Radiation-induced graft

The theory of radiation-induced grafting has received extensive treatment. The direct effect of ionizing radiation in material is to produce active radical sites. A material s sensitivity to radiation ionization is reflected in its G value, which represents the number of radicals in a specific type (e.g., peroxy or allyl) produced in the material per 100 eV of energy absorbed. For example, the G value of poly(vinyl chloride) is 10-15, of PE is 6-8, and of polystyrene is 1.5-3. Regarding monomers, the G value of methyl methacrylate is 11.5, of acrylonitrile is 5.6, and of styrene is >0.69. 

There are a number of important factors that must be considered before applying gamma radiation-induced grafting. These factors include the radiation sensitivity of the polymer/monomer system, radiation dose and dose rate, type and concentration of inhibitor, type of solvent or diluent, and monomer concentration. The effect of such parameters on the grafting efficiency during mutual grafting is given below. 

Ionizing radiation is unselective and has its effect on the monomer, the polymer, the solvent, and any other substances present in the system. The radiation sensitivity of a substrate is measured in terms of its G value or free radical yield G(R). Since radiation-induced grafting proceeds by generation of free radicals on the polymer as well as on the monomer, the highest graft yield is obtained when the free radical yield for the polymer is much greater than that for the monomer. Hence, the free radical yield plays an important role in grafting process [85]. 

The correct choice of solvents is essential to the success of radiation-induced graft copolymerization. Their influence on radiation grafting has been the subject of many studies. It has been established that solvents play an important role in grafting because of the significance of polymer swelling. The grafting patterns to PP are solvent-dependent, thus, it is essential to examine the role of solvents. It was found that grafting in the alcohol is better than when other polar solvents such as dimethyl-... 

Radiation-induced graft polymerization may be carried out by the following procedures [69] ... 

Radiation-induced grafting and curing processes have been discussed in a number of reviews.203 28 291 The process is widely used for surface modification. Recent applications are the modification of fuel cell membranes and improving... 

Three main processes for radiation-induced grafting arc described ... 

Hoffman and his coworkers have done a lot of work on the apphcation of radiation-induced graft polymerization for medical apphcation. The hydrophilic polymers that have been used for radiation-induced grafting are Al-vinyl pyrohdone (NVP), 2-hydroxyethyl methacrylate (HEMA), acrylamide (AAm), acrylic acid (AAc), glycidyl methacrylate (GMA), ethyleneglycol dimethacrylate (EGDMA), and ethyl methacrylate (EMA) onto sihcone rubber were widely smdied. 

Kabanov VY, AUev RE, and Kudryavtsev VN. Present status and development trends of radiation-induced graft pol3fmerization. Radiat Phys Chem, 1991, 37, 175. 

The theory of radiation-induced grafting has received extensive treatment [21,131,132]. The typical steps involved in free-radical polymerization are also applicable to graft polymerization including initiation, propagation, and chain transfer [133]. However, the complicating role of diffusion prevents any simple correlation of individual rate constants to the overall reaction rates. Changes in temperamre, for example, increase the rate of monomer diffusion and monomer... 

The y-radiation-induced grafting of diethylene glycol dimethacrylate and its mixture with (3-hydroxy ethyl methacrylate in ethanol-water systems onto silicone rubber has been reported [ 164]. The grafting yield increases as the radiation dose, concentration of monomer and concentration of transfer agent increase. At the same radiation dose, the degree of grafting decreases, as the dose level increases. However, at the same dose rate, the grafhng level increases with radiation dose. 

Radiation Treatment NVP, 2-hydroxyethylmethacrylate (HEMA), and acrylamide (AAm) have been grafted to the surface of ethylene-propylene-diene monomer (EPDM) rubber vulcanizates using the radiation method (from a Co 7 source) to alter surface properties such as wettability and therefore biocompatibility [197]. Poncin-Epaillard et al. [198] have reported the modification of isotactic PP surface by EB and grafting of AA onto the activated polymer. Radiation-induced grafting of acrylamide onto PE is very important... 

Odain, G. and Chandler, H.W., Radiation induced graft polymerization, in Advances in Nuclear Science and Technology, Vol. 1, Henley, E.S. and Kauts, H., Eds., Academic Press, New York, 1962, 65. 

Gupta, B. and Anjum, N. Plasma and Radiation-Induced Graft Modification of Polymers for Biomedical Applications. Vol. 162, pp. 37-63. 

Stone, C. 2003. Low-cost PEM based on radiation induced graft polymerization. Fifth International Symposium on New Materials for Electrochemical Systems, Montreal. 

---