The initiation of styrene polymerization by phenyl titanium tri iso propoxide and titanous tri iso propoxide

Abstract

The polymerization of styrene initiated by phenyl titanium tri iso propoxide has been found to be a free-radical reaction in the region 15 to 50 °C. The photosensitized decomposition of this compound is a first-order reaction yielding free radicals and titanous triisopropoxide. In absence of illumination the presence of titanous triisopropoxide is also necessary to initiate polymerization. The overall rate of polymerization has been found to be expressed by an equation of the form R p = k p k i 1/2 / k i 1/2 [ M ] 3/2 [ Ti ] 1/2 , where the rate constants have their usual significance and [ Ti ] is the concentration of either phenyl titanium triisopropoxide or titanous triisopropoxide, whichever is present in smaller concentration. A kinetic scheme has been presented in which initiation is effected by reaction of monomer with a 1:1 complex of three- and four-valent titanium . The initiation rate constant k i has been evaluated as 7·7 ± 0·2 x 10 -7 mole/l, s, and is constant over the temperature range studied. Titanous tri iso propoxide also undergoes a termination reaction with free radicals resulting in a four-valent titanium compound. The rate constant for this reaction has been evaluated as 4·0 x 10 6 exp [ — (2·8 kcal/mole)/ RT ] mole 1. -1 s -1 .