Segmented Polymer Networks Research Articles

Covalent segmented polymer networks composed of poly(2-isopropenyl-2-oxazoline) and selected aliphatic polyesters: designing biocompatible amphiphilic materials containing degradable blocks.

To promote facile and efficient synthesis of segmented covalent networks, we developed a cross-linking process with reactive polymeric components in a system without catalysts or side products. To achieve the direct formation of amphiphilic networks, an addition reaction was performed between the polyesters containing carboxyl terminal groups with pendant groups distributed along poly(2-isopropenyl-2-oxazoline) chains. Covalent cross-linking was achieved from predetermined amounts of components dissolved in DMSO at 140 °C. To tune the properties of the resulting networks, the composition and length of the polyester segments and the degree of cross-linking were changed in the feed. The chemical structure of the networks was characterized using Fourier transform infrared-attenuated total reflection spectroscopy and 13C magic-angle spinning NMR. The swelling ability of the formed networks was investigated in aqueous and organic media. Moreover, mechanical properties were tested during uniaxial compression. The cytocompatibility of the scaffolds was confirmed by MTT assay. Through the results obtained, the first report describing the cross-linking of polyesters on hydrophilic PiPOx was provided to prepare new, biocompatible materials with tuneable properties that are promising for potential biomedical applications.

Multifunctional Membranes for Solvent Resistant Nanofiltration and Pervaporation Applications Based on Segmented Polymer Networks

Hydrophilic bis(acrylate)-terminated poly(ethylene oxide) was used as macromolecular cross-linker of different hydrophobic polyacrylates for the synthesis of amphiphilic segmented polymer networks (SPNs). Multifunctional composite membranes with thin SPN toplayers were prepared by in situ polymerization. As the support consisted of hydrolyzed polyacrylonitrile, the high chemical resistance of the composite membrane allowed applications of the SPN-based membranes in solvent-resistant nanofiltration (SRNF) and pervaporation (PV). The membranes show very high retention on Rose Bengal (RB) in different solvents, especially in strong swelling solvents such as tetrahydrofuran (THF) and dimethylformamide (DMF). The membranes were also tested in pervaporation for dehydration of ethanol and isopropanol (IPA). The selectivity of the membranes greatly depends on the composition or the ratio of the hydrophilic and hydrophobic phases of the SPN.

Solid state NMR study of segmented polymer networks: fine-tuning of phase morphology via their molecular design

Segmented polymer networks (SPNs) based on thermo-sensitive poly(N-isopropyl acryl amide) (PNIPAA) and poly(tetrahydrofuran) (PTHF) have been synthesized by free radical copolymerization of PTHF bis-macromonomers with N-isopropyl acrylamide. The nature of the polymerizable end group on the bis-macromonomer has been varied, respectively from acrylate to acrylamide end groups. The multiphase behaviour of the corresponding SPNs has been examined as a function of the nature of the end group by making use of solid-state 13C CP/MAS NMR relaxometry, 1H wideline NMR relaxometry and dynamic mechanical analysis (DMA). When PTHF with acrylate end groups was used during the SPN formation, analysis of proton spin-lattice relaxation times (T1H) and proton spin-lattice relaxation times in the rotating frame (T1ρH) revealed phase separation with domain sizes larger than 5nm when the PTHF fraction exceeds 10wt%. Only for lower PTHF-amounts, the SPNs were homogeneous on the nanometer scale. On the other hand, when PTHF with acrylamide end groups was used as macromolecular cross-linker, the NMR results showed the absence of any domain formation for SPNs with PTHF fractions up to 50wt%. The major impact of the molecular design on the ultimate phase morphology of bicomponent polymer networks has been confirmed in all cases by DMA-analysis.

