Unconjugated Monomers Research Articles

Binary Hybridization Strategy toward Stable Porphyrinic Zr‐MOF Encapsulated Perovskites as High‐Performance Heterogeneous Photocatalysts for Red to NIR Light‐Induced PET‐RAFT Polymerization

AbstractStable binary nanohybrids based on all‐inorganic halide perovskite encapsulated in porphyrinic Zr‐MOF (PCN‐222) are constructed for photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization. The synergistic effect of perovskite and PCN‐222 endows the photocatalyst with high‐efficiency photogenic charge carrier separation and light absorption property. CsPbI3@PCN‐222 (20%) is finally screened out as the oxygen and solvent‐resistant photocatalyst for highly efficient photo‐controlled polymerization of conjugated and unconjugated monomers under red to near infrared (NIR) light with high monomer conversion and narrow molecular weight distribution well‐defined polymers (Đ < 1.20). Controllable polymers and ultrahigh molecular weight polymers (up to 1730000 g mol−1) are successfully obtained by chain extension and block copolymerization of various monomers. The constructed photocatalysts easily achieve excellent light and temporal control, and even show high MMA conversion with NIR light under a thick barrier.

Organocatalyzed Controlled Copolymerization of Perfluorinated Vinyl Ethers and Unconjugated Monomers Driven by Light

Organocatalyzed Controlled Copolymerization of Perfluorinated Vinyl Ethers and Unconjugated Monomers Driven by Light

Achieving Ultrahigh Molecular Weights with Diverse Architectures for Unconjugated Monomers through Oxygen‐Tolerant Photoenzymatic RAFT Polymerization

AbstractAchieving well‐defined polymers with ultrahigh molecular weight (UHMW) is an enduring pursuit in the field of reversible deactivation radical polymerization. Synthetic protocols have been successfully developed to achieve UHMWs with low dispersities exclusively from conjugated monomers while no polymerization of unconjugated monomers has provided the same level of control. Herein, an oxygen‐tolerant photoenzymatic RAFT (reversible addition‐fragmentation chain transfer) polymerization was exploited to tackle this challenge for unconjugated monomers at 10 °C, enabling facile synthesis of well‐defined, linear and star polymers with near‐quantitative conversions, unprecedented UHMWs and low dispersities. The exquisite level of control over composition, MW and architecture, coupled with operational ease, mild conditions and environmental friendliness, broadens the monomer scope to include unconjugated monomers, and to achieve previously inaccessible low‐dispersity UHMWs.

Achieving Ultrahigh Molecular Weights with Diverse Architectures for Unconjugated Monomers through Oxygen-Tolerant Photoenzymatic RAFT Polymerization.

Achieving well-defined polymers with ultrahigh molecular weight (UHMW) is an enduring pursuit in the field of reversible deactivation radical polymerization. Synthetic protocols have been successfully developed to achieve UHMWs with low dispersities exclusively from conjugated monomers while no polymerization of unconjugated monomers has provided the same level of control. Herein, an oxygen-tolerant photoenzymatic RAFT (reversible addition-fragmentation chain transfer) polymerization was exploited to tackle this challenge for unconjugated monomers at 10 °C, enabling facile synthesis of well-defined, linear and star polymers with near-quantitative conversions, unprecedented UHMWs and low dispersities. The exquisite level of control over composition, MW and architecture, coupled with operational ease, mild conditions and environmental friendliness, broadens the monomer scope to include unconjugated monomers, and to achieve previously inaccessible low-dispersity UHMWs.

Aluminum Tralen Complex Meditated Reversible-Deactivation Radical Polymerization of Vinyl Acetate.

The AlIII(tralen)Cl complex (tralenH2 = N,N'-di(cyclohepta-2,4,6-trien-1-one-2-yl)-1,2-diaminobenzene) has been synthesized and applied to mediate the reversible-deactivation radical polymerization (RDRP) of vinyl monomers. The polymerization of unconjugated monomers such as vinyl acetate (VAc) and N-vinylpyrrolidone (NVP) with AlIII(tralen)Cl showed the living characters of linearly increased molecular weight with conversion and formation of block copolymer. However, the control manners in the polymerization of conjugated monomers like acrylates and styrene were limited. The electron paramagnetic resonance (EPR) spectrum indicated that AlIII(tralen)BArF (BArF = tetrakis(3,5-trifluormethylphenyl)borate) and propagating radicals formed a paramagnetic dormant species, possibly PVAc-AlIII(tralen)BArF, via the single-electron transfer to the tralen ligand.

