RADIATION POLYMERISATION

Radiation has been employed for the synthesis of various microgel dispersions. P Ulanski etal. [11] exposed an aqueous solution of linear poly acrylic acid (PAA) to pulse irradiation produced by fast electrons. The irradiation energy facilitated the formation of PAA radicals and these radicals imderwent a major reaction path of intramolecular recombination. This reaction led to an interlinking process within the polymer molecules and the final formation of nano-gel particles. 

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Solid phase polymerisation is used for chain polymerisation processes which are carried out at low temperatures. In such processes the thermal activation is difficult and so for activation of such processes radiation-activation technique is used. These processes are very slow. An example of such a solid phase polymerisation is the preparation of Polyformaldehyde by the radiation polymerisation of solid trioxane. 

The most important casualties of this campaign are the rate-constants much quoted in textbooks but shown here to be unacceptable these comprise most of those from Bawn s group and those derived from radiation polymerisations. 

Any carbenium ions which are not paired have both their complexation sites occupied by the most polar or polarisable species available, which can be the solvent or the monomer, according to their relative polarities, polarisabilities, and concentrations for paired cations, the picture applies to their other, still vacant, site. Such a situation will generally prevail in nonpolar solvents because in these the concentration of paired cations is dominant. In a polar solvent, both sites at an unpaired cation can be occupied by solvent, or one by solvent and one by monomer, or both by monomer. In the radiation polymerisations, one sees clearly that as the monomer concentration is reduced from bulk monomer, the kinetics change and they eventually become first order in monomer, whatever the solvent the critical monomer concentration at which this happens depends on the polarity of the solvent [12]. 

This explanation for the acid effect on the radiation polymerisation of styrene solutions has a direct application in a grafting context in that higher G(H) yields or lowered effective concentrations of radical scavenging impurities will enhance existing hydrogen abstraction reactions from the substrate to create potential grafting sites as well as increasing the... 

Compounds of the types (12.87) and (12.88) have been patented for use as dental adhesives, adhesion promoters and radiation polymerisable films to protect wood, glass and metal. In dental applications, these compounds are applied to the surface of the tooth cavity before the filler canent is put in [31]. 

NOVEL UV AND RADIATION POLYMERISATION METHODS FOR MODIFYING POLYOLEFINS, CELLULOSE AND LEATHER... 

J.L, Garnett, S.V, Jankiewicz and D.F, Sangster, Acid effects in radiation polymerisation and grafting reactions, JoRad. Phys.Chem, in press. 

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