Cristina Lavilla

High Tg bio-based aliphatic polyesters from bicyclic D-mannitol

The carbohydrate-based diol 2,4:3,5-di-O-methylene-d-mannitol (Manx) has been used to obtain aliphatic polyesters. Manx is a symmetric bicyclic compound consisting of two fused 1,3-dioxane rings and bearing two primary hydroxyl groups. In terms of stiffness, it is comparable to the widely known isosorbide, but it affords the additional advantages of being much more reactive in polycondensation and capable of producing stereoregular polymers with fairly high molecular weights. A fully bio-based homopolyester (PManxS) has been synthesized by polycondensation in the melt from dimethyl succinate and Manx. The high thermal stability of PManxS, its relatively high glass transition temperature (Tg = 68 °C) and elastic modulus, and its enhanced sensitivity to the action of lipases point to PManxS as a polyester of exceptional interest for those applications where biodegradability and molecular stiffness are priority requirements. In addition, random copolyesters (PBxManxyS) covering a broad range of compositions have been obtained using mixtures of Manx and 1,4-butanediol in the reaction with dimethyl succinate. All PBxManxyS were semicrystalline and displayed Tg values from -29 to +51 °C steadily increasing with the content in Manx units. The stress-strain behavior of these copolyesters largely depended on their content in Manx and they were enzymatically degraded faster than PBS.

Renewable terephthalate polyesters from carbohydrate-based bicyclic monomers

Poly(alkylene terephthalate)s, PET and PBT in particular, are materials of great relevance and growing projection in the thermoplastic field but are today almost totally produced from fossil resources. The current huge consumption of these polyesters necessitates urgent actions addressed to make them renewable by using naturally-occurring raw materials. Among the different approaches that are being followed to develop bio-based poly(terephthalate)s, the use of bicyclic carbohydrate-derived difunctional compounds as building-blocks is receiving much attention in the last few years because partially renewable polyesters with high Tg may be thus obtained. This review presents a critical account of the terephthalate homopolymers and copolymers that have been synthesized using the two types of carbohydrate-based bicyclic monomers, isohexides and diacetals, explored to date. The properties displayed by the novel bio-based poly(terephthalate)s in relation to the bicyclic structure of the used monomers are comparatively reviewed and their potential as emergent materials for thermoplastic applications is evaluated.

PET copolyesters made from a D-mannitol-derived bicyclic diol

The carbohydrate-based bicyclic diol 2,4:3,5-di-O-methylene-D-mannitol (Manx) was made to react in the melt with ethylene glycol and dimethyl terephthalate to produce random PExManxyT copolyesters covering the whole range of molar compositions. The copolyesters had weight-average molecular weights in the 33000–41000 g mol−1 interval and were thermally stable up to nearly 380 °C. They displayed Tg in the 81 to 137 °C range with values largely increasing with the content in Manx units. Copolyesters containing minor amounts of Manx were semicrystalline whereas those with contents equal to or more than 30% of Manx were amorphous. Stress–strain parameters were affected by composition, increasing tensile strength and elastic modulus and reducing elongation at break when introducing Manx units. These bio-based PET copolyesters showed enhanced susceptibility to hydrolysis.

Carbohydrate-based PBT copolyesters from a cyclic diol derived from naturally occurring tartaric acid: a comparative study regarding melt polycondensation and solid-state modification

2,3-O-Methylene-L-threitol (Thx) is a cyclic carbohydrate-based diol prepared by acetalization and subsequent reduction of the naturally occurring tartaric acid. The structure of Thx consists of a 1,3-dioxolane ring with two attached primary hydroxyl groups. Two series of partially bio-based poly(butylene terephthalate) (PBT) copolyesters were prepared using Thx as a comonomer by melt polycondensation (MP) and solid-state modification (SSM). Fully random copolyesters were obtained after MP using mixtures of Thx and 1,4-butanediol in combination with dimethyl terephthalate. Copolyesters with a unique block-like chemical microstructure were prepared by the incorporation of Thx into the amorphous phase of PBT by SSM. The partial replacement of the 1,4-butanediol units by Thx resulted in satisfactory thermal stabilities and gave rise to an increase of the Tg values, this effect was comparable for copolyesters prepared by MP and SSM. The partially bio-based materials prepared by SSM displayed higher melting points and easier crystallization from the melt, due to the presence of long PBT sequences in the backbone of the copolyester. The incorporation of Thx in the copolyester backbone enhanced the hydrolytic degradation of the materials with respect to the degradation of pure PBT.

