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Biodegradation of polyesters driven by enzymes is considered as one of the most effective way of degradation of these materials, as a way to control plastics accumulation in the environment. In this study, we present two different strategies to tune the enzymatic degradation of PBS films triggered by a lipase from Pseudomonas cepacia. Firstly, the kinetics of enzymatic degradation of PBS films was regulated by applying multilayer coats of polysaccharide alginate and chitosan (Alg/Chi) films. Secondly, self-degradable PBS films were prepared by embedding lipase-filled alginate particles. For comparison purposes, a detailed enzymatic degradation study of neat PBS films exposed to a lipase from P. cepacia in solution was made to determine the main experimental parameters influencing their degradation in solution. The results showed that an increase in enzyme concentration increased the degradation extent and rate of neat PBS films. At a fixed enzyme concentration, stirring of the solution containing the enzyme and the PBS also increased the biodegradation rate. In the case of the PBS films coated with a different number of Alg/Chi layers by spray-assisted LbL and subjected to enzymatic degradation experiments in solution, the extent of degradation was found to be dependent on the number of protective coating layers. Therefore, the Alg/Chi biobased coating constitutes an effective barrier to the diffusion of the lipase, thus proving its effectiveness in modulating the enzymatic activity as a function of coating thickness. In the case of self-degradable PBS containing lipase-embedded alginate beads (employed to protect the enzyme during high-temperature processing), only limited biodegradation was observed as the amount of encapsulated enzyme employed was too small. Nonetheless, these results are promising, as the enzymatic activity –indicative of the degradation capacity of the enzyme– determined for all these samples was about 2 orders of magnitude lower than that of previous assays., This research was funded by the projects MAT2017-83014-C2-1-P, MAT2017-83014-C2-2-P, PID2020-113045GB-C21 and PID2020-113045GB-C22 funded by MCIN/ AEI /10.13039/501100011033 and by the Basque Government through grant IT1503-22. We would also like to acknowledge the financial support from the BIODEST project; this project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement No. 778092. M.I.P. is supported with an FPI contract (PRE2018-086104) to develop a PhD thesis. R.H. is member of the CSIC Interdisciplinary Thematic Platform (PTI+) Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy+ (PTI-SusPlast+). J.M.R. is a FRS-FNRS Senior Research Associate. Authors would also like to thank Dr. Ana Beloqui for helpful discussions on enzymatic activity.

Diblock copolymers (PPDLx-b-pPAAy) were prepared from ω-pentadecalactone and l -glutamic acid or l -lysine amino acids by ring opening polymerization initiated by amino groups. Telechelic amino-ended poly(ω-pentadecalactone) with a length of 15–20 repeating units was firstly synthesized by enzymatic polymerization by means of CALB and then used as macroinitiator for the polymerization of the N-carboxyanhydrides of the two α-amino acids conveniently protected as benzyl and eN-carbobenzoxy derivatives, respectively. The molecular weight of the polypeptide block was accurately controlled by adjusting the amino acid/macroinitiator ratio used in the feed. Copolymers with Mn ranging between ∼5000 and ∼40,000 g·mol−1 and varying ester/peptide ratio were obtained and characterized in detail by GPC and NMR spectroscopy. The thermal properties of these copolymers were evaluated by TGA and DSC, and their structure in the solid-state including their response to heating, were examined by FTIR and XRD at variable temperature. It was shown that the polypentadecalactone segment was crystallized for all compositions and that the polypeptide counterpart adopted a two-dimensional hexagonal packing of α-helices at temperatures above melting of the polyester block. SAXS revealed the presence of a biphasic nanostructure with a repeating distance of 27 nm for the case of glutamic-based copolymers. It was demonstrated that both glutamic and lysine-based PPDLx-b-pPAAy copolymers could self-assemble in well-shaped nanospheres with a diameter in the ∼200–400 nm range and a negative zeta-potential.