Segmented polymer networks based on poly( N-isopropyl acrylamide) and poly(tetrahydrofuran) as polymer membranes with thermo-responsive permeability

Segmented polymer networks (SPNs) containing a polymer with a lower critical solution temperature were prepared by free radical copolymerization of poly(tetrahydrofuran) (PTHF) bis-macromonomers with N-isopropyl acrylamide (NIPAA). The PTHF bis-macromonomers, which were prepared by living cationic polymerization of tetrahydrofuran, were provided with acrylate or acrylamide end-groups by end-capping the living polymer chains with acrylic acid and 3-acrylaminopropanoic acid, respectively. Differential Scanning Calorimetry (DSC) experiments showed clearly that, for the same fractions of both network components, the phase morphology of the SPNs was highly influenced and adjustable by the nature of the end-groups of the bis-macromonomer as a result of their copolymerization behavior with NIPAA. For the same type of multi-component networks, the morphology changed from a heterogeneous up to a rather homogeneous nature by application of bis-macromonomers with, respectively, acrylate or acrylamide end-groups during their preparation. Swelling and DSC experiments on the swollen SPNs revealed, respectively, that the swelling properties and the cloud point temperature ( T cp) could be controlled by the network composition. The thermo-responsive water permeability and the possible application of the SPNs as pervaporation membranes for the separation of a water/isopropanol mixture were investigated as a function of temperature and network composition. The permeability and selectivity of the membranes decrease when the T cp is reached. The permeability increases while the selectivity decreases with decreasing crosslink density or higher overall hydrophilicity of the SPNs.

Functional segmented polymer networks based on polytetrahydrofuran and poly(vinylbenzyl chloride)

Abstract Functional segmented polymer networks (FSPNs) were synthesised via free radical initiated copolymerisation of polytetrahydrofuran (PTHF) bis-macromonomers with vinylbenzyl chloride (VBCl). The purpose of this work was to create FSPNs, providing supports with a functional group that can be substituted and may serve to immobilise other reagents such as catalysts. After the preparation and detailed characterisation of several PTHF bis-macromonomers, FSPNs were prepared with varying molecular weight of the PTHF chain and varying PTHF/ PVBCl ratio. Measurements of the soluble fraction and elemental analyses demonstrated that FSPNs with a wide composition range could be prepared. From dynamic-mechanical and thermal analyses, it could be concluded that most FSPNs showed some degree of compatibility and complete absence of crystallinity. The mechanical properties of the FSPNs are directly related to their composition. The degree of substitution of all networks is close to quantitative.

Thermo‐Responsive and Emulsifying Properties of Poly(N‐vinylcaprolactam) Based Graft Copolymers

AbstractThermo‐responsive graft copolymers have been synthesized based on a poly(N‐vinylcaprolactam) (PVCL) backbone and either hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(tetrahydrofuran) (PTHF) side chains. The phase separation behavior of the graft polymers in water was studied by transmittance measurements and compared to that of the corresponding swollen segmented polymer networks and aqueous solutions of both polymers. The influence of the concentration and length of the grafts on the cloud point temperature (TCP) has been demonstrated. PVCL‐g‐PTHF copolymers have been synthesized by using the macromonomer technique, i.e. the radical copolymerization of VCL with a PTHF macromonomer. A special feature of these amphiphilic graft copolymers is their ability to stabilize aqueous emulsions below the TCP and to suddenly break them above the TCP. PVCL‐g‐PEO copolymers were prepared by a grafting onto method. First, succinimide groups were introduced in the backbone, to which amino terminated PEO chains were grafted in the second step. This leads to di‐hydrophilic copolymers that become amphiphilic after heating their aqueous solutions above the TCP.magnified image

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

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.

