LIVING CARBOCATIONIC POLYMERIZATION .41. POLYISOBUTYLENE-CONTAINING BLOCK POLYMERS BY SEQUENTIAL MONOMER ADDITION .2. POLYSTYRENE POLYISOBUTYLENE POLYSTYRENE TRIBLOCK POLYMERS - SYNTHESIS, CHARACTERIZATION, AND PHYSICAL-PROPERTIES

New linear and three-arm star thermoplastic elastomers (TPEs) comprising a rubbery polyisobutylene (PIB) midblock flanked by glassy polystyrene (PSt) blocks have been synthesized by living carbocationic polymerization in the presence of select additives by sequential monomer addition. First, isobutylene (IB) was polymerized by bi- and trifunctional tert-ether (dicumyl- and tricumyl methoxy) initiators in conjunction with TiCl4 coinitiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at -80-degrees-C. After the living, narrow molecular weight distribution PIB (MBAR(w)/MBAR(n) = 1.1-1.2) has reached the desired molecular weight, styrene (St) together with an electron air donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to block PSt from the living chain ends. Uncontrolled initiation by protic impurities that produces PSt contamination is prevented by the use of DtBP. PSt-PIB-PSt blocks obtained in the absence of additives are contaminated by homopolymer and/or diblocks due to inefficient blocking and initiation by protic impurities, and exhibit poor physical properties. In contrast in the presence of the strong ED N,N-dimethylacetamide (DMA) and DtBP the blocking of St from living PIB chain occurs efficiently and block copolymers exhibiting good mechanical properties can be prepared. Virgin TPEs can be repeatedly compression molded without deterioration of physical properties. The products exhibit a low and a high temperature T(g) characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing approximately 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.