Robust and flexible free-standing films made of spin-coated poly(lactic acid) (PLA) and poly(3,4-ethylenedioxythiophene) (PEDOT) nanolayers have been prepared. A steel sheet coated with a sacrificial layer of PEDOT:poly(styrenesulfonate) (PSS) and a spin-coated nanolayer of PLA was used as working electrode for the anodic polymerization of 3,4-ethylenedioxythiophene monomer. The latter was only successfully accomplished when rounded-shape nanoperforations of average diameter 49¿±¿14¿nm were introduced into PLA layers, which was achieved by combining the phase segregation processes undergone by immiscible PLA:poly(vinyl alcohol) (PVA) mixtures with selective solvent etching to remove PVA domains. Nanoperforations allowed the utilization of the semiconducting PEDOT:PSS sacrificial layer to immobilize the electropolymerized PEDOT chains. Morphological and topographical studies show the templating effect of PEDOT layers. In addition of flexibility and mechanical strength, free-standing 5-layered films present good electrochemical activity, evidencing their potential ability to reversibly exchange ions with the medium. These properties offer important advantages with respect to those of neat PLA and supported PEDOT films, as has been illustrated by cell culture and protein adsorption assays. Cell cultures evidenced the superior behavior of 5-layered films as bioactive platforms for fibroblast and epithelial cells proliferation, while adsorption assays reflected their potential as selective bioadhesive surfaces for protein separation

Cyclic oligomers of isomannide 2,5-furandicarboxylate were synthesized using the high dilution condensation method. A mixture of dimer, trimer, and tetramer species largely enriched in dimer was obtained. These cyclic oligomers were made to react with oligo(butylene 2,5-furandicarboxylate) in bulk at 220 °C by ring opening polymerization using Sn(Oct)2 as a catalyst. A series of random poly(butylene 2,5-furandicarboxylate) copolyesters containing isomannide in a range of 5–50 mol % and with weight-average molecular weights between 30,000 and 50,000 g·mol–1 were prepared. These copolyesters started to decompose above 300 °C, and only those containing less than 10 mol % of isomannide showed signs of crystallinity. They displayed glass-transition temperatures in the 40–100 °C range with values increasing steadily with the content in isomannide. At difference with poly(butylene 2,5-furandicarboxylate) homopolyester that is reluctant to undergo hydrolysis, the isomannide-containing copolyesters were noticeably degraded by water, much more rapidly when exposed to lipases.

Sugar-based polyesters derived from sorbitol and isohexides were obtained via solvent-free enzymatic catalysis. Pendant hydroxyl groups, coming from the sorbitol units, were present along the polyester backbone, whereas the two isohexides, namely, isomannide and isoidide dimethyl ester monomers, were selected to introduce rigidity into the polyester chains. The feasibility of incorporating isomannide as a diol compared to the isoidide dimethyl ester as acyl-donor via lipase-catalyzed polycondensation was investigated. The presence of bicyclic units resulted in enhanced Tg with respect to the parent sorbitol-containing polyester lacking isohexides. The different capability of the two isohexides to boost the thermal properties confirmed the more flexible character provided by the isoidide diester derivative. Solvent-borne coatings were prepared by cross-linking the sugar-based polyester polyols with polyisocyanates. The increased rigidity of the obtained sugar-based polyester polyols led to an enhancement in hardness of the resulting coatings.

In the present study poly (butylene sebacate- co -terephthalate)s having different compositions were synthesized with a high yield and a random distribution by thermal transesterification of poly (butylene sebacate) and poly (butylene terephthalate) homopolymers. The copolymer with the highest comonomer ratio was the least crystalline sample, although the melting peaks corresponding to both, sebacate and terephthalate-rich phases were still observable in calorimetric heating runs. This copolymer was associated with interesting thermal and mechanical properties, as the maximum melting point was higher than 100 °C and the storage modulus was also high (i.e. 1.1 × 10 9 N/m 2 and 1.7 10 8 N/m 2 were determined just before and after the main glass transition temperature of −12 °C). As all studied samples were thermally stable up to temperatures clearly higher than the fusion temperature, they could be easily processed. Increasing the terephthalate content of the copolymers resulted in higher hydrophobicity, which had a minor influence on cell adhesion and proliferation of both fibroblast-like and epithelial-like cells. Hydrolytic and enzymatic degradability were assessed and the effect of composition and crystallinity on the degradation rate was investigated. Molecular weight measurements during exposure to a hydrolytic media indicated a first order kinetic mechanism during the initial stages of degradation before reaching a limiting molecular size, which was indicative of solubilization. The most amorphous sample appears as a highly promising biodegradable material since it showed a significant weight loss during exposure to all selected degradation media, but also exhibited good performance and properties that were comparable to those characteristic of polyethylene.

