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Levulinic acid derived from lignocellulose is an important biobased building block. Here, we report on the synthesis and polymerization of a rigid spirocyclic diester monomer to produce polyesters and copolyesters. The monomer was prepared via a one-step acid catalyzed ketalization involving ethyl levulinate and pentaerythritol by employing a straightforward, solvent-free, and readily scalable method which required no chromatographic purification. Still, careful removal of traces of water from the spiro-diester prior to polycondensations proved crucial to avoid side reactions. A preliminary life cycle assessment (LCA) in terms of greenhouse gas (GHG) emissions indicated that the corresponding spiro-diacid tended to be environmentally favourable, producing less CO2 emission than e.g., biobased succinic acid and adipic acid. A series of aliphatic polyesters with reasonably high molecular weights was subsequently prepared in melt and modified melt polycondensations of the spiro-diester with 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and 1,4-cyclohexanedimethanol, respectively. The resulting fully amorphous polyesters showed glass transition temperatures in the range 12–49 °C and thermal stability up to 300 °C. Hot-pressed films of the polyesters based on neopentyl glycol and 1,4-cyclohexanedimethanol were transparent and mechanically strong, and dynamic melt rheology showed stable shear moduli over time to indicate good processability. In addition, the spiro-diester monomer was employed in copolycondensations with diethyl adipate and 1,4-butanediol and demonstrated good reactivity and stability. Hence, the results of the present study indicate that the spiro-diester based on levulinic acid is an effective monomer for the preparation of aliphatic polyesters and other condensation polymers.

A rigid diol with a cyclic acetal structure was synthesized by facile acetalation of fructose-based 5-hydroxymethyl furfural (HMF) and partly bio-based di-trimethylolpropane (di-TMP). This diol (Monomer T) was copolymerized with potentially bio-based flexible polytetrahydrofuran and diisocyanates to prepare thermoplastic poly(cycloacetal-urethane)s. A modified one-step solution polymerization protocol resulted in relatively high molecular weights (Mn ∼ 41.5–98.9 kDa). All the obtained poly(cycloacetal-urethane)s were amorphous with tuneable glass transition temperatures up to 104 °C. Thermogravimetric analysis indicated that these polymers were thermally stable up to 253 °C and had a relatively high pyrolysis char residue, which may indicate potential inherent flame resistance. Melt rheology measurements were performed to determine a suitable processing window between 165–186 °C, after which the polymer was successfully melt-spun into ∼150 meters of homogeneous fibres at 185 °C. The resulting fibres could be readily hydrolysed under acidic conditions, resulting in partial recovery of the original chemical building blocks.

Bio-based rigid diols are key building blocks in the development and preparation of high performance bioplastics with improved thermal and dimensional stability. Here, we report on the straightforward two-step synthesis of a diol with a spirocyclic acetal structure, starting from bio-based vanillin and pentaerythritol. According to a preliminary life cycle assessment (LCA), the greenhouse gas emissions of this bio-based diol are significantly lower than that of bio-based 1,3-propanediol. Copolymerization of the rigid spiro-diol with 1,6-hexanediol and dimethyl terephthalate by melt polymerization yielded a series of copolyesters, which showed improved glass transition temperature and thermal stability upon the incorporation of the spiro-acetal units. The crystallinity and melting point of copolyesters decreased with increasing content of the spirocyclic backbone structures. The copolyesters containing 10% of the new diol was semicrystalline while those with 20 and 30% spiro-diol incorporated were completely amorphous. Moreover, dynamic mechanical analysis indicated that the copolyesters showed comparable storage moduli as AkestraTM, a commercial fossil-based high-performance polyester.

There is currently an intensive development of sugar-based building blocks toward the production of renewable high-performance plastics. In this context, we report on the synthesis of a rigid diol with a spirocyclic structure via a one-step acid-catalyzed acetalation of fructose-sourced 5-hydroxymethylfurfural and pentaerythritol. Preliminary life cycle assessment (LCA) indicated that the spiro-diol produced 46% less CO2 emission than bio-based 1,3-propanediol. Polymerizations of the spiro-diol together with another sugar-based flexible 1,6-hexanediol for the production of polyesters and poly(urethane-urea)s were investigated, and reasonably high molecular weights were achieved when up to 20 and 60 mol% spiro-diol was used for polyesters and poly(urethane-urea)s, respectively. The glass transition temperatures (Tgs) of the polyesters and poly(urethane-urea)s significantly increased upon the incorporation of the rigid spirocyclic structure. On the other hand, it was observed that the spiro-diol was heat-sensitive, which could cause coloration and partial crosslinking when >10% (with respect to dicarboxylate) was used for the polyester synthesis at high temperatures. The results indicated that the polymerization conditions have to be carefully controlled under these conditions. However, when the spiro-diol was used for the synthesis of polyurethanes at lower temperature, the side reactions were insignificant. This suggests that the new spiro-diol can be potentially suitable toward the production of sustainable rigid polyurethane materials like coatings or foams, as well as renewable polyesters after further optimization of the polymerization conditions.