Methylthiohexa-1,3-diene : anionic polymerization of a diene with thioether moiety enables post-polymerization modification and antimicrobial materials

Abstract

Anionic polymerization of 1,3-dienes is a highly established approach for the synthesis of synthetic rubber and plays a key role for thermoplastic elastomers like poly(styrene-b-butadiene-b-styrene) (SBS). Aiming at novel concepts for tailoring the property profile of synthetic rubber in post-polymerization reactions, we introduce the thioether-containing 6-methylthio-hexa-1,3-diene (MTHD) as a diene monomer derived from the biobased methional. The obtained isomeric cis-/trans-mixture was successfully polymerized via anionic techniques. In situ 1H nuclear magnetic resonance (NMR) kinetics revealed different reactivities of the trans- and cis-isomer and dispersities of Ɖ = 1.21–1.35. Copolymerization with isoprene afforded a series of well-defined statistical copolymers with molar masses up to 50 kg mol−1, permitting precise adjustment of MTHD content from 2% to 10%. These copolymers exhibited moderate to narrow distributions (Ɖ < 1.19). Targeting the thioether groups via post-polymerization modifications (i.e., alkoxylation and alkylation) permitted tailoring of the properties of the diene-based copolymers. The respective sulfoxide was obtained selectively by mild oxidation and represents an internal antioxidant group. Introduction and testing of sulfonium functional polyisoprenes regarding their inhibition of the growth of gram-negative and gram-positive bacteria strains showed significant antimicrobial performance of the copolymers against Escherichia coli and Staphylococcus aureus.