Formation of Graft Copolymers

This is an important part of polymer syntheses that is used in many industrial processes. In 1967 Battaerd and Tregear published a book on the subject that contains 1000 references to journal publications and 1200 references to patents. In addition, there are several monographs and many review papers. The synthetic methods developed to date range from using free-radical attacks on 

---

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

Grafting provides a convenient means for modifying the properties of numerous polymers. It is often required that a polymer possess a number of properties. Such diverse properties may not be easily achieved by the synthesis of homopolymers alone but can be achieved through the formation of copolymers or even terpoly-mers. The formation of graft copolymer with sufficiently long polymeric sequences of diverse chemical composition opens the way to afford speciality polymeric materials. 

Compatibilization along with dynamic vulcanization techniques have been used in thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber by Moffett and Dekkers [28]. In situ formation of graft copolymer can be obtained by the use of suitably functionalized rubbers. By the usage of conventional vulcanizing agents for EPDM, the dynamic vulcanization of the blend can be achieved. The optimum effect of compatibilization along with dynamic vulcanization can be obtained only when the compatibilization is done before the rubber phase is dispersed. 

Scheme 4 Reaction scheme for the formation of graft copolymer between amine terminated NBR and modified polypropylenes.

Macromonomers always lead to the formation of graft copolymers. For example, the vinyl-terminated polystyrene can be copolymerized with ethylene to produce a graft copolymer of polyethylene, whereby the vinyl moiety of polystyrene is integrally polymerized into the linear polyethylene backbone ... 

The formation of graft copolymers of PAN with oligomeric diisocyanates proceeds in accordance with the following scheme ... 

The formation of graft copolymers leads to the possibility of combining incompatible polymers in such a way that the components may be distributed homogeneously or they are at least firmly fixed to each other at the phase boundaries, for example, with high-impact polystyrene, where the two components, polystyrene, ( 90%) and rubber ( 10%), are combined through... 

Deters, and Huang (129) describe the formation of graft copolymers of cellulose triacetate and vinyl chloride in vibratory mill treatments. Through hydrolytic degradation of the triacetate backbone, they isolated the polyvinyl chloride side chains and characterized them by infrared spectroscopy and cryoscopic molecular weight determination. The length of the side chains has been found to be between 15 and 30 vinyl chloride units. 

In processes I and II, the acetyl and methyl radicals react with solvent molecules giving respectively acetaldehyde and methane. In the third process chain degradation occurs followed eventually by disproportionation. Evidently the same photolysis carried out in the presence of a second monomer (acrylonitrile yields graft copolymers (I and II) and, possibly, some block copolymers (III), together with homopolymer initiated by the methyl and acetyl radicals. The formation of graft copolymers seems more likely on account of the greater stability of the radicals produced in reaction schemes I and II compared to scheme III. 

The emulsifier-free emulsion terpolymerization of PEO-MA macromonomer, BA, and acrylic acid (AA) led to the formation of graft copolymers and stable latexes [101]. At the beginning of terpolymerization, the PEO-MA macromonomer polymerized more quickly than BA or AA. Conversion of the macromonomer increased with increasing initiator concentration and with decreasing mo-... 

In this paper, the surface grafting of rayon fabrics with nitrogen and phosphorus containing polymers in cold plasma is studied. The analytical data (IR spectroscopy, TGA, electron microscopy, elemental analysis, etc.) indicate the formation of grafted copolymers. The grafted rayon fabrics present improved flame-retardant properties, the best behavior was proved by those grafted with polyurea of phosphinic acid. 

Infrared Spectra of Grafted Bamboo. It has been demonstrated that the occurrence of graft copolymerization of methyl methacrylate onto bamboo can be accertained by the presence of characteristic absorptions of polymer branches in the infrared spectrum (17-19), in addition to the weight increased in bamboo samples. In this study, similar procedures were conducted for the grafting of acrylonitrile. The formation of graft copolymer could easily be detected by the... 

The appearance of the nitrile absorption at 2260 cm-1 can be used as a criterium for the formation of graft copolymers. 

Similar work was performed by Asami on the copolymerization of poly-THF macromonomers The formation of graft copolymers was evidenced though their molecular weights, determined by GPC, were obviously underestimated. 

This involves the formation of graft copolymers from a reaction between polymers and monomers. " Monomer units can be propagated onto the polymer backbone to form a graft structure. Free radicals, air, or ionizing radiations are used to initiate the reaction. A... 

Copolymers containing PB (SBS and K-resin) were irradiated with UV light in the presence of anthracene, which acts as a photosensitizer, to create free radicals along the polymer chain. These radicals were used as initiation sites for the polymerization of methacrylic acid leading to the formation of graft copolymers [83]. Molecular characterization data were not provided in this study. 

The formation of graft copolymers by radical polymerization of a monomer in the presence of a saturated polymer quite probably occurs through chain transfer reactions. The free radicals derived from the decomposition of the initiator or the growing chains of the monomer are generally supposed to transfer their activity to the preformed polymer chain, thereby originating radical active centers on which the monomer chains grow (18). 

Grafting of vinyl chloride and of styrene in the presence of EPDM elastomers occurred under the described conditions with formation of graft copolymers of rubber and of poly (vinyl chloride) and polystyrene homopolymers. 

Reactions between chain-end of one polymer and side group of another leading to formation of graft copolymers. 

Reactions between anhydride and amino groups predominate in the formation of grafted copolymers that are obtained during reactive processing in the presence of anhydride-containing compatibilizers (41,43 5). 

The formation of grafted copolymer is evidenced by a change in solubility, fractionation attempts, a second glass transition temperature, and gel permeation chromatography data. 

When a polymer chain is ruptured mechanically, terminal-free radicals can be generated, and these can be utilized to initiate block copolymerization. Under an inert atmosphere, block copolymers can be produced by cold milling, or mastication of two different polymers or of a polymer in the presence of a second monomer. This generally results in the formation of graft copolymers in addition to the block copolymers since radicals can be located in nonterminal positions by chain transfer. However, predominant yield of block copolymers is obtained by milling monomer-swollen polymers. The success of this technique depends on the physical state of the polymer. Generation of radical is favored if the polymer exists at or near the glassy state otherwise, polymer flow rather than bond rapture will occur. Table 5.5 shows some block copolymers prepared by this technique. 

---