Poly(ethylene succinate) (PES) with weight-average molecular weight above 60,000 g mol-1 was efficiently obtained by enzymatic ring opening polymerization of cyclic oligo(ethylene succinate)s c(ES)n, which in turn were prepared by lipase-catalysed cyclocondensation in solution of dimethyl succinate and ethylene glycol. The methodology was demonstrated to be also applicable to the synthesis of high molecular weight PES-copolyesters containing butylene succinate, e-hydroxycaproate or L-lactate units with a random distribution.

New biodegradable polymeric materials have been developed in order to minimize the environmental impact caused by the traditional packaging found in the market. Polyhydroxyalkanoates (PHAs) are biopolymers with important features such as biodegradability and biocompatibility; however, the costs associated with PHAs production and the limited mechanical properties reduce their application. Whey is a residual product from dairy industry and gelatin is a biopolymer with good processing characteristics. In this context, a filmogenic solution based on these two biopolymers was incorporated into pure PHA films to improve their optical, mechanical, and structural properties. The filmogenic solution was prepared from gelatin, cheese whey and PHAs, using glycerol as plasticizer agent. The multilayers films (gelatin concentrations at 3 and 5%, w/v) showed higher values for all properties when compared with the PHA standard film. In this sense, the addition of this solution was responsible for the improvement of the film properties. The 5% gelatin multilayers films added of cheese whey and PHAs showed better results when compared with the multilayers films with gelatin at 3%. The film composed of gelatin 5% and cheese whey showed a water vapor permeability ranging from 0.45 g mm/m2/d/kPa, elongation of 2.18%, and opacity of 14.5%. However, the results of the morphological analysis showed that both films presented a homogeneous surface without cracks. Moreover, the results of the thermal analysis of both films indicate polymeric miscibility. Thus, the choice of the best film will depend on its applicability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44458.

Three series of polyalkanoates (adipates, suberates and sebacates) were synthesized using as monomers three sugar-based bicyclic diols derived from D-glucose (Glux-diol and isosorbide) and D-mannose (Manx-diol). Polycondensations were conducted in the melt applying similar reaction conditions for all cases. The aim was to compare the three bicyclic diols regarding their suitability to render aliphatic polyesters with enhanced thermal and mechanical properties. The ensuing polyesters had molecular weights (Mw) in the 25,000–50,000 g mol-1 range with highest values being attained for Glux-diol. All the polyesters started to decompose above 300 °C and most of them did not display perceivable crystallinity. On the contrary, they had glass transition temperatures much higher than usually found in homologous polyesters made of alkanediols, and showed a stress– strain behavior consistent with their Tg values. Glux-diol was particularly effective in increasing the Tg and to render therefore polyesters with high elastic modulus and considerable mechanical strength.

The synthesis, characterization and comparative evaluation of properties of two series of cationic PBS copolyesters bearing respectively ammonium and tributylphosphonium side groups, are reported. The copolyesters with contents in ionic units up to 50 mole-% as well as the fully ionic homopolyesters were prepared by polycondensation in the melt catalyzed by CALB or TBT. Their Mn ranged between 20,000 and 5000 g mol-1 depending of composition and the type of ionic group that is involved. All the copolyesters were non-water soluble and showed good thermal stability. They were semicrystalline with melting temperatures and enthalpies decreasing with the ionic contents. The interactions interplayed by the ionic groups restricted largely the molecular mobility and caused a significant increase in the melt viscosity and glass transition temperature of PBS and a decrease in crystallization rate. Both ammonium and phosphonium containing PBS copolyesters were able to be coupled with sulfonated PBS to generate ionic polymer blends with modified crystallizability. The presence of both ammoniums and phosphoniums provided PBS with remarkable antimicrobial activity against gram-positive and gram-negative bacteria.

