Photocrosslinking of functionalized rubber. II. Photoinitiated cationic polymerization of epoxidized liquid natural rubber

Low molecular weight epoxidized natural rubber has been crosslinked within seconds by UV irradiation in the presence of a triarylsulfonium salt. The photoinitiated cationic ring-opening polymerization was studied quantitatively by infrared spectroscopy and shown to proceed with surprisingly long kinetic chains in such solid medium. The high conversion (60%) needed for complete insolubilization, together with the presence of tetrahydrofuran structures, argue in favor of an intramolecular polymerization process involving neighboring epoxy groups. The photoinitiator concentration has a strong influence on the rate and extent of the reaction, as well as on the depth of cure profile. Because of an efficient dark process, close to 100% conversion was reached upon storage of the irradiated elastomer at ambient, with a concomitant increase of the gel fraction and the polymer hardness. The grafting of pendent acrylate groups onto the polymer chain leads to a three-fold decrease of the initial rate of polymerization of the epoxide. The photocuring of natural rubber bearing both epoxy and acrylate groups generates a dual polymer network which combines the properties of the two moieties. © 1995 John Wiley & Sons, Inc.     

Polymerization kinetics and volume relaxation behavior of photopolymerized multifunctional monomers producing highly crosslinked networks

Multifunctional monomers (trimethylol propane trimethacrylate, trimethylol propane triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol monohydroxy pentaacrylate) were photopolymerized with 2,2-dimethoxy-2-phenylacetophenone as the photoinitiator to produce highly crosslinked networks. The volume shrinkage behavior and the reaction kinetics were studied under various reaction conditions. The volume shrinkage and maximum functional group conversion were dependent on the number of functional groups, type of functional group, and the curing conditions. The maximum functional group conversion was also dependent on the reaction temperature. All the polymerized systems exhibited a strong coupling between the volume relaxation and the reaction kinetics. The kinetic constants were also determined as a function of conversion, and the termination mechanism was found to be reaction diffusion dominated even at low conversions. The importance of these results on the prediction of the reaction behavior for multifunctional monomers producing highly crosslinked polymers is discussed. © 1994 John Wiley & Sons, Inc.     

Photocrosslinking of acrylated natural rubber

Photocrosslinkable elastomers with pendent acrylate groups have been synthesized by ringopening reaction of epoxidized natural rubber with acrylic acid. The kinetics of the acrylation reaction has been studied by infrared spectroscopy and shown to obey a simple first-order law. The acrylated natural rubber undergoes a fast crosslinking-polymerization when it is exposed to UV radiation in the presence of an aryl ketone photoinitiator, with formation of a tridimensional polymer network within a few seconds. The cure kinetics has been studied in real time by monitoring the disappearance of the IR absorption of the grafted acrylate double bond. The rate of polymerization was found to increase linearly with the degree of acrylation of the rubber, reaching values up to 3 mol kg^?1 s^?1. The isoprene double bond, which is inactive in virgin natural rubber, also undergoes polymerization upon UV exposure when epoxy or acrylate groups are present. The UV-cured polymer becomes totally insoluble in the organic solvents and exhibits remarkable mechanical properties, such as hardness, flexibility, and impact resistance. The gel fraction and the hardness were both shown to increase with the degree of acrylation and with the cure extent. © 1993 John Wiley & Sons, Inc.     

Novel photocurable multifunctional acrylate monomers containing perfluorinated aromatic units and their copolymers for photonic applications

