Preparation and characterization of three-dimensionally ordered macroporous styrene/p-methylstyrene syndiotactic copolymer

Three-dimensionally ordered macroporous (3DOM) styrene/p-methylstyrene syndiotactic copolymer (sPMS) with pore size 170 nm were fabricated by means of silica templates using (dbm)₂ Ti(OPh)₂/MAO catalytic system. The resulting materials were characterized by NMR, SEM, GPC and DSC. The results indicated that the 3DOM sPMS were highly syndiotacic, and the pore contraction was approximately 20.6%. Compared with bulk sPMS, 3DOM sPMS possessed the lower number-average molecular weight and broader molecular weight distribution. In terms of DSC results, the bulk sPMS exhibited the lower glass transition temperature than that of 3DOM one.     

Mechanical and thermal properties of syndiotactic polystyrene blends with poly(p-phenylene sulfide)

Melt blends of syndiotactic polystyrene (sPS) and poly(p-phenylene sulfide) (PPS) have been prepared by using an internal mixer at 300 °C. The thermal, mechanical and morphological properties of binary blends of sPS with PPS have been investigated in this paper. The thermal and morphological properties show the immiscible binary blend evidences, which have a clear phase separation between the components at all compositions and a lack of adhesion at the interface. According to the X-ray diffraction patterns of blends, the crystalline structure of sPS in the blend is not altered from α form to β form. Indeed, the results for tensile test reveal that there is no synergism of the modulus of elasticity for sPS/PPS blend system.     

Morphology and structure of poly(p-dioxanone)

The morphology of solution grown single crystals of poly(p-dioxanone) was investigated. Different crystallization conditions (solvent, precipitant agent and temperature) were tested. Dendritic growth, screw dislocations and striations were observed. Crystals usually exhibited a lozenge morphology, whose apex angle changed with the crystallization conditions. In all cases, however, a single crystal electron diffraction pattern was recorded. Spherulitic morphologies were obtained by evaporation of formic acid solutions. Lamellae gave rise to well resolved electron diffraction patterns that allowed determination of the main packing characteristics. Patterns of tilted specimens helped establish an orthorhombic unit cell, whose parameters indicate a deviation from the all trans molecular conformation. Quantum mechanical calculations were performed on small model compounds to study the conformational preferences. Simulated diffraction patterns were consistent with a unit cell containing four repeat units and a P2₁2₁2₁ space group. Molecular packing suggests the existence of different kinds of folds for an assumed adjacent reentry. Polyethylene decoration hardly highlighted a crystal sectorization. Also enzymatic degradation of lamellar crystals was evaluated by using a Pseudomonas cepacia lipase.     

Thermal degradation of poly(p-phenylene-graft-?-caprolactone) copolymer

The thermal degradation of poly(p-phenylene-graft-?-caprolactone) (PPP), synthesized by Suzuki polycondensation of poly(?-caprolactone) (PCL) with a central 2,5-dibromo-1,4-benzene on the chain with 1,4-phenylene-diboronic acid, has been studied via direct pyrolysis mass spectrometry. The thermal degradation occurred mainly in two steps. In the first step, decomposition of PCL chains occurred. A slight increase in thermal stability of PCL chains was noted. In the second stage of pyrolysis, the decomposition of the polyphenylene backbone takes place. The evolution of CL monomer or small CL segments left on the phenyl ring continued also in the temperature region where degradation of PPP backbone started.     

A facile approach to preparation of long-chain-branched poly(p-dioxanone)

Long-chain-branched poly(p-dioxanone)s (LCB-PPDOs) with different branch densities were prepared via the chain-extending reaction of hydroxyl group terminated linear bi-functional PPDO (2a-PPDO) and star-like tri-functional PPDO (3a-PPDO) prepolymers, which were synthesized by the ring-opening polymerization of p-dioxanone (PDO) using 1,4-butanediol (BD) and trimethylolpropane (TMP) as multi-functional initiators, respectively. The undesirable gelation was successfully depressed by adjusting the chain length and feed ratio of prepolymers. The average molecular weight between branch points (M_b) and the average number of branch per 100,000 g/mol (B_n) of LCB-PPDOs were calculated from the ¹H NMR spectra. The average number of branch ranged from 0 to 6.72 branch points per 100,000 g/mol, and the number-average molecular weights between branch points ranged from 6900 to 20,500 g/mol. The results of differential scanning calorimetry (DSC) showed that the crystallization behavior of LCB-PPDOs was changed evidently with the branch density. Small-amplitude dynamic oscillatory rheometer was used to investigate the rheological properties of the melts of LCB-PPDO including zero-shear viscosity, storage modulus, relaxation times and loss angle, which largely depended on the branch density and length of LCB-PPDOs. Therefore, the rheological behaviors of PPDO can be well-controlled via synthesizing LCB-PPDOs with the desired architectures.     

