Synthesis and characterization of novel random copolyesters from trans-4-hydroxy-l-proline and functional cyclic esters

The melt polycondensation reaction of trans-4-hydroxy-N-benzyloxycarbonyl-l-proline (N-CBz-Hpr) and functional cyclic esters containing protected functional groups (carboxyl, and amino) at a wide range of molar fractions in the feed produced new degradable poly(N-CBz-Hpr-co-functional-ε-CL)s with stannous 2-ethylhexanoate (Sn(Oct)₂) as a catalyst. The optimal reaction conditions for the synthesis of the copolymers were obtained with 1.5 wt% Sn(Oct)₂ at 140 °C for 24 h. The copolymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), ¹H NMR, differential scanning calorimetry, gel permeation chromatography, and Ubbelohde viscometry. The copolymers synthesized exhibited oligomeric molecular weights (3000-5000 g mol⁻¹) with modestly narrow molecular weight distributions (1.11-1.37). The values of the glass-transition temperature (T_g) of the copolymers depend on the compositions, and the molar fractions of cyclic lactone. For the poly(N-CBz-Hpr-co-4-EtC-ε-CL) system, with a decrease in 4-EtC-ε-CL contents from 79 to 3 mol%, the T_g increased from −34 to 67 °C In vitro degradation of these copolymers was evaluated from weight-loss measurements.     

基于间苯二甲胺单体的聚酰亚胺的合成与性能

以间苯二甲胺（MXDA）为二胺单体分别与五种芳香族二酐：4,4''-氧双邻苯二甲酸酐 （ODPA）、3,3'',4,4''-二苯甲酮四甲酸二酐（BTDA）、3,3'',4,4''-联苯四羧酸二酐（BPDA）、4,4''-（六氟异丙烯）二酞酸酐（6FDA）和4,4''-(4,4''-异亚丙基二苯氧基)双(邻苯二甲酸酐)（BPADA）在间甲酚中通过一步法合成了五种聚酰亚胺（PI）。采用FTIR、1HNMR分析了聚合物的分子结构，用DSC、TGA、UV-Vis等仪器研究了聚合物的性能。结果表明，所制备的PI特性黏数在0.36~1.44 dL/g，在酚类溶剂中均具有良好的溶解性；PI的玻璃化转变温度（Tg）在184~243 ℃之间，氮气气氛下5%热失重温度为485~538 ℃，热稳定性优异；PI薄膜在400 nm处的透过率为24%~85%，500 nm的透过率可达69%~88%，截止波长区间308~367 nm，具有良好的透明性；PI薄膜的拉伸强度、杨氏模量和断裂伸长率分别在41.1~85.3 MPa、1.7~2.1 GPa和2.5~8.7%的范围内，具有良好的机械性能。     

Synthesis and properties of polyimides from isomeric bis(dicarboxylphenylthio)diphenyl sulfone dianhydrides

4,4′-Bis(3,4-dicarboxyphenylthio)diphenyl sulfone dianhydride(4,4′-PTPSDA) and 4,4′-bis(2,3-dicarboxyphenylthio)diphenyl sulfone dianhydride(3,3′-PTPSDA) were synthesized from chlorophthalic anhydrides and bis(4-mercaptophenyl)sulfone. Their structures were determined via IR spectra, ¹H NMR and elemental analysis. A series of polyimides were prepared from isomeric PTPSDAs and aromatic diamines in 1-methyl-2-pyrrolidinone (NMP) via the conventional two-step method. Polyimides based on 4,4′-PTPSDA and 3,3′-PTPSDA have good solubility in polar aprotic solvents and phenols. The 5% weight-loss temperatures of isomeric polyimides were near 500 °C in N₂. DMTA and DSC analyses indicated that the glass-transition temperatures of polyimides from 3,3′-PTPSDA are higher than those of polyimides from 4,4′-PTPSDA. The wide-angle X-ray diffraction showed that all polyimides are amorphous. The polyimides from 3,3′-PTPSDA showed higher permeability but lower permselectivity compared with those from 4,4′-PTPSDA.     

