2,3-Butanediol-based Polyesters. Challenges and Solutions in Rigid Polyester Synthesis

Concerns regarding the sustainability of plastics are rising, as the vast majority (~99%) are derived from fossil resources. Consequently, there is increasing interest in replacing fossil-based feedstocks with alternative building blocks for plastic production. An alternative is 2,3-butanediol (2,3-BDO), which can be produced from biomass and/or CO 2 . Substituting ethylene glycol with 2,3-BDO yields a polyester with the same backbone structure as poly(ethylene terephthalate) (PET), but is distinguished by the presence of two additional methyl side groups per repeating unit. The use of 2,3-BDO offers an advantage: its incorporation into polyesters leads to increased chain rigidity compared to EG. This results in a higher glass transition temperature (T g ), enabling use at higher temperatures. For example, PET bottles are not suitable for hot beverages because they deform above their T g of approximately 80 °C. In contrast, replacing EG with 2,3-BDO could increase the T g to above 100 °C. However, a drawback of 2,3-BDO is its lower reactivity compared to EG, combined with its tendency to undergo thermal degradation at the high temperatures required for polyester production. The work described in this thesis primarily focuses on the use of 2,3-BDO as a monomer in polyester synthesis and specifically targets rigid polyesters, in which the diol is combined with aromatic comonomers such as terephthalate. Alongside 2,3-BDO, 1,2-propanediol, a potentially bio-based diol and structurally “intermediate” between EG and 2,3-BDO, is also studied. In addition, an alternative synthesis method is used for 2,3-BDO polyesters and is further explored for the production of catalyst-free poly(ethylene furanoate) (PEF).

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