Juan A. Galbis

Synthetic polymers from readily available monosaccharides.

The low degradability of petroleum-based polymers and the massive use of these materials constitute a serious problem because of the environmental pollution that they can cause. Thus, sustained efforts have been extensively devoted to produce new polymers based on natural renewing resources and with higher degradability. Of the different natural sources, carbohydrates stand out as highly convenient raw materials because they are inexpensive, readily available, and provide great stereochemical diversity. New polymers, analogous to the more accredited technical polymers, but based on chiral monomers, have been synthesized from natural and available sugars. This chapter describes the potential of sugar-based monomers as precursors to a wide variety of macromolecular materials.

Synthesis of L-arabinitol and xylitol monomers for the preparation of polyamides. Preparation of an L-arabinitol-based polyamide.

Dihydrochlorides of 1,5-diamino-1,5-dideoxy-2,3,4-tri-O-methyl-L-arabinitol (and xylitol) and pentachlorophenyl esters of 2,3,4-tri-O-methyl-L-arabinaric (and xylaric) acids have been prepared as suitable bifunctional monomers for linear polycondensations. A new aregic AABB-type L-arabinitol-based polyamide is also described from the corresponding monomers. It was crystalline with T(m) 250 degrees C, optically active, and soluble in the usual organic solvents, including chloroform, and in water. Its M(w) obtained by GPC was 27,500 with a polydispersity of 1.4.

Synthesis and characterization of some new homo- and co-poly(vinylsaccharides). Some preliminary studies as drug delivery

Abstract Homopolymers P1 and P3 were prepared by free radical polymerization reactions of 1,3,4,6-tetra- O -acetyl-2-acrylamido-2-deoxy-α- d -glucopyranose monomer ( M1 ) and 1,2:3,4-di- O -isopropylidene-6- O -acryloyl-α- d -galactopyranose monomer ( M2 ), respectively. Both monomers were also copolymerized at two different ( M1 / M2 ) feed ratios (1:1, and 3:1) to yield P4 and P5 , respectively. The free radical polymerization reactions were carried out in a mixed solvent system under either nitrogen atmosphere or vacuum at 60°C using AIBN as free radical initiator. P1 was deacetylated to P2 , while P4 was first deacetylated to P6 and then deacetonated to hydrophilic P7 . The new poly(vinylsaccharides) were characterized by elemental analysis, DSC, GPC, and FT IR, 1 H- and 13 C-NMR spectroscopies. Inherent viscosities and specific optical rotations were also recorded. Some preliminary rheological studies have demonstrated that the hydrophobic, non-swelling acrylic polymer P4 seems to be a good substrate for employment as matrix-forming material for controlled release tablets as drug delivery systems.

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.

New derivatives of D-mannaric and galactaric acids. Synthesis of a new stereoregular Nylon 66 analog from carbohydrate-based monomers having the D-manno configuration

2,3,4,5-Tetra-O-methyl-D-mannaric and galactaric acids and their bis(pentachlorophenyl) esters have been prepared as crystalline compounds, in good yields, from D-mannitol and galactitol, respectively. A new stereoregular polyamide, analogous to Nylon 66, has been prepared by polycondensation of bis(pentachlorophenyl) 2,3,4,5-tetra-O-methyl-D-mannarate with 1,6-diamino-1,6-dideoxy-2,3,4,5-tetra-O-methyl-D-mannitol dihydrochloride. The polymer has a M(w) of 31,100 with a polydispersity of 1.5 (GPC). It was highly hygroscopic and soluble in ethanol, acetone, dimethyl sulfoxide, N,N-dimethylformamide and chloroform, but only slightly soluble in water.

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.

Synthesis of 2,3,4,5-tetra-O-methyl-d-glucono-1,6-lactone as a monomer for the preparation of copolyesters

2,3,4,5-tetra-O-methyl-D-glucono-1,6-lactone has been prepared as a crystalline compound in acceptable yield by two different routes. An initial assay of copolymerization with L-lactide by ring-opening polymerization was carried out. The incorporation of the carbohydrate monomer into the polymer chain was about 2%.

Synthesis and properties of stereoregular poly(ester amides) derived from carbohydrates

Two poly(ester amides) containing three methoxy groups stereoregularly attached to the main chain have been prepared by using naturally occurring L-arabinose and D-xylose as the starting materials. The polymers were prepared by the active ester polycondensation method and characterized by elemental analysis, IR, and 1H- and 13C-NMR spectroscopies. Both viscosimetry and GPC were used to estimate the molecular weights. The polymers are hydrophilic, one of them being water soluble, and exhibited moderate optical activity. Thermal and X-ray diffraction studies revealed that they are slightly crystalline and stable up to 250°C under nitrogen.

Biodegradable Nanoparticles of Partially Methylated Fungal Poly(β-L-malic acid) as a Novel Protein Delivery Carrier

The preparation of nanoparticles from 75% methylated poly(beta-L-malic acid) is described. Their degradation in aqueous environments was examined and the influence of pH and lipase on the rate of hydrolysis was evaluated. Six proteins were used to estimate the loading efficiency of the nanoparticles. The amount of protein retained in the nanoparticles was found to depend on the acid/basic character of the protein. Protein release from the loaded nanoparticles upon incubation in water under physiological conditions encompassed polymer hydrolysis and happened steadily within 3-10 d. The activity loss of entrapped alpha-chymotrypsin caused by loading and releasing depended on the method used for loading.