Design and syntheses of two threefold interpenetrating 2-D networks

Two new interpenetrating networks, [Ni(2,2′-bpy)(5-npa)(bpe)_0.5(H₂O)] _n (1) and [Ni(2,2′-bpy)(5-npa)(bpa)_0.5(H₂O)] _n (2) (2,2′-bpy?=?2,2′-bipyridine, 5-npa?=?5-nitroisophthalato, bpe?=?1,2-bis(4-pyridyl)ethylene, bpa?=?1,2-bis(4-pyridyl)ethane), have been synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, X-ray powder diffraction, and single-crystal X-ray diffraction. Complexes 1 and 2 have similar structures and show a threefold interpenetrating topology constructed by three 2-D wave-like networks. Secondary building unit (SBU), [Ni(2,2′-bpy)(5-npa)(H₂O)] _n , was used as starting material of the multistep reaction. Replacing one coordination bond of chelating carboxyl group of SBUs by bpe and bpa afford the two threefold interpenetrating complexes.     

Protein release from interpenetrating polymer network hydrogels triggered by endogenous biomarkers

A biocompatible drug delivery system with a high-sensitive stimuli-responsive behavior is reported. Calcium alginate hydrogels interpenetrated with polyvinyl alcohol–diboronate polymer network (IPN) effectively respond to the presence of hydrogen peroxide through oxidative degradation of boronate esters. The degradation of the IPN entails the reopening of the original alginate pores, resulting in a 5–9 times increase in release rates of encapsulated proteins with molecular masses ranging from 16.7 to 66 kDa. The release can be triggered by hydrogen peroxide concentrations as low as 50 μM in the bulk solution. Alternatively, hydrogen peroxide can also be generated inside the hydrogels by incorporation of oxidase enzymes in the presence of their substrates, such as lactate, glucose, or hypoxanthine, which can serve as biomarkers of certain physiological disorders.     

A simple route to interpenetrating network hydrogel with high mechanical strength

A simple two-step method was introduced to improve the hydrogel mechanical strength by forming an interpenetrating network (IPN). For this purpose, we synthesized polyacrylate/polyacrylate (PAC/PAC), polyacrylate/polyacrylamide (PAC/PAM), polyacrylamide/polyacrylamide (PAM/PAM) and polyacrylamide/poly(vinyl alcohol) (PAM/PVA) IPN hydrogels. The PAC/PAC IPN and PAC/PAM IPN hydrogels showed compressive strength of 70 and 160 kPa, respectively. For the PAM/PAM IPN and PAM/PVA IPN hydrogels, they exhibited excellent tensile strength of 1.2 and 2.8 MPa, and elongations at break of 1750% and 3300%, respectively. A strain relaxation was also observed in the case of PAM series IPN hydrogels. From FTIR, TGA and SEM measurements, we confirmed that physical entanglement, hydrogen bonds and chemical crosslinking played major roles in improving hydrogel strength and toughening. The two-step technique contributes to the understanding of ideal networks, provides a universal strategy for designing high mechanical strength hydrogels, and opening up the biomedical application of hydrogels.     

Gas barrier and adhesion of interpenetrating polymer networks based on poly(diurethane bismethacrylate) and different epoxy-amine networks

Interpenetrating polymer networks (IPNs) composed of poly(methacrylate) and epoxy-amine networks made in situ between two oriented polypropylene sheets were examined in terms of their oxygen barrier and adhesion to the substrate properties. A particular attention was devoted to a system presenting an obvious phase separation. Kinetics of network formation and phase behavior were investigated by infrared and UV-visible spectroscopy, respectively. Since the poly(methacrylate) network could be instantaneously generated by photoirradiation, IPNs differing in network sequence formation were prepared. The influence of the moment at which irradiation was induced, on gas barrier properties of different films was examined. It was shown that similar oxygen transmission rates are obtained whatever the moment of irradiation.     