Synthesis of spherical trans-1,4-polyisoprene/trans-1,4-poly(butadiene-co-isoprene) rubber alloys within reactor

Trans-polydiene rubber family as high-performance tire stock possessed excellent dynamic properties, including excellent anti fatigue, low rolling resistance, low heat buildup, good green strength, and low abrasion loss. Here, Reactor Granule Technology (RGT) was introduced into the field of synthetic rubber for the first time to produce trans-1.4-polyisoprene/trans-1,4-poly(butadiene-co-isoprene) rubber alloy, which showed significant improvement in rubber synthetic technologies and great development in abundance of trans-rubber family. A series of trans-polyisoprene alloys with excellent spherical morphology were successfully synthesized by using sequential multistage polymerization. The alloy was fractionated into four fractions by temperature-gradient fractionation, and the fractionation was analyzed by ¹H NMR, ¹³C NMR, DSC and WAXD.     

Studies on the thermal degradation of cis-1,4-polyisoprene

cis-1,4-Polyisoprene is pyrolyzed under an inert atmosphere at different temperature ranges by using differential thermal analysis and pyrolysis-gas chromatography. Fourier transform-infrared is used for investigating the pyrolysis residue. The pyrolyzed gaseous products are analyzed by gas chromatography. The effect of temperature range on the relative yields of the major decomposition products is studied. Based on these data, the thermal degradation mechanism of cis-1,4-polyisoprene is also proposed.     

Vibrational dynamics of trans-1,4-polyisoprene (β-form)

The earlier work on the vibrational dynamics of trans-1,4-polyisoprene (β-TPI) suffered from several infirmities. This work has been redone with all infirmities removed. It not only leads to a few different assignments but also better values of interactive constants. Two significant outcomes of the present work are; one change in the profile of the dispersion curves and repulsion between the two acoustic modes at the phase values away from the zone center. The present work leads to a fuller interpretation of observed spectra. Several observed unassigned modes have been accounted for due to the presence of regions of high density-of-states such as von Hove type singularities. Predictive values of heat capacity as a function of temperature are reported.     

Molecular dynamics simulation of cis-1,4-polybutadiene. 1. Comparison with experimental data for static and dynamic properties

Molecular dynamics (MD) calculations of cis-1,4-polybutadiene in bulk amorphous phase were performed under constant pressure and constant temperature conditions. The static and dynamic properties were evaluated from the results of MD calculations. The obtained density and coefficient of thermal expansion are in good agreement with experimental data. The feature of the calculated static structure factor is similar to the observed one. Molecular motion is examined with mean square displacements and intermediate scattering functions. An onset of a new motion, which corresponds to so-called fast process, was clearly observed in the temperature dependence of the mean square displacement above 100 K. The dynamic structure factors obtained by the Fourier transformation of the intermediate scattering functions are compared with those obtained from quasielastic neutron scattering measurements. The peaks corresponding to the elastic scattering and the low energy excitation at around 2 meV are reproduced in the dynamic structure factors. The excessive intensity observed in the dynamic structure factor, which corresponds to the fast process, is also reproduced above 140 K in our simulation.     

Synthesis and properties of flourine-containing polyimides

A series of new flourine-containing polyimides have been synthesized from the condensation of 2,2,-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-amino-phenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, or 2,2bis[4-(4-amino-2-trifluoro-methylphenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane with various aromatic dianhydrides. The electric constant at 1 KHz in the flourine-containing polyimides decreases from 3.51 to 2.72 as flourine content increases. The poly(amic acid)s had inherit viscosities of 0.52–1.23 dL/g, depending on the diamines and dianhydrides. Most of the resulting polymers showed an amorphous nature and afforded flexible and tough films. The amount of moisture absorption decreases as flourine content in polyimides increases. The glass transition temperatures of these polyimides were in the range of 287–328°C, and the 10% weight loss temperatures were above 542°C in the nitrogen. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 609–617, 1997     

Synthesis of well defined amino telechelic cis-1,4-oligoisoprenes from carbonyl telechelic oligomers; first studies of their potentialities as polyurethane or polyurea materials precursors

