Radical copolymerization of N-alkylmaleimides with isobutene and the properties of the resulting alternating copolymers

Radical copolymerization of N-methylmaleimide (MeMI) as well as other N-alkylmaleimides (RMI) and isobutene (IB) was carried out with 2,2′-azobis(isobutyronitrile) as an initiator at 60°C. The initial rate of the copolymerization (R_p) was dependent on the monomer composition and was maximum at the 40 mol % of MeMI in the feed. A solvent effect on the R_p and the monomer reactivity ratio was observed in this copolymerization system, i.e., copolymerization in chloroform produced a higher R_p and an alternating tendency compared with those in dioxane (r_MeMI = 0.14, r_1B = 0 in chloroform and r_MeMI = 0.47, r_1B = 0 in dioxane). The alternating copolymer of RMI and IB shows a high glass transition temperature (T_g) and excellent thermal stability, e.g., the T_g and the thermal decomposition temperature (T_d) were 152 and 363°C, respectively, for the alternating copolymer of MeMI and IB. Both the T_g and T_d increased as the concentration of the MeMI unit in the copolymers increased. Colorless transparent sheets were obtained from press molding the alternating copolymers. They showed excellent mechanical and optical properties. © 1996 John Wiley & Sons, Inc.     

Effect of curing accelerators on thermal imidization of polyamic acids at low temperature

The effect of new additives on the thermal conversion of a range of polyamic acids to polyimides at temperatures lower than 100°C was investigated using infrared spectroscopy. Additives such as m-hydroxybenzoic acid, p-hydroxyphenylacetic acid, and p-hydroxybenzenesulfonic acid were found to be highly effective as curing catalysts or accelerators. The degree of imidization of polyamic acids in the presence of additives increased with an increase in the reaction temperature, and complete imidization was achieved at 140–200°C. The reaction was characterized by a rapid rate that slowed with time. © 1996 John Wiley & Sons, Inc.     

Soluble aromatic polyamide and polyimides derived from di(aminophenyl) acetylenediurea

New aromatic polyamide and polyimides were prepared from di(aminophenyl)acetylenediurea. In addition, model compounds were synthesized and their IR spectra were in agreement with those of the corresponding polymers. The polymers were amorphous and readily soluble in polar aprotic solvents (DMF, NMP, DMSO) and certain acids (H₂SO₄, CCl₃COOH). The hydrophilicity of polyamide was estimated by measuring the isothermal water absorption. The polyamide softened at 260°C but no softening was observed for polyimides. The glass transition temperatures of polymers were determined by the TMA method and they were in the range of 235–310°C. The polymers were stable up to 359–404°C in N₂ or air and afforded char yields of 53–65% at 800°C in N₂. © 1996 John Wiley & Sons, Inc.     

Isobaric thermal expansivities of polyethylenes with various crystallinities over the pressure range from 0.1 to 300 MPa and over the temperature range from 303 to 393 K

A pressure-controlled scanning calorimeter (PCSC) has been applied for measuring the isobaric volume thermal expansivities (α_p) of crystalline polymers as a function of pressure up to 300 MPa at various temperatures. The measurements have been performed for several well-defined polyethylenes with various degrees of crystallinity at 302.6, 333.0, 362.6, and 393.0 K. The results are reported as values of coefficients in a correlation equation, which facilitates the use of reported data over large ranges of temperature and pressure. The general pressure-temperature behavior of α_p for all polyethylenes under study is such that α_p increases with temperature and decreases with pressure. The increase with temperature is smaller at high pressures and the isotherms of α_p have a tendency to converge at high pressures; α_p decreases linearly with the crystallinity of the polyethylene over the whole range of pressure and temperature under investigation. From the linear approximation of experimental data for polyethylenes with various crystallinities the estimated α_p for both crystal and amorphous phases of polyethylenes have been determined as a function of pressure up to 300 MPa at 302.6, 333.0, and 362.5 K. The obtained results have been compared with available literature crystallographic data and with the values derived from the Pastine theoretical equation of state for both crystalline and amorphous phases. © 1996 John Wiley & Sons, Inc.     

