A. Martínez de Ilarduya

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.

Optically active polyamides containing 1,3-dioxolane cycles in the backbone

Abstract The structure in the solid state of two optically active polyamides obtained from 2,3- O -methylene- l -tartaric acid and linear α,ω-alkanediamines with 9 and 12 carbon atoms, abbreviated P9MLT and P12MLT respectively, was investigated. Two ordered phases, one of smectic liquid crystal-type and another showing crystalline order, were characterized for P12MLT. Crystallization of the former into the second was induced by annealing. Infrared spectroscopy showed that hydrogen bonds are intermolecularly set in both phases and that they are weaker in the crystal phase. Quantum mechanical calculations found the O–C–C O sequence of the tartaric unit to be in a gauche conformation. CP-MAS 13 C NMR revealed that the dioxolane ring is a mixture of the C 2 - exo and C 2 - endo puckered forms in equal amounts and that the polymethylene segment crystallizes in the all- trans conformation. X-ray diffraction of fibers and electron microscopy of solution grown single crystals afforded data consistent with a crystal lattice with orthorhombic geometry and parameters a=7.8 A , b=5.8 A , c=20.0 A . Experimental data obtained from P9MLT indicated a similar behavior for this system.

Hydrolyzable Aromatic Copolyesters of p-Dioxanone

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 (1)H and (13)C 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.

Stereoregular polyamides entirely based on tartaric acid

Two new stereoregular polyamides, namely PTA-LL and PTA-LD, derived from (2S,3S)-(−)-2,3-dimethoxy-1,4-butanediamine and (2R,3R)-(+)- or (2S,3S)-(−)-2,3-dimethoxybutanedioic acid are described. The two diastereoisomeric polymers contain two pairs of stereocenters in the main chain of the repeating unit, one in the diamine and the other in the diacid counterpart. L and D refer to the configuration of the tartaric acid unit from which they proceed. These polyamides were prepared by polycondensation in solution and were fully characterized by elemental analysis, DSC, and IR/NMR spectroscopies. Number average molecular weights around 30,000 were estimated by GPC and viscosimetry. Both compounds are soluble in water and display large optical activity. CD and 1H-NMR measurements in chloroform solution suggested the presence of definite secondary structures in this solvent. Solid samples were found to crystallize upon annealing and the crystal structure of both polyamides was investigated by X-ray diffraction. PTA-LL crystallized in an orthorhombic lattice in the space group P22121 whereas PTA-LD seemed to adopt a P1 triclinic structure. In both cases the polymer chain appears to be in a folded conformation more contracted than in the common γ-form of conventional nylons.

Synthesis and structure of random and block copoly(β,l-aspartate)s containing short and long alkyl side chains

Copoly(α-alkyl-β,l-aspartate)s containing n-octadecyl and n-butyl side groups at different ratios were prepared by anionic ring-opening polymerization of the corresponding optically pure (S)-4-alkoxycarbonyl-2-azetidinones. Random copolymers were obtained by polymerization of comonomer mixtures. Diblock copolymers were achieved by sequential copolymerization using the living poly(α-n-octadecyl-β,l-aspartate) block to initiate the polymerization of (s)-4-n-butoxycarbonyl-2-azetidinone as a second block. Composition and sequence distribution were characterized by NMR with the help of a model copoly(β,l-aspartate) made of α-n-dodecyl and α-benzyl β,l-aspartate units. All the copolymers were found to adopt the layered structure made of 13/4 helices described previously for comb-like poly(α-n-alkyl-β,l-aspartate) homopolymers. Copolymers containing at least 50% of n-octadecyl side groups have these groups crystallized in an interlayer microphase and aligned normal to the main helical chain. Melting of the paraffinic crystallites happened within the 40–60°C temperature range with formation of a liquid-crystal phase in which side chains are molten but retain the alignment of the low temperature phase. Different from what is known to happen to poly(α-n-octadecyl-β,l-aspartate), no indications on the occurrence of a second structural transition were observed at higher temperatures.

Poly(α-isobutyl-β-D,L-aspartate)s: Polymerization effects on configuration and crystal structure of the stereocopolymers

Different polymerization methods were used for the preparation of poly(α-isobutyl-β-D,L-aspartate)s containing variable ratios of D- to L-aspartic units and the microstructure of the resulting stereocopolymers was examined by NMR spectroscopy. Anionic ring-opening polymerization in solution of enantiomeric mixtures of α-isobutyl-β-D- and L-aspartalactams was found to proceed stereoselectively rendering block copolymers composed of right- and left-handed helical sequences. Configurationally statistical copolymers were obtained instead when the enantiomeric lactam mixtures were polymerized in the bulk. Random stereocopolymers could be prepared also by polycondensation in solution of mixtures of pentachlorophenyl α-isobutyl-β-D and -L-aspartates. The conformation in solution and the crystal structure of the resulting copolymers were investigated in connection with their stereochemical configuration and these features compared with those displayed by optically pure poly(α-isobutyl-β-L-aspartate).

Miscibility windows of poly(vinyl methyl ether) with modified phenoxy resin

Blends of poly(vinyl methyl ether) with partially methylated and benzoylated poly(hydroxy ether of bisphenol A) (phenoxy resin, PH) have been studied. The optical appearance of the mixtures and their glass transition temperatures as measured by differential scanning calorimeter has been used as macroscopic criteria for miscibility. All miscible blends showed phase separation (LCST) when increasing temperature as determined by optical microscopy. The PH degree of modification reduced the intrinsic miscibility of the blends as well as the values of the cloud point temperatures. This behaviour has been qualitatively discussed in terms of the reduction of the intermolecular strong interaction sites and its influence on the association equilibria, which stabilise the blends.

Thermal behavior of poly(α-n-alkyl β-L-aspartate)s

A series of poly(α-n-alkyl β-L-aspartate)s (n being the number of carbon atoms in the linear alkyl side chain, withn=1, 2, 4, 6, 8, 12, 18 and 22), was studied by differential scanning calorimetry and thermogravimetric analysis. The effect of the length of the alkyl group on thermal properties such as stability, melting and crystallization of side chains, was investigated. For the polymers with n≥12, two endothermic peaks at T1 and T2 were detected separating three distinct phases A, B and C. The peak at T1 corresponds to the melting of the crystallized paraffinic side chains (transition A-B), and the peak: at T2 may be attributed to a transition (B-C), implying a liquid crystal phase.