Carbonyl telechelic cis-1,4-oligoisoprene (CTPI) obtained from high molecular weight polyisoprene through an oxidative chain cleavage reaction have been chemically modified. Thus, new well defined amino telechelic cis-1,4-oligoisoprenes have been obtained in a mass range of 1600-2300 g/mol according to two different pathways. The first approach involved a standard mesylate displacement by sodium azide followed by smooth reduction using triphenylphosphine. The second pathway implied a reductive amination sequence. Primary or secondary amine functions have thus been selectively obtained at both oligomer chain-ends depending on reaction conditions. Peculiar NMR experiments conducted on these functional oligomers confirmed a precise control of functionality during the chemical modification. Moreover, their abilities to react with toluene diisocyanate or bis(succinimidyl)carbonate have been investigated.     

Molecular dynamics simulation of cis-1,4-polybutadiene. 2. Chain motion and origin of the fast process

Molecular dynamics (MD) simulations of cis-1,4-polybutadiene in bulk amorphous state were performed to elucidate the origin of a fast relaxation process observed by quasielastic neutron scattering (QENS) measurements. The details of the torsional motion for each dihedral angle were investigated with the torsional auto- and cross-correlation functions for several temperatures in this study. Temperature dependence of the correlation between the torsional autocorrelation and cross-correlation functions is also evaluated. The origin of the fast process of cis-1,4-polybutadiene is found to be mainly the cooperative conformational transitions of two dihedral angles located at both sides of the CH₂-CH₂ bond when the bond is in the trans conformation. The cooperative conformational transitions exhibit even below the glass transition temperature of cis-1,4-polybutadiene. The cooperative motion appears at about 50 K below the glass transition temperature, corresponding to the Vogel-Fulcher temperature.     

Synthesis and properties of polyimides containing polybutadiene blocks

Polyimides containing polybutadiene blocks were prepared by copolycondensation of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride, diphenylmethane-4,4′-diisocyanate and isocyanate-endcapped polybutadiene LBD-3000. ¹³C NMR CP-MAS and FTIR spectroscopies were used to determine the chemical structure of the copolymers. TGA showed that the thermal stability of the copolymers in inert atmosphere is almost independent of the polybutadiene content in the copolymer (as follows from the temperature of 10% and 20% weight loss). Stress–strain experiments showed that copolymers containing amounts of polybutadiene higher than 59 wt% exhibited elastomeric behaviour. © 1999 Society of Chemical Industry     

Synthesis of highly fluorescent coumarinyl chalcones derived from 8-acetyl-1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one and their spectral characteristics

A series of novel coumarin based chalcones were synthesized by the classical crossed aldol condensation reaction of 8-acetyl-1,4-diethyl-1,2,3,4-tetrahydro-7H-pyrano[2,3-g]quinoxalin-7-one and various substituted benzaldehydes. These novel ketocoumarin derivatives having a 1,4-diethyl-1,2,3,4-tetrahydroquinoxaline framework exhibited brilliant fluorescence. The novel chalcones absorbed in the range of 458-523 nm in various solvents. The wavelength of maximum absorption of these chalcones was found to be significantly longer than their simple acyl derivative known in the literature. The dyes displayed longer wavelength of absorption in the high polarity solvents compared to non-polar solvents. Thermogravimetric analysis of the chalcones revealed that the chalcones possess good thermal stability.     

Preparation of polyimides derived from biphenyltetracarboxylic dianhydrides and aromatic diamines bearing alkylene spacers

Four series of aromatic polyimides (PIs V–VIII) composed of biphenyltetracarboxylic dianhydrides (BPDAs) and aromatic diamines bearing alkylene spacers were prepared by two methods. Most polymers could be readily prepared in a one‐step method for the combination of a‐BPDA with α,ω‐bis(3‐aminophenoxy)alkanes, a‐BPDA with α,ω‐bis(4‐aminophenoxy)alkanes, and s‐BPDA with α,ω‐bis(3‐aminophenoxy)alkanes. However, the polymerization of s‐BPDA with α,ω‐bis(4‐aminophenoxy)alkanes gave powders. On the other hand, all four monomer combinations afforded the desired polyamic acid solution in a two‐step method. These polymer solutions could be cast into tough and flexible films, which were characterized by their inherent viscosity, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical spectrometry measurements. The glass transition temperatures (T_gs) of the polymers were in the range of 110–240°C, but they were not clearly defined for PIs VIII and VI. The 5% weight loss temperatures were around 450°C for all prepared PIs. For PI VIII an “odd–even” behavior of the tensile properties of the films was detected, corresponding to the reported behavior of the melting temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2404–2413, 1999     

