Polyamides vinyl monomer grafting

Grohn and Vasiliu-Oprea (18,31,32,41) studied the grafting of several vinyl monomers on polyamide, mainly polycaprolactam. [Their work was summarized in the Simionescu and Vasiliu-Oprea book (73).] In each case, the polymer was first purified by extraction, dissolution and reprecipitation. The grinding was performed at 0.42 fraction packing and by using 16 mm diameter steel balls, at an amplitude of 1.75 mm and at 1420 rpm. With vinyl chloride the air was eliminated from the reaction jar and the monomer was introduced at up to two... 

Several ester monomers have also been studied. In methanol solution, methyl acrylate (16,21), ethyl acrylate (21,54), 2-ethyl hexyl acrylate (55), allyl acrylate (44), glycidyl acrylate (56,57) usually in methanol solution, have been extensively studied. Methyl methacrylate (19, 21, 28, 30, 36, 39, 58) in diversified media composition, has been successfully grafted on polyamides. Vinyl acetate is reported also for grafting on polyamide backbone (19, 28, 35, 58), as well as n-butyl maleate in methanol solution (55). Diallyl maleate as cross-linking agent for polyamide chains is reported (44). Other less usual ester monomers have been mentioned in the literature to form grafts (41,59,60). 

X-Ray irradiation is less frequently employed as the technique for grafting vinyl monomers on polyamides (84). 

Similarly the ozonization of several polyamides, mixed polyamides and polyethylene terephthalate followed by grafting of vinyl monomers has been successfully attempted (134, 135). 

The simplest procedure for grafting copolymerization, in terms of number of components in the reaction medium, is a bulk polymerization of the monomer in mixture with the molten polyamide. This has been claimed in an earlier patent (2), related to improvements in dyeability and hydrophylic properties of the resulting yam, obtained by melt spinning of the product of reaction with monomers such as 2,5-dichloro styrene, lauryl methacrylate, N-vinyl pyrrolidone, and N-vinyl carbazole. 

Other monomers have been successfully grafted on polyamide under UV light sources. Hence, organic acids as acrylic (72,73), methacrylic (74), ftimaric (73), itaconic (73), and styrene sulfonic in 25% aqueous solution (73). Methyl acrylate and acrylamide in the presence of photosensitizers (74,75) and acrylonitrile (76) are reported as well. Heterocyclic derivatives as vinyl pyridine and vinyl pyrrolidone under UV light using photosensitizers as benzophenone were grafted on Nylon 66 cloth (77). 

A critical appreciation of this review shows that there has been a large interest on the subject in the last twenty years. Most of the papers and patents deal with immersion techniques. Irradiation with gamma-rays seems to be the field to which more attention has been given. Practically all common unsaturated monomers have been studied more or less extensively, in specially styrene, acrylonitrile, methyl methacrylate, and vinyl acetate, respectively. In more recent years, grafts have been attached to the backbone polymer through reactions of the branch polymer with active centers generated on the polyamide matrix. 

In a similar way, Iwasaki et al. [145] modified the surface of polyamide 6 films or fibers after ozonization. These authors grafted in a second step hydrophilic monomers such as acrylamide, and also vinyl acetate or methyl methacrylate. Once more, oxidation mechanisms and preferential sites of attack of ozone have not been clearly described in the literature. 

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