1999 рік

The copolymer 7 of quaternary ammonium salt, N,N-diallyl-N-carboethoxymethyl-N-methylammonium chloride (5) and sulfur dioxide were synthesized in excellent yield. The polyelectrolyte 7 on acidic hydrolysis gave the polyampholyte 8 readily in excellent yield. The solution properties of these polymers are discussed in detail. The polyampholyte 8 was found to be insoluble in water but dissolved readily in the presence of low molecular weight common salts. The polyampholyte shows “anti-polyelectrolyte” behavior; the viscosity of the polyampholyte increases by increasing the ionic strength of its aqueous solutions.

Детальніше...  

An n.m.r. investigation of the chemical and morphological changes occurring during erosion in pH 7.4 phosphate buffer at 37°C of meltfabricated polyanhydride devices formed from copolymers of 1,3-bis(p-carboxyphenoxy)propane (CPP) and sebacic acid (SA) is reported. From sequence distributions determined using solution-state 1 H n.m.r. spectroscopy, the following order of anhydride bond lability was determined: SA–SA ⬇ SA–CPP q CPP–CPP, leading to preferential hydrolysis of aliphatic blocks within the copolymer chain. Solid-state 1 H and 2 H n.m.r. spectroscopy were used to investigate morphological changes occurring during erosion. Both indicated significant absorption of mobile water after ca. 10 h. Subtle variations in the symmetry of the narrow signals confirmed the changes in chemical composition apparent from high resolution 1 H n.m.r. analysis. In the initial stages, there was an increase in crystallinity attributed to preferential erosion of amorphous regions.

Детальніше...  

The miscibility in binary blends of a ferroelectric (vinylidene fluoride–trifluorethylene) copolymer (PVDF–TrFE) and amorphous poly(methyl–methacrylate) (PMMA) has been investigated over the full range of compositions for the copolymer with 50% wt. of trifluorethylene (TrFE). The kinetics of glassy and ferroelectric phase transitions have been studied and we demonstrate the miscibility of the components in the range of 5% to 15% wt. of PMMA. From 20 to 35 wt.% of PMMA, the system can still crystallize and present ferroelectricity, but it becomes strongly thermal history dependent. Above 40% wt., it is completely amorphous. The relationship between optical scattering in the visible range and a room temperature crystallization process has been established. The 15% wt. PMMA sample has been suggested as a very promising host material for non-linear optical and thermoluminescence applications.

Детальніше...  

The gel point and characterization of sol–gel transition of UHMWPE/decalin systems were investigated. In this study rheological method and DSC method were used to measure the gel point of UHMWPE gel at various concentrations. The result showed that the gel point increased with increasing gel concentration. Meanwhile pulsed NMR was also utilized to investigate 6 wt% UHMWPE gel. It was found that when sol–gel transition temperature was approximately 100°C, large amount of UHMWPE gel turned into solution state. Therefore, it produced re-entanglement and increased the random region within the UHMWPE molecular chain, which led to the decrease of interaction force among the polymer.

Детальніше...  

Semiconducting poly(aniline-co-o-ethoxyaniline) was synthesized by chemical oxidation polymerization of aniline and o-ethoxyaniline with two different molar ratios in an acidic media. Its chemical structure and other physical properties, such as conductivity, thermal stability and density of the polymer particles, were examined. Electrorheological (ER) fluids were then prepared by dispersing the copolyaniline particles in silicone oil and their rheological properties under electric field were investigated. It was found that the ER fluids using copolyanilines show different ER behaviors than that of the homopolyaniline.

Детальніше...  

