Formation Of Semi-interpenetrating Polymer Networks Research Articles

A photosensitive composition based on an aromatic polyamide for LCD 4D printing of shape memory mechanically robust materials

High-temperature shape memory polymers (SMPs) draw growing interest from researchers due to their potential as materials for application in the field of high-temperature smart devices. However, in the majority of cases the processing of high-temperature SMPs is limited by fabrication of two-dimensional films. Here, we have prepared a photosensitive composition based on high-performance heat resistant poly-N,N′-(m-phenylene)isophthalamide (MPA) and photosensitive components (N,N-dimethylacrylamide and bisphenol A ethoxylate diacrylate (BAEDA)). It has been shown by IR spectroscopy, that LCD 3D printing followed by post-curing at 150 °C results in the formation of semi-interpenetrating polymer networks, while thermal processing at a temperature ≥200 °C leads to the formation of fully crosslinked structures due to the interaction of NH groups from MPA and acrylic groups from BAEDA via the Michael addition. The post-curing temperature has a significant effect on the thermal and mechanical properties of materials. Thermal post-curing of 3D printed samples at 250 °C for 1 h results in the fabrication of materials with the highest tensile strength (92.4 ± 6.1 MPa), glass transition temperature (148 °C) and thermal decomposition temperature (above 350 °C). Remarkably, MPA-based materials exhibit an excellent shape memory performance at temperatures >150 °C, with fixity ratio (Rf) of 99.7 % and recovery ratio (Rr) of 99.9 %. Moreover, we showed that the glass transition temperature decreased by no more than 1 % after γ-radiation of 200 Gy. In addition, the material maintains a high storage modulus and good shape memory performance after being irradiated, and thus has a great potential in the field of aerospace structural materials.

Photo-induced topological self-reorganization and self-growth of polymer based on dynamic reversible aromatic pinacol units

Crosslinked polyurethane containing aromatic pinacol units as novel reversible C–C bonds provider is synthesized. For the first time, photo-induced topological self-reorganization through the reversible C–C bonds leads to the transformation of micro-phase separation structure, realizing improvement of the tensile strength and failure strain from 23 MPa to 34 MPa and from 1205% to 1695%, respectively. In contrast, mechanical properties of the reference sample without pinacol moieties decrease sharply after the same UV irradiation. Internal structural variations are analyzed in detail by equilibrium swelling experiment, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), small angle neutron scattering (SANS) and positron annihilation lifetime spectroscopy (PALS). Moreover, the carbon radicals generated from homolysis of the aromatic pinacol are found to be able to further initiate polymerization of vinyl monomers, which helps to achieve crack healing, surface self-growth and formation of semi-interpenetrating polymer networks. This kind of macromolecular initiator-embedded polymer could re-initiate polymerization when the surface arrays are wiped away to expose the fresh underlying aromatic pinacol units. It is believed that the outcomes may enrich and expand the applications of dynamic covalent polymers.

Preparation and characterization of alginate-PVA-based semi-IPN: controlled release pH-responsive composites

The objective was to develop naturally derived polymer-based hydrogels with high mechanical strength and a controlled delivery of drug for extended period of time. Here, we report the fabrication of chemically cross-linked polyvinyl alcohol-graft-poly(acrylic acid)/sodium alginate hydrogel as a semi-interpenetrating polymer network (SIPN). For the preparation of SIPN hydrogels, SA and PVA were cross-linked with AA monomer in the presence of co-monomer EGDMA through free-radical polymerization reaction, using APS as an initiator. Loxoprofen sodium was loaded as a model drug. FTIR, XRD, TGA, and DSC were performed for the characterization of copolymer. Surface morphology was studied by SEM. Swelling studies were carried out at low and higher pH to evaluate pH-dependent swelling of formed SIPN hydrogels. FTIR, XRD, TGA, and DSC studies confirmed the formation of a new copolymer. Developed SIPN hydrogels showed maximum swelling, drug loading, and drug release at pH 7.4 while low at pH 1.2. Moreover, formulations with higher AA contents showed maximum swelling at 7.4 pH. High drug loading and higher drug release have been observed at pH 7.4. In vitro release profile of loxoprofen sodium was found dependent on pH, concentration of monomers, and cross-linking agent. Gel% and yield% for the prepared SIPN hydrogels were determined and found that gel% or yield% is directly proportional to the concentration of polymers, i.e., SA and PVA, due to their behavior as macromolecule radicals for monomer. The results from FTIR analysis showed that both SA and PVA react with the acrylic acid monomer during the polymerization process and result into the formation of SIPN. The formation of semi-IPN structure significantly improved the surface morphology of SIPN hydrogels as evident by SEM, which corresponds to their improved swelling ability and mechanical strength. Drug release mechanism from the formed SIPN was explained by kinetic modeling and found that first-order, Higuchi model, and Korsmeyer–Peppas model are the best fit models to explain drug release from hydrogels. Conclusively, prepared hydrogels were highly pH-responsive and showed good mechanical strength and time-dependent drug release. SIPN hydrogels could be a potential carrier network for controlled delivery of loxoprofen sodium for extended period of time.

