Free Radical Promoted Cationic Polymerization Research Articles

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.

Copper-Based (Photo)redox Initiating Systems as Highly Efficient Systems for Interpenetrating Polymer Network Preparation

Simultaneous redox free radical polymerization (FRP) and redox cationic polymerization (CP) are combined for the synthesis of methacrylate/diepoxide interpenetrating polymer networks (IPN). At first, the Cu(acac)2/phosphine/iodonium salt operates according to the principles of free radical promoted cationic polymerization (FRPCP). A photoactivation of the reaction for that system was necessary to enhance the mild methacrylate and diepoxide conversions. Second and at least, two complementary copper catalytic cycles are used simultaneously: the recently developed Cu(II)/reducing agent/peroxide FRP system combined with the older Cu(II)/reducing agent/iodonium salt redox CP system. For this latter hybrid system, outstanding efficiency was observed with more than 90% of epoxy functions conversion for the cationic difunctional monomers and 78% conversion for the vinylic functions conversion for difunctional monomers. The radical and cation generations are discussed in order to fill the interrogations raised by ...

Meta-Terphenyl Derivative/Iodonium Salt/9H-Carbazole-9-ethanol Photoinitiating Systems for Free Radical Promoted Cationic Polymerization upon Visible Lights

In the present paper, new photoinitiators based on the meta-terphenyl scaffold in combination with an iodonium salt and 9H-carbazole-9-ethanol (CARET) are proposed for the free radical promoted cationic polymerization of epoxides upon visible light exposure using light emitting diodes at 405, 455, and 470 nm. Remarkably, a new high performance additive (i.e., CARET) is proposed here for cationic polymerizations. CARET shows some important advantages compared to other reported additives such as N-vinylcarbazole or benzyl alcohol used as references. Excellent polymerization initiating abilities are found and a full picture of the involved chemical mechanisms is provided.

Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources.

Photoinitiators (PI) or photoinitiating systems (PIS) usable in light induced cationic polymerization (CP) and free radical promoted cationic polymerization (FRPCP) reactions (more specifically for cationic ring opening polymerization (ROP)) together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.

Polyethylene-g-poly(cyclohexene oxide) by Mechanistic Transformation from ROMP to Visible Light-Induced Free Radical Promoted Cationic Polymerization

A novel polymerization mechanism transformation strategy, combining ring-opening metathesis polymerization (ROMP) and visible light induced cationic polymerization, is successfully applied for the synthesis of polyethylene-graft-poly(cyclohexene oxide) (PE-g-PCHO). First, cis-cyclooctene (COE) was polymerized via ROMP in the presence of a chain transfer agent and quantitatively hydrobrominated to give bromo functional polyethylene (PE-Br). Subsequent irradiation of PE-Br in the visible range using dimanganese decacarbonyl (Mn2(CO)10) and diphenyl iodonium hexafluorophosphate (Ph2I+PF6–) as radical generator and oxidant, respectively, initiated cationic polymerization of cyclohexene oxide (CHO) resulting in the formation of PE-g-PCHO. The effect of irradiation time and Mn2(CO)10 concentration on the grafting density and efficiency was evaluated. Both the precursor polymers and the corresponding graft copolymers were characterized by 1H NMR and Fourier transform infrared (FT-IR) spectroscopy, gel-permeation chromatography (GPC), and differential scanning calorimetric (DSC) analyses.

N-Vinylcarbazole: An Additive for Free Radical Promoted Cationic Polymerization upon Visible Light.

N-Vinylcarbazole is proposed as an additive for epoxy ring-opening polymerization ROP upon visible light exposure. This compound can convert hardly oxidizable radicals to carbon centered radicals by an addition process onto the N-vinylcarbazole double bond. The generated radicals can be further easily oxidized by an iodonium salt thereby leading to efficient initiating cations for the ROP of epoxides. Different visible light photoinitiating systems have been investigated: Type I photoinitiators (derived from phosphine oxides) and dye/iodonium salt couples. The underlying chemical mechanisms are investigated by electron spin resonance (ESR) experiments.