Synthesis and properties of new poly(ether sulfone)amides

High molecular-weight aromatic polyamides were obtained from 1,5- and 2,6-bis-(4′-carboxy-4-phenylenoxy-sulfonyl)naphthalene by direct polycondensation reaction in N-methyl-2-pyrrolidone with various aromatic diamines, using triphenyl phosphite and pyridine as condensing agents. The polymers were characterized by elemental analysis, thermogravimetric analysis, differential scanning calorimetry, and infrared analysis. The polyamides, obtained in quantitative yield, possessed inherent viscosities in the range 0.42–1.70 dL/g, glass transition temperatures between 245–310°C, and 10% weight loss temperatures in nitrogen and air above 435 and 424°C, respectively. Most of the polymers were soluble in aprotic solvents. The effect of the structure on properties, such as solubility, T_g, and thermal behavior, were also studied. © 1996 John Wiley & Sons, Inc.     

后处理法合成高热稳定性的中孔Ti-P-Al材料

 以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂,采用水热合成法制备了中孔氧化钛原粉,再采用磷酸和氯化铝溶液依次对中孔氧化钛原粉进行后处理,得到了具有高热稳定性的中孔Ti-P-Al材料. 通过粉末X射线衍射、透射电子显微镜和氮物理吸附等方法对样品进行了表征. 结果表明,反应凝胶组成对样品的中孔结构有较大的影响,当反应凝胶配比为Ti(SO4)2∶CTAB∶H2O=1∶0.54∶430, 温度为363 K, 处理时间为10～20 min时,所得的TiO2原粉具有较规整的中孔结构. 此样品经过0.25 mol/L的磷酸处理后有序性有较大程度的提高. 将磷酸处理过的样品进一步用氯化铝溶液处理,得到了中孔结构的Ti-P-Al材料,此材料经过873 K焙烧后仍具有典型的中孔特征,其比表面积为 382 m2/g, 孔径为3.13 nm.     

Synthesis of Oligomeric Axially Bridged Ruthenium Phthalocyanines and 2,3-Naphthalocyanines

Bridged 2,3-naphthalocyaninatoruthenium oligomers {[MacRu(L)] _n } were synthesized and characterized using solid-state methods. For comparison, soluble t-butyl substituted phthalocyaninatoruthenium oligomers were prepared and their chain length examined by ¹H NMR spectroscopy. The powder conductivities of all bridged compounds ([MacRu(L)] _n ) were measured and the dependence of the conductivities on the bridging ligands is discussed.     

Influence of the styrene–maleate ratio on the structure–property relationships of unsaturated polyester networks

Several structural series of unsaturated polyester networks which had different isophthalic acid–maleic anhydride ratios or different precentage rates of styrene incorporated in the network were studied by means of thermomechanical tests. It was demonstrated that the transition zone (α and β) did not correspond specifically to a polytyrene phase but could be linked to the presence of microdomains of different structures within the polyester network. It is the successive setting in motion of these microdomains, under the effect of a rise in temperature, which creates a broad transition zone. Structural chain formations based on the resin components (prepolymer and styrene) were proposed and linked to the transition temperatures detected. The improved knowledge of the structure and the various microdomains present within the networks will provide a better apprehension of the hydrolytic stability of unsaturated polyester materials.     

Comparative study of the thermal properties of related aromatic polyhydrazides and poly(1,3,4-oxadiazole)s

Studies were undertaken to ascertain the thermal behavior of several new types of aromatic polyhydrazides and poly(1,3,4-oxadiazole)s containing different functional groups. Results of thermal analysis investigations indicate that all the polyoxadiazoles are remarkably heat-resistant when heated in nitrogen at elevated temperature but somewhat less heat-resistant than fully aromatic polyoxadiazoles. Most of the new polyoxadiazoles decompose when heated to about 450°C. The incorporation of tetraphenyl silane, hexafluoroisopropylidene, phthalido or phenoxytherephthalic groups into the main chain decrease the glass transition temperature of aromatic poly(1,3,4-oxadiazole)s. In the case of the silicon-containing polymers the glass transition temperature is independent of the other groups incorporated in the same macromolecule. The cyclization process of all investigated polyhydrazides takes place in the range between 320 and 390°C.