Topochemically controlled solid-state polymerization

Scheme 11-4 Topochemically controlled solid-state polymerization pattern of 1,3-butadiynes.

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]. 

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. 

Controlled preparation of thin films of P(DiAc)s can be obtained by topochemical (solid state) polymerization of thin films of monomer previously deposited by evaporation under high vacuum, followed by UV or gamma irradiation [569] such thin films possess high order and alignment. Variation of the substrate crystallinity yields thin films or crystals of varying crystallinity [569]. Innovative methods, such as application of pressure on a mobile monomer phase between two optical plates... 

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. 

Keywords Crystal engineering Solid-state photoreaction Topochemical polymerization Controlled radical polymerization Dimerization Isomerization Topotactic reaction... 

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]. 

Thirty years later, we discovered the topochemical polymerization of various 1,3-diene monomers giving a highly stereoregular polymer in the form of polymer crystals. When ethyl (Z,Z)-muconatc was photoirradiated in the crystalline state, a tritactic polymer was produced [18, 19], in contrast to the formation of an atactic polymer by conventional radical polymerization in an isotropic state. Thereafter, comprehensive investigation was carried out, for example, the design of monomers, the crystal structure analysis of monomers and polymers, and polymerization reactivity control, in order to reveal the features of the polymerization of 1,3-diene monomers [20-23], Eventually, it was revealed that the solid-state photoreaction... 

Matsumoto, A., Tanaka, T. and Oka, K. (2005) Stereospecific radical polymerization of substituted benzyl muconates in the solid state under topochemical control. Synthesis, 1479-1489. 

Epitaxial polymerization may allow complete topochemical control of a variety of solid state reactions to produce single crystals. This technique should continue to prove to be a powerful tool in the molecular engineering of thin polymer films. 

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.

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. 

Abstract. The asymmetric synthesis of chiral polymers by topochemically controlled polymerization in chiral crystals is discussed. Following a short survey of topochemical polymerization in the solid state and some comments on chiral crystals, we present the requirements for the performance of asymmetric polymerization based on [2+2]-photocycloaddition. The planning and execution of two successful polymerizations of this sort are described. In the first, we start with a chiral non-racemic monomer and obtain optically active cyclobutane oligomers. The optical yields of the dimer and trimer were quantitative on the scale of N.M.R. sensitivity. In the second reaction we start with a racemate, and by the processes of crystallization in a chiral structure and solid-state reaction we generate an optically active polymer, in the absence of any outside chiral agent. The possible application of this novel method to additional systems is discussed. 

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. 

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. 

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