Polymerization Of Acrylate Research Articles

Toward an Efficient Process for the Cu(0)‐Mediated Synthesis and Chain Extension of Poly(methyl acrylate) Macroinitiator Using PMDETA as Ligand

AbstractMe6TREN (tris[2‐(dimethylamino)ethyl]amine) is commonly used in Cu(0)‐mediated polymerization of acrylates due to its ability to promote high reaction rates while maintaining excellent control of chain growth. However, its cost presents a significant barrier to commercialization. Thus, the use of PMDETA (N,N,Nʹ,Nʹʹ,Nʹʹ‐pentamethyldiethylenetriamine), a ligand that is significantly less expensive than Me6TREN but is known to reduce the polymerization rate as well as control, is explored. The continuous production of low molecular weight (MW) poly(methyl acrylate) using PMDETA ligand in a copper tubular reactor is demonstrated, with conversions >70% achieved with a residence time of 32 min at 70 °C. The resulting macroinitiator solution can be stored and chain extended with methyl acrylate (MA) to high conversion in a semibatch reactor using either PMDETA or Me6TREN as additional ligand, increasing the versatility of a newly developed process to efficiently produce block copolymers using either ligand, or a combination of the two. First results suggest that the two‐step process can also be used to chain extend the macroinitiator with methacrylates, thus extending the range of materials that can be produced.

Effective Singlet Oxygen Sensitizers Based on the Phenazine Skeleton as Efficient Light Absorbers in Dye Photoinitiating Systems for Radical Polymerization of Acrylates.

A series of dyes based on the phenazine skeleton were synthesized. They differed in the number of conjugated double bonds, the arrangement of aromatic rings (linear and/or angular system), as well as the number and position of nitrogen atoms in the molecule. These compounds were investigated as potential singlet oxygen sensitizers and visible light absorbers in dye photoinitiating systems for radical polymerization. The quantum yield of the singlet oxygen formation was determined by the comparative method based on the 1H NMR spectra recorded for the tested dyes in the presence of 2,3-diphenyl-p-dioxene before and after irradiation. The quantum yield of the triplet state formation was estimated based on the transient absorption spectra recorded using the nanosecond flash photolysis technique. The effectiveness of the dye photoinitiating system was characterized by the initial rate of trimethylolpropane triacrylate (TMPTA) polymerization. In the investigated photoinitiating systems, the sensitizer was an electron acceptor, whereas the co-initiator was an electron donor. The effectiveness of TMPTA photoinitiated polymerization clearly depended on the arrangement of aromatic rings and the number of nitrogen atoms in the modified phenazine structure as well as the quantum yield of the triplet state formation of the photosensitizer in the visible light region.

Free radical polymerization of acrylates bearing acetylene for preparation of clickable polymers

It is still a challenge to directly, without any control means, synthesize polymers bearing acetylene groups by normal free radical polymerization (FRP) of acetylenyl vinyl monomers, such as propargyl (meth)acrylates, because the reactive acetylene groups result in chain branching and gelation. Some propargyl acrylates with alkyl substitutes, however, can afford linear and soluble polymers. To clarify the substitute effects the FRP behaviours of a series of acrylates bearing acetylene groups with or without substitutes are studied. Homopolymerizations of acetylenyl acrylates without or with mono-substitute on propargyl led to branched polymers at early reaction stage, and became gelled after 0.5 h with monomer conversion over 12% and gel content over 50%. The acetylenyl acrylates with di-substitutes on propargyl can afford linear and soluble homo- and copolymers with‾Mn up to over 10,000 and with 45–75% monomer conversion, except for monomer 2-(2-methylbut-3-yn-2-yloxy)ethyl acrylate (DMPOEA) which has di-substitutes and a spacer connecting to the propargyl. Reactivities of vinyl and acetylene groups were found within 20 times difference by laser flash photolysis (LFP) experiments. The substitute effects of acetylenyl acrylates on FRP are explained by the intramolecular cycloaddition between CC and CC to form lactone from the s-cis conformers of the di-alkyl substituted acetylenyl acrylates. Propagating radicals can transform to stable allyl radicals by α-H atom transfer and thus the chain propagations stop. Both real-time FT-IR monitoring of photo-polymerization and high resolution 13C NMR spectra of the polymer confirmed the existence of lactone units on polymer chains. The hypothesis is also accordance with facts obsorved in the FRP. Finally postpolymerization modification through acetylene groups on polymer chains by photo thiol-yne click reaction is exemplified.

