Highly efficient,polymerizable, sulfur‐containing photoinitiator comprising a structure of planar N‐phenylmaleimide and benzophenone for photopolymerization

In a continuation of research on chemically bonded photoinitiators comprising a structure of planar N‐phenylmaleimide (NPMI) and benzophenone (BP), a novel, highly efficient, polymerizable, sulfur‐containing photoinitiator, 4‐[(4‐maleimido)thiophenyl]benzophenone (MTPBP), was synthesized by the introduction of an NPMI group into BP. Another chemically bonded photoinitiator, 4‐[(4‐maleimido)phenoxy]benzophenone (MPBP), was selected to evaluate its photoefficiency. The results showed that MTPBP possessed a greatly redshifted UV maximal absorption and a very weak fluorescence emission. Electron spin resonance spectra indicated that the C? S bond in its molecule underwent photolysis reactions to generate radicals to initiate the polymerization. Three representative types of different functionality monomers—methyl methacrylate, 1,6‐hexanediol diacrylate, and trimethylolpropane triacrylate—were chosen to be initiated through dilatometry and differential scanning photocalorimetry with unsaturated tertiary amine N,N‐dimethylaminoethyl methacrylate as the coinitiator. The results showed surprisingly high efficiency of MTPBP due to the mutual influence between NPMI and BP as in their physical mixtures and photolysis reactions at the C? S bond. Both MPBP and MTPBP behaved with similar regularity toward different monomers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3738–3750, 2006     

Synthesis of PS‐b‐PPOA‐b‐PS triblock copolymer via sequential free radical polymerization and ATRP

A novel ABA triblock copolymer comprising double‐bond‐containing poly(phenoxyallene) (PPOA) and polystyrene (PS) segments was synthesized by sequential conventional free radical polymerization and atom transfer radical polymerization (ATRP) via the site transformation strategy. A new bifunctional initiator containing azo and Br‐containing ATRP initiating groups was prepared using 2‐bromopropionyl chloride, hydroquinone, and 4,4′‐azobis(4‐cyanopentanoic acid) as starting materials. Conventional free radical homopolymerization of phenoxyallene with cumulated double bond was performed in toluene to provide a polyallene‐based macroinitiator bearing ATRP initiating groups at both ends, which is stable under UV irradiation and free radical circumstances. PS‐b‐PPOA‐b‐PS triblock copolymer was then obtained by bulk ATRP of styrene initiated by PPOA‐based macroinitiator. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1366–1372     

Photoinduced and thermally induced cationic polymerizations using S,S‐dialkyl‐S‐(3,5‐dimethylhydroxyphenyl)sulfonium salts

A study of the photoinitiated and thermally initiated cationic polymerizations of several monomer systems with S,S‐dialkyl‐S‐(3,5‐dimethylhydroxyphenyl)sulfonium salt (HPS) photoinitiators bearing different lengths of alkyl chains on the positively charged sulfur atom has been conducted. HPS photoinitiators are capable of photoinitiating the cationic polymerization of a wide variety of epoxy and vinyl ether monomers directly on irradiation with short‐wavelength UV light. Aryl ketone photosensitizers are effective in extending the spectral response of these photoinitiators into the long‐wavelength UV region. Kinetic studies with real‐time infrared spectroscopy show that HPS photoinitiators exhibit good efficiency in the polymerization of epoxide and vinyl ether monomers. Comparative studies also demonstrate that S,S‐dimethyl‐S‐(3,5‐dimethyl‐2‐hydroxyphenyl)sulfonium salts are more active photoinitiators than their isomeric S,S‐dimethyl‐S‐(3,5‐dimethyl‐4‐hydroxyphenyl)sulfonium salt counterparts. Both types of HPS photoinitiators display reversible photolysis as a result of facile termination reactions that take place between the growing chains ends with the photogenerated sulfur ylides. Preliminary studies have shown that HPS photoinitiators can also be employed as thermal initiators for the cationic ring‐opening polymerization of epoxides at moderate temperatures. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2570–2587, 2003     

Synthesis of α‐maleimide‐ω‐dienyl heterotelechelic poly(methyl methacrylate) and its cyclization by the intramolecular Diels–Alder reaction

The synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α‐maleimide‐ω‐dienyl end‐groups and its subsequent intramolecular cyclization are described. The anionic polymerization of methyl methacrylate was carried out with 3‐tert‐butyldimethylsilyloxypropyl‐1‐lithium and 5‐bromo‐1,3‐pentadiene as the initiator and terminator, respectively, to synthesize α‐hydroxy‐ω‐dienyl‐PMMA. The introduction of the maleimide group to the α chain end by the reaction of the sodium salt of the polymer with N‐(3‐chloromethylphenyl)‐maleimide or N‐(3‐bromomethylphenyl)‐maleimide was not successful because of the nucleophilic addition of alkoxide to the carbon carbon double bond of the maleimide group. When 4,4′‐bismaleimidediphenylether was allowed to react with the alkoxide, the aimed α‐maleimide‐ω‐dienyl‐PMMA was obtained in a good yield. Ring closure by the intramolecular Diels–Alder reaction was carried out by the heating of the dilute polymer solution in tetrahydrofuran. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 237–246, 2000     

Regiospecific design strategies for 3‐arylpolythiophenes with pendant stable radical groups

Carbon—carbon bond‐forming polymerization of 2‐bromo‐3‐(3′,5′‐di‐t‐butyl‐4′‐methoxyphenyl)‐thiophene yields poly[3‐(3′,5′‐di‐t‐butyl‐4′‐methoxyphenyl)‐2,5‐thienylene] with regiospecific connectivity and a degree of polymerization of about six. Lewis‐acid‐moderated‐cleavage of the methoxy groups on the pendant phenyl group yield the corresponding polyphenolic polymer, which is oxidized under solution conditions to yield the title polyradical. Poly[3‐(3′,5′‐di‐t‐butyl‐4′‐oxyphenyl)‐2,5‐thienylene] exhibits a strong, persistent electron spin resonance spectrum and a UV–visible spectrum consistent with formation of the pendant phenoxyl spin‐bearing units. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 779–788, 1999     

Polymerizable benzophenone derivatives for labeling vinyl acetate‐butylacrylate latex particles

We describe the synthesis and characterization of three new polymerizable benzophenone derivatives [2‐acryloxy‐5‐methyl benzophenone ( 8 ), 4′‐dimethylamino‐2‐acryloxy‐5‐methyl benzophenone ( 9 ), and 4′‐dimethylamino‐2‐(β‐acryloxyethyl)oxy‐5‐methyl benzophenone ( 10 )]. We show that these monomers can successfully be incorporated into vinyl acetate (VAc) copolymer latex particles. These particles were prepared by semicontinuous emulsion polymerization and mini‐emulsion polymerization of VAc with butylacrylate (BA) for VAc/BA = 4/1 by weight. The two monomers 9 and 10 bearing the 4′‐dimethylamino group satisfy the important spectroscopic criteria required of a dye to serve as an acceptor chromophore for nonradiative energy transfer from phenanthrene (Phe) as the donor. Their UV absorption spectra suggest significant overlap with the emission spectrum of Phe, which can be incorporated into P(VAc‐co‐BA) latex through copolymerization with 9‐acryloxymethyl Phe ( 2 ). In addition, these chromophores provide a window in their absorption spectra for excitation of the Phe chromophore at 300 nm. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3001–3011, 2002     

N‐alkoxypyridinium salts as coinitiators in radical polymerization: Synthesis and Photochemical Properties

A few N‐alkoxypyridinium salts are developed as photoinitiators for efficient polymerization reactions. They are characterized by absorption properties below 300 nm, and generate alkoxy radicals on UV‐Vis light exposure. The squarylium dye was used as a blue‐light photosensitizer. Polymerization results are correlated with the photochemistry of N‐alkoxypyridinium salts. The quenching of the excited singlet state of squarylium dye by pyridinium salt and the formation of the semioxidized species of squaraine suggests an electron transfer from an excited dye to a coinitiator, and that the resulting oxygen‐centered radical initiates the polymerization process. The chemical mechanism was investigated by steady state photolysis and nanosecond laser flash photolysis experiments. Photoinitiating activity of new photoinitiators for initiation of polymerization of trimethylolpropane triacrylate in the UV‐blue light region was compared with photoinitiating ability of selected commercially available initiators. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2840–2850     

2,2,2‐trifluoroacetophenone‐based D‐π‐A type photoinitiators for radical and cationic photopolymerizations under near‐UV and visible LEDs

