Gradient interpenetrating polymer networks

The methods of synthesis and properties of gradient interpenetrating polymer networks (IPN) are discussed based on literature and authors' own experimental data. Gradient IPN can be treated as a sequence of an infinite number of layers of IPNs, whose composition and properties vary gradually from the surface to the core of specimens. These are analysed the most important properties of gradient IPNs: temperature transitions, thermodynamic and physico-mechanical characteristics and the main direction of practical application of gradient IPN-based materials.     

Thermodynamic state of reinforced interpenetrating polymer networks

The free energies of mixing of two networks in the interpenetrating polymer network based on crosslinked polyurethane and poly(ester acrylate) have been determined by the vapour sorption method. It was established that the constituent networks in the IPN are not miscible. The introduction of fillers of different chemical nature increases the compatibility. The thermodynamic affinity of the fillers to the individual networks and IPN was estimated. It was established that when the free energy of interaction of one or both components of the IPN with the filler is negative, reinforcement leads to the formation of a compatible and equilibrium system. For fillers having no affinity to the polymers, compatibilization is observed, which is connected with slowing down of phase separation in the system in the presence of filler.     

Semi‐interpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. II. Dielectric relaxation and thermal behaviour

Semi‐interpenetrating polymer networks (semi‐IPNs) based on crosslinked polyurethane (PU) and linear polyvinylpyrrolidone (PVP) were synthezised, and their thermal and dynamic mechanical properties and dielectric relaxation behavior were studied to provide insight into their structure, especially according to their composition. The differential scanning calorimetry results showed the glass transitions of the pure components: one glass‐transition temperature (T_g) for PU and two transitions for PVP. Such glass transitions were also present in the semi‐IPNs, whatever their composition. The viscoelastic properties of the semi‐IPNs reflected their thermal behavior; it was shown that the semi‐IPNs presented three distinct dynamic mechanical relaxations related to these three T_g values. Although the temperature position of the PU maximum tan δ of the α‐relaxation was invariable, on the contrary the situation for the two maxima observed for PVP was more complex. Only the maximum of the highest temperature relaxation was shifted to lower temperatures with decreasing PVP content in the semi‐IPNs. In this study, we investigated the molecular mobility of the IPNs by means of dielectric relaxation spectroscopy; six relaxation processes were observed and indexed according the increase in the temperature range: the secondary β‐relaxations related to PU and PVP chains, an α‐relaxation due to the glass–rubber transition of the PU component, two α‐relaxations associated to the glass–rubber transitions of the PVP material, and an ionic conductivity relaxation due to the space charge polarization of PU. The temperature position of the α‐relaxation of PU was invariable in semi‐IPNs, as observed dynamic mechanical analysis measurements. However, the upper α‐relaxation process of PVP shifted to higher temperatures with increasing PVP content in the semi‐IPNs. We concluded that the investigated semi‐IPNs were two‐phase systems with incomplete phase separation and that the content of PVP in the IPNs governed the structure and corresponding properties of such systems through physical interactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1191–1201, 2003     

Structure–properties investigations in hydrophilic nanocomposites based on polyurethane/poly(2–hydroxyethyl methacrylate) semi‐interpenetrating polymer networks and nanofiller densil for biomedical application

Nanocomposites based on sequential semi–interpenetrating polymer networks (semi–IPNs) of crosslinked polyurethane and linear poly(2‐hydroxyethyl methacrylate) filled with 1–15 wt % of nanofiller densil were prepared and investigated. Nanofiller densil used in an attempt to control the microphase separation of the polymer matrix by polymer–filler interactions. The morphology (SAXS, AFM), mechanical properties (stress–strain), thermal transitions (DSC) and polymer dynamics (DRS, TSDC) of the nanocomposites were investigated. Special attention has been paid to the raising of the hydration properties and the dynamics of water molecules in the nanocomposites in the perspective of biomedical applications. Nanoparticles were found to aggregate partially for higher than 3 and 5 wt % filler loading in semi–IPNs with 17 and 37 wt % PHEMA, respectively. The results show that the good hydration properties of the semi–IPN matrix are preserved in the nanocomposites, which in combination with results of thermal and dielectric techniques revealed also the existence of polymer–polymer and polymer–filler interactions. These interactions results also in the improvement of physical and mechanical properties of the nanocomposites in compare with the neat matrix. The improvement of mechanical properties in combination with hydrophilicity and biocompatibility of nanocomposites are promising for use these materials for biomedical application namely as surgical films for wound treatment and as material for producing the medical devises. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43122.     

Filler effect on formation and properties of interpenetrating polymer networks based on polyurethane and polyesteracrylate

The formation processes of unfilled and filled interpenetrating polymer networks (IPNs) and some of their physico-mechanical properties have been investigated. The IPN formation kinetics and the constituent network curing rates determine the rate and degree of microphase separation. This in turn determines the boundary layer composition and structure. Introduction of filler into the IPN during formation affects greatly the crosslinking reaction and the microphase segregation of homopolymers. It has been shown that the degree of phase segregation in filled IPNs differs from that in unfilled ones. All the fillers were found to shorten the time of internal stress appearance and to increase its value for IPNs with predominantly high-modulus component content. Some filled IPNs were shown to have greater thermodynamic stability than unfilled ones.     

