Home About us Contact
|
Home About us Contact | ||
|
|
||
Residual Monomer (residual + monomer)
Selected AbstractsPolylactide copolymers: Effect of copolymer ratio and end capping on their propertiesADVANCES IN POLYMER TECHNOLOGY, Issue 2 2005D. M. Bigg Abstract Racemic copolymers of polylactic acid were investigated to determine the effect of copolymer ratio on melting point, degree of crystallinity, mechanical properties, and processing behavior. The copolymer ratio was found to have a strong influence on the crystallization behavior of the polymer. In addition to the ratio of the L -form to a random mixture of the D and L forms of the lactic acid in the copolymer, the effect of the polymer's molecular weight was examined. The copolymers were produced from the lactide form of the monomer to achieve weight average molecular weights above 100,000. The molecular weight had a profound influence on processability and rate of crystallization. Other notable factors influencing the properties and processing of the copolymers were the concentration of residual monomer in the polymer, the processing time-temperature history, and the extent of molecular weight degradation during processing. An important factor in the commercial development of biodegradable polymers is the ability to control the rate of degradation. Ideally, the polymer should not degrade during functional use, but degrade quite rapidly when discarded. This paper discusses various aspects associated with the control of the rate of degradation of polylactide copolymers; both from the perspective of stabilizing the polymer during processing and product use, and subsequently accelerating the rate of degradation after disposal. Of particular interest are the influences of molecular weight, crystallinity, end capping, and plasticization. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24:69,82, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20032 [source] Bending strength and depth of cure of light-cured composite resins irradiated using filters that simulate enamelJOURNAL OF ORAL REHABILITATION, Issue 1 2004H. Arikawa summary, This study evaluates the light-attenuating effects of enamel on the properties of light-cured restorative resins using simple experimental filters. Three filters were designed to replicate the light transmittance characteristics of 0·5, 1·0 and 1·5 mm thick human enamel. The bending strength, depth of cure, and levels of residual monomer for 12 shades of three commercial light-cured composite resins were examined. These resins were cured either using direct irradiation from a light source or irradiation through one of the filters. For all materials, the bending strength and depth of cure of specimens irradiated through a filter were lower and the levels of residual monomer were higher than those found in specimens irradiated directly. The results indicate that the light-attenuating effect of enamel reduces the polymerization efficiency, resulting in poorer mechanical properties of light-cured composite resins. [source] In vitro cytotoxicity of dental composites based on new and traditional polymerization chemistries,JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2007M. Goėl Brackett Abstract The biological response to dental restorative polymer composites is mediated by the release of unpolymerized residual monomers. Several new composite formulations claim to reduce unpolymerized residual mass. The current study assessed the cytotoxic responses to several of these new formations and compared them with more traditional formulations. Our hypothesis predicted that if these new polymerization chemistries reduce unpolymerized residual mass, the cytotoxicity of these materials also should be reduced relative to traditional formulations. Methods: Materials (HerculiteXRV, Premise, Filtek Supreme, CeramxDuo, Hermes, and Quixfil) were tested in vitro in direct contact with Balb mouse fibroblasts, initially, then after aging in artificial saliva for 0, 1, 3, 5, or 8 weeks. The toxicity was determined by using the MTT assay to the estimate SDH activity. Knoop hardness of the materials also was measured at 0 and 8 weeks to determine whether surface breakdown of the materials in artificial saliva contributed to cytotoxic responses. Results: Materials with traditional methacrylate chemistries (Herculite, Premise, Filtek Supreme) were severely (>50%) cytotoxic throughout the 8-week interval, but materials with newer chemistries or filling strategies (Hermes, CeramXDuo, and Quixfil) improved over time of aging in artificial saliva. Hermes showed the least cytotoxicity at 8 weeks, and was statistically equivalent to Teflon® negative controls. Hardness of the materials was unaffected by exposure to artificial saliva. Conclusions: Newer polymerization and filling strategies for dental composites show promise for reducing the release of unpolymerized components and cytotoxicity. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Fabrication of high-performance, gradient-refractive-index plastic rods with surfmer-cluster-stabilized nanoparticlesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2006Jui-Hsiang Liu Abstract A novel method was developed with surfmer-cluster-stabilized silver nanoparticles to prepare high-performance, gradient-refractive-index (GRIN) plastic rods based on methyl methacrylate. To fabricate the GRIN plastic rods, a novel polymerizable surfactant (surfmer) of 4-(11-acryloxyundecyloxy)benzoic acid (AUBA) was synthesized. Silver nanoparticles were prepared with a reverse micelle method in the presence of the novel surfmer. During the fabrication of the silver nanoparticles, the sodium salt of AUBA was formed. GRIN plastic rods were fabricated through centrifugal polymerization and then were heat-treated at 100 °C under 0.1 Torr for 24 h to remove residual monomers and water. The distribution of the surfmer-cluster-stabilized nanoparticles inside the plastic rods was studied with transmission electron microscopy (TEM). The real-image transmission through the fabricated rods was also confirmed. The results obtained in this investigation suggested that the control of the distribution of surfmer-cluster-stabilized nanoparticles could be used to fabricate GRIN rods. Furthermore, the existence of the crosslink-like surfmers increased the thermal stability of the plastic rods. The GRIN distribution of the rods was established by the dispersion of nanoparticles inside the plastic rods through TEM analysis, refractive-index analysis, and real-image transmission. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5933,5942, 2006 [source] | ||||||||||