Microwave-assisted synthesis of kC/Xylan/PVP-based blend hydrogel materials: physicochemical and rheological studies

Hydrogel systems composed of kC/Xylan (kC/OSX or kC/BX) blends and linear polyvinylpyrrolidone (PVP) were prepared in the presence of water soluble initiator sodium persulphate (KPS) with microwave irradiation. The hydrogel materials were investigated by measuring their syneresis, swelling, gel fraction, and rheological properties. Physicochemical and rheological properties of the natural polysaccharide (kC/Xylans) blends were modified significantly after blending with PVP. The introduction of PVP and the formation of semi-interpenetrating polymer network (semi-IPN) structure improved the gelling properties of the resulting hydrogels. It has been proven, that a high incorporation of PVP could only be obtained if the hydrogels were prepared using KPS initiator and microwave irradiation in combination. FTIR, CP-MAS 13C NMR, and elemental analysis confirmed the presence of PVP in the blends but no direct evidence for covalent bonds could be obtained.

Phase separation in semi-interpenetrating polymer networks based on crosslinked poly(urethane) and linear poly(methyl methacrylate) containing iron, copper, and chromium chelates

Phase separation that occurs during formation of semi-interpenetrating polymer networks of various compositions based on crosslinked poly(urethane) and linear poly(methyl methacrylate) containing 1 wt % iron, copper, and chromium chelates has been studied by the methods of DSC and DMA. It has been shown that, in contrast to chromium chelates, the incorporation of iron and copper β-diketonates into the semi-interpenetrating polymer networks (PU : PMMA = 50 : 50) causes retardation of phase separation owing to high rates of poly(urethane) and poly(methyl methacrylate) formation and the appearance of chelate complexes with both blend components at the interface. A more complete phase separation in metal-containing semi-interpenetrating polymer networks (PU : PMMA = 70 : 30) is associated with the fact that chemical kinetics and complexation processes act in opposite directions. The latter processes prevail, and the influence of the type of metal ion in a chelate that predominantly interacts with PU in the blend is diminished.

Porous Polycaprolactone−Polystyrene Semi-interpenetrating Polymer Networks Synthesized within High Internal Phase Emulsions

PolyHIPE are highly porous, open-pore, cross-linked polymers synthesized within high internal phase emulsions (HIPE). Biodegradable polycaprolactone (PCL) oligomers were incorporated into polyHIPE using two approaches. The first approach involved copolymerization with a vinyl-terminated PCL (PCL-VL). This approach yielded a typical polyHIPE structure with voids on the order of tens of microns. The covalent bonds formed by PCL-VL prevented its removal during emulsifier extraction. The second approach involved the formation of semi-interpenetrating polymer networks (semi-IPN) with a PCL diol (PCL-OL). The relatively hydrophilic PCL-OL destabilized the HIPE and produced voids on the order of hundreds of microns, a size more appropriate for tissue engineering applications. The PCL-OL, which is more mobile than the covalently bound PCL-VL, underwent more extensive phase separation. In addition, a significant amount of PCL-OL was removed during emulsifier extraction. Cells were successfully attached to the surface of a semi-IPN polyHIPE, forming a monolayer. Eventually, spontaneous differentiation of the cells and the formation of myotubes were observed.

Preparation of semi-interpenetrating polymer networks composed of chitosan and poloxamer

Through semi-interpenetration of polymer networks with poloxamer, mechanical properties of chitosan (CS) sponge were increased for wound dressing application. Synthesis of poloxamer macromer was confirmed by proton nuclear magnetic resonance ( 1H NMR) spectra. Possible interactions between CS and poloxamer in semi-interpenetrating polymer networks (SIPNs), and changes in crystalline structures of both polymers were evaluated by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. Swelling behavior, thermal analysis, mechanical properties, and morphology of SIPNs were studied by thermal gravimetric analysis, differential scanning calorimetry (DSC), compressive modulus measurement, and scanning electron microscopy (SEM), respectively. Preparation of poloxamer macromer, and intermolecular hydrogen bonding between CS and poloxamer were confirmed by NMR and FTIR, respectively. Melting temperature of poloxamer in SIPNs decreased due to prevention of crystallization by incorporation of CS. Formation of SIPNs with poloxamer and increasing poloxamer content in CS/poloxamer SIPNs increased mechanical strength of CS sponge compared with CS/poloxamer blend. Formation of SIPNs with poloxamer remarkably increased water content of CS due to hydrophilicity of CS and poloxamer. These results suggest CS/poloxamer sponges prepared by SIPNs method have good possibility for wound dressing application owing to rapid water adsorption, high mechanical strength, and interconnected cross-sectional morphology of SIPNs.

