Grafting efficiency, vinyl graft

A series of graft polymers on polychloroprene were made with isobutjiene, /-butyl vinyl ether, and a-methylstyrene by cationic polymerization in solution. The efficiency of the grafting reaction was improved by use of a proton trap, eg, 2,6-di-/-butylpyridine (68). 

Independently the Mn"5 pyrophosphate complexes were developed as efficient initiators at very low concentrations (1 to 3 mmole/1) for grafting of vinyl monomers to starch. High yields of polymer (over 90%) and very high grafting efficiencies (98-99%) were obtained by reactions for 1 to 3 h at room temperature ( 30°C) in moderately acidic aqueous media (pH = 1.5 to 2.0). Co rresponding grafting experiments have later been carried... 

MBS (methyl methacrylate-butadiene-styrene) graft copolymers are known as one of the most efficient non-reactive impact modifiers for PET and also poly(vinyl chloride) (PVC). MBS is used commercially as an effective impact modifier for PET recyclate [27], Typical MBS rubber particles contain an elastomeric core of... 

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

Tsubokawa et al. (12-14) have introduced radical sources of azo or peroxy groups by another methods, and successively conducted the radical polymerization of vinyl compounds, such as styrene or methyl methacrylate, to give polymer-grafted particles see Reaction (3). The grafting by the radical polymerization of methyl methacrylate, initiated from a peroxy group introduced on silica, takes place at relatively high efficiency, compared with those from azo group-introduced particles. 

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-... 

During the polymerization of the styrene, the poly(butadiene) or butadiene copolymer is grafted onto the styrene polymer chain. To increase the grafting efficiency of the poly(butadiene), it is desirable for the poly(butadiene) to have end segments having a high vinyl content rather than cis- or trans-configurations. 

When, in the case of low-density polyethylene, a vinyl chloride/ polyethylene ratio near 1 is used, the system is close to saturation and a few per cent of a fine powder containing principally PVC may form. This is avoided when a vinyl chloride/polyethylene ratio of 0.6 is used, with injection of the rest of the vinyl chloride during the polymerization. This way, the system is always definitely below saturation. Moreover, this technique improves the grafting efficiency (defined by the ratio grafted VCx 100/total polymerized VC), which increases with a decreasing vinyl chloride/polyethylene ratio during polymerization. 

In this type of system, the backbone rubber acts as a chain transfer site for the monomer, and an initiator is chosen which preferably attacks the a-hydrogen position on the vinyl polymer backbone. Efficiency of the grafting reaction based solely on the chain transfer mechanism depends on several competing reactions (5). 

Co+3, Mn+2 and Fe+2 have been found to be effective in producing free radical sites on the polymer backbone through the alcohol groups present on them [75]. In an alternative method, free radical initiators like BPO and AIBN are thermo-chemically activated to give rise to macro-radical sites on polymer backbone to initiate grafting of desired vinylic monomer. The efficiency of these initiators was found to be predominantly dependent on the nature of monomer while the course of reaction depended on the relative reactivity of monomer versus that of the macro-radical. 

PS macromonomers have been efficiently applied to the synthesis of well-defined polymer hybrids with controlled length of grafts. They are, in general, prepared via living anionic polymerization of styrene monomers and their treatment with vinyl compounds, such as -allyl, -undecenyl, and styryl compounds. 

Graft copolymers of starch and vinyl acetate (VA) have been prepared using Co60 irradiation.110 Near-quantitative conversions of monomer to polymer were reported when the radiation dose was l.OMrad, although the grafting efficiency was <50%. Lower radiation doses gave lower conversions and add-ons. When 10% methacrylate was added to the monomer mixture, grafting efficiency was improved to 70%. Selected copolymers were treated with methanolic sodium hydroxide to yield starch-poly(vinyl... 

A similarly poor efficiency in extraction can also be seen in Fig. 11, where the extraction result for the product obtained by the radiation grafting of styrene onto polyethylene terephthalate)(PET) fibers13 is shown. In this case the unreacted PET can be extracted after most of PS homopolymer has been extracted by repeated solution-precipitation of the sample. It should be mentioned here that the solution procedure is also necessary to extract the unreacted PET. Such a solution-precipitation procedure is also necessary for nylon-styrene13 and poly(vinyl chloride)-acrylo-nitrile14 graft products so as to remove the homopolymers to a sufficient extent. 

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. 

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