Block-Sequence-Specific Glycopolypeptides with Selective Lectin Binding Properties

Glycopolypeptides with defined block sequences were prepared by sequential addition of two different N-carboxyanhydrides (NCAs), followed by selective deprotection and functionalization of predefined positions within the polypeptide backbone. The sequential arrangement of the galactose units and the block-sequence length have been systematically varied. All the glycopolypeptides have been obtained with a similar overall composition and comparable molecular weights. Circular dichroism measurements revealed some dependence of the secondary structure on the primary composition of the glycopolypeptides at physiological pH. While statistical, diblock, and tetrablock glycopolypeptides adopted a random coil conformation, the octablock glycopolypeptide was mostly α-helical. The ability to selectively bind to lectins was investigated by turbidity measurements as well as surface plasmon resonance (SPR) studies. It was found that the extent of binding was dependent on the position of the galactose units and thus the primary glycopolypeptide structure. The octablock glycopolypeptide favored interaction with lectin RCA120 while the tetrablock glycopolypeptide demonstrated the strongest binding activity to Galectin-3. The results suggest that different lectins are very sensitive to glyco coding and that precise control of carbohydrate units in synthetic polymeric glycopeptides will remain important.

Green and selective polycondensation methods toward linear sorbitol-based polyesters : enzymatic versus organic and metal-based catalysis

Renewable polyesters derived from a sugar alcohol (i.e., sorbitol) were synthesized by solvent-free polycondensation. The aim was to prepare linear polyesters with pendant hydroxyl groups along the polymer backbone. The performance of the sustainable biocatalyst SPRIN liposorb CALB [an immobilized form of Candida antarctica lipase B (CALB); SPRIN technologies] and the organo-base catalyst 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) were compared with two metal-based catalysts: dibutyl tin oxide (DBTO) and scandium trifluoromethanesulfonate [also known as scandium triflate, Sc(OTf)3 ]. For the four catalytic systems, the efficiency and selectivity for the incorporation of sorbitol were studied, mainly using (13) C and (31) P NMR spectroscopies, whereas side reactions, such as ether formation and dehydration of sorbitol, were evaluated using MALDI-TOF-MS. Especially the biocatalyst SPRIN liposorb CALB succeeded in incorporating sorbitol in a selective way without side reactions, leading to close-to-linear polyesters. By using a renewable hydroxyl-reactive curing agent based on l-lysine, transparent and glossy poly(ester urethane) networks were successfully synthesized offering a tangible example of bio-based coatings.

Polypeptides by light: photo-polymerization of N-carboxyanhydrides (NCA)

The synthesis of polypeptides by N-carboxyanhydride (NCA) photopolymerization is demonstrated. The active initiator cyclohexylamine was produced in situ by the UV-induced breakdown of photoamine generators. Real-time FTIR and MALDI-ToF-MS analyses provide clear evidence for the proposed photoinitiation mechanism as well as the attachment of the active initiator to the polypeptide chain. NCA photopolymerization generates new possibilities for designing polypeptides both in solution and on surfaces.

Sustainable coatings from bio-based, enzymatically synthesized polyesters with enhanced functionalities

Bio-based sorbitol-containing polyester polyols were synthesized via enzymatic polycondensation. The selectivity of the biocatalyst for primary vs. secondary hydroxyl groups allowed for the preparation of close to linear renewable polyester polyols with enhanced hydroxyl functionalities, both as pendant groups and end-groups. In some cases, the sorbitol units were homogeneously distributed in the polyester polyol chains, whereas changes in the comonomers used and experimental conditions led to inhomogeneous and unique distributions of sorbitol, implying that some polyester polyol chains contained none and others contained multiple sorbitol units. Solvent-borne coatings were prepared by cross-linking the functional polyester polyols with polyisocyanate curing agents. An increased functionality of the polyester polyols led to an enhancement of the properties of the resulting cured coatings. Furthermore, when sorbitol units were non-homogeneously distributed, a significant improvement in the chemical resistance and mechanical properties of the cured poly(ester urethane) network was noted. By employing the bio-based diisocyanate EELDI (ethyl ester L-lysine diisocyanate) as a curing agent, almost fully renewable coatings with satisfactory mechanical properties were obtained.