LIVING CARBOCATIONIC POLYMERIZATION .31. A COMPREHENSIVE VIEW OF THE INIFER AND LIVING MECHANISMS IN ISOBUTYLENE POLYMERIZATION

The polymerization of isobutylene (1B) has been studied by use of a 1,4-bis(l-chloro-l-methylethyl)benzene (DiCumCl)/BCl3 initiating system in CH3CI, CH2Cl2, and C2H5Cl solvents and a 90:10 v/v CH3Cl/n-hexane mixture at -75°C. It has been found that in these media the polymerizations are living and that they occur in two phases: an initial phase during which simultaneous slow initiation and chain transfer to plus propagation and reversible termination occur (i.e., a phase characterized by simultaneous inifering and living polymerization) and, after the DiCumCl is consumed, a living phase during which only propagation and reversible termination proceed (i.e., a phase characterized by exclusively living polymerization). Further, the initial phase is characterized by low initiating efficiencies (Ieff<100%) while in the subsequent living phase Ieff ~100%. The absence of irreversible termination (kt/kp ~0) during the initial phase has been demonstrated by inifer plots, which also led to the inifer constants (ktr, I/kp = CI) of 0.96 in CH3Cl and 0.49 in CH2Cl2 diluent. Diagnostic -In (1 - Ieffj) - Iefff versus jCj plots indicate that DiCumCl is consumed by slow initiation and chain transfer. Evidently DiCumCl is a true inifer (initiator and transfer agent), and inifering proceeds till it is completely consumed. After the inifer has been depleted, the living phase commences during which Mn increases linearly with the amount of polymer formed. Termination is reversible (i.e., for all practical purposes absent) and involves polyisobutylene ended with chlorine on the tertiary carbon (PIB-Clt) plus excess BCl3 in polar media at low temperature. By increasing the temperature or by decreasing the medium polarity, termination becomes irreversible. Carbocation stability during the polymerization is strongly affected by solvation effects. © 1990, American Chemical Society. All rights reserved.