The effect of acid on the radiation-induced grafting of styrene to polyethylene
Abstract
It is well known that the addition of methanol to styrene accelerates the rate of the radiation-induced grafting of styrene to polyethylene. Work at this laboratory has provided an explanation of the role of methanol (1). The alcohol does not permeate the polyethylene appreciable and so its principal effect is to reduce the equilibrium concentration of the styrene in the polyethylene; despite the reduced monomer concentration, the concomitant increase in viscosity in the amorphous region of the film produces an acceleration of the grafting rate. Garnett and Yen (2) have shown that the addition of acid to the methanol-styrene system enhances the grafting rate of styrene to polypropylene still further and they attribute the effect to hydrogen atoms. Pinkerton and Stacewicz (3) point out that the experiments of Garnett and Yen were done with O2-saturated solutions. From their studies of the grafting to polypropylene of methyl methacrylate from methanol solutions, they conclude that the addition of the acid does not enhance the grafting rate, but that the addition of H2O to the alcohol-monomer solution reduces the equilibrium concentration of oxygen and, therefore, reduces the inhibiting effects associated with its presence.
In this work experiments were performed in O2-free systems. Irradiation of polyethylene films immersed in styrene-methanol solutions both with and without acid, show the grafting rate is enhanced by the presence of acid despite the fact that the acid does not permeate the film. Clearly the acid has an effect beyond that suggested by Pinkerton. Experimental results are presented to show how the grafting rate depends on the composition of both the film and the liquid in which it is immersed. The results indicate that hydrogen atoms are not involved in the grafting reaction.
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Grafting: A versatile means to modify polymers: Techniques, factors and applications
2004, Progress in Polymer Science (Oxford)The modification of polymers has received much attention recently. Among the methods of modification of polymers, grafting is one of the promising methods. In principle, graft co-polymerization is an attractive method to impart a variety of functional groups to a polymer. Graft co-polymerization initiated by chemical treatment, photo-irradiation, high-energy radiation technique, etc. is documented in this review. Several prime controlling factors on grafting are discussed. In the past several years, there has been increased emphasis on applications of grafted polymers. The modified polymers through grafting have a bright future and their development is practically boundless. In this review, we have tried to cover two important applications employing grafting technique, viz. membrane separation science and conducting polymers.
High energy radiation grafting of fluoropolymers
2003, Progress in Polymer Science (Oxford)Fluoropolymers are known as chemically inert materials with good high temperature resistance, so they are often the materials of choice for harsh chemical environments. These properties arise because the carbon–fluorine bond is the strongest of all bonds between other elements and carbon, and, because of their large size, fluorine atoms can protect the carbon backbone of polymers such as poly(tetrafluoroethylene), PTFE, from chemical attack. However, while the carbon–fluorine bond is much stronger than the carbon hydrogen bond, the G values for radical formation on high energy radiolysis of fluoropolymers are roughly comparable to those of their protonated counterparts. Thus, efficient high energy radiation grafting of fluoropolymers is practical, and this process can be used to modify either the surface or bulk properties of a fluoropolymer. Indeed, radiation grafted fluoropolymers are currently being used as separation membranes for fuel cells, hydrophilic filtration membranes and matrix substrate materials for use in combinatorial chemistry. Herein we present a review of recent studies of the high energy radiation grafting of fluoropolymers and of the analytical methods available to characterize the grafts.
Grafting of methyl methacrylate to cellulose and polypropylene with UV and ionising radiation in the presence of additives including CT complexes
1999, Radiation Physics and ChemistryDetailed studies of the grafting of polar methyl methacrylate (MMA) to two representative backbone polymers, cellulose and polypropylene (PPE) in the presence of additives, using ionising radiation and UV as initiating sources, are reported. The results are compared with analogous grafting work with non polar styrene previously studied. The additives chosen for examination were predominantly components used in radiation curing formulations since grafting and curing are known to be mechanistically related. The additives were mineral acid, photoinitiators, vinyl ethers, oligomers, polyfunctional monomers including multifunctional acrylates (MFAs) and methacrylates (MFMAs). For the first time charge transfer (CT) monomer complexes have been used as additives in the current work. The CT complexes themselves, being monomers, have also been directly radiation grafted to cellulose. Mechanisms for the above grafting processes are proposed. The significance of this grafting work in analogous radiation curing is discussed. The grafting of the CT complexes, themselves, is shown to lead to new copolymers with potential industrial applications.
Radiation grafting of styrene and acrylonitrile to cellulose and polyethylene
1999, Radiation Physics and ChemistryRadiation induced graft polymerization is one of the best methods for obtaining material with new properties. In this work, radiation grafting of styrene, mixture of styrene and acrylonitrile to cellulose and polyethylene in the presence of methanol as a solvent by mutual method is discussed. At a low dose rate, high grafting yields were obtained from the two systems used, due to lesser termination of free radicals with the polymer growing radicals and recombination of primary radicals, resulting in a longer chain length of the grafted copolymer. In the system of styrene and acrylonitrile, comonomer technique was used and the styrene controlled the homopolymer formation during graft polymerization.
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Additive effects common to radiation grafting and wood plastic composite formation
1996, Radiation Physics and ChemistryA range of additives has been developed for enhancing grafting yields in a variety of systems initiated by ionizing radiation. Cellulose has been adopted as the predominant naturally occurring model backbone polymer in these studies because of its structural relationship to wood which is the reference substrate for the work reported in the related second part of this paper concerning composites. Some experiments have been performed with the other major naturally occurring polymer, wool. For comparison purposes with synthetic materials, some studies have also been performed with polypropylene as trunk polymer. Styrene has been used as a predominant monomer in grafting with some experiments utilizing the acrylates like methyl methacrylate. The role of solvent in grafting has been evaluated. UV has been used as initiator to replace ionizing radiation for certain experiments. The additives used were mineral acids, lithium salts, multifunctional acrylates and their methacrylate analogues, urea, oligomer acrylates, silane, fluorinated alkyl esters and thermal free radical initiators. A mechanism to explain the additive effect in terms of reagent partitioning has been proposed. The most efficient of the additives in grafting have been applied to the radiation synthesis of wood-polymer composites using two different types of wood, namely simul from Bangladesh and Pinus radiata from Australia with two different monomers with and without solvent, namely butyl methacrylate and methyl methacrylate. The effect of the additives on the physical properties, such as polymer loading and tensile strength, of the wood composites were determined. The partition concept developed for grafting has been used to explain the reactivity of the additives in wood plastic formation. The polymerization of monomers in wood plastic systems is shown to be related to simple homopolymerization of monomers in solution, a reaction which is also shown to be capable of interpretation in terms of partition phenomena.