Room temperature synthesis and mechanical properties of two kinds of elastomeric interpenetrating polymer networks based on castor oil

Two kinds of interpenetrating polymer networks (IPNs) composed of two-component polyurethane (PU) and vinyl or methacrylic polymer (PV), namely, (polyether-castor oil)PU/PV IPN(I) and (polybutadiene-castor oil)PU/PV IPN(II), were synthesized at room temperature using benzoyl peroxide and N,N-dimethylaniline as redox initiator and dibutyltin dilaurate as catalyst. The former IPN was prepared by polymerization of castor oil, NCO-terminated polyether and vinyl or methacrylic monomer together and the latter IPN was obtained by polymerization of castor oil, NCO-terminated polybutadiene, NCO-terminated castor oil and vinyl or methacrylic monomer together. Various synthesis conditions affecting mechanical properties of the two kinds of IPNs were studied. Acrylonitrile (AN) is a good monomer for synthesizing IPN(I), but is a poor monomer for preparing IPN(II). At optimum conditions for the synthesis, both the (polyether-castor oil)PU/PAN IPNs and the (polybutadiene-castor oil)PU/polystyrene (PSt) IPNs possess permanent set about 10%, tensile strength over 13 and 11 MPa and ultimate elongation over 240% and 270%, respectively, thus behaving as elastomers. TEM micrograph of a (polybutadiene-castor oil)PU/PSt IPN showed a microphase separation in the IPN.     

Effects of reaction temperature and reaction time on positive thermosensitivity of microspheres with poly(acrylamide)/poly(acrylic acid) IPN shells

We have successfully prepared monodispersed positively thermoresponsive core-shell hydrogel microspheres with poly(acrylamide-co-styrene) [P(AAM-co-St)] cores and IPN(interpenetrating polymer network)-based shells composed of poly(acrylamide)/poly(acrylic acid). The submicron-sized monodispersed P(AAM-co-St) core seeds were prepared by using a surfactant-free emulsion polymerization method, and the IPN-based shell layers were fabricated onto the core seeds by using a method of sequential IPN synthesis. Effects of reaction time and reaction temperature during preparation of IPN on the particle size, monodispersity, and thermoresponsive characteristics of microspheres were investigated. The results show that the sizes of particles with IPN shell layer are smaller than that of seeds, and the change of monodispersity among them is not obvious and the monodispersity of particles prepared under higher reaction temperature is higher than that of seeds and those particles prepared under lower reaction temperature. With increasing reaction time, thermoresponsive characteristics of microspheres increases. While thermoresponsive characteristics of microspheres decreases sharply with increasing reaction temperature. The results display preparation of IPN-structured microspheres is so careful to need longer reaction time and lower reaction temperature.     

Electrical response characterisation of poly(ethylene glycol) macromer (PEGM)/chitosan hydrogels in NaCl solution

Interpenetrating polymer network hydrogels composed of poly(ethylene glycol) macromer (PEGM) and chitosan were synthesised by UV irradiation of solutions in a mild aqueous media. The IPN hydrogels exhibited the equilibrium water content (EWC) in the range of 86-94%. The hydrogels were characterised using FT-IR, FT-Raman spectroscopy and differential scanning calorimetry (DSC). The results from DSC measurements indicate that the melting endotherms of PEGM, within the hydrogels, decreased in intensities and shifted to lower temperatures comparing with a linear PEGM. This was due to the decrease of the crystallinity in the IPN hydrogels with higher contents of PEGM. The electrical response of the IPN hydrogels was also investigated by applying electrical current to the hydrogels immersed in a NaCl solution. The extent of a bending degree of the IPN hydrogel depends on the IPN hydrogel composition and applied electric field strength.     

Surface interpenetrating networks of polyacrylamide in poly(ethylene terephthalate) as a means of surface modification

Surface interpenetrating network (IPN) polymers are emerging hybrid materials in which the surface of existing polymers can be modified to preserve their chemical structure and bulk properties. A detailed structural characterization of poly(ethylene terephthalate) (PET) thin films on nanoscopically flat silicon wafers has been carried out by Scanning Probe Microscopy (SPM) and X-ray photoelectron spectroscopy (XPS). Examination of the surface of spin-coated annealed PET film by the SPM in tapping mode revealed a two-phase structure. One phase appeared as a dense crystalline fraction of the polymer while the other was identified as amorphous. These findings were supported by Differential Scanning Calorimetry (DSC), which recognized the crystallinity of annealed PET film at 30%. Modification of the PET surface with interpenetrating polyacrylamide (PAM) increased the roughness of the surface with uniform properties. The depth profiling with XPS revealed that PAM interpenetration extended down to 7.2 nm, confirming a three-dimensional character of the polymer modification, with a relative mass concentration of PAM at about 30.7% in the IPN interface.     