Synthesis of Block Copolymers by Combination of Atom Transfer Radical Polymerization and Visible Light‐Induced Free Radical Promoted Cationic Polymerization

A new synthetic approach for the preparation of block copolymers by mechanistic transformation from atom transfer radical polymerization (ATRP) to visible light-induced free radical promoted cationic polymerization is described. A series of halide end-functionalized polystyrenes with different molecular weights synthesized by ATRP were utilized as macro-coinitiators in dimanganese decacarbonyl [Mn(2) (CO)(10) ] mediated free radical promoted cationic photopolymerization of cyclohexene oxide or isobutyl vinyl ether. Precursor polymers and corresponding block copolymers were characterized by spectral, chromatographic, and thermal analyses.

Branched and Network Polysilanes as Cleavable Macrophotoinitiators

AbstractThe branched polysilane [(PhMeSi)0.8‐co‐(Et3Si(CH2)2Si)0.2]n (PS‐1) as well as the network polysilane [Et3Si(CH2)3Si]n (PS‐2) have been investigated as new polymerization photoinitiating structures. The behavior of PS‐1 was compared with that of [(PhMeSi)]n to demonstrate the enhancement of the photoinitiation for the branched system. As a result of the Si–Si bond cleavage under light and the formation of reactive silyl radicals or silyl cations, these compounds act as efficient photoinitiators (PIs) for free radical photopolymerization (FRP) and free radical promoted cationic polymerization (FRPCP). The polymerization initiating ability of PS‐1 is higher than that of PS‐2 under air. The initiating ability for the ring‐opening polymerization of epoxides is excellent for PS‐1. These polymeric PIs overcome the classical oxygen inhibition in FRP or FRPCP.

A Breakthrough toward Long Wavelength Cationic Photopolymerization: Initiating Systems Based on Violanthrone Derivatives and Silyl Radicals

The silyl radical chemistry is used here for the free radical promoted cationic polymerization (FRPCP) of epoxy monomers ((3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate EPOX and limonene dioxide LDO) and the free radical photopolymerization FRP of an acrylate monomer (trimethylolpropane triacrylate TMPTA). The new three-component photoinitiating systems are based on violanthrone derivatives, diphenyl iodonium salt and a silane. The use of very soft irradiations (household fluorescent and LED bulbs, sunlight and xenon lamp as visible light sources) is described. Excellent polymerization profiles are obtained. Addition of ruthenium tris(bipyridine) still enhances the performance. A sunlight irradiation of 2 min leads to a conversion ∼70% of EPOX. The specific role of the silyl radicals generated in this system is investigated and discussed. Comparative assessments with existing initiating systems are also provided evidencing the very high efficiency of the new proposed approach.

New Opportunities in Free Radical Photopolymerization and Free Radical Promoted Cationic Polymerization Based on the Silyl Radical Chemistry.

New compounds based on the silyl radical chemistry are presented as coinitiators for free radical photopolymerization (FRP) or sources of radicals for free radical promoted cationic photopolymerization (FRPCP). The ability of these structures in the initiation of both FRP and FRPCP processes is investigated. High rates of polymerization and high final conversions are obtained. Laser flash photolysis is used for the analysis of the silyl radical formation.

Radical and cationic photopolymerization: New pyrylium and thiopyrylium salt‐based photoinitiating systems

AbstractNew thiopyrylium and pyrylium salt‐based photoinitiating systems for visible light induced free radical polymerization (FRP) or free radical promoted cationic polymerization (FRPCP) under visible lights are presented. The reaction mechanisms are investigated by laser flash photolysis and the structure/reactivity trend is discussed. The abilities of two different classes of coinitiators are investigated (thiols/disulfides and silanes). In FRP, upon irradiation with a xenon lamp (λ > 390 nm), the (thio)pyrylium salts in combination with thiols or disulfides lead to very high polymerization rates, compared to the reference eosin Y/methyldiethanolamine system. In FRPCP, silanes are found much better coinitiators: a high efficiency of the photopolymerization under air is noted. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7369–7375, 2008

Visible Light Initiated Free Radical Promoted Cationic Polymerization Using Acylgermane Based Photoinitiator in the Presence of Onium Salts

