Reversible Addition Fragmentation Chain Transfer (RAFT) and Hetero-Diels−Alder Chemistry as a Convenient Conjugation Tool for Access to Complex Macromolecular Designs

Abstract

The combination of RAFT chemistry and the hetero-Diels-Alder (HDA) cycloaddition was successfully utilized in the synthesis of poly(styrene) (PS) star polymers with up to 4 arms. This variant of the "coupling onto" method of star polymer synthesis was investigated for two different RAFT end groups (diethoxyphosphoryldithioformate and pyridin-2-yldithioformate) and coupling agents bearing 2, 3, or 4 diene functional groups. When a diethoxyphosphoryldithioformate terminated polymer was reacted with the 2-, 3-, and 4-fold functionalized coupling agents, the yields of 2-arm star, 3-arm star, and 4-arm star polymers were 81%, 77%, and 65%, respectively, and when a pyridin-2-yldithioformate terminated polymer was reacted with the same coupling agents, the yields of 2-arm star, 3-arm star and 4-arm star polymers were 91%, 86% and 82% respectively. The HDA coupling reaction was monitored via UV/vis spectroscopy from the perspective of the RAFT end group as well as by 1 H NMR spectroscopy from the perspective of the diene functionality. The results of these investigations indicated that the phosphoryldiethoxydithioformate terminated polymer achieves 92% conversion within a 24 h time frame and the pyridin-2-yldithioformate terminated polymer achieves 96% conversion in 10 h. The 4-arm star polymers were also subjected to high-temperature environments, and GPC measurements indicated that complete cleavage of all 4 arms from the core was achieved in 24 h at 160°C.

Living Radical Polymerization by the RAFT Process - A Second Update

“…iBA [223] St [223,224] 385 [104] 388 [104] 389 [104] (Continued) MAA [225] MAA-b-St [225] S Br Ϫ ϩ S N 64 [226,227] St [226] S S Si(OCH 3 ) 3…”

“…266 [209] St [223,224,418] St [419] 267* [34] S S S S S S 268* S S AN [420] AN [420] AN/MA [420] AN/MMA [420] A See footnote A of Table 3. B See footnote B of Table 3.…”

“…[209,223,224,418,419,484,485] The process has also been developed as a route to block copolymers [223,418] and star polymers. [224,418,484] Other End-Group Modification Processes PNVP chain ends formed with xanthate RAFT agents are susceptible to hydrolysis and can be converted into aldehyde chain ends (Scheme 12). [379] The aldehyde chain ends can be used for bioconjugation.…”

“…[502] Star Polymers by 'Grafting-To' Various combinations of RAFT, ATRP, click, ring opening polymerization, and other methods have been used to synthesize star polymers, including mikto-arm stars. [174,223,224,330,418,514] Hetero-Diels-Alder coupling was used to synthesize a 12-armed star as shown in Scheme 26 from a star polymer precursor prepared by ATRP and a PSt macro-RAFT agent. [418] ZЈ S …”

Reversible Diels‐Alder Chemistry as a Modular Polymeric Color Switch

“…[ 33 ] In search of improved effi ciencies, we have applied the ultrarapid hetero-Diels-Alder (HDA) reaction in a reversible fashion: in this approach, electron defi cient dithioesters [ 34 ] are used as reactive heterodienophiles in a HDA cycloaddition. This versatile concept has been employed in the synthesis of complex macromolecular architectures such as blocks, [ 35 ] stars, [ 36 ] star-shaped block copolymers, [ 37 ] modifi cation of Si surfaces, [ 36 ] and surface-functionalized microspheres. [ 38 ] Since dithioesters are colored by virtue of the forbidden π → π * transition of the C=S moiety, one benefi ts -in addition to the high effi ciency (at 1:1 stoichiometry) of the rapid HDA reaction -from two advantages: 1) The reaction progress can be directly monitored by UV-Vis spectroscopy, as the concentration of the dithioester is directly proportional to its absorption; and 2) a system where the controlled release of the dithioester behaves as a modular polymeric color switch.…”