Mechanism of Depolymerization of Polymeric p-Dinitrosobenzene in Vulcanization of Unsaturated Rubbers: A Quantum-Chemical Study

Abstract

The mechanism of depolymerization of polymeric p-dinitrosobenzene in vulcanization of unsaturated rubbers is analyzed. The results obtained explain why the vulcanizing activity of p-dinitrosobenzene decreases in the course of its prolonged storage.p-Dinitrosobenzene (DNB) is a component of rubber3substrate adhesion systems [1] and a low-temperature vulcanizing agent for stocks based on unsaturated rubbers [2]. DNB is a polymeric compound virtually insoluble under common conditions in any solvent [3].The vulcanizing activity of DNB is known to change in the course of its storage [4,5]; this fact calls for theoretical substantiation. Furthermore, data on the structure of polymeric p-dinitrosobenzene (poly-DNB) are contradictory, and nothing is known about the mechanism of its depolymerization in the course of addition to unsaturated compounds (in particular, in vulcanization of unsaturated rubbers).In the papers concerning the kinetics and mechanism of addition of poly-DNB to unsaturated compounds [6,7], the authors, as a rule, presented the monomeric DNB structure; some authors assumed the structure has a dimeric sandwich form (Fig. 1) [739], but this structure does not stand up to criticism.It is known that IR spectra of poly-DNB contain a strong band at 1264 cm !1 [10,11], characteristic of nitrosoarene trans dimers [10,12], with a C3N3N angle in the sandwich structure close to 120o. At the same time, the C3N3N angle in the sandwich structure is close to 90o, and, therefore, this structure should be strained and thermodynamically unstable.Experimental determination of the poly-DNB structure is complicated by its high dispersity and insolubility in all the solvents under common conditions. Therefore, to study the geometry of poly-DNB and energy effects of its reactions, we used quantumchemical calculations. We chose the relatively reliable DFT B3LYP method with the 6-31G(d) basis set. The calculations were performed with a computer cluster of the Kazan State Technological University, using the GAUSSIAN 98 program package [13], with full geometry optimization. For the model structures, we calculated the force constants, vibration frequencies, thermodynamic quantities, and variation of the relative energy in extension of the (O)N3N`(O`) bond of model structures. To reduce the number of basis functions, we used 2-butene and 2-pentene as structures modeling a fragment of an unsaturated rubber. Fig. 1. Presumed dimeric sandwich structure of DNB.

Dimerization of Aromatic C-Nitroso Compounds

“…In particular, poly­( trans -1,4-phenyleneazo- N , N ′-dioxide) has been used as a photosensitive resin and is widely employed as a vulcanizing agent in the cross-linking of rubber by nitroso–ene reactions . The generally accepted mechanism for cross-linking first involves thermolysis of the polymer to regenerate 1,4-dinitrosobenzene, followed by a nitroso–ene reaction and final dehydration of the resulting hydroxylamine. − …”

New ways of processing and application of the croton fraction of waste from the production of JSC “Navoiazot”

“…O.R. Klyuchnikov proved that quinol esters of N-benzoxinondioxime can be used as low-temperature vulcanization accelerators [18,19].…”

Synthesis and characterization of polymers from soybean oil and p‐dinitrosobenzene

“…p ‐Dinitrosobenzene (DNB) is a finely crystalline, green substance that is sparingly soluble in dimethyl formamide, alcohol, hot xylene, and water. This compound exists as an amorphous polymeric solid (PDNB) at room temperature, and the monomeric DNB can be obtained by fast heating in xylene or by sublimation in vacuum onto a surface cooled by liquid nitrogen 13. The relative stabilities of monomeric, dimeric cis , and trans structures of DNB are dependent on the physical state, the temperature, and the solvent properties (Fig.…”