Two D‐π‐A‐type 2,2,2‐trifluoroacetophenone derivatives, namely, 4′‐(4‐( N,N‐diphenyl)amino‐phenyl)‐phenyl‐2,2,2‐trifluoroacetophenone (PI‐Ben) and 4′‐(4‐(7‐(N,N‐diphenylamino)‐9,9‐dimethyl‐9H‐fluoren‐2‐yl)‐phenyl‐2,2,2‐trifluoroacetophenone (PI‐Flu), are developed as high‐performance photoinitiators combined with an amine or an iodonium salt for both the free‐radical polymerization of acrylates and the cationic polymerization of epoxides and vinyl ether upon exposure to near‐UV and visible light‐emitting diodes (LEDs; e.g., 365, 385, 405, and 450 nm). The photochemical mechanisms are investigated by UV‐Vis spectra, molecular‐orbital calculations, fluorescence, cyclic voltammetry, photolysis, and electron‐spin‐resonance spin‐trapping techniques. Compared with 2,2,2‐trifluoroacetophenone, both photoinitiators exhibit larger redshift of the absorption spectra and higher molar‐extinction coefficients. PI‐Ben and PI‐Flu themselves can produce free radicals to initiate the polymerization of acrylate without any added hydrogen donor. These novel D‐π‐A type trifluoroacetophenone‐based photoinitiating systems exhibit good efficiencies (acrylate conversion = 48%–66%; epoxide conversion = 85%–95%; LEDs at 365–450 nm exposure) even in low‐concentration initiators (0.5%, w/w) and very low curing light intensities (1–2 mW cm^?2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1945–1954     

Photopolymerization of maleimide perfluoropolyalkylethers without a photoinitiator

Perfluoropolyalkylethers derived from hexafluoropropylene oxide were functionalized with maleimide groups. Irradiated by UV‐light, the new maleimide macromonomers demonstrated very fast polymerization kinetics with a curing time as fast as 8 s. The effect on photopolymerization of different features such as the molecular weight of the fluorinated chain and the chain length of the hydrogenated spacer were studied, as well as the influence of the type of photoinitiator and the presence of air. Thermal and surface properties of the UV‐cured polymers were examined and were typical to fluoropolymers in view of water–oil repellent coatings. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 699–707     

Photoinitiating monomers based on di‐ and triacryloylated hydroxylamine derivatives

The purpose of our study was to design a new class of acrylate‐based monomers with an UV‐cleavable heteroatom bond, offering the possibility to initiate radical polymerization upon irradiation with UV‐light. A method to derive the double bond conversion from the ATR‐IR spectra of the monomers and the cured polymers was employed, that enabled us to calculate the theoretical polymerization heats of the new monomers. Their photopolymerization properties were determined by Photo Differential Scanning Calorimetry. Surprisingly, some of these new compounds exhibited high photoinitiation activity, comparable to well‐established Type II photoinitiator systems like benzophenone/triethanolamine. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 392–403, 2009     

Novel polymeric,thio‐containing photoinitiator comprising in‐chain benzophenone and an amine coinitiator for photopolymerization

A novel thio‐containing diamine with a benzophenone structure, 4‐amino‐4′‐[4‐aminothiophenyl]benzophenone (AATBP), was synthesized. Two kinds of polymeric photoinitiators, PUPIA and PUPI, were synthesized through the polycondensation of toluene‐2,4‐diisocyanate with AATBP and/or N‐methyldiethanolamine (MDEA). A macroamine, PUPA, was also synthesized for comparison. Fourier transform infrared, ¹H NMR, and gel permeation chromatography analyses confirmed the structures of all the polymers. The ultraviolet–visible spectra of PUPIA, PUPI, and AATBP were similar, and all exhibited the maximal absorption above 325 nm. The photopolymerization of two monomers with different functionalities, poly(propylene glycol)diacrylate and trimethylolpropane triacrylate initiated by PUPIA, PUPI/MDEA, PUPI/PUPA, AATBP/MDEA, and AATBP/PUPA, was studied through differential scanning photocalorimetry. The results showed that both PUPIA and PUPI/MDEA had high photoefficiency, and their low‐molecular‐weight counterparts could hardly initiate the photopolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 576–587, 2007     

Preparation and properties of novel benzoxazine and polybenzoxazine with maleimide groups

