A facile method for the preparation of gold nanoparticles (AuNPs) with various morphologies, including triangles, cubes and nanospheres into a urethane methacrylate polymer matrix, has been developed. The hybrid nanocomposites have been obtained by photoreduction of a gold precursor in the presence of a 30 wt% urethane methacrylate containing quaternary ammonium structure and 70 wt% functional monomer, carboxyl oligo-urethane dimethacrylate. The final materials contain gold nanoparticles with a morphology dependant on the reaction conditions. The influence of photonic and chemical parameters on the shape of the nanoparticles has been examined. Specific interactions between the macromolecular network and the nascent particles play an important role insofar as they control the access of metal atoms to the different crystalline planes of the growing nanoparticles, which is necessary to obtain anisotropic objects. A common mechanism for the formation of the various types of AuNPs is proposed. Coupling the intrinsic characteristics of metal nanoparticles with those of the copolymer substrate could result in materials with innovative properties.

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New urethane dimethacrylate oligomers functionalized with carboxylic acid groups (CAd-1Ä4) were synthesized and evaluated as co-monomers in dental resin composites. Photopolymerization of these oligomers containing polyethylene oxide spacer was monitored by FT-IR spectroscopy comparatively with the low molecular monomer (CAd-M), as well as by fluorescence technique. The polymerization shrinkage for several mixtures including the urethane oligomers and BisGMA/ TEGDMA system was determined and, for some cured specimens, the equilibrium water uptake, water sorption and contact angle were measured to establish their behaviour into a wet environment. The compatibility between the organic and inorganic phase was investigated by SEM analysis in fractured surfaces indicating the formation of compact homogeneous materials. Aspects of the crack propagation behaviour of some composites subjected to Vickers indentation were examined by polarizing optical microscopy (POM) and atomic force microscopy (AFM), a visible crack being visible only in AFM image. Mechanical properties (compressive and diametral tensile strengths), determined for several resins composites, sustains the formation of materials with a hardness comparable to those frequently encountered in dental practice.KEY WORDS: Dimethacrylate Oligomers / Carboxylic Groups / Dental Composites / For decades, the commercial monomer systems intended for dental anatomy restorative applications continue to utilize bisphenol A-glycidyl dimethacrylate (BisGMA) as main component taken in combination with triethyleneglycol dimethacrylate (TEGDMA) as viscosity diluents, the latter being responsible of some deficiencies that restrict the service life and performance of the resin composites.1,2 Previous studies revealed that all acrylic formulations manifest a significant volumetric contraction that accompanies ambient polymerization of the composite matrix, followed by a polymer ageing that creates undesired effects to the users.3-5 Moreover, susceptibility to water sorption and incomplete conversion of the double bonds affects the physical and mechanical properties of the formed composites. 6,7 In order to improve the characteristics of the composite materials, the approached strategies include maximization of the filler amount and/or formulating of organic phase based on BisGMA analogous, 8,9 liquid crystalline or hiperbranched monomers, 10,11 sol-gel polycondensates 12 among other things. In tandem, a series of multi-ethylene glycol dimethacrylates of various lengths were also used as co-monomers (up to 30%) in the organic phase owing to the notable effect on the ultimate conversion, volumetric shrinkage and mechanical properties. 13 Moreover, an increased double-bond conversion in the final polymer matrix is desirable to enhance biocompatibility and reduce swelling in the later systems, compared to that of lowmolecular weight monomers (diethylene glycol dimethacrylate (DEGDMA) or TEGDMA) used currently in dental filling composites.14 Among the mentioned issues, performing of...

New polyurethane cationomers synthesized by a two-step substitution postreaction of urethane hydrogen atoms with nitroazobenzene groups were studied. As a starting polymer, a polyurethane based on poly(tetramethylene oxide)diol, isophorone diisocyanate, and 2,6-bis(hydroximethyl)pyridine was used. After a preliminary metalation of the above polymer with natrium hydride, by reaction of polyurethane N-sodate with 4-nitro-4Ј(␤Ϫiodoethylurethane)azobenzene, chromophoric groups between 2.85 and 10.53 wt % could be incorporated instead of hydrogen. Such polymers partially functionalized with azobenzene and further quaternized with methyl iodide led to the formation of pyridinium polyurethane cationomers N-modified with nitroazo groups. The photosensible properties of the azobenzene chromophore in a polymer solution and film state indicated important differences in their photoresponse. In the polymer solution, the trans-cis photoisomerization of the chromophore is accompanied by an irreversible photobleaching effect, while under the same UV irradiation conditions, the ionomeric films exhibited an enhanced photostability.

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