Search results for "Plastics"
showing 10 items of 2724 documents
Cooperative structure formation by combination of covalent and association chain polymers: 4. Designing functional groups for supramolecular structur…
1991
Abstract A small number of polar functional groups are attached to polybutadiene by a polymer analogous reaction. Depending on their molecular structure, different degrees of supramolecular ordering result from the aggregation of these polar groups. In the case of phenylurazole units, which carry a single site for hydrogen-bond complexation, binary contacts are formed; whereas linear association chain structures are formed in the case of polybutadiene carrying phenylurazole units additionally substituted with a carboxy group in meta or para positions of the phenyl ring. In the latter case, association chains aggregate cooperatively to an ordered supramolecular structure. The different struc…
Hairy Aramide Rod−Coil Copolymers
2010
We have synthesized monodisperse “hairy rod oligomers” based on oligo(p-benzamide)s carrying alkyl side chains and conjugated them with polydisperse poly(ethylene glycol) (PEG) chains. The well-defined oligomers were synthesized from 4-amino-2-hexyloxybenzoic acid using a commercial peptide synthesizer. The PEG conjugated hairy rod−coil block copolymers self-assemble in polar and nonpolar organic solvents. The self-organization in solution was investigated by dynamic light scattering (DSL) and transmission electron microscopy (TEM) as a function of solvent, equilibration time, and polarity of the substrate. Individual fibers and fiberlike bundles of aggregates could be observed. As all hydr…
Chemoenzymatic synthesis of a poly(hydroquinone)
1999
Chemoenzymatic synthesis of a poly(hydroquinone) was achieved by enzymatic oxidative polymerization of 4-hydroxyphenyl benzoate, followed by alkaline hydrolysis of the resulting polymer. The polymerization of 4-hydroxyphenyl benzoate was performed using a peroxidase and hydrogen peroxide as catalyst and oxidizing agent, respectively, in an aqueous organic solvent. Soybean peroxidase afforded the polymer in good yields. IR analysis of the polymer showed the formation of the polymer consisting of a mixture of phenylene and oxyphenylene units. By alkaline hydrolysis of the resulting polymer, benzoate moiety was completely removed to give poly(hydroquinone).
A Facile Two-Step Route to Branched Polyisoprenes via ABn-Macromonomers
2007
A facile two-step synthesis for branched poly(isoprene)s (PI) based on polyaddition of AB n -type macromonomers is described. The synthesis of the macromonomers was achieved by anionic polymerization of isoprene and subsequent end-capping of the polymers by addition of chlorodimethylsilane to the living carbanions. This led to PI-based macromonomers with narrow polydispersity (M w /M n < 1.15) and molecular weights in the range of 1700 -22100 g mol -1 . Synthesis of the branched polymers was carried out by a hydrosilylation-based polymerization of the macromonomers. Characterization via SEC, SEC-MALLS, coupled SEC-viscosimetry and 1 H-NMR-spectroscopy supported the formation of branched str…
Synthesis of aldonamide siloxanes by hydrosilylation
1998
Abstract The synthesis of hydrophobic/hydrophilic hybrid polymers based on polydimethylsiloxanes (PDMS) and carbohydrate derivatives involving a hydrosilylation step is reported. Starting with poly(dimethyl- co -hydromethyl)siloxanes (PDMS- co -HMS), O -acetylated N -allylaldonamides of various sugars can be attached to the siloxane backbone using platinum catalysts. The characteristics of different transition metal complexes in the polymer-analogous formation of SiC bonds are investigated. A generalized reaction pathway applicable to several reducing carbohydrates is established to synthesize aldonamide siloxanes in a broad variety of molecular weight and composition. The products obtaine…
Immobilization of enzymes by multilayer microcapsules
1994
A method is described to obtain a new type of microcapsules for immobilization of enzymes or living cells. The wall of these capsules consists of several layers of poly(ethyleneimine) and poly(acrylic acid). The idea is that diverging properties of the whole assembly can be better controlled when the membrane is built up by several consecutive steps, each being optimized with respect to a special property, for example, permeability or mechanical strength. The encapsulation of acidic phosphatase and the cleavage of p-nitrophenyl phosphate was used as a model system. The charged capsules were characterized by their enzymatic activity, as a function of membrane composition (number and sequence…
Gamma-radiation ageing of a low density polyethylene. Effects of irradiation temperature and dose rate
1993
Abstract Ageing due to gamma radiation of a low density polyethylene at various dose rates and temperatures is studied; the effect of thermal treatment only is also considered. The modifications induced in the molecular and crystallinity behaviour of the polymer are investigated by means of gel extraction, measurements of intrinsic viscosity and thermal analysis. Results indicate the occurrence of both crosslinking and oxidative degradation; the extent of the latter increases on decreasing the irradiation dose rate and on increasing the irradiation temperature. Some exceptions are found because of the increase in the mobility of free radicals at high temperature. These effects modify also t…
Comparison of living polymerization systems
1994
Recent developments in the field of living polymerization are surveyed. Comparison of the available mechanistic and kinetic information is made for living anionic, cationic, free radical, group transfer, ring-opening metathesis, Ziegler-Natta and immortal polymerizations. This evaluation indicates that the majority of living polymerizations involve quasiliving equilibrium between active (propagating) and dormant (nonpropagating) polymer chains. On the basis of the kinetics of a general model for quasiliving and ideal living polymerizations it is concluded that ideal living polymerization is a special subclass of quasiliving polymerizations. Classification of living polymerization systems is…
Rapid Synthesis and MALDI-ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers
2009
Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well-defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5-8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30000g · …
Microstructure analysis of biocompatible phosphoester copolymers
2013
Copolymers with varying compositions of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane (EEP) and 2-ethoxy-4-methyl-2-oxo-1,3,2-dioxaphospholane (EMEP) have been synthesized via 1,5,7-triazabicyclo[4.4.0]dec-5-ene-catalyzed anionic ring-opening polymerization. The molecular weights and comonomer ratios were well controlled and polymers with reasonable molecular weight distributions (<1.5) were obtained in all cases. The copolymers were investigated by 1H and 31P NMR spectroscopies to determine the underlying microstructure via detailed dyad analysis. The copolymers were found to be nontoxic to HeLa cells. Furthermore, the obtained copolymers of EEP and EMEP show thermoresponsive properties, i.e., exh…