Some Interesting Things about Polysiloxanes
Department of Chemistry and the Polymer Research Center, The University of Cincinnati, Cincinnati, OH 45221-0172, USA. Accounts of Chemical Research
(Impact Factor: 22.32).
04/2005; 37(12):946-53. DOI: 10.1021/ar030279z
Poly(dimethylsiloxane) [-Si(CH3)(2)O-] is by far the most studied of the polysiloxanes and is known to exhibit some intriguing physical properties, in particular very high permeability to gases. Simulations are underway in an attempt to understand some of these peculiarities. In addition, other symmetrically substituted polysiloxanes exhibit mesophases that are not understood at all. In the case of cross-linked polysiloxanes, there have been many important developments, including (i) elastomers undergoing strain-induced crystallization through control of chain stiffness or stereochemical structure, (ii) model elastomers (including dangling-chain networks), (iii) possible thermoplastic elastomers, (iv) bimodal network chain-length distributions, and (v) cross linking in solution. Interesting elastomeric composites include those with (i) in-situ-generated ceramiclike particles, (ii) ellipsoidal fillers, (iii) claylike-layered fillers, (iv) polyhedral oligomeric silsesquioxane (POSS) particles, (v) porous fillers, (vi) controlled particle-elastomer interfaces, and (vii) elastomeric domains generated within ceramic phases. Also of interest are some new techniques that have been used to characterize polysiloxane networks.
Available from: Yu-Qi Feng
- "Therefore, facile and versatile fabrication schemes to richen the surface end vinyl groups in the magnetic hybrid architecture for preparing efficient magnetic MIPs as SPE sorbents are highly desirable . Polyhedral oligomeric silsesquioxanes (POSS) are organic–inorganic hybrid materials at a molecular level . A typical polyhedral oligomeric silsesquioxane molecule possesses a cubic rigid (T 8 ) structure represented by the formula R 8 Si 8 O 12 , where the central inorganic core (Si 8 O 12 ) is functionalized with organic moieties (R) at each of the eight vertices . "
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ABSTRACT: This paper reports a nanomagnetic polyhedral oligomeric silsesquioxanes (POSS)-directing strategy toward construction of molecularly imprinted hybrid materials for antibiotic residues determination in milk samples. The imprinted polymeric layer was facilely obtained through the copolymerization of active vinyl groups present on the nanomagnetic POSS (Fe3O4@POSS) surface and functional monomer (methacrylic acid) binding with template (enrofloxacin). Herein, the octavinyl POSS acted as not only the building blocks for hybrid rigid architectures but also the cross-linker for the formation of effective recognition sites during the imprinting process. The molecularly imprinted Fe3O4@POSS nanoparticles (Fe3O4@MI-POSS) demonstrated much higher adsorption capacity and selectivity toward enrofloxacin molecules and its analogs than the non-imprinted Fe3O4@POSS (Fe3O4@NI-POSS) materials. The imprinted particles were applied as a selective sorbent in solid-phase extraction focusing upon sample pretreatment in complex matrices prior to chromatographic analysis. The three FQs (ofloxacin, enrofloxacin, danofloxacin) could be selectively extracted from the biological matrix, while the matrix interferences were effectively eliminated simultaneously under the optimum extraction conditions. A simple, rapid and sensitive method based on the Fe3O4@MI-POSS material combined with HPLC-UV detection was then established for the simultaneous determination of three FQs from milk samples. The average recoveries of the three FQs were in the range of 75.6-108.9%. The relative standard deviations of intra- and inter-day ranging from 2.91 to 8.87% and from 3.6 to 11.5%, respectively. The limits of detections (S/N=3) were between 1.76 and 12.42ngmL(-1). It demonstrates the effectiveness of trace analysis in complicated biological matrices utilizing magnetic separation in combination with molecularly imprinted solid-phase extraction, the rich chemistry of POSS makes it possible to be an ideal platform for generating molecular imprinted hybrid materials is also exhibited.
Journal of Chromatography A 08/2014; 1361. DOI:10.1016/j.chroma.2014.07.089 · 4.17 Impact Factor
Available from: Paulette Spencer
- "In this context, if siloxane groups could be incorporated into the dentin adhesive, it is expected that the durability of the dentin adhesives and compatibility with the silorane composite would be improved. However, polymers with siloxane groups are usually soft, and their mechanical strength may be low because of the flexibility of the siloxane groups   . "
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The objectives of this study were to synthesize two new siloxane-methacrylate (SM) monomers for application in dentin adhesives and to investigate the influence of different functionality of the siloxane-containing monomers on the adhesive photopolymerization, water sorption, and mechanical properties.
Two siloxane-methacrylate monomers (SM1 and SM2) with four and eight methacrylate groups were synthesized. Dentin adhesives containing BisGMA, HEMA and the siloxane-methacrylate monomers were photo-polymerized. The experimental adhesives were compared with the control adhesive (HEMA/BisGMA, 45/55, w/w) and characterized with regard to degree of conversion (DC), water miscibility of the liquid resin, water sorption and dynamic mechanical analysis (DMA).
The experimental adhesives exhibited improved water miscibility as compared to the control. When cured in the presence of 12 wt% water to simulate the wet environment of the mouth, the SM-containing adhesives showed DC comparable to the control. The experimental adhesives showed higher rubbery modulus than the control under dry conditions. Under wet conditions, the mechanical properties of the formulations containing SM monomer with increased functionality were comparable with the control, even with more water sorption.
The concentration and functionality of the newly synthesized siloxane-methacrylate monomers affected the water miscibility, water sorption and mechanical properties of the adhesives. The experimental adhesives show improved water compatibility compared with the control. The mechanical properties were enhanced with an increase of the functionality of the siloxane-containing monomers. The results provide critical structure/property relationships and important information for future development of durable, versatile siloxane-containing dentin adhesives.
Dental materials: official publication of the Academy of Dental Materials 06/2014; 30(9):1073-1087. DOI:10.1016/j.dental.2014.06.004 · 3.77 Impact Factor
Available from: Dongzhi Chen
- "m/ l o ca t e / p o l y d e g s t a b elastomeric networks make the polymer to be a promising precursor for the preparation of new hybrid materials [18e20]. The Sie OeSi backbone, which provides this polymer with unique characteristics , of PDMS chains is one of the most flexible chains, owing to the strength of the SieO bond giving siloxane polymers considerable thermal stability . Up to present, PDMS has been still intensively explored for its unique properties, such as high permeability , low surface free energy, low viscosity, unexpected mesophase , low gas transition temperature, excellent thermal stability and low chemical reactivity [22e24]. "
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ABSTRACT: A novel cross-linker (denoted as PH) prepared using vinyl-POSS and poly(methylhydrogensiloxane) (PMHS), was introduced to vinyl terminated polydimethylsiloxane (VPDMS) matrix to prepare a series of addition-type silicone rubbers (ASR) for the first time. Morphology, thermal properties and mechanical properties of these ASR were respectively studied by means of scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and universal tensile testing machine. The results revealed that the thermal stabilities and mechanical properties of ASR were significantly enhanced by the addition of PH compared with the traditional cross-linker PMHS. It was found that the tensile strength of ASR prepared using PH as cross-linker was strikingly increased by 43.8% compared with the one prepared using PMHS as cross-linker. The striking enhancements in thermal properties and improvements on mechanical properties of ASR were likely attributed to the increase of dimensionality of novel cross-linked networks in novel ASR.
Polymer Degradation and Stability 04/2013; 98(4):916–925. DOI:10.1016/j.polymdegradstab.2013.01.009 · 3.16 Impact Factor
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