Block Copolymers between Styrene and Isobutylene by a Direct Route

Abstract

ABSTRACT:The possibility of synthesizing two-or three-block copolymers between styrene and isobutylene via a direct cationic polymerization has been investigated. Previous studies had shown that the polymerization of these monomers with syncatalytic systems composed of aluminium organic compounds and chlorine are affected by transfer reactions, whereas terminations are almost absent. However, preliminary experiments have shown that the production of two-and three-block copolymers can be achieved to some extent, provided that appropriate experimental conditions leading to a substantial limitation of the importance of transfer reactions are adopted. A mathematical model has been developed which describes satisfactorily the polymerization pattern. This model is being used to determine, with the aid of a computer, the most convenient conditions for the production of block copolymers. Previous studies carried out in these laboratories had shown that the polymerization of isobutylene, initiated by syncatalytic systems, for example the Et 2 A1Cl +chlorine system, is characterized by a reaction with a relatively slow start and by the absence of important termination reactions. 1 -8 Such polymerization presents kinetic characteristics similar to those belonging to "living polymerizations": further additions of monomer, in fact polymerize completely at a speed which decreases only slightly along the series of subsequent monomer additions, transfer reaction with the monomer is also absent. It had been demonstrated, however, that the molecular weight of the polymer obtained through the subsequent additions of monomer to the same system, increased only slightly with each successive addition. This indicated that the molecular weight of the polymer was regulated by transfer reactions with substances the concentrations of which are proportional mainly to the concentration of chlorine (or the Me 3 CC1). However, it seemed interesting to study experimentally the possibility of obtaining, even though with limited yields, block polymers of the AB type, introducing at the end of the polymerization of the isobutylene, a monomer such as styrene, capable of bringing about a plastomeric block. Moreover if these catalytic systems should show the same behaviours for the polymerization of styrene, we could try to obtain new thermoplastic elastomers styrene-isobutylene-styrene by the successive polymerizations of these two monomers. The results of this research work, already described 9 were partially successful in producing block copolymers.During this work we discovered that in experiments carried out in CH 2 Cl 2 a catalytic addition of isobutylene to a quiescent solution of styrene and A1Cl3 causes a process of polymerization of styrene with quantitative yield and with an acceleration period. This polymerization seemed less dominated by transfer than that initiated by Cl 2 + A1Et 2 Cl system and this catalytic system has been also used to produce block copolymers between styrene and isobutylene. 10 Very recently we have investigated the...

Modeling of polymerization reactions. I. The cationic polymerization of isobutylene by aluminum organic compounds

“…Reaction mechanisms which well explain most of the features of these systems have been proposed, and according to them some kinetic models have been derived. 17 The aim of this series of papers is the treatment of these kinetic models in order to derive, through mathematical or statistical methods, the theoretical time-conversion and time-conductivity curves as well as the theoretical molecular weight and molecular weight distribution which may be compared with the experimental ones.…”