Novel interpenetrating smart polymer networks grafted onto polypropylene by gamma radiation for loading and delivery of vancomycin

Gamma radiation was used in every step of the synthesis of a sequential interpenetrating polymer network made of two “smart” polymers: poly(acrylic acid) (PAAc) and poly (N-isopropylacrylamide) (PNIPAAm), the latter grafted onto polypropylene (PP) films (PP-g-PNIPAAm) with the aim of developing medicated coatings for medical devices. Three steps were followed for obtaining net-PP-g-PNIPAAm-inter-net-PAAc: graft copolymerization of PNIPAAm onto PP films by gamma pre-irradiation oxidative method, cross-linking of PP-g-PNIPAAm by gamma irradiation in water to form the first network, with or without N,N′-methylenebis(acrylamide) (MBAAm), and finally the formation of the second network through the polymerization and cross-linking of AAc inside cross-linked PP-g-PNIPAAm by a low gamma radiation dose of 2.5 kGy. The films were characterized regarding the amount of grafted polymers and their composition (FTIR-ATR), thermal behavior (DSC), temperature- and pH-responsive swelling and contact angle (critical pH 6 and lower critical solution temperature ∼33 °C), and loading and release rate of vancomycin. Drug loading was driven by specific interactions between vancomycin and PAAc. Drug-loaded films sustained the delivery for several hours at pH 7.4 and provided release rate values adequate for killing bacteria attempting to adhere the surface of the films.     

The current status of interpenetrating polymer networks

An interpenetrating polymer network, IPN, is defined as a combination of two or more polymers in network form, at least one of which is polymerized and/or crosslinked in the immediate presence of the other(s). The synthesis, morphology and mechanical properties of recent works are reviewed, with special emphasis on dual phase continuity, and the number of physical entanglements that arise in homo-IPNs. The concepts of phase diagrams are applied, especially to simultaneous interpenetrating network phase separations and gelations. Recent engineering applications are discussed.     

Damping characteristics and mechanical properties of silica filled PUR/PEMA simultaneous interpenetrating polymer networks

Simultaneous polyurethane/poly(ethyl methacrylate) interpenetrating polymer network was synthesised by the one-shot route at the 70PUR/30PEMA composition ratio. This semi-miscible IPN exhibited its potential as a material for damping application by a broad loss factor (tan δ) ? 0.3 spanning a temperature range of 132 °C. The TEM micrographs revealed a multiphase morphology where the mixing between the two polymers was extensive. Incorporation of silica was made in order to study the effects of filler on the IPN properties in terms of glass transition temperature, dynamic mechanical properties, and mechanical and thermal properties. Dynamic mechanical thermal analysis indicated that the filler enhanced the damping ability of the IPN at certain temperature range. Furthermore, the addition of filler resulted in improved material strength.     

Fracture Behavior of Two Highly Stretchable Double Network Hydrogels

The static and dynamic mechanical behavior of two double network (DN) hydrogels, alginate/polyacrylamide (PAAm) hybrid hydrogel and sodium poly(2-acrylamido-2-methylpropanesulfonic acid) PNaAMPS/PAAm, is presented to understand the role played by different cross-linked networks on fracture and recovery properties. Although with a smaller modulus, alginate/PAAm hybrid hydrogel had a much higher stretchability, whether with or without notches, in the tensile tests. Continuous step strain measurement by using a strain-controlled parallel-plate rheometer showed that alginate/PAAm can immediately recover its mechanical properties after breakdown, while PNaAMPS/PAAm didn't show mechanical recovery at all.     

Influence of temperature and nature of photoinitiator on the formation kinetics of an interpenetrating network photocured from an epoxide/methacrylate system

This paper deals with the synthesis of an interpenetrating network made of dimethacrylate and dicycloepoxide oligomers by photopolymerization. More particularly, the influence of several parameters (among which the photoinitiator nature and the reaction temperature) on the polymerization kinetics of each oligomer was studied. Two complementary analysis techniques were then used : the photocalorimetry and the RTIR spectroscopy. The study proceeded in several steps. Firstly, photopolymerization of each monomer was studied. Then, the same study was carried out on mixture of both monomers under conditions in such way than only one network is formed. It was shown that the second compound played the role of plasticizer on the network formed by the first monomer. Finally, the dimethacrylate/dicycloepoxide mixture was studied in the presence of both radical and cationic photoinitiators to synthesize an interpenetrating network (IPN). At 30 °C, ultimate products show a very incomplete epoxide conversion whereas the yield in methacrylic double bonds reaches 70%. On the other hand, epoxy functions react a little more than methacrylic double bonds at 90 °C. It was also shown that the presence of a radical photoinitiator is not necessary, and even slightly unfavourable, since the cationic photoinitiator is able to initiate both radical and cationic polymerization mechanisms.     

