L. V. Karabanova

Semiinterpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. I. Thermodynamic state and dynamic mechanical analysis

Semiinterpenetrating polymer networks (semi-IPNs) based on polyurethane (PU) and polyvinylpyrrolidone (PVP) have been synthesized, and their thermodynamic characteristics, thermal properties, and dynamical mechanical properties have been studied to have an insight in their structure as a function of their composition. First, the free energies of mixing of the two polymers in semi-IPNs based on crosslinked PU and PVP have been determined by the vapor sorption method. It was established that these constituent polymers are not miscible in the semi-IPNs. The differential scanning calorimetry results evidence the T g of polyurethane and two T g for PVP. The dynamic mechanical behavior of the semi-IPNs has been investigated and is in accordance with their thermal behavior. It was shown that the semi-IPNs present three distinct relaxations. If the temperature position of PU maximum tan δ is invariable, on the contrary, the situation for the two maxima observed for PVP is more complex. Only the maximum of the highest temperature relaxation is shifted to lower temperature with changing of the semi-IPNs composition. It was concluded that investigated semi-IPNs are two-phase systems with incomplete phase separation. The phase composition was calculated using viscoelastic properties.

Gradient semi-interpenetrating polymer networks based on polyurethane and poly(2-hydroxyethyl methacrylate) for biomedical applications

Gradient semi-interpenetrating polymer networks (gradient semi-IPNs) as well as the traditional semi-interpenetrating polymer networks (semi-IPNs) were synthesized using polyurethane (PU) and poly(2-hydroxyethyl methacrylate) (PHEMA). The materials were characterized with respect to thermodynamic miscibility, NIR imaging, mechanical properties and morphological structure by tapping mode atomic force microscopy (TM AFM). The positive values of Gibbs free energy indicated that polymeric systems were thermodynamically immiscible. The dynamic mechanical analysis as well as TM AFM demonstrated that the systems under investigation were two-phase systems with incomplete phase separation. The gradient semi-IPNs were shown to have unique mechanical properties dependent on the composition and on the degree of microphase separation. The ability to create a layer of biocompatible polymer, such as PHEMA, at the surface, or create nanostructured surface consisting of nanodomains of different polymeric compositions, and engineer the improvements in the mechanical properties of the materials through the use of gradient systems should allow the creation of novel materials for biomedical application through the optimisation of mechanical properties, surface chemistry and biological properties.

Hybrid Polyurethane-Poly(2-hydroxyethyl methacrylate) Semi-IPN–Silica Nanocomposites: Interfacial Interactions and Glass Transition Dynamics

Polyurethane-poly(2-hydroxyethyl methacrylate) semi-IPN-silica nanocomposites with low content (0.25 and 3 wt%) of differently functionalized 3-D fumed silica nanoparticles were studied using a combined AFM/DSC/CRS approach over the −100 to 160°C range. The pronounced heterogeneity of the PHEMA and PU glass transitions’ dynamics and the effects of considerable suppression of dynamics and increasing elastic properties by silica additives were shown. It was caused by formation of peculiarly cross-linked structures due to “double hybridization,” in particular via selective covalent bonding of the silica surface, functionalized by ‒OH, ‒NH2 or ‒CH˭CH2 groups, with the matrix constituents. The silica dispersion remained unchanged in these nanocomposites; therefore the relationships between interfacial interactions and dynamics/modulus behavior could be followed.