Bacterial polyesters such as polyhydroxyalkanoates (PHAs) are of great interest for a large number of applications both because of their properties and because they come from renewable resources, despite having a higher cost than commodity polymers. Their foaming—although it presents some difficulties—could be an option to increase their competitiveness. In this work, two strategies have been studied to enhance the poly(3-hydoxybutyrate-co-4-hydroxybutyrate) (P3HB4HB) foamability by extrusion foaming. The effect of the cooling system (water-quenching or air-cooling), chain extender (CE) addition and chemical blowing agent (CBA) amount were evaluated. Density, cellular morphology, mechanical and thermal properties were studied. Optimal density reduction was achieved with use of CE and 3–4 wt.% of CBA masterbatch. The most effective strategy on density reduction was the addition of CE, while the water quenching had only a slight influence on the samples in which CE was not present. CE addition decreased the viscosity and the degradation rate of the polymer, thus leading to lighter foams with larger cells but with equal or even slightly better resistance to compressive and tensile stress, in general terms.

Entropically driven ring-opening copolymerization of mixtures of a fraction of cyclic oligo(hexamethylene terephthalate)s composed of cycle sizes from 2 to 5 and p-dioxanone was used to prepare random copolyesters covering a range of aromatic (HT) to aliphatic (DO) units ratios from 9 to 1.3. The composition and microstructure of the copolyesters were accurately determined by 1H and 13C NMR, respectively. The copolyesters showed thermal degradation and glass transition temperatures in good agreement with their comonomeric composition and microstructure, and they crystallized for contents in DO less than 30%, adopting the same crystal structure as poly(hexamethylene terephthalate). The copolyesters appeared to be sensitive to hydrolytic degradation, which was observed to take place superficially with the generation of non-water-soluble degraded fragments and with the release of water-soluble dioxanoic acid to the aqueous medium.

Multifunctional electrospun scaffolds were prepared from two polylactide (PLA) grades having slightly different d-lactide content (4.2 wt % and 2.0 wt %). Triclosan (TCS), ketoprofen (KTP), and p-coumaric acid (CUM) were selected as bactericide, anti-inflammatory, and antioxidant agents, respectively. Single, binary, and ternary drug-loaded microfibers having a unimodal diameter distribution could be prepared using a common chloroform:acetone:dimethylsulfoxide mixture and similar operational parameters (i.e., voltage, flow rate, and tip-collector distance). FTIR spectra were sensitive to the low amount of drugs loaded and even showed slight differences in PLA conformation. DSC heating scans clearly demonstrated the ability of electrospinning to induce molecular orientation of PLA and also the nucleation effect of incorporated drugs to induce crystallization. Thus, crystallinity of binary drug-loaded scaffolds was significantly higher than observed for unloaded samples. Release behavior of the three drugs from loaded scaffolds and PLA matrices in PBS:ethanol medium was evaluated. A rapid release was always detected, together with partial drug retention which was higher when the more stereoregular PLA matrix was employed. A strong bactericidal effect was found when scaffolds were loaded with 3 wt/vol % of TCS, but incorporation of a small percentage of KTP (i.e., 1 wt/vol %) had a bacteriostatic effect even in the absence of TCS. The inherent cytotoxicity of TCS could be well neutralized by enhancing cell viability by incorporation of CUM and/or KTP. Multifunctional electrospun scaffolds were prepared from two polylactide (PLA) grades having slightly different d-lactide content (4.2 wt % and 2.0 wt %). Triclosan (TCS), ketoprofen (KTP), and p-coumaric acid (CUM) were selected as bactericide, anti-inflammatory, and antioxidant agents, respectively. Single, binary, and ternary drug-loaded microfibers having a unimodal diameter distribution could be prepared using a common chloroform:acetone:dimethylsulfoxide mixture and similar operational parameters (i.e., voltage, flow rate, and tip-collector distance). FTIR spectra were sensitive to the low amount of drugs loaded and even showed slight differences in PLA conformation. DSC heating scans clearly demonstrated the ability of electrospinning to induce molecular orientation of PLA and also the nucleation effect of incorporated drugs to induce crystallization. Thus, crystallinity of binary drug-loaded scaffolds was significantly higher than observed for unloaded samples. Release behavior of the three drugs from loaded scaffolds and PLA matrices in PBS:ethanol medium was evaluated. A rapid release was always detected, together with partial drug retention which was higher when the more stereoregular PLA matrix was employed. A strong bactericidal effect was found when scaffolds were loaded with 3 wt/vol % of TCS, but incorporation of a small percentage of KTP (i.e., 1 wt/vol %) had a bacteriostatic effect even in the absence of TCS. The inherent cytotoxicity of TCS could be well neutralized by enhancing cell viability by incorporation of CUM and/or KTP.

