Solid state reactions 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. 

Solid-state polymerization of D3, initiated by 7-irradiation, has been known for a long time. The reaction proceeds according to the cationic polymerization mechanism.3,5 Solid-state anionic polymerization of hexaphenylcyclotrisi-loxane in the presence of KOH or potassium oligosiloxanolate was recently reported. The crystalline structure of the polymers obtained in high yield in the heterogenous reaction was determined.1... 

There are numerous examples of solid state polymerizations. Here we will briefly describe examples based on addition polymers. Generally, the crystalline monomer is irradiated with electrons or some form of high-energy radiation, such as gamma or x-rays. Since many monomers are solids only below room temperature, it is customary to begin irradiation at lower temperatures with the temperature raised only after initial polymerization occurs. (Some reactions are carried to completion at the lower temperature.) After polymerization, the monomer is removed. Table 6.10 contains a list of some of the common monomers that undergo solid-state irradiation polymerization. 

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. 

An example is the photopolymerization of 2,5-distyrylpyrazine (DSP) (Fig. 17), with polymerization occurring via intermolecular [2-1-2] photocyclization reactions at each end of the monomer molecule. Although this reaction is regarded as a classic solid-state reaction, having been studied extensively around 40 years ago [121,122], structure determination of the polymeric product phase was only carried... 

Colourless diacetylene monomer crystals can be polymerized under heat, ultraviolet. X-ray or y-ray irradiation to form single-crystal, highly coloured polyacetylenes. The solid state reaction transforms the entire monomer crystal to polymer crystal without phase separation the polymer forms a solid solution with the monomer over the entire... 

Glass transition determinations Decomposition reaction Reaction kinetics Phase diagrams Dehydration reactions Solid-state reactions Heats of absorption Heats of reaction Heats of polymerization Heats of sublimation Heats of transition Catalysis... 

The solid n-hexadecene-1 system has also been studied.76 It was concluded that the experimental results were incompatible with a free-radical reaction and an ionic mechanism was proposed. An enhancement in the polymerization yield by a factor of 2 on going from the liquid at 20 °C. to the solid at 0°C. was observed. Solid-state ionic polymerizations induced by high-energy radiation have been reviewed by Magat.76... 

The compound HggAs Bi r is obtained by solid state reaction. The structure consists of a polymeric cationic framework [Hg7(HgBr)2As4+] (Figure 26) formed by chains of Hg+As tetrahedra, which are connected by mercury atoms.87 At several positions this connection is truncated by terminal HgBr groups (Hg—As = 242.8-253.0 pm). 

Quite a number of interesting solid-state reactions have been observed that do not quite fit into the categories of earlier sections. These include reactions of coordinated ligands, changes of coordination number or geometry and polymerization reactions. Limitations of space do not permit detailed discussions of these reactions. 

One of the best-studied solid-state reactions is the photopolymerization of distyrylpyrazine (9) and related compounds to give crystalline polymers containing cyclobutane rings (Scheme 10). This reaction is reminiscent of Schmidt s early work on cinnamic acids, although the presence of two double bonds per monomer can lead to oligomeric or polymeric rather than solely dimeric products. The four-center reaction of 9, and other related polymerizations, have been reviewed in detail by Hasegawa, who has played a central role in the study of these systems... 

Catalytic molecular surface species may undergo drastic changes in their structure in the presence of reactants. For example, polymeric clusters may transform into highly distorted monomeric species. A crystalline phase may become mobile at its Tammann temperature, as shown by Raman spectroscopy, and it may spread over oxide supports driven by the reduction of the overall surface free energy. Reactive environments trigger many structural transformations, exemplified by particle sintering, dispersion of bulk phases, segregation of surface species into bulk phases, and solid-state reactions between supported oxides and supports. 

Such approach of the synthesis by solid-state reaction is especially attractive with precursors that present silanol functions. Here again, the supramo-lecular association promoted by these functions combined with their reactivity allows to directly transform by a simple thermal treatment a molecular precursor to a polymeric hybrid material. Liu, et al. have reported on the possibility to polycondense silanols in the solid state [95], and Corriu et al. have obtained the formation of layered materials by condensation of bis-trisilanol precursors [96,97],... 

The reaction mechanisms of this extraordinary solid state reaction has strongly attracted the interest of the polymer chemists from the very beginning. Valuable information on several aspects of the thermal polymerization reaction mechanisms, have been obtained from X-ray structural and physico-chemical investigations, discussed by Wegner Baughman and Chance . However, the identifi-... 

Reactivity in the solid-state is always connected with specific motions which allow the necessary contact between the reacting groups. In most cases solid-state reactions proceed by diffusion of reactions to centers of reactivity or by nucleation of the product phase at certain centers of disorder. This leads to the total destruction of the parent lattice. If the product is able to crystallize it is highly probable that nucleation of the crystalline product phase at the surface of the parent lattice will lead to oriented growth under the influence of surface tension. In such topotactic reactions certain crystallographic directions of parent and daughter phases will coincide. Typical examples for this behaviour are the solid-state polymerizations of oxacyclic compounds such as trioxane, tetroxane or 3-propiolactone... 

The possibility of covalent interfullerene bond formation in solid and in some of its salts, results in a variety of dimers and polymers. Both the dimerization and the polymerization of Cgo are characteristic solid state reactions, up to now, neither of them were carried out in solution. In the fee lattice of C g the concentration of the reacting molecules is about 3 orders of magnitude higher than that in solution. The free rotation of the molecules allows for the geometrical conditions required by the transition state of the polymerization and the rigid polymer rods or sheets can form by a small rearrangement of the precursor structure. 

FIGURE 18,2. The solid-state polymerization (at wavelengths greater than 340 nm). (a) The reaction occurring in the solid state, and (b) a diagram of the solid-state reaction. The ene dione double bonds of adjacent molecules in the crystal have a C C distance (indicated by hatched lines) of 3.62 A. Cyclobutane dimerization occurs across a center of symmetry. (Refs. 10 and 14). 

In this chapter, we describe the isomerization, dimerization, and topochemical polymerization of benzyl muconates with various kinds of substituents on the benzyl ester group (Scheme 24.1), in order to reveal the solid-state reaction mechanism by the direct observation of crystal structures which change during the reactions. 

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