Desulfurization–bromination: direct chain-end modification of RAFT polymers

Abstract

We report a simple and efficient transformation of thiol and thiocarbonylthio functional groups to bromides using stable and commercially available brominating reagents. This procedure allows for the quantitative conversion of a range of small molecule thiols (including primary, secondary and tertiary) to the corresponding bromides under mild conditions, as well as the facile chain-end modification of polystyrene (PS) homopolymers and block copolymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. Specifically, the direct chain-end bromination of PS prepared by RAFT was achieved, where the introduced terminal bromide remained active for subsequent modification or chain-extension using classical atom transfer radical polymerization (ATRP). This transformation sets the foundation for bridging RAFT and ATRP, two of the most widely used controlled radical polymerization (CRP) strategies, and enables the preparation of chain-end functionalized block copolymers not directly accessible using a single CRP technique.

RAFT-Based Polymers for Click Reactions

“…The conversion of thiocarbonylthio moiety in the ZC(=S)S group occurs through reactions with appropriate nucleophiles [ 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 ] ( Table 2 ) that include mainly primary amines [ 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 ] and hydrazine (or hydrazine hydrate) [ 116 , 117 , 118 , 119 , 120 , 121 ], alkali [ 122 ], and NaN 3 [ 115 ], along with reducing agents such as NaBH 4 [ 123 , 124 , 125 , 126 , 127 ] and LiB(C 2 H 5 ) 3 H [ 128 ]. The choice of the nucleophile depends on the chemical nature of the stabil...…”

Evolution and Future Directions of Metal-Free Atom Transfer Radical Polymerization

“…Importantly, it should be noted that the use of room temperature metal-catalyzed ATRP variations still leads to undesired high molecular weight distributions when using protected maleimide initiators, illustrating a further, unseen advantage of metal-free systems . Increasing the scope of available initiators remains a critical area for expanding the overall impact of α-chain-end functional materials accessible using metal-free ATRP, and concurrent efforts to further develop the extent and efficiency of ω-chain-end functionalization of these materials will facilitate its integration with other polymerization techniques , and broaden the general field of ATRP as a whole.…”

Recent advances on synthesis and biomaterials applications of hyperbranched polymers

“…Both ATRP and RAFT techniques enable controlled synthesis, which can even be carried out in one‐pot but sequential monomer polymerizations for construction of hierarchal structures. Both thioester (Lee et al, 2017; Willcock & O'Reilly, 2010) and halide (Anastasaki, Willenbacher, Fleischmann, Gutekunst, & Hawker, 2017) terminated polymers can undergo transformation to functionalize, or inert (Chong, Moad, Rizzardo, & Thang, 2007; Gutekunst et al, 2017) chain ends. In addition to the use of vinyl‐containing inimer and transmer in radical‐based SCVP, other feed stocks are capable of forming hyperbranched polymers by ring‐opening polymerizations using acid or base catalysts.…”