Biotechnologically accessible 1,4-butanediol and vegetal oil-based diethyl sebacate were copolymerized with bicyclic acetalized d-glucose derivatives (Glux) by polycondensation both in the melt at high temperature and in solution at mild temperature mediated by polymer-supported Candida antarctica lipase B (CALB). Two series of random copolyesters (PBxGluxySeb and PBSebxGluxy) were prepared differing in which d-glucose derivative (Glux diol or Glux diester) was used as comonomer. The three parent homopolyesters PBSeb, PBGlux, and PGluxSeb were prepared as well. Both methods were found to be effective for polymerization although significant higher molecular weights were achieved by melt polycondensation. The thermal properties displayed by the copolyesters were largely dependent on composition and also on the functionality of the replacing Glux unit. The thermal stability of PBSeb was retained or even slightly increased after copolymerization with Glux, whereas crystallinity and melting temperature were largely depressed. On the contrary, the glass-transition temperature noticeably increased with the content in Glux units. PGluxSeb distinguished in displaying both Tg and Tm higher than PBSeb because a different crystal structure is adopted by this homopolyester. The hydrolytic degradability of PBSeb in water was enhanced by copolymerization, in particular, when biodegradation was assisted by lipases.

The use of NMR spectroscopy in solution to investigate the chemical structure of engineering poly(alkylene terephthalate)s such as poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) is reviewed. Chemical defects present in the polyester chain, such as oxydialkylene units, as well as accompanying side products such as cyclic oligomers generated in the polycondensation, are well detected in 1H NMR spectra. The technique is also demonstrated to be effective for identifying, and even for quantifying in certain cases, the end groups of these polyterephthalates, including those that are generated in small amounts as a consequence of thermal degradation. The application of NMR to the study of the chemical microstructure of copolyesters derived from such polyterephthalates is also reviewed for its unique ability to determine comonomeric sequence lengths and degree of randomness (R). Copolyesters synthesized by either melt polycondensation or entropically driven ring opening polymerization, in addition to those prepared by solid-state modification or melt blending, are the object of this review.

Random copolymers derived from 1,4-butanediol and two dicarboxylic units differing in the parity of the number of methylene groups and length of the polymethylene sequence (i.e. succinic and azelaic acids) were studied in terms of thermal properties, crystalline structure and morphology, crystallization kinetics and biodegradability. All samples were semicrystalline and their thermal properties varied in a wide temperature range. Copolymers crystallized according to the monoclinic α-form of polybutylene succinate and the orthorhombic structure postulated for polybutylene azelate depending on the predominant dicarboxylate unit. The behavior of the copolymer with an intermediate composition was complex due to strong dependence of the predominant crystalline form on crystallization and processing conditions. Interestingly, crystallization into the azelate structure was favored when samples were rapidly cooled from the melt, resulting in an unexpected increase in the degree of crystallinity. Spherulitic morphologies were clearly different (i.e. ringed spherulites and axialites) depending on the preferential crystalline structure. Enzymatic degradability of the two homopolyesters was highly different and could be enhanced by incorporation of comonomer units. Preferential enzymatic attack on amorphous regions highlighted the spherulitic morphologies of copolymers having well developed, distinctive ringed structures.

A series of poly(hexamethylene terephthalate- co -hexamethylene 5-sodium sulfoisophthalate) copolyesters containing from 5 to 50 mol % of sulfonated units as well as the two parent homopolymers are prepared by melt polycondensation. The polyesters are obtained with high molecular weights, which decrease with the increased content of sulfonated units in the copolymer. Polyesters with 5 and 10 mol % of sulfonated units are semicrystalline whereas for contents equal or above 20 mol % they are unable to crystal- lize from the melt. Thermogravimetric analysis show that the thermal stability decreases with the content in sulfonated units. Isother- mal crystallizations of semicrystalline copolyesters show that the insertion of the sulfonated units causes a reduction of crystallizabil- ity, most probably due to the occurrence of ionic aggregations. It is observed a synergistic effect on the mechanical properties for copolymers with contents of around 5 mol % where the elongation at break increases drastically. Moreover, the hydrolytic degrada- tion of the copolymer is enhanced with the content in sulfonated units

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 sti ff ness, it is comparable to the widely known isosorbide, but it a ff ords 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 ( T g =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 sti ff ness are priority requirements. In addition, random copolyesters (PB x Manx y S) covering a broad range of compositions have been obtained using mixtures of Manx and 1,4-butanediol in the reaction with dimethyl succinate. All PB x Manx y S were semicrystalline and displayed T g 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.