Synthesis and characterization of novel polyimides starting from 1,2‐bis(p‐dimethylaminobenzylideneimino)alkane homologues and various dianhydrides

The objective of this research was the preparation of polyimides from 1,2‐bis(p‐dimethylaminophenylimino)alkane homologues and various dianhydrides in N‐methylpyrrolidone by one‐stage polycondensation. The monomers were prepared via condensation of p‐dimethylaminobenzaldehyde and the corresponding diamines, 1,4‐diaminobutane, 1,3‐diaminopropane and 1,2‐diaminoethane. The influence of the incorporation of this moiety into the polymer backbone on the properties of the polyimides has been evaluated. The thermogram of the polyimides indicated that PI‐10 to PI‐32 had T_g values ranging from 181 to 290 °C. The inherent viscosities of the polymers ranged from 0.99 to 2.05 dl g^?1, and the highest solubility was obtained without significant loss of the thermal properties. Copyright © 2004 Society of Chemical Industry     

Synthesis and characterization of a novel unsaturated polyester based on poly(trimethylene terephthalate)

Unsaturated aromatic polyesters were obtained by glycolysis of poly(trimethylene terephthalate) with cis-2-buten-1,4-diol followed by a solid-state polymerization. The glycolysis was performed in a batch mode as well as through a continuous process in a twin screw extruder. The degradation and subsequent rebuilding of the polymer chain during the course of reaction was followed by means of inherent and melt viscosity measurements, and ¹H NMR terminal group analysis of the intermediates and the final products. Structural investigations revealed that this new approach resulted in melt processible unsaturated polyesters with cross-linkable sites having similar characteristics to that of the virgin saturated polyester. Although the processing temperature for the different reaction steps was sufficiently high (180−260 °C), no thermally induced cross-linking of the incorporated unsaturated bonds could be evidenced indicating that the obtained products remained stable during the production stage. For comparison purposes, a commercial unsaturated polyester (Vestodur^©) was included in the investigations. UV irradiation of thin polyester films did not result in cross-linked products but in cis-trans isomerization of the incorporated bisoxybutenyl unit.     

Synthesis and properties of novel side-chain-type sulfonated polyimides

A series of side-chain-type sulfonated polyimides (SPIs) were synthesized from 4,4′-ketone dinaphthalene-1,1′,8,8′-tetracarboxylic dianhydride (KDNTDA), 2,2′-(4-sulfophenoxy) benzidine, and nonsulfonated diamines. The SPIs showed anisotropic membrane swelling in water with 2–4 times larger swelling in thickness direction than that in plane one, being much different from SPIs derived from 1,4,5,8-naphthalenetetracarboxylic dianhydride. They exhibited good solubility in dimethyl sulfoxide and 1-methyl-2-pyrrolidone even in proton form, which is favorable for processing in fuel cell applications. KDNTDA-based SPIs displayed good mechanical properties with reduced viscosities ranged from 1.1 to 2.4 dl g⁻¹ at 35 °C in triethylamine salt form. They also showed reasonably high proton conductivity and thermal stability.     

Synthesis and characterization of melt-processable polyimides derived from diaminodiphenylsulfone and benzophenone tetracarboxylic dianhydride with excellent heat resistance and thermoplasticity

