Development of Thermal and Photochemical Strategies for Thiol−Ene Click Polymer Functionalization

Abstract

A series of alkene-functional polymers were synthesized by controlled polymerization techniques in order to investigate and compare the efficiency and orthogonality of both photochemically and thermally initiated thiol-ene click coupling reactions. The copolymers were designed to have single or multiple alkene-functional groups along the backbone, and to evaluate the robustness of these procedures, functionalization reactions with a library of mercaptans were studied. In comparing the photoinitiated reaction to its thermal counterpart, the thiol-ene photocoupling was found to proceed with higher efficiency, require shorter reaction times for complete conversion, and displayed a higher tolerance to various backbones and functional groups. To examine the orthogonality of the thiol-ene click reaction, an asymmetric telechelic polymer based on PS was designed with alkene functionality at one end and an azide at the other. The thermally initiated thiol-ene coupling was found to be completely orthogonal with the traditional azide/alkyne click reaction allowing the individual chain ends to be quantitatively functionalized without the need for protection/deprotection strategies. From these studies, the demonstrated efficiency and orthogonality of thiol-ene chemistry shows it to be a practical addition to the family of click reactions that are suitable for polymer functionalization.

Photoinitiated Polymerization: Advances, Challenges, and Opportunities

“…46,47 These reactions were also utilized as environmentally friendly "click" coupling processes in various synthetic applications, since in contrast to the other methods, they usually proceed in the absence of solvent under benign reaction conditions without the use of any potentially toxic metal. [48][49][50][51] For many curing applications fully formulated mixtures, which contain all initiators monomers and additives, are supplied to customers. However, such formulations may not exhibit a good shelf life due to the initiation on storage.…”

Living Radical Polymerization by the RAFT Process - A Second Update

“…St [184] MMA [88] 323 [185] 40 [186] S S O O St [186] St-b-MAH [186] St-b-MAH-b-NIPAM [186] 41* [187,188] S S (MMA) [64,187,189] BA [187] EHA [188] St [190] TBAM [191] DEAM [187] DMAM [187] NAM [191] NIPAM [187,189] BA/St [192] EHA-b-MA [188] TBAM-b-NAM [191] DMAM/NAS [193] NAM-b-TBAM [191] 42* S S Ph CN MMA [194] 376 [195] 376-b-MMA [195] BA [196] MMA [189] NIPAM [189] MMA-b-NIPAM [189] MMA/283 [197] MMA/284 [197] St/2VP [198] St/348 [199] THPA-b-St [200] THPA-b-St/373 [201] 44 [202] [200] 47 [203] …”

“…Styrene derivatives subjected to RAFT polymerization 348 [100,199] O 349 [138] O N N N 350 [158,309] N VBTAC 351 [159] Cl Ϫ Nϩ 352 [459] HN O 353 [321] O F F F F 354 [313] O F F F F 355 [313] [244] VBTPC 359 [34] Cl Ϫ P ϩ 360 [244] 361 [250] O N O 362 [207] O O O 363 [134] O O O Fe 364 [102] N 365 [102] N Table 23. Vinyl derivatives subjected to RAFT polymerization 366 [380] N 367 [380] N 368 [380] N 369 [390] N O O G. Moad, E. Rizzardo, and S. H. Thang [111,135] 370 [135,146] 375 [136] 376 [195] 377 [150] 378 [410] O O (H 3 C) 3 Si 372 [338,346,347] 373 [201] 374 [459] O [466] NAS 380 [160,299,317,345,347] 381 [178] 382 [222] [149,…”

Advanced functionalization of polyhydroxyalkanoate via the UV-initiated thiol-ene click reaction

“…The UV-initiated thiol-ene click reaction was performed according to the method described by Campos et al (Campos et al 2008). In a vial, the prepared PHA bearing vinyl groups (PHAund60), thiol (10 eq with respect to the vinyl group), and DMPA (0.2 eq) were dissolved in either chlorobenzene or acetone.…”

“…In addition to the CuAAc, the thiol-ene reaction is also important in the realm of click chemistry (Carioscia et al 2007;Hoyle andBowman 2010, Hoyle et al 2004;Li et al 2007). Campos et al reported the synthesis of various macromolecules via the UV-initiated thiol-ene click reaction, which proceeded quantitatively, with a high degree of specificity in a matter of minutes (Campos et al 2008;Killops et al 2008). However, the majority of PHAs studied to date contain no functional groups, and few groups have reported such modification of PHAs (Constantin et al 1999;Gagnon et al 1994a, b;Park, Lenz and Goodwin 1998).…”