Eric J. Goethals

Phase behaviour of poly(N-vinyl caprolactam) in water

Abstract The solution behaviour of the system poly(N-vinyl caprolactam)/water has been studied. Experiments and theoretical calculations indicate a typical Flory–Huggins (Type I) demixing behaviour with a lower critical solution temperature (LCST). The critical concentration and LCST shift to lower values with increasing molar mass of the polymer. The phenomenological description of such a system predicts a continuous temperature controlled swelling behaviour of the corresponding network. A comparison with literature data confirms this prediction. A calorimetric study of the crystallisation and melting behaviour of water and the concentration dependence of the glass transition temperature, gives no evidence for the formation of a polymer/solvent complex.

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.

Polymer networks containing crystallizable poly(octadecyl vinyl ether) segments for shape-memory materials

New polymer networks were prepared by free radical initiated copolymerization of crystallizable α,ω-bismethacrylate-terminated poly(octadecyl vinyl ether) (polyODVE) with butyl acrylate (BA). The polyODVE bismacromonomers were obtained by end-capping the bifunctionally living cationic polymerization of ODVE with 2-hydroxyethyl methacrylate (HEMA). The segmented networks show a high degree of phase separation over a wide range of compositions. The shape memory properties of a material containing 20 wt.-% of polyODVE are reported.

End group analysis of commercial poly(ethylene glycol) monomethyl ether's

SummaryAnalysis of the hydroxyl content of a series of commercial poly(ethylene glycol)monomethy1 ethers by means of 360 MHz 1H NMR spectroscopy of the trichloroacetyl isocyanate modified polymers has shown that some compounds contain considerable amounts of poly(ethylene glycol).

Segmented network structures for the separation of water/ethanol mixtures by pervaporation.

α,ω-Acrylate terminated poly(1,3-dioxolane) (polyDXL), was used as a hydrophilic cross-linker of hydrophobic poly(methyl methacrylate) (polyMMA) chains for the synthesis of amphiphilic AB-block copolymer networks. The application of these segmented networks as membranes for dehydration of water/ethanol mixtures by the pervaporation technique was investigated. Because the cross-links inhibit to a great extent phase separation between the components of these materials, as revealed by dynamic mechanical thermal analysis, an optimal control of the membrane characteristics could be achieved by variation of the hydrophilicity–hydrophobicity balance and the cross-link density. The combination of desorption experiments, determination of swelling degrees and calculation of deviation coefficients (e) allowed us to demonstrate in these membranes the existence of a so-called coupling effect. It was shown that polyDXL plays a predominant role in the specific interactions between the membrane and the solvents, which cause the preferential water transport in all the membranes over the whole composition range of the feed mixture.

New synthesis of linear polyethyleneimine

SummaryLinear polyethyleneimine was synthesized by the cationic ringopening polymerization of N(2-tetrahydropyranyl)aziridine, followed by acidic hydrolysis of the corresponding substituted polyamine. The linear structure of the end product was proved by 13C-NMR spectroscopy and by its physical properties. Molecular weights up to 25,000 were obtained.

Thermoresponsive Properties of Poly(N‐vinylcaprolactam)‐Poly(ethylene oxide) Aqueous Systems: Solutions and Block Copolymer Networks

Two- and three-dimensional phase diagrams have been constructed for thermosensitive poly(N-vinyl-caprolactam)-poly(ethylene oxide) (PVCL-PEO) aqueous systems. Both solutions and swollen block copolymer networks have been investigated to elucidate the effect of th copolymer content and crosslinking density on their temperatures of phase separation (T ph.s ). The introduction of hydrophilic PEO into an aqueous solution of PVCL decreases its T ph.s . This suggests that the strength of the hydrogen bonds within the thermoresponsive PVCL-water system is weakened by the introduction of PEO that also interacts with water. Based on the DSC investigation the swollen networks, it was found that the influence of PEO on the phase behavior of weakly crosslinked networks is comparable with that of PVCL-PEO-H 2 O solutions. For networks with a higher degree of crosslinking, the presence of the crosslinks is of major importance for the explanation of the T phs location. This detailed phase analysis led to the proposal of an irregular water distribution in these swollen networks.

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.

New Materials from poly(vinyl ethers)

This paper gives an overview of the synthesis and properties of various kinds of amphiphilic segmented copolymers in which at least one of the segments is a poly(alkyl vinyl ether). Copyright

Synthesis and reactions of poly-tetrahydrofuran with azetidinium salt end-groups

The bulk polymerization of tetrahydrofuran (THF) intiated by methyl trillate or triflic anhydride leads to poly-THFs of polydispersity < 1.2 and possessing one or two oxonium chain ends, if the conversion is kept below 15%. Reaction of these “living” polymers with an N-substituted azetidine leads to the corresponding poly-THFs with one or two quaternary azetidinium chain ends. These polymers can be isolated in pure form by precipitation in water without affecting the azetidinium functions. At increased temperature, these functions undergo ring-opening reactions with nucleophiles. This process has been used to prepare block-copolymers and polymer networks containing poly-THF segments and to synthesize mono or bifunctional ester-terminated poly-THFs. The last reaction is achieved by simple precipitation of the azetidinium-terminated poly-THF into an aqueous solution of the sodium carboxylate at room temperature.