Controlled Radical Polymerization of Acrylates Regulated by Visible Light (original) (raw)
Related papers
Macromolecules, 2014
Photoinduced living radical polymerization of acrylates is achieved upon UV irradiation (λ max ≈ 360 nm) in the presence of an aliphatic tertiary amine ligand (Me 6 -Tren) in the presence of low concentrations of CuBr 2 , yielding poly(acrylates) with near perfect retention of end group fidelity. The effect of the nature of the solvent on the rate of polymerization was investigated in order to expand the scope and identify the limitations of the system. Subsequently, a range of acrylic monomers containing hydrophobic and hydrophilic substituents have been screened, including lauryl acrylate, octadecyl acrylate and diethylene glycol ethyl ether acrylate, all of which present low dispersities (Đ ≈ 1.1) at very high conversions. Functional monomers, including glycidyl acrylate and solketal acrylate, were also found to be tolerant to the photomediated reaction. Finally, solketal acrylate was copolymerized with methyl acrylate which, following deprotection of the pendant ketal group, furnished an amphiphilic diblock copolymer. Self-assembly of this block copolymer into polymer micelles in aqueous media was exemplified by dynamic light scattering (DLS) and transmission electron microscopy (TEM).
Journal of the American Chemical Society, 2015
Nature has developed efficient polymerization processes, which allow the synthesis of complex macromolecules with a perfect control of tacticity as well as molecular weight, in response to a specific stimulus. In this contribution, we report the synthesis of various stereopolymers by combining a photoactivated living polymerization, named photoinduced electron transfer−reversible addition−fragmentation chain transfer (PET-RAFT) with Lewis acid mediators. We initially investigated the tolerance of two different photoredox catalysts, i.e., Ir(ppy) 3 and Ru(bpy) 3 , in the presence of a Lewis acid, i.e., Y(OTf) 3 and Yb(OTf) 3 , to mediate the polymerization of N,N-dimethyl acrylamide (DMAA). An excellent control of tacticity as well as molecular weight and dispersity was observed when Ir(ppy) 3 and Y(OTf) 3 were employed in a methanol/toluene mixture, while no polymerization or poor control was observed with Ru(bpy) 3. In comparison to a thermal system, a lower amount of Y(OTf) 3 was required to achieve good control over the tacticity. Taking advantage of the temporal control inherent in our system, we were able to design complex macromolecular architectures, such as atactic block-isotactic and isotactic-block-atactic polymers in a one-pot polymerization approach. Furthermore, we discovered that we could modulate the degree of tacticity through a chemical stimulus, by varying [DMSO] 0 /[Y(OTf) 3 ] 0 ratio from 0 to 30 during the polymerization. The stereochemical control afforded by the addition of a low amount of DMSO in conjunction with the inherent temporal control enabled the synthesis of stereogradient polymer consisting of five different stereoblocks in one-pot polymerization.
Macromolecules, 2018
We detail a polymer synthetic methodology that merges the techniques of insertion and radical polymerization methods into a single organometallic catalyst. This metal−organic insertion/light initiated radical (MILRad) polymerization technique proves successful at polymerizing methyl acrylate (MA) and hexene, using light as a critical stimulus to activate the dormant photoresponsive nature of the insertion catalyst. In this study, we describe a novel approach that uses visible light (460 nm) to switch the catalytic activity of a cationic palladium catalyst from an insertion route to a radical process when desired. We discovered that in a mixture of MA and hexene one monomer can be selectively polymerized using light and dark cycles, respectively. As a result, this polymerization process enables the copolymerization of MA and hexene to create homo-and block copolymer architectures facilitated solely by visible light. In this work, we show the synthesis of MA homopolymers in molecular weight ranges (M n 50−400 kDa) with dispersities of ∼1.7. Synthesis of MA (A) and hexene (B) block copolymers were accomplished with a single catalyst in both a sequential and novel one-pot approach, relying solely upon visible light irradiation. A series of BA block copolymers were prepared with tunable monomer compositions, molecular weight ranges of (M n 11−36 kDa), and well-controlled polydispersities (∼1.3−1.6) in a robust rapid synthesis. MILRad polymerization circumvents the need for quantitative conversions during block formation afforded by the orthogonal monomer reactivity dependent upon a light stimulus to acquire distinct polymer architectures with variable block compositions. The use of a photocontrollable "switch" affecting a single organometallic catalyst allows access to block polymers from nonpolar and polar olefins in a novel and facile approach.
