N. V. Kozak

Structure–thermal property relationships for polycyanurate–polyurethane linked interpenetrating polymer networks

Chemical structure and thermal-oxidative degradation of sequential IPNs based on crosslinked polyurethane (CPU) and polycyanurate network (PCN) have been studied. As a result of chemical interaction between monomer, dicyanate ester of bisphenol A (DCEBA) and CPU during PCN formation (polycyclotrimerization of DCEBA into CPU matrix), covalent bonding between the networks occurs, leading to creation of linked IPNs (LIPNs). The formation of a new hybrid network (HN) structure has been confirmed. The coexistence of CPU, PCN and HN structures in the LIPNs, confirmed by infrared spectroscopy and by the observation of degradation stages characteristic for each structure, depends on the ratio of the components. Three structures were found for the 90/10 CPU/PCN; HN and PCN were observed in the 70/30 LIPN and the hybrid network was the main structure detected for the 50/50 LIPN.

Complexation of Fe3+, Cu2+, and Cr3+ β-diketonates with poly(urethane) and poly(methyl methacrylate) in semi-interpenetrating networks: Effect on phase separation

Complexation of iron, copper, and chromium β-diketonates with poly(urethane) and poly(methyl methacrylate) in semi-interpenetrating polymer networks was studied by IR spectroscopy and ESR using various paramagnetic probes. It was shown that types of complexes arising in semi-interpenetrating polymer networks depend on the central metal ion in a chelate. In the networks containing iron and copper β-diketonates, formation of complexes between chelates of these metals and donor groups of PUR and PMMA promotes mutual penetration of poly(urethane) and poly(methyl methacrylate) phases. As a consequence, the degree of their separation decreases and the interphase region widens.

The Effect of multi-reprocessing on the structure and characteristics of thermoplastic elastomers based on recycled polymers

The effect of multi-reprocessing on the phase structure and characteristics is studied for thermoplastic elastomers based on recycled high-density polyethylene (HDPE), ethylene-propylene-diene rubber (ternary copolymer of ethylene, propylene, and 5-ethylidene-2-norbornene) (EPDM), and recycled ground tire rubber (RGTR). Analysis of the viscous flow characteristics of thermoplastic elastomers shows that, independently of the number of processing cycles, all samples are characterized by the required flow characteristics at elevated temperatures. Processing of thermoplastic elastomers is accompanied by the competing processes of crosslinking and degradation of macromolecules in a polymer mixture. The results of DSC study and dynamic mechanical thermal analysis show that, as the number of processing cycles is increased, phase separation between amorphous and crystalline phases in thermoplastic elastomers decreases. Insignificant intermolecular crosslinking induced by the processing of thermoplastic elastomers appears to have almost no effect on the physicomechanical characteristics of the final material.

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.

Investigation of the structure of polyurethanes cross-linked with the ions of divalent 3d metals by a paramagnetic probe method

Polyurethanes cross-linked with Ni(2+), Cu(2+), and Zn(2+) ions were studied by ESR with two types of paramagnetic probes, 2,2,6,6-Tetramethylpiperidin-1-oxyl and copper ethylacetoacetate were used as probes. The different effects of close d-metal ions on the macrocharacteristics of the ion-linked polyurethanes may be due to the formation of additional complexes of the metal ion with the macroligands.

ANALYSIS OF CONFORMATIONS OF ORGANIC ISOCYANATES

In connection with the study of the spectral properties and reactivity of R-nNCO isocyanates, many experimental and theoretical publications have been devoted to investigation of their geometric structure [1-6]. However, most of the publications involve the elucidation of only the mutual arrangement of the NCO group and R, with the isocyanate group being assumed to be both linear [i, 2, 5] and nonlinear [3-6].

Structural changes in blends of linear polymers during their physical aging

Structural transformations in the blends of linear polymers polyurethane and polystyrene during multistage physical aging are studied. Effects of the temperature and time of heat treatment and the rate of cooling after heat treatment on the dynamic mechanical properties of the blends are analyzed. Aging at T = 110°C is accompanied by noticeable structural transformations in the polyurethane phase, while chemical changes are absent, as evidenced by thermogravimetric analysis and IR spectroscopy. Additional physical bonds and topological entanglements presumably form between chains in the blends of linear polymers during physical aging.

Quantum-chemical analysis of the reactivity of methanol dimers in their reaction with isocyanates

The CNDO/2 method has been used to investigate the reactivity of methanol dimers of various structures in nucleophilic addition reactions at the N=C bond of isocyanates. It is shown that effect of dimerization on the reactivity of the alcohol is in the same direction as the effect of an electron donating catalyst on the monomer, depending on the structure of the dimer and, in some instances, also on the conformation of the isocyanate.

Analysis of the possibility of anionic homoaddition of isocyanates to zwitterionic active centers

An investigation of the complexation of an R3+NCH2CH2O− zwitterion with HNCO and the subsequent interaction of the complex formed with a second molecule of HNCO has been carried out by the CNDO/2 method. It has been shown on the basis of an analysis of the structure of the frontier MOs of the reactants and their electronic structure that the successive homoaddition of isocyanates is unlikely. This raises some question as to the possibility of the anionic mechanism of the cyclotrimerization of isocyanates in the presence of zwitterions.

Activation of molecules of proton donors in the catalytic system amine-epoxide-proton donor

We present the results of a quantum-chemical study by the CNDO/2 method of the system trimethylamine-ethylene oxide-proton donor (water, alcohol, carbamide, carbamate, biuret, allophanate) and we consider the nature of the activation of the proton donor on complex formation. The results of the calculations are analyzed from the point of view of the catalytic activity of the system in the cyclotrimerization of isocyanates.