The present state of knowledge of the topochemical polymerization of diacetylenes is reviewed with regard to structural properties. Principles and mechanisms of topochemical reactions are described. Solid-state polymerization of diacetylenes utilizes the special packing properties of monomer units in their crystals. Rules relating reactivity in the solid-state and packing properties are given and the relation between reaction mechanism, molecular mobility and polymer morphology are discussed. The growth of the macromolecules in the monomer crystal, the molecular weight and its distribution with regard to the reaction kinetics and phase transitions are outlined. The electronic structure of the polydiacetylene chain is best represented by the acetylene resonance structure consisting of alternating double, single and triple bonds.

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Structural aspects of the topochemical polymerization of diacetylenes

Synthesis of a series of asymmetrically substituted diacetylenes containing a thienyl moiety or a quinolyl moiety as one of the side groups directly bound to diacetylene and a urethane group as the other one was carried out. Though some of the prepared diacetylenes could be polymerized in solid state by using UV and γ-radiation, all of them were stable when heat was used as the stimulus. The monomer to polymer conversion for the polymerizable ones was found to be in the range 35−60%. Various spectroscopic techniques, such as FTIR, solid state 13C NMR and visible absorption spectroscopies, and powder X-ray diffraction were used to elucidate the structures of the polydiacetylenes. One of the polymers containing quinolyl moiety as directly bound side group showed unusually long and sharp absorption maximum indicating long and uniform conjugated chains. Third-order nonlinear optical susceptibility, χ(3), of two of the polymers were measured using Maker's fringe technique. The largest value for χ(3) in the res...

Polydiacetylenes from Asymmetrically Substituted Diacetylenes Containing Heteroaryl Side Groups for Third-Order Nonlinear Optical Properties

Nonferroic phase transitions are defined as the structural transitions occurring with a breaking of translational symmetry within the same crystal class. They involve no new macroscopic tensor components below the transition point, and they are generally identified experimentally through the onset of superlattice reflections denoting the multiplication of the crystal's unit cell. A theoretical analysis of these transitions is presented, based on Landau's symmetry criteria for continuous transitons, of the order-parameter symmetries, space-group changes, and free-energy expansions. We establish that the order parameters of such transitions are necessarily related to one-dimensional (real or complex) small representations of the group of the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ vector. Their symmetry characteristics are, in general, simpler than those of other types of structural transitions. Most of them possess a one-component order parameter inducing a doubling of the unit cell. The remaining ones are associated with order-parameter dimensions as high as six, and unit-cell multiplications up to thirty-two. The coupling of the order parameter to macroscopic quantities, illustrated by the example of dielectric ones, is shown to belong to two possible schemes. The relation between nonferroics and antiferroelectrics is discussed. The theoretical results are compared to the available experimental data which pertain mainly to organic compounds and metallic alloys.

Nonferroic phase transitions

The solid-state polymerization of disubstituted diacetylenes, either thermally or with ionizing radiation, can lead to a macroscopic polymer crystal product. The recent intensive investigations of this polymerization are reviewed. A brief outline of the history of diacetylene polymerization is presented. The constraints on the crystal structures of the monomers necessary for solid-state reactivity are outlined. X-ray structural data is used to identify the most important criterion for reactivity. The models developed to describe the kinetics of polymerization are presented in the context of available experimental data. Finally the details of the polymerization mechanism, as revealed by spectroscopic studies, are discussed.

The Polymerization of Disubstituted Diacetylene Crystals

The first measurement of a one-dimensional relaxation law is reported. The photocurrent decay of the polydiacetylene PDA-10H has been measured in the time range (1-2*104)s. The measurements can be extremely well described by an exp(-bt13/) law, characteristic of deep trapping in a one-dimensional system. Comparing experiment and theory the authors are able to estimate trap concentrations and effective jump rates.

http://iopscience.iop.org/article/10.1088/0022-3719/16/18/005/pdf

One-dimensional recombination of charge carriers

The second order phase transition at 195 K which occurs in bis (p-toluene sulfonate) diacetylene polymer crystals has been studied by optical reflection and transmission, Raman and far-infrared spectroscopy. Order parameter fitting to the data suggests that at low temperatures the transition has a two dimensional character while closer to the transition it appears to be three dimensional. There are indications of a broad transition region which might be expected for a predominately two dimensional phase transition in which fluctuations dominate the behaviour of the system. Analysis of new X-ray crystallographic data gives some support to a structural model in which the transition would have a substantial two dimensional character.

D. A. Fisher

Papers

A Spectroscopic Study of the Second Order Phase Transition in Bis (p-toluene sulfonate) Diacetylene Polymer Crystals

Structure of 3,5-octadiyne-1,8-diol at 120 K

Structure of 2,4-hexadiyn-1-ol at 110 K