Applications of magnetochemistry to polymers and polymerization

Abstract

After a brief review of fundamental definitionE, experimental methods, theoretical and semiempirical res ults on diamagnetic s ubstances, two topics are considen~d: First, st udies of the diamagnetic anisotropy of crystalline and oriented materials. Using solid naphthalene as an illustration , it is shown how to obtain the principal molecular s usceptib ilities from the meas urcd parameters of the si ngle crystal and t he molec ular orientat ions in the unit cell as derived from X-ray st udies. Conversely, the direction cosines for solid diphenyl a re calculated from the measured macroscop ic s usceptibilit ies and the s usceptibilities of the molecule. R es ults recently obtained on the anisotropy of eellulose, protcin fib ers, and stretched rubber indicate the value of s uch methods, part icularl y for ori ented polymcrs containing aromatic groups, because of the large eff ects of the latter. Next, attention is devoted to the paramagnetism of oxygen and free radicals t hat can be ut ilized as a meas ure of the concentration of t he species. Radical concentrations as low as 10-6 mole per liter may be estimated by m eans of a modification of the Gouy-balance. It has bccn employed in a s tudy of the t hermal polymerization of styrene at 66° C. From the changes in diam agnetism in the course of thc r eaction , thc rate of consumption of oxygen present is determincd. Assnming this to be du e to combination with styre ne rad icals, t he rate of thermal init iation is estimated to be 3.8 X 10_14 mol I liter sec-I. However, . in order to obtain by magnetic methods directly the free radical concent ration in ordinary chain polymerization processes, t he sensitivity would have to be improved by several orders of magnitude.