Yu. N. Nizel'skii

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.

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].

Spectroscopic study of complex formation by methanol and phenyl isocyanate with bis(acetylacetonato) copper

It has been shown that the reaction of phenyl isocyanate with methanol in dioxane in the presence of bis(acetylacetonato) copper involves the formation of intermediate complexes. The isocyanate is coordinated to the copper ion of the catalyst, and the alcohol is joined to the oxygen of the chelate rings of bis(acetylacetonato) copper together and hydrogen bond. This brings the reacting molecules closer together and orients them relative to one another, thus facilitating their interaction. The phenylmethylurethan formed is also coordinated to the catalyst, and when it appears in the system, equilibrium is established between the complexes formed by the catalyst with the solvent, the isocyanate, and the urethan.

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.

Conformational selection of channel of cyclotrimerization of isocyanates by the tertiary amine/epoxide catalytic system

A study has been made of the role of conformational control in each elementary stage of addition in selecting a channel of cyclotrimerization of isocyanates, and an explanation is given for the selectivity of the tertiary amine/epoxide catalytic system for this reaction.

Complex formation between copper β-diketonates and polyoxypropylene glycols

The complex formation between copper (II) dipivaloylmethanate Cu(dpm)2 and copper (II) hexafluoroacetylacetonate Cu(hfacac)2 and polyoxypropylene glycols (PPG) with molecular masses of 200 and 1050 was studied by spectrophotometry in the visible region and by ESR. The compositions of the complexes (1∶1) and the thermodynamic parameters of complex formation were determined. In complexing power Cu(dpm)2 is inferior to Cu(hfacac)2. Complex formation between Cu(hfacac)2 and PPG is accompanied by structural changes in the β-diketonate.

Dependence of the reactivity of allophanates on the conformation of the main chain

The CNDO/2 method was used to investigate the conformation and structure of alkylsubstituted allophanates. The possibility of the existence of isomers both with coplanar and with noncoplanar main chains NCNC was studied. It was shown that the formation of conformers with a cis-structure of the ester group is more probable. On the basis of an analysis of the dependence of the reactivity on the structure of the main chain, hypotheses were advanced on the role of the more stable conformers in various channels of polyaddition of isocyanates.