Combined nitroxide mediated radical polymerization techniques for block copolymer synthesis

Nitroxide mediated radical polymerization (NMP) is one of the most powerful method for advanced polymer synthesis. However, NMP suffers from some limitations, in particular to mediate the polymerization of unconjugated monomers or to conduct the polymerization of conjugated monomers under low temperatures. The combination of NMP with other reversible-deactivation radical polymerization techniques, such as reversible addition–fragmentation chain transfer (RAFT), atom transfer radical polymerization (ATRP) or organometallic mediated radical polymerization (OMRP), offered new possibilities in macromolecular engineering. In this contribution we report different strategies of ‘combined NMP’, i.e., the exchange of the polymer chain-end controlling agents for sequenced polymerization or the introduction of different polymerization-initiating sites onto alkoxyamines or polymers.

Visible-Light-Induced Living Radical Polymerization (LRP) Mediated by (salen)Co(II)/TPO at Ambient Temperature

Visible-light-induced living radical polymerization of acrylates (MA, nBA, tBA), acrylamides (DMA, AMO), and vinyl acetate (VAc) at ambient temperature mediated by (salen)Co(II)/TPO was described. Effects of light intensity, feeding ratio of monomer and equivalent of TPO for the polymerization of MA were investigated. Well-defined homopolymers and block polymers with predetermined molecular weight and narrow polydispersity were obtained under mild conditions. The mechanism of the polymerization was proposed based on polymerization behavior and polymer structure analysis. The (salen)Co(II)/TPO system was suitable for both conjugated and unconjugated monomers under mild conditions.

Photoinduced Electron Transfer–Reversible Addition–Fragmentation Chain Transfer (PET-RAFT) Polymerization of Vinyl Acetate andN-Vinylpyrrolidinone: Kinetic and Oxygen Tolerance Study

Photoinduced electron transfer–reversible addition–fragmentation chain transfer (PET-RAFT) polymerization was employed for the polymerization of unconjugated monomers, including vinyl acetate, vinyl pivalate, N-vinylpyrrolidinone, dimethyl vinylphosphonate, vinyl benzoate, and N-vinylcarbazole, in the presence of low concentration (ppm range) of photoredox catalyst, fac-[Ir(ppy)3], under low energy visible light irradiation. Kinetic studies of vinyl acetate indicated excellent control of molecular weights and molecular weight distributions (Mw/Mn = 1.09–1.2), even with high monomer conversion (>75%), in different catalyst concentrations. High molecular weights of poly(vinyl acetate) (Mn > 100 000 g/mol) and poly(N-vinylpyrrolidinone) (Mn > 40 000 g/mol) with low dispersities (Mw/Mn < 1.25) were obtained in bulk polymerizations. Moreover, the online kinetic study using Fourier transform near-infrared (FTNIR) showed comparable kinetic rates for the polymerizations in the absence and presence of relatively l...

A Robust and Versatile Photoinduced Living Polymerization of Conjugated and Unconjugated Monomers and Its Oxygen Tolerance

Controlled/living radical polymerization techniques have transformed polymer chemistry in the last few decades, affording the production of polymers with precise control over both molecular weights and architectures. It is now possible to synthesize almost an infinite variety of macromolecules using nonspecialized equipment, finding applications in high-tech industry. However, they have several shortcomings. Until recently, living radical polymerizations could not be controlled by an external stimulus, such as visible light, pH, mechanical, chemical, etc. Moreover, they are usually sensitive to trace amounts of oxygen in the system. In this Article, we report a photoinduced living polymerization technique, which is able to polymerize a large range of monomers, including conjugated and unconjugated monomers, using ultralow concentrations of an iridium-based photoredox catalyst (typically 1 ppm to monomers) and a low energy visible LED as the light source (1-4.8 W, λ(max) = 435 nm). The synthesis of homopolymers with molecular weights ranging from 1000 to 2,000,000 g/mol was successfully achieved with narrow molecular weight distributions (M(w)/M(n) < 1.3). In addition, chain extensions of poly(methacrylate)s, poly(styrene), poly(N-vinyl pyrrolidinone), poly(vinyl ester)s, and poly(acrylate)s were performed to prepare diblock copolymers. The reusability of the catalyst was demonstrated by the synthesis of a decablock polymer by multiple chain extensions. Most importantly, this process was employed to prepare well-defined polymers and multiblock copolymers in the presence of air.