Mixtures of the dimethyl esters of adipic acid and 2,3:4,5-di-O-methylene-galactaric acid (Galx) were made to react in the melt with either 1,6-hexanediol or 1,12-dodecanediol to produce linear polycyclic copolyesters with aldarate unit contents varying from 10 up to 90 mole %. The copolyesters had weight–average molecular weights in the ∼35,000–45,000 g mol−1 range and a random microstructure, and were thermally stable up to nearly 300 °C. They displayed Tg in the -50 to -7 °C range with values largely increasing with the content in galactarate units. All the copolyesters were semicrystalline with Tm between 20 and 90 °C but only those made from 1,12-dodecanediol were able to crystallize from the melt at a crystallization rate that decreased as the contents in the two comonomers approached each other. Copolyesters containing minor amounts of galactarate units adopted the crystal structure characteristic of aliphatic polyesters but a new crystal polymorph was formed when the cyclic sugar units became the majority. Stress–strain parameters were sensitively affected by composition of the copolyesters with the mechanical behavior changing from flexible/ductile to stiff/brittle with the replacement of adipate units by the galactarate units.

A series of poly(ethylene terephthalate) terpolyesters containing varying amounts of both 1,4-cyclohexylenedimethylene and isosorbide units were prepared by melt phase polycondensation. These terpolymers were obtained with high molecular weights and polydispersities around 2.0–2.5. The nuclear magnetic resonance data revealed that they were all random terpolymers and that small amounts of isosorbide were lost during the polycondensation reaction. Thermal data showed that terpolymers with 90 mol% of ethylene units were crystalline, whereas the two other series containing 80 and 70 mol% were unable to crystallize from the melt. For the three series studied, it was observed that the glass transition temperature increased steadily with the content of isosorbide units, and that they had similar thermal stability.

2,4:3,5-Di-O-methylene-D-mannitol, abbreviated as Manx, is a D-mannitol-derived compound with the secondary hydroxyl groups acetalized with formaldehyde. The bicyclic structure of Manx consists of two fused 1,3-dioxane rings, with two primary hydroxyl groups standing free for reaction. A homopolyester made of Manx and dimethyl terephthalate as well as a set of copolyesters of poly(butylene terephthalate) (PBT) in which 1,4-butanediol was replaced by Manx up to 50% were synthesized and characterized. The polyesters had Mw in the 30 000−52 000 g mol−1 range and a random microstructure and were thermally stable up to nearly 370 °C. They displayed outstanding high Tg with values from 55 to 137 °C which steadily increased with the content in Manx. Copolyesters containing up to 40% of Manx were semicrystalline and adopted the crystal structure of PBT. Their stress− strain parameters were sensitively affected by the presence of carbohydrate-based units with elongation at break decreasing but tensile strength and elastic moduli steadily increasing with the degree of replacement.

