Polyisobutylene‐containing block polymers by sequential monomer addition. II. Polystyrene–polyisobutylene–polystyrene triblock polymers: Synthesis, characterization, and physical properties

Abstract

New linear and three‐arm star thermoplastic elastomers (TPEs) comprising a rubbery polysobutylene (PIB) midblock flanked by glass 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 conintiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at −80°C. After the living, narrow molecular weight, distribution PIB (M̄w/M̄n = 1.1‐1.2) has reached the desired molecular weight, styrene (St) together with an electron pair 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 Tg characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing ∼ 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.

Novel thermoplastic elastomers. II. Properties of star-block copolymers of PSt-b-PIB arms emanating from cyclosiloxane cores

“…PIB and PSt contaminations were extracted using hexanes and MEK, respectively, and the products were characterized by published techniques. 4,5 As shown in Figure 1, GPC (RI) analysis of the products showed narrow symmetrical traces indicating the virtual absence of diblock contaminant.…”

“…Figure 8 shows a representative DSC thermogram of a primary star-block, D 6 [PIB(30)-PSt (9)] 5 . The DSC trace clearly indicates two distinct T g s (PIB at ϳ Ϫ61°C and PSt at ϳ 99°C) and suggests microphase separation between the PSt and PIB domains.…”

Thermoplastic Elastomers Based on Block, Graft, and Star Copolymers

“…Many cationically synthesized TPEs used polyisobutylene (PIB) as the elastic middle block due to its softness and chemical resistance. Triblock copolymer PS-PIB-PS prepared by sequential living cationic polymerization through a difunctional initiator displayed an ultimate tensile stress of 26 MPa, which was competitive with commercial Kraton SIS TPEs [41,42].…”

From thermoplastic elastomers to designed biomaterials

“…Ultimately, this breakthrough led to the synthesis of a new TPE, poly(styrene-b-isobutylene-b-styrene), by my group, which included Gabor Kaszas, Judit Puskas, and Bill Hager, whose Ph.D. thesis was on this subject. 3,4 Toward the end of my highlight, in the section ''A Glimpse into the Future'', among the many possibilities that I foresaw for living cationic polymerizations, I predicted a bright future for polyisobutylene (PIB)-based TPEs. In view of their unique combination of properties, such as good mechanical properties, softness, outstanding chemical resistance, and barrier properties, combined with excellent processing characteristics and recyclability, I expected these TPEs to be suitable for new hot-melt adhesives, sealants, blending agents, and so forth.…”