Polyurethanes from Renewable Resources

A series of polyurethane (PU) and polyurethane-urea (PUU) elastomers derived from a renewable source have been synthesised and characterised extensively. Comparisons have been made to analogous series of elastomers utilising petroleum derived diisocyanates.
The renewable elastomers utilised a difuranic diisocyanate (DFDI) derived from furfural, a readily available raw material synthesised from agricultural waste. DFDI was synthesised using a modified version of a published procedure, utilising triphosgene for the formation of the diisocyanate.
The reaction kinetics of the diisocyanates used were compared using an adiabatic temperature rise technique in both catalysed and uncatalysed reactions, showing that DFDI reacts at approximately one fifteenth the rate of MDI with primary alcohols.
The polyurethane series comprised MDI/DFDI and 1,4-butanediol (BD) hard segments (HS) and polytetrahydrofuran (PTHF) soft segments (SS) at 1, 2 and 2.9 kDa molecular weights. The PUU series utilised the 2kDa PTHF SS and the amine precursor to the diisocyanate, in effect simulating the HS produced in a water blown (polyurethane-urea) foam.
In all PU elastomers the DFDI variants displayed much greater degrees of phase separation as evidenced by lower soft segment (SS) Tgs observed by both DSC and DMTA measurements, greater invariants observed in SAXS frames, more SS crystallinity observed in WAXS data and a much more clearly defined morphology observed in tapping mode AFM images. Crystallinity within the SS was found to be much higher in DFDI based elastomers, whereas crystalline hard segments were only observed in MDI based PU elastomers and was more pronounced at higher HS contents and at lower SS molecular weights.
The PUU elastomers showed very clear morphologies in AFM images but were found to possess a lower degree of phase separation overall, agreeing with previous literature suggesting that the stronger hydrogen bonding of urea groups can hinder phase separation.