Search results for "PLASTICS"
showing 10 items of 2724 documents
Polymerization of long chain alkyl glycidyl ethers: a platform for micellar gels with tailor-made melting points
2018
Controlled polymerization of long-chain alkyl glycidyl ethers (AlkGE) under anionic ring opening polymerization conditions is enabled by the addition of a crown ether (18-crown-6, K+). Homopolymers with molecular weights in the range of 4000 to 9000 g mol−1 and side chain melting temperatures of 14 °C (C12-AlkGE) and 43 °C (C16-AlkGE), respectively were synthesized. Furthermore, a series of amphiphilic ABA polyether triblock copolymers with polyethylene glycol (PEG) as the hydrophilic central block (Mn = 6k, 10k, and 20k g mol−1) with total molecular weights in the range of 7000 to 28 000 g mol−1 and narrow dispersity (1.12 to 1.34) were prepared. Separate melting endotherms of the triblock…
Role of Topology and Amphiphilicity for Guest Encapsulation in Functionalized Hyperbranched Poly(ethylenimine)s
2004
The promising potential of dendrimers in a variety of areas, such as catalysis, materials science and biomedicine is related to their globular shape, large number of modifiable surface functionalities and the presence of internal reservoirs.1 Their use in liquidliquid-phase transfer protocols, based on the encapsulation of guest molecules as drug delivery vehicles for pharmaceutical application, represents an important issue.2 Unfortunately, dendrimer synthesis is timeconsuming, which currently limits practical use to laboratory scale. For that reason, hyperbranched polymers prepared from ABm-type monomers in one-step processes have gained increasing interest.3 The development of the slow m…
The role of association/complexation equilibria in the anionic polymerization of (meth)acrylates
1992
The kinetics of the anionic polymerization of methacrylates and acrylates in THF as well as the MWD of the polymers formed depend on the concentration of active centres and of additives, such as lithium halides and lithium alkoxides. These results are discussed on basis of multiple equilibria between non-associated, associated, and complexed ion pairs which are supported by viscosity measurements. The position of these equilibria determines the rate of polymerization, whereas the dynamics of interconversion determine the polydispersity. In the absence of additives the rate of monomer addition to non-associated ion pairs competes with the rate of association. Addition of lithium chloride mai…
Composition-dependent Flory-Huggins parameters: molecular weight influences at high concentrations
1995
Flory-Huggins interaction parameters X were determined by means of equilibrium vapor pressures (measured via a combination of a head-space sampler with a gas chromatograph) and light scattering as a function of composition and temperature for the systems cyclohexanone/polystyrene [CHO/PS] and cyclohexanone/poly(butyl methacrylate) [CHO/PBMA]. The investigation of molecular weight influences on X with the system CHO/PBMA demonstrates that they persist almost up to the pure polymer. In order to rationalize this result, it is postulated (in accord with experimental findings and theoretical predictions) that the dimensions of polymer chains may vary upon the addition of solvent even in highly c…
Functional PEG-based polymers with reactive groups via anionic ROP of tailor-made epoxides
2012
In this review article functional epoxide monomers that are suitable for controlled ring-opening polymerization (ROP) are discussed. Functional epoxides possess reactive groups, which either are directly accessible or carry suitable protective groups that can be removed in a facile one-step reaction after polymerization. The methods used to obtain linear, functional aliphatic polyethers rely on living polymerization techniques for the synthesis of well-defined structures. Materials properties, such as thermo-responsive behavior in combination with different functional groups that can be addressed selectively, render these novel materials interesting for a variety of applications.
A road less traveled to functional polymers: epoxide termination in living carbanionic polymer synthesis.
2010
Functional polymers possess tremendous potential both in academia and in industry. In particular, oxiranes offer manifold possibilities for the introduction of single hydroxyl or multiple orthogonal functionalities in carbanionic polymerization. Here, we present a brief overview of the fascinating possibilities arising from the employment of common as well as individually designed epoxide derivatives for the synthesis of end-functional polymers. Continuous flow techniques can be utilized for the rapid generation and screening of precisely defined hydroxyl-modified polymers. The utilization of functionalized polymers as precursors for the formation of complex macromolecular architectures (e.…
Multihydroxyl-Functional Polystyrenes in Continuous Flow
2010
We describe the synthesis of end-functionalized polystyrenes by living anionic polymerization in a microstructured reactor via termination by acetal-protected functional epoxides. Initiation of styrene polymerization by alkyllithium takes place in a micromixing device with efficient heat and mass transfer properties. A newly developed continuous polymerization−termination sequence enabled quantitative functionalization of the living carbanions by nucleophilic displacement with different, specifically designed glycidyl ethers (ethoxy ethyl glycidyl ether (EEGE), 1,2-isopropylidene glyceryl glycidyl ether (IGG), and trans-2-phenyl-1,3-dioxane glycidyl ether (PDGE)). Upon acidic hydrolysis the…
On the viscosity of moderately concentrated solutions of poly(ether imide) in a mixed solvent of marginal quality
2000
Abstract Viscosities η were measured for moderately concentrated (15.5 wt%) solutions of poly(ether imide) (PEI) as a function of the composition of the cosolvent tetrahydrofuran (THF) plus γ-butyrolactone (γ-BL). The solutions are almost by a factor of four less viscous when THF predominates than when γ-BL is the major component of the solvent mixture. Furthermore, the viscosity passes a minimum as the composition of the mixed solvent is varied. Both observations can be well understood in terms of the viscosities of the mixed solvents and the hydrodynamic interaction between the polymer molecules. The pronounced dissymmetry of η as a function of the composition of the mixed solvent η resul…
Preferential evaporation of precipitants from polymer solutions in mixed solvents
2000
Partial vapor pressures were measured for the volatiles of solutions of polysulfone or polyethersulfone in mixtures of N,N-dimethylformamide (DMF, solvent) and water or acetone (precipitants) by means of headspace gas chromatography. The results demonstrate that the enrichment of water in the gas phase increases exponentially with rising polymer concentration, in contrast to that of acetone which remains constant. The reinforced expulsion of water resulting from the presence of polymers is theoretically conceivable and should be useful in the field of separation techniques.