Organocatalyzed Photocontrolled Radical Polymerization of Semifluorinated (Meth)acrylates Driven by Visible Light

Abstract

Fluorinated polymers are important materials that are widely used in many areas.Herein, we report the development of ametal-free photocontrolled radical polymerization of semifluorinated (meth)acrylates with an ew visible-lightabsorbing organocatalyst. This method enabled the production of av ariety of semifluorinated polymers with narrowm olarweight distributions from semifluorinated trithiocarbonates or perfluoroalkyl iodides.T he high performance of "ON/OFF" control and chain-extension experiments further demonstrate the utility and reliability of this method. Furthermore,t o streamline the preparation of semifluorinated polymers,ascalable continuous-flowapproach has been developed. Given the broad interest in fluorinated materials and photopolymerization, we expect that this method will facilitate the development of advanced materials with unique properties.The development of synthetic methods to prepare semifluorinated polymers is of great interest because these materials often possess interesting characteristics,s uch as high hydrophobicity,t unable lipophilicity,a nd improved thermal and chemical stability. [1,2] As ar esult, av ariety of methods have been developed for the preparation of such polymers. [3] Controlled/living radical polymerization (CRP), [3a] which enables the operationally simple polymerization of semifluorinated (meth)acrylates,isamong the most useful synthetic methods.[3] Fore xample,a tom-transfer radical polymerization (ATRP) [4] and its variants, [5] reversible addition-fragmentation chain transfer (RAFT) polymerization, [6] and nitroxide-mediated polymerization (NMP; [7] Scheme 1A,t op) have shown promising results for the preparation of precisely fluorinated materials.H owever,i n contrast to the CRP of nonfluorinated monomers, [4a,6a, 7a] most methods suffer from one or several of limitations,i ncluding 1) decreased control over molecular-weight distribution () at high conversion;2 )the use of af luorinated solvent; 3) undesired side reactions (e.g.,t ransesterification);o r 4) the use of am etal catalyst. Furthermore,c ontrol of the polymerization of semifluorinated monomers with an external stimulus, [8] such as visible light, has rarely been possible.[5]Recently,p hotoredox catalysis has found widespread application in ATRP, [9] RAFT/iniferter polymerization, [10] ring-opening metathesis polymerization, [11] and cationic polymerization, [12] thus providing arange of photo-CRP methods with excellent spatiotemporal control over chain growth. [13] Forthese processes,(meth)acrylates,acrylamides,and styrene derivatives are the most frequently investigated monomers. [13] Hawker and co-workers recently reported the precise synthesis of semifluorinated poly(meth)acrylates from activated alkyl bromides by the copper-catalyzed photo-ATRP method.[5] In their study,ametal catalyst and UV light were used to ensure efficient polymerization. Additionally,asemifluorinated tertiary alcohol solvent was required to suppress the transesterification.[5] Am etal-free method usi...

Droplet-Flow Photopolymerization Aided by Computer: Overcoming the Challenges of Viscosity and Facilitating the Generation of Copolymer Libraries

“…Therefore, in order to overcome the viscosity problem, flow polymerizations have generally been conducted using diluted solutions containing no more than 35 wt % of monomers. 13−24 On the basis of our experiences in both flow chemistry and polymerization, 19,31,32 we reasoned that the viscosity issue could be addressed by a precisely regulated droplet-reactor system 33,34 with a continuous-flow carrier phase (Figure 1c). While dropletflow was used in organic synthesis to enhance the mass/heat transfer under heterogeneous conditions (i.e., gas−liquid phases), 35,36 a combination of droplet-flow chemistry and photo-CRP has not been reported to our knowledge.…”

RAFT Polymerization-Induced Self-Assembly as a Strategy for Versatile Synthesis of Semifluorinated Liquid-Crystalline Block Copolymer Nanoobjects

“…Controlled radical polymerization techniques − have been employed to synthesize fluorinated polymers of varying fluorine contents either in the side chain (e.g., perfluoroalkylethyl (meth)­acrylate) or on the backbone (e.g., vinylidene fluoride). − Despite great success, these synthetic protocols are often limited by poor solubility of fluoropolymers, lack of breadth in monomer family, or use of fluorinated ligands, initiators or solvents. Significant progress has recently been made via light-mediated atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) for various semifluorinated (meth)­acrylates. − However, only oligomers were reported for monomers with a relatively large number of fluorocarbons, presumably due to insolubility of the corresponding polymers with high DPs. Therefore, development of a new paradigm that can circumvent these limitations encountered in traditional homogeneous solution polymerization with facile accessibility to various materials is of significant interest.…”

Investigation of the Locked‐Unlocked Mechanism in Living Anionic Polymerization Realized with 1‐(Tri‐isopropoxymethylsilylphenyl)‐1‐phenylethylene

“…[6] Can some or all of the living centers be controllably locked and unlocked, and can this control be extended to other controlled chain polymerization methods?This target is desirable but difficult to reach because there are many challenges in the quantitative locking of nonradical living centers,a nd other centers will continue to undergo chain propagation. [6] Can some or all of the living centers be controllably locked and unlocked, and can this control be extended to other controlled chain polymerization methods?This target is desirable but difficult to reach because there are many challenges in the quantitative locking of nonradical living centers,a nd other centers will continue to undergo chain propagation.…”

“…Step-chain propagation can be observed when the living centers go through cycles of locking and unlocking by controlling light exposure. [6] Can some or all of the living centers be controllably locked and unlocked, and can this control be extended to other controlled chain polymerization methods?This target is desirable but difficult to reach because there are many challenges in the quantitative locking of nonradical living centers,a nd other centers will continue to undergo chain propagation. Thus, novel either chemical reactions or mechanisms are necessary to achieve this goal.…”