Macromonomers end-groups

Macromonomer End group Comonomer Copol)maerization Reference... 

The reactions associated with RAFT equilibria are in addition to those that occur normally during conventional radical polymerization (i.e. initiation, propagation and termination). The RAFT agent is a transfer agent. Since radicals are neither formed nor destroyed as a consequence of the RAFT process, termination is not directly suppressed. Retention of the macromonomer end group in the polymeric product is responsible for the living character of RAFT polymerization and renders the process potentially suitable for synthesizing block copolymers and end functional polymers. 

It is of interest that thermogravimetric analysis has been used as a means of determining end group purity of PM VIA macromonomers formed by catalytic chain transfer. 

As in the case of PS (Section 8.2.1) polymers formed by living radical polymerization (NMP, ATRP, RAFT) have thermally unstable labile chain ends. Although PMMA can be prepared by NMP, it is made difficult by the incidence of cross disproportionation.42 Thermal elimination, possibly by a homolysis-cross disproportionation mechanism, provides a route to narrow polydispersity macromonomers.43 Chemistries for end group replacement have been devised in the case of polymers formed by NMP (Section 9.3.6), ATRP (Section 9.4) and RAFT (Section 9.5.3). 

A side reaction in NMP is loss of nilroxide functionality by thermal elimination. This may occur by disproportionation of the propagating radical with nitroxide or direct elimination of hydroxy lam ine as discussed in Section 9.3.6.3. In the case of methacrylate polymerization this leaves an unsaturated end group.1" The chemistry has also been used to prepare macromonomers from PMMA prepared by ATRP (Section 9.7.2.1),... 

The synthesis of PDMS macromonomers with vinyl silane end-groups and their free-radical copolymerization with vinyl acetate, leading to poly(vinyl acetate)-PDMS graft copolymers, was described 346). The copolymers produced were later hydrolyzed to obtain poly(vinyl alcohol)-PDMS graft copolymers. 

The functionality of the end groups were also determined by NMR or UV analysis which should provide identical molecular weights for perfectly monofunctional materials. As can be seen in Table I, a good correspondence was obtained. Incorporation of the macromonomers into copolymers via free radical copolymerization can also be used as a check on functionality since nonfunctional materials obviously will not be incorporated. Proton NMR was used to confirm the amount of PSX... 

Macromonomers carrying mono-, bi- or trifunctional end groups are sometimes important constituents of a network. Through them, terminating, chain-extending, or crosslinking units are introduced to modify the network... 

To the first category belong the homo- and copolymerization of macromonomers. For this purpose, macromolecules with only one polymerizable end group are needed. Such macromonomers are made, for example, by anionic polymerization where the reactive chain end is modified with a reactive vinyl monomer. Also methacrylic acid esters of long-chain aliphatic alcohols or monofunctional polyethylene oxides or polytetrahydrofurane belong to the class of macromonomers. 

Macromonomers with norbornene end groups were synthesized by living anionic polymerization. The norbornene groups were polymerized by molybdenum catalysts. A series of other a>-nor-bornenyl macromonomers were synthesized and polymerized by metathesis polymerization. 

The graft copolymers were already used for preparation and stabilization of polymer particles by Barrett [1]. He synthesized a poly(12-hydrostearic acid) macromonomer with a methacrylate end group. This macromonomer was copolymerized with MMA to obtain a preformed comb-graft copolymer, which was successfully used as stabilizer in nonaqueous dispersions of MMA. 

Similarly, the rate of polymerization of PEO-MA macromonomers was found to increase with increasing hydrophobicity around the MA end group in the order [71 ]... 

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