The cationic polymerization of cyclohexene oxide (CHO) was achieved by UV irradiation (λ = 350−420 nm) of methylene chloride solutions containing benzoyltrimethylgermane (BTG) and onium salts, such as diphenyliodonium hexafluorophosphate (Ph2I+PF6−) or N-ethoxy-2-methylpyridinium hexafluorophosphate (EMP+PF6−). A feasible initiation mechanism involves the photogeneration of germyl radicals and benzoyl radicals in the first step. Subsequent oxidation of germyl radicals by onium salts yields germanium ions capable of initiating the polymerization of CHO. In agreement with the proposed mechanism, the polymerization was completely inhibited by a radical scavanger such as 2,2,6,6-tetramethylpiperidinyl-1-oxy, and polymerization efficiency was directly related to the reduction potential of the onium salts, i.e. Ph2I+PF6− (Ered1/2 = −0.2 V) was found to be more efficient than EMP+PF6− (Ered1/2 = −0.7 V). The results were compared to the other photoinitiators generally used in free radical promoted cationic polymerizations. In addition to CHO, vinyl monomers such butyl vinyl ether and N-vinyl carbazole, and a bisepoxide such as 3,4-epoxycyclohexyl-3′,4′-epoxycyclohexene carboxylate, were polymerized in the presence of BTG and iodonium salt with high efficiency.

A Mechanistic and Kinetic Study of the Photoinitiated Cationic Double Ring-Opening Polymerization of 2-Methylene-7-phenyl-1,4,6,9-tetraoxa-spiro[4.4]nonane

Efficient photopolymerization of a potentially expandable monomer is of practical importance for a variety of polymeric applications demanding dimensional stability, particularly if the polymerization process is well controlled based on a detailed investigation of the reaction. In the current study, photoinitiated polymerization kinetics of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane (MPN) either with cationic initiation alone or with combined cationic/free radical initiation was examined using real-time FT-IR. A proposed mechanism based on the simplified propagation steps of the cationic double ring-opening polymerization of MPN was confirmed by both computer modeling and NMR spectroscopic analysis of resulting polymers as well as the experimentally observed apparent activation energy. According to this mechanism, alpha-position attack is the predominant mode for the second ring opening during cationic polymerization of MPN. Further, cationic photopolymerization was performed along with a free radical co-initiator or with exposure to moisture to get an improved understanding of the complex cationic double ring-opening polymerization. As a result, free radical-promoted cationic polymerization helps increase the polymerization rate of MPN while even a trace amount of moisture was found to significantly impact both the reaction kinetics and the polymerization course.

Synthesis of Block Copolymers by Transformation of Free Radical Promoted Cationic Polymerization to Atom Transfer Radical Polymerization

The transformations of free radical promoted cationic polymerization to atom transfer radical poly- merization (ATRP) to form the block copolymers of cyclohexene oxide (CHO) with styrene (St) were performed. In the first step, bromine terminated poly(CHO)s (PCHO-Br) were prepared by free radical promoted cationic polymerization of CHO monomer in the presence of 2-oxo-1,2-diphenylethyl-2-bromopropanoate, shortly bromo benzoin, (B-Br) and an onium salt namely 1-ethoxy-2-methylpyridinium hexafluorophosphate (EMP þ SbF6 � ) as the initiating system. The bromine functionalized polymers thus prepared were used as initiators in ATRP of St, in bulk, in conjunction with CuBr/2,2 0 -bipyridine as catalyst gave well-defined block copolymer of CHO and St. Block copolymer formations were evidenced by 1 H NMR and gel permeation chromatography (GPC) measurements. (DOI 10.1295/polymj.37.700)

A Visible Light Initiating System for Free Radical Promoted Cationic Polymerization

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA Visible Light Initiating System for Free Radical Promoted Cationic PolymerizationYubai Bi and Douglas C. NeckersCite this: Macromolecules 1994, 27, 14, 3683–3693Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/ma00092a001RIGHTS & PERMISSIONSArticle Views1300Altmetric-Citations180LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts