ELSEVIER Synthetic Metals 71 (1995) 1825-1826 FTIR and NIR-FT-Raman study of potential molecular ferromagnetics substituted with nitroxyl radicals poly(diacetylenes) AN. Shchegolikhin, Olga L.Lazareva A.AOvchirmikov, and V.N.Spector Institute of Chemical Physics, 4 Kossygin St., Moscow, 117977, Russia Abstract Structural transformations during thermal treatment of several nitroxyl substituted diacetylene (DA) monomers have been studied by using EA, TGA, DSC, EPR FTIR, NIR-FT Raman (FTR) and X-ray analysis. Peculiarities of the solid state polymerization reactions of these monomers are discussed based mainly on the FTIR and FTR data obtainable for both the nitrontyl-substituted and “classic” diacetylenes and PDAs. 1. INTRODUCTION Polymers. in principle obtainable by the solid-state topochemical polymerization (SSTP) starting from radical- substituted DA monomers, such as ( l), (2) or (3) below, would contain a system of topologically or&red unpaired spins in the vi~&tity of the x-conjugated PDA backbone. Accordingly, they are useful models for probing ways to, e.g., polymer ferromagnetics or “self-doped” PDA’s [l]. In terms of Ovchinnikov model an ideal DA monomer should be unsym- metrical should have a crystal packing proper for 1,4-truns polyaddition reaction and should bear an unpaired spin center situated as close to the DA hagment as possible. Obviously, the crystal packing of such a DA monomer will be responsible for both the very possibility of the polymerization reaction and for involvment of the spin centers in the reaction. A number of N- oxyl containing DA monomers, prepared by the authors [2], did not polymerize under UV- or y-irradiation, but thermal annealing of the crystals did led to the conjugated polymeric products. These monomers are exemplified by the formulas: The monomer (I), though having crystal packing quite proper for SSTP [3], lost mass during heat treatment. The system of hydrogen bonds between the N-oxyl fragment and the hydroxyl group, preventing readjustment of the crystal lattice during SSTP, was responsible for eventual destruction of the material. The monomers (2) and (3). on the other hand, thermally polymerized in the solid state smoothly. Dynamic and isothermal DSC showed that (2) and (3) polymerized with temperature dependent induction periods, heats of the poly- merization reaction being of 45 and 67 kcal/moL respectively. 0379-6779/95/$09.50 0 1995 Elsevier Science S.A. All rights reserved SSDI 0379-6779(94)03069-I EPR data showed the spin concentration decrease by an order of value in the course of the reaction [4]. Gel permeation chro- matography (GPC) of THF-soluble polymerization products of (2) and (3) showed that these were oligomeric (n = 4 - 7). EPR r-correlation times for spin-bearing fragments. rigidly bound to the polymer backbone, for different GPC fractions of the polymerized (2) and (3) were in 5.8 10.” - 8.6 lo-” s and 1.57 lo-” - 6.75 10.” s intervals, respectively, also indicating on the oligomeric nature of these products. However, the molecular structure of the oligomers was still unclear. According to X-ray analysis, the crystal structure of (2) is not suitable for traditional SSTP [5]. Although shape of the crystal had not changed aReI the heat treatment the long range order disappeared. Since (3) crystallized only as thin platelets ummitable for X-ray analysis, exact structure of the pristine monomer and that of the annealed crystals was not known. Moreover, NMR spectroscopy was of little help in this study because of the spin centers presence, making interpretation of the NMR spectra 1.00 umbiguous. All these circumstances made us to rely mainly on the vibrational spectroscopy to probe molecular structure of the products and/or mechanism(s) of the reaction(s). 2. EXPERIMENTAL Synthesis of the monomers (1). 1-(2,2,6,6-Tetramethyl-l- oxyl-1,2,5,6-tetrahydropyridinyl-4)-penta-1,3-diyne-5-o1 (PP), (2). 1-(2,2,6,6-Tetramethyl-l-oxyl-1,2,5,6-tetrahydropyridinyl- 4)-5-(N-carbaaolyl)-penta-1,3-diyne (PC), and (3). l-(9- (2,2,4,4-Tetramethyl-1,2,3,4-tetrahydro-3-oxyl-y-carbolynyl))- 6-(N-carbazolyl)-hexa-2,4-diyne (CC), has been reported elsewhere [2]. Thermal treatment of the PP. PC and CC was carried out, using the monomers crystals, sealed under vacuum in glass ampules, in thermostate at 1OO’C (PP and PC) and at 12O’C (CC). Infrared spectra were run using a Perkin-Rhner (PE) 1725-X FTIR instrum ent. A K.Rr-pellet (tmnsmission) or a modified diffuse reflection-absorption (DRA) [6] FTIR techniques have been used. Nd:YAG Laser (1 .Oci4 pm) excited NIR-FT Raman spectra were run by using a PE NIR-FTR attachement coupled with the PE 1725-X FTIR instrument [7]. Typically , the spectra were run using liquid nitrogen cooled InGaAs detector and laser power of 100-300 mW. Thermal studies were run using PE DSC 7 and TGA 7 analysers.