Polymerization of diacetylene

Enkelmann, V. Structural Aspects of the Topochemical Polymerization of Diacetylenes. Vol. 63, pp. 91-136. 

Figure 8. Solid-state polymerization of diacetylenes. A crystalline array of monomer units polymerizes through intermediate states to the final crystalline polymer chain.

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. 

The second reaction we will treat here that in many cases proceeds by a homogeneous mechanism is the solid-state polymerization of diacetylenes. The photolability of these compounds has long been known (189), but it was not until the appearance of the pioneering works of Hirshfeld and Schmidt (168) and of Wegner (190) that some real understanding of the process was introduced. This led to an explosive interest in the subject, and more than 200 diacetylene derivatives have now been studied, by a wide variety of techniques (191). 

Independent evidence for local stress is provided by measurements of the frequency of the antisymmetric stretching vibration of C02 eliminated in crystalline undecanoyl peroxide on photolysis (253). The results indicate that local pressures of tens of kilobars are established. This is very much larger than the lattice strain that has been considered as developing during the polymerization of diacetylenes (254). McBride points out (246) that virtually all reactions cause changes in shape that should create local stress in a solid, so that subsequent... 

Fig. 17 Schematic diagram showing the molecular packing and topochemical polymerization of diacetylenes [30] in crystals. There are two idealized packing arrangements either (a), (b) or (c), (d) in crystals and each has two modes of polymerization. The polymerization in the solid state is said to occur smoothly when, v = 240 400 pm and y = 45° (Baughman, 1974 Baughman and Yee, 1978).

The polymerization proceeds under photo- [49,50],X-ray [51], and y-ray [52] irradiation in the dark in vacuo, in air, or even in water or organic solvent as the dispersant (nonsolvent) for the crystals, similar to the solid-state polymerization of diacetylene compounds [ 12]. The process of topochemical polymerization of 1,3-diene monomers is also independent of the environment surrounding the crystals. Recently, the thermally induced topochemical polymerization of several monomers with a high decomposition and melting point was confirmed [53]. The polymer yield increases as the reaction temperature increases during the thermal polymerization. IR and NMR spectroscopies certified that the polymers obtained from the thermally induced polymerization in the dark have a stereoregular repeating structure identical to those of the photopolymers produced by UV or y-ray irradiation. 

The present polymerization principle (the 5 A rule) for the 1,3-diene monomers seems to have features similar to the empirical rules for the polymerization of diacetylene compounds reported in the literature dg 5 A and 0-45°... 

Currently, topochemical polymerization is opened not only to the diacetylene library but also to the diene library, which is more popular and a larger collection. Diene polymerization has the potential of being applied to the construction of advanced organic materials in the solid state, because the topochemical polymerization of diacetylene and diene monomers provides different types of polymers, that is, conjugate and nonconjugate polymers, respectively (Scheme 8) [16,61]. 

Lauher and Fowler et al. have proposed an elegant strategy for the control of topochemical polymerization based on the host-guest cocrystal concept. They used the ureylene and oxalamide functionality to form layered supramolecu-lar structures for the topochemically controlled polymerization of diacetylenes and 1,3-butadienes in the solid state [62,63]. 

Baughman RH. Sohd-state polymerization of diacetylenes. J Appl Phys 1972 43 4362-4370. 

Yang Y, Lu Y, Lu M, Huang J, Haddad R, Xomeritakis G, Liu N, Malanoski AP, Sturmayr D, Fan H, Sasaki DY, Assink RA, Shelnutt JA, van Swol F, Lopez GP, Bums AR, Brinker CJ. Functional nanocomposites prepared by self-assembly and polymerization of diacetylene surfactants and silicic acid. J Am Chem Soc 2003 125 1269-1277. 

Polymerization of diacetylene (Fig. 8.13) is one of the most elegant examples of the topochemical principle. Wegner (1971, 1979) showed that diacetylene monomers, R—C = C—C = C— R, polymerize in the solid state by a 1,4-addition reaction at the diacetylene group to produce a polymer that can be represented by the mesomeric structures ... 

The correct alignment of surfactants in some, but not all, SUVs is an essential requirement for polymerization. Polymerization of diacetylenes is topochemically controlled and only occurs below the phase transition temperature of the surfactant. In contrast, SUVs prepared from styrene-containing surfactants could be polymerized in their fluid states [55]. The degree of polymerization varied from very low (10-20 for SUVs prepared from styrene containing surfactants) to rather high (several hundred for SUVs prepared from diacetylene-containing surfactants). 

Besides the polymerization of diacetylenes, butadienes and acrylates, the polycondensation behavior of long-chain ot-amino acids, diamines and diesters has been investigated in monolayers 52. ... 

Grim, P. C. M., De Feyter, S., Gesquiere, A., etal, Submolecularly resolved polymerization of diacetylene molecules on the graphite surface observed with scanning tunneling microscopy. Angew. Chem., Int. Ed. 1997, 36, 2601-2603. 

Another class of photoinduced reactions known to produce large refractive-index changes is the polymerization of diacetylenes (29). These reactions are typically carried out in crystals of the monomer, and result in the production of a fully conjugated polymer backbone. Optical data on these materials are not very extensive, but from what information is available we estimate that nQ 10 22 cm3. (This is for light polarized parallel to the polymer backbone. For the perpendicular polarization the index change is about half as large.)... 

Figure 1. Solid-state polymerization of diacetylenes shown schematically (left) an array of monomer molecules in the crystal lattice frightj the resulting polydiacetylene chain.

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