Antxon Martínez de Ilarduya

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.

New comb-like poly(n-alkyl itaconate)s with crystalizable side chains

A series of poly(mono n-alkyl itaconate)s, poly(methyl n-alkyl itaconate)s and poly(di n-alkyl itaconate)s with n ¼ 12; 14, 16, 18 and 22 have been prepared by radical polymerization. NMR studies point out that poly(methyl n-alkyl itaconate)s and poly(di n-alkyl itaconate)s are mainly syndiotactic polymers whereas poly(mono n-alkyl itaconate)s are obtained as almost atactic polymers. The characterization performed by DSC, solid state 13 C CP/MAS NMR and X-ray diffraction, indicates that the side chains of poly(mono n-alkyl itaconate)s and poly(methyl n-alkyl itaconate)s derivatives with more than 12 carbon atoms are able to crystallize in hexagonal lattices. In the case of poly(di n-alkyl itaconate)s, when the side chains contain 12 or more carbon atoms, they are able to crystallize also in hexagonal lattices. q 2003 Elsevier Science Ltd. All rights reserved.

Bio-based PBT copolyesters derived from D-glucose: influence of composition on properties

Two series of bio-based PBT copolyesters were obtained by polycondensation in the melt of 2,4:3,5-di-O-methylene-D-glucitol (Glux-diol) or dimethyl 2,4:3,5-di-O-methylene-D-glucarate (Glux-diester) with 1,4-butanediol and dimethyl terephthalate. The glucose-based bicyclic compounds used as comonomers were synthesized from commercially available 1,5-D-gluconolactone. The prepared PBT copolyesters had weight-average molecular weights in the 30000–50000 range; they had a random microstructure, and they were stable above 300 °C. The copolyesters containing less than 30% of sugar-based units were semicrystalline and were found to adopt the triclinic structure of PBT. These copolyesters with low contents in Glux were able to crystallize from the melt but at lower rates than PBT. The Tg value of PBT steadily increased with the incorporation of Glux units in the polyester chain with an increasing ratio of ∼1.7 °C or ∼1 °C per %Glux point, depending on which unit, the diol or the diacid, was replaced. The copolyesters hydrolyzed at higher rates than PBT, and those containing glucarate units displayed an appreciable susceptibility towards biodegradation.

D-Glucose-derived PET copolyesters with enhanced Tg

2,4:3,5-Di-O-methylene-D-glucitol (Glux-diol) and dimethyl 2,4:3,5-di-O-methylene-D-glucarate (Glux-diester) have been copolymerized with ethylene glycol and dimethyl terephthalate by polycondensation in the bulk to produce PET copolyesters as well as their respective homopolyesters. These sugar-based bicyclic monomers were synthesized from 1,5-D-gluconolactone, a commercially accessible compound derived from D-glucose. The PET copolyesters with either the diol or the diacid counterpart partially replaced by Glux had molecular weights in the 20000–40000 range and a random microstructure, and they were stable well above 300 °C. The PET copolyesters containing more than 10–15% of sugar-based units were amorphous while those displaying crystallinity were observed to crystallize from the melt at much lower rates than PET. The glass transition temperature of PET dramatically increased with the incorporation of Glux, whichever unit, diol or diacid, was replaced, but the enhancing effect was stronger in the former case. A preliminary evaluation of the mechanical behaviour of these copolyesters indicated that the genuine properties of PET were not substantially impoverished by the insertion of Glux. Compared to PET, the copolyesters exhibited a higher hydrolysis rate and an appreciable susceptibility towards biodegradation. The homopolyesters made of these sugar-based monomers could not be obtained with high enough molecular weights so as to be comparatively evaluated with copolyesters.

