RAFT polymerization macromonomer agents

A novel approach to RAFT emulsion polymerization has recently been reported.461529 In a first step, a water-soluble monomer (AA) was polymerized in the aqueous phase to a low degree of polymerization to form a macro RAFT agent. A hydrophobic monomer (BA) was then added under controlled feed to give amphiphilic oligomers that form micelles. These constitute a RAFT-containing seed. Continued controlled feed of hydrophobic monomer may be used to continue the emulsion polymerization. The process appears directly analogous to the self-stabilizing lattices approach previously used in macromonomer RAFT polymerization (Section 9.5.2). Both processes allow emulsion polymerization without added surfactant. 

RAFT Polymerization with Macromonomer RAFT Agents... 

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. 

Chain transfer to methacrylate and similar maeromonomers has been discussed in Section 6.2.3.4. The first papers on the use of this process to achieve some of the characteristics of living polymerization appeared in 1995.380 The structure of macromonomer RAFT agents (163) is shown in Figure 9.3. An idealized reaction scheme for the case of a MMA terminated macromonomer is shown in Scheme 9.36. 

Transfer constants of the macromonomers arc typically low (-0.5, Section 6.2.3.4) and it is necessary to use starved feed conditions to achieve low dispersities and to make block copolymers. Best results have been achieved using emulsion polymerization380 395 where rates of termination are lowered by compartmentalization effects. A one-pot process where macromonomers were made by catalytic chain transfer was developed.380" 95 Molecular weights up to 28000 that increase linearly with conversion as predicted by eq. 16, dispersities that decrease with conversion down to MJM< 1.3 and block purities >90% can be achieved.311 1 395 Surfactant-frcc emulsion polymerizations were made possible by use of a MAA macromonomer as the initial RAFT agent to create self-stabilizing lattices . 

There have been several studies on the use of RAFT to form polymer brushes by polymerization or copolymerization of macromonomers 348-350. " Systems examined include copolymerizations of 349 with MMA using RAFT agent 175,... 

A wide variety of macromonomer (7, X=CH2) and thiocarbonylthio RAFT agents (7, X = S) have now been repotted. The effectiveness of RAFT agent depends on the monomer being polymerized and depends strongly on the properties of the... 

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