Gamma radiation polymers

M.A. Khan, R. A. Khan, H. S. Ghoshal, M.N.A. Siddiky, and M. Saha, Study on the physico-mechanical properties of starch-treated jute yarn-reinforced polypropylene composites effect of gamma radiation. Polym. Plast. Technol. Eng. 48, 542-548 (2009). 

Solution polyacrylamides can also be prepared at high polymer soHds by radiation processes (80,81). Polyacrylamides with molecular weights up to 20 million can be prepared by inradiation of acrylamide and comonomers in a polyethylene bag with cobalt-60 gamma radiation at dose rates of 120-200 J/kg-h. The total dose of radiation is controlled to avoid cross-linking. 

The synthesis of the high molecular weight polymer from chlorotrifluoroethylene [79-38-9] has been carried out in bulk (2 >—21 solution (28—30), suspension (31—36), and emulsion (37—41) polymerisation systems using free-radical initiators, uv, and gamma radiation. Emulsion and suspension polymers are more thermally stable than bulk-produced polymers. Polymerisations can be carried out in glass or stainless steel agitated reactors under conditions (pressure 0.34—1.03 MPa (50—150 psi) and temperature 21—53°C) that require no unique equipment. 

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. 

Photodegradation of polyethylene waste can be markedly accelerated via its grafting with acrylamide [98], In contrast, photostabilization of polyethylene and polypropylene can be achieved as a result of the grafting of 2-hydroxy-4-(3-methacryloxy-2-hydroxy-propoxy) benzophenone using gamma radiation [ 147], In this case, the grafted compound acting as a U V stabilizer is chemically bound to the backbone chain of the polymer and its evaporation from the surface can be avoided. 

An alternative approach to stationary phase immobilization, and the most popular method in contemporary practice, is the free radical crosslinking of the polymer chains, using peroxides [201,202,245-248], azo-oospounds [202,249-251], ozone [252], or gamma radiation [253-255] as free radical generators. In this case, crosslinking occurs through the formation of (Si-C-C-Sl) bonds as shown below ... 

Precipitation polymerizations dominated the early work which aimed at preparing industrially important hydrocarbon polymers in C02. In 1968, Hagiwara and coworkers explored the polymerization of ethylene in C02 using both gamma radiation and AIBN as free radical initiators [79]. Reactions were conducted at pressures of 440 bar and over the temperature range of 20-45 °C. 

In dispersion polymerization, the monomer and initiator are dissolved in the continuous phase, which acts as a nonsolvent for the developing polymer. The continuous phase can be organic, aqueous, or a mixture of miscible phases. Two methods of initiation have been employed, including gamma radiation [75] and chemical initiation by potassium perox-odisulphate [76]. As the polymer is formed, it precipitates as nanoparticles. These particles are not polymeric precipitates as in precipitation polymerization. Rather, they are swollen by a mixture of the monomer and the continuous phase [39],... 

The primary event which takes place when high energy radiation, such as gamma radiation, interacts with a polymer molecule involves the ejection of an electron, with formation of the polymer cation radical, as shown in Equation (1) ... 

The increase in the modulus for Bis A PSF and Hq/Bp PSF with irradiation indicated that crosslinking predominated for both polymers and that the crosslink structures were probably basically similar. Hq/Bp(50) PSF was considerably more radiation resistant than Bis-A PSF, as shown by the rate of decrease in the elongation at failure. For both polymers, there was an initial rapid decrease in the elongation at failure followed by a slower decrease. This effect was also demonstrated by the variation in the fracture toughness (KI(.) with irradiation for Bis-A PSF. This work with cobalt-60 gamma radiation complements earlier studies of these materials using high dose rate electron beam irradiation (6). 

Radiolysis Effects. Radicals formed in solvent (SH) and trunk polymers (PH) are important in the grafting of monomers (MH) with gamma radiation. With polymers such as polyethylene, grafting sites are formed by direct bond rupture (Equation 1). Additional sites are also... 

