16 Radiation Grafting of Vinyl Monomers to Wool D A N I E L C A M P B E L L , J. L . W I L L I A M S , and VIVIAN S T A N N E T T
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0066.ch016
Camille Dreyfus Laboratory, Research Triangle Institute, Durham, N . C .
Further details of the mutual radiation grafting of styrene to wool have been elucidated. Substantial grafting takes place in air. Mainly postirradiation effects were found with machine irradiation. The grafting was diffusion controlled, and the grafted side chains and in situ homopolymer have molecular weights between 25,000 and 100,000, believed to be caused by chain transfer. A brief discussion of the graft ing kinetics is presented. ESR spectroscopy was used to determine second-order radical decay constants as 0.03, 1.9, and 4.8 χ 10- radical- gram seconds- for the dry wool, 10% methanol, and 18% methanol-monomer solutions, re spectively. The G(radical) values were found to be 0.8 for dry wool and 0.4 for the monomer solutions after correcting for the different decay rates. 22
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Qome general features of the mutual radiation grafting of vinyl mono^ mers to wool were described earlier (9). Styrene was chosen for study in detail in an attempt to ascertain the kinetic features of the process. To achieve measurable levels of grafting, it was necessary to have a swelling agent such as water or methanol present in the monomer solution. A typical set of grafting-dose curves is presented in Figure 1. The amounts of grafting increase greatly with increasing methanol con tent. Similar results were obtained by substituting water for methanol. On the other hand, the yield of homopolymer produced in the free solu tion was found to be unaffected, within the experimental error. It is believed that adding water or methanol is necessary to swell the wool fibers and increase the rate of diffusion of monomer to the active centers (free radicals) formed by the irradiation. All the experiments reported previously (9) were performed under high vacuum and at a constant dose rate. Further details of the styrene-wool grafting system have now 221 Irradiation of Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1967.
Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0066.ch016
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IRRADIATION OF POLYMERS
DOSE, MRADS
Figure 1. Percent grafting of styrene to wool vs. radiation dose at various methanol concentrations in monomer-dioxane solution been investigated. In particular, a combination of electron spin resonance (ESR) and grafting data has been used to elucidate additional features of the mutual process. Experimental
Details of the wool used and the grafting techniques have been described (9). The irradiations were carried out in a 1500-curie cobalt-60 room type source. The dose rate could be varied continuously by chang ing the distance from the source. After removing any residual homopolymer by benzene extraction, the grafted polystyrene was separated from the wool by treating with a two-phase toluene-5% sodium hypochlorite solution. Two separate 24-hour treatments were necessary to dissolve the polystyrene completely and render it soluble in benzene. The technique previously used (5% potassium hydroxide and benzene) left about half the polystyrene in soluble in benzene because of attached amino acid residues. ESR Measurements. Samples were sealed in 3-mm. o.d. Suprasil quartz tubes after thorough degassing of both the wool and monomer
Irradiation of Polymers Advances in Chemistry; American Chemical Society: Washington, DC, 1967.
16. C A M P B E L L E T A L .
Radiation Grafting
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solutions. They were then irradiated at room temperature with a dose rate of 0.3 Mrad per hour for varying lengths of time. ESR measurements were carried out at room temperature, but at all other times the samples were maintained at liquid nitrogen temperature to prevent decav of the free radicals. Radiation-induced paramagnetic centers in the quartz were removed by flame-annealing one end of the tube in the usual manner. ESR spectra were recorded with a Varian V.4502-10 spectrometer and were presented either as first or second derivatives of the resonance absorption curve. The number of free radicals was determined by inte grating the first-derivative curve and by comparing with a-