Miscibility and thermal and dynamic mechanical behaviour of semi‐interpenetrating polymer networks based on polyurethane and poly(hydroxyethyl methacrylate)

The thermodynamic miscibility and thermal and dynamic mechanical behaviour of semi‐interpenetrating polymer networks (semi‐IPNs) of crosslinked polyurethane (PU) and linear poly(hydroxyethyl methacrylate) (PHEMA) have been investigated. The free energies of mixing of the semi‐IPN components have been determined by the vapour sorption method and it was established that the parameters are positive and depend on the amount of PHEMA in the semi‐IPN samples. Thermal analyses glass transition temperatures evidenced two in the semi‐IPNs in accordance with the investigation of the thermodynamic miscibility of these systems. Dynamic mechanical analysis revealed a pronounced change in the viscoelastic properties of the PU‐based semi‐IPNs with different amounts of PHEMA in the samples. The semi‐IPNs have two distinct tan δ maxima related to the relaxations of the two polymers in their glass temperature domains. The temperature position of PU relaxation maximum tan δ is invariable but its amplitude decreases in the semi‐IPNs with increasing amount of PHEMA in the systems. The tan δ maximum of PHEMA is shifted to a lower temperature and its amplitude decreases with increasing amount of PU in the semi‐IPNs. The segregation degree of components α was calculated using the viscoelastic properties of semi‐IPNs. It was concluded that the studied semi‐IPNs are two‐phase systems with incomplete phase separation. The different levels of immiscibility lead to the different degree of phase separation in the semi‐IPNs with compositions. Copyright © 2004 Society of Chemical Industry     

Gradient interpenetrating polymer networks

The methods of synthesis and properties of gradient interpenetrating polymer networks (IPN) are discussed based on literature and authors' own experimental data. Gradient IPN can be treated as a sequence of an infinite number of layers of IPNs, whose composition and properties vary gradually from the surface to the core of specimens. These are analysed the most important properties of gradient IPNs: temperature transitions, thermodynamic and physico-mechanical characteristics and the main direction of practical application of gradient IPN-based materials.     

Synthesis and characterization of new polymethacrylate bearing cyclopropane ring as side group

A cyclopropanation reaction of allylmethacrylate (1) with ethyldiazoacetate (2) lead to the formation of 2-(2-methyl-acryloyloxymethyl)-cyclopropanecarboxylic acid ethyl ester (3) as a mixture of cis/trans isomers in molar ratio 2:1. The cis isomer could be selectively hydrolyzed by use of Pig liver esterase (PLE). An isolated cis-2-(2-methyl-acryloyloxymethyl)-cyclopropanecarboxylic acid (4) exhibited optical activity. The monomer 3 was easily polymerized using AIBN and benzopinacol as free radical initiators at 65 and 130 °C, respectively. ¹H NMR and FT-IR analyses confirmed the presence of the chemically stable cyclopropane ring in both monomer and polymers. The obtained polymers were also characterized by GPC and DSC measurements. A depolymerization behaviour was observed heating the polymers at 200-250 °C. The regeneration of starting cis/trans isomers of 3 can be taken as a proof of the high thermal stability of the cyclopropane ring.     

Formation of silicon nanocrystals in multilayer nanoperiodic <Emphasis Type="Italic">a</Emphasis>-SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/insulator structures from the results of synchrotron investigations

The problem of the efficiency of the controllable formation of arrays of silicon nanoparticles is studied on the basis of detailed investigations of the electronic structure of multilayer nanoperiodic a-SiO _x /SiO₂, a-SiO _x /Аl₂О₃, and a-SiO _x /ZrO₂ compounds. Using synchrotron radiation and the X-ray absorption near edge structure (XANES) spectroscopy technique, a modification is revealed for the investigated structures under the effect of high-temperature annealing at the highest temperature of 1100°C; this modification is attributed to the formation of silicon nanocrystals in the layers of photoluminescent multilayer structures.     

Polyurethane/poly(hydroxyethyl methacrylate) semi-interpenetrating polymer networks for biomedical applications

The thermodynamic miscibility, morphology, phase distribution, mechanical properties, surface properties, water sorption, bacterial adhesion and cytotoxicity of semi-interpenetrating polymer networks (semi-IPNs) based on crosslinked polyurethane (PU) and poly(hydroxyethylmethacrylate) (PHEMA) were studied to give an insight into their structure and properties. The free energies of mixing of the two polymers in semi-IPNs have been determined and it was shown that the values are positive and depend on the amount of PHEMA. This demonstrates that the components are immiscible, the extent of which is dependent upon variations in composition. The morphology of the semi-IPNs was analyzed with scanning electron microscopy and tapping mode atomic force microscopy (TMAFM). The micrographs of the semi-IPNs and TMAFM phase images indicated that distinct phase separation at the nanometer scale is observed. The mechanical properties reflect the changes in structure of semi-IPNs with composition. The stress at break increases from 3.4 MPa to 23.9 MPa, and the Young’s modulus from 12.7 MPa up to 658.5 MPa with increasing amounts of PHEMA, but strain at break has a maximum at 40.4% PHEMA. The bacterial adhesion and cytotoxicity data suggest that semi-IPNs with PHEMA content above 22% may be used for biomedical material applications.