Amphiphilic Polymer Conetworks Research Articles

Wide Range of Functionalized Poly(N-alkyl acrylamide)-Based Amphiphilic Polymer Conetworks via Active Ester Precursors

A versatile strategy for the fabrication of functional and nanostructured poly(N-alkyl acrylamide)-based amphiphilic polymer conetworks (APCNs) from hydrophobic precursor networks is presented. The active ester monomer pentafluorophenyl acrylate (PFPA) fulfills a dual role: it provides miscibility with hydrophobic macromonomer cross-linkers and activates the acrylate for amidation reactions. Thereby, it acts as a general hydrophobic masking group for N-alkyl acrylamides, and enables the transformation of PFPA-based hydrophobic precursor networks into a multitude of different poly(N-alkyl acrylamide)-l-PDMS APCNs. These optically transparent APCNs possess nanophase-separated morphologies with domain sizes in the nanometer range. Variation of the amide results in different types of APCNs, despite them being derived from the same precursor network and having identical network structures. Accordingly, the properties of these APCNs can be tailored to the desired application by simple variation of the amide fun...

Near-Model Amphiphilic Polymer Conetworks Based on Four-Arm Stars of Poly(vinylidene fluoride) and Poly(ethylene glycol): Synthesis and Characterization

Amphiphilic polymer conetworks (APCN) were prepared in N,N-dimethylformamide (DMF) by the interconnection of four-arm star poly(vinylidene fluoride) (PVDF, Mn = 8800 Da) end-functionalized with benzaldehyde groups and four-arm star poly(ethylene glycol) (PEG, Mn = 10 kDa) end-functionalized with benzaacylhydrazide groups. The PVDF stars were prepared via the reversible addition–fragmentation chain transfer polymerization of vinylidene fluoride using a tetraxanthate chain transfer agent. Equilibrium swelling of the APCNs in various solvents was dependent on the compatibility of the APCN components with the solvent, with the degrees of swelling (DS) varying from 22 in DMF (a good solvent for both PEG and PVDF), down to 8 in water (a good and selective solvent for PEG), and even down to 3 in diethyl ether (a nonsolvent for both polymers). Characterization of the conetworks in D2O using small-angle neutron scattering (SANS) indicated phase separation at the nanoscale, as evidenced by a (broad) correlation pea...

Amphiphilic Polymer Conetworks Based on Interconnected Hydrophobic Star Block Copolymers: Synthesis and Characterization

SummaryHerein we report on the preparation and structural characterization of six amphiphilic polymer conetworks (APCN) based on end‐linked amphiphilic “core‐first” star block copolymers, comprising methyl methacrylate and 2‐(dimethylamino)ethyl methacrylate as the monomer repeating units in the hydrophobic and hydrophilic blocks, respectively. The various APCNs differed either in the arm composition or in the arm molecular weight. APCN synthesis was accomplished via the one‐pot, sequential group transfer polymerization (GTP) of cross‐linker, hydrophobic monomer, hydrophilic monomer, and cross‐linker again. The soluble precursors to the APCNs, i.e., the star homopolymers, the star block copolymers and the initial cross‐linker cores, were characterized in terms of their composition, size and size dispersity. The degrees of swelling in tetrahydrofuran were found to increase with the molecular weight of the arms of the stars of the APCNs, whereas the degrees of swelling in water increased with the content in hydrophilic units in the arms of the constituting stars. Small‐angle neutron scattering (SANS) indicated that most APCNs nanophase separated in D2O. The structure and size of the hydrophobic domains determined by fitting the SANS data to an appropriate model could be correlated with the molecular architecture of the APCNs. Finally, polarized light microscopy showed that all APCNs were birefringent both in water and in the dried state.

