The RAFT Process as a Kinetic Tool: Accessing Fundamental Parameters of Free Radical Polymerization

Abstract

IntroductionLiving/controlled free radical polymerization (LFRP) techniques such as nitroxide-mediated polymerization, atom transfer polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization gave rise to new designs and syntheses of well-defined materials with respect to size, shape, polydispersity and functionality. For example, macromolecular architectures such as stars, combs, block copolymers, core-shell nanoparticles and branched structures have become feasible [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], rendering these materials ideal for applications in biomaterials (e.g. drug delivery devices and diagnostic nanoparticles) and molecular electronics [1,8,[16][17][18][19].The reason why LFRPs give access to such a vast number of highly specific microstructure is that they yield materials with high-functionality and lowpolydispersity indices, PDI, as all radical chains nearly grow uniformly with increasing monomer consumption, i.e. polymerization time (see equation 4.1). Ideally, the chain length i depends solely on the fraction of monomer consumed, c 0 M X (where X denotes monomer conversion and c 0 M the initial monomer concentration) and c 0 LFRP , which is the concentration of the mediating agent before the reaction commenced, that is at t = 0 [1,[5][6][7][20][21][22][23][24].This feature is utilized in many ways for synthetic purposes because the chain length of the polymer product can be conveniently tuned -widely independent from the outer reaction conditions -simply by changing the monomer and mediating agent concentrations. Less realized is, however, that the correlation of equation 4.1 can also be a powerful tool in the hands of a physical chemist for the very same reason: it gives easy access to reactions and kinetic information of radicals with known, and moreover, adjustable size.

Living Radical Polymerization by the RAFT Process - A Second Update

“…The past 2 years has seen the publication of further general reviews detailing the RAFT process which include works by Moad, Rizzardo, and Thang, [9][10][11][12] a Handbook of RAFT Polymerization, [13] and a highlight article by Barner-Kowollik and Perrier [14] on the future of RAFT. Reviews on specific areas include the kinetics and mechanism of RAFT polymerization, [15][16][17][18] the use of RAFT to probe the kinetics of radical polymerization, [19,20] the use of RAFT in organic synthesis, [21] amphiphilic block copolymer synthesis, [22,23] the synthesis of end functional polymers, [24] the synthesis of star polymers and other complex architectures, [25,26] the use of trithiocarbonate RAFT agents, [27] the use of xanthate RAFT agents (MADIX), [28] polymerization in heterogeneous media, [29][30][31][32] RAFT polymerization initiated with ionizing radiation, [33] polymer synthesis in aqueous solution, [34][35][36][37] surface and particle modification, [38,39] synthesis of self assembling and/or stimuli responsive polymers, [36,40] RAFT-synthesized polymers in drug delivery, [22,41] and other applications of RAFTsynthesized polymers. [30,42,43] The process is also given substantial coverage in most recent reviews that, in part, relate to polymer synthesis, living or controlled polymerization, or novel architectures.…”

“…[429] The use of RAFT polymerization and kinetic simulation with Predici have been applied to determine chain length dependent termination rate constants in radical polymerizations (the RAFT-CLD-T method) has been previously reviewed. [19] Criteria for selecting conditions for the determination of termination rate constants by the RAFT-CLD-T method have been proposed and justified by kinetic simulation. [430] The RAFT-CLD-T method has been used to determine chain length dependent termination rate constants in MMA polymerization in various conversion regimes up to high conversion [119,120] and termination rate constants during formation of star polymers based on MMA, MA, and St. [20,256] In the SP-PLP-NIR-RAFT method, polymerization is induced by a single laser pulse (SP) and the resulting decay in monomer concentration, c M , is monitored by NIR spectroscopy with a time resolution of microseconds.…”

Contact Lens Materials: A Materials Science Perspective

“…This has been a popular area of growth in polymer science, including examining the potential in other bio-applications [53,54,55]. The chain-transfer agent accurately mediates the growth of the polymer chain, so that the molecular weight can be pre-designed [39,56,57]. This results in a low-dispersity polymer, meaning the resulting properties and structure are more reliable than FRP (Figure 4).…”

The future of reversible addition fragmentation chain transfer polymerization

“…However, in the hands of physical chemists, it can be turned into a powerful tool to map the chain length dependence of bimolecular radical-radical reactions occurring during free radical polymerization processes. 20 There exists a sizeable body of work where chain length dependent termination rate coefficients have been determined for variable monomer systems; however, further exploitation is still possible: The socalled RAFT-CLD-T (RAFT Chain Length DependentTermination) technique holds the potential to map the chain length dependency of macroradicals of disparate lengths, as well as determine the individual rates of termination of macroradicals in dense matrices as well as those of branched structures.…”