Diacetylenes topochemically controlled

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]. 

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). 

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. 

CHjNHjJj MtX are shown in Figs. 23a and b. They demonstrate effects on the photoreactivity due to a variation of the substituent R, and the inorganic salt MtXj From Fig. 23b a topochemical control of the reaction caused by the nature of the MF ions is evident. Similar effects are also reported for corresponding diacetylene derivatives (Chapt. 2.7). The butadiene polymerization in layer perovskite halide salts is schematically represented in Fig. 24 . ... 

The polydiacetylenes and polytriacetylenes differ from polyacetylene because preorganization of the diacetylene and triacetylene is required for a successful polymerization (7). This remarkable observation was first recognized (8,9) in 1969 and marks the beginning of modern polydiacetylene and polytriacetylene chemistry. In a few cases, this topochemically controlled polymerization occurs from a crystal of the monomer to a crystal of the polymer, giving rare examples of macroscopic single polymer crystals (9). 

Preparation of Polydiacetylene. The preorganization for the 1,4-polymerization of diacetylenes has been discussed previously (7,14,15). Successful polymerization occurs when the diacetylenes have a translational repeat distance (d) of about 0.49 nm and an angle (tt) of about 45° with respect to the translational direction and van der Waals contact (i v) of the polydiacetylene functionalities (Fig. 1). If these structural parameters are met then the Cl and C4 carbon atoms of adjacent diacetylenes will be in a position for a topochemically controlled polymerization. Because the 0.49 nm translational repeat distance (d) of the monomer is about the same as the repeat distance in the polymer, the pol5nnerization process can occur with little disruption of the reactant packing. 

The most critical structural parameter shown in Figure 1 is the transitional repeat distance d of the diacetylene. The ideal value for d is about 0.49 nm. This is a necessary structural parameter for a topochemically controlled polymerization. If this structural condition is achieved and the diacetylene functionalities close pack then a simple calculation demonstrates that the angle will be about 45° and the 1-4 carbons of the diyne will be in close contact. 

Fig. 5. The use of carbamates and host-guest chemistry to organize diacetylenes for a topochemically controlled polymerization.

Fig. 6. A lipid monolayer with the diacetylene functionalities properly oriented for a topochemically controlled polymerization.

Preparation of Polytriacetylene. Soon after the early understanding of the diacetylene polymerization was reported (8,9), attempts were made to polymerize a triacetylene to produce a polytriacetylene (45). However, these early attempts as well as more recent efforts (7) were not successful. The difficulty of the topochemically controlled polymerization is the organization of the triacetylene monomer with a translational repeat distance of about 0.74 nm. 

The polyreaction of diacetylenes is topochemically controlled (16), i.e. it is only possible in the solid-analogue state. 

There is no doubt that these principles are applicable too to other systems which undergo topochemically controlled polymerizations, such as the diacetylenes [33] and, to a lesser extent perhaps, to mixed crystals (to give copolymers) and to inclusion complexes, in urea for example. Trans, fraws-pentadiene in urea has been reported to give a stereoregular polymer [42]. Further, it is known that crystals of the urea channel complexes have chiral structures. Thus we expect that this polymerization in a single crystal would give rise to an asymmetric polypentadiene, and therefore would provide a further example of absolute synthesis. 

Fig. 5 Topochemical polymerization of diacetylenes in the solid state (a) topochemical requirements and (b) a host-guest strategy for controlling polymerization of diacetylenes using an oxalamide of glycine as a supramolecular host.

The preparation of new polydiacetylenes and polytriacetylenes is complicated by the fact that no one has demonstrated a direct 1,4-diacetylene or a 1,6-triacetylene polymerization in solution, 1,2-polymerizations being more favorable. However, the polymers can be prepared in the solid state as the result of a topochemical polymerization. Topochemical reactions are solid state reactions in which the product and the regio- and stereochemistry of a reaction are directly controlled by the preorganization of the reactants. 

Topochemical Polymerization The Ught-induced soUd-state polymerization of certain monomers at ambient temperature is a very intriguing phenomenon that has been dealt with in numerous articles and books [55-64]. Diacetylenes and dialkenes (see Charts 3.7 and 3.8) polymerize imder crystal-lattice control... 

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. 

---