Effect of N‐phenylmaleimide on a novel chemically bonded polymerizable photoinitiator comprising the structure of planar N‐phenylmaleimide and benzophenone for photopolymerization

A novel chemically bonded polymerizable photoinitiator 4‐[(4‐maleimido)phenoxy]benzophenone (MPBP) comprising the structure of planar N‐phenylmaleimide (NPMI) and benzophenone (BP), compared with the physical mixtures of NPMI/BP or NPMI/4‐hydroxybenzophenone, was investigated to disclose the mutual influence between NPMI and BP. A BP derivative, 4‐phenoxylbenzophenone, was selected as the model compound. Electron spin resonance spectra of such photoredox systems indicated MPBP and BP possess the same initiation mechanism. The large red‐shifted π–π* absorption of MPBP should be because of the phenoxyl group in MPBP but not the maleimide group. The photopolymerization of methyl methacrylate (MMA) and 1,6‐hexanediol diacrylate (HDDA) initiated by those systems, using the unsaturated tertiary amine N,N‐dimethylaminoethyl methacrylate (DMAEMA) as the coinitiator (H donor), was studied through dilatometry and photo‐differential scanning calorimetry. The results showed that MPBP was more efficient for the photopolymerization of MMA and HDDA than its physical mixture counterpart. The high efficiency of MPBP may be mainly because of the interaction between NPMI and BP group but not the phenoxyl group alone. A certain amount of NPMI can accelerate the photopolymerization when added to the formulations, but too much NPMI will eventually decrease the photoefficiency. Copyright © 2006 Society of Chemical Industry     

Novel polymerizable N‐aromatic maleimides as free radical initiators for photopolymerization

Four kinds of polymerizable N‐aromatic maleimides (MIs)—4‐[(4‐maleimido)phenoxy]benzophenone (MPBP), 4,4′‐bis[(4‐maleimido)phenoxy]benzophenone (BMPBP), 4‐maleimidobenzophenone (MBP), and 4,4′‐bismaleimidobenzophenone (BMBP)—were synthesized as free radical photoinitiators, by introducing directly N‐phenylmaleimide groups or maleimide groups into the molecule of benzophenone (BP). Compared with BP, their UV‐visible spectra have a significantly red‐shifted maximum absorption. The maximum absorption of MIs containing bifunctional maleimide groups is slightly larger than the corresponding monofunctional ones. Choosing an unsaturated tertiary amine N,N‐dimethylaminoethyl methacrylate (DMAEMA) as coinitiator, the photopolymerization of 1,6‐hexanediol diacrylate (HDDA), initiated by these four MIs, was studied through photo‐DSC. The results show that all the MIs are dramatically more efficient than BP. Among them, MPBP is the most efficient, in which the polymerization rate is almost three times as high as that of the BP system. Photoinitiators containing bifunctional maleimide groups, though having higher final conversion, are less efficient than the corresponding monofunctional ones. These polymerizable photoredox systems significantly reduced the migration of the active species, leading to their higher efficiency. Copyright © 2006 Society of Chemical Industry     

Novel sulfur—containing benzophenone derivative as radical photoinitiator for photopolymerization

A novel, highly efficient, polymerizable sulfur‐containing photoinitiator for free radical polymerization, benzophenone thio‐acetic acid (BP‐S‐CH₂‐COOH) was synthesized, characterized, and compared to photoinitiator parameters of the benzophenone (BP) and benzophenone/(phenylthio)acetic acid couple. The photoinitiator possesses a greatly redshifted UV maximal absorption in comparison to BP. Laser flash photolysis studies suggest that photoinitiator radicals are generated by photocleavage of C? S bond. Photopolymerization of 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate (TMPTA) demonstrated that one‐component system BP? S? CH₂? COOH is more efficient for polymerization than two‐component system. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel chemical-bonded polymerizable sulfur-containing photoinitiators comprising the structure of planar N-phenylmaleimide and benzophenone for photopolymerization

