Oligomerization template-controlled

Feldman et a .210 211 and Wulff et ul v have examined other forms of template controlled oligomerization of acrylic monomers. The template (23) has initiator and transfer agent groups attached to a rigid template of precisely defined structure.210 "11 Polymerization of MMA in the presence of 23 gave a 3 unit oligo(MMA) as ca 66% of the polymeric product. The stereochemistry of the oligomer was reported to be different" from that of atactic PMMA. 

Scheme 8-4 Kammerer s strategy for template control of acrylate oligomerization.

Exploration of the template controlled free-radical oligomerization of other activated olefins began with standard monomers utilized in bulk polymer synthesis and the template 63. Vinyl acetate and acrylonitrile led only to uncontrolled polymerization, while vinylene carbonate did not react under the standard experimental conditions. More exotic monomers, such as vinyl trifluoroacetate and rert-butyl acrylate, were also unsuccessful. Only methyl acrylate polymerization was arrested by template 64 to provide the macrocyclized product 96 in modest yield as a mixture of five diastereomers (Scheme 8-25). Subsequent studies with the more effective thiophenyl-bearing template 63 at lower temperatures improved this yield to 35%. The diastereomer distribution was reminiscent of the methyl methacrylate-derived product, although no stereochemical assignments were made in this case either. 

As the ladderanes have rigid rodlike structures consisting of C-C a bonds, they have been used as spacer for electron-transfer reactions32,33 and as templates for controlling oligomerization.34... 

Synthesis of silica-based materials with controlled skeleton structures, such as zeolites, requires controlling the structure of oligomeric silicate species at the first reaction step. Organic quaternary ammonium ions, which are known as organic templates in zeolite synthesis (1 ), have a role in making up the specific structures of silicate anions, whereas silicate anions randomly polymerize in aqueous solutions containing alkali metal ions, resulting in the presence of silicate anions with different structures. 

Two distinct but related strategies that rely on templates to control the number of monomers incorporated into an oligomeric product can be envisioned. One of these approaches, shown in Scheme 8-2, relies on templated radical macrocyclization reactions to control telomer size [14, 15]. This strategy requires attachment of all of the monomer units to the template backbone and uses macrocyclization, which faces competition from intermolecular chain transfer, to control the telomer length. The chain transfer agent T-I (i.e., telomerization terminator) is not attached to the template. 

Scheme 8-2 Oligomerization control via template-bound monomers. I =radical initiator, T-1 = chain transfer agent.

Scheme 8-3 Oligomerization control via template-bound initiator and terminator. I = radical initiator, T = radical terminator.

Controlled Oligomerizations with a Polynorbornane-based Template... 

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