We designed and synthesized novel UV‐curable multifunctional acrylate monomers with perfluorinated aromatic units and their copolymers. The UV‐curable multifunctional acrylate monomers with perfluorinated aromatic units were synthesized as follows. Perfluorinated aromatic methylmethane derivatives were prepared through the reaction of pentaerythritol with hexafluorobenzene and decafluorobiphenyl in the presence of sodium hydride. They were sequentially substituted with 2,2,3,3,4,4,5,5‐octafluoro‐6‐(tetrahydropyran‐2‐yloxy)‐hexan‐1‐ol, and this yielded hydroxy‐functional compounds after tetrahydropyran deprotection. Finally, the reaction of the resultant hydroxy compounds with acryloyl chloride generated the perfluorinated multifunctional acrylate monomers in high yields of greater than 85%. The novel photocrosslinked and perfluorinated copolyacrylates, obtained after the UV and thermal curing of these monomers, satisfied the material requirements for photonic devices. Most of these copolymers were thermally stable over 370 °C, and their glass‐transition temperatures were not detected because of their highly crosslinked nature. The refractive indices of the copolymers ranged from 1.410 to 1.441. The refractive indices of the photocrosslinked and perfluorinated copolyacrylates were easily tuned by the variation of the copolymer composition. Some of these copolymers exhibited a birefringence of less than 0.0003. This was much lower than the birefringence of fluorinated polyacrylate‐based materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6375–6383, 2004     

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites

Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks.     

Preparation and characterization of acidified chitosan immobilized in epoxidized natural rubber

Biocomposites comprising chitosan (CTS) trapped in an epoxidized natural rubber (ENR) was prepared by homogenizing CTS in ENR50 (ENR with about 50% epoxy content) latex in the presence of curing agents and acetic acid. Micrographs of CTS-t-ENR reveal no phased-out entity. Infrared spectra of CTS-t-ENR show only vibrational bands belonging to CTS and ENR, affirming that the former was not bonded but immobilized in the matrix of the latter. CTS loading up to 5 phr resulted in the increase in the tensile strength and elongation at break, modulus of the CTS-t-ENR. Thermal stability of CTS-t-ENR is higher than that of CTS but lower than that of ENR. Increase in CTS loading from 2.5 to 20 phr resulted in the decrease in toluene absorbency but increase in water uptake of CTS-t-ENR.     

Silica reinforcement of epoxidized natural rubber by the sol-gel method

The sol-gel technique was employed to prepare silica-reinforced vulcanizates using tetraethylorthosilicate (TEOS) and epoxidized natural rubber (ENR). The rubber was first precured with 3-aminopropyltriethoxysilane (APS) by heat pressing at 180°C for a range of cure time. The resultant rubber sheets or vulcanizates were swelled in TEOS, and subsequently subjected to a sol-gel reaction in butylamine aqueous solution. Hydrolysis and condensation of the TEOS resulted in the formation of silica particles in the rubber network yielding silica-contained vulcanizates. Silica content as high as 28% and TEOS-to-silica conversion of over 60% were observed. When prepared under certain reaction conditions, the sol-gel vulcanizates obtained were more rigid and stronger than a typical sulfur-cured ENR vulcanizate that contained comparable amount of silica. Comparative stress-strain and dynamic mechanical property analysis suggest that chemicals bond are formed between the silica particles and the rubber network in the ENR-APS-sol-gel vulcanizate. Thus, the in situ silica reinforcement of ENR was successfully established.On leave from School of Industrial Technology, University Sains Malaysia, Minden, 11800, Penang, Malaysia.     

Processing characteristics and thermal stabilities of gel and sol of epoxidized natural rubber

The processing performances and aging behaviours of gel and sol separated from epoxidized natural rubber (ENR) using organic solvents were studied by using rubber processing analyzer (RPA), thermogravimetric analysis (TGA) and difference FT-IR method. As the gel with intermolecular ether structure is formed by the ring-opening reactions of a part of epoxy groups during the preparation and storage of ENR, the molar percentage of epoxy groups of gel is lower than that of sol. The gel shows higher elastic moduli to temperature and frequency responses, lower tan δ to frequency and strain response and higher elastic torque to strain response as comparing to those of sol. Therefore, the formation of gel will reduce processing performance of ENR. When the aging behaviours of gel and sol were analyzed by different methods, the aging reactions and their degrees were different because of the differences of aging conditions. Compared to gel, the sol is easy to be crosslinked, leading to a higher Δtan δ from the RPA analysis and it is also easy to be oxidized into small molecules, leading to lower onset temperature and apparent activation energy when being analyzed by TGA. However, the variations of functional groups of gel are more obvious than those of sol when analyzed by difference FT-IR method. As the mechanical properties of ENR will be varied with the variations of molecular structures, the formations of gel during preparation and storage of ENR will reduce the oxidative aging resistance of ENR.     