Zn(II), Cd(II) and Hg(II) complexes with 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole: Syntheses, structures and luminescence

Five coordination compounds Zn(mbmpbi)₂Cl₂ (1), Zn(mbmpbi)₂Br₂ (2), Cd(mbmpbi)₂Cl₂ (3), Hg(mbmpbi)₂Cl₂ (4) and Hg(mbmpbi)₂Br₂ (5) were synthesized by the reaction of 1-(p-methoxybenzyl)-2-(p-methoxyphenyl)benzimidazole (mbmpbi) with the corresponding metal halides. The complexes have been characterized by elemental analysis, conductance measurements, FT-IR, ¹H NMR and photoluminescence spectral studies. The ligand mbmpbi exhibits the N-benzimidazole coordination. The structures of 3-5 have been determined by single crystal X-ray diffraction. These three complexes are isostructural, crystallizing in the monoclinic system, P2/n space group with a distorted tetrahedral geometry around the metal ion. Zn(II) and Cd(II) complexes show strong blue emission in solid state at room temperature.     

New confined p-phenylenevinylene (PPV)-type polymer analogue of poly(phenylene sulfide)

A new confined p-phenylenevinylene (PPV)-type polymer (PPVS) has been synthesized using Wittig condensation. The chemical structure of the polymer was well defined by ¹H NMR, ¹³C NMR, and FTIR spectroscopic analysis. PPVS contains oligomeric PPV units separated by sulfide bridges in the main chain; it is fully soluble in common organic solvents and has a number-average molecular weight of 3500 g mol⁻¹. Thermogravimetric analysis and differential scanning calorimetry indicate that PPVS is amorphous, stable up to 360 °C in air and displays a glass transition temperature of 98 °C. The optical properties of the polymer were investigated by UV-visible absorption and photoluminescence spectroscopies. The polymer film absorbs at 375 nm and emits at 517 nm with a narrow emission spectrum. From the cyclic voltammetry analysis, the electrochemical bandgap was estimated to be 2.78 eV. A single-layer diode device of the configuration indium-tin oxide/PPVS/aluminium has been fabricated and has a relatively low turn-on voltage of 3.4 V. An electroluminescent emission similar to photoluminescence is demonstrated in a multilayer device.     

Synthesis of oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) triads as antenna molecules for energy transfer

The oligo(p-phenylene vinylene)-porphyrin-oligo(p-phenylene vinylene) (P-OPVn, n=2, 4, where n is the number of phenyl rings) and the complex with Zn²⁺ based on P-OPVn were synthesized for investigating their photophysical properties via UV-vis, voltammetry, steady-state and time-resolved fluorescence spectra. In these molecules two OPV moieties as energy donors were linked to porphyrin center by virtue of Wittig reaction. The detailed studies of photophysical properties indicate that OPV group can act as an antenna unit for effective intramolecular energy transfer.     

Vibration and X-ray photoelectron spectroscopies of FeCl3-doped poly(p-diethynylbenzene)

The doping mechanism of poly(p-diethynylbenzene), chemically doped with FeCl₃, was investigated. Absorption, infrared, far infrared, Raman, X-ray photoelectron spectroscopies were used to determine the nature of the dopant in doped polymer. The experimental results suggest that the charge transfer reaction between the polymer chain and the dopant results in the formation of FeCl₄⁻ species, the π electron charge delocalization along the polymeric chain and the reduction of π-π^* transition energy.     

The first metal complex of p-nitrobenzoxasulfamate. Synthesis, spectral and structural characterization of triaquabis(p-nitrobenzoxasulfamato)copper(II) monohydrate

The local structure of molten LaCl₃ was investigated by X-ray absorption fine structure of the La K-edge. The nearest La³⁺-Cl⁻ distance and coordination number were 2.89±0.01 Å and 7.4±0.5 from the curve fitting of the first peak in the Fourier transform magnitude |FT|. The coordination number larger than 6 suggests that the local structure of molten LaCl₃ is not a simple octahedral coordination (LaCl₆)³⁻, but 7-fold (LaCl₇)⁴⁻ and/or 8-fold (LaCl₈)⁵⁻ complexes. The first La³⁺-La³⁺ distance, of which correlation was observed as a weak second peak in the |FT|, was evaluated to be 4.9 Å. It suggests that the distorted corner-sharing connection of the complex species is predominant in the melt, in contrast with molten YCl₃ in which the edge-sharing connection of the 6-fold (YCl₆)³⁻ mainly exists.     