Synthesis of Concentrated Polymer Brushes via Surface-Initiated Organotellurium-Mediated Living Radical Polymerization

An organotellurium chain transfer agent (CTA) bearing a triethoxysilyl group at one end and a 2-methyltellanyl-2-methylpropionate group at the other was prepared and immobilized on the surface of a silicon wafer and silica nanoparticle (SiP). Surface-initiated organotellurium-mediated living radical polymerization (SI-TERP) from the immobilized CTA in the presence of nonimmobilized (free) organotellurium CTA was examined. Concentrated polymer brushes (CPBs) having surface occupancies above 0.1 were prepared by polymerization of various monomers, including styrene, methyl methacrylate, butyl acrylate, N-isopropyl acrylamide, N-vinyl pyrrolidone (NVP), and N-vinyl carbazole (NVC). All CPBs were formed in a controlled manner, with number-average molecular weights close to the theoretical values and low polydispersity indices (<1.41). Structurally well-controlled CPBs comprising unconjugated monomers, NVP and NVC, were prepared for the first time. Atomic force microscopy and transmission electron microscopy analyses of the CPBs revealed the highly stretched and anisotropic structure of the grafted polymer chain in a good solvent.

Organoselenium compounds: development of a universal “living” free radical polymerization mediator

A new versatile mediator for conducting “living” radical polymerization was developed based on diselenocarbonyl compounds. After the optimization of substitution groups, a “universal” diselenocarbonyl compound (O4) was developed and successfully applied to the controlled polymerization of both conjugated and unconjugated vinyl monomers, and the desired polymers with predetermined molecular weights and narrow molecular weight distributions were obtained in excellent yields. The characteristic feature of this method is exemplified by the synthesis of block copolymers composed of conjugated and unconjugated monomers, which would be of great importance as functional smart organic nanomaterials. Furthermore, the existence of organoselenium groups in the final polymers would be especially valuable for bio-related applications.

Invention of organotellurium and organostibine mediators for highly controlled degenerative transfer polymerization

Polymer-end mimetic organotellurium and organostibine compounds mediate highly controlled living radical polymerizations that allow the molecular weight to be controlled accurately and give well-defined end-groups. A variety of both conjugated (including styrene, acrylate and methacrylate derivatives) and unconjugated monomers (including 1-vinyl-2-pyrrolidinone and vinyl acetate) have been successfully polymerized in a controlled manner. The higher controllability of organotellurium- and organostibine-mediated polymerization compared to organoiodine-mediated polymerization is due to the faster degenerative transfer of organotellanyl and organostibino groups compared to iodine atom. AB-diblock, ABA-triblock and ABC-triblock copolymers have also been synthesized by the successive addition of different families of monomers. Transformations of the end-groups via radical and ionic reactions yielded polymers with a range of different functional groups and well-defined structures. (Communicated by Hitosi NOZAKI, M.J.A.)

Highly Versatile Organostibine Mediators for Living Radical Polymerization

A new versatile method for conducting living radical polymerization has been developed in which organostibines induce consecutive group-transfer radical reactions with alkenes. The method has been successfully applied, for the first time, to the controlled polymerization of both conjugated and unconjugated vinyl monomers, and the desired polymers with predetermined molecular weight and low polydispersity index were obtained in excellent yields. This characteristic feature of this method is exemplified in the first synthesis of block copolymers composed of conjugated and unconjugated monomers, which would be of great importance as functional smart organic nanomaterials.

Structure‐reactivity relations of conjugated and unconjugated monomers: Acrylates and methyl vinyl ketone in copolymerization with styrene compared with vinyl esters in copolymerization with ethylene

AbstractThis article describes the copolymerization of methyl vinyl ketone (MVK), methyl acrylate (MA), and methyl methacrylate (MMA) with styrene (St) as reference monomer at 3.4 MPa and 335 K with toluene as solvent. In addition, the effect of pressure on the binary copolymerizations of St‐Ma‐MMA is discussed. It appearsthat in case of conjugated monomers reactivity decreases as the electron‐donating character of the substituents increases, whereas the reverse is found in unconjugated monomers. This is explained by the finding that in conjugated monomers resonance effects induced by polar factors play a dominant role, whereas in unconjugated monomers mainly polar factors are governing the relative reactivities. The r values at 3.4 MPa are compared with those predicted by means of the Q‐e scheme and Patterns. No definite conclusions could be drawn about the applicability and validity of either scheme, although Patterns shows excellent result in case of the H function of Mayo. In vinyl ester copolymerizations and Le Noble and Asano's example of the menshutkin reaction one single factor (polarity and steric hindrance, successively) dominates ΔG#, ΔG and ΔV#. This allows a straight forward interpretation of the result with the Hammond postulate and is in full agreement with Evan's potential‐energy calculations. In conjugated monomers, however, an interplay of reasonance and polar factors is found. The general validity of these findings needs further experimental and theoretical support.

