Polyethers with defined end group functionalities are indispensable building blocks to produce polyurethane based materials and high-performance adhesives. Currently polyether polyols are obtained by the poly- and oligomerization of cyclic ethers from petrochemical feedstocks, e.g. proplyleneoxide (PO), ethylene oxide (EO) and tetrahydrofuran (THF). The lack of bio-based alternatives prompted us to investigate 2-methyl tetrahydrofuran (2-MeTHF), thus far mainly used as a solvent or fuel additive, as co-monomer. In contrast to THF, 2-MeTHF is regarded as non-polymerizable. However, we present the first reported methodology to co-polymerize 2-MeTHF with PO to hydroxy terminated polyethers. The obtained materials are low in cyclic oligomers, which is otherwise difficult to achieve in cationic polymerization.

Initial investigations showed that with strong Lewis acids, with or without a nucleophile as initiator, mostly cyclic oligomers were obtained; these presumably form via a backbiting reaction, a common side reaction in cationic ring opening polymerization. On the other hand, with only 0.02 mol-% phosphotungstic acid as catalyst the incorporation of 2-MeTHF and the molecular weight of the polymer could be directly controlled by the ratio between the initiator alcohol and PO, i.e. a living copolymerization (Figure 1); of the investigated bifunctional alcohols 1,4-butanediol (1,4-BDO) performed best.

NMR and ESI-MS studies proved the absence of cyclic oligomers and an average incorporation of 2-MeTHF up to 43 mol-%, which is close to the theoretical maximum of 43.3%. Subsequently, we performed a scale-up producing 300g of copolymer. Crosslinking experiments with 4,4-methyl phenyl isocyanate show promising applicability in two component adhesives.

<b>Scheme 1:</b> Methodology for the copolymerization of 2-MeTHF and PO to OH terminated polyether polyols.

Scheme 1: Methodology for the copolymerization of 2-MeTHF and PO to OH terminated polyether polyols.

<b>Figure 1:</b> Predicted vs. experimental <i>M</i><sub>n</sub> at different ratios of fed PO and 1,4-BDO

Figure 1: Predicted vs. experimental M_n at different ratios of fed PO and 1,4-BDO

Alexander Kux

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