Porosity development in chars from thermal decomposition of poly(p-phenylene terephthalamide)

The main objective of this work was to investigate the development of porosity in solid residues from the thermal decomposition of the polymer, poly(p-phenylene terephthalamide) (PPTA). PPTA chars were prepared at different temperatures and characterized by X-ray diffraction and physical adsorption of CO₂ at 0 °C. The carbonization temperatures were selected on the basis of thermogravimetric analysis results. The effect of introducing an isothermal treatment at 500 °C on the characteristics of the resulting chars was also studied. It was found that this pre-treatment lowers the decomposition temperature of PPTA and yields a somewhat less ordered material than in the case of pyrolysis under a constant heating rate. The micropore volume increases with increasing heat treatment temperature for both series of samples. The mean micropore size decreases for the two series of chars until the 700-800 °C interval; above these temperatures, this evolution is reversed. The micropore volume of the samples submitted to the isothermal treatment is higher than when PPTA is treated under a constant heating rate. Likewise, the pore size distribution is more heterogeneous when the intermediate isothermal treatment at 500 °C is introduced during PPTA pyrolysis. Some differences between porosity development in chars from PPTA and other high thermal stability polymers were explained on the basis of different mechanistic features in polymer pyrolysis.     

Porosity development in chars from thermal degradation of poly(p-phenylene benzobisoxazole)

The main objective of this work was to investigate porosity development in carbonaceous materials formed by thermal degradation of the high thermal stability polymer, poly(p-phenylene benzobisoxazole) (PBO). Two varieties of PBO, as-spun (AS) and high-modulus (HM) were studied. Chars obtained at various polymer decomposition temperatures (selected on the basis of thermogravimetric and differential thermal analysis results) were characterized by elemental analysis, infrared spectroscopy, X-ray diffraction and CO₂ adsorption at 273 K. The obtained adsorbents essentially contained narrow micropores, and maximum pore development took place at ca. 1000 K, when the polymer was not yet completely decomposed. At higher temperatures, there is a certain pore widening along with a displacement towards smaller pore sizes, and the pore volume significantly decreases.     

On the clathrate structures of syndiotactic poly(m-methylstyrene)

The crystal structures of clathrate forms of syndiotactic poly(m-methylstyrene) containing guest molecules having different steric hindrance (CS₂, benzene and orto-dichlorobenzene) are presented. The structures are all characterized by polymer chains in s (2/1)2 helical conformation and guest molecules packed in an orthorhombic unit cell according to the space group Pcaa. All the presented clathrates belongs to β class indipendently from the dimensions of the guest molecule. In this aspect they differ both from clathrate forms of syndiotactic polystyrene, all belonging to α class, and from clathrate forms of syndiotactic poly(p-methylstyrene) that belong to α or β class according to the steric hindrance of the guest molecule.     

Synthesis of poly(p-phenylene)s having alternating sugar and alkyl substituents by Suzuki coupling polymerization and evaluation of their main-chain conformations

This paper reports synthesis of poly(p-phenylene)s (PPPs) having alternating sugar and alkyl substituents by Suzuki coupling polymerization of a 1,4-dibromobenzene monomer having peracetylated glucose residues with a 1,4-benzene bis(boronic acid) having alkyl chains using Pd(PPh₃)₄ in a mixed solvent of THF and NaHCO₃ aq. at reflux temperature. The polymerization proceeded with the progress of frequent deacetylation, and thus, the crude product was acetylated, followed by the isolation procedures, giving the PPP having alternating peracetylated glucose and alkyl substituents. The structure of the isolated product was confirmed by the ¹H and ¹³C NMR measurements to be the desired PPP derivative. The M_n values were estimated by GPC analysis with DMF as the eluent to be 5400-12,700. The deacetylation of the polymer completely took place using sodium methoxide in methanol/THF. The conformation of the main-chain was evaluated by the CD spectrum in comparison with that of PPP only with the glucose substituents, indicating that the present PPP derivative had the flexible nature of the main-chain by introduction of the alkyl-substituted units between glucose-substituted units. The Suzuki coupling of a 1,4-dibromobenzne monomer having disaccharide substituents with the benzene bis(boronic acid) monomer was also performed under the similar conditions. The product was precipitated from the reaction mixture, which was simply isolated by filtration. The isolated polymer was purified further by reprecipitation into diethyl ether and its structure was a PPP having free disaccharide or monosaccharide residues. This indicated occurrence of complete deacetylation as well as partial degradation of the glycosidic linkages in the disaccharides during the polymerization. The main-chain of the obtained polymer had also the flexible nature. The fluorescence spectra of the obtained PPP derivatives in this study were also measured.     