Isothermal Photo Differential Scanning Calorimetry. Crosslinking polymerization of multifunctional monomers in presence of visible light photoinitiators

The effect of photoinitating (camphorquinone/amines) system concentration and sample thickness on the photopolymerization of triethyleneglycol dimethacrylate/2-hydroxypropyl methacrylate has been investigated. The rate of photopolymerization reaches a maximum and then decreases as the concentration of photoinitiating system increases. This effect has been intepreted as inner filter effect. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gel formation in cationic polymerization of divinyl ethers. I. 1,4-Bis(2-vinyloxyethoxy)benzene

Polymerization of 1,4-bis(2-vinyloxyethoxy)benzene (CH₂C O CH₂ CH₂ O C₆H₄ O CH₂CH₂ O CCH₂; 1 ) was investigated in CH₂Cl₂ at 0°C with the use of a variety of cationic initiators. SnCl₄, SnBr₄, AlEtCl₂, and BF₃OEt₂ (strong Lewis acids) and CF₃SO₃H (a strong protonic acid) yielded crosslinked insoluble polymers immediately after the polymerizations were initiated. The binary initiating systems such as HCl/ZnCl₂ and (C₆H₅O)₂P(O)OH/ZnCl₂ also produced insoluble poly( 1 )s. At the low initial concentration of ZnCl₂, however, the (C₆H₅O)₂P(O)OH/ZnCl₂ system gave the soluble polymers quantitatively, and gelation occurred only when the reaction mixture was stored for a long time after complete consumption of the monomer. The content of the unreacted pendant vinyl ether groups of the soluble polymers decreased with monomer conversion, and almost all the pendant vinyl ether groups were consumed in the soluble polymer obtained at 100% monomer conversion; this may be ascribed to frequent occurrence of intramolecular crosslinking. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 675–683, 1998     

Latex‐state NMR spectroscopy for quantitative analysis of epoxidized deproteinized natural rubber

Method of quantitative analysis through latex‐state ¹³C NMR spectroscopy was established for in situ determination of epoxy group content of epoxidized natural rubber in latex stage. The epoxidized natural rubber latex was prepared by epoxidation of deproteinized natural rubber with freshly prepared peracetic acid in latex stage. The resulting epoxidized deproteinized natural rubber (EDPNR) latex was characterized through latex‐state ¹³C NMR spectroscopy. Chemical shift values of signals of latex‐state ¹³C NMR spectrum for EDPNR were similar to those of solution‐state ¹³C NMR spectrum for EDPNR. Resolution of latex‐state ¹³C NMR spectrum was gradually improved as temperature for the nuclear magnetic resonance (NMR) measurement increased to 70°C. Signal‐to‐noise ratio of latex‐state ¹³C NMR measurement was similar to that of solution‐state ¹³C NMR measurement at temperature above 50°C. The epoxy group content determined through latex‐state NMR spectroscopy was proved to be the same as that determined through solution‐state NMR spectroscopy. Copyright © 2017 John Wiley & Sons, Ltd.     

Novel photocurable monomers: The synthesis of difunctional vinyl ethers with a phosphonate group and difunctional 1‐propenyl ethers with a phosphonate group and their photoinitiated cationic polymerization

Phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were prepared by the regioselective addition reaction of glycidyl vinyl ether (GVE) or 1‐propenyl glycidyl ether with diaryl phosphonates with quaternary onium salts as catalysts. The reaction of GVE with bis(4‐chlorophenyl) phenylphosphonate gave bis[1‐(4‐chlorophenoxy methyl)‐2‐(vinyloxy)ethyl]phenylphosphonate in a 68% yield. The structures of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were confirmed by IR and ¹H NMR spectra and elemental analysis. Photoinitiated cationic polymerizations of the resulting phosphorus‐containing vinyl ether monomers and 1‐propenyl ether monomers were investigated with photoacid generators. The polymerization of vinyl ether groups and 1‐propenyl ether groups of the obtained monomers proceeded very smoothly with a sulfonium‐type cationic photoinitiator, bis[4‐(diphenylsulfonio)phenyl]sulfide‐bis(hexafluorophosphate), upon UV irradiation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3105–3115, 2005     