As we mentioned before, G(s) is a structure dependent constant that describes the number of scissions per unit absorbed dose and in that sense can be compared to a photochemical quantum efficiency. The G(s) of a radiation-sensitive polymer is a figure of merit that can be used in comparing one material with another. There is a very high correlation between G(s) values to gamma radiation (the radiation most commonly used for determining G(s)) and high sensitivity for lithographic materials used in either electron beam, ion beam or x-ray exposure. 

An early commercial interest in poly (olefin sulfones) was sparked by the low raw materials cost, but this interest waned when it became apparent that thermal instability is a general characteristic of this class of materials. In 1970 Brown and O Donnell reported that poly (butene-1-sulfone) is degraded by gamma radiation with a G(s) approaching 10, making it one of the most radiation-sensitive polymers known (38-39). The potential for use of this radiation sensitivity in the design of electron beam resists was quickly realized by several members of the electronics industry. Bell Laboratories, RCA, and IBM published studies demonstrating the potential of poly (alkene... 

M.C. Porte-Durrieu, C. Aymes-Chodur, N. Betz, Ch. Baquey, Development of heparinlike polymers using swift heavy ion and gamma radiation. I. Preparation and characterization of the materials, J. Biomed. Mater. Res. 52(1) (2000) 119-127. 

Initial yields for conversion to the trans-vinylene isomer can be derived by adding to the apparent yield the rate of destruction calculated from the initial concentration of trans-vinylene groups and the first-order rate constants determined for the amorphous trans polymer. The initial yield of trans-vinylene groups is 6.8 for gamma radiation and 4.4 for the reactor. The value for gamma radiation is similar to Golub s value of 7.2 for both gamma and electrons. 

Irradiation Conditions and Dosimetry. All irradiations were carried out in the gamma-radiation field of either a nominally 10 or 18 kilocurie cobalt-60 source. Dosimetry of the gamma-radiation field was carried out using the Fricke method (ASTM test D 1671-59). Since the effective mass absorption coefficient for y-rays of this energy is nearly equal for the polymer and for the dosimetric solution, no correction was made for the change in media. 

Another exposure tool is available in gamma radiation. While the correlation is not always perfect, there is a high degree of similarity in the response of polymers to the radiation from 60Co and from 50 keV electrons. Because of the penetrating nature of gamma rays, the exposure is not restricted to thin films or small amounts of polymer. Also, the absorbed dose is not complicated by the depth-dose function which must be used when electron-... 

Gamma radiation can be used with macroscopic amounts of polymer. This is particularly welcome when polymers are not compatible with the GPC technique. Larger samples can be characterized by viscosity changes, usually measured in dilute solutions. All that is needed is a suitable solvent. If the Mark-Houwink parameters are known, it is possible to calculate viscosity-average molecular weight, Mv, from dilute solution viscosities. However, even the raw viscosity-concentration data in terms of the reduced viscosity may be enough to indicate the sensitivity of a given polymer in qualitative terms. The reduced viscosity at concentrations c is isp/c where t]sp — (solution viscosity — solvent viscosity)/solvent viscosity. 

A cobalt source was used to provide gamma radiation for a powdered polymer sample under a nitrogen atmosphere. A total dose of 20 Mrad was applied. Solutions with 1.0 dl/g were made of the initial and exposed polymer in THF at 30 °C. In the usual fashion, the reduced viscosity, risp/c was calculated for each. From an original value of 1.81, the i)sp/c fell to 0.14 after irradiation. 

Highlights of both studies are summarized and shown in Table 1. The primary difference between the two studies was the time at which the polymers were thermally treated. Both systems were heat treated at 500 °C in an inert atmosphere. Samples of the halo pendent system were further treated by heating between 425-450 °C for l-20h. As-spun monomethyl PBZT exhibited the highest measured compressive properties unfortunately, after heat treatment, the polymer lost 60% of its compressive strength. Within the series of fibers, there was no systematic trend of correlation between methyl pendent content and compressive strength. Gamma radiation of the as-spun fiber showed no... 

Nishioka, A., K. Matsumae, M. Watanabe, M. Tajima and M. Owaki Effects of gamma radiation on some physical properties of polytetrafluoroethylene resin. J. Appl. Polymer Sci. 2, 114 — 119 (1959). 

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