Mechanical and Adhesive Properties of Ploy(ethylene glycerol) Diacrylate Based Hydrogels Plasticized with PEG and Glycerol

Using polyethylene glycol(PEG) or glycerol as the plasticizer, we synthesized the hydrogels from poly(ethylene glycol) diacrylate(PEGDA), polyvinylpyrrolidone(PVP) and poly(vinyl alcohol)(PVA) under UV radiation. The effects of different plasticizers on the mechanical properties and adhesion properties of the hydrogels were investigated. The results show that the plasticizer can improve the elongation and peeling force. The most pronounced changes in the tensile property of the hydrogels are due to the addition of glycerol followed by PEG, the lower the plasticizer's molecular weight, the greater its effect. The maximum peeling force is 0.317 or 0.257 N with PEG or glycerol as plasticizer, respectively, and their adhesion properties are due to the formation of hydrogen bonds.     

Improved oxygen permeability and mechanical strength of silicone hydrogels with interpenetrating network structure

<正>The interpenetrating polymer network(IPN) silicone hydrogels with improved oxygen permeability and mechanical strength were prepared by UV-initiated polymerization of monomers including methacryloxypropyl tris(trimethylsiloxy)silane(TRIS),2-hydroxyethylmethacrylate(HEMA) and N-vinyl pyrrolidone(NVP) in the presence of free radical photoinitiator and cationic photoinitiator.The polymerization mechanism was investigated by the formation of gel network.The structure of IPN hydrogels was characterized by Fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry(DSC) and transmission electron microscopy(TEM).The results showed that the IPN hydrogels exhibited a heterogeneous morphology.The mechanical properties,surface wettability and oxygen permeability were examined by using a tensile tester,a contact angle goniometer and an oxygen transmission tester,respectively.The equilibrium water content of the hydrogels was measured by the gravimetric method.The results revealed that the IPN hydrogels possessed hydrophilic surface and high water content.They exhibited improved oxygen permeability and mechanical strength because of the incorporation of TRIS.     

Fabrication of a high-strength hydrogel with an interpenetrating network structure

Hydrogels have potential applications in many fields, but the poor mechanical strength has limited their further development. In this article, we designed a high-strength hydrogel with an interpenetrating network (IPN) structure from polyacrylamide (PAM) and poly(vinyl alcohol) (PVA). Synthesis parameters, such as PVA/AM mass ratio, crosslinker dosage and elongation time were carried out for high tensile strength and elongation. The results showed that chemical crosslinking, physical entanglement and PVA precipitates were the dominant parameters for the improvement of mechanical properties. The PVA structure transferred from crystal to amorphous due to intermolecular and intramolecular interactions (such as hydrogen bond and self-crosslinking). PVA precipitates scatterred in the brittle PAM matrix homogeneously which dispersed the applied stress and improved the hydrogel toughness. The tensile strength and elongation were extremely high, they were 2.4 MPa and 3100%, respectively. The simple method is versatile in synthesizing high-strength IPN hydrogels using many kinds of polymer species.     

Radiation preparation and thermo-response swelling of interpenetrating polymer network hydrogel composed of PNIPAAm and PMMA

Interpenetrating polymer network (IPN) hydrogel composed of hydrophilic poly(N-isopropylacrylamide) (PNIPAAm) and hydrophobic poly(methyl methacrylate) (PMMA) were synthesized by sequential IPN method using γ-rays from ⁶⁰Co source. Compared with pure PNIPAAm hydrogel, PNIPAAm/ PMMA IPN hydrogel not only behaved with obvious temperature sensitivity, but also had higher mechanical strength. The shrinking rate of the prepared IPN hydogel was slower than that of PNIPAAm hydrogel and the relative shrinkage was higher than that of PNIPAAm hydrogel. The IPN hydrogel with less PMMA was not stable while with more PMMA it was quite stable. In addition, the release of Methylene Blue (MB) from the IPN hydrogel was slower than that from PNIPAAm hydrogel as well.     