Nanoparticles Made of Microbial Poly(γ-glutamate)s for Encapsulation and Delivery of Drugs and Proteins

This study focused on the preparation and evaluation of nanoparticles made of alkyl esters of microbial poly(γ-glutamic acid) (PGGA) to be used as drugs and proteins carrier and delivery systems. Racemic PGGA of bacterial origin was fully methylated or partially esterified to render non-water-soluble polymers. A set of co-polymers containing poly(glutamic acid) and ethyl, hexyl, dodecyl and octadecyl glutamate units with alkyl contents of 50 and 75% was prepared. Spherical nanoparticles with a diameter of 200–250 nm and a narrow distribution were generated from the alkylated polymers by the precipitation-dialysis method. These nanoparticles readily degraded hydrolytically upon incubation in simulated physiological medium at a rate dependent on the alkylation degree and the length of the alkyl group. All these nanoparticles were able to encapsulate efficiently erythromycin. Those made of carboxyl containing polyglutamates were also effective to load α-chymotrypsin. The release of such compounds from nanoparticles upon incubation proceeded essentially following the same profile that is followed in the hydrolysis of the corresponding substrate polymers. The loss of enzyme activity of the incubated protein diminished significantly upon encapsulation in these systems.

Bio-based aromatic copolyesters made from 1,6-hexanediol and bicyclic diacetalized D-glucitol

The diacetalized diol 2,4:3,5-di-O-methylene-D-glucitol (Glux), a bicyclic compound derived from D-glucose, was used as a comonomer of 1,6-hexanediol in polycondensation in the melt with dimethyl terephthalate to produce a set of aromatic copolyesters (PHxGluxyT) with Glux contents ranging from 5 to 32%-mole. These sustainable copolyesters had molecular weights within the 12,000 to 45,000 g mol−1 range, and polydispersities between 2.0 and 2.5. They all had a random microstructure and displayed slight optical activity. PHxGluxyT showed a good thermal stability and were semicrystalline with both crystallinity degree and crystallization rate decreasing as the content in Glux increased. Conversely, Tg increased with the incorporation of Glux going from 8 °C in PHT to near 60 °C in the copolyester containing 32%-mole Glux. Compared to PHT, PHxGluxyT copolyesters showed not only an enhanced susceptibility to hydrolysis but also an appreciable biodegradability in the presence of lipases.

Copolyesters made from 1,4-butanediol, sebacic acid, and D-glucose by melt and enzymatic polycondensation

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 (PB(x)Glux(y)Seb and PBSeb(x)Glux(y)) 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 T(g) and T(m) 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.

Synthesis, Degradability, and Drug Releasing Properties of Methyl Esters of Fungal Poly(β,L-malic acid)

Methyl esters of microbial poly(beta,L-malic acid) for conversion degrees of 25, 50, 75, and 100% were prepared by treatment of the polyacid with diazomethane. Esterification proceeded with retention of the molecular weight of the parent polyacid and the copolymers displayed a blocky microstructure consisting of short segments of malic and methyl malate sequences. The thermal stability of the copolyesters was lower than those of the parent homopolymers and all of them were fairly crystalline with melting temperatures within the range of 170-175 degrees C. They were degraded rapidly by water, the hydrolysis rate being highly dependent on the methylation degree. Microspheres with mean-average diameters in the range of 1-20 microm were prepared from the 100% methylated product by the emulsion-evaporation solvent method. Encapsulation of erythromycin was efficiently performed in these microparticles and its releasing upon incubation in simulated physiological medium was evaluated for different drug loads. Drug delivery was observed to occur by a releasing mechanism largely determined by the hydrodegradation of the host polymer and independent of the amount of loaded drug.

Synthesis of heterotelechelic poly(ethylene glycol)s and their characterization by MALDI-TOF-MS

Departamento de Ingenieri´a Qui´mica, Universidad Polite´cnica de Catalun˜a,E. T. S. de Ingenieros Industriales, Diagonal 647, 08028 Barcelona, Spain(Received: October 2, 1998; revised: November 26, 1998)SUMMARY: Two heterotelechelic poly(ethylene glycol)s were synthezised by end group modification of a-hydro-x-hydroxy-poly(oxyethylene) (PEG). The first reaction route starts from heterobifunctionala-hydro-x-octadecanoyloxy-poly(oxyethylene) (400) and comprises the synthesis ofa-hydro-x-carboxymethoxy-poly(oxyethylene). The second pathway starts from homotelechelic PEG(400) and leads to a-(2-propenyl)-x-carboxymethylthio-poly(oxyethylene). Purification of the desired products was accomplished by means ofion exchange chromatography on DEAE Sephadex. PEG derivatives were characterized by means of NMR,IR, HPLC and GPC. MALDI-TOF-MS recorded in the reflectron mode served as a fine method that providesinformation on chemical composition as well as molecular weight.