| 1. |
- Mankar, Smita, et al.
(författare)
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Synthesis, life cycle assessment, and polymerization of a vanillin-based spirocyclic diol toward polyesters with increased glass transition temperature
- 2019
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Ingår i: ACS Sustainable Chemistry & Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:23, s. 19090-19103
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Mankar, Smita V., et al.
(författare)
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Short-Loop Chemical Recycling via Telechelic Polymers for Biobased Polyesters with Spiroacetal Units
- 2023
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Ingår i: ACS Sustainable Chemistry & Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 11:13, s. 5135-5146
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Tidskriftsartikel (refereegranskat)abstract
- Spirocyclic acetal structures have recently received growing attention in polymer science due to their dual potential to raise the glass transition temperature (Tg) and enable chemical recycling of biobased polymers. In the present work, a vanillin-based diol with a spirocyclic acetal structure was incorporated in a series of rigid amorphous polyesters based on neopentyl glycol and dimethyl terephthalate (DMT). Up to 50 mol % of spirocyclic diol (with respect to DMT) could be incorporated in the copolyesters, but a reasonably high molecular weight was only achieved when ≤30 mol % of the spirocyclic diol was used. The presence of the spiroacetal units in the polyesters not only enhanced the Tg (up to 103 °C) and thermal stability (T5 ≥ 300 °C) but also the oxygen barrier of solution-cast films. We found that the acetal units in the copolyesters could be selectively hydrolyzed under acidic conditions while virtually retaining all of the ester bonds in the polymer backbone. After acidic hydrolysis, telechelic polymers exclusively terminated by two aldehyde end groups were obtained. In this work, we have demonstrated that these telechelic polyesters can be conveniently converted back into poly(acetal-ester)s via cycloacetalization reactions with pentaerythritol.
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| 5. |
- Valsange, Nitin, et al.
(författare)
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Biobased aliphatic polyesters from a spirocyclic dicarboxylate monomer derived from levulinic acid
- 2021
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Ingår i: Green Chemistry. - 1463-9270. ; 23:15, s. 5706-5723
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Tidskriftsartikel (refereegranskat)abstract
- Levulinic acid derived from lignocellulose is an important biobased building block chemical. 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 spirodiester prior to the polycondensations proved crucial to avoid side reactions. A preliminary life cycle assessment (LCA) in terms of greenhouse gas (GHG) emissions indicated that the corresponding spirodiacid 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 (Tgs) in the range 12-49 °C and thermalstability 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.
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| 6. |
- Valsange, Nitin G., et al.
(författare)
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Semi-Crystalline and Amorphous Polyesters Derived from Biobased Tri-Aromatic Dicarboxylates and Containing Cleavable Acylhydrazone Units for Short-Loop Chemical Recycling
- 2024
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Ingår i: Macromolecules. - 0024-9297. ; 57:6, s. 2868-2878
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Tidskriftsartikel (refereegranskat)abstract
- Recycling polymers by site-specific scission into short-chain oligomers/polymers, followed by recoupling these to form the original polymer presents an energetically more favorable shorter-loop chemical recycling in comparison to recycling into monomers. Here, we present the synthesis and polymerization of triaromatic diesters to prepare polyesters with acylhydrazone units as weak structural links. Two diester monomers were prepared by combining methyl 5-chloromethyl-2-furoate, obtained from 5-chloromethylfurfural (CMF), with potentially biobased hydroquinone and resorcinol, respectively. The two diesters having a central phenyl ring flanked by two furan rings were polymerized with 1,6-hexanediol and 1,4-butanediol, respectively, together with controlled amounts of monofunctional ethyl levulinate to form telechelic ketone-terminated polyesters. Subsequent reactions of these telechelic polyesters with adipic dihydrazide yielded corresponding chain-extended polyesters with increased molecular weights ([η] = 0.29−0.52 dL g−1) with acylhydrazone units in the backbone. Thermogravimetric analysis showed a high thermal stability of the polyesters with thermal decomposition only above 275 °C. The polyesters containing the linear hydroquinone units were found to be semicrystalline materials with melting points at 158 and 192 °C, respectively, while those containing the kinked resorcinol units were fully amorphous with glass transition temperatures at 35 and 44 °C, respectively. Initial investigations of the chemical recyclability of the polyesters demonstrated that acylhydrazone units could be selectively cleaved to recover the original telechelic ketone-terminated polyesters, which could again be chain-extended to obtain a recycled polymer with molecular weights and properties very similar to those of the original polymer.
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| 8. |
- Valsange, Nitin, et al.
(författare)
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Improved chemical recyclability of 2,5-furandicarboxylate polyesters enabled by acid-sensitive spirocyclic ketal units
- 2024
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Ingår i: Green Chemistry. - 1463-9270. ; 26:5, s. 2858-2873
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Tidskriftsartikel (refereegranskat)abstract
- Incorporating hydrolytically sensitive functional groups into polymer backbones provides a feasible strategy to trigger their degradation to the starting monomers, thus enabling chemical recycling of the material. Here, we present two series of copolyesters in which a biobased spirocyclic ketal-functional diester monomer was incorporated into poly(butylene 2,5-furandicarboxylate) (PBLF) and poly(hexamethylene 2,5-furandicarboxylate) (PHLF), respectively. A two-step melt polycondensation resulted in copolyesters with moderate to high molecular weights, as confirmed by intrinsic viscosity values between 0.5-1.04 dL g-1. Thermogravimetric analysis showed a thermal stability up to 275 °C, and increasing char yields upon incorporation of the spirocyclic monomer. The crystallinity and melting points of the copolyesters decreased with the increasing content of the spirocyclic ketal units in the backbone. Copolyesters containing up to 15% of the spiro-ketal units were semicrystalline, while those containing 20 and 50% spiro-ketal units were completely amorphous. The hydrolytic degradation of copolyesters from the PHLF series was investigated using 3-12 M aq. HCl, and were found to degrade faster than the corresponding homopolyesters. Acid-catalyzed cleavage of the randomly distributed spiro ketal units promoted the rapid fragmentation of the polymer chain into small oligomers, which were subsequently hydrolyzed to the original chemical building blocks. The ketone-terminated telechelic oligomers obtained after the degradation of spirocyclic ketal units were also investigated in the direct polymerization with pentaerythritol. The initial results implied that the oligomers can be re-polymerized into the original polymer. Hence, this work demonstrated a feasible pathway towards chemically recyclable 2,5-furandicarboxylate polyesters with a tuneable degree of crystallinity
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