The influence of diffusion time on the properties of sequential interpenetrating PEG hydrogels

Four sets comprising a total of 16 sequential interpenetrating network (SeqIPN) hydrogels were efficiently fabricated via UV initiated thiol‐ene coupling chemistry and from 2 kDa or 8 kDa primary poly(ethylene glycol) (PEG) networks (S2 and S8). Each primary system delivered four different SeqIPNs constructed after 2, 4, 20, and 44 h diffusion of secondary network PEG precursors, 2 kDa and 8 kDa. This allowed the assessment of both mechanical and swelling properties for a wide range of novel hydrogels ranging from loosely crosslinked SeqIPN 8‐8 to densely crosslinked SeqIPN 2‐2 systems. All gel fractions of secondary networks were above 83% and 44 h of diffusion was found sufficient to fully saturate the primary networks. Disperse red functionalized PEGs (2 kDa and 8 kDa) were further used as probes to investigate the diffusion mechanisms. The impact of diffusion time on loosely crosslinked S8 network with a swelling degree of 970% and tensile modulus of 175 kPa displayed a significant change in the final properties. For instance, a 2 h diffusion of 2 kDa PEG precursors generated a SeqIPN 8‐2:2 comprising a secondary network solid content of 34% with a water swelling degree 580% and a tensile modulus of 365 kPa. On saturation, that is, 44 h of diffusion, SeqIPN 2‐8:44 exhibited 64% of secondary network solid content, a swelling capacity of 380% and over fourfold of tensile modulus (758 kPa) when compared with the primary network S8. SeqIPN hydrogel with the highest tensile modulus and lowest degree of water swelling was obtained after 44 h diffusion of 2 kDa PEG precursors within the densely crosslinked S2 primary network. In this case, SeqIPN 2‐2:44 noted a water swelling capability of 280% and a tensile modulus over 1 MPa. The latter was twofold when compared with S2 with a tensile modulus of 555 kPa. Consequently, the diffusion time of secondary network is a promising parameter to control and that enables the fabrication of PEG hydrogels with a wider window of mechanical and swelling properties. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effects of organophilic montmorillonite on hydrogen bonding, free volume and glass transition temperature of epoxy resin/polyurethane interpenetrating polymer networks

Epoxy resin nanocomposites containing organophilic montmorillonite (oM) and polyurethane were prepared by adding oM to interpenetrating polymer networks (IPNs) of epoxy resin and polyurethane (EP/PU). The dispersion degree of oM in EP/PU matrix was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectrometry (FT-IR) showed that strong interactions existed between oM and EP/PU matrix, and oM had some effect on hydrogen bonding of these EP/PU IPNs nanocomposites. Positron annihilation spectroscopy (PALS) and differential scanning calorimetry (DSC) measurements were used to investigate the effect of oM and PU contents on free volume and glass transition temperature (T_g) of these nanocomposites. The PALS and DSC results clearly showed that the presence of oM led to a decrease in the total fractional free volume, which was consistent with increasing T_g upon addition of oM, ascribed to increasing hydrogen bonding in interfacial regions of oM and EP/PU matrix and enhancing the miscibility between EP phase and PU phase. In addition, with increasing PU content, the total fractional free volume increased, corresponding to decreasing T_g.     

Quenching of pyrene fluorescence as a technique for characterisation of swelling of interpenetrating polymer network: polyethylene/poly(styrene-co-butylmethacrylate)

A real-time monitoring of oxygen quenching of monomer fluorescence of bound probes: 1-pyrenemethyl methacrylate (PyMMA) and 1-pyrenemethyl(4-vinylbenzyl)ether (4-(1-pyrenyl)methoxymethylstyrene, PyMMS) was used for study of swelling of interpenetrating polymer network (IPN) consisting of polyethylene/poly(styrene-co-butylmethacrylate) (PE/P(S-co-BMA)) with different network density. The curves of oxygen quenching of pyrene chromophore were fitted to the monoexponential form of second Fick Law. The estimated diffusion coefficient of oxygen was in the range of 1-10 × 10⁻⁶ cm² s⁻¹ depending on the solvent and phase of IPN system. There is no dependence of fluorescence quenching by oxygen on cross-link density in this IPN systems.