|536. Hahn, C.; Wagner, M.; Müller, A.H.E.; Frey, H.: MyrDOL, a protected di-hydroxyfunctional diene monomer derived from β-myrcene: Functional polydienes from renewable resources via anionic polymerization, Macromolecules 55, 4046 (2022) -- DOI: 10.1021/acs.macromol.2c00367|
The protected functional diene monomer 2,2,4,4-tetramethyl-5-(3-methylenepent-4-en-1-yl)-1,3-dioxolane (myrcene dioxolane, MyrDOL) is introduced, based on β-myrcene. The monomer is suitable for carbanionic polymerization, since its acetal func-tionality as a protective group for diols is stable under carbanionic conditions. The polymerization of MyrDOL in cyclohexane at 25°C using sec-butyllithium as an initiator resulted in homopolymers with well-controlled molecular weights in the range of 4.0 to 31 kg mol 1 (SEC, PMMA calibration) and low dispersities, Đ, between 1.07 and 1.13. In pronounced contrast to polymyrcene, which contains 95% 1,4-myrcene microstruc-ture (obtained in cyclohexane by anionic polymerization, Tg=-67°C), microstructure characterization of P(MyrDOL) shows 30-33% of 3,4-units and a Tg of 11°C. The acetal groups can be quantitatively removed under mild conditions, using acidic deprotecting agents (e.g. DOWEX resin), resulting in well-defined poly(myrcene-2,3-diol). The co-polymerization of MyrDOL with the dienes myrcene, styrene and isoprene, respectively was investigated in great detail via in-situ 1H NMR spectroscopy kinetics. The substitu-tion pattern of the 1,3-diene in combination with the polarity of the monomer has sig-nificant influence on the copolymerization behavior, resulting in disparate reactivity ratios and formation of tapered copolymers in statistical copolymerizations. Myrcene copolymers with varying MyrDOL content, in the range between 10 - 100 mol% MyrDOL, were synthesized (Đ ≤ 1.15) and characterized regarding their glass-transition temperatures and polydiene microstructure. An increase in the 3,4-microstructure content was observed, as a consequence of both increasing MyrDOL content and polarity of the polymerization medium, resulting in an increase in Tg from −67 to 9 °C. The protected, functional MyrDOL monomer is promising with respect to polar, hydroxyl-functional rubbers.