Segmented polymer networks containing amino‐dendrimers

AbstractPolymer networks in which poly(propylene imine) dendrimers (Astramol™) are connected to each other by linear polytetrahydrofuran (polyTHF) segments, were prepared by two methods. The first method was a one‐step procedure in which bifunctionally living polyTHF, obtained by initiation of the THF polymerization with trifluoromethane sulfonic anhydride (triflic anhydride), was reacted with an amino‐dendrimer. This reaction was very fast but did not allow formation of the end products. The second method was a two‐step procedure. In a first step, living polyTHF, prepared with acryloyloxybutyl triflate as initiator, was grafted on an amino‐dendrimer, to form a star‐like, acrylate‐terminated polyTHF multi‐macromonomer with the dendrimer as core. In a second step, networks were obtained by Michael addition between the acrylate end‐groups and unreacted amino‐groups of the dendrimer. This cross‐linking reaction occurred spontaneously upon heating of the solution of the multi‐macromonomer with gelation times varying from a few minutes to a few hours, depending on the temperature and the composition of the prepolymers. With this method it was possible to prepare networks in the form of coatings or films.© 2003 Society of Chemical Industry

Thermotropic Networks Based on Poly(Methyl Vinyl Ether)

Segmented polymer networks consisting of poly(methyl vinyl ether) (PMVE) and a second polymer were synthesized by copolymerization of PMVE-α,ω-bis-methacrylate with a hydrophilic vinyl monomer (hydroxyethyl methacrylate, HEMA) or a hydrophobic vinyl monomer (styrene, St or butyl acrylate, BA). Such networks, swollen to equilibrium in water, show thermotropic properties in the case of the PMVE-PSt and PMVE-PBA systems due to the lower critical solution temperature (LCST) properties of the PMVE segments. The PMVE-PHEMA networks showed an inverse thermotropic behavior, i.e., the swollen networks are turbid at lower temperature and become transparent at higher temperature. The PMVE-PSt networks containing a small fraction of PSt are the best materials for thermotropic properties because the swelling is limited to a few percent which results in materials free of cracks after repeated heating–cooling (with corresponding de-swelling–swelling) processes.

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.

Thermo-Responsive Solid-Phase Extraction Using Poly(methyl vinyl ether)-Containing Segmented Polymer Networks

Segmented polymer networks containing poly(methyl vinyl ether) (PMVE) segments were prepared by free-radical-initiated copolymerization of PMVE-α,ω-dimethacrylate with styrene or 2-hydroxyethyl methacrylate (HEMA). These networks were evaluated as thermo-responsive solid-phase extraction materials. Suspension-derived polymer networks consisting of 80% of PMVE and 20% of HEMA adsorb toluene from an aqueous solution at 40°C and release the adsorbed toluene quantitatively at 20°C.

Thermosensitive polymer structures based on segmented copolymer networks

Segmented polymer networks with LCST-behavior have been prepared by free radical initiated copolymerization of α,ω-bis-methacrylate terminated poly(methyl vinyl ether) (PMVE) with 2-hydroxy ethyl methacrylate (HEMA) or butyl acrylate (BA). The PMVE bis-macromonomers have been obtained via a semi-continuous process by end-capping the living cationic polymerization of methyl vinyl ether (MVE) with HEMA. The phase separation temperature can be varied by changing the PMVE/comonomer ratio. Incorporation of PMVE-grafts in the hydrogels increases the rate of deswelling and improves the mechanical properties. The application of the segmented networks for thermo-controllable solid phase extraction has been demonstrated by their thermosensitive adsorption behavior of toluene from a water solution.

Poly(vinyl ethers) as building blocks for new materials

AbstractThe living cationic polymerization of vinyl ethers has been used to prepare a number of new polymers with special properties. Sequential polymerization of the hydrophilic methyl vinyl ether (MVE) and the hydrophobic octadecyl vinyl ether (ODVE) has lead to amphiphilic block‐copolymers with emulsifying properties for water/decane mixtures. Poly(vinyl‐ether) macromonomers were obtained by end‐capping of living polymers with hydroxyethyl acrylate. Copolymerization of polyODVE‐macromonomer with usual acrylates lead to highly branched hydrophobic polymers. When the end‐capping was performed with bifunctionally living polymers, the corresponding “bis‐macromonomers” were obtained. Copolymerization of such bis‐macromonomers with styrene or butyl acrylate, leads to the formation of segmented polymer networks. In the case of polyODVE‐poly(butyl acrylate), these networks showed a pronounced phase separation. Due to the crystallinity of the polyODVE domains, these materials showed shape memory properties.