A wide range of infinite urethane polymer networks were prepared from poly(ethy1-ene glycol) (PEG) and hexamethylene diisocyanate (HMDI) using l,l,l-tris-(hydroxymethy1)ethane (THME) as the cross-linking agent. The influence of temperature, cross-linking, and crystallinity on the swelling character of the hydrogel has been discussed. The toxicity of the network polymer by intravaginal implants in rats was studied. Implantation of the polymer did not result in alteration in behavior and feed intake or any pathological changes in the tissue. Vaginal fluids from the polymer-implanted rats or the polymer extract when inoculated on a listeria monocytogene culture plate were unable to inhibit the bacterial growth.

Bis(dibutyldithiocarbamato)metal complexes of cadmium and zinc were synthesized as precursors for growth of thin films of cadmium sulfide (CdS) and zinc sulfide (ZnS) by aerosol-assisted chemical vapor deposition on glass substrates. The decomposition of the precursor complexes was observed by thermogravimetric analysis, and it took place at 350-450 • C with toluene used as the solvent. The CdS and ZnS films were analyzed by X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray analysis. The preferred orientation of the crystallites within the films changed with respect to the deposition temperature. The scanning electron microscopy and energy-dispersive X-ray analysis results showed the uniform distribution of CdS and ZnS in the films, which makes them useful photoconducting materials on a structured surface.

The impregnation of the fiber with a resin system, the polymeric matrix with the interface needs to be properly cured so that the dimensional stability of the matrix and the composite is ensured. A modified epoxy resin matrix was obtained with a reactive toughening agent and anhydride as a curing agent. The mechanical properties of the modified epoxy matrix and its fiber reinforced composites were investigated systematically. The polymeric matrix possessed many good properties, including high strength, high elongation at break, low viscosity, long pot life at room temperature, and good water resistance. The special attentions are given to the matrix due to its low out gassing, low water absorption and radiation resistance. In addition, the fiber-reinforced composites showed a high strength conversion ratio of the fiber and good fatigue resistance. The dynamic and static of the composite material were studied by thermo gravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) with EDX. The influences of processing technique such as curing and proper mixing on the mechanical and interfacial properties were determined. The results demonstrated that the modified epoxy resin matrix is very suitable for applications in products fabricated with fiber-reinforced composites.

SYNOPSISThe polyurethane networks were based on poly(ethy1ene glycol) 6000 (PEG), crosslinked with l,l,l-tris(hydroxy methy1)ethane and with the stoichiometric equivalence of hexamethylene diisocyanate. Radioactive steroids were incorporated into cylindrical hydrogels over a wide range of compositions. The release profiles were drawn from dried down hydrogel of polyurethane networks. The scintillation counter was used for the release study of steroids after different intervals. In viuo, the loaded hydrogels were implanted into rats. The results for constant release studies were recorded. 0 1995 John Wiley & Sons, Inc. I NTRO DUCT10 NStudies of drug release rates from polymeric materials have been made by a number of investigat o r~. ' -~ In a polymeric controlled release system the drugs are released by diffusion, chemicals, swelling, and magnetic processes. The most common mechanism is diffusion through hydrogels, whereby the drug migrates from its initial position in the plastic to the outer surface. In earlier it has been proposed that under certain conditions the rate of diffusion from the surface of the matrix to the surrounding bulk solution makes a significant contribution to the total diffusion process. Haleblian et al.7 also suggested the possibility that the rate of solute transfer across the matrix solution may control the release.In the matrix or monolithic system where the drug is distributed uniformly throughout the polymeric matrix, the drug release does not follow zero-order.8 Lee' has described a n approach to zero-order drug delivery by immobilizing non-uniform drug distribution in hydrogels. Hydrogels can absorb a significant amount of water to form a n elastic gel and a t the same time release the dissolved drug by diffusion through the swollen region.'0," CCC OOZl-8995/95/091301-05 In the present work the influence of hydrogel composition on the resulting release characteristics has been studied. In uiuo, the delivery rates of the drug were determined by surgically implanting or hypodermically injecting the polymeric materials into animals and measuring the radioactivity of steroids at fixed intervals of time. In-vitro, the delivery rates were determined by releasing the steroids in buffer solution a t fixed intervals of time.

Polymer composites are used in numerous applications. In spite of this fact, new developments are still under way to explore in other field of application of these materials and to tailor their properties for more extreme condition. A particular emphasis is focused on fillers content is summarized. Some steps towards the functionally graded materials are illustrated. The FT-IR spectroscopic studies revealed the information about curing of epoxy with fillers. It was observed that mechanical properties like tensile strength, hardness etc get enhanced up with filler contents. The effect of the different formulations were investigated and discussed for optimum process condition.