A benzoxazine compound with a maleimide group, 3‐phenyl‐3,4‐dihydro‐2H‐6‐(N‐maleimido)‐1,3‐benzoxazine (HPM‐Ba), was prepared from N‐(4‐hydroxyphenyl)maleimide, formaldehyde, and aniline. The chemical structure of HBM‐Ba was identified by FT‐IR, ¹H‐NMR, and elemental analysis. HPM‐Ba showed a melting point of 52–55 °C and good solubility in common organic solvents. HPM‐Ba showed a two‐stage process of thermal polymerization. The first stage arose from the polymerization of maleimide groups, and the second one was the ring‐opening reaction of benzoxazine groups. Fusible polymaleimides with a Tg of around 100 °C could be obtained by thermally polymerizing HPM‐Ba at 130 °C. Further polymerizing the polymaleimides at 240 °C resulted in a completely cured resin showing a Tg at 204 °C. Good thermal stability and self‐extinguishing behavior was observed with the cured polybenzoxazine resins. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5954–5963, 2004     

Cuso4‐amine redox‐initiated radical polymerization of methyl methacrylate mediated by a CuCl2 complex: Homogeneous reverse ATRP

Kinetic results of CuSO₄/2,2'‐bipyridine(bPy)‐amine redox initiated radical polymerization of methyl methacrylate (MMA) at 70 to 90 °C in dimethylsulfoxide suggest that such initiation is characteristic of a slow rate and a low initiator efficiency, but tertiary amines exhibit a relatively higher rate. UV‐Vis spectroscopy confirms the alpha‐amino functionality of PMMA chains. CuCl₂/bPy successfully mediates the redox‐initiated radical polymerization of MMA with aliphatic tertiary amines in a fashion of slow‐initiated reverse atom transfer radical polymerization (ATRP), i.e. both the initiator efficiency of aliphatic tertiary amines and the average molecular weight of PMMA increase gradually, while the molecular weight distribution remains narrow but become broader with the conversions. As the PMMA chains contain alpha amino and omega C‐Cl moieties, UV‐induced benzophenone‐initiated radical polymerization and Cu^ICl/bPy‐catalyzed ATRP initiated from PMMA lead to block copolymers from terminal functionalities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2562‐2578     

1,5‐Diphenyl‐1,4‐diyn‐3‐one: A highly efficient photoinitiator

In a continuation of our research on new chromophores for photoinitiators (PIs), we investigated a triple‐bond‐containing benzophenone derivative. 1,5‐Diphenyl‐1,4‐pentadiyn‐3‐one ( 2 ) was prepared from phenylacetylene and ethyl formate by a one‐pot reaction. Differential scanning photocalorimetry experiments in lauryl acrylate of 2 showed surprisingly high activity for the double‐bond conversion and rate of polymerization at the lowest PI concentrations and even without any coinitiator. By the application of monomers with abstractable hydrogens, significant improvement in the photoreactivity was observed. Ultraviolet–visible spectroscopy revealed strong absorption up to 350 nm. Steady‐state photolysis experiments proved that the photochemistry of this compound was faster than that of benzophenone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 101–111, 2005     

A Diels‐Alder/retro Diels‐Alder strategy to synthesize polymers bearing maleimide side chains

Polymers containing thiol‐reactive maleimide groups on their side chains have been synthesized by utilization of a novel methacrylate monomer containing a masked maleimide. Diels‐Alder reaction between furan and maleimide was adapted for the protection of the reactive maleimide double bond prior to polymerization. AIBN initiated free radical polymerization was utilized for synthesis of copolymers containing masked maleimide groups. No unmasking of the maleimide group was evident under the polymerization conditions. The maleimide groups in the side chain of the polymers were unmasked into their reactive form by utilization of retro Diels‐Alder reaction. This cycloreversion was monitored by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and ¹H and ¹³C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4545–4551, 2007     

Bis‐substituted thiophene‐containing oxime sulfonates photoacid generators for cationic polymerization under UV–visible LED irradiation

Three novel types of thiophene‐containing oxime sulfonates with a big π‐conjugated system were reported as non‐ionic photoacid generators. The irradiation of the newly synthesized photoacid generators using near UV–visible light‐emitting diodes (LEDs) (365–475 nm) results in the cleavage of two weak N O bonds in single molecules, which lead to the generation of different sulfonic acids in good quantum and chemical yields. The mechanism for the N O bond cleavage for acid generation was supported by the UV–visible spectra and real‐time ¹H NMR spectra. They are developed as high‐performance photoinitiators without any additives for the cationic polymerization of epoxide and vinyl ether upon exposure to near‐UV and visible LEDs (365–475 nm) at low concentration. In the field of photopolymerization, especially visible light polymerization, it has great potential for application. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 776–782     

