摘要:

AbstractCopolyimides containing BTDA‐3DDS and BTDA‐4ODA units have been synthesized by solution imidization methods. The copolyimides have highTg's (267–283°C) and high decomposition temperatures (540–575°C; nitrogen); both properties are dependent on composition. Those copolymides with low concentrations of BTDA‐4ODA are generally soluble in organic solvents, whereas those copolyimides with higher BTDA‐4ODA content are only partially soluble or insoluble. However, all the copolyimides prepared can be compression molded. It has also been found that segmental motion aboveTgis heavily suppressed in the BTDA‐4ODA homopolymer relative to that in the BTDA‐3DDS homopolymer. This reduction in molecular motion may severely hinder the solubility and fusibility of the BTDA‐4ODA homopolymer. © 1993

ISSN:0021-8995    

DOI:10.1002/app.1993.070470501

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe surface compositions and characteristics of perfluorodecanoic acid (PFDA)‐grafted polyurethane (PU) were investigated to understand its enhanced blood compatibility. The grafting of PFDA was identified by attenuated total reflectance–Fourier transform infrared (ATR–FTIR). The results from angular‐dependent electron spectroscopy for chemical analysis (ADESCA) demonstrated the fluorocarbon enrichment at the outermost layer in PFDA‐grafted PU. Static secondary ion mass spectroscopy (SIMS) experiments supported the results drawn from ATR–FTIR and ADESCA data about the surface compositions. Energy‐dispersive X‐ray analysis (EDXA) data by fluorine mapping also indicated a considerable coverage with fluoroalkyl groups on the PU–PFDA surface. The critical surface tension, γc, of the highly hydrophobic PU–PFDA surface revealed an extremely low value of 6.9 dyn/cm due to the optimal orientation of CF3groups to the uppermost surface. Therefore, such an inert low‐energy surface may contribute to improve blood compatibility of PFDA‐grafted PU.

ISSN:0021-8995    

DOI:10.1002/app.1993.070470502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe amount of solute sorbed per unit weight of sorbent,qe, and the equilibrium solubility (partition) coefficient were measured using a gravimetric method for various types of organic chemicals in thermoplastics and elastomers. A thermodynamic model was derived to predict the activity‐dependent partition coefficient andqefor a wide range of organic chemicals. The thermodynamic model produced a better fit to the measuredqevalues than did the Flory–Huggins equation. Partition coefficients andqeincreased with increase in activity. For nonpolar compounds,qeincreased logarithmically but decreased for polar compounds with an increase in the saturation organic chemical vapor concentration. Elastomers had 14–28 times greaterqevalues than did thermoplastics. A structure–activity relationship was found to accurately predict the partition coefficient for liphophilic organic chemicals at a specific activity. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070470503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

Abstract4′‐[Oligo(ethylene oxide) monomethyl ether carbonyl] biphenyl‐4‐yl 4‐(alkenyloxy) benzoate side‐chain liquid crystalline (LC) polysiloxane polymers with various lengths of a terminal group and spacer were prepared. The mesophase structure and transition temperature of those polymers were investigated using methods of X‐ray diffraction, polarized optical microscopy, and differential scanning calorimetry, respectively. The mesophases of the polymers were smectic ones. The layer spacingd1s and the side‐chain distance ofd2s obtained were around 29–34 Å and 4.4–4.6 Å, respectively.d1s were much shorter than twice the lengths of the side chains presumed in the fully extended conformation. Hence, the two‐layer end‐on packings or the packing with overlapping of tails model seemed not able to interpret the mesophase structure of those polymers studied. The effects of temperature on the mesophase microstructure of 4′‐[ethylene oxide monomethyl ether carbonyl] biphenyl‐4‐yl 4‐(pentenyloxy) benzoate side‐chain LC polysiloxane polymer were also studied using the X‐ray diffraction method. It was found that bothd1 andd2 of the polymer in the mesophase temperature range became shorter with decreasing temperature and the long‐and short‐range order could remain, to some extent, at temperatures above the isotropic transition temperature and temperatures below the melti

ISSN:0021-8995    

DOI:10.1002/app.1993.070470504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractShrinkage, retractive stress, and infrared dichroism of the drawn low‐density polyethylene (LDPE) as‐drawn and irradiated by60Co‐ray have been measured under different annealing conditions. The shrinkage and the disorientation of the irradiated sample was undergone more rapidly than that of unirradiated one as the temperature was continuously increased, surpassing a certain value, and a higher degree of shrinkage and disorientation was achieved finally for the irradiated sample when the samples were annealed with free ends. For the samples heated isothermally with fixed ends, the retractive stress went through a maximum and then attenuated to a limited value, and the degree of such a stress attenuation for the unirradiated sample was much more than that for the irradiated sample. These results show that the taut tie molecules (TTMs) in drawn PE can relax by the pulling of chain segments out of crystal blocks that they anchored in at elevated temperatures higher than the α transition and also by the displacing of microfibrils if the samples were annealed with free ends. The cross‐links produced by irradiation prohibit the former process. It was further observed that the dependence of the average extinction coefficient of the band at 2016 cm−1on that of the band at 1894 cm−1is related to irradiation and annealing conditions, which has also been explained by the relaxation of TTMs and the function of irradiation‐induced cross‐linking on the relaxation. © 1993 Joh