Fluorination of poly(p-phenylene) using TbF4 as fluorinating agent

The fluorination using TbF₄ as fluorinating agent was successfully performed on poly(p-phenylene). The method allows the fluorine content of the polymer to be controlled and the formation of structural defects, such as dangling bonds, to be significantly decreased by comparison with the direct fluorination using pure F₂ gas. The aromatic character of the phenyl ring is partly maintained through the fluorination contrary to the direct fluorination (using pure F₂ gas), for which a quasi-perfluorination and a partial decomposition of the polymer occur. Complementary analytical techniques have been used, such as ¹⁹F and ¹³C solid state NMR, FT-IR and EPR to compare the samples as a function of the reaction conditions.     

Crystal structure and luminescence property of novel three-dimensional network of {Eu2(p-BDC)3(Phen)2(H2O)2}n

The single crystal of a supramolecule, {Eu₂(p-BDC)₃(Phen)₂(H₂O)₂}_n (p-BDC=1,4-benzenedicarboxylate), with characteristic luminescence of Eu³⁺ was obtained by means of soft chemistry. The crystal structure determination reveals that each Eu³⁺ ion is coordinated by five oxygen atoms of p-BDC anions, one oxygen atom from water molecule, and two nitrogen atoms of Phen, respectively, resulting in an eight-coordinated Eu³⁺ center and a distorted square antiprism coordination polyhedron. Four bridges, two carboxylates of μ₄-p-BDC and two of μ₃-p-BDC, connect two Eu atoms into a binuclear unit. Moreover, the μ₃-p-BDC integrates the binuclear building blocks at the direction of b axis and the μ₄-p-BDC polymerizes the structure roughly along the direction of the sum vector of axis b and c, respectively, forming two-dimensional layers. Hydrogen bonds between layers make the structure a three-dimensional network. The luminescence spectra measured under 77 K demonstrate the antenna effect of Phen and the ⁵D₁→⁵D₀ energy transfer path within Eu³⁺ ion. Both luminescence spectra and crystal structure lead to the conclusion that the local symmetry around the Eu³⁺ ion is C₁ and that more than one Eu³⁺ ion sites having slight environmental difference are present.     

Synthesis and properties of novel poly(p-phenylenevinylene) copolymers for near-infrared emitting diodes

A series of novel near-infrared (NIR) electroluminescence (EL) copolymers based on a host poly(p-phenylenevinylene) (PPV) derivative of poly(2-methoxy-5-octyloxy-p-phenylenevinylene) (PMOPV) with different content of narrow band-gap (NBG) unit 4,7-bis(2-thienyl)-2,1,3-benzothiadiazolevinylene (DBTV) or 4,7-bis(2-thienyl)-2,1,3-benzoselenadiazolevinylene (TBSV) was prepared by Stille coupling reaction. All the copolymers are soluble in common organic solvents, most of which emit NIR light accompanied by gradually red-shifting with increasing the content of the NBG units. The peak EL emission of the copolymers with around 30% TBSV content is at about 800 nm.     

Kinetics of thermal degradation and thermal oxidative degradation of poly(p-dioxanone)

The kinetics of the thermal degradation and thermal oxidative degradation of poly(p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F₁ mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A₂ mechanism).     

In vitro degradation of poly(lactide-co-p-dioxanone)-based shape memory poly(urethane-urea)

The degradation of poly(lactide-co-p-dioxanone)-based shape memory poly(urethane-urea) (SMPU) in vitro was investigated by observing the changes of the pH value of incubation media, weight loss rate, molecular weight and scanning electron microscopy (SEM) during degradation duration of 12 weeks. Moreover, ¹H NMR was used to precisely study the degradation position by calculating the change of characteristic peaks value. The results revealed that the introduction of p-dioxanone (PDO) and -NH-(CO)- and -HN-(CO)-NH- would increase the hydrophilicity of polymer, so the degradation of SMPUs is higher than PDLLA control in the initial time, however, the degradation rate decreased in the anaphase of degradation, which can be attributed to the alkalic -NH₂ from the NH₂ and -NH-(CO), -NH-(CO)-NH-.