Photoinduced Cationic Polymerization Research Articles

Use of pyridine derivatives as inhibitor/retarding agent for photoinduced cationic polymerization of epoxides

In this study, the cationic photopolymerization of epoxy controlled by pyridine derivative was investigated. Two pyridines were selected in order to explore the impact of the associated pKa and the amine steric hindrance on the polymerization. The inhibition, the polymerization rate, the heat flow and the conversion during dark polymerization were found to be affected depending of the pyridine derivative structure. Two mechanisms seem to be involved. 1) During the initiation step, the proton is trapped by pyridine derivative, a fact which delays the polymerization reaction, because of less growing chains and lower exothermicity. 2) During the propagation reaction, an interaction between the oxonium ion and the pyridine derivative takes place, which results in a decrease of the rate of polymerization. These two mechanisms depend on the concentration, but also on the associated pKa and on the steric hindrance of the amine, which allows a tailorable control over the cationic polymerization kinetics.

Photochemically generated ionic species for cationic and step-growth polymerizations

Developing innovative photochemical methods for the purpose of attaining green chemistry and mitigating global warming has recently become a very important concept. While we have to move towards a more sustainable world, daily life is becoming increasingly dependent on the use of polymeric materials. Conventional thermal polymerization systems fail to fulfill the requirements of sustainable chemistry, resulting in an increase in energy demand. This article outlines cationic and step-growth polymerizations of various monomers initiated by different photochemically generated ionic species and their advantages over conventional polymerization systems. Typical examples of photoinduced cationic and step-growth polymerizations performed under UV, visible and near-infrared (NIR) light are summarized under two main categories; direct and indirect initiating systems. In direct initiating systems the use of commercially available and structurally modified onium salts as one-component photoinitiators for both polymerizations are summarized. Indirect initiating systems, proceeding through i) photoinduced electron/energy transfer (PET), ii) charge-transfer complexation and iii) free-radical promoted cationic polymerization (FRPCP), are summarized with a focus on the recent step-growth methods developed in our laboratory.

Ternary hybrid materials based on the photoinduced cationic polymerization of functional twin monomer and epoxides

Homogeneous ternary silicone hybrid materials comprising phenolic resins and disubstituted polysiloxane with crosslinked epoxy resin were conveniently prepared by the photoinduced cationic ring-opening copolymerization of twin monomer (2-methyl-2-(3-glycidoxypropyl)-4H-1,3,2-benzodioxa-siline, MGS) and epoxy monomer (3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane, EPOX). The two monomers had good compatibility, and no phase separation occurred during long-term storage. Under the excitation, the cationic ring-opening polymerization of MGS rapidly occurred to form polysiloxane and phenolic resin, and EPOX played the role of a crosslinking agent. The reaction mechanism was explicitly proven by infrared spectroscopy, solid-state 13C and 29Si nuclear magnetic resonance spectroscopy, surface contact angle, and X-ray photoelectron spectroscopy. SEM showed that the photocured film had no macroscopic phase separation, and the film had very good light transmittance. This study provided a new rapid method of preparing highly transparent ternary hybrid materials at room temperature through photopolymerization. It has potential applications in the fields of coatings, photoresists, and optical devices.

Novel perfluoropolyalkylethers monomers: synthesis and photo-induced cationic polymerization

Several difunctional oligomers were synthesized by functionalizing perfluoropolyalkylether (PFPAE) chains with different vinyl ethers and epoxides end-groups. Due to their innate synthetic challenges and demanding purification protocols, the PFPAE derivatives were obtained in low yield and with an average functionality lower than 2. However, the functionalized PFPAE oligomers were successful in being used in photo-induced cationic polymerization processes, obtaining transparent and soft films. The influences of the fluorinated chains, and various end-groups on the photopolymerization process were investigated, as well their chemical stability, thermal degradation, and surface properties.Graphical abstract

Continuous-Flow Synthesis of Pyrylium Tetrafluoroborates: Application to Synthesis of Katritzky Salts and Photoinduced Cationic RAFT Polymerization.

Katritzky salts have emerged as effective alkyl radical sources upon metal- or photocatalysis. These are typically prepared from the corresponding triarylpyrylium ions, in turn an important class of photocatalysts for small molecules synthesis and photopolymerization. Here, a flow method for the rapid synthesis of both pyrylium and Katrizky salts in a telescoped fashion is reported. Moreover, several pyrylium salts were tested in the photoinduced RAFT polymerization of vinyl ethers under flow and batch conditions.

Radical photoinduced cationic frontal polymerization in porous media

AbstractTwo different interpenetrating phase composites were produced using a radical photoinduced cationic frontal polymerization process. The composites were based on polyurethane (PU) and aluminium open‐cell foams impregnated with a formulation of a cycloaliphatic epoxy with different concentrations of a cationic photoinitiator and a thermal initiator. The influence of both types of initiators on the frontal polymerization features was systematically evaluated for the PU foam. It was found to occur only when the concentration of both initiators was greater than 0.5 wt%, leading to full conversion of the epoxy in the whole volume of the 15 mm thick composite samples within less than 100 s. The maximum temperature reached by the propagation front was in the range 275–305 °C depending on the type of formulation, leading to pores in the epoxy phase and extensive degradation of the PU phase. In the case of the opaque aluminium foam, an additional layer of pure resin was required on the UV‐exposed surface, which corresponded to a critical mass of a few grams to ensure sufficient heat generation and trigger the front propagation. © 2020 Society of Chemical Industry

Vinyl ethers and epoxides photoinduced copolymerization with perfluoropolyalkylether monomers

New perfluoropolyalkylether (PFPAE) monomers, chain extended with different alkyl groups and functionalized with vinyl ether or epoxide end-groups, were employed, together with trimethylolpropane trivinyl ether or trimethylolpropane triglycidyl ether, to produce fluorinated copolymers. The photoinduced cationic polymerization was investigated, and the PFPAE-based copolymer properties were thoroughly characterized. Interesting surface properties and two different values of refractive index were observed: thus, these fluorinated copolymers can be suitable materials for the manufacture of self-cleaning coatings and optical waveguides.

Photoinduced cationic frontal polymerization of epoxy–carbon fibre composites

AbstractUV‐activated frontal polymerization was exploited for the preparation of epoxy–carbon fibre composites. The curing process was investigated showing the frontal behaviour, and the final properties of UV‐cured composites were compared with those of the same composites obtained by thermal curing in the presence of amine as hardener. The best curing formulations were designed, defining the photoinitiator‐to‐thermal initiator ratio, which was 1.5:1.5. It was observed that the presence of the carbon fibres induced an acceleration of the front velocity. By comparing the thermomechanical properties of the thermally cured composite and the same composite crosslinked using the frontal process, we could observe that the latter showed higher Tg value and lower σf. This was attributed to the formation of a different polymeric network structure. © 2019 Society of Chemical Industry

Tailoring Thermo‐Mechanical Properties of Cationically UV‐Cured Systems by a Rational Design of Vinyl Ether Ester Oligomers using Enzyme Catalysis

AbstractThere is a demand for new sustainable polymeric materials. Vinyl ethers are, in this context, attractive oligomers since they polymerize fast, are non‐toxic, and can be polymerized under ambient conditions. The availability of vinyl ether oligomers is, however, currently limited due to difficulties in synthesizing them without using tedious synthesis routes. This work presents the synthesis of a series of vinyl ether ester oligomers using enzyme catalysis under solvent‐free conditions and the subsequent photoinduced cationic polymerization to form polymer thermosets with T gs ranging from −10 to 100 °C. The whole process is very efficient as the synthesis takes less than 1 h with no need for purification and the crosslinking is complete within 2 min.

Synthesis and characterization of an A2B2-type miktoarm star copolymer based on poly(ε-caprolactone) and poly(cyclohexene oxide)

An A2B2-type miktoarm star copolymer with two linear poly(e-caprolactone) (PCL) and two linear poly(cyclohexene oxide) (PCHO) arms was synthesized by using ring-opening polymerization (ROP), click chemistry, and photoinduced cationic polymerization, respectively. The ROP of e-CL with a dihydroxy functional initiator, 3-cyclohexene-1,1-dimethanol, produced a well-defined two-arm PCL with a cyclohexene end-functional group, (PCL)2-CH. The subsequent bromination of (PCL)2-CH followed by azidation gave a diazido end-functionalized PCL, (PCL)2-(N3)2. Then, a well-defined two-arm PCL macrophotoinitiator with benzoin end-functional groups, (PCL)2-(PI)2, was prepared by the azide/alkyne click reaction of this (PCL)2-(N3)2 and PI-alkyne, a separately prepared benzoin photoinitiator bearing a terminal alkyne group. Solid data obtained from the 1H NMR, FT-IR, GPC, UV, and fluorescence spectroscopic studies proved the successful formation of the macrophotoinitiator having a core connected to two PCL chains and two benzoin photofunctional groups (PI). Finally, a novel A2B2-type miktoarm star copolymer was synthesized via photoinduced free radical-promoted cationic polymerization of cyclohexene oxide (CHO) monomer using (PCL)2-(PI)2 as photoinitiator. The obtained star copolymer consists of two PCL arms as A blocks and two PCHO arms as B blocks, (PCL)2-(PCHO)2, and was characterized by 1H NMR, FT-IR, and GPC measurements. The thermal behaviors of all the intermediate and final polymers were studied by thermogravimetric and differential thermal analysis (TG/DTA).

