Radiation sensitivity of polymer

The radiation sensitivity of polymers and monomers is characterized by a G value the number of radicals formed per 100 e.v. (16 aJ) absorbed. Radiation sensitive groups include -COOH, C-halogen, -S02-, -NH2 and -C=C, Radiation resistant groups are aromatic rings. It appears that the presence of aromatic moieties also offers some degree of radiation protection to the polymer chain as a whole. 

The diversity of new structures resulting firom the radiation processing of polymers, either as monocomponent systems or as blends, demands the tmderstanding of mechanisms through which modified properties are reached. The extension in the radical abundance is determined by energy requires for further scission to primary radicals. The existence of different substituents on molecular chain modifies the energy required for bond break inside radicals (Fig. 32). The radiation sensitivity of polymers and the parameters and environment of exposure are the decisive factors configurating the features of processed structure. 

Electron diffraction provides information about crystal structure similar to that obtained by WAXS, but with the difference that the sample size (the beam size) can be made very small so that the diffraction pattern from isolated crystallites can be recorded. This is a great advantage for the electron diffraction technique. A sample analysed by WAXS contains many crystals which at best are oriented, but the diffraction pattern is not of the same quality as that obtained by electron diffraction. The (electron) radiation sensitivity of polymers causes rapid deterioration of the electron diffraction patterns, which is obviously a drawback of this technique. 

Radiation sensitive cast polymers from DADC are also used in resists for microelectronic circuitry. Relief images result from differential rates of solution in alkali induced by exposure to high energy radiations. 

The radiation sensitivity of a substrate is measured in terms of its GR value or free radical yield, which is the number of free radicals formed per 100 eV energy absorbed per gram. The highest grafting yields will occur for polymer monomer combinations in which the free radical yield of the polymer is much greater than for the monomer. It also follows that the grafting yield will increase at a lower monomer concentration. 

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. 

The high radiation sensitivity of substituted silane polymers is an interesting phenomenon upon which a number of current applications are based. Detailed... 

Resist systems may be more complicated than just a single polymer in a single solvent. They may be composed of polymer, polymer/dye, or polymer/polymer combinations (where the small molecule dye or additional polymer increases the radiation sensitivity of the resist film) with one or more solvents. The more complicated polymer/dye or polymer/polymer systems have the added possibilities of phase separation or aggregation during the non-equilibrium casting process. Law (16 I investigated the effects of spin casting on a... 

Direct Radiation Grafting of Polymer in the Presence of Vinyl Monomer. This leads to the formation of free radicals on both polymer and monomer, resulting in graft polymerization and homopolymerization. The extent of homopolymerization depends on the sensitivity of the monomer used. 

Areas of application of radiation degradation of polymers can be usefully classified into (1) modification of polymers, e.g. molar mass or structure, (2) radiation-sensitive polymers, and (3) radiation-resistant polymers. Within the constraints of the required material properties of the polymers, either maximization or minimization of the response to radiation is usually the objective. 

The conventional wisdom predicts cross-linking on the basis of radiation studies of ordinary vinyl polymers. On the other hand, there seems to be no previous mention of the radiation sensitivity of maleic anhydride polymers in the literature. 

Pulse radiolysis experiments on solid polymers have provided new insight into the mechanism of radiation damage of polymers. Recent studies on some practically important polymers clarified the pathways of transfer of radiation-induced excitation energy from polymer matrix to additives thus the roles of additives in the radiation resistance or sensitivities of polymers are understood in terms of elementary energy transfer processes. The usefulness of this method is verified not only in the basic science but also in the field of application. 

JUBINSKY ET AL. Sensitivity of Polymer Blends to Synchrotron Radiation 151... 

Jubinsky, J. A., Groele, R. J., Rodriguez, F, Namaste, Y. M. N. and Obendorf, S. K., Sensitivity of Polymer Blends to Synchrotron Radiation, Office of Naval Research, Contract N00014-85-K-0474, Technical Report no. 3 (1986). 

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