Synthesis of a novel hexaarylbiimidazole with ether groups and characterization of its photoinitiation properties for acrylate derivatives

A novel photoinitiator 2,2′‐bis‐(2‐chlorophenyl)‐4,4′,5,5′‐tetra‐[3‐(2‐hydroxylmethyl‐2‐triethylene glycol monoethylene ether‐ethane‐1‐oxy)‐phenyl]‐1,2′‐biimidazole (BCTE‐HABI) was synthesized from 3,3′‐dimethoxy benzoin. Ultraviolet spectra, fluorescence spectra, ESR, photodilatometer, and photo‐DSC measurements indicate that its photoinitiating activity for acrylate derivatives is better than 2,2′‐bis‐(2‐chlorophenyl)‐4,4′,5,5′‐tetraphenyl‐1,2′‐biimidazole (o‐Cl‐HABI), which is one of the most widely studied and used derivatives of HABI. POLYM. ENG. SCI., 46:474–479, 2006. © 2006 Society of Plastics Engineers.     

Photopolymerization of methyl methacrylate initiated by thioxanthone derivatives: photoinitiation mechanism

The photopolymerization of methyl methacrylate initiated by substituted thioxanthones in the presence of an amine has been investigated. The polymerization rates in acetonitrile were measured at several amine concentrations. The dependence of the polymerization rates with the amine concentration and the photoinitiation efficiency at a given amine concentration are highly dependent on the ketone structure. The rate constants for the quenching of thioxanthones excited states by the monomer and the amine were measured by fluorescence and laser flash photolysis, under the polymerization conditions. These data show that the reactivity of the ketone is also highly dependent on the ketone structure. The values of the quenching rate constants show that the initiation efficiency is controlled by the competition between the quenching of the excited states by the monomer and also the amine. From the latter a mechanism is proposed to simulate the dependence of the polymerization rates with amine concentration.     

Photoinitiation properties of heterocyclic hexaarylbiimidazoles with high UV‐vis absorbance

Four heterocyclic hexaarylbiimidazoles, BFuTM‐HABI, BThTM‐HABI, BCTFu‐HABI, and BCTTh‐HABI, were synthesized to improve the UV‐vis absorption properties of hexaarylbiimidazoles. UV‐vis spectra, fluorescence spectra, ESR measurements, photo‐dilatometer experiments, and photo‐DSC measurements indicate that BCTFu‐HABI and BCTTh‐HABI exhibit better UV‐vis absorption abilities and photoinitiation activities for acrylate derivatives with different functionalities than BFuTM‐HABI and BThTM‐HABI, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Photopolymerization of poly(melamine-co-formaldehyde) acrylate for dental restorative resins

This paper describes the investigation of photoinitiated polymerization of poly(melamine-co -formaldehyde) acrylate (PMFA) by camphorquinone (CQ) and amines (AMH) by visible light (λ>400 nm). It was shown that as the concentration of CQ and/or AMH increases, the rate of polymerization reaches a maximum and then decreases. The double bond conversion of PMFA was 20–35%, whereas monomer conversion was 90–96%, depending on the polymerization conditions. Addition of inorganic filler up to 70 wt% did not significantly influence the polymerization kinetics. The final hardness of the photocured samples (with 70 wt% filler) was about half that found in a commercial dental restorative composite. The shrinkage of a composite with 70 wt% filler was 2.12%. Dental formulations based on photocuring of PFMA can be considered for clinical applications, after biological and toxicological evaluation. © 1999 Society of Chemical Industry     

Photopolymerization kinetics of cycloaliphatic epoxide–acrylate hybrid monomer

An epoxide–acrylate hybrid monomer was synthesized by the controlled reaction of a cycloaliphatic epoxide and acrylic acid. The photopolymerization kinetics was investigated using a real‐time infrared spectroscopy technique. The influences of photoinitiator concentration, free radical initiator and polymerization atmosphere on the polymerization were studied. The hybrid monomer showed unique photopolymerization kinetics in the photopolymerization process and the final conversions of epoxy groups and acrylate double bonds were improved synchronously. Dynamic mechanical analysis results demonstrated that the hybrid monomer cured film formed a more uniform polymer network than the blend of epoxy acrylate and epoxide. Copyright © 2007 Society of Chemical Industry     