Recent Advances in bis-Chalcone-Based Photoinitiators of Polymerization: From Mechanistic Investigations to Applications.

Over the past several decades, photopolymerization has become an active research field, and the ongoing efforts to develop new photoinitiating systems are supported by the different applications in which this polymerization technique is involved—including dentistry, 3D and 4D printing, adhesives, and laser writing. In the search for new structures, bis-chalcones that combine two chalcones’ moieties within a unique structure were determined as being promising photosensitizers to initiate both the free-radical polymerization of acrylates and the cationic polymerization of epoxides. In this review, an overview of the different bis-chalcones reported to date is provided. Parallel to the mechanistic investigations aiming at elucidating the polymerization mechanisms, bis-chalcones-based photoinitiating systems were used for different applications, which are detailed in this review.

Additive manufacturing of highly fluorescent organic 3D-metastructures at sub-wavelength resolution

Functional metastructures exhibiting unique optical properties are desirable for advancements in microfluidics, optoelectronics, nonlinear photonics, biochemical sensing, and metamaterials. Additive manufacturing techniques are expected to enable rapid prototyping of complex 3D architectonics required for such applications. We report the fabrication of highly fluorescent all-organic metastructures via carbon quantum dot assisted in-situ polymerization of acrylate and carbon dot composite resin. The polymerized structures fabricated from acrylate and carbon dot composite resin exhibit excellent linear and nonlinear optical properties due to the presence of two-photon active carbon quantum dots incorporated in the resin. By activating the two-photon process, we eliminated the need for adding two-photon absorbing toxic chemicals for initiating the polymerization process. The fabrication of functional nanostructures using acrylate and carbon dot composite resin opens the door for rapid prototyping of metastructures for various applications such as developing functional metamaterials, solid-state lighting, live monitoring of cells in cultures, fluorescent tagging and detection of counterfeiting among others.

Photoenzymatic RAFT Emulsion Polymerization with Oxygen Tolerance

Photoenzymatic reversible addition-fragmenatation chain transfer (RAFT) emulsion polymerization, surfactant-free or ab initio, of various monomers is reported with oxygen tolerance. In surfactant-free emulsion polymerizatoin, poly(N, N-dimethylacrylamide)s were used as stabilizer blocks for emulsion polymerization of methyl acrylate, n-butyl acrylate and styrene, producing well-defined amphiphilic block copolymers, including those with an ultrahigh molecular weight, at quantitative conversions. The controlled character of surfactant-free emulsion polymerization was confirmed by kinetic studies, chain extension studies and GPC analyses. Temporal control was demonstrated by light ON/OFF experiments. In ab initio emulsion polymerization of methyl acrylate and methyl methacrylate, low-dispersity hydrophobic polymers were synthesized with predictable molecular weights. This study extends the monomer scope suitable for photoenzymatic RAFT polymerization from hydrophilic to hydrophobic monomers and demonstrates that oxygen-tolerance can be equally achieved for emulsion polymerization with excellent RAFT control.

Remote effect of substituents on the properties of phenyl thienyl thioether-based oxime esters as LED-sensitive photoinitiators

Visible light-sensitive photoinitiators (PIs) are essential for light-emitting diode (LED) photopolymerization as LEDs are becoming the predominant light sources. In this work, five phenyl thienyl thioether-based oxime esters with different electron-donating and -withdrawing substituents on the para-position of the phenyl ring were designed and synthesized as LED-sensitive PIs. These oxime esters exhibited a maximum absorption band matched with the LED emission spectra (e.g., 365–425 nm). The remote substituents clearly affected the absorption of the oxime esters, and the principle was investigated via DFT calculations. The substituents also enhanced the initiation activities with the increase in the quantum yields of photo-induced free radical generation. Besides, upon comparison of the quantum yields of fluorescence, photolysis, and free radicals, a fast intersystem crossing was proposed for the excited states of these oxime esters, and results revealed the photoreactions were mainly from the triplet states. Finally, photo-DSC was employed to evaluate the actual photopolymerization. Results suggested that they could all efficiently initiate the free radical polymerization of acrylates under LED irradiation, making them suitable PIs for LED polymerization. This study could provide some significance to the design of PIs with improved efficiency.

