Lattice control, solid-state polymerization

The solid-state polymerization of diacetylenes is an example of a lattice-controlled solid-state reaction. Polydiacetylenes are synthesized via a 1,4-addition reaction of monomer crystals of the form R-C=C-CeC-R. The polymer backbone has a planar, fully conjugated structure. The electronic structure is essentially one dimensional with a lowest-energy optical transition of typically 16 000 cm-l. The polydiacetylenes are unique among organic polymers in that they may be obtained as large-dimension single crystals. 

At present there is considerable interest in studying various topics relating to or deriving from solid-state polymerization. This has come about because of interesting and potentially useful properties of several polymers formed by lattice-controlled processes and because of the natural desire to increase the number of systems available for additional study. The experimental results alluded to have been achieved in the last several years, and it is now appropriate to take stock of these activities to understand how and why they have come to their present state and also to see how they might be given greater breadth and depth. 

Recently, the term design of a solid-state polymerization was introduced with a view toward discovery and development of new lattice-controlled processes (. The term implies not easily separedile crystallographic and mechanistic issues, and it was suggested 7) that mechanistic aspects of initiation and propagation may hold the key to progress along these lines. 

While some of the above discussion is in the general reedm of prognostication, some mote specific comments are appropriate. It is appeuent that em increase in both the number and types of solid-state polymerization is a desirable research objective. Here, the major initial burden lies with the chemist to design (, new reactive molecular structure and appropriately oriented monomer crystal structures. Successful development of new lattice-controlled processes resulting in the availability of well-defined fully ordered mticromolecules will readily attract the more physically and theoreticedly oriented research communities. The PDA and poly (sulfur nitride) cases bear strong witness to this point. 

This article describes the solid state polymerization of 1,i-disubstituted butadiene derivatives in perovskite-type layer structures, in layered structures of organic ammonium halide salts, and in lipid layer structures. Recent investigations by spectroscopic methods and x-ray structure analyses are described. The studies clearly indicate that the photolysis in the crystalline state leads to the formation of 1,i-trans-polymers exclusively. Crystal structure analyses of monomeric and polymeric layer perovskites demonstrate that upon y-irradiation a stereoregular polymer is obtained in a lattice controlled polymerization. 

This paper presents studies of solid state polymerization aimed towards formulating a dynamic model of reactivity in the condensed phase. Phonon spectroscopy is successfully used to elucidate the mechanism of lattice control of the reaction. Novel concepts of phonon-assisted thermal and photochemical reactions are introduced, supported by experimental data. Non-linear laser spectroscopy is used to find the importance of biexcitonic processes in photopolymerization. Also, spectroscopic studies of reactions in Langmuir-Blodgett films and at gas-solid interface which produce ordered polymers are presented. 

Yesinowski, J.P. Eckert, H. Sandman, D.J. Velazquez, C.S. In "Solid State Polymerization and the Structure and Properties of Polymers Produced by Lattice-Controlled Processes Sandman, DJ., Ed. ACS SYMPOSIUM SERIES, to be published. 

We have established an effective and simple method for preparing a variety of organic microcrystals in water. The solid-state polymerization of 4BCMU microcrystals was estimated to proceed from one end to the other end. The possibility of preparing PDAs with controlled molecular weight was qualitatively demonstrated. In the case of microcrystals of 14-8ADA, size-dependent conversion is found and can be explained by the looseness or thermal vibrations of the crystal lattice. 

What are the requirements for an absolute asymmetric polymerization First, we need an achiral or,chiral-racemic monomer crystallizing in a chiral structure in the latter case this entails disorder in the crystal with respect to the chiral handle. Second, the solid-state polymerization must be such that both the initiation and propagation steps are controlled by the crystal lattice (topochemical control) for this to be so requires a structure in which adjacent reactant centers are the correct distance apart and have the correct relative orientation [10]. 

Two other types of system undergo solid-state polymerization which is to a considerable extent lattice controlled. One such type consists of lattice inclusion complexes ... 

The solid-state polymerizations of trioxane [32,33] and of diacetylenes [34], proceed as topochemical reactions - that is, the polymerization is crystal-lattice controlled and proceeds with a minimum of atomic and molecular movement. Upon ring-opening, trioxane molecules form helical polyoxyraethylene chains lying in the direction of the c-axis of the trioxane crystals. Such polymerization affords only a very small volume change. 

An obvious extension of the studies on photodimerization of crystalline olefins is to solid-state vinyl polymerization (with light, if absorbed, or y-irradiation), with the aim of achieving stereoregular polymers. In fact, an immense effort has been made in this direction, but with singular lack of success. The explanation is that, for various reasons, the lattice in the vicinity of the chain front becomes progressively more damaged as polymerization proceeds, so that after relatively few steps there is loss of stereochemical control. 

Eq. 2-248) [Braun and Wegner, 1983 Hasegawa et al., 1988, 1998]. This polymerization is a solid-state reaction involving irradiation of crystalline monomer with ultraviolet or ionizing radiation. The reaction is a topochemical or lattice-controlled polymerization in which reaction proceeds either inside the monomer crystal or at defect sites where the product structure and symmetry are controlled by the packing of monomer in the lattice or at defect sites, respectively. 

The lattice-controlled diyne polymerization can occur in lipid bilayers only, if the amphiphiles are present in the solid-condensed state. Several studies dealt with the characterization of the monolayer properties of diyne surfactants. Fatty acids, for example, were investigated concerning influences of a chain length variation and headgroup ionization on the Glm stability (Fig. 9a) sv.eo. 62-64,70) number of... 

These characteristics can be derived from a polymerization of crystalline monomers controlled topochemically. Topotactic reaction geno-ally involve a strong correspondence between the lattices of the monomer crystal and the resulting polymer crystal. Hence, the topochemical solid state reaction occurs when sufficiently intense thermal mobility of molecules takes place in the lattice, and the distance between active centers for the polymerization in the neighboring molecules should not exceed 3.7 A for C — O interactions All monomers mentioned above show quite close C — O interactions. 

Thus solid-state vinyl polymerization is in general not under topochemical control, or at most only partially so. We ask ourselves then what sorts of processes do proceed under lattice control. 

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