Reactive telechelic oligomer

Figure 1.6 Schematic representation of the formation of supramolecular polymer (7) by chain extension of reactive telechelic oligomer with UPy. (After Folmer et al., 2000.)...

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Thus, we must consider those reactions (of termination of macroradical with primary radical (Eq. (9)) which have not necessarily the same reactivity ratio, as the termination of two macroradicals. And this makes it often possible to obtain telechelic oligomers for monomers which give a non-negligible amount of disproportionation reactions in traditional polymerization. 

Boutevin [2], in his review on Telechelic oligomers by radical reactions developed the categories of functional initiators, i.e., diazoic compounds, hydrogen peroxide, and oxygenated substances. He examined the different reactivities and combinations of such initiators with monomers in order to synthesize telechelic oligomers. Boutevin [2] also summarized the monomers able to totally recombine or to avoid termination by disproportionation. He showed a quantitative amount of recombination only for styrene, acrylates, dienes, and acrylonitrile [31-33]. 

The number of works in which authors took advantage of the reactivity of double bonds towards ozone to get telechelic oligomers is quite important. In Table 12, we have gathered some studies concerning the synthesis of a,codihydroxy oligomers, presenting a peculiar interest in the research into new materials like polyurethanes. 

ADMET has been extensively used to synthesize telechelic oligomers, or oligomers possessing functionalized end groups. Telechelics with functionalities close to 2.0, meaning each chain has exactly two reactive functional groups, are difficult to synthesize, but they are required for the stoichiometric balance needed in polycondensation reactions. 

This was followed by the preparation of p-terphenyl and stiff aromatic oligomers terminated by reactive end-groups (telechelic oligomers or telomers in short). 

Very varied applications have been proposed soil release properties of easy care cotton, assymetric solvents for the resolution of racemates and ligand exchange chromatography, " flame retardant properties, polymeric dyes which were reviewed by Marechal, chemical modification of surfaces, " chelating resins, photoresponsive polymers, " modification of polymers to alter or to remove unstable groups " and photoresists. " Chemical modification of telechelic oligomer end groups is of major importance to increase their reactivity and their selectivity. ... 

A typical formulation of a photocurable composite resin contains four basic components a radical-type photo initiator, an acrylate functionalized oligomer, a reactive diluent and the clay mineral filler. The photoinitiator is usually an aromatic ketone which cleaves into two radical fragments upon UV exposure. The telechelic oligomer consists of a short polymer chain (polyurethane, polyether, polyester) end-capped by the very reactive acrylate double bond. An acrylate monomer is generally used as reactive diluent to reduce the resin viscosity. Figure 7.2 shows some typical compounds used in UV-curable acrylic resins. Different types of phyllosilicates were selected as mineral filler an organophilic clay (Nanomer I-30E from Nanocor), native hydrophilic clays (montmorillonite KIO and bentonite) and a synthetic clay (beidellite). 

Finally, some polymerisations can be directed such that the final oligomer or polymer contains two or more reactive end groups capable of extended polymerisation with different monomers. These materials are named telechelic macromers or telechelic polymers. 

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