Radical Cations of Phenoxazine and Dihydrophenazine Photoredox Catalysts and Their Role as Deactivators in Organocatalyzed Atom Transfer Radical Polymerization.

Radical cations of photoredox catalysts used in organocatalyzed atom transfer radical polymerization (O-ATRP) have been synthesized and investigated to gain insight into deactivation in O-ATRP. The stability and reactivity of these compounds were studied in two solvents, N,N-dimethylacetamide and ethyl acetate, to identify possible side reactions in O-ATRP and to investigate the ability of these radical cations to deactivate alkyl radicals. A number of other factors that could influence deactivation in O-ATRP were also probed, such as ion pairing with the radical cations, radical cation oxidation potential, and halide oxidation potential. Ultimately, these studies enabled radical cations to be employed as reagents during O-ATRP to demonstrate improvements in polymerization control with increasing radical cation concentrations. In the polymerization of acrylates, this approach enabled superior molecular weight control, a decrease in polymer dispersity from 1.90 to 1.44, and an increase in initiator efficiency from 78 to 102%. This work highlights the importance of understanding the mechanism and side reactions of O-ATRP, as well as the importance of catalyst radical cations for successful O-ATRP.

Direct Determination of Interchain Transfer Constants of Benzyl Acrylate to Poly(Ethyl Acrylate) by RAFT Polymerization and Polymer Chromatography

AbstractInterchain transfer is an important side reaction in radical polymerization of acrylates and has significant effects on both reaction kinetics and the resulting polymer microstructures. In this study, an effective method for direct determination of the interchain transfer constant (Ctr) is established via the combination of RAFT polymerization of a monomer in the presence of another prepared polymer and subsequent separation using polymer chromatography. The Ctr of benzyl acrylate (BzA) to poly(ethyl acrylate) (PEA) is determined with benzyl N‐carbazole dithiocarbamate (BCBD) as the RAFT agent and the effects of polymerization recipe, such as BzA/BCBD mole ratios, BzA/PEA mass ratios, and solvent amounts on Ctr determination investigated. The results indicate that interchain transfer reactions show clear short chain radical effects in early stage of RAFT polymerization and the experimental recipes have little influence on the determination. The Ctr values are in the range of 1–2 × 10−4 at 90–120 °C and the activation energy of Ctr at 47.8 kJ mol−1.

Solvent-Free UV Polymerization of n-Octadecyl Acrylate in Butyl Rubber: A Simple Way to Produce Tough and Smart Polymeric Materials at Ambient Temperature.

One of the most fascinating challenges in recent years has been to produce mechanically robust and tough polymers with smart functions such as self-healing and shape-memory behavior. Here, we report a simple and versatile strategy for the preparation of a highly tough and highly stretchable interconnected interpenetrating polymer network (c-IPN) based on butyl rubber (IIR) and poly(n-octadecyl acrylate) (PC18A) with thermally induced healing and shape-memory functions. Solvent-free UV polymerization of n-octadecyl acrylate (C18A) at 30 ± 2 °C in the presence of IIR leads to IIR/PC18A c-IPNs with sea-island or co-continuous morphologies depending on their IIR contents. The lamellar crystals with a melting temperature Tm of 51-52 °C formed by side-by-side packed octadecyl (C18) side chains are responsible for more than 99% of effective cross-links in c-IPNs, the rest being hydrophobic associations and chemical cross-links. The c-IPNs exhibit varying stiffness (9-34 MPa), stretchability (72-740%), and a significantly higher toughness (1.9-12 MJ·m-3) than their components, which can be tuned by changing the IIR/PC18A weight ratio. The properties of c-IPNs could also be tuned by incorporating a second, noncrystallizable hydrophobic monomer, namely, lauryl methacrylate (C12M), in the melt mixture. We show that the lamellar clusters acting as sacrificial bonds break at the yield point by dissipation of energy, while the ductile amorphous continuous phase keeps the structure together, leading to the toughness improvement of c-IPNs. They exhibit a two-step healing process with >90% healing efficiency with respect to the modulus and a complete shape-recovery ratio induced by heating above Tm of alkyl crystals. The temperature-induced healing occurs via a quick step where C18 bridges form between the damaged surfaces followed by a slow step controlled by the interdiffusion of C18A segments in the bulk. We also show that the strategy developed here is suitable for a variety of rubbers and n-alkyl (meth)acrylates of various side-chain lengths.