自引发纯丙烯酸酯的合成及光聚合性质研究

合成了一种全新的自引发纯丙烯酸酯,利用实时红外光谱技术研究了自引发感光高分子的光聚合过程,比较了不同引发剂浓度下的聚合速率和转化率;结果表明,引入到高分子侧链的自由基引发剂仍具有较高的引发活性,双键基团也具有很好的光聚合反应活性。     

邻羟基环己基丙烯酸酯光聚合动力学研究

采用实时红外光谱技术(RTIR)研究了邻羟基环己基丙烯酸酯(HCA)光聚合反应动力学,探讨了光照强度、光引发剂种类和浓度对其光聚合动力学的影响,并与脂肪族羟基丙烯酸酯单体丙烯酸羟乙酯(HEA)进行了对比。结果表明,最终双键转化率和相对反应速率随光强增大而增加;光引发剂浓度对最终双键转化率和反应速率的影响随引发剂不同呈现不同规律;与HEA相比,HCA具有更高的反应活性,但最终双键转化率较低。     

Photopolymerization of clay/polyurethane nanocomposites induced by intercalated initiator

An intercalated initiator was synthesized and used for preparation of clay/polyurethane nanocomposites by UV irradiation. Organoclays containing initiator groups were prepared by cationic exchange process which acted as both suitable intercalant and photoinitiator. These modified clays were then dispersed in the mixture of urethane acrylate and hexanediol diacrylate in different loading, then situ photopolymerized. Intercalated and exfoliated nanocomposite structure were evidenced by both X‐ray diffraction spectroscopy and Transmission Electron Microscope. Thermal properties and morphologies of the resultant nanocomposites were also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

UV‐initiated free radical and cationic photopolymerizations of acrylate/epoxide and acrylate/vinyl ether hybrid systems with and without photosensitizer

Various properties of UV‐initiated acrylate/epoxide and acrylate/vinyl ether hybrid photopolymerizations with and without photosensitizer in the presence of free radical and cationic‐type photoinitiators have been determined by dynamic mechanical thermal analysis (DMTA), calorimetric analysis (photodifferential scanning calorimetry, photo‐DSC; and differential scanning calorimetry), and scanning electron microscopy. DMTA experiments revealed that the UV curing of hybrid systems may produce interpenetrating polymer networks. Photo‐DSC analyses indicated that the acrylates polymerized faster than the epoxide and vinyl ether in the hybrid systems; the addition of a photosensitizer, isopropylthioxanthone (ITX), increased the polymerization rate of the epoxide and vinyl ether in the hybrid systems. SEM analysis confirmed that the free radical system seemed to be significantly affected by oxygen inhibition, while the cationic and hybrid systems were not nearly inhibited by oxygen; the presence of photosensitization produced by the addition of ITX enhanced the surface curing of the hybrid systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1473–1483, 2004     

二苯甲酮/一缩二乙二醇光引发丙烯酸丁酯聚合机理

以二苯甲酮（BP）与一缩二乙二醇（DEG）为光引发剂引发丙烯酸丁酯（BA）聚合,利用核磁共振波谱¹H NMR、¹³C NMR和液相色谱-串联质谱（Q-TOF）对产品结构进行分析。¹³C NMR结果表明,聚合物链上存在叔碳及季碳原子。Q-TOF分析结果表明,聚合物主要由DEG自由基引发,聚合度主要为6、7的链转移终止的低聚物构成,此外,链自由基可以经歧化及偶合终止。快速链转移反应及叔碳、季碳原子的存在表明聚合物的形成过程可能经历了自由基在DEG分子链上“游走”的机理。自由基在DEG链上的转移及链增长的相互竞争,导致形成多取代的聚合产物。聚合反应存在严重的氧阻聚效应,链自由基与氧气快速反应形成过氧化自由基,经终止反应及分解反应形成多1～3个氧原子的低聚物。     

氧化还原引发丙烯酸酯乳液共聚物的合成研究

本文以丙烯酸丁酯－苯乙烯－丙烯酸－丙烯酸羟乙酯为聚合体系，以过硫酸铵／亚硫酸氢钠为氧化还原引发剂。考察了不同氧化剂／还原剂用量、不同反应温度、不同乳化剂用量对单体转化率、特性上度、乳液稳定性的影响，并与过硫酸铵单组分引发进行了比较，用红外光谱（IR）和差热分析（DSC）对共聚物进行了表征。结果表明：采用氧化还原引发剂可以使聚合反应低温快速进行，过量的还原剂起阻聚或缓聚的作用，采用复合乳化剂体系可提高聚合反应速度和乳液的稳定性，合成的共聚物为无规共聚物。     

