Allyl sulfides chain transfer

Table 9 Number-average molar mass, conversion, chain transfer constant, and functionality (f) for polymerizations carried out in the presence of allylic sulfide CTAs...

Selected examples of each type of functional oligomers are shown below. In the case of monofunctional oligomers, the functional group can be derived from the chain transfer agent, e.g. by using allylic sulfides with one functional residue. Difunctional oligomers can be obtained by the addition-elimination mechanism, e.g. from allylic sulfides with 2 functional residues or from styryl ethers.23... 

Figure 12.3. Addition-Jhagmenlation chain transfer mechanisms based on a) allyl sulfides and b) trithiocarbonates. Reproduced with permission from [SCO 06] and [AMA 11], respectively...

The mechanism of chain transfer is shown in Scheme 11 for allyl sulfide 24. The product, macromonomer (25), may undergo further reaction under the polymerization conditions particularly at high conversion (Section 3.07.3). 

Scheme 11 Mechanism of addition-fragmentation chain transfer with an allyl sulfide transfer agent. Reproduced from Moad, G. Rizzardo, E. Thang, S. H., Radical addition-fragmentation chemistry in polymer synthesis. Polymer 2008, 49,1079-1131." ...

Abstract Macromonomers of structure 4. prepared by the free radical polymerization of MMA using cobalt complexes as chain transfer agents, become incorporated into polymer chains by copolymerization but also act as efficient chain transfer agents by an addition-fragmentation reaction. Macromonomers of general structure 1 have been prepared by utilizing appropriately substituted allylic sulfides as chain transfer agents in free radical polymerizations. 

Macromonomers by Chain Transfer with Allylic Sulfides... 

The NMR spectrum of a polystyrene macromonomer, 19, prepared by chain transfer with allylic sulfide 17, is shown in Figure 4. The end group olefinic protons appear at 6 -5.1 and 4.7 ppm and the t-butyl end group at 6 -1.2 ppm. (The sharp signals at 5 2.0 and 2.2 ppm are due to ds-acetone and water respectively, present in the solvent). 

The preliminary results described in this paper suggest that macromonomers derived from chain transfer with cobalt complexes or allylic sulfides have potential for the convenient synthesis of unusual graft copolymers. Work in this area is continuing. 

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