Solid-state polymerization of a cyclic diacetylene

Large polymeric single crystals of a unique ring-bridged polymer have been produced by the solid-state polymerization of a cyclic diacetylene (o,o′-diacetylenyldiphenyl glutarate). These crystals are of high thermal stability, metallic in appearance with an asbestos-like texture, infusible, and insoluble. Single-crystal x-ray diffraction investigation indicates that the polymer is monoclinic (probable space group C2/c or Cc) with a unit cell containing four monomer units of dimensions α = 20.8 Å, b = 8.0 Å, c = 9.7 Å, and β = 106°. Infrared spectra eliminate the previously suggested possibility that the solid-state reactivity of the above monomer corresponds to either reaction of the carbonyl function with the acetylenic bond or the cleavage of the ester linkage. Diffraction, dichroism, and Raman spectral studies indicate instead that the reaction proceeds by 1,4-addition polymerization at the diacetylene group to produce a trans–trans polymer of structure where the curved lines represent the di-(o-phenyl)-glutarate linkages which are on opposite sides of the chain for adjacent monomer units.     

Quantum-chemical investigation of the mechanism of ionic polymerization in crystals

The results of quantum-chemical investigations of radiation-induced polymerization in molecular crystals are presented. The detailed calculations of the potentials energy curves characterizing the chain generation and propagation reactions, with explicit account of the reacting system interaction with the crystalline environment, provide a reasonable interpretation of the experimental observations. The basic conclusion is that the addition of the growing polymer ion to the monomer molecule placed at a lattice point needs no activation energy. The polymer chain is spontaneously moving in the interlayer space of the crystalline lattice at every propagation step, the overall displacement reaching a macroscopic value. Several termination mechanisms are briefly discussed. The possibility of molecular tunneling cannot be completely eliminated, however, it is expected to occur at the nonchemical preliminary stage of the reaction.     

The optical intermediates of the low-temperature photopolymerization of TSHO diacetylene crystals

Information about the mechanism of the solid-state photoreaction in bis(p-toluene sulphonate) ester of 2,4-hexadiyne-1,6-diol (TSHD) is deduced from optical spectra. The photoinduced generation and decay kinetics and the structure of the short-chain singlet intermediates (optical intermediates) observed in the optical absorption spectra during the low-temperature photoreaction are discussed.     

Solid-state polymerization of diacetylene: 1,11,13,23-tetracosatetrayne

The solid-state polymerization of a diacetylene, 1,11,13,23-tetracosatetrayne, was studied using x-ray powder diffraction and electron diffraction. It is shown that the material exhibits polymorphism. Thermochromic transitions, which are generally observed for diacetylenes, are related to the particular crystalline phase using x-ray powder diffraction. The unit cell dimensions and space group of one polymorph were determined by electron diffraction analysis: a = 20.83 Å, b = 4.84 Å, c = 10.08 Å, β = 92.4°, space group: P2₁/n. © 1995 John Wiley & Sons, Inc.     

Dielectric properties of single crystals of the substituted diacetylene pTS: effect of the solid-state polymerization and phase transitions

Dielectric permittivities of the polymerizable organic solid, pTS diacetylene have been measured between 115 and 330 K in the directions parallel and perpendicular to the direction of polymer chain growth. The upper phase transition in monomer, polymer and mixed crystals at various stages of the solid-state polymerization manifests itself as a maximum in the temperature dependence of ε measured in the direction parallel to the molecular stacks, being particularly well pronounced in fully polymerized crystals. The transition was identified as an antiferroelectric one, the sublattice polarization being most probably the order parameter. The lower phase transition could be observed only in monomer and monomer-rich crystals as a shoulder on the ε(T) dependence. This transition could be detected only in the crystals containing less than ≈ 10–15% of polymer. The dielectric permittivity was found to be independent of frequency up to 3 GHz. The polymerization results in changes of the dielectric permittivity. In samples where the direction of measurements coincides with the b axis, these changes follow the monomer-polymer conversion curve.     

Pressure dependence of phase transitions in two diacetylene crystals

The phase transitions which occur in a diacetylene polymer crystal (PTS) at 195 K and a diacetylene monomer crystal (DCH) at 142 K have been studied as a function of pressure. For the second-order phase transition in PTS the pressure dependence of the transition temperature was found to be less than 0.05 K MPa^?1; for the first-order transition in DCH it was 0.63 ± 0.08 K MPa^?1.     

On low temperature fluorescence of perylene crystals

At low temperatures, the broad excimer fluorescence band of α-perylene crystals is replaced by a weakly structured emission at higher energy. This emission originates from a new crystal state (Y-state) which is populated independently of the high temperature excimer (E-state). Due to the temperature dependence of its first order decay rate and due to the thermally activated formation of the E-state, the Y-emission grows rapidly at temperatures below 90 K. The Y-emission differs from the fluorescence of the monomeric β-perylene at 5.5 K by its Stokes shift of 1300 cm^?1, the lack of vibronic structure, the long first order decay time of 40 ns and the absence of bimolecular annihilation indicating a localized state. The Y-state is attributed to a less relaxed pair state formed upon contraction of the dimeric crystal lattice.     

Excited quintet states during the photopolymerization of diacetylene single crystals

During the photopolymerization of perdeuterated PTS diacetylene single crystals at low temperatures, excited quintet states (S = 2) are observed Nine ESR transitions per quintet were detected. They are analyzed in terms of a spin hamiltonian for S = 2. They are due to bicarbenes of, probably, short oligomers.     