Gel formation in cationic polymerization of divinyl ethers. II. 2,2-Bis{4-[(2-vinyloxy)ethoxy]phenyl}propane

Cationic polymerization of 2,2-bis{4-[(2-vinyloxy)ethoxy]phenyl}propane [CH₂CH O CH₂CH₂O C₆H₄ C(CH₃)₂ C₆H₄ OCH₂CH₂ O CHCH₂; 2], a divinyl ether with oxyethylene units adjacent to the polymerizable vinyl ether groups and a bulky central spacer, was investigated in CH₂Cl₂ at 0°C with the diphenyl phosphate [(C₆H₅O)₂P(O)OH]/zinc chloride (ZnCl₂) initiating system. The polymerization proceeded quantitatively and gave soluble polymers up to 85% monomer conversion. In the same fashion as the polymerization of 1,4-bis[2-vinyloxy(ethoxy)]benzene (CH₂CH O CH₂CH₂O C₆H₄ OCH₂CH₂ O CHCH₂; 1) that we already studied, the content of the unreacted pendant vinyl ether groups of the produced soluble polymers decreased with monomer conversion, and almost all the pendant vinyl ether groups were consumed in the soluble products prior to gelation. Alternatively, endo-type double bonds were gradually formed in the polymer main chains by chain transfer reactions and other side reactions as the polymerization proceeded. The polymerization behavior of isobutyl vinyl ether (3), a monofunctional vinyl ether, under the same conditions, showed that the endo-type olefins in the polymer backbones are of no polymerization ability with the growing active species involved in the present polymerization systems. These results indicate that the intermolecular crosslinking reactions occurred primarily by the pendant vinyl ether groups, and the final stage of crosslinking process leading to gelation also may occur by the small amount of the residual pendant vinyl ether groups (supposedly less than 2%). The formation of the soluble polymers that almost lack the unreacted pendant vinyl ether groups is most likely due to the frequent occurrence of intramolecular crosslinking reactions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1931–1941, 1999     

Evaluation of air permeability characteristics on the hybridization of carbon black with graphene nanoplatelets in bromobutyl rubber/epoxidized natural rubber composites for inner‐liner applications

Nanotechnology has been explored recently as a means of enhancing the properties of conventional elastomers for engineering applications. In the current study, the effect of nanofillers on air impermeability properties of Brominated isobutylene‐isoprene rubber (BIIR)/Epoxidized natural rubber (ENR) blend has analyzed for automotive applications. The ENR chosen is ENR 25 and ENR 50 (25 and 50% epoxidation) and prepared the blends in a ratio of 75:25 (BIIR:ENR), and from both blend based composites, a part of carbon black replaced with graphene nanoplatelets (GNP). The physical and thermal properties were compared for both binary blend nanocomposites to study the level of exfoliation and reinforcement behavior of GNP. Morphology studies were employed to reveal the level of interaction between GNP and carbon black in both blends. The influence of epoxidation in the formation of nanostructures in both blends have been evaluated, and the effect of nanostructures on air permeability properties was studied. The air impermeability of BIIR‐ENR 50 nanocomposites were improved with increasing platelet concentration, a 30% improvement in air permeability is obtained for BIIR‐ENR 50 composites over BIIR ‐ENR 25.     

Effect of naturally occurring crosslinking junctions on green strength of natural rubber

The effect of the naturally occurring crosslinking junctions on green strength of natural rubber, isolated from Hevea brasiliensis, was investigated by using rubber extracted from Parthenium argentatum Gray (Guayule) as a model. Guayule rubber and natural rubber were characterized through nuclear magnetic resonance spectroscopy and size exclusion chromatography. The non‐rubber components of Guayule rubber and natural rubber were characterized by Kjeldahl method and Fourier transform infrared spectroscopy. It was found that Guayule rubber contains a much higher amount of fatty acids and their esters while it contains no proteins. The gel content, determined by swelling method, was related to a number of naturally occurring crosslinking junctions of Guayule rubber and natural rubber. The outstanding green strength of natural rubber was attributed to the effect of naturally occurring crosslinking junctions, when stress–strain curve and tensile properties of unvulcanized Guayule rubber were compared with those of unvulcanized natural rubber. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and thiol–ene photopolymerization of allyl‐ether functionalized dendrimers

