Ring-opening synthesis of polyethylene furanoate (PEF) as a renewable resource-based substitute for polyethylene terephthalate (PET)
May 10-15, 2015
As alternatives to their established fossil-based counterparts, biomass-derived plastics can have a major impact on the anticipated shift of our societies from fossil-fuel based economies towards more sustainable civilizations. This project seeks to develop a novel synthesis route to produce furanic polymers to substitute one of the world’s most dominant plastics, oil-based polyethylene terephthalate (PET) by promising furan-based polymers, especially polyethylene furanoate (PEF) and polybutylene furanoate (PBF). Those alternative polymers have already been investigated and produced by research groups, including Gandini et al. (2011), Ma et al. (2012), Min et al. (2012), and a few companies such as Avantium [1-4]. Their approaches were invariably based on polycondensation and their products have proven to possess favorable material properties over PET, e.g. reduced CO2- and O2-permeability and improved processability. Our aim is to explore novel synthesis pathways based on ring-opening polymerization (ROP) to push furan-based polymer technology further towards industrially applicable processes. This research is focused on the two major process steps: (1) the synthesis of cyclic PEF oligomers (cyOEF) with sufficient purity at high conversion, and (2) their polymerization by ring-opening (ROP) to yield high molecular weight PEF at high conversion. In the first step, two synthetic strategies have been investigated to produce cyOEF. The first is a fast cycle formation using the rapid esterification of acid chlorides with alcohols. The second one exploits the thermodynamically preferred cycle formation at high dilutions by depolymerization of a prepolymer of PEF. For the first route, yields of a cyclic oligomer population of around 30% have been achieved after purification. The depolymerization route, bearing the advantage of a “green” process without the necessity of prior chlorination of furanic acid, has proven to yield a similar distribution of cyclic species. Possible purification routes include precipitation and adsorption processes, which have both been applied to yield cycles at high purity from linear species (>99% by HPLC area). In the second step, high molecular weight polymer synthesis was shown feasible at a purity >90% and Mw up to 20,000 g/mol and PDI < 2, following a previously established reaction and purification protocol. Reactions were employing tin and titanate catalysts, and temperatures as high as 300°C to polymerize in bulk above the high melting point of the cyOEF monomers. While titanates proved ineffective at the elevated temperatures, tin catalysts were more effective at lower temperatures. PEF products usually showed strong coloring, presumably stemming from degradation reactions of the furan ring. Currently, the reaction steps are being optimized in terms of catalyst content, potential dilution and reaction temperature, before a quantitative yield evaluation and deeper material properties analysis for comparison with PET will be undertaken.
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