Lyudmila M. Sergeeva

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(vinyl pyrrolidone)

Gradient semi-interpenetrating polymer networks (gradient semi-IPNs) were synthesized using polyurethane (PU) and poly(vinyl pyrrolidone) (PVP). The materials were characterized with respect to thermodynamic miscibility, IR-spectroscopy, mechanical properties and morphological structure. The positive values of Gibbs free energy indicated that the polymeric systems were thermodynamically immiscible. The gradient semi-IPNs were shown to have unique mechanical properties dependent on the composition and the subsequent degree of microphase separation. Given the ability to control both the mechanical properties and surface chemistry, these materials offer the potential for further development as biocompatible biomedical materials for the fabrication of medical implants.

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.

Influence of carbon fibre on formation kinetics of crosslinked copolymer from bisphenol A dicyanate and epoxy oligomer

The influence of carbon fibre on the curing kinetics of the prepolymer based on bisphenol A cyanurate and epoxy resin has been studied using infra-red spectroscopy. It was found that the curing process of the prepolymer is very complicated. It is shown that in curing the prepolymer a number of the sequential transformations of one ring structure into others occurs. An introduction of the carbon fibre (CF) of two types, original CF and modified CF (MCF) containing phosphate groups, affects strongly the prepolymer curing. Both CF and MCF accelerate the conversion rate of epoxy groups. In the case of cyanate groups, the former has practically no effect on their conversion whereas the latter decelerates strongly this process. In the present paper the influence of CF on the mechanism of the copolymer formation is considered.

Dynamic mechanical study of filled semi‐interpenetrating polymer networks: Influence of γ‐Fe2O3 on microphase structure

The preparation of filled two-component semi-interpenetrating polymer networks (semi-IPNs) is described and the results of an investigation of their morphology by means of dynamic mechanical spectroscopy are considered. The influence of an active dispersed filler (γ-Fe 2 O 3 ) on the semi-IPNs phase structure is studied. A comparison is made between filled and unfilled semi-IPNs consisting of compatible or incompatible polymers. In the case of a semi-IPN of compatible polymers, the introduction of γ-Fe 2 O 3 was observed to cause phase separation. With a two-phase semi-IPN the introduction of the filler enhanced the phase separation. The presence of two distinct peaks (the dynamic glass transition temperatures) corresponding to those of the two initial homopolymers shows the semi-IPN to have a two-phase structure.