Optimization of a 3D-printed tubular reactor for free radical polymerization by CFD

A flow reactor for the complex reaction network of the free radical solution polymerization of n-butyl acrylate was optimized by a combination of kinetic modeling, computational fluid dynamics (CFD) and additive manufacturing. CFD was used to model a flow reactor with SMX mixing elements. An optimized geometry was 3D-printed from polypropylene. The modeled residence time behavior was compared to relevant experiments, giving a validation for the flow behavior of the reactor. A kinetic model for the free radical solution polymerization of n-butyl acrylate (BA) was in addition implemented into the CFD model. It was used to predict the polymerization behavior in the flow reactor and the resulting product properties. The experimental and computational results were in acceptable agreement.Graphical abstract

Water-Resistant Latex Coatings: Tuning of Properties by Polymerizable Surfactant, Covalent Crosslinking and Nanostructured ZnO Additive

This paper deals with the development of acrylic latexes providing high-performance water-resistant coatings. For this purpose, mutual effects of anionic surfactant type (ordinary and polymerizable), covalent intra- and/or interparticle crosslinking (introduced by allyl methacrylate copolymerization and keto-hydrazide reaction, respectively) and ionic crosslinking (provided by nanostructured ZnO additive) were investigated. The latexes were prepared by the standard emulsion polymerization of methyl methacrylate, butyl acrylate and methacrylic acid as the main monomers. The addition of surface-untreated powdered nanostructured ZnO was performed during latex synthesis, resulting in stable latexes comprising dispersed nanosized additive in the content of ca 0.9−1.0 wt.% (based on solids). The coating performance with emphasis on water resistance was evaluated. It was determined that the application of the polymerizable surfactant improved coating adhesion and water-resistance, but it wasn′t able to ensure high water-resistance of coatings. Highly water-resistant coatings were obtained provided that covalent intra- and interparticle crosslinking together with ionic crosslinking were employed in the coating composition, forming densely crosslinked latex films. Moreover, coatings comprising nanostructured ZnO additive displayed a significant antibacterial activity and improved solvent resistance.

Assessing the Effect of CeO2 Nanoparticles as Corrosion Inhibitor in Hybrid Biobased Waterborne Acrylic Direct to Metal Coating Binders

CeO2 nanoparticles were incorporated in waterborne binders containing high biobased content (up to 70%) in order to analyze the anticorrosion performance for direct to metal coatings. Biobased binders were synthesized by batch miniemulsion polymerization of 2-octyl acrylate and isobornyl methacrylate monomers using a phosphate polymerizable surfactant (Sipomer PAM200) that lead to the formation of phosphate functionalized latexes. Upon the direct application of such binders on steel, the functionalized polymer particles were able to interact with steel, creating a thin phosphatization layer between the metal and the polymer and avoiding flash rust. The in situ incorporation of the CeO2 nanoparticles during the polymerization process led to their homogeneous distribution in the final polymer film, which produced outstanding anticorrosion performance according to the Electrochemical Impedance Spectroscopy measurements. In fact, steel substrates coated with the hybrid polymer film (30–40 µm thick) showed high barrier corrosion resistance after 41 days (~1000 h) of immersion in NaCl water solution and active inhibition capabilities thanks to the presence of the CeO2 nanoparticles. This work opens the door to the fabrication of sustainable hybrid anticorrosion waterborne coatings.

Kinetic Measurement of Acrylic Acid Polymerization at High Concentrations under Nearly Isothermal Conditions in a Pendula Slug Flow Reactor

This work discusses a new measurement concept that uses contactless Raman spectrometry of free radical polymerization (FRP) in a milliscale reactor. The setup is based on a multiphase system with u...