The isothermal crystallization behavior of a segmented copolymer constituted by hard blocks of polyglycolide and soft segments derived from the copolymerization of glycolide and trimethylene carbonate was investigated. This polymer has applied relevance because it is one of the most widely used for bioabsorbable surgical sutures. Calorimetric, optical microscopy, and infrared techniques were combined to understand the thermal properties and the different factors that influence the crystallization process. Basically, only the hard blocks crystallized, although certain processing conditions allowed performing an additional crystallization associated with small lamellar domains of the soft segment. Crystallization from both the melt and the glass state rendered positive spherulites with a fibrillar texture. The observed unusual sign of birefringence was a consequence of the close packing structure of polyglycolide, which was also corroborated by electron diffraction patterns. Crystallization was characterized by an athermal nucleation, which allowed accurate estimation of the secondary nucleation parameter by using the calorimetric data only. Significant differences in the Avrami exponent (from 2.32 to 1.45) were found between the cold and hot isothermal crystallizations. The stronger geometric constraints observed in the crystallization from the glass state were also corroborated by FTIR analyses. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The synthesis of a series of poly(ester amide)s constituted by glycolic acid, adipic acid, and different ratios of 1,3-pentanediamine and 1,5-pentanediamine units was studied and the derived copolymers were characterized. Thermal polycondensation between the potassium adipate salt and the appropriate ratio of N,N′-bis(chloroacetyl)-1,3-pentanediamine and N,N′-bis(chloroacetyl)-1,5-pentanediamine was proved to be effective, proceeded with high yield, and rendered samples with moderate molecular weight for carefully controlled competitive thermal degradation reactions. Physical properties were highly dependent on the final composition. In particular, crystallinity and thermal stability decreased with 1,3-pentanediamine unit content, that is, with the incorporation of lateral ethyl groups into the main chain. The presence of these units also changed solubility in solvents like methanol and degradability in a protease K enzymatic medium. Specifically, incorporation of 1,3-pentanediamine units led to a gradual increase in degradability. All poly(ester amide)s were able to establish intermolecular hydrogen bonding interactions, which in semicrystalline samples pointed to typical sheet structures of polyamides according to X-ray diffraction and infrared spectroscopic data. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40102.

The backbone of poly(butylene terephthalate) (PBT) was modified with 2,4:3,5-di- O -methylene- D -glucitol (Glux) using solid-state modification (SSM). The obtained copolyest- ers proved to have a non-random overall chemical microstruc- ture. The thermal properties of these semicrystalline, block- like, Glux-based materials were extraordinary, showing higher melting points, and glass transition temperatures compared with other sugar-based copolyesters prepared by SSM. These remarkable thermal properties were a direct result of the inher- ently rigid structure of Glux and the relatively slow randomiza- tion of the block-like chemical microstructure of the Glux- based copolyesters in the melt. SSM proved to be a versatile tool for preparing partially biobased copolyesters with superior thermal properties

Electrospun scaffolds constituted by different mixtures of two biodegradable polyesters are prepared. Specifically, materials with well differentiated properties can be derived from the blending of hydrophilic polyglycolide (PGA) and hydrophobic poly(e-caprolactone) (PCL), which are also two of the most applied polymers for biomedical uses. Electrospinning conditions are selected in order to get homogeneous and continuous fibers with diameters in the nano/micrometric range. These conditions are also applied to load the different scaffolds with curcumin (CUR) and polyhexamethylene biguanide (PHMB) as hydrophobic and hydrophilic bactericide compounds, respectively. Physicochemical characterization of both unloaded and loaded scaffolds is performed and involved Fourier transform infrared and 1H NMR spectroscopies, morphological observations by scanning electron microscopy, study of thermal properties through calorimetry and thermogravimetric analysis, and evaluation of surface characteristics through contact angle measurements. Release behavior of the loaded scaffolds is evaluated in two different media. Results point out a well differentiated behavior where the delivery of CUR and even PHMB are highly dependent on the PGA/PCL ratio, the capability of the medium to swell the polymer matrix, and the diffusion of the selected solvent into the electrospun fibers. All samples show a bactericide effect in both hydrophilic cell culture and hydrophobic agar media.

The two cyclic acetals, 2,3-di-O-methylene-l-threitol and dimethyl 2,3-di-O-methylene-l-threarate, were used for the synthesis of two series of PBS copolyesters differing in which unit, butylene or succinate, was replaced, in addition of the corresponding parent homopolyesters. Polycondensation reactions were carried out in the melt affording polymers with satisfactory molecular weights. Copolyesters were prepared with contents in tartaric acid-based units over the whole range of compositions and they all had a random chemical microstructure. The physical properties of the novel copolyesters varied widely depending not only on their composition but also on the type of unit that was replaced. They showed higher glass transition (Tg), lower melting temperatures (Tm), and lower crystallinity compared to the parent PBS homopolyester. Regarding mechanical properties, the presence of the stiff cyclic acetal units in the PBS chain caused an increase in the elongation at break and also a reduction in both elastic modulus and tensile strength of the polyester. Upon copolymerization the PBS notably increased its hydrolytic degradability and more slightly its susceptibility to be degraded by lipases.