Well‐defined, allyl‐ether functional, first‐generation dendrimers have been synthesized. The convergent growth approach was utilized, using the anhydride of the allyl‐ether terminated building block. Three different core moieties were used: trimethylolpropane, trisphenol, and ditrimethylolpropane. The coupling reactions proceeded in good yields and all compounds were characterized by NMR, MALDI‐TOF, and SEC. The allyl‐terminated dendrimers were crosslinked by thiol–ene chemistry, using a multifunctional thiol, TriThiol, to give clear and smooth films. The photopolymerization was conducted in the presence of a photoinitiator, Irgacure 651, and no traces of either allyl‐ether groups or thiols were observed by FT‐Raman after cure. All crosslinked films were characterized with respect to mechanical (DMA) and thermal (DSC) properties. It was found that homogeneous networks were formed and that the core functionality and structure had little effect on the network properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1339–1348, 2008     

光引发阳离子聚合反应的研究：Ⅲ.硫翁盐BDS引发环氧化合物光聚合的DSC…

用改装的国产ＣＤＲ－１型ＤＳＣ仪研究了苯基缩水甘油醚（ＰＧＥ）和环氧树脂（Ｅ－５１）以双－［４－（二苯硫翁基）苯基］硫－二－六氟化磷引发的光聚合。研究了引发剂浓度，光强，温度等因素对聚合反应的影响。对于ＰＧＥ，聚合速率与引发剂浓度的０．９０次方，与光强的０．７８次方成比例。对于Ｅ－５１，聚合速率与引发剂浓度的０．８７次方式成比例，而与光强的关系则比较复杂。温度分别超过７０℃（对ＰＧＥ）或８０℃（对     

Gel formation in cationic polymerization of divinyl ethers. III. Effect of oligooxyethylene chain versus oligomethylene chain as central spacer units

Cationic polymerizations of two series of divinyl ethers were carried out to clarify the effects of their central spacer chain structure on their crosslinking polymerization behavior. One series of the monomers involves divinyl ethers with an oligooxyethylene central spacer chain: diethylene glycol divinyl ether ( O‐3 ), triethylene glycol divinyl ether ( O‐4 ), tetraethylene glycol divinyl ether ( O‐5 ), pentaethylene glycol divinyl ether ( O‐6 ), and heptaethylene glycol divinyl ether ( O‐8 ) (see Scheme 1 ). The other series includes divinyl ethers with an oligomethylene central spacer chain: 1,4‐butanediol divinyl ether ( C‐4 ), 1,6‐hexanediol divinyl ether ( C‐6 ), and 1,8‐octanediol divinyl ether ( C‐8 ). Cationic polymerizations of these monomers were carried out with the hydrogen chloride/zinc chloride (HCl/ZnCl₂) initiating system in methylene chloride (CH₂Cl₂) at ?30 °C ([Monomer]₀ = 0.15 M; [HCl]₀ = 5.0 mM; [ZnCl₂]₀ = 0.5 mM). The polymerizations of the oligomethylene‐based divinyl ethers C‐6 and C‐8 caused gel formation at high monomer conversions (～90%), whereas C‐4 formed soluble polymers even at almost 100% monomer conversion. The oligooxyethylene‐based divinyl ethers O‐3 , O‐4 , O‐5 , and O‐6 underwent gel‐free polymerizations up to 100% monomer conversion and O‐8 did so at least up to ～80% conversion. The content of unreacted pendant vinyl groups of the obtained soluble polymers was measured by ¹H NMR spectroscopy. In the polymerizations of the oligomethylene‐based divinyl ethers ( C‐4 , C‐6 , and C‐8 ), the vinyl contents of the polymers decreased monotonously with increasing