ESR Studies of Copolymerization of Water-Soluble Monomers with Acrylonitrile

Copolymerization of water-soluble unconjugated monomers (M1) with acrylonitrile (AN) has been studied by ESR using a flow system.The M1-monomers studied were maleic anhydride (MA), sodium allyl sulfonate (SAS), sodium methallyl sulfonate (SMAS), allyl alcohol (AA), sodium vinyl sulfonate (SVS), allyl acetate (AAc), with vinyl acetate (VAc) as reference standard. The initiation reactions and the addition of AN units to monomer radicals (M1·) at pH 1.4 and 7.0 were studied. The addition of small amounts of AN to M1 monomers caused a sharp decrease in the concentration of monomer radicals (M1·), whereas the concentration of allylic monomer radicals (in the cases of AA and SAS), AN· and, especially, the co-polymer radicals M1—AN· formed from M1· increased. The reactivity of sulfonic acid monomer radicals, such as SVS and SMAS, increased almost to double upon changing pH from 1.4 to 7.0. All results show the very low reactivity of water-soluble unconjugated monomers and their radicals. The M1—AN· copolymer radicals are characterized by lower aHβ-values than the AN monomer radical. This is interpreted as due to restricted rotation caused by steric hindrance from the M1 units attached to the β-carbon of the AN radicals.

Remote Unit Effects in the Copolymerization of Unconjugated Monomers

Abstract The kinetics of the radical copolymerization of the three binary systems vinyl chloride (C)-vinyl acetate (Ac), vinylidene chloride (V)-vinyl acetate, and vinyl chloride-vinylidene chloride have been investigated in the whole range of monomer feed composition using the chromatographic method. Penultimate or antepenultimate effects have been observed in all cases. The better values of the corresponding reactivity ratios are: For C-Ac copolymers, rAc = 0.29, rCCC = 1.67, rAcCC. = 4.60, and rAcC = 2.05. For V-Ac copolymers, rAc = 0.07, rVVV = 5.30, rAcVV = 11.5, rAcAcV = 8.0, and rVAcV = 6.0. For C-V copolymers, rVAcV = 0.22, rVV = 2.94, and rCV = 4.31. An internal transfer mechanism is suggested for the antepenultimate effect in the vinyl acetate copolymers.

Generality of product probability values in unifying and predicting relationships among monomers in copolymerization

AbstractIt is shown that a knowledge of the reactivity ratios for the binary systems A–B and B–C allows reactivity ratios for the copolymer system A–C to be calculated from the relationship: PabPbcPca = PacPcbPba = (a constant). The various probabilities include the possibilities of adding A, B, or C monomers to any of the corresponding radicals and can be expressed in terms of binary reactivity ratios. At equimolar concentrations it is shown that for systems of three conjugated or three unconjugated monomers approximates 0.037. Similarly, for systems of two conjugated and one unconjugated monomers or two unconjugated and one conjugated monomers approximates 0.006. Once the appropriateness of these constants is established, it is shown how the relationship may be used to assess the most probable values among widely varying reported reactivity ratios. It is shown that the values of the constant for different combinations of monomers allow the assessment of the reactivity of conjugated monomers compared with unconjugated monomers for conjugated or unconjugated radicals. It develops that the reactivity of unconjugated monomers is between 5 and 10% of that of conjugated monomers for unconjugated radicals. For more precise assessment of unknown reactivity ratios it is suggested that is a product function of unique reactivity parameters characteristic of the individual monomers involved.

THE PHOTOINITIATED ADDITION OF BUTYL MERCAPTAN TO CONJUGATED AND UNCONJUGATED DOUBLE BONDS

This study elucidates the details of a typical initiation encountered in polymerization. A kinetic mechanism for the photoinitiated addition of normal butyl mercaptan to single and conjugated double bonds is proposed, and the corresponding velocity constants namely the attack kα, the transfer kct, and the termination kt have been measured employing a sector method. For the concentrations employed in this work the over-all rate of addition to the double bond is determined by the transfer rate of the composite mercapto monomer radical, while the capture of initiating radicals depends on the rate of attack of the mercaptyl radicals on the double bonds. The transfer rate is about 1000 times faster for a pentenyl than for a conjugated styryl radical, while the attack step is estimated to be several hundred times faster for the conjugated monomer. These conclusions are shown to be consistent with results observed when conjugated and unconjugated monomers are in competition, and are in agreement with the quantum mechanical structure of the radicals and molecules involved. This work reports a general survey of the field, and subsequent papers will extend the observations.