Transport-Limited Adsorption of Plasma Proteins on Bimodal Amphiphilic Polymer Co-Networks: Real-Time Studies by Spectroscopic Ellipsometry

Traditional hydrogels are commonly limited by poor mechanical properties and low oxygen permeability. Bimodal amphiphilic co-networks (β-APCNs) are a new class of materials that can overcome these limitations by combining hydrophilic and hydrophobic polymer chains within a network of co-continuous morphology. Applications that can benefit from these improved properties include therapeutic contact lenses, enzymatic catalysis supports, and immunoisolation membranes. The continuous hydrophobic phase could potentially increase the adsorption of plasma proteins in blood-contacting medical applications and compromise in vivo material performance, so it is critical to understand the surface characteristics of β-APCNs and adsorption of plasma proteins on β-APCNs. From real-time spectroscopic visible (Vis) ellipsometry measurements, plasma protein adsorption on β-APCNs is shown to be transport-limited. The adsorption of proteins on the β-APCNs is a multistep process with adsorption to the hydrophilic surface initially, followed by diffusion into the material to the internal hydrophilic/hydrophobic interfaces. Increasing the cross-linking of the PDMS phase reduced the protein intake by limiting the transport of large proteins. Moreover, the internalization of the proteins is confirmed by the difference between the surface-adsorbed protein layer determined from XPS and bulk thickness change from Vis ellipsometry, which can differ up to 20-fold. Desorption kinetics depend on the adsorption history with rapid desorption for slow adsorption rates (i.e., slow-diffusing proteins within the network), whereas proteins with fast adsorption kinetics do not readily desorb. This behavior can be directly related to the ability of the protein to spread or reorient, which affects the binding energy required to bind to the internal hydrophobic interfaces.

Double-networks based on pH-responsive, amphiphilic “core-first” star first polymer conetworks prepared by sequential RAFT polymerization

Double-networks based on amphiphilic polymer conetworks synthesized using RAFT polymerization were prepared, exhibiting pH-responsiveness, nanophase separation and enhanced mechanical properties.

Noncollapsing polyelectrolyte conetwork gels in physiologically relevant salt solutions

In consequence of some unique properties, such as nanophase separation, biocompatibility and mechanical stability, amphiphilic polymer conetworks (APCNs) have received significant attention in recent years. APCNs are composed of hydrophilic and hydrophobic polymer chains connected with covalent bonds. The unique properties of APCNs make them suitable for many specialized applications. Although APCNs were widely investigated and described in the literature, this is the first study on the swelling behavior of these materials in the solutions of physiologically relevant salts. Homopolymer polyelectrolyte hydrogels are known to suffer phase transition like rapid gel collapse at a certain salt concentration in the solutions of bi- or multivalent metal salts. Systematic swelling investigation of poly(methacrylic acid)-l-polyisobutylene (PMAA-l-PIB) conetwork series in CaCl2 salt solutions led to unexpected findings. Our results indicate that these polyelectrolyte APCNs do not behave the same way in salt solutions as the homopolymer hydrogels, i.e. APCNs do not suffer gel collapse, the change of the swelling degree remains continuous with increasing salt concentration. The gel contraction was reversible by changing the solute to NaOH solution, i.e. the gels returned to their original volume by reswelling. This non-collapsing swelling means that the presence of hydrophobic polymer segments as cross-linkers in amphiphilic polyelectrolyte gels radically change the swelling behavior of such materials, which become substantially different from that of homopolymer polyelectrolyte gels.

Investigations on “near perfect” poly(2-oxazoline) based amphiphilic polymer conetworks with a crystallizable block

Amphiphilic polymer conetworks (APCNs) of “near perfect” structure were prepared by cross-linking defined poly(2-oxazoline)-based block copolymers. To this end, ABA triblock copolymers with poly(2-methyloxazoline) (PMOx) as A block and poly(2-heptyloxazoline) (PHepOx) as B block in different compositions and with different cross-linkable end groups were prepared and crosslinked. The resulting amphiphilic polymer conetworks were characterized with atomic force microscopy (AFM) and small as well as wide angle X-ray scattering (SAXS/WAXS). The results show that the PHepOx block crystallizes in the APCNs if the content is larger than 19vol.%, but shows no thermal signature in the differential scanning calorimetry if the polymer content is below 68vol.%. Further, the size of the polymer phase is the same in a composition range of 38–58vol.% PHepOx. The phase size was confirmed by AFM. The found very regular interconnected structure over a wide range of compositions seems to be the generic structural motive in APCNs and is also formed when inserting a crystallizable polymer block.

