225 research outputs found
Ring opening polymerization of macrocyclic oligoesters derived from renewable sources
Macrocyclic oligoesters (MCOs) derived from biomass such as those prepared from alkylene alkanedioates and 2,5-furandicarboxylates are suitable compounds for ring opening polymerization (ROP) to produce high molecular weight bio-based polyesters. The synthetic procedures that have been recently developed to obtain these MCOs in good yields, their ROP either alone or together with other cyclic compounds, and their recovery by cyclodepolymerization of the final polyesters are the main topics covered in this review. Both organometallic compounds and enzymes such as Candida antarctica lipase B are the catalytic systems used for all reactions. This synthetic approach based on ROP of MCOs derived from renewable sources opens a green pathway for a circular economy in plastics.Postprint (author's final draft
Sugar-based bicyclic monomers for aliphatic polyesters: a comparative appraisal of acetalized alditols and isosorbide
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 25,000â50,000 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 stressâ 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.Peer ReviewedPostprint (published version
Triblock copolyesters derived from lactic acid and glucose: synthesis, nanoparticle formation and simulation
ABA triblock copolyesters were synthesized by ring-opening polymerization (ROP) of l-lactide in solution initiated by a telechelic d-glucose-based polyester macroinitiator. The macroinitiator with a number-average molecular weight about 2500 g mol-1 was synthesized by non-stoichiometric polycondensation in the melt of 2,4:3,5-di-O-methylene-d-glucitol and dimethyl succinate. Two triblock copolyesters of Mn ranging between ~6000 and ~9000 g mol-1, and differing in the length of the polylactide blocks were prepared. These copolyesters started to decompose when heated at ~220 °C and degraded slowly upon aqueous incubation under physiological conditions. They did not display any perceivable crystallinity and showed a single glass transition temperature (Tg) around 60 °C with the higher value corresponding to the larger content in glucitol units. The copolyesters were able to form nanoparticles with average diameters of ~100â130 nm and satisfactory dispersity. The effect of the block lengths on size, Âż-potential values and physical stability of the nanoparticles was evaluated. A molecular dynamics simulation study allowed modelling the two-phase structure of the nanoparticles and evidenced the preference of the glucose-based block to be peripherally located.Peer ReviewedPostprint (author's final draft
Nanoparticles made of poly(gama-glutamic acid) derivatives for drug delivery systems
One of the treatments for cancer is chemotherapy but most anticancer drugs have a low therapeutic index, which causes toxicity complications in the healthy tissues [1]. To minimize these complications and improve the effect of the existing drugs, drug delivery by nanoparticles have drawn more attention as they are easy to produce and can also be prepared through biocompatible polymers [2]. Here, we report the preparation of polymer nanoparticles derived from esters of poly(Âż-glutamic acid) which could be able to encapsulate hydrophobic drugs that can be used as drug delivery systems (DDS) for the treatment of different tumours. In this work, PGGA has been modified in order to improve its solubility in organic solvents and its processing capacity of this water-soluble polymer. Due to the fact that most of the anticancer drugs are lipophilic, the hydrophobic modification of PGGA will enhance the drug encapsulation.Postprint (published version
Bio-based aliphatic polyesters from aliphatic diacids and bicyclic alditols: A comparative study
In this work we have prepared and compared the thermal and mechanical properties of aliphatic polyesters made from aliphatic diacids with different polymethylene chain lengths (2, 4, 6, 8) and three bicyclic sugar derived diols namely, dianhydro-1,4:3,6-D-glucitol (also known as isosorbide, Is), and two bicyclic diazetalized hexitols, 2,4:3,5-di-O-methylene- D-mannitol (Manx-diol) and -D-glucitol (Glux-diol) derived from D-mannose and D-glucose respectively (Fig. 1)Postprint (published version
Isohexide and sorbitol-derived, enzymatically synthesized renewable polyesters with enhanced Tg
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.Peer ReviewedPostprint (author's final draft
Crystalline structure and thermotropic behavior of alkyltrimethylphosphonium amphiphiles
Quaternary organophosphonium salts bearing long alkyl chains are cationic surfactants of interest owing to their physical and biological properties. In the present work, the crystal structure and thermotropic behavior of the homologous series of alkyltrimethylphosphonium bromides (nATMP·Br), with the alkyl chain containing an even number (n) of carbon atoms from 12 to 22, have been examined within the 0â300 °C range of temperatures. These compounds were shown to be resistant to heat up to ~390 °C. The phases adopted at different temperatures were detected by DSC, and the structural changes involved in the phase transitions have been characterized by simultaneous WAXS and SAXS carried out in real-time, and by polarizing optical microscopy as well. Three or four phases were identified for n = 12 and 14 or n = 16, respectively, in agreement with the heat exchange peaks observed by DSC. The phase existing at room temperature (Ph-I) was found to be fully crystalline and its crystal lattice was determined by single-crystal X-ray diffraction methods. Ph-II consisted of a semicrystalline structure that can be categorized as Smectic-B with the crystallized ionic pairs hexagonally arranged in layers and the molten alkyl chain confined in the interlayer space. Ph-II of 12ATMP·Br and 14ATMP·Br directly isotropicized upon heating at ~220 °C, whereas for n = 16, it converted into a Smectic-A phase (Ph-III) that needed to be heated above ~240 °C to become isotropic (Ph-Is). The correlation existing between the thermal behavior, phase structure and length of the alkyl side chain has been demonstrated.Peer ReviewedPostprint (published version