Multi-mode Polymerizations Involving Photoinduced Radical Polymerization
Journal of Photopolymer Science and Technology
Multi-mode polymerizations provide a facile route to synthesis of block and graft copolymers that cannot be made by a single polymerization mode. In such strategy, photoinduced free radical polymerization as one of the polymerization mode play a crucial role due to its simplicity, wavelength flexibility, applicability to wide range of monomers and minimized side reactions. In this article, various combinations of photoinduced conventional and controlled/living radical polymerizations with other polymerization methods, namely cationic, free radical promoted cationic, ring opening, and ring opening metathesis polymerizations are presented and mechanistic details are evaluated. Moreover, the possibilities for the simultaneous or sequential processes are discussed.
Journal of the American Chemical Society, 2017
A highly efficient photomediated atom transfer radical polymerization protocol is reported for semi-fluorinated acrylates and methacrylates. Use of the commercially available solvent, 2-trifluoromethyl-2-propanol, optimally balances monomer, polymer, and catalyst solubility while eliminating transesterification as a detrimental side reaction. In the presence of UV irradiation and ppm concentrations of copper(II) bromide and Me6-TREN (TREN = tris(2-aminoethyl amine)), semi-fluorinated monomers with side chains containing between three and 21 fluorine atoms readily polymerize under controlled conditions. The resulting polymers exhibit narrow molar mass distributions (Đ ≈ 1.1) and high end group fidelity, even at conversions greater than 95%. This level of control permits the in situ generation of chain-end functional homopolymers and diblock copolymers, providing facile access to semi-fluorinated macromolecules using a single methodology with unprecedented monomer scope. The results d...
Controlled/living radical polymerization: Features, developments, and perspectives
Recent mechanistic developments in the field of controlled/living radical polymerization (CRP) are reviewed. Particular emphasis is placed on structure-reactivity correlations and ''rules'' for catalyst selection in atom transfer radical polymerization (ATRP), for chain transfer agent selection in reversible addition-fragmentation chain transfer (RAFT) polymerization, and for the selection of an appropriate mediating agent in stable free radical polymerization (SFRP), including organic and transition metal persistent radicals. Novel methods of fine tuning initiation, activation, and deactivation processes for all techniques are discussed, including activators regenerated by electron transfer (ARGET) and initiators for continuous activator regeneration (ICAR) ATRP, whereby Cu catalyst concentrations in ATRP can be lowered to just 10 ppm. Progress made in each technique related to the synthesis of both high and low molecular weight polymers, end functional polymers, block copolymers, expanding the range of polymerizable monomers, synthesis of hybrid materials, environmental issues, and polymerization in aqueous media is thoroughly discussed and compared. r
Macromolecules, 2012
Different polyaromatic structures (truxene derivatives and tris(aza)pentacene) are presented as new metal-free organic photocatalysts (OPC) to promote free radical polymerization FRP and ring-opening polymerization (ROP) under halogen lamp, household LED bulb, and laser diode (405 nm). These OPCs exhibit interesting light absorption properties and lead, through an oxidative catalytic cycle, to the formation of radicals and ions that can initiate both free radical polymerization FRP and ring-opening polymerization ROP. Interestingly, excellent polymerization profiles are obtained even upon visible light exposure. Using these very soft irradiation conditions, acrylate/epoxide blends are also easily polymerized under air and lead to the formation of interpenetrated polymer networks IPN exhibiting no phase separation.
Visible Light‐Induced Atom Transfer Radical Polymerization
Macromolecular Chemistry and Physics, 2012
Visible light‐induced reverse and simultaneous reverse and normal initiation (SR&NI) atom transfer radical polymerizations of vinyl monomers are examined using various dyes and type I photoinitiators. The effect of photoinitiator types on the control of molecular weight and distribution is described. In both dye and type I photoinitiator sensitized SR&NI ATRP systems, the molecular weights increase linearly with conversion. However, the experimental molecular weights are considerably higher than the theoretical values and the polymers show broad‐molecular‐weight distributions ranging from 1.28 to 1.60 in the dye‐sensitized SR&NI ATRP. However, the polymers obtained by SR&NI ATRP using type I photoinitiator system had molecular weight values close to the theoretical ones and very narrow‐molecular‐weight distributions ranging from 1.11–1.18.
Polymer, 2013
Seven difunctional acridinediones DAD were prepared and investigated for their abilities to initiate a ring-opening cationic photopolymerization in combination with an iodonium salt (and optionally Nvinylcarbazole) upon UV/visible light (XeeHg lamp; >330 nm) or visible light (halogen lamp) exposure. The structural effects in the DADs and the role of the radical cation are outlined. The cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure leads to the formation of an interpenetrated polymer network. The photochemical mechanisms are studied by fluorescence, steady state photolysis, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques.