Styrene radiation grafting

Applications of radiation grafting in the coating industry for improving adhesion and other properties has been an active field. For instance, grafting of styrene onto polyester fibers was found to improve the interfa-cial adhesion between grafted chopped polyester fibers and polystyrene used as a matrix [139]. 

Consistent with the preceeding acid work, when TMPTA is added to the monomer solutions containing either lithium salt or urea, synergistic effects are observed for the radiation grafting of styrene to polypropylene (Table IV). Again the maximum increase in yield occurs in the monomer solution corresponding to the Trommsdorff peak. 

The inclusion of mineral acid in the grafting solution has recently been shown to increase the radiation copolymerisation yield, particularly when styrene is grafted to trunk polymers like wool (3) and cellulose (4) i.e. polymers which readily swell in polar solvents such as methanol. This acid effect is important since for many copolymerisation reactions, relatively low radiation doses are required to yield finite graft. The process is particularly valuable for monomers and/or polymers that are either radiation sensitive or require high doses of radiation to achieve the required graft. 

A theory for this acid effect has been developed essentially from the wool and cellulose work (3,4). Recently, in a brief communication, we reported analogous acid enhancement effects in the radiation grafting of monomers such as styrene in methanol to nonpolar synthetic backbone polymers like polypropylene and polyethylene (5). In the present work, detailed studies of this acid enhancement effect are discussed for the radiation grafting of styrene in various solvents to polyethylene. The results are fundamentally important since most of the experiments reported here have been performed in solvents such as the low molecular weight alcohols which, unlike cellulose and wool systems, do not swell polyethylene. 

TABLE I. Acid Effect in Radiation Grafting to Polyethylene using Styrene in Low Molecular Weight Alcohols.a... 

TABLE V. Effect of Acid on Homopolymer Formation in the Radiation Grafting of Styrene in Methanol to Polyethylene.0... 

TABLE VI. Acid Effect in Radiation Grafting using Styrene in DMF, DMSO, Acetone, Dioxan, Chloroform and Hexane.0 ... 

TABLE VIII. Effect of Acid in Methanol to in the Radiation Grafting of Styrene Polyethylene using Open Tubes.a ... 

The parameters which predominantly influence the acid effect in radiation grafting of styrene monomer to polyethylene film are the structure of solvent, the concentration of monomer and the dose rate. Because these three variables are inter-related, it is difficult to predict, a priori, the conditions required to yield an optimum in grafting. In this respect the type of solvent used is particularly important. 

Acid enhancement in the radiation grafting of styrene in methanol to cellulose (4), wool (3) and in preliminary work with the polyolefins (5 6) has been proposed as being predominantly due to such reactions. 

Rouilly, M. V., Koetz, E. R., Haas, O., Scherer, G. G. and Chapiro, A. 1993. Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto Teflon-EEP films Synthesis and characterization. Journal of Membrane Science 81 89-95. 

Effect of Solvents on Radiation Grafting of Styrene to Polypropylene ... 

Reaction Rates and Physical Properties in the Radiation Graft-Copolymer System Poly(vinyl chloride)—Styrene... 

Finally, various attempts have been reported to interpret the kinetics of radiation grafting. The study by Mock, and Vanderkooi (123) concerned the mutual radiation grafting of styrene from the vapor phase to ethyl cellulose film at 50° C. The radical flux was determined separately using electron spin resonance. The kinetic scheme rigorously took account of the diffusion controlled nature of the reaction and the appropriate diffusion constants were separately determined (124). The value for the ratio of for the graft polymerization was determined as... 

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