Fully bio-based aromaticâaliphatic copolyesters: poly(butylene furandicarboxylate-co-succinate)s obtained by ring opening polymerization
Poly(butylene 2,5-furandicarboxylate-co-succinate) copolyesters (coPBFxSy) have been synthesized by
ring opening polymerization (ROP). Cyclic butylene 2,5-furandicarboxylate and butylene succinate
oligomer mixtures, to be used as monomers for ROP, were prepared by high dilution condensation
and enzymatic cyclization reactions, respectively. Two different catalytic systems, tin dioctanoate and
supported Candida antarctica lipase B (CALB), were used for polymerization. Thus two series of copolyesters
covering the whole range of compositions were prepared and their properties comparatively
examined. In both cases, random copolyesters with compositions close to those used in their respective
feeds were obtained. The influence of composition on reaction kinetics with respect to time and
temperature was evaluated for the two series. Chemically catalyzed ROP rendered copolyesters with Mw
in the ~50 000â65 000 g mol-1 range, whereas values between 15 000 and 45 000 g mol-1 were attained
when the ROP reaction was assisted by CALB. The thermal behavior of coPBFxSy obtained by ROP was
similar to that reported for such copolymers prepared by melt polycondensation. They all start to decompose
above 300 °C and display melting enthalpy and temperatures that decrease with copolymerization,
attaining minimum values when the comonomer contents are approximate to balance. On the
contrary, the glass-transition temperature increased almost linearly with the content of butylene furandicarboxylate
units, covering the whole range of values between those of the two parent homopolyesters.
Small deviations in thermal properties observed between the two series could be attributed to their differences
in molecular weights. Hydrolytic and enzymatic degradation studies revealed that coPBFxSy
became more degradable with increasing content of succinic units, whereas the homopolyester PBF
remained practically unaffected when incubated under similar conditions.Peer ReviewedPostprint (author's final draft
Hydrophobic modification of poly(gamma-glutamic acid) by grafting 4-phenyl-butyl side groups for the encapsulation and release of doxorubicin
The delivery of drugs is a great challenge, since most of active pharmaceutical ingredients developed today are hydrophobic and poorly water soluble. From this perspective, drug encapsulation on biodegradable and biocompatible polymers can surpass this problem. Poly(gamma-glutamic acid) (PGGA), a bioedible and biocompatible polymer has been chosen for this purpose. Carboxylic side groups of PGGA have been partially esterified with 4-phenyl-butyl bromide, producing a series of aliphaticâaromatic ester derivatives with different hydrophilicâlipophilic balances. Using nanoprecipitation or emulsion/evaporation methods, these copolymers were self-assembled in a water solution, forming nanoparticles with average diameters between 89 and 374 nm and zeta potential values between -13.1 and -49.5 mV. The hydrophobic core containing 4-phenyl-butyl side groups was used for the encapsulation of an anticancer drug, such as Doxorubicin (DOX). The highest encapsulation efficiency was reached for a copolymer derived from PGGA, with a 46 mol % degree of esterification. Drug release studies carried out for 5 days at different pHs (4.2 and 7.4) indicated that DOX was released faster at pH 4.2, revealing the potential of these nanoparticles as chemotherapy agents.Peer ReviewedPostprint (published version
Copolymacrolactones grafted with L-glutamic acid: Synthesis, structure, and nanocarrier properties
The enzymatic ring-opening copolymerization (eROP) of globalide (Gl) and pentadecalactone (PDL) was performed in solution from mixtures of the two macrolactones at ratios covering the whole range of comonomeric compositions. The resulting P(Glx-r-PDLy) random copolyesters were aminofunctionalized by thiol-ene reaction with aminoethanethiol. ROP of Âż-benzyl-l-glutamate N-carboxyanhydride initiated by P(Glx-r-PDLy)-NH2 provided neutral poly(Âż-benzyl-L-glutamate)-grafted copolyesters, which were converted by hydrolysis into negatively charged hybrid copolymers. Both water-soluble and nonsoluble copolymers were produced depending on copolymer charge and their grafting degree, and their capacity for self-assembling in nano-objects were comparatively examined. The emulsion solvent-evaporation technique applied to the chloroform-soluble copolymers grafted with benzyl glutamate rendered well-delineated spherical nanoparticles with an average diameter of 200â300 nm. Conversely, micellar solutions in water were produced from copolyesters bearing grafted chains composed of at least 10 units of glutamic acid in the free form. The copolymer micelles were shown to be able to load doxorubicin (DOX) efficiently through electrostatic interactions and also to release the drug at a rate that was markedly pH dependent.Peer ReviewedPostprint (published version
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