SynopsisCarbon fiber surfaces were coated in various thickness with polyamic acids (PAA) prepared from ( 1 ) benzophenone tetracarboxylic dianhydride (BTDA) and 4,4'-diaminodiphenyl ether (ODA) , (2) BTDA and 4,4'-diaminodiphenyl sulfone (DAS), and ( 3 ) BTDA and ODA modified with bisaminopropyldisilane, designated as PAA-1, PAA-2 and PAA-3 respectively. The treated carbon fiber, with or without imidization, was embedded in thermoplastic polyetheretherketone (PEEK), polyetherimide (PEI), polyethersulfone (PES), polysulfone (PSF), and polyphenylsulfide (PPS) by the microbond method, and the interfacial shear strength was measured by pulling out the fiber from the embedded resin. Maximum increments in interfacial bonding strength from 24% to 35% were obtained from PAA-1 in PEEK and PEI, PAA-2 in PEEK, PEI, PSF, and PPS, and PAA-3 in PEEK and PES. Imidization of PAA-1 and PAA-2 before resin application reduced their bonding capability. A linear relationship between the length of the embedded fiber and debonding load was found in the case of PEEK, PEI, and P S F scattered results were obtained in the case of PES and PPS. Inadequate specimen annealing was believed to be the cause for PES, Brittle fracture appeared to occur in the case of PPS.

SynopsisBlock copolymers of bisphenol A isophthalate and sebacate were prepared by a two-step interfacial polycondensation. The copolymers had sebacate contents of 1 : 5 and 1 : 3 molar with block lengths (m) of 4,9, and 19. Thermal analysis of the copolymers by DSC showed the T,,, of PBI.The crystallizability of PBI chain segments in the block copolymers was confirmed by X-ray diffraction. The T,,, of the copolymers was primarily influenced by the DP of the chain segments rather than the sebacate content. The Tg of the copolymers was mainly affected by the sebacate content rather than the DP of chain segments. The independent Tg of sehacate in the copolymers was not detected by DSC, i.e., the two polymer chains were compatible without phase separation.Phase separation was only observed in the rheometric spectrum of a 1 : 1 blend of the two homopolymers. The sebacate, being Compatible with the isophthalate, had a plasticizing effect upon the polyarylate, which resulted in an improvement in toughness of the copolymers.

Synopsis"Vinyl esters" were prepared by reacting an epoxy resin (DGEBA) with acrylic and methacrylic acids, modified with Hycar VTBN, and cured at 90°C for 4 h with t-butyl perbenzoate. The resultant materials showed a two-phase structure in electron micrographs and dynamic mechanical spectra. The domain of the dispersed phase was estimated to be on the order of 10 nm in size. Infrared spectroscopy indicated extensive copolymerization of the internal double bonds or pendant vinyl groups in VTBN during the cure of the resin. The mechanical properties of the modified materials were measured, and the differences in mechanical behavior between the acrylic and methacrylic vinyl esters were discussed

Poly(amic acids) (PAAs) were prepared from pyromellitic dianhydride (PMDA) and diamines such as 2,2'-difluoro-, 3,3 '-difluoro-and 2,2'-dichloro-4,4'-methylenedianiline. These PAAs form liquid crystals in N-methyl-2-pyrrolidone (NMP) solution, in addition to the PMDA/4,4'methylenedianiline (MDA) system reported previously. NMP was the only solvent in which liquid crystals were formed. The "liquid crystal" was shown to be a polymer crystallosolvate (PCS) of PAA and NMP. ' H NMR spectroscopy revealed that PAAs derived from PMDA contain isophthalamide and terephthalamide repeating units in nearly equal proportion, which varies slightly between samples prepared in NMP and dimethylacetamide (DMAc). WAXS showed that the PAA from PMDA/MDA is non-crystalline but forms a liquid crystalline state in NMP solution. The rate of crystallization is, however, vastly different between samples prepared in different solvents. This was attributed to their difference in chain conformation, which has to be an extended one for PCS formation. The morphologies of PCS are given, and limitations in PCS formation are discussed in terms of PAA structure and solvent.

SYNOPSISWe have examined the rheological properties of a Co-adsorbed y-Fe203 magnetic suspension with polyurethane (PU) as a binder and methyl ethyl ketone (MEK) or cyclohexanone (CH) as a solvent. A Haake RV20 viscometer was used to measure the suspension viscosity and the vane method was adopted to determine the fluid yield stress. A rheological model which can be viewed as a combination of the Casson model and the Bingham model is proposed to describe the suspension viscosity. The effects of temperature, particle content, and binder concentration are included in the model.