A. S. Angeloni

Poly(ethylene glycol) imidazolyl formates as oligomeric drug-binding matrices

Abstract Poly(ethylene glycol)s of molecular weight 200 and 1000 have been functionalized by reaction with N,N-carbonyldiimidazole. The resulting imidazolyl formates could be isolated in a pure state and proved to be able to react with model amines and hydroxylated compounds giving the corresponding urethanes or carbonates. These results indicate that the new activated matrices can be used for the preparation of oligomeric derivatives of aminated or hydroxylated drugs.

Phase and orientational behaviors in liquid crystalline main‐chain/side‐group block copolymers

The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field.

Hybrid Liquid-Crystalline Block Copolymers with Polystyrene and Polyester Blocks

SummaryThe synthesis and some thermal and dynamic-mechanical properties of a novel class of hybrid block copolymers comprised of polystyrene and liquid-crystalline polyester blocks are reported. The two blocks appear to be incompatible in the solid and melt phases and undergo distinct thermal transitions. The mesophase transition temperatures of the block copolymers are constant within all the composition range. The mesophase transition enthalpies are directly proportional to the weight fraction of the liquid-crystalline polyester block.

Isothermal crystallisation kinetics of liquid crystal semiflexible polyesters

Abstract The isothermal crystallisation from the nematic phase of five thermotropic liquid crystalline TR m polyesters formed from two mesogenic p -oxybenzoyl diads alternately flanked by a trioxyethylene segment and a polymethylene spacer of variable length ( m = 6–10) was investigated. The melting behaviours, thermodynamic melting temperatures and crystallisation kinetic parameters are discussed in terms of the polymer structure. The activation energy for the formation of critical nuclei proved to be dependent on the inherent flexibility and parity of the spacer.

Thermotropic liquid crystalline poly(β-thioester)s containing azoxybenzene mesogenic units

Abstract A new homologous series of thermotropic liquid crystalline poly(β-thioester)s was prepared by a Michael-type polyaddition of various α,ω- polymethylenedithiols to a diacrylate containing the mesogenic azoxybenzene unit. The mesomorphic properties were studied as a function of the dithiol spacer length. Analyses by DSC and optical microscopy demonstrated the occurrence of enantiotropic behaviour in the polymer containing the ethanedithiol residue, and of monotropic behaviour in the polymers containing the dithiol spacers with 3/6 methylene segments. The systems based on longer dithiol segments did not show mesomorphism. The poly(β-thioester)s were characterized by greater thermal stability than the corresponding poly(β-aminoester)s previously investigated. In the case of the poly(β-thioester) incorporating the pentanedithiol spacer, nematic schlieren textures with quite unusual high strength singularities S = 3 2 and S = 2 were detected.

Monotropic liquid crystalline poly(β-thioester)s containing bis (p-oxybenzoate) mesogenic units

SummaryA new series of thermotropic liquid crystalline poly(β-thioester)s was prepared by a Michael-type polyaddition of α,ω-polymethylenedithiols of different length to a mesogenic diacrylate containing two bis(p-oxybenzoate) units symmetrically connected through a dodecamethylene segment. The thermotropic behaviour was studied by combined DSC and thermal-optical analyses. All the poly(β-thioester)s investigated exhibited quite unusual monotropic mesomorphism.

Chiral liquid crystal polymers. VIII Thermotropic poly(ester-β-sulphide)s based on variously spaced twin p-oxybenzoate diads

Abstract The synthesis and characterization both in solution (chiroptical properties) and in bulk (thermotropic properties) of a new series of structurally defined chiral liquid-crystalline poly(ester-β-sulphide)s are described. The functional polyesters are constituted by repeating units consisting of two p-oxybenzoate diads interconnected by a linear segment of m methylene groups (m = 6-10, 12), and strictly sequenced by the chiral (R)-3-methyl-1,6-hexanedithiyl spacer. The thermotropic behaviour deviates from the regular profiles generally established in homologous series of mesomorphic polymers and results in peculiar alternations of the liquid-crystalline properties, enantiotropism being exhibited by only a few, mainly odd-numbered, homologues of the series.

Synthesis and liquid-crystalline properties of thermotropic poly(ester-urethane)s

Abstract Seven new mesogenic diol monomers CmCn, consisting of two bis(p-oxybenzoyl) units interconnected by a polymethylene segment containing n methylene groups and flanked by two linear ω-hydroxyalkyl segments containing m methylene groups were reacted with 1,6-hexamethylenediisocyanate (HDI) to give a new series of liquid-crystalline poly(ester-urethane)s HDI-CmCn. All of the precursors CmCn exhibited a nematic phase, and in two of them a smectic mesophase also occurred. Poly(ester-urethane)s HDI-CmCn were semicrystalline and formed a monotropic mesophase. The mesomorphic properties of the polymers were studied as a function of their chemical structure by changing alternatively m or n. The effect of the molecular weight of the polymers on the stability of the mesophase was also investigated for various samples of poly(ester-urethane) HDI-C6C6 (Mn = 3000-22,000). It was found that a competition existed between the tendencies of the polymer to crystallinity and liquidcrystallinity, and the molecular weight dependence of the crystallization temperature determined the onset of a monotropic mesophase.

Liquid-crystalline polyesters containing alternating alkylene and oxyalkylene spacers

Abstract Three new series of thermotropic polyesters were prepared in which the structural units consisted of two p-oxybenzoyl dyads alternately flanked by a polymethylene segment and an oxyethylene oligomer. In each series the length of the oxyethylene residue was fixed (n = 2, 3 or 4) and the length of the alkylene segment was varied (m = 6-10 and 12). Details of the synthesis and characterization of the polymers are reported. The effect of the parity and length of the oxyethylene and polymethylene segments on the incidence of mesophases and on their thermodynamic parameters is stressed. The substitution of methylene groups by oxygen atoms in the polymethylene spacer of a fourth series of polymer analogues completely inhibited the nematogenicity of the polymers incorporating even powerful mesogens such as the p-oxybenzoyl dyads.

Azobenzene containing polymers: what is yet viable with aged liquid crystals

A Commentary on the paper ”Photochromic liquid crystalline polymers. Main chain and side chain polymers containing azobenzene mesogens„, by A. S. Angeloni, D. Caretti, C. Carlini, E. Chiellini, G. Galli, A. Altomare, R. Solaro and M. Laus. First published in Liquid Crystals, 4, 513‐527 (1989).