As a continuation of the research on chemical-bonded photoinitiators comprising the structure of planar N-phenylmaleimide (NPMI) and benzophenone (BP), three novel polymerizable sulfur-containing photoinitiator MTPBP, CMTPBP and BMTPBP were synthesized by introducing NPMI group into benzophenone (BP). BP was selected as the reference to evaluate their photoefficiency. These novel photoinitiators possess greatly red-shifted UV maximal absorption, and their fluorescence emission varies. Three representative types of different functionality monomers, methyl methacrylate (MMA), 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), initiated by the three novel photoinitiators were studied through dilatometer and photo-DSC using unsaturated tertiary amine N,N-dimethylaminoethyl methacrylate (DMAEMA) as the coinitiator. The results show surprising high efficiency of these chemical-bonded photoinitiators towards different monomers in contrast to BP, and they can initiate photopolymerization without the coinitiator because of the photolysis at C-S bond. The results also verify that the higher viscosity of monomers and the larger molecular size of the photoinitiators may restrict the bimolecular H-abstraction reaction.     

Novel benzoxazine resins as photoinitiator comprising benzophenone and coinitiator amine for photopolymerization

A novel kind of benzoxazine precursors made of 4‐dihydroxybenzophenone (DHBP), formaldehyde and N, N′‐diethylethylenediamine was developed. The striking feature of this class of precursors is that it can be acted as an effective photo initiator for polymerization of acrylate monomers. In addition, this kind of precursors could be directly dispersed in water and its aqueous solution exhibited very sharp response to temperature, with a well‐defined cloud point. The structure of this precursor has been confirmed by Proton Nuclear Magnetic Resonance Spectroscopy (¹H‐NMR) and Fourier Transform Infrared spectroscopy (FTIR) and its curing behaviors are investigated by Differential Scanning Calorimetry (DSC). The photopolymerization of acylate monomers, initiated by this precursor, was studied through photo‐DSC. The results show that this precursor is dramatically more efficient than benzophenone (BP), in which the polymerization rate is almost four times as high as that of the BP system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A polymerizable photosensitizer and its photopolymerization kinetics

A previously reported polymerizable benzophenone photosensitizer, 2‐methacryloxyethyl 4‐benzoylbenzoate (MEBB), was synthesized and characterized. The photopolymerization kinetics of methyl α‐hydroxymethylacrylate (MHMA) and 1,6‐hexanediol diacrylate (HDDA) initiated with MEBB or benzophenone (BP) in the presence or absence of amine co‐initiators were determined by photo‐differential scanning calorimetry. The results indicate that benzophenone with a p‐carbonyl substitutent is more efficient in photoinitiation when compared to the non‐substituted benzophenone analogue. The final monomer conversions in the presence of amine co‐initiators are slightly higher than without them. Copyright © 2005 Society of Chemical Industry     

Synthesis and photopolymerization characterization of a novel difunctional photoinitiator

A novel difunctional photoinitiator HBP‐TDI‐HBP based on 4‐hydroxybenzophenone (HBP) and toluene‐2,4‐diisocyanate (TDI) was synthesized and characterized by ¹H NMR and UV–Vis absorption spectroscopy. The kinetics of photopolymerization was studied by real‐time infrared spectroscopy. It showed that HBP‐TDI‐HBP was a more effective photoinitiator than benzophenone. When this photointiator and amine were used to efficiently initiate polymerization of acrylates and methacrylates, both rate of polymerization and final conversion increased with increase of HBP‐TDI‐HBP concentration, light intensity, and amine concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Efficiency of 4,4′‐bis(N,N‐diethylamino) benzophenone for the polymerization of dimethacrylate resins in thick sections

The efficiency of 4,4′‐bis(N,N‐diethylamino)benzophenone (DEABP) for the polymerization of dimethacrylate monomers in thick sections ( 1 – 2 mm) was studied. DEABP (λ_max = 365 nm) represents a complete initiating system as it contains both ketone and amine functional groups. During irradiation, DEABP photobleaches at a fast rate causing deeper penetration of light through the underlying layers, but the photoinitiation efficiency (rate of polymerization per photon absorption rate) is relatively poor. As a result, irradiation of methacrylate monomers at 365 nm results in a slow average polymerization rate and a reduced monomer conversion for thick sections due to the light attenuation caused by the high absorptivity of DEABP and photolysis products. These results highlight the inherent interlinking of light attenuation and photobleaching rate in polymerization of thick sections. Copyright © 2011 Society of Chemical Industry     

