Grafting with Polyfunctional Monomers

Thus a number of studies have been concerned with the irradiation of polyfunctional monomers, such as diacrylates, which have been incorporated in polymers such as polyethylene (Odian and Bernstein, 1963), polypropylene (Odian and Bernstein, 1964), polyisobutylene (Odian and Bernstein, 1963), unsaturated polyesters (Charlesby and Wycherly, 1957), and, especially, poly(vinyl chloride) (Bonvicini et ai, 1963 Gladstone et a/., 1971 Hammon, 1958 Harmer, 1967 Izumi et ai, 1965 Koozu et al, 1963 Miller, 1959 Nicholl, 1969 Pinner, 1960 Stanton and Traylor, 1962 Szymczak, 1970  

Szymczak and Manson, 1974a,b White and Mann, 1967). As with electron-irradiated polyethylene, crosslinked poly(vinyl chloride) formulations (usually plasticized) are now of commercial interest as wire and cable coatings and insulation [see, for example, Nicholl (1969)]. In the following sections, typical properties will be described and discussed details of other standard polymer-monomer graft polymerizations are given by, e.g., Chapiro (1962) and Charlesby (1960). 

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Comparison of Acid with Polyfunctional Monomers as Additives in Polyethylene Grafting. New additives, as well as acid, have been found to accelerate grafting in the presence of ionizing radiation. Much of this recent work has been performed with polyethylene. Only very preliminary studies of these new additives have been carried out with cellulose, however these early results suggest that these latest additives will also be very valuable for copolymerization reactions with cellulose. The more comprehensive polyethylene data will therefore be presented here to act as a guide for what might be predicted when cellulose is used as backbone polymer. 

Table 4. Synergistic effect of acid with polyfunctional monomers in the radiation grafting of styrene to polyethylene, (a)... 

During mutual graft copolymerization, homopolymerization always occurs. This is one of the most important problems associated with this technique. When this technique is applied to radiation-sensitive monomers such as acrylic acid, methacrylic acid, polyfunctional acrylates, and their esters, homopolymer is formed more rapidly than the graft. With the low-molecular weight acrylate esters, particularly ethyl acrylate, the homopolymer problem is evidenced not so much by high yields as by erratic and irreproducible grafting. 

Multifunctional monomers, such as acrylates (e.g., TMPTA), were found to have a dual function to enhance the copolymerization and to cross-link the grafted trunk polymer chains. An addition of an acid along with a polyfunctional monomer has synergistic effects on grafting. ... 

Solvent resistant laminates for printed circuits were manufactured by coating of copper foil with a solution of PPO, BPA/DC, bis(4-maleimidophenyl) ether and Zn octoate in toluene the coated foil was laminated with PPO-impregnated glass fabric [47]. Similar result was achieved by the modification of PPO with polyfunctional cyanates or maleimides, liquid polybutadiene and a polymerization catalyst [48], A solvent and heat resistant composition for printed circuits consists of copoly [(2,6-dimethylphenylene)-(2,3,6-trimethylphenylene)]oxide, maleic anhydride grafted poly-1,2-butadiene, bis(4-maleimidophenyl)methane, BPA/DC and toluene. BPA/DC prepolymer may be used instead of the monomer [49]. 

UV- or y-radiation-induced grafting of cellulose films with styrene in methanol solution was significantly enhanced in the presence of H2SO4, lithium salts, urea, and other organic compounds and polyfunctional monomers... 

Comparison of Polyfunctional Monomers with Acid as Additives in Grafting... 

With radiation grafting, there is also an additional mechanism for enhancement unique to acid and not applicable to the polyfunctional monomer additives. This process is particularly relevant to irradiations performed in air and involves the acid induced decomposition of peroxy species formed radiolytically in the backbone polymer, thus generating further sites where copolymerisation may occur (Equation 3). Current evidence (17) indicates that the contribution... 

More recent preliminary studies show that the grafting results for DVB and TMPTA can be extended to other polyfunctional monomers, including tetrafunctional compounds. The enhancement observed with these additives thus appears to be a general phenomenon in radiation copolymerisation and is of value in a preparative context since the radiation dose required to achieve a particular percentage graft can be significantly reduced with the consequence that potentially less radiation damage occurs in the backbone polymer. 

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