Photopolymerization of hydroxypropyl acrylate and tetraethylene glycol dimethacrylate initiated by uranyl ion

Uranyl nitrate, acetate, sulfate, and dibutyl phosphate were used in solution for the photoinitiation of homopolymerization and copolymerization of hydroxypropyl acrylate and tetraethylene glycol dimethacrylate. Solvents used included water, water-ethylene glycol mixtures, and dimethylformamide. Polymer yields in excess of 90% can readily be obtained by exposing solutions containing 0.014M UO₂²⁺ to light from a tungsten bulb for 1 hr. The rigidity of the polymers varied directly, the affinity for water in-versely, with the concentration of tetraethylene glycol dimethacrylate in the monomer mixture. Poly(hydroxypropy1 acrylate) contained 52% water and poly(tetraethy1ene glycol dimethacrylate) 34% water, a t equilibrium.     

Photopolymerization of butyl acrylate microemulsions 1. Post-polymerization

The oil-in-water-type microemulsion polymerization of butyl acrylate initiated by UV light was investigated. The polymerization showed two nonstationary rate intervals with a short rise to a maximum. The rate of polymerization was found to be proportional to the 0·7th power of the incident light intensity. The number of radicals per particle was found to be much below 0·5. The initiating radicals are supposed to be formed by the decomposition of the excited (SDS/BA)^* intermediates (micelles). Desorbed radicals were found to increase the number of new particles after the cessation of illumination. The number of polymer particles increased during the whole polymerization. The micellar mechanism was proved to apply to the present system. The dependence of the molecular weight, or the relative viscosity of the microemulsion versus conversion is described by a curve with a maximum.     

Imparting antifouling properties of silicone hydrogels by grafting poly(ethylene glycol) methyl ether acrylate initiated by UV light

Both hydrophilic and antifouling surfaces were prepared on silicone hydrogels with poly(ethylene glycol) methyl ether acrylate (PEGMA) grafted by UV-induced radical polymerization. The PEGMA-grafted silicone hydrogels were characterized by graft yield and static water contact angle measurements. According to the results, the graft yield reached a maximum at 8 min of UV exposure time and 20 wt% PEGMA concentration. The modified silicone hydrogels possessed hydrophilic surfaces with the lowest water contact angle of 36°. The oxygen permeability and transparency of the PEGMA-grafted silicone hydrogels were as high as the unmodified silicone hydrogel. The mechanical property of silicone hydrogels was maintained at about 95% of the tensile strength and elastic modulus after the PEGMA grafting. The in vitro single protein adsorption on the PEGMA-grafted silicone hydrogels decreased by 70–80% compared to the unmodified silicone hydrogel. The PEGMA-grafted silicone hydrogel is expected to be a novel biomaterial, which possesses excellent surface hydrophilicity, antifouling property, oxygen permeability, and mechanical property. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Photopolymerization of 1‐adamantyl acrylate pohotoinitiated by free radical photoinitiators

1‐Adamantyl acrylate was synthesized by reacting of 1‐adamantanol with acryloyl chloride in the presence of tertiary amine. The structure of monomer was characterized by FTIR and ¹H NMR spectroscopy. The influence of photoinitiator and monomer types on the photopolymerization kinetics of this monomer was investigated by real‐time infrared spectroscopy (RTIR). In the UV curing system, the introduction of 1‐adamantyl acrylate could significantly reduce the polymerization shrinkage. Thermogravimetric analysis of 1‐adamantyl acrylate indicated that 1‐adamantyl acrylate polymer has higher thermal stability than that of general commercial products. The results indicated that the synthesized monomer has good curing performance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and photopolymerization of acrylic acrylate copolymers

Acrylate‐functionalized copolymers were synthesized by the modification of poly(butyl acrylate‐co‐glycidyl methacrylate) (BA/GMA) and poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate). ¹³C‐NMR analyses showed that no glycidyl methacrylate block longer than three monomer units was formed in the BA/GMA copolymer if the glycidyl methacrylate concentration was kept below 20 mol %. We chemically modified the copolymers by reacting the epoxy group with acrylic acid to yield polymers with various glass‐transition temperatures and functionalities. We studied the crosslinking reactions of these copolymers by differential scanning calorimetry to point out the effect of chain functionality on double‐bond reactivity. Films formed from acrylic acrylate copolymer precursors were finally cured under ultraviolet radiation. Network heterogeneities such as pendant chains and highly crosslinked microgel‐like regions greatly influenced the network structure and, therefore, its viscoelastic properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 753–763, 2002     

