Styrenes synthesis

Each of the derivatives may be regarded as a substituted styrene, and classical styrene syntheses have been employed. Radical polymerization of the phenolic monomers (salicylate esters, 2-hydroxybenzophenones and hydroxyphenylbenzotriazoles) proceeds normally with AIBN as initiator, at least when oxygen is carefully excluded. It is expected that polymeric ultraviolet stabilizers, perhaps in combination with conventional stabilizer will make an important contribution to photostabilization technology. 

A related problem of interest is when a polymer is not crystalline as prepared, but is potentially crystallizable. This situation is commonly encountered in crys-tallizable copolymers, and is also found in homopolymers. Some typical examples of this phenomenon are found in poly(styrene) synthesized by means of alfin type catalysts,(50) poly(methyl methacrylate), prepared by either free-radical or ionic methods,(39,51,52) and poly(carhonate).(53) Treatment with particular solvents or diluent at elevated temperatures can induce crystallinity in these polymers. The reason for the problem is kinetic restraints to the crystallization process. Treatment with appropriate diluents alleviates the problem. The principles involved, and the diluent requirements will he enunciated in the discussion of crystallization kinetics. For present purposes it should be recognized that the crystallizability of a polymer, particularly a copolymer, cannot be categorically denied unless the optimum conditions for crystallization have been investigated. Thus, in light of the previous discussion regarding the minimum concentration of chain units required for crystallization, and the need to have favorable kinetic conditions, the lack of crystallization in any given situation needs to be carefully assessed. 

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