Polyimide has excellent heat resistance, dielectric properties, and mechanical properties, and has a wide range of applications in aerospace, electronic packaging, and insulating materials. However, traditional polyimide is difficult to melt and dissolve, and its processing is difficult, which has become an important reason limiting its practical application. Therefore, the development of high temperature-resistant thermoplastic polyimide has become a research hotspot. To prepare high temperature-resistant thermoplastic polyimide materials, a series of thermoplastic polyimides was successfully prepared using 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,3′-diaminodiphenylsulfone, 2,3′,3,4′-benzophenone tetracarboxylic dianhydride, 9,9-bis(4-aminophenyl)fluorene, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane via a two-step method. The effects of non-coplanar structure and bulky groups on the solubility, processability, and thermal properties of polyimide were studied. The structure, heat resistance and thermoplasticity of polyimide were characterized via various methods. The results show that the glass transition temperature of the prepared thermoplastic polyimide is between 292 and 302°C, and has excellent thermal resistance. The processing viscosity of polyimides is as low as 9210 Pa.s, and it has a certain degree of processing properties. It may be designed to be used in high temperature-resistant hot melt adhesives for structural components, high temperature-resistant melt processing resins, or thermoplastic composite materials used in the field of aerospace in the future.     

Gas hydration of trans-1,2-dimethylcyclohexane with cooperative assistance of methane and cis-1,2-dimethylcyclohexane

It has been regarded that the limit of the largest cage occupancy for the structure-H hydrate is between the 1,2-dimethylcyclohexane stereo-isomers, because the cis-isomer is able to generate the structure-H hydrate in the presence of methane while the trans-isomer is not. In the present study, gas hydration of trans-1,2-dimethylcyclohexane in the presence of methane and cis-1,2-dimethylcyclohexane is found from stability boundaries for the structure-H hydrate system.     

Synthesis and properties of novel polyimides derived from 2,6-bis(4-aminophenoxy-4′-benzoyl)pyridine with some of dianhydride monomers

A new kind of aromatic diamine monomer containing pyridine unit, 2,6-bis(4-aminophenoxy-4′-benzoyl)pyridine (BABP), was synthesized successfully. The Friedel-Crafts acylation of phenyl ethyl ether with 2,6-pyridinedicarbonyl chloride formed 2,6-bis(4,4′-dihydroxybenzoyl)-pyridine (BHBP), BHBP was changed into 2,6-bis(4-nitrophenoxy-4′-benzoyl)-pyridine (BNBP) by the nucleophilic substitution reaction of it and p-chloronitrobenzene, and BNBP was reduced with SnCl₂ and HCl in ethanol to form the diamine monomer BABP finally, the diamine monomer BABP could be obtained in quantitative yield. A series of novel polyimides were prepared by polycondensation of BABP with various aromatic dianhydrides in N-methy-2-pyrrolidone (NMP) via the conventional two-step method. Experimental results indicated that some of the polyimides were soluble both in strong dipolar solvents (N-methy-2-pyrrolidone or N,N-dimethylacetamide) and in common organic solvents tetrahydrofuran. The resulting polyimides showed exceptional thermal and thermooxidative stability, no weight loss was detected before a temperature of 450 °C in nitrogen, and the values of glass-transition temperature of them were in the range of 208-324 °C. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.     

Use of hydroxytelechelic cis-1,4-polyisoprene (HTPI) in the synthesis of polyurethanes (PUs). Part 1. Influence of molecular weight and chemical modification of HTPI on the mechanical and thermal properties of PUs

New telechelic cis-1,4-polyisoprene oligomers bearing an hydroxyl group at the end of the polyisoprene backbone and possessing controlled molecular weights were used as soft segments in the elaboration of polyurethane elastomers. Besides, the well defined hydroxytelechelic cis-1,4-polyisoprene (HTPI) structure obtained through a controlled methodology, was chemically modified leading to hydrogenated and epoxidized oligomers based polyurethanes. The influence of the structural changes of these precursors on the polyurethanes properties have been studied. Thus, mechanical parameters as well as glass transition and mechanical transition temperature measurements indicated an increase in PUs hardness when the length of soft segment decreases and when the degree of epoxidized and hydrogenated isoprenic moieties increases. Moreover, based on thermogravimetric analysis (TGA), a linear relationship was established between the weight loss in the urethane stage degradation and the amount of hard segments in the PUs. Otherwise, the hydrogenated soft segments were found more thermally stable than the epoxidized and the non modified ones. By comparison with similar investigations developed from commercial oligodienes (PBHT R20 LM^® and EPOL^®), this study mainly showed that the PUs based on hydrogenated hydroxytelechelic cis-1,4-polyisoprenes were more thermally stable and softer than the EPOL^® based analogues.