Nano-structured polymeric microparticles produced via cationic aerosol photopolymerization

Abstract Microparticles with non-full structures are interesting in many applications. In their production, however, issues related to purification are common. To overcome these issues, in this study a continuous polymerization process was developed in order to obtain powdered, nano-structured microparticles using neither surfactants nor a liquid medium. More specifically, a photo-induced cationic polymerization in aerosol was applied. A monomer solution was sprayed and irradiated with UV-light. During the reactor passage, both polymerization and phase separation occurred inside the single droplet. By adjusting the solvents amounts and ratios, different structures could be realized. Nano-structured particles with tunable pore shapes and dimensions were obtained. Capsule-like structures were obtained with the addition of a co-solvent able to get involved in the polymerization. An active ingredient was encapsulated within the particles. Results showed that the addition of the active ingredient did not affect the synthesis; furthermore, the particles structure had an impact on the release kinetics.

Tandem Photoinduced Cationic Polymerization and CuAAC for Macromolecular Synthesis

A novel synthetic strategy involving sequential photoinduced cationic and copper-catalyzed azide–alkyne cycloaddition (CuAAC) click processes for the synthesis of complex macromolecular structures such as side-chain functional polymers, graft copolymers, and organogels is described. In the approach, first a set of copolymers possessing side-chain alkyne or halide functionalities, namely, poly(cyclohexene oxide-co-glycidyl propargyl ether) (P(CHO-co-GPE)), poly(cyclohexene oxide-co-epichlorohydrin) (P(CHO-co-ECH)), and poly(tetrahydrofuran-co-epichlorohydrin) (P(THF-co-ECH)), were synthesized by photoinitiated free-radical-promoted cationic copolymerization of the corresponding monomers using phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) and diphenyl iodonium hexafluorophosphate (Ph2I+PF6–) as free radical photoinitiator and oxidant, respectively. While P(CHO-co-GPE) readily contained clickable alkyne side-chains, the halide groups of P(THF-co-ECH) were converted to azide groups by conventional a...

Graft Copolymers with Complex Polyether Structures: Poly(ethylene oxide)‐graft‐Poly(isobutyl vinyl ether) by Combination of Living Anionic and Photoinduced Cationic Graft Polymerization

A novel polymerization mechanism transformation strategy, involving anionic ring‐opening polymerization and photoinduced cationic polymerization, is successfully applied for the synthesis of poly(ethylene oxide)‐graft‐poly(isobutyl vinyl ether) (PEO‐g‐PIBVE). First, poly(ethylene oxide‐co‐ethoxyl vinyl glycidyl ether) [P(EO‐co‐EVGE)] is synthesized by living anionic polymerization. The vinyl moieties of the functional PEO‐based polymer are converted to the hydrogen iodide adduct by photolysis of diphenyliodonium iodide, monitored using NMR spectroscopy. A modified mode of Lewis acid‐catalyzed living cationic polymerization is performed as a “grafting from” method to generate PIBVE segments grafted onto the PEO main chain. Both the intermediates and the final graft copolymers are characterized by gel‐permeation chromato­graphy (GPC) and 1H NMR analysis. image

ChemInform Abstract: Pentavalent Organobismuth Reagents in Organic Synthesis: Alkylation, Alcohol Oxidation and Cationic Photopolymerization

AbstractReview: 102 refs.

Visible light polymerization of epoxy monomers using an iodonium salt with camphorquinone/ethyl-4-dimethyl aminobenzoate

A visible light initiator system for the photoinduced cationic polymerization of epoxy monomers is reported. The system consists of camphorquinone (CQ) in combination with ethyl-4-dimethyl aminobenzoate (EDMAB) and a diaryliodonium salt (Ph2ISbF6.) The three-component system efficiently photoinitiates the polymerization of monomers containing an epoxycyclohexane group, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate (UVR) and 1,3-bis(3,4-epoxycyclohexyl-2-ethyl),1,1,3,3-tetramethyldisiloxane (SIB), under irradiation with blue light (λ = 467 nm). Very rapid photopolymerization resulted from irradiation of SIB containing Ph2ISbF6 in combination with CQ and better results were obtained in the presence of EDMAB. On the other hand, no polymerization was detected after irradiation of UVR photoactivated with Ph2ISbF6 and CQ. However, this monomer polymerized readily and to high conversion when EDMAB was present. Moreover, almost complete conversion of UVR occurs in the absence of external heating. The polymer resulting from UVR displayed higher values of compressive and flexural properties than the polymer prepared from SIB. This is explained in terms of a higher density of crosslinking points in UVR which is accompanied by a lower content of non-reacted monomer; this has a plasticizing effect on the hardened material. © 2013 Society of Chemical Industry