Unexpected visible‐light‐induced free radical photopolymerization at low light intensity and high viscosity using a titanocene photoinitiator

Most visible‐light photoinitiators are based on electron transfer processes and are comprised of two or more components. These initiators can lose effectiveness in viscous systems because the underlying reactions are diffusion controlled. In this contribution, the visible‐light photoinitiator bis(cyclopentadienyl) bis[2,6‐difluoro‐3‐(1‐pyrryl)phenyl]titanium is characterized for polymerization of viscous systems and low light intensities. This compound absorbs visible light at wavelengths up to 550 nm, and does not rely on diffusion‐controlled electron transfer reactions because it undergoes unimolecular decomposition. In contrast to trends observed for other photoinitiators, the effectiveness of the compound is found to increase markedly with the addition of protonic acids and with increasing system viscosity. For a given concentration of initiator and acid, a remarkably low optimal light intensity for effective polymerization is observed. The origins of these surprising results are discussed in terms of the mechanism of decomposition of the photoinitiator. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Low‐temperature photopolymerization and post‐cure characteristics of acrylates

Near‐infrared spectroscopy was used to investigate the post‐cure characteristics of acrylates polymerized from ? 75 °C up to room temperature. The results obtained showed that the double bond conversion increased with increasing initiator concentration. Post‐cure was much more striking for samples cured at lower temperatures. The chemical structure of monomer and photoinitiator had a great effect on the post‐cure process. The greater the functionality, the lower the final double bond conversion and the more distinct the post‐cure effect. Copyright © 2006 Society of Chemical Industry Society of Chemical Industry     

Preparation and performance of thermosensitive poly(N‐isopropylacrylamide) hydrogels by frontal photopolymerization

In this study, frontal photopolymerization was applied to the fabrication of thermosensitive poly(N‐isopropylacrylamide) (PNIPAm) hydrogels. The influence of experimental conditions and reactant components on the feature of the polymerization front was investigated. The morphology of the samples indicated the successful preparation of PNIPAm hydrogels. The mechanical properties and thermal stability of the obtained hydrogels are discussed. The results indicated that the performance of the hydrogels is related to their microstructure and the type of crosslinkers. The swelling behavior and drug delivery ability were determined under different temperature conditions. The hydrogels exhibit a classical thermoresponsive behavior, which was also demonstrated by the DSC results. Therefore, frontal photopolymerization can be an alternative method for the preparation of PNIPAm hydrogels under mild conditions. © 2019 Society of Chemical Industry     

Graft copolymerization of methylmethacrylate with N‐substituted maleimide‐styrene copolymer by ATRP

Atom transfer radical polymerization (ATRP) was employed to prepare graft copolymers having poly(MBr)‐alt‐poly(St) copolymer as backbone and poly(methyl methacrylate) (PMMA) as branches to obtain heat resistant graft copolymers. The macroinitiator was prepared by copolymerization of bromine functionalized maleimide (MBr) with styrene (St). The polymerization of MMA was initiated by poly(MBr)‐alt‐poly(St) carrying bromine groups as macroinitiator in the presence of copper bromide (CuBr) and bipyridine (bpy) at 110°C. Both macroinitiator and graft copolymers were characterized by ¹H NMR, GPC, DSC, and TGA. The ATRP graft copolymerization was supported by an increase in the molecular weight (MW) of the graft copolymers as compared to that of the macroinitiator and also by their monomodal MW distribution. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Synthesis and characterization of optically active star‐shaped poly (N‐phenylmaleimide)s with a calixarene core

Two N‐phenylmaleimide derivatives bearing a chiral oxazoline group, N‐[o‐(4‐phenyl‐4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenyl]maleimide [(R)‐PhOPMI] and N‐[o‐(4‐isopropyl‐4,5‐dihydro‐1,3‐oxazol‐2‐yl)phenyl]maleimide [(S)‐PrⁱOPMI], were polymerized using in situ generated calixarene‐based phenates as initiators to yield optically active polymers. The formation of star‐shaped architectures was strongly dependent on both polymerization conditions and calixarene moieties. In the case of polymerization conducted in toluene at 80–100 °C, the arm‐chain numbers achieved their respective maxima for the polymers with these multifunctional initiators. In contrast, the polymers obtained in polymerizations at lower temperature possessed fewer arm chains. The structure and chiroptical properties were investigated on the basis of ¹³C NMR, multiangular laser light scattering, gel permeation chromatography, and circular dichroism for the macromolecules with calixarene cores. Copyright © 2006 Society of Chemical Industry     

A study of the photopolymerization kinetics of methyl methacrylate using novel benzophenone initiators

A series of novel bifunctional photoinitiators with benzophenone moieties were synthesized. Characterization of these molecules was performed using IR, UV, ¹H NMR, ¹³C NMR and mass spectroscopy. Photopolymerization of methyl methacrylate, a model acrylate‐type monomer, was carried out with the bifunctional benzophenone molecules functioning as the photoinitiator and triethylamine as the co‐initiator. The progress of the polymerization was followed by dilatometry. The resulting plots of monomer conversion with time were used to evaluate the initial rates of polymerization. The relative enhancement/lowering of the rates of polymerization, with respect to benzophenone as the model photoinitiator, are interpreted in terms of the structure, and the photophysics of the initiator evaluated by nanosecond laser flash photolysis. © 2001 Society of Chemical Industry     

Modification of bismaleimide with allyl compound and N‐phenylmaleimide

Three different formulas with low‐cost resins, made up of N,N′‐bismaleimidephenylmethane (BMI), O,O′‐diallybisphenol A(BA), and N‐phenylmaleimide (NPMI) were developed. The properties of prepolymers, such as activation energies, enthalpy, and constants of reaction rate, were obtained by a kinetic programmer on DSC. Thermal and mechanical properties of neat resins were also studied. The results showed that the systems had low melting point and low viscosity. All cured resins presented excellent thermal and good mechanical properties. The mechanical properties could be affected by the quantity of NPMI and postcuring process. The water absorption is ≤1.98%; heat deflection temperature (HDT) is ≥250°C after aging for 100 h in distilled water of 90°C. The data indicate that the BMI can be effectively improved by adding BA and NPMI, while its heat resistance and hot/wet mechanical properties can be fairly retained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2518–2522, 2001     

Study on microemulsion polymerization of N‐butyl maleimide

By using sodium dodecyl sulfate (SDS) as an emulsifier, polymerization of N‐butyl maleimide (NBMI) was carried out in ternary oil‐in‐water microemulsion, initiated with potassium persulfate (KPS). The kinetics of microemulsion polymerization were measured by dilatometry. The effects of initiator concentration, polymerization temperature, monomer concentration, and emulsifier concentration on polymerization kinetics were investigated. On this basis, the polymerization kinetics were discussed. The experiment result showed that the microemulsion polymerization kinetics of N‐butyl maleimide were almost consistent with the prediction of the Smith‐Ewart theory in conventional emulsion polymerization, except that the emulsifier showed a special effect on polymerization. At the same time, the polymer was characterized by IR, ¹H‐NMR, DSC, and TGA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 805–809, 2000     

Long‐Lasting and Rapid‐Responsive Media for Rewritable Information Storage Based on Low‐Cost N‐Substituted Maleimides Oligomers

Controllable synthesis of high‐performance materials with low‐cost is critical for the development of functional devices. Herein, a series of sequence‐controlled low‐dispersity oligomers with acid–base chromotropic capability via simple copolymerization between N‐substituted maleimides (NMI) and methyldiallylamine (MDAA) are synthesized. The structure and molecular weight of the oligomers are characterized. Owing to the presence of strong electrophilic carbonyl oxygen and imine nitrogen, a rapid‐responsive color switching system is achieved. This change is attributed to the acid/base‐triggered isomerization between enolate state and the enol or keto tautomer via intramolecular proton transfer. More importantly, the color of P(MDAA/NMI) is regulated by the variation of the substituent group of the N‐substituted maleimide. A new type of rewritable paper based on the designed N‐substituted maleimide oligomers is fabricated by a simple spin‐coating process, on which images with high resolution can be acid‐printed and base‐erased for over ten cycles. The writing and erasure times can be as short as 10 s and the legible time can be more than 90 days under ambient conditions. The as‐formed rewritable paper with excellent rewriting performances is low‐cost and easy for large‐scale production and may find more advanced potential applications in memory devices, rewritable labels, an sensors.     