Real-Time Monitoring of Chemical and Topological Rearrangements in Solidifying Amphiphilic Polymer Co-Networks: Understanding Surface Demixing.

Amphiphilic polymer co-networks provide a unique route to integrating contrasting attributes of otherwise immiscible components within a bicontinuous percolating morphology and are anticipated to be valuable for applications such as biocatalysis, sensing of metabolites, and dual dialysis membranes. These co-networks are in essence chemically forced blends and have been shown to selectively phase-separate at surfaces during film formation. Here, we demonstrate that surface demixing at the air-film interface in solidifying polymer co-networks is not a unidirectional process; instead, a combination of kinetic and thermodynamic interactions leads to dynamic molecular rearrangement during solidification. Time-resolved gravimetry, low contact angles, and negative out-of-plane birefringence provided strong experimental evidence of the transitory trapping of thermodynamically unfavorable hydrophilic moieties at the air-film interface due to fast asymmetric solvent depletion. We also find that slow-drying hydrophobic elements progressively substitute hydrophilic domains at the surface as the surface energy is minimized. These findings are broadly applicable to common-solvent bicontinuous systems and open the door for process-controlled performance improvements in diverse applications. Similar observations could potentially be coupled with controlled polymerization rates to maximize the intermingling of bicontinuous phases at surfaces, thus generating true three-dimensional, bicontinuous, and undisturbed percolation pathways throughout the material.

2,2′:6′,2′′-Terpyridine-functionalized redox-responsive hydrogels as a platform for multi responsive amphiphilic polymer membranes

Amphiphilic polymer co-networks were functionalized with spyropiran and terpyridine yielding multi-responsive membranes with switchable properties and potential applications in drug delivery and medical sensors.

Synthesis and Selective Loading of Polyhydroxyethyl Methacrylate-l-Polysulfone Amphiphilic Polymer Conetworks.

Polyhydroxyethyl methacrylate-linked by-polysulfone amphiphilic polymer conetworks of two types of segments with Tg above room temperature are presented. The conetworks are prepared by free radical copolymerization of methacryloyl-terminated PSU macromers with 2-ethyl methacrylate, followed by removal of the TMS protecting groups by acidic hydrolysis. Phase separation in the nanometer range due to the immiscibility of the two covalently linked segments is observed using transmission electron and scanning force microscopy. The swelling of the conetworks in water and methanol as polar solvents and chloroform as nonpolar solvent are studied gravimetrically and then in a more detailed fashion by solid-state NMR spectroscopy. Selective swelling and also targeted loading of a small organic model compound specifically to one of the two phases are demonstrated.

Amphiphilic Polymer Conetworks Based on End-Linked "Core-First" Star Block Copolymers: Structure Formation with Long-Range Order.

Amphiphilic polymer conetworks are cross-linked polymers that swell both in water and in organic solvents and can phase separate on the nanoscale in the bulk or in selective solvents. To date, however, this phase separation has only been reported with short-range order, characterized by disordered morphologies. We now report the first example of amphiphilic polymer conetworks, based on end-linked "core-first" star block copolymers, that form a lamellar phase with long-range order. These mesoscopically ordered systems can be produced in a simple fashion and exhibit significantly improved mechanical properties.

Self-Sealing and Puncture Resistant Breathable Membranes for Water-Evaporation Applications.

Breathable and waterproof membranes that self-seal damaged areas are prepared by modifying a poly(ether ester) membrane with an amphiphilic polymer co-network. The latter swells in water and the gel closes punctures. Damaged composite membranes remain water tight up to pressures of at least 1.6 bar. This material is useful for applications where water-vapor permeability, self-sealing properties, and waterproofness are desired, as demonstrated for a medical cooling device.

Amphiphilic polymer conetworks with defined nanostructure and tailored swelling behavior for exploring the activation of an entrapped lipase in organic solvents

Amphiphilic polymer conetworks (APCNs) are nanomaterials that greatly activate entrapped enzymes in organic solvents. We have designed two novel APCNs with similar nanostructure, but different swelling behavior in toluene and n-heptane to explore the true origin of enzyme activation. They were realized by copolymerization of telechelic methacrylamide terminated poly(2-methyl oxazoline) (PMOx) with butyl acrylate (BuAc) and 2-ethylhexyl acrylate (EhAc), respectively. While the first APCN swells in toluene but not in n-heptane, the latter swells in both solvents. Lipase Cal B entrapped in the conetworks is most active at a composition that contains some 50 wt% PMOx in all cases. Further, the maximal activation of Cal B with respect to the suspended powder is some 20-fold independent on the solvent as long as the APCN is swellable.

A Well-Defined Amphiphilic Polymer Conetwork from Sequence Control of the Cross-Linking in Polymer Chains

Well-defined amphiphilic polymer conetworks with precisely controlled number and position of cross-links were prepared by copper-catalyzed azide–alkyne cycloaddition (CuAAC) using linear polystyrene (PS) and poly(ethylene glycol) (PEG) as the building blocks. In this approach, linear polystyrene containing a specific number of bromo groups at a predetermined position of polymer chains was synthesized by multistep reversible addition–fragmentation chain transfer polymerization and chain extension using styrene and N-bromopropyl maleimide (PBMI) as the monomers. Subsequently, the bromo groups were transformed into the azido moieties via nucleophilic substitution. The well-defined linear multialkynyl PEG was prepared from PEG diglycidyl ether and propargylamine via epoxy-amine chain extension. The as-prepared PS–PEG amphiphilic polymer conetworks showed unique hydrophilic and hydrophobic phase separation with a variable swelling capacity and rheological behavior in both polar and nonpolar solvents and exhibited excellent mechanical properties with increased cross-linking density.

Impact of the configuration of a chiral, activating carrier on the enantioselectivity of entrapped lipase from Candida rugosa in cyclohexane

Lipase from Candida rugosa was loaded into an amphiphilic polymer co-network (APCN) composed of the chiral poly[(R)-N-(1-hydroxybutan-2-yl) acrylamide] [P-(R)-HBA] and P-(S)-HBA, respectively, linked by poly(dimethylsiloxane). The nanophase-separated amphiphilic morphology affords a 38,000-fold activation of the enzyme in the esterification of 1-phenylethanol with vinyl acetate. Further, the enantioselectivity of the entrapped lipase was influenced by the configuration of the chiral, hydrophilic polymer matrix. While the APCN with the (S)-configuration of the APCN affords 5.4 faster conversion of the (R)-phenylethanol compared to the respective (S)-enantiomer, the (R)-APCN allows an only a 2.8 faster conversion of the (R)-enantiomer of the alcohol. Permeation-experiments reveal that the enantioselectivity of the reaction is at least partially caused by specific interactions between the substrates and the APCN.

A well-defined amphiphilic polymer co-network from precise control of the end-functional groups of linear RAFT polymers

Linear polystyrene (PS) with well-defined molecular structure and accurate numbers of bromo groups on both ends were synthesized via multiple-step alternative RAFT polymerization of N-bromopropyl maleimide and β-pinene monomers. The bromo end groups were transformed into the azido moieties via nucleophilic substitution. The reaction of as-synthesized linear PS having a named number of azide groups on ends ((N3)x–PS–(N3)x) with mono- and dialkynyl-terminated PEG (dA-PEG) via copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) leads to the formation of the well-defined PS–PEG amphiphilic copolymers and polymeric co-networks (APCNs). The as-prepared APCNs exhibit unique ordered separated hydrophilic and hydrophobic phases, and a variable swelling capacity both in polar and non-polar solvents.

