|539. Wadkaonkar, S.; Wagner, M.; Baptista, L. A.; Cortes-Huearto, R.; Frey, H.; Müller, A.H.E.: Anionic polymerization of the terpene-based diene beta-ocimene: Complex mechanism due to stereoisomer reactivities, Macromolecules (2023) -- DOI: 10.1021/acs.macromol.2c02241|
Motivated by the need for sustainable, bio-based materials, the living anionic polymerization of the under-explored terpene monomer β-ocimene (Oc) was investigated for the first time. Ho-mopolymers with Mn up to 50 kg mol-1 of the Oc isomeric mixture (E:Z = trans:cis = 70:30) were synthesized in cyclohexane and were analyzed with respect to molecular weight control, disper-sity, microstructure and glass transition temperature, Tg. Employing styrene as a comonomer, diblock copolymers and a series of statistical copolymers with Mn up to 20 kg mol-1 with varying comonomer compositions offered the opportunity to tailor the glass transition of the copoly-mers. Real-time 1H NMR kinetics indicated a remarkably divergent reactivity of the trans- and cis isomers. This unveiled the unique observation that the homopolymerization of Oc is in fact a copolymerization of the cis and trans isomers, which one might name as ’stereo-copolymerization’ (rtrans = 3.16; rcis = 0.32). Kinetic studies of the statistical copolymerization of the Oc isomeric mixture with styrene revealed an astonishingly contradictory reactivity of the two isomers (rtrans < rcis). The reactivity differences of the cis and trans isomers in the polymeri-zation were utilized to isolate the individual isomers for the first time. Subsequently they were independently homo- and copolymerized with styrene. The complex mechanism of these polymerizations and the rather high polymer dispersities (Đ ≈ 1.6-2) are discussed using various kinetic models, supported by Density Functional Theory modelling. The surprisingly different behavior of the two isomers with styrene was validated experimentally via a 1H NMR-monitored chemical titration.