Synthesis of novel macrophotoinitiator for the photopolymerization of acrylate

A new kind of macrophotoinitiator (MPI) was synthesized through the copolymerization of acrylic monomers and the polymerizable photoinitiator monomer 2959‐AA. Monomer 2959‐AA was obtained by an esterification reaction between acrylic acid (AA) and the water‐soluble photoinitiator Irgacure 2959 [2‐hydroxy‐4‐(2‐hydroxyethoxy)‐2‐methylpropiophenone]. By adjusting the monomer proportions in the MPIs, two series of MPIs with different 2959‐AA contents and different glass transition temperatures were obtained. The molecular structure of 2959‐AA was characterized by Fourier‐transform infrared spectroscopy, nuclear magnetic spectrometry, and mass spectrometry. Polymerization of 1, 6‐hexanediol diacrylate was initiated using Irgacure 2959 and 2959‐AA, and two series of MPIs to be polymerized were studied with a photo‐DSC test. Results showed that 2959‐AA had higher chemical reactivity than Irgacure 2959 because of the higher solubility of the former. It was evident from the experiments that 2959‐AA content in the MPI progressively increased the polymerization rate and monomer conversion when the glass transition temperatures of MPIs were similar. At the same 2959‐AA content, the polymerization rate slightly slowed down with increased glass transition temperature. However, the radical lifetime and polymerization time were prolonged. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40352.     

1‐(bromoacetyl)pyrene and its arsonium salt as novel photoinitiators for styrene polymerization

The photopolymerization of styrene (Sty) in DMSO induced by pyrene (Py), 1‐Acetylpyrene (AP), 1‐(Bromoacetyl) pyrene (BP), and 1‐Acetylpyrene triphenyl arsonium bromide (APAS) has been investigated. Under all conditions employed, Py was completely ineffective. Incorporation of a chromophoric (? COCH₃) moiety introduces photoinitiating activity into Py. It was observed that introduction of Br into AP markedly accelerated the rate of UV irradiation‐induced polymerization. BP was further modified to its arsonium salt (APAS). The kinetics and mechanism of polymerization using BP and APAS as initiators have been investigated in detail. The polymerization with BP followed nonideal kinetics (R_p ∝ [BP]^0.8 [Sty]^1.1) with respect to initiator concentration whereas ideal kinetics (R_p ∝ [APAS]^0.48 [Sty]^1.1) was observed when APAS was used as initiator. Degradative transfer is thought to be mainly responsible for this unusual kinetic behavior for BP–Sty system. The kinetic data proved that BP was more effective and faster initiator than APAS. In both the cases, the mechanism of polymerization was free radical as evident by inhibiting the effect of hydroquinone and ESR studies. IR and NMR spectra showed the atactic nature of polystyrene. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1793–1798, 2006     

Thermal analysis of solution copolymers of styrene with N‐phenylmaleimide

Free‐radical–initiated copolymerization of N‐phenylmaleimide (NPMI) with styrene (St) at 110°C in a toluene solution initiated by AIBN was carried out by a semibatch method. The compositions of the copolymers were determined by using an elemental analyzer. The glass‐transition temperatures of the copolymers were measured by differential scanning calorimetry. All the semibatch copolymers show a single glass‐transition temperature that increases markedly with increasing NPMI content in the copolymers. The thermal stabilities of the copolymers were studied by using a programmed thermogravimetric analysis technique. Copolymers show a considerable increase in thermal stability and different degradation reaction mechanisms with increasing content of NPMI. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 417–422, 2002