Different effects of tri(acryloyloxyethyl) phosphate on the thermal degradation of photopolymerized epoxy acrylate and polyurethane acrylate films

Tri(acryloyloxyethyl) phosphate (TAEP) was blended in different ratios with epoxy acrylate EB600 and polyurethane acrylate EB270 to obtain a series of UV curable flame retardant resins. The thermal degradation mechanisms of their cured films in air were studied by thermogravimetric analysis, in situ Fourier‐transform infrared spectroscopy, and direct pyrolysis/mass spectrometry measurements. The results showed that the phosphate group in TAEP first degraded to form poly(phosphoric acid) before the degradation of EB600. Then, the formed poly(phosphoric acid) effectively promoted the conversion of EB600 to form char, which prevented the sample from further burning. However, urethane group in EB270 degraded simultaneously with phosphate group in TAEP, leading to not effectively increase the conversion of EB270 to char during the thermal degradation. It was thus found that the addition of TAEP more effectively improved the thermal stability, flame retardance, and the char yield during combustion of EB600 than those of EB270. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3130–3137, 2006     

Mechanism of the polymerization of n-butyl acrylate initiated by N,N-diethyldithiocarbamate derivatives. Part 2. Investigation of the reaction mechanism

The polymerization of n-butyl acrylate (BuAc) initiated with a model compound (butyl-2-(N,N-diethyldithiocarbamyl)propionate, RTC) has been investigated. The living character of this polymerization has been assessed and compared with those of styrene and methyl methacrylate. The small variation of M_n with yield is explained by the faster propagation than for styrene and methyl methacrylate, which leads to slow initiation and extensive transfer to the initiator. Predominant reversible termination (or deactivation) of the growing chains by the dithiocarbamyl radicals gives, however, polymers of functionality near to unity, which are photoinitiated at the same rate as RTC and reinitiate the polymerization of BuAc with a linear growth of the M_n up to 40% yield. This is better than was obtained with methyl methacrylate. Side reactions also take place leading to a decrease of functionality, to the formation of tetraethylthiuram disulphide and of carbon disulphide. Possible mechanisms are proposed for the secondary reactions. © 1998 SCI.     

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate (BA) without added initiator has been studied. The experimental results show that high conversion of BA can be reached in a short time by employing an ultrasonic irradiation technique with a high purge rate of N₂. The viscosity average molecular weight of poly(n‐butyl acrylate) (PBA) obtained reaches 5.24 × 10⁶ g mol^?1. The ultrasonically initiated emulsion polymerization is dynamic and complicated, with polymerization of monomer and degradation of polymer occurring simultaneously. An increase in ultrasound intensity leads to an increase in polymerization rate in the range of cavitation threshold and cavitation peak values. Lower monomer concentration favours enhancement of the polymerization rate. ¹H NMR, ¹³C NMR and FTIR spectroscopies reveal that there are some branches and slight crosslinking, and also carboxyl groups in PBA. Ultrasonically initiated emulsion polymerization offers a new route for the preparation of nanosized latex particles; the particle size of PBA prepared is around 50–200 nm as measured by transmission electron microscopy. © 2001 Society of Chemical Industry     

Curing kinetics of UV‐initiated cationic photopolymerization of divinyl ether photosensitized by thioxanthone

Photodifferential scanning calorimetry was used to investigate the photocuring kinetics of UV‐initiated cationic photopolymerizations of 1,4‐cyclohexane dimethanol divinyl ether (CHVE) monomer with and without a photosensitizer, 2,4‐diethylthioxanthone (DETX), in the presence of a diaryliodonium‐salt photoinitiator. Two kinetics parameters, the rate constant (k) and the order of the initiation reaction (m), were determined for the CHVE system with different amounts of added DETX photosensitizer (0–1 wt %) and at different isothermal temperatures (25–55°C) using an autocatalytic kinetics model. The photosensitized CHVE system exhibited much higher k and m values than did the nonphotosensitized system, which was attributable to the effects of photosensitization. Furthermore, the values of k and m for both CHVE systems increased significantly with increasing isothermal temperature because of a thermal contribution toward increasing the mobility of active species. The addition of DETX lowered the activation energy for the UV‐curable vinyl ether system. The collision factor for the system with DETX was higher than that obtained for the system without DETX, indicating that the reactivity of the former was greater than that of the latter because of the photosensitization effect. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1345–1351, 2005