Well-Defined PIII-Terminated Polymers from Phosphorylated Carbodithioate RAFT Agents

Five S-alkyl di-tert-butylphosphorylated carbodithioates, Z–C(S)SR, were studied as chain transfer agents (CTAs) in the RAFT polymerization of vinyl monomers. These phosphorus-containing CTAs involve new PIII and PV moieties in the Z group (phosphine-borane or free phosphine). Two of them, with an S-bonded 1-methoxycarbonylethyl group as leaving group, have not previously been described. The CTAs with a PV Z group provide good control over the polymerization of styrene (St) and n-butyl acrylate (nBA). Molar masses are close to theoretical values, and dispersities are consistently low during polymerization. The monitoring of polymerization by 31P NMR spectroscopy supports the controlled character and the integrity of the polymer chain ends. Conversely, they inhibit the polymerization of the less-activated monomer vinyl acetate (VAc). The reactivity of the CTAs with a PIII Z group mainly depends on the reaction medium, and their performance for St, nBA, and VAc was surprising and unexpected. Theoretical calculations were carried out to rationalize their behavior. Finally, an innovative strategy was developed to obtain well-controlled polymers with free phosphine ω-chain ends.

Investigation on mechanical and conductive properties of polypyrrole/UV cured acrylate nanocomposite coatings

Conductive polypyrrole/UV cured acrylate nanocomposite coatings were prepared via a facile approach called simultaneous photopolymerization. In our previous study, the mechanisms of the polymerizations of pyrrole and acrylate in this process were discussed. In the current work, the mechanical and conductive properties were investigated by correlating them with the structural and compositional changes observed in the coating systems. Various percentages of pyrrole and acrylate monomers along with their corresponding UV activators, AgNO3 and DAROCUR 1173 respectively, were used to prepare the polypyrrole/UV cured acrylate composite coatings. The percentage of the mixture of pyrrole and AgNO3 in the formulation varied from 25 % to 60 %. Scanning electron microscopy (SEM) results indicated that the deposition of polypyrrole/Ag composite particles occur closer to the substrate. Based on the conductive atomic force microscopy (AFM) results, all the coatings in this study exhibited higher current densities on the bottom side of the coatings and the only coatings prepared with the formulations containing 45 % or higher of pyrrole and AgNO3 mixture exhibited conductivity on top side of the coatings. From the thermogravimetric analysis (TGA) results, it can be inferred that the increase in percentage of polypyrrole/Ag in the coating results in changes in the chemical structure of the UV cured acrylate binder. Dynamic mechanical analysis (DMA)results suggested that the incorporation of polypyrrole/Ag composite during the photopolymerization process leads to plasticization of polymer network causing an increase in dissipative-like behavior in the coatings.

A novel thioxanthone-hydroxyalkylphenone bifunctional photoinitiator: Synthesis, characterization and mechanism of photopolymerization

A novel bifunctional photoinitiator (named as TX-EG-IPDI-2959) with thioxanthone and hydroxyalkylphenone moieties was synthesized by the reaction of isophorone diisocyanate with Irgacure 2959 and 2-(2-hydroxyethoxy) thioxanthone. The molecular structure of TX-EG-IPDI-2959 was characterized by 1H NMR, high-resolution mass spectroscopy, UV–vis and FT-IR. The photochemical behavior of TX-EG-IPDI-2959 was investigated through the photolysis and polymerization of butyl acrylate by UV–vis and HRMS. Compared with the combination of Irgacure 2959 and 2-(2-hydroxyethoxy) thioxanthone, the CC bond cleavage of hydroxyalkylphenone to produce free radical fragments was effectively done under the irradiation of visible LED light. The obvious intramolecular synergistic effect between the hydroxyalkylphenone and thioxanthone moieties has been confirmed based on HRMS analysis of photobleach and photopolymerization. In addition, the photopolymerization kinetic of an UV gel and trimethylolpropane triacrylate initiated by TX-EG-IPDI-2959 were also investigated. The plausible photochemical reaction mechanism of TX-EG-IPDI-2959 was proposed.