Effect of compatibilizers on kinetic of interpenetrating polymer networks formation and their microphase structure

The effects of various potential compatibilizers on the viscoelastic properties and kinetics of formation of semi-interpenetrating polymer networks (semi-IPN) based on cross-linked polyurethane and linear poly (butyl methacrylate) has been investigated. All the additives investigated affect the reaction rate of formation of components of IPNs. It was established depending on the nature of compatibilizers the phase separation in forming system may be accelerated or eliminated. The investigation of the effects of some compatibilizers, which differ on chemical constitution, allows to establish two different types of their compatibilizing action.

Preparation of semi-interpenetrating polymer networks composed of silk fibroin and poly(ethylene glycol) macromer

Semi-interpenetrating polymer networks (SIPNs) composed of silk fibroin (SF) and a poly(ethylene glycol) (PEG) diacrylate macromer were synthesized and characterized. The conformation of SF in SIPNs was changed from a random coil to a β-sheet structure by formation of SIPNs with PEG, while the crystalline structures of SF and PEG in SIPNs was not changed. The decomposition temperature of SF in the SIPNs was inner-shifted, an indication of SIPN formation between the SF and the PEG macromer. The tensile strength and elongation of the SIPNs were much higher than were those of SF itself or the SF/PEG blend and increased with an increase of the PEG content. The equilibrium water content of SF was remarkably increased by formation of SIPNs with PEG due to the hydrophilic property of PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1848–1853, 2001

Studies of the stability of thermoplastic-modified bismaleimide resin

The stability of bismaleimide-o,o'-diallyl bisphenol A (BMI-DABA) blends modified with high-performance amorphous thermoplastic bisphenol A polysulfone (PSF), polyether ketone (PEK-C), and polyether sulfone (PES-C) bearing a phthalidylidene group has been studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The extent of stability of thermoplastic components has been compared with the area of the endothermic peak that appears within the glass transition region for thermoplastic component in cured blends aged at temperature below the glass transition temperature (T g ). The stability of thermoplastic can be improved by the formation of semi-interpenetrating polymer networks (semi-IPNs). The stability of thermoplastic with higher T g is more easily controlled.

Morphology Development During the Polymerization of Styrene Within a Polyurethane Network: Investigations by Small-angle X-ray and Light Scattering

Phase separation that takes place during the formation of semi-interpenetrating polymer networks based on crosslinked polyurethane and linear polystyrene was studied by small-angle X-ray scattering and light scattering. The kinetics of the chemical reactions was followed by Fourier transform infrared spectroscopy. The occurrence of broad peaks in the X-ray scattering curves was interpreted in terms of distances between the urethane crosslinks. Small modulations on these curves were assigned to sphere-like structures with a diameter of around 5 nm which might be related to the urethane crosslink regions. Small modulations on the light-scattering curves at the beginning of styrene polymerization were assigned to spheres with diameters of around 4.5 μm, which can be related to the polystyrene-rich phase. These modulations disappear with time, which might indicate an increasing polydispersity of the domain sizes. The final morphology was found to depend on the time at which polymerization of styrene is initiated with respect to the time of gelation of polyurethane.

Microphase separation at incipient formation of semi-interpenetrating polymer networks

Phase separation that takes place during the formation of semi-interpenetrating networks based on a styrene-divinylbenzene copolymer and poly(butyl methacrylate) has been studied by the light scattering method. Phase separation occurs because at a certain stage of the polymerization the components become thermodynamically incompatible, and proceeds by the mechanism of spinodal decomposition. Kinetics of formation of the semi-interpenetrating network is decisive for the onset of phase separation and governs the process of phase segregation as a whole. The diffusion coefficients of the components have been calculated and the dimensions of the spinodal structures have been determined.

Some aspects of zwitter ion polymerization in the processes of formation of interpenetrating polymer networks based on diisocyanates

In model conditions with polymerization of methylthiirane on exposure to a tertiary amine in presence of phenylisocyanate additions the authors study the kinetic patterns of the second stage of the process of formation of semi-interpenetrating polymer networks based on the diisocyanates and polar monomers. Assumptions are advanced on the complex nature of the reaction centre responsible for the development of phases I and II of formation of the interpenetrating networks.