Toughened unsaturated polyesters were prepared by chemical reaction, physical blending, and block copolymerization method, respectively. Mechanical proper ties of thus formed unsaturated polyesters after curing were compared. The superior per formance of block copolymers was explained with dynamic test and morphology study. Mechanical properties of their sheet molding compounds were studied as well.
Block copolymers of unsaturated polyester were prepared by cocondensation polymerization of hydroxyl-or carboxyl-terminated liquid rubbers or polyethylene glycols in the presence of maleic anhydride, phthalic anhydride, and propylene glycol. The resultant unsaturated polyesters were then diluted with styrene monomer and cured by using peroxide and heat. The mechanical properties of the cured block copolymers were determined and compared with those of a control resin or a corresponding toughened physical blend. In addition, the sheet-molding compounds made with these polyesters were obtained and investigated. (1-3). Chemical mod ifications by introducing either long-chain glycols (e.g., diethylene, dipropylene, or triethylene glycol) or long-chain saturated dibasic acids (e.g., adipic acid or sebacic acid) are common practice. However, a significant amount of such long-chain substances is needed to impart a sufficient im provement in toughness. This requirement, in turn, results in a large sacrifice of other mechanical properties. IMPROVEMENT OF THE FRACTURE TOUGHNESS and impact resistance of rigid unsaturated polyester has played an important role in the development of high-performance polymeric composites. Unsaturated polyesters can be modified by numerous chemical and physical methodsAmong physical modifications, the use of dispersed elastomers for en hancement of toughness in unsaturated polyester resins and molding ma terials has frequently been reported (4-17). These elastomers include both solid and liquid rubbers.
Polyurethane (PU) has outstanding properties, and has been applied in many fields. In general, it is prepared by the reaction of diisocyanate, polyol, chain extender, surfactant, catalyst, filler, reinforcement and blowing agent, etc. Most studies are based on the use of aliphatic chain extender such as 1,4-butanediol. The disadvantage is their low sag temperature.In this study, the aromatic diols such as bis (hydroxyethyl) terephthalate, bisphenol A and hydroquinone are used to replace aliphatic diols commonly used in the conventional PU recipe. Thus, formed products are characterized and their mechanical and thermal properties are investigated. Results show that the products have the better mechanical property and the outstanding thermal resistant property.Due to the high melting point or the higher viscosity of the aromatic diols at room temperature, products are prepared by high temperature reaction molding. This system can be performed by modified RIM process.
Most treatments of moving spatially extended sources in some way model the source as a point. Thus, in effect they approximate the solution by the first term in a multipole expansion. The latter is similar to a Taylor expansion in the sense that it is valid when evaluated at a retarded time at which the velocity has time derivatives of all orders [T. J. Eisler, J. Acoust. Soc. Am. 52, 210 (1972)]. In contrast, the present treatment is similar to an eigenfunction expansion which can be used for less regular functions, for example, a velo-city-versus-time curve which has a corner. We find that such singularities cause a burst of sound radiation. Our method, which is applicable to source distributions which move as a rigid sphere, is based on an expansion theorem for spherical wave functions [R. A. Sack, J. Math. Phys. 5, 252 (1964)]. This is used to expand the integrand of the retarded solution of the wave equation, and the resulting expansion can be summed in certain special cases. The solution is found to depend on the history of the source over an interval of finite duration which includes the retarded time of the center. The method has been applied to a moving rigid sphere using the theory of Ffowcs-Williams and Hawkings [Phil. Trans. Roy. Soc. London A264, 321 (1969)].
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