Fabrication of polymer electrolyte via lithium salt-induced surface-initiated radical polymerization for lithium metal batteries

The fabrication of flexible polymer electrolytes (PEs) which possess simultaneously high thermal stability, robust mechanical strength, and high ionic conductivity is very challenging for lithium (Li) batteries. Herein, cellulose-based PE is fabricated via a Li salt-induced surface-initiated radical polymerization of polyethylene glycol methyl ether acrylate (PEGA). The polymerization of PEGA is catalyzed by various Li salts, such as Li perchlorate (LiClO4), bis(trifluoromethane)sulfonimide Li (LiTFSI), Li difluoro(oxalato)borate (LiDFOB), and LiClO4/LiDFOB, which also serve as charge transfer carriers in PEs. The Li salt can be used as the catalyst to promote the cleavage of C–Br bond on the surface of Br-modified cellulose, and then initiate the polymerization of PEGA. The PE obtained from the dual salt (LiClO4/LiDFOB)-induced radical polymerization system exhibits high ionic conductivity of 3.5 × 10−5 S cm−1 at 30 °C, good thermal stability (up to 240 °C), and wide electrochemical stability window (5.0 V vs. Li/Li+). Moreover, Li/PE/Li symmetric cells show good interfacial stability between PE and Li foil and the assembled Li/PE/LiFePO4 cells possess 150 mA h g−1 at 0.1C. Li salt-induced surface-initiated polymerization provides a simple and efficient method for fabricating PE for high-performance Li metal batteries (LMBs).

Kinetic importance of the missing step in dithiobenzoate-mediated RAFT polymerizations of acrylates

The effect of retardation exhibited in dithiobenzoate-mediated polymerizations is perhaps the most controversial kinetic phenomenon discussed in polymer chemistry in the last 20 years. However, the Missing Step reaction (MSR), which involves the termination between a propagating radical and a 3-arm star product, has emerged as a hypothesis to explain the full kinetic picture for acrylate polymerizations. Here, a kinetic model, the most detailed of its kind, is developed to describe and study the MSR. The model is based on the method of moments and includes RAFT pre-equilibrium and equilibrium, backbiting, cross-termination, MSR and chain-length dependent radical termination. After validation through comparison with experimental data available in the literature, the model is used to demonstrate that the kinetic behavior of the propagating and intermediates radicals can be described by the quasi-steady state assumption and that backbiting does not significantly influence predicted conversion profiles and product molecular weights. It is also shown that the induction period observed experimentally can be represented by either slow initiation/reinitiation of primary radicals or by assuming that radical intermediates formed by addition of primary radicals to the RAFT agent have increased stability; however, the associated rate constants for these reactions had to be adjusted from literature values. A comparison between the MSR and Intermediate Radical Termination (IRT) representations RAFT-mediated acrylate polymerization identifies chain end-group functionality (EGF) as a means to further discriminate between these theories.

N-ethyl carbazole-1-allylidene-based push-pull dyes as efficient light harvesting photoinitiators for sunlight induced polymerization

In this article, the free radical polymerization of acrylates was successfully achieved with a series of twelve push-pull chromophores comprising the N-ethyl carbazole-1-allylidene group as the electron-donating group. Using this strong donor, the resulting dyes, never synthesized before, could efficiently initiate the free radical photopolymerization of acrylates upon mild irradiation conditions e.g. using sunlight. These novel multi-component systems comprising the above mentioned push-pull dyes, a tertiary amine (ethyl dimethylaminobenzoate EDB) and an iodonium salt could act as efficient photoinitiating systems (PISs) in free radical polymerization (FRP), leading to the formation of 3D patterns with precise shapes under the direct laser write (DLW) approach. Among these new PISs, dyes 3, 6, 7 and 8 were selected due to their efficient photoinitiation performances for chemical mechanism studies including steady state photolysis, fluorescence quenching measurements, electron spin resonance (ESR) spin-trapping experiments and cyclic voltammetry. Markedly, their excellent photochemical reactivities prompted us to investigate the performance of these multi-component photoinitiating systems upon sunlight as an ecofriendly approach. As a result, this research proved that sunlight could be used as a potential light source that can advantageously replace LEDs when highly reactive push-pull dyes are used as photosensitizers for the free radical photopolymerization of acrylate resins. Finally, 3D patterns could be prepared with the new photocomposites, and silica fillers could be even incorporated within the photosensitive resins so that a gradient of resolution could be successfully demonstrated.