Nicolae Hurduc

Synthesis and characterization of some aliphatic–aromatic poly(Schiff base)s

Abstract Polymers with azomethine structure containing 1,5-naphthyl or 1,4-phenyl moieties were synthesised through polycondensation of some dialdehydes with diamines. Both monomers and polymers were characterised by IR and 1 H-NMR techniques. Thermogravimetric analyses were made for all the synthesised polymers in order to study their thermal behaviour.

Microwave effects in the synthesis of polyethers by phase transfer catalysis

Phase transfer catalysis processes with or without microwave fields are studied. A polycondensation reaction was used as a model, starting from 3,3-bis(chloromethyl)oxetane and various bisphenols. The results obtained show the advantages of microwave fields, concerning the molecular weights for crystalline polymers and the reaction time for all types of structures.

Phase transfer catalysis in polycondensation processes—XI. Liquid crystalline copolyethers based on 4,4′-dihydroxydiphenyl, bisphenol-a, 4,4′-dihydroxyazobenzene and 3,3-bis(chloromethyl)oxetane

Abstract Copolycondensations of 3,3-bis(chloromethyl)oxetane with various diphenols under phase transfer conditions have been performed. The copolyethers show mesomorphism; investigations of their LC properties by optical polarization microscopy and DSC analyses were carried out.

Liquid crystalline polymers: 14. Synthesis and thermal behaviour of some polyethers containing azo-mesogens

Abstract The paper presents a study on the relationship between the structure of macromolecular chain and its capacity to generate a mesophase, when mesogens with an azobenzene structure are implied. The polymers have been synthesized by phase transfer catalysis starting from 1,9-dichlorononane and different bisphenols: diphenyl-4,4 ′ -bis[(azo-4-)phenol], 4,4 ′ -dihydroxyazobenzene, 4,4 ′ -dihydroxydiphenyl, bisphenol A and 4,4 ′ -dihydroxybenzophenone. The polymers have been characterized by 1 H-NMR spectroscopy, DSC calorimetry, optical microscopy in polarized light and thermogravimetrical analysis. Theoretical conformational studies, using molecular simulations have also been performed. Due to their particular geometry, bis-(azobenzene) units are better mesogenic groups as compared with the azobenzene ones. The highly aromatic structure makes impossible the samples isotropisation, as the degradation processes starting advance. For these polymers, under UV irradiation, due to the presence of two azo groups in each mesogen unit, strong conformational modifications are expected. The replacement of the bis-(azobenzene) moieties with azobenzene ones reduces the transition temperatures, making possible the samples isotropisation.

Molecular simulation of thermophysical properties of aromatic polymers containing oxetane ring in the main chain

Molecular simulation techniques have been applied to newly synthesized aromatic polymers, containing oxetane rings in the main chain, to characterize the shape of rod-like macromolecules. Single chains and periodic unit cells of a series of aromatic polymers with degree of polymerization 15 were used in the simulations, in accordance with the experimentally obtained one. The total potential energy was minimized and then NVE and NPT molecular dynamics simulations were performed for 1,000 ps at 11 temperatures between 10 and 1,000 K. The coefficient of asymmetry was calculated from the computer-generated structures. The predictive capability of the NPT molecular dynamics simulation and Polymer Properties modules of Cerius2 were used to estimate the orientational properties (order parameter), glass transition temperature, cohesive energy, and decomposition temperature of the polymers simulated. In general, there is a good-to-excellent agreement between simulated results and available experimental data of the above investigated properties.

Liquid crystalline polymers: molecular simulation of some polyethers containing oxetanic rings in the main chain

Abstract This paper presents a conformational analysis of some polyethers containing the oxetanic ring in the main chain. The studied polymers were synthesized by phase transfer catalysis, using 3,3-bis(chloromethyl)-oxetane and various bisphenols. The analysis was performed using the Cerius 2 program (version 2.0) molecular simulation software for material science, designed by Molecular Simulations Incorporated (MSI). This study tries to elucidate some aspects concerning the difficulties appearing in the liquid crystalline propertys characterization. These difficulties are induced by the cross-linking processes that take place in certain situations due to the opening of the oxetanic rings at high temperature.

Phase transfer catalysis of polycondensation processes—III. Liquid-crystalline properties of polyethers with oxetane pendant groups

Abstract The polycondensation of 3,3-bis(chloromethyl)oxacyclobutane with bisphenol-A under phase transfer conditions is reported a possible mesomorphism of these polymers is discussed. Investigations by optical polarization microscopy and DSC are described.

Liquid crystalline polymers—VI. A study of the thermal behavior of some ternary copolyethers, containing 4,4′-dihydroxyazobenzene, bisphenol a and 1,1-bis(4-hydroxyphenyl)ethane

Abstract Copolyethers based on 3,3-bis(chloromethyl)oxetane and several bisphenols [4,4′-dihydroxyazobenzene, bisphenol A and 1,1-bis-(4-hydroxyphenyl)ethane] were synthesized. The influence of chain geometry and flexibility on the possible appearance of liquid crystalline behavior was investigated. Polymer properties were studied using 1 H NMR spectroscopy, DSC, optical microscopy in polarized light and theoretical conformational analyses. The optimal mesogen/nonmesogen ratios, correlated with the flexibility of the chain and anisotropic behavior was established.

Molecular simulation of aromatic polyesters containing oxetane rings in the main chain

Abstract Molecular simulation is a powerful research tool for gaining new insights into polymer chemical structures and processes. This paper presents a computational conformational analysis of some aromatic polyesters containing either an oxetane ring or propylene moieties in the main chain. The studied polyesters were synthesised by phase transfer catalysis using 3,3-bis-(chloromethyl)-oxetane, 1,3-dibromopropane and various aromatic diacids. The computational analysis and calculations were performed using the Cerius2 program (version 3.5), molecular simulation software for material science, designed by Molecular Simulations Incorporated. This study elucidates some aspects and properties dependent upon supramolecular arrangement of the macromolecular chains. In order to verify the agreement between simulated and experimental results the coefficient of asymmetry, order parameter and glass transition temperature were calculated for each studied aromatic polymer.

Phase transfer catalysis of polycondensation processes—V. Internal rotation energies in polyethers based on oxetane and bisphenol-A

Abstract Rotation possibilities and rotational barriers in the polyether chain obtained from bisphenol-A with 3,3-bis(chloromethyl) oxetane were considered. From the computed values, it was concluded that in such structures the bisphenol-A unit might become mesogenic.