Nanophase separated amphiphilic polymer co-networks as efficient matrices for optical sensors: Rapid and sensitive detection of NO2

A disposable and irreversible sensor for nitrogen dioxide detection, based on the reaction of NO2 with N,N′-diphenyl-1,4-phenylenediamine (DPPD) is described. This work focuses on the application of silicone-containing amphiphilic co-networks (APCNs) as immobilisation matrices for UV/VIS transmission spectroscopy for gas sensors. The developed flow-through gas sensor is based on a DPPD doped APCN, for real-time spectrophotometric detection of the oxidation product, and is formed in a 34μm thin film. The measurement principle presented here describes the NO2 concentration as a function of the temporal development of absorption at 450nm. A linear relationship between the change of absorption and the concentration of NO2 at different humidity is obtained in the range from 0.1 to 5.0ppm at ambient temperatures. As a consequence, the sensor response is reproducible with a very low detection threshold (20ppb) and detection times within seconds.

Chiral pH-Responsive Amphiphilic Polymer Co-networks: Preparation, Chiral Recognition, and Release Abilities

Novel amphiphilic polymer co-networks (APCNs), poly(N-acryloyl-L-alanine)-l-polydimethylsiloxane (denoted as PNAA-l-PDMS), are prepared, and exhibit remarkable pH-responsiveness, chiral-recognition, and enantioselective-release abilities. The APCNs are prepared by free-radical copolymerization starting from N-acryloyl-L-alanine (NAA) and methacrylate-terminated poly(dimethylsiloxane) (M-PDMS) as co-(macro)monomers. The APCNs show pronounced pH-sensitivity, evidenced by a reversible swelling–deswelling transition upon a cyclicly altering pH. The chiral co-networks are applied for enantioselective recognition and release. A maximum adsorption is achieved towards D-proline (61%), whereas for L-proline, it is only 10%. More interestingly, the release for the L-proline is 90%, whereas for the D-proline, only 70% is released.

Investigations on diffusion limitations of biocatalyzed reactions in amphiphilic polymer conetworks in organic solvents

The use of enzymes as biocatalysts in organic media is an important issue in modern white biotechnology. However, their low activity and stability in those media often limits their full-scale application. Amphiphilic polymer conetworks (APCNs) have been shown to greatly activate entrapped enzymes in organic solvents. Since these nanostructured materials are not porous, the bioactivity of the conetworks is strongly limited by diffusion of substrate and product. The present manuscript describes two different APCNs as nanostructured microparticles, which showed greatly increased activities of entrapped enzymes compared to those of the already activating membranes and larger particles. We demonstrated this on the example of APCN particles based on PHEA-l-PDMS loaded with α-Chymotrypsin, which resulted in an up to 28,000-fold higher activity of the enzyme compared to the enzyme powder. Furthermore, lipase from Rhizomucor miehei entrapped in particles based on PHEA-l-PEtOx was tested in n-heptane, chloroform, and substrate. Specific activities in smaller particles were 10- to 100-fold higher in comparison to the native enzyme. The carrier activity of PHEA-l-PEtOx microparticles was tenfold higher with some 25-50-fold lower enzyme content compared to a commercial product.

Amphiphilic Polymer Conetworks Based on End Group Cross-Linked Poly(2-oxazoline) Homo- and Triblock Copolymers

Novel amphiphilic polymer conetworks (APCNs) were prepared via end group cross-linking. To this end, poly(2-methyloxazoline) (PMOx), poly(2-butyloxazoline) (PBuOx), and the triblock copolymers PMOx-b-PBuOx-b-PMOx were synthesized by cationic ring-opening polymerization in varying block lengths and telechelically modified with N,N-bis(2-aminoethyl)ethylendiamine (TREN). First the cross-linking with 1,4-dibromo-2-butene (DBB) was established for the homopolymers. The swelling of those matches the theoretical value for full cross-linking, indicating that in this way “near perfect” networks could be obtained. Mixtures of the homopolymers and the triblock copolymers were cross-linked with DBB to give APCNs with similar polymer segments but different network topology. AFM showed that all formed APCNs are nanophase separated with slight structural differences in the nanostructures when comparing conetworks with similar composition but different cross-linking strategies. The more drastic difference between APCNs ...