Cyclohexene oxide mid‐chain functional macromonomer of poly(ε‐caprolactone): Synthesis, characterization, and photoinitiated cationic homo‐ and copolymerization

AbstractIn this study, a novel well‐defined epoxy mid‐chain functional macromonomer of poly(ε‐caprolactone) (PCL) has been synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) and epoxidation on workup with 3‐chloroperoxybenzoic acid. The ROP of ε‐CL monomer in bulk at 110°C, by means of a dihydroxy functional initiator namely, 3‐cyclohexene‐1,1‐dimethanol in conjunction with stannous‐2‐ethylhexanoate, (Sn(Oct)2), yielded a well‐defined PCL with a cyclohexene mid‐chain group. The epoxidation of the cyclohexene (CH) mid‐chain group of PCL was performed using 3‐chloroperoxybenzoic acid. GPC, IR, and 1H‐NMR analyses revealed that a low‐polydispersity macromonomer of PCL with the desired cyclohexene oxide (CHO) functionality at the mid‐chain was obtained. The photoinduced cationic polymerizations of this macromonomer yielded comb‐shaped and graft copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Well‐Defined Cyclohexene Oxide Mid‐Chain Functional Polystyrene Macromonomer: Synthesis, Characterization and Photoinitiated Cationic Homo‐ and Copolymerization

AbstractIn this article, we present the results of a study of the preparation of a cyclohexene oxide (CHO) mid‐chain functional macromonomer via ATRP of styrene (St) and epoxidation on work‐up with 3‐chloroperoxybenzoic acid. The ATRP initiator, BrCHBr, was synthesized by the condensation of 3‐cyclohexene‐1,1‐dimethanol with 2‐bromopropanoyl bromide. The ATRP of St with BrCHBr and Cu(I)/bpy yielded well‐defined polystyrene with a cyclohexene mid‐chain group (PStCHPSt). Epoxidation of the PStCHPSt was performed using 3‐chloroperoxybenzoic acid. GPC, IR and 1H NMR analyses revealed that a low polydispersity macromonomer of polystyrene with CHO functionality at the mid‐chain (PStCHOPSt) was obtained. The photoinduced cationic polymerization of PStCHOPSt yielded comb‐shaped and graft copolymers. magnified image

Synthesis and characterization of cyclohexene oxide functional polystyrene macromonomers by ATRP and their use in photoinitiated cationic polymerization

In this study, a novel well-defined macromonomer of epoxy end-functionalized polystyrene was synthesized by atom transfer radical polymerization (ATRP). The compound 3-cyclohexenylmethyl-2-bromopropanoate was synthesized by the condensation of 3-cyclohexene-1-methanol with 2-bromopropanoyl bromide. Subsequently, the epoxidation of the obtained 3-cyclohexenylmethyl-2-bromopropanoate using 3-chloroperoxybenzoic acid results in a new epoxy functional ATRP initiator. The ATRP of styrene (St) in bulk at 110 °C, by means of this initiator in conjunction with the cuprous complex Cu(I)Br/bipyridine, yields a well-defined macromonomer of polystyrene with an epoxy end group. GPC, IR, and 1H NMR analyses revealed that a low-polydispersity polystyrene with the desired functionality at the end of the chain was obtained. The photoinduced cationic polymerization of this macromonomer yielded graft and block copolymers.

Macromol. Chem. Phys. 7/2009

Cover: The cover image presents the design of a phosphorescent Ir(III) complex equipped with an oxetane unit. Admixed to crosslinkable matrix moieties the emitter can be copolymerized by a photoinduced cationic ring opening polymerization forming an insoluble network. Applied as emissive layer, fully solution processed multi‐layer OLEDs can be obtained. Further details can be found in the article by C. Ulbricht, N. Rehmann, E. Holder, D. Hertel, K. Meerholz,* U. S. Schubert* on page 531.

Synthesis and cationic photopolymerization of electroactive monomers containing functional groups

AbstractThe synthesis and cationic photopolymerization of different cationically polymerizable monomers containing electroactive groups are reviewed with 98 references. The preparation of various compounds containing electron‐donor or electron‐acceptor moieties and photopolymerizable functional groups is described. After a short discussion of basic principles of cationic polymerization, photoinduced cationic polymerizations of various cationically polymerizable monomers containing both electron‐donor or electron‐acceptor chromophores and the functional groups such as epoxy, vinyl, thiiranyl, oxetanyl and others are reviewed. Copyright © 2005 John Wiley & Sons, Ltd.