X-ray diffraction and DSC investigations indicate that poly(dipropylphosphazene) is characterized by one ordered crystalline modification and a thermotropic mesophase, which is formed at temperatures higher than 248°C and appears to maintain a 2D order. The structure of the crystalline phase has been determined: the unit cell is monoclinic, space group P21/c, and the cell parameters are: a ˆ 9.10(5) Å, b ˆ 4.88(4) Å, c ˆ 19.05(10) Å, b ˆ 92.43(1)°. The refinement indicates a twofold helical conformation with a nearly planar (CT)2 backbone. The cyclic trimer was studied by DSC and single crystal X-ray diffraction: the unit cell is monoclinic, space group P2/c, cell parameters are a ˆ 10.0131(5) Å, b ˆ 7.8342(4) Å, c ˆ 15.1782(11) Å, b ˆ 95.844(7)°. The conformations of the side chains in the polymer and the trimer are closely related, as already found in polydiethylphosphazene. In the polymer, however, the side chains probably show some disorder yet to be characterized.

Детальніше...  

A series of five fluorinated poly(phenylquinoxaline-amide)s were synthesized by a polycondensation reaction of a diacid chloride containing the hexafluoroisopropylidene (6F) group, namely 2,2-bis(p-chlorocarbonylphenyl)-hexafluoropropane, with various aromatic diamines incorporating two phenyl-substituted quinoxaline rings. These polymers were easily soluble in polar aprotic solvents such as N-methylpyrrolione (NMP), dimethylformamide (DMF), and tetrahydrofurane (THF), and showed a high thermal stability with decomposition temperatures above 400°C and glass transition temperatures in the range of 260–290°C. Polymer solutions in NMP were processed into free-standing films that showed low dielectric constant values, in the range of 3.4–3.9, and good mechanical properties, with tensile strength in the range of 40–80 MPa and elongation to break in the range of 22–55%. Very thin films, in the range of tens of nanometer, which were deposited onto silicon wafers exhibited very smooth surfaces, free of pinholes when studied by atomic force microscopy (AFM).

Детальніше...  

The polymerization behaviour of methyl methacrylate (MMA) in p-xylene in the presence of CuCl/L [L ¼ 1,10-phenanthroline (phen) or 4,7-diphenyl-1,10-phenanthroline (DPP)] and tetrachlorocarbon has been studied. For the CCl 4/CuCl/phen/MMA/p-xylene system, the linear relationship between the number-average molecular weight of the resulting poly(methyl methacrylate) (PMMA) and MMA conversion, as well as between ln[M] 0/[M] and time, demonstrate the 'living’ nature of this system. When phen is replaced by DPP the polymerization becomes slower, but the molecular weight and molecular weight distribution are better controlled. The stereochemistry of PMMA synthesized in the CCl 4/CuCl/DPP/MMA/p-xylene system indicates that the MMA monomer adds to the living polymer chain end in an atactic fashion.

Детальніше...  

It is shown that a fibril structure of a thermotropic liquid crystalline polymer (TLCP)(poly(ester amide)) can be developed in the shear flow field of a thermoplastic matrix (polyamide, nylon 66) when the viscosity of the latter is lower than that of the former. The addition of a third component, a functionalized polypropylene (maleic-anhydride-grafted polypropylene, MA-PP) that interacts with both the matrix polymer (nylon 66) and the thermotropic liquid crystalline polymer facilitates the structural development of the TLCP by acting as a compatibilizer at the interface. Morphological observations have demonstrated the significance of compatibilization in immiscible polymer blends. The compatibilizer brings about good adhesion at the interface, reduces the droplet size, and enables a finely dispersed liquid crystalline polymer to be deformed by shear flow without strong elongation, even when the viscosity of the matrix is much lower than that of the liquid crystalline polymer. The mechanical properties of the ternary blends are increased when a proper amount of MA-PP is added. This is attributed to fine strand generation induced by the addition of MA-PP. Enhanced adhesion at the interface invokes better elongation in the ternary blends.

Детальніше...  

Miscibility and thermal behavior of blends of synthetic biodegradable aliphatic polyester (BDP) with poly(epichlorohydrin) (PECH) were investigated by both differential scanning calorimetry and a dynamic mechanical thermal analyzer. Single glass transition temperatures in agreement with the Fox equation indicate that these blend mixtures are miscible. This was further clarified from the cryogenically fractured surface of BDP–PECH blends by scanning electron microscopy.

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