Co-Oligomers of Renewable and “Inert” 2-MeTHF and Propylene Oxide for Use in Bio-Based Adhesives

Abstract

Commercial polyether polyols are usually obtained by the ring-opening polymerization of epoxides or tetrahydrofuran. 2-Methyl-tetrahydrofuran (2-MeTHF) could be an alternative bio-based building block for the synthesis of these polyols. Although 2-MeTHF cannot be polymerized, we did achieve the copolymerization of 2-MeTHF with propylene oxide (PO) using Lewis and Bronsted acids as catalysts and water or diols as initiators. The resulting polyether polyols have a molecular weight range, which allows their use as components for adhesives. The molar content of 2-MeTHF in the oligomers can be up to 48%. A 1:1 copolymer of 2-MeTHF and PO is produced when stoichiometric amounts of BF3·OEt2 are used. Here, the monomeric units in the chains alternate, but also cyclic or other nondiol products are formed that are detrimental to its further use in adhesives. Linear dihydroxyl-terminated polyether chains were formed when the heteropolyacid H3PW12O40·24H2O was used as a catalyst and a diol as an initiator. The formation of cyclic products can be drastically reduced when the accumulation of propylene oxide during the reaction is avoided. 1H NMR experiments indicate that the step of 2-MeTHF incorporation is the alkylation of 2-MeTHF by protonated PO. It was shown that the 2-MeTHF/PO copolymer had increased tensile strength compared to polypropylene glycol in a two-component adhesive formulation.