Search results for " Plastics"
showing 10 items of 2628 documents
Ferrocenyl-functionalized long chain branched polydienes
2009
A convenient two-step approach for the synthesis of ferrocenyl-functionalized long chain branched polydienes, based on both butadiene and isoprene, respectively, is presented. Classical living anionic polymerization was used to synthesize different AB n type poly(diene) macromonomers with moderate molecular weights between 1700 and 3200 g/mol and narrow polydispersity. Quantitative end-capping with chlorodimethylsilane resulted in the desired AB n macromonomer structures. In the ensuing Pt-catalyzed hydrosilylation polyaddition, branched, functionalized polydienes were obtained by a concurrent AB n + AR type of copolymerization with mono-and difunctional ferrocenyl silanes (fcSiMe 2 H or fc…
Interrelation between the thermodynamic and viscometric behaviour of aqueous solutions of hydrophobically modified ethyl hydroxyethyl cellulose
2000
Abstract Aqueous solutions of a commercial sample of hydrophobically modified ethyl hydroxyethyl cellulose (HC, Mw=100 kg/mol, nonylphenol substitution ca. 1.7 mol%) were studied with respect to their demixing behaviour and flow characteristics. Phase separation temperatures were measured turbidimetrically and by determining the first discernible macroscopic phase separation. In some cases demixing was also monitored viscometrically. Phase volume ratios yielded a critical polymer concentration of 1.87 wt.% HC (displaced considerably out of the minimum of the demixing curve towards higher polymer concentrations) and a lower critical solution temperature of 47°C. Model calculations of the spi…
Synthetic approaches towards new polymer systems by the combination of living carbocationic and anionic polymerizations
1996
This study summarizes recent efforts to obtain by combination of living carbocationic and anionic polymerizations block copolymers which are potential precursors for building new well-defined polymeric architectures with microphase separated morphology. Living carbocationic polymerization (LCCP) yields telechelic polyisobutylene (PIB) chains with a variety of useful endgroups, such as tert-chlorine, isopropenyl, primary hydroxyl, tolyl etc. When tolyl-ended PIB was used as precursor for macroinitiator of living anionic polymerization of 2-(tert-butyldimethylsilyloxy)ethyl methacrylate (tBuMe2SiOEMA), mixtures of homopolymers and block copolymers were formed due to incomplete lithiation of t…
Insight into the synthesis of N-methylated polypeptides
2020
The ring-opening polymerization (ROP) of N-carboxy anhydrides (NCAs) is mostly divided into two classes: NCAs of α-substituted amino acids and N-methylated NCAs of α-unsubstituted glycine derivatives (NNCAs). The use of both monomer types offers different mechanistic features and results in a multitude of functional materials. To combine these properties, the synthesis and ROP of α-substituted and N-methylated NCAs (αNNCAs) of several amino acids were investigated. The current study provides insight into the influence of polymerization conditions and the limitations caused by the enhanced steric demand of the amino acid NCA monomers and their N-methylated derivatives. Namely, the effects of…
Stable Expression of Heterologous Sulfotransferase in V79 Cells: Activation of Primary and Secondary Benzylic Alcohols
1994
Abstract A sulfotransferase (ST) capable of activating 1-hydroxymethylpyrene (HMP) and 9-hydroxymethylanthracene (HMA) to mutagens was purified from rat liver. This enzyme appeared to be identical with hydroxysteroid STa, whose cDNA was cloned and stably expressed in Chinese hamster V79 cells. Several primary and secondary benzylic alcohols derived from polycyclic aromatic hydrocarbons induced gene mutations, sister chromatid exchanges (SCE) and/or cytotoxicity in these cells.
Surfactant Assisted Polymerization of Tetrafluoroethylene in Supercritical Carbon Dioxide with a Pilot Scale Batch Reactor.
2008
Chain-free radical polymerization of tetrafluoroethylene (TFE) was carried out in supercritical carbon dioxide (scCO2), at 50 °C and 121–133 bar, with tertiary-amyl-per-pivalate as a free radical initiator, using a 5-L pilot scale batch reactor. Experiments were carried out both in the absence and in the presence of perfluoropolyether (PFPE) carboxylate surfactants. Stabilizers were employed under the free acid form and as sodium and calcium salts. An expanded fibrillated poly(TFE) was obtained in all experiments. In the case of surfactant-free polymerizations, the product was mainly constituted by irregular shape macroparticles having size in the range 200–500 μm. Quite interestingly, when…
Monte Carlo methods for polymer chains in two - dimensional geometries (polymers at surfaces and interfaces)
1993
Coarse-grained models of polymers at interfaces can be defined such that their treatment by Monte Carlo simulation is most convenient and efficient for the problem at hand. This simulation strategy is briefly illustrated with three examples: (1) The orientational ordering of rigid rod-like polymers grafted to a surface, where “table methods” can be used, applying a fine discretization of the angles describing rod orientation. (2) Surface enrichment of one species in a polymer blend is treated by a semi-grand-canonical technique. (3) The number of configurations and structure of a star polymer attached with its center to a wall is studied by a “growth technique” generalizing simple sampling …
Sustainable nanocomposites based on halloysite nanotubes and pectin/polyethylene glycol blend
2013
Abstract This study was focused on the preparation and characterization of biofilms based on pectin/polyethylene glycol 20000 (PEG) blend and halloysite nanotubes (HNTs). The obtained blends loaded with a natural nanoclay are proposed as sustainable alternative to the polymers produced from non-renewable resources such as fossil fuels. Properties of technological interest have been monitored and they were correlated to the structural features of the nanocomposites. It turned out that the wettability of the films can be tuned by changing the composition and the distribution of HNTs into the material as well as the surface roughness. The tensile properties of the blend are enhanced by the pre…
Hetero-Multifunctional Poly(ethylene glycol) Copolymers with Multiple Hydroxyl Groups and a Single Terminal Functionality
2009
Hetero-multifunctional poly(ethylene glycol-co-glycerol) random copolymers with multiple hydroxyl functionalities and a single terminal functionality have been prepared by copolymerization of ethylene oxide (EO) and ethoxy ethyl glycidyl ether (EEGE) with the use of a suitable initiator, introducing a protected amino group or a double bond, respectively. Acidic deprotection was used for removal of the acetal protecting groups in the chain, and the terminal amino group was regenerated by catalytic hydrogenation. A series of copolymers with narrow polydispersity was obtained, varying comonomer fractions from 3 to 67% and molecular weights in the range of 5 000-32 000 g · mol(-1) (1.05 < $\ove…
Networks of Partially Hydrogenatedcis-1,4-Polybutadiene and ‘Rigid Rods’
1996
Networks of 'flexible' and 'rigid' chains were synthesized. As 'flexible' component we have used different partially hydrogenated cis-1,4-polybutadiene. The 'rigid' component was synthesized from bis(1,2,4-triazoline-3,5-dione)s and biscyclohexadienes via repetitive Diels-Alder reaction. A slight excess of bis(1,2, 4-triazoline-3,5-dione)s leads to polymers with 1,2,4-triazoline-3,5-dione end groups, which can easily react with the partially hydrogenated cis-1,4-polybutadiene. The influence of the extent of hydrogenation and the amount of crosslinker on the mechanical and thermal behaviour is described.