Proton spin-relaxation study of the polymerization of diacetylene in a single crystal

Proton spin-lattice relaxation experiments on the bis-(p-toluenesulfonate) of 2,4-hexadiyne-1,6-diol (TSHD) as a function of temperature (25 to 353 K), of frequency (22 and 44 MHz), and of conversion to polymer were performed to determine the molecular motions in this crystal and to follow the conversion via the changes in the relaxation time T₁. It was found that T₁ is dominated below 125 K by weakly hindered (ΔE = 2.8 kJ/mole) tunneling (Λ = 220 MHz) CH₃ groups, at about 160 K by order-disorder fluctuations around the phase-transition temperature ?_c which depends strongly on the conversion, and above 200 K by the motion of the whole side group. T₁ can be used as sensitive probe for the conversion: The change in T₁ at about 44 K is directly proportional to the conversion, whereas the change at high temperatures (e.g., 353 K) occurs essentially at low conversions (?10%). This is explained by distorted (stressed) areas around the isolated polymer chains, which are estimated to be about 16 times the size of the chains. After an induction period the stresses are relieved by further polymerization.     

Analysis of the optical absorption spectra of diradical oligomers in diacetylene crystals

We report on electronic and vibrational properties of the diradical short-chain reaction intermediates of the low-temperature polymerization reaction in diacetylene single crystals. The positions, shapes and intensities of the zero-phonon lines and of vibronic lines of the polarized optical absorption series are analyzed. Theoretical model calculations concerning the vibrational and excitonic states in the molecular aggregates are performed and applied to the experiments.     

Temperature dependent optical absorption of partially polymerized diacetylene crystals

The temperature dependence of the absorption of diacetylene chains dispersed in partially polymerized monomer matrices has been measured over the range from 2 to 380 K for a number of different monomers. The results are interpreted in terms of the effects of the different lattice environments on the polymer chains. It is shown that, in general, the polymer chain length does not have a major effect on the absorption spectrum.     

Pyroelectric effect in crystals of the bis-toluene sulphonate diacetylene monomer and polymer

The pyroelectric properties of the monomer and partially and fuly polymerized crystals of the bis(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol (TS) were measured along their b axes from 100 to 300 K. Two peaks in the pyroelectric current of monomer crystals were found at 192 and 151 K. It is concluded that these crystals lack a centre of symmetry.     

Controlled polymerization of substituted diacetylene self-organized monolayers confined in molecule corrals

We have shown that STM-tip-induced chain polymerization of 10,12-tricosadiynoic acid (TCDA) in a self-organized monolayer at the liquid-solid interface of TCDA on highly oriented pyrolytic graphite is possible. The oligomers thus produced started at the point where a voltage pulse was applied between the STM tip and the sample during a short period when the feedback condition was momentarily suspended (as it is for scanning tunneling spectroscopy). Polymerization probabilities depended upon the length of the applied voltage pulse and were generally higher for longer pulse widths in the 10-ms to 100-micros time scales, approaching unit probability for the former and decreasing quickly to a few tens of percent for the latter. The polymerization could be confined to certain nanometer-sized areas by using "molecule corrals,"and polymerization appeared to be governed by topochemical constraints. Polymerization across domain boundaries, or over molecule corral edges, was never observed in over approximately 150 observations. Due to the constant supply of nonpolymerized molecules from the covering solution, a dynamic exchange between molecules on the surface and in the solution was possible. This exchange occurred on a time scale that was comparable to the image acquisition time (approximately 10(1) s), and appeared to depend weakly upon the length of the desorbing oligomer. The desorption process was probably also influenced by interactions with the STM tip.     

Mechanism of low temperature decomposition of NiO single crystals

The decomposition of NiO single crystal was investigated under dissociative conditions in the temperature interval between 330 and 850 °C in the absence of reducing gas species. An unusually fast and constant decomposition rate was measured at the lowest temperatures, coupled with an unusual largely porous microstructure of the metallic product layer. This anomalous high reaction rate was interpreted on the basis of a decomposition mechanism implying the dissociative vaporization of the oxide followed by the condensation of the metal. The proposed mechanism is supported by the microstructure of the product and of the reacting interface. The complex dependence of reaction rate from temperature was shown to be related to a collapse of the porous product to form a compact metal layer at higher temperatures due to sintering.     

Identification and correlation of the short-chain intermediates and final photoproducts in diacetylene crystals

We report on three optical absorption series observed in the course of the low-temperature photopolymerization reaction of diacetylene crystals. The series are assigned to diradical and asymmetric carbene intermediates and to final stable oligomer photoproducts. The chain-length dependence of the photoproduct series is described by a one dimensional electron gas theory.     

High molecular weight and low dispersity polyacrylonitrile by low temperature RAFT polymerization

High molecular weight polyacrylonitrile (PAN) with low dispersity has been successfully synthesized utilizing reversible addition‐fragmentation chain transfer (RAFT) polymerization. A comprehensive study was performed to understand the influence of reaction temperature, RAFT agent structure, and [M]₀:[CTA]₀[I]₀ on the polymerization kinetics, molecular weight, and dispersity. Enhanced control is attributed to reduction of side reactions by conducting the polymerization at lower temperature, and optimizing the radical exchange between active and dormant states via appropriate selection of RAFT agent and initiator. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 553–562