ISSN:0021-8995    

DOI:10.1002/app.1993.070470505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDuring the carbonization process of a lignite source available in the southern part of India, a very cheap byproduct, crude multivalent phenol, was obtained. This crude consisting of substituted phenols and carbonaceous pitch was distilled to get a pitchfree distillate of about 60% yield. The distillate mixture was used along with other phenols for synthesis of resol varnish using a base catalyst. The properties of the resols were evaluated and found to be similar to that of pure phenol (C6H5OH) resins. The resol varnishes prepared were used for making cotton paper phenolic laminates by hand impregnation and the compression‐molding technique. The paper laminates have been evaluated for physical, chemical, mechanical, and electrical properties. The experimental investigations indicate that the distillate of multivalent phenol is a useful inexpensive substitute for conventionally used phenols in the manufacture of P3grade laminates. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070470506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPolyurethane oligomers from 1,4‐butanediol (BD) and toluene diisocyanate (TDI) with a various excess of BD were synthesized. Their molar masses were measured by gel permeation chromatography and the molar mass distribution correlated with the statistic theory.1H‐,13C‐,1H–1H‐COSY–, ATP–, and15N‐NMR spectra of reaction products were recorded, and from the ratio of proton integrals of characteristic terminal and inner urethane groups, the reactivity ratio of theparaandorthoNCO groups in 2,4‐TDI was calculated to be approximately 1.8 at a lower excess of BD.15N‐NMR spectroscopy was found not to be selective enough to detect small amounts of side reactions. © 1993

ISSN:0021-8995    

DOI:10.1002/app.1993.070470507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn aqueous solution [2‐(diethylamino)ethyl]dextran hydrochloride (EA) was reacted with potassium metaphosphate (MPK) to form a series of water‐insoluble macromolecular complexes (MC) at different hydrogen‐ion concentrations (EA–MPK system). EA was also reacted with MPK in the presence of CaCl2(EA–MPK–CaCl2system). The structure and properties of MC obtained were compared with each other; elemental analysis, IR spectroscopy, solubilities, thermogravimetric analysis, and scanning electron microscopy were used to characterize these complexes. The molecular structure and properties of each MC were dependent on the hydrogen‐ion concentration and whether the Ca2+ion coexisted. It was suggested that MC prepared at acidic pH were composed of a relatively loose network including a small quantity of MPK, whereas those prepared at neutral and alkaline pH were composed of a relatively tight network including a large quantity of MPK. This seemed to be due to changes in the degree of dissociation and the conformation of EA and MPK with the hydrogen‐ion concentration. MC in the EA–MPK–CaCl2system were supposed to have a rather tightly bound network structure due to the Ca2+ion as compared with those in the EA–MPK system. © 199

ISSN:0021-8995    

DOI:10.1002/app.1993.070470508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractModel epoxy networks based on a diglycidylether of bisphenol A (DGEBA) or of butanediol (DGEBU) and cured with different mixtures of monoamines and diamines were prepared to allow changes in cross‐link density. The choice of aliphatic or aromatic amines permitted assessment of the influence of network chain flexibility. Solid state13C‐NMR spectra showed that no secondary reactions leading to the creation of ether linkage occur during the condensation reaction. Glass transition temperatures (Tg) and the temperatures of the maximum of the exothermic cross‐linking reaction (Texo) were determined. A rectilinear increase ofTgas a function of the density of cross‐links was observed for all the systems under study. Similarly, an increase in the stiffness of the backbone units resulted in an increase inTg. Time‐temperature‐transformation (TTT) isothermal cure diagrams were constructed and infrared kinetics were performed at 90°C. Gelation and vitrification times were shown to be dependent on the nature of the amines used to create the network structure. © 1993 John Wi

ISSN:0021-8995    

DOI:10.1002/app.1993.070470509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractGraft polymerization of methacrylic acid to polycaproamide, initiated by the K2S2O8Na2S2O3Cu2+reversible redox system, has been studied. Kinetic characteristics of graft polymerization have been investigated in a wide concentration range of every component of the initiating system. Cu2+ions have been found to catalyze graft polymerization in the 1.0 · 10−5−1.2 · 10−4Mconcentration range, whereas at concentrations higher than 1.2 · 10−4M, Cu2+ions are involved in the kinetic chain termination. A mechanism of graft polymerization is proposed. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070470510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY