End-functionalized polymer chain

A cationic mono-Cp-based cobalt complex FlO-6 can initiate the living polymerization of ethylene, which has been successfully applied to the preparation of chain-end-functionalized polymers (see Section 11.20.4.5.4). " ... 

The chain-end functionalized polymer is a very attractive material that possesses an unperturbed polymer chain with desirable physical properties (such as melting temperature, crystallinity, glass transition temperature, melt flow, etc.) that are almost the same as those of the pure polymer. Nevertheless, the terminal reactive group at the polymer chain end has good mobility and can provide a reactive site for many applications. This includes adhesion to the substrates, reactive blending, and formation of block copolymers. 

The methodology of living anionic polymerization, especially alkyllithium-initiated polymerization, is very useful for the preparation of chain-end functionalized polymers with well-defined structures (9,10). Since these living polymerizations generate stable, anionic polymer chain ends (P Li ) when all of the monomer has been consumed, post-polymerization reactions with a variety of electrophilic species can be used to generate a diverse array of chain-end functional groups as shown in eq. 1,... 

Functionalizations via Silyl Hydride Functionalization and Hydrosilation A new general functionalization method based on the combination of living anionic polymerization and hydrosilation chemistry has been developed as illustrated in Scheme 7.26 [281]. First, a living polymeric organolithium compound is quantitatively terminated with chlorodimethylsilane to prepare the corresponding co-silyl hydride-functionalized polymer. The resulting co-silyl hydride-functionalized polymer can then react with a variety of readily available substituted alkenes to obtain the desired chain-end functionalized polymers via efficient regioselective transition-metal-catalyzed hydrosilation reactions [282-284]. 

Bertrand A, Lortie F, Bernard J (2012) Routes to hydrogen bonding chain-end functionalized polymers. Macromol Rapid Commun 33(24) 2062-2091... 

Scheme 5.15 Synthesis of chain-end-functionalized polymer by reactions of iiving anionic polymers with functionalized...

Scheme 5.16 Synthesis of chain-end-functionalized polymers by 1 1 addition reaction of living anionic polymers to protected DPE derivatives.

In addition to chain-end functionalization, polymer properties can be significantly altered by the introduction of pendant functionality along a polymer backbone. 

End functionalization can be achieved by the addition of allyl bromide to form the corresponding vinyl-functionalized polymer. Allyl bromide acts as a chain transfer agent (CTA) in free-radical polymerizations and can be used to prepare chain-end-functionalized polymer via controlled free-radical polymerizations. The functionalization reaction proceeds via addition followed by fragmentation (i.e., elimination of a bromine radical). When ATRP is quenched with allyl bromide, a bromine radical is eliminated resulting in the formation of a Cu (II) species. The Cu(II) drives the equilibrium to the deactivated species, reducing the propensity of the chain end to add to allyl bromide. In order to overcome this, Cu(0) needs to be added to... 

The exo-olefin is a precursor to a variety of chain-end-functionalized polymers via postpolymerization reaaions as shown in Scheme 37. Hydroxy-functionalized PIB has been utilized as a precursor for the preparation of RAFT macromo-lecular CTAs and carboxylic acid end-fimctionalized polymers. Telechelic PIB diols have been prepared using p-dicumyl chloride/BCU initiator system followed by dehydro-chlorination, hydroboration, and alkaline peroxide oxidation. Aldehyde end-fiinctionalized PIBs have been used to prepare carboxyl- and hydroxyl-terminated poly-mers. Carboxylic acid-functionalized PIBs have also been prepared from the oxidation of the methyl ketone-functionalized PIBs." The hydroxyl-functionalized PIBs have also been used to prepare methacrylate macromonomers by their reaction with methacryloyl chloride in the presence of triethylamine. The homopolymerization and copolymerization of these maaomonomers with methyl methacrylate were also reported. Cyanoacrylate-funaionalized PIBs prepared via the hydroxyl-functionalized PIB were also reported by Kennedy et al. ... 

All these a,w-di(oxazoline) oligomers can be useful starting materials for the preparation of regular copolymers, alternating block copolymers, pol3nner networks, or other chain-ended functional polymers. 

Chain-End Functionalized Polymers, in principle, the propagating car-banionic center that remains at the end of the polymerization can react with a variety of electrophilic species to incorporate functional groups (—X) at the chain end, as shown in equation 5 (12-14) ... 

The preparation of chain-end functionalized polymers has been largely limited to living polymerization techniques, used in combination with a controlled initiation or termination (functionalization) reaction. Unfortunately, there are only a few transition metal coordination catalysts that exhibit living polymerization behavior, and the utility of most of these is limited to the preparation of polyethylene. Furthermore, living polymerization only produces one polymer chain per initiator, which presents a very low rate of catalyst activity for a typical polyolefin preparation. 

Problem 11.11 Write the structures of chain end functionalized polymers obtained by ATRP of styrene and methyl acrylate from the following functionalized initiators (I) ... 

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