. 

It is well known that primary amines are efficient initiators for the polymerization of Leuch s anhydrides (oxazolidinediones) and that initiation proceeds by the addition of the amine to the monomer. This pathway has been utilized recently to synthesize polypeptide macromonomers bearing a terminal p-vinylbenzyl group 88). Copolymerization of these macromonomers with a vinylic or acrylic comonomer yields graft copolymers with polypeptide grafts. Alternately, the monomer adduct (IV) was copolymerized with styrene, and the primary amine functions of this polymer were used to initiate the polymerization of an oxazolidinedione whereby polypeptide grafts are formed 89). Such graft copolymers may be of interest for biomedical applications. 

Vainio et al. (27) have studied the grafting of ricinoloxazoline maleate to PP and reported that the use of styrene did not increase the reaction efficiency in some instances it decreased the latter while the degradation of polypropylene decreased markedly. The copolymerization constant value could be the basic point in explaining the effect of styrene on the grafting of vinyl monomers to polyolefins and concurrent secondary reactions (27). 

For reasons not explained, but perhaps due to improved grafting efficiency, an addition lithiation step was included in the copolymerization procedures (see Figure 2.3(b)) [74]. sec-BuLi in the presence of tetramethylethylendiamine (1 1 mol ratio) was used to lithiate the cw-polybutadiene carrier backbone in cyclohexane at room temperature. Formation of car-banion at the allylic positions, not limiting to 1,2-vinyl units, was expected. The carbanions are capable of an alkylation or transmetallation exchange reaction with Ti(OBu)4 to form new Ti-carbon sigma bonds. The Ti(IV) was then allowed to reduce to the active Ti(III) species by another Li-polymeryl species before acet-... 

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