Rumiana Velichkova

New thermo-responsive polymer materials based on poly(2-ethyl-2-oxazoline) segments

Abstract First, the solution behavior of poly(2-ethyl-2-oxazoline) (PEtOx) in water has been investigated. The dependence of the cloud points on the molecular weight and concentration indicates a typical Flory–Huggins (Type I) demixing behavior with a lower critical solution temperature (LCST). Secondly, the synthesis and properties of temperature-responsive hydrogels and segmented polymer networks, based on PEtOx bis-macromonomers, are reported. PEtOx hydrogels have been prepared by UV-induced radical polymerization of the corresponding α,ω-bis-acrylates. The networks exhibited a continuous shrinkage with increasing temperature. Series of segmented networks with LCST-behavior have been obtained by free radical copolymerization of PEtOx bis-macromonomer with the comonomers 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl acrylate (HPA) or methyl methacrylate (MMA). The LCST-behavior of the materials is controlled by varying the philicity of the comonomer and the fraction of PEtOx in the networks. PHEMA–PEtOx and PHPA–PEtOx hydrogels exhibited a large and reversible swelling–deswelling process, whereas the volume changes in PMMA–PEtOx swollen networks were small and occurred in a broad temperature interval.

Amphiphilic segmented polymer networks based on poly(2-alkyl-2-oxazoline) and poly(methyl methacrylate)

Amphiphilic segmented polymer networks (SPNs) have been prepared by free radical copolymerization of methyl methacrylate with α,ω-bisacrylate terminated poly(2-methyl-2-oxazoline) and poly(2-ethyl-2-oxazoline). DSC and DMTA analysis demonstrated the influence of the copolymer composition, the molecular weight and nature of the poly(2-alkyl-2-oxazoline)s and the polymerization conditions on the final phase morphology of the networks. A comparative phase morphology study of the polymer blends and SPNs revealed the more compatible phase morphology of the networks. The compatibility could be further increased by UV-induced network formation. The investigation of the solvent uptake in different solvents clearly demonstrated the amphiphilic nature of the SPNs.

Amphiphilic polyelectrolyte networks derived from 2-oxazolines

Abstract Ionene graft copolymers and networks containing quaternary ammonium groups as linkages have been prepared by termination of living mono- and bifunctional poly(2-methyl-2-oxazoline) and poly(2-phenyl-2-oxazoline) with poly(dimethylaminoethyl methacrylate). Ionene networks of different density with p , p ′-dichloroxylene and poly(2-alkyloxazoline)s as cross-linkers have been synthesized. The obtained graft and crosslinked copolymers are well defined and with controlled hydrophilic–hydrophobic balance. Viscosity examination and potentiometric titration of some of the products were carried out. Sorption ability towards Cu 2+ , Ni 2+ , Mn 2+ , Fe 3+ and anion-exchange capacity were investigated as well. The pH dependence of the sorption of metal ions was evaluated.

Preparation and hydrolysis of poly(ethylene-graft-oxazoline)s and poly(vinyl acetate-graft-oxazoline)s

Abstract Polyvinyl acetate- co -polyvinyl tosylates and polyethylene- co -polyvinyl tosylates were synthesized via tosylation of poly(vinyl acetate- co -vinyl alcohol) and poly(ehhylene- co -vinyl alcohol). Grafting of 2-methyl-2-oxazoline and 2-phenyl-2-oxazoline was performed using polytosylates as macroinitiators. Appropriate hydrolyzed analogues were prepared. The swelling properties and sorption capacity towards Cu 2+ and Fe 3+ of the graft copolymers and their corresponding hydrolyzed products were investigated.

Branched polymers starting from ethylene-vinyl acetate copolymers

Abstract Polyethylene-graft-poly-2-phenyl-2-oxazoline, polyethylene-graft-poly-2-methyl-2-oxazoline and polyethylenegraft-poly(ethylene oxide) were prepared using poly(ethylene-co-vinyl chloroformate) as macroinitiator or polyfunctional precursor. The vinyl acetate groups of ethylene-vinyl acetate copolymer were hydrolyzed, the corresponding alcohol functions were converted into chloroformate, which in turn was used for grafting of oxazolines. Comb-like polymers with hydrophilic poly(ethylene oxide) grafts with definite length were synthesized as well. The resulting graft copolymers were characterized by GPC, IR, and 1 H-NMR spectroscopy and differential scanning calorimetry.

Glutaraldehyde-crosslinked poly(glycidol-block-ethylene oxide-block-glycidol) networks with temperatureresponsive swelling behaviour

Abstract In order to obtain temperature-responsive hydrogel networks, poly- (glycidol-block-ethylene oxide-block-glycidol) copolymers were chemically crosslinked by using glutaraldehyde and tetraethoxysilane in a sol-gel reaction. The crystallinity of copolymer networks prepared has been estimated by differential scanning calorimetry. Thermo-responsive properties were evaluated by measuring the equilibrium swelling degree for a series of copolymer hydrogels as a function of temperature.

Synthesis and Properties of Amphiphilic and Functional Copolymers and Networks

Well-defined amphiphilic and functional copolymers and networks based on cyclic ethers, oxazolines and aziridines were prepared. The synthesis of copolymers with controlled hydrophilic-hydrophobic balance, composition and structure was achieved using sequential living cationic polymerization, copolymerization of macromonomers, functionalization of conventional polymers and following grafting or crosslinking by telechelic polymers. Properties, displaying the amphiphilic nature of the copolymers were examined: solubility, swelling in water and hydrocarbons. Anion-exchange and sorption capacity towards metal ions of the copolymers bearing quatemary ammonium groups were evaluated. Environmentally responsive conformational changes, aggregation and microphase separation were observed for some of the products.