Polyisobutylene-Based Thermoplastic Elastomers. 5. Poly(styrene-b-isobutylene-b-styrene) Triblock Copolymers by Coupling of Living Poly(styrene-b-isobutylene) Diblock Copolymers

Abstract

Poly(styrene-b-isobutylene-b-styrene) (PSt−PIB−PSt) triblock copolymers have been prepared for the first time via coupling of living PSt-PIB diblock copolymers in a one-pot procedure. The PSt−PIB diblock copolymer was synthesized by living sequential cationic polymerization in methylcyclohexane (MeChx)/methyl chloride (MeCl) or hexane (Hex)/MeCl solvent mixtures at −80 °C using TiCl4 as co-initiator. It was found that, due to decomposition of the living PSt ends, the crossover efficiency (C eff) from living PSt to IB decreases precipitously with time at close to 100% St conversion. To obtain high C eff, IB must therefore be added at ≤95% St conversion. It was also found that in the presence of unreacted St the rate of IB block copolymerization decreases with time; this was attributed to the formation of relatively unreactive −St−IB−Cl ends. Due to the relatively high concentration of these ends, coupling of living PSt−PIB was slow and incomplete. The obtained PSt−PIB−PSt triblock copolymers exhibited reasonable but significantly lower tensile strength (16−20 MPa) than that (23−25 MPa) reported for model PSt−PIB−PSt triblock copolymers of similar composition.

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].…”

Polyisobutylene‐based biomaterials

“…[22][23][24] Various amphiphilic blocks and networks containing PIB and poly(vinyl ether) derivatives were also reviewed. 25,26 PIB-polysiloxane block copolymers were synthesized via the anionic ring-opening polymerization of hexamethylcyclotrisiloxane, initiated by PIB-OH with n-BuLi 27 (Scheme 2).…”

Synthesis of Polyisobutylene-Based Block Copolymers with Precisely Controlled Architecture by Living Cationic Polymerization

“…For instance IB and styrene (St) possess similar reactivity, therefore, diblock copolymers poly(IB-b-St) [7] as well as the reverse order poly(St-b-IB) [8,9] could be readily prepared via sequential monomer addition (Scheme 2). Moreover, identical reaction conditions (80 C and TiCl 4 as Lewis acid) could be employed for the living cationic polymerization of both monomers.…”

“…The first order plot, which is linear for homopolymerization, however, is curved downward for block copolymerization, indicating decreasing concentration and/or reactivity of active centers with time. This is attributed to the slow formation of -St-IB-Cl chain ends, which are much less reactive than -IB-IB-Cl [8,9]. A similar effect of a g-phenyl substituent has been observed by comparing the overall addition rate of 1,1-diphenylethylene and 2-phenylfuran to 2-chloro-2,4,4-trimethylpentane and 2-chloro-2,4-dimethyl-4-phenylpentane [13].…”

“…As a result, high coupling efficiency was also observed, even when excess BDPEP was used. This coupling agent is therefore best suited for the synthesis of ABA triblock copolymers by coupling of living AB diblock copolymers, and has been employed to obtain poly(St-b-IB-b-St) [9] and poly(aMeSt-b-IB-b-aMeSt) [22] triblock copolymers. For the synthesis of poly(St-b-IB-b-St) triblock copolymers, however, the two step monomer addition method is superior.…”