Novel PU‐type polymeric photoinitiator comprising side‐chain benzophenone and coinitiator amine for photopolymerization of PU acrylate

A novel diamine 3,5‐diamino‐4′‐phenoxylbenzophenone (DAPBP) was synthesized from the reaction of 3,5‐diamino‐4′‐chlorobenzophenone (DACBP) and phenol. Then through the polycondensation of DAPBP, toluene‐2,4‐diisocyanate (TDI), and N‐methyldiethanolamine (MDEA), we obtained a PU‐type polymeric photoinitiator containing side‐chain benzophenone (BP) and tertiary amine in the same macromolecule (PUSOA). Another polymeric photoinitiator without coinitiator amine in polymer chain (PUSO) was also synthesized for comparison. FT‐IR, ¹H NMR, and GPC analyses confirmed the structures of monomer and polymeric photoinitiators. The UV–Vis spectra of PUSOA, PUSO, and DAPBP are similar, and all exhibit the maximal absorption near 290 nm. ESR spectra indicate that PUSOA can generate active species most efficiently. The photopolymerization of PU acrylate, initiated by PUSOA, PUSO/MDEA, DAPBP/MDEA, and BP/MDEA, was studied by differential scanning photocalorimetry (photo‐DSC). The results show that the in‐chain coinitiator amine can significantly improve the photoefficiency of the polymeric photoinitiator and the PUSOA is more efficient for the polymerization of PU acrylate than its low‐molecular‐weight counterpart. Copyright © 2008 John Wiley & Sons, Ltd.     

One‐component,double‐chromophoric thioxanthone photoinitiators for free radical polymerization

Two one‐component, double‐chromophoric thioxanthone photoinitiators, namely TX‐EDA and TX‐DETA were synthesized by the reaction of thioxanthone aldehyde (TX‐A) with ethylenediamine (EDA) and diethylenetriamine (DETA), respectively via a facile Schiff base reaction. Both photoinitiators were characterized by spectral analysis and photobleaching studies. DFT calculations are employed to reveal the contribution of the different orbitals to the excitation of the initiators. The double‐chromophoric nature of the initiators gives rise to an increased absorption in the near UV region when compared with the pristine TX‐A. Photoinitiated polymerization of various vinyl monomers with TX‐EDA and TX‐DETA has been investigated in the presence and absence of a co‐initiator and compared for formulations consisting of precursor TX‐A. In addition, real‐time FTIR spectroscopic studies were performed in methyl methacrylate polymerization with both initiators. The higher efficiency observed with TX‐DETA may be attributed to the additional hydrogen donating sites adjacent to nitrogen atoms. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3475–3482     

Synthesis of photoactive single‐chain folded polymeric nanoparticles via combination of radical polymerization techniques and Menschutkin click chemistry

This contribution reports that synthesis of polystyrene based photoactive polymeric nanoparticles by radical copolymerization and Menschutkin Chemistry methodology. In the first step, poly(styrene‐co‐chloromethyl styrene) was achieved by thermally initiated radical copolymerizations and subsequently copolymers were reacted to commercially available Type II photoiniator (Michler's ketone) in dilute condition in order to achieve intramolecular crosslinked polymeric nanoparticles. After the characterization studies, polymeric nanoparticles were used for free radical photopolymerization of methacrylic formulations to determine the initiation efficiency. Upon UV irradiation, resulting polymeric nanoparticle lost its globular structure by releasing benzophenone part and transformed into linear copolymer analogue. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1998–2003     

Efficient photopolymerization of thick pigmented systems using upconversion nanoparticles‐assisted photochemistry

Photopolymerization of thick pigmented systems still remains challenging due to the light screening effect of the pigments. Here, we present a facile method based on upconversion nanoparticles (UCNPs)‐assisted photochemistry to achieve efficient photopolymerization and improved curing depth of pigmented systems. Under a 980‐nm laser irradiation, UCNPs are able to convert NIR light into UV and visible light to activate photoinitiators for the initiation of polymerization. Influencing factors on photopolymerization were systematically investigated. With optimal parameters, 25.5 mm of photopolymerization depth combined with 70% of maximal double bond conversion was obtained. The peak temperature of 120.4 °C during UCNPs‐assisted photopolymerization is comparable with or lower than that of some reported frontal photopolymerization applied to prepare functional composite polymeric materials. Both indentation hardness and reduced modulus of the photocured materials using UCNPs as internal lamps were higher than those of the reference cured under traditional blue LED light. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 994–1002