Topochemical polymerization diacetylenes

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

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. 

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]. 

Diacetylene monolayer photopolymerization was found to be topochemical it only occurred in the two-dimensional solid state of the surfactants. Polymerized diacetylenes, both in monolayers and in LB films, were found to be rather rigid and prone to cracking [160]. This undesirable property somewhat limits the exploitation of polymerized diacetylene LB films for potential electronic applications. 

The fact that the polyreaction of diacetylenes is topochemically controlled is especially well documented by the polymerization behavior of the sulfolipid (22)23 . (22) forms two condensed phases when spread on an acidic subphase at elevated temperatures (Fig. 10). UV initiated polymerization can only be carried out at low surface pressures in the first condensed phase, where the molecules are less densely packed. Apparently, in the second phase at surface pressures from 20 to 50 mN/m the packing of the diyne groups is either too tight to permit a topochemical polymerization or a vertical shift of the molecules at the gas/water interface causes a transition from head packing to chain packing (Fig. 10), thus preventing the formation of polymer. 

Due to the topochemical restrictions of diacetylene polymerization, diacetylenic lipids are solely polymerizable in the solid—analogous phase. During the polyreaction an area contraction occurs leading to a denser packing of the alkyl chains. In addition to surface pressure/area isotherms the polymerization behavior of diacetylenic lipids containing mixed films give information about the miscibility of the components forming the monolayer ... 

Fig. 32 (a) Topochemical polymerization mechanism for a typical diacetylene monomer, (b) Crystal structure of a typical poly diacetylene... 

Figure 4.10 UV-induced topochemical polymerization, (a) UV spectra of compounds F-l did not show any indication of poly(diacetylene) formation, (b, c) Macromonomers A-D were successfully converted into poly(diacetylene)s. (d) The reactivity toward topochemical polymerization was related to the total number of hydrogen bonds, (e) Upon addition of HFIP to a sample solution in DCM after UV irradiation, helical fibrillar...

Some important aspects of topochemical polymerizations can be understood by inspection of Eq. (1), All reactivity comes about by very specific rotations of the monomers and by 1,4-addition of adjacent units and an extended, fully conjugated polymer chain is formed. The unique feature of the topochemical polymerization of diacetylenes is the fact that in many cases the reaction can be carried out as a single phase process. This leads to macroscopic, defect-free polymer single crystals which cannot be obtained, in principle, by crystallization of ready-made polymers by conventional methods. Thus, polydiacetylenes are ideal models for the investigation of the behaviour of macromolecules in their perfect three dimensional crystal lattice. 

Owing to the mechanism of the topochemical reaction the polyconjugated polymer chain is of exceptional purity and stereochemical regularity. Polydiacetylene crystals are thus ideally suited to study the inherent optical and electrical properties of polyconjugated chains. These unique features have attracted considerable attention and in recent years the topochemical polymerization of diacetylenes has developed to... 

Homogeneous topochemical reactions are quite rare. The topochemical polymerization of diacetylenes and with special precautions some four center photodimerizations are examples for this reaction mode. 

The topochemical polymerization of diacetylenes proceeds by a 1,4-addition reaction according to ... 

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