| Abstract: | A convenient method has been developed for the polymerization of vinyl chloride at low temperatures (to at least ?75°C) by using a tungsten–iodine rather than an ultraviolet lamp, and uranyl nitrate as sensitizer. The use of predominantly visible light minimizes degradation reactions sometimes encountered with ultraviolet light. Measurements of the fraction of racemic (or syndiotactic) diads and per cent crystallinity confirm that the products resemble polymers prepared by other techniques, such as polymerization initiated by a boron alkyl. It is concluded, therefore, that the method can provide a useful alternate to the more common, organometallic system. Measurements of torsional modulus as a function of temperature were also made. As the temperature of polymerization is lowered, the fraction of racemic diads and the per cent crystallinity are increased. The higher the per cent crystallinity, the higher the glass temperature, the broader the glass transition, and the higher the modulus in the rubbery state. Thus, the increased stereoregularity permits the development of a higher level of crystallinity which, in turn, restricts the mobility of the polymer chains. |