An overview on the synthesis, structure and properties of polyamides and aromatic copolyesters produced by using monomers derived from carbohydrates is provided. Two examples are selected for illustration: (a) aliphatic polyamides prepared from aldaric acids and (b) aromatic copolyesters containing alditols units. Polycondensation in solution of n-alkanediamines ( n taking even values from 6 to 12) with activated pentaric (l- arabino and xylo) and hexaric ( galacto and d- manno) acids bearing the secondary hydroxyl groups protected as methyl ether, afforded linear polyaldaramides PA- nSu with Mw oscillating between 25 000 and 150 000 g mol−1. They are stable above 300°C and are semicrystalline even so only PA- nMn are stereoregular. Melting temperatures of PA- nSu range between 140 and 230°C and most of them are able to crystallize from the melt at a rate that increases with the length of the polymethylene segment. Both melting and glass transition temperatures decrease with the content in sugar units. Spherulitic films, oriented fibers and lamellar single crystals could be obtained from PA -nSu. All these polyamides seem to adopt a common crystal structure made of hydrogen-bonded sheets with the sugar residue skewed to attain an efficient side-by-side packing of the polymer chains. Aromatic homopolyesters and copolyesters derived from terephthalic acid and mixtures of butylene glycol and O-methylated alditols were prepared by polycondensation in the melt with Mw in the 20 000–50 000 g mol−1 range and a random microstructure. The thermal properties of PBT containing alditols units are very depending on the sugar constitution and copolyester composition. In general they are thermally stable above 300°C and display crystallinity for contents in alditols up to 30%. Melting temperatures decrease with the content in alditols whereas an opposite trend is observed for glass transition temperatures. The crystalline structure of PBT is preserved in the crystalline copolyesters whereas a different crystal lattice is adopted by homopolyesters entirely made of alditol units. In general, polyamides and polyesters containing sugar derived units are widely soluble in organic solvents, markedly hydrophilic and more susceptible to hydrolysis than their parent polymers.

The preparation of cyclic ethylene and butylene 2,5-furandicarboxylate oligoesters and their conversion to furan-based polyesters poly(ethylene furanoate) (PEF) and poly(butylene furanoate) (PBF) by ring-opening polymerization (ROP) are described. The cyclic oligoesters were obtained in high yields by both high dilution condensation and thermal cyclodepolymerization methods, and they consisted of mixtures of small size species. Cyclic dimer, trimer and tetramer oligoesters were isolated by semipreparative chromatography and found to be crystalline compounds melting within the 140–200 °C range. ROP catalyzed by Sn(Oct) 2 of both mixtures and individual species afforded PEF and PBF with weight-average molecular weights between 50,000 and 60,000 g mol −1 . Polymerization rate was found to be higher for butylene than for ethylene cyclic oligofuranoates, and also to increase slightly as cycle size decreased. The thermal properties of PEF and PBF prepared by ROP were in full agreement with those reported for these polyesters obtained by melt polycondensation.

Bio-based triblock copolyesters were synthesized by ring-opening polymerization of l -lactide in solution using a hydroxyl-ended polytartrate as di-functional macroinitiator. This telechelic polyester with a Mn about 3000 g·mol−1 was obtained by non-stoichiometric melt polycondensation of dimethyl 2,3-di-O-isopropylidene- l -tartrate and 1,4-butanediol. Two symmetrical triblock copolyesters with Mn in the 5000–7000 g·mol−1 range and differing in the length of the polylactide blocks were prepared. The protecting isopropylidene group was removed in trifluoracetic acid to generate amphiphilic triblock copolyesters bearing free hydroxyl groups in the central block. All copolyesters started to decompose approximately at 260–280 °C, were semicrystalline, and readily degraded by hydrolysis of the main chain under both acid and basic conditions. The acetalized copolyesters had a single Tg, whereas free-hydroxyl bearing copolyesters showed two Tg indicative of blocks phase separation. All copolyesters were able to form nanoparticles with average diameters within the ~200–450 nm range. The influence of the block lengths and protection/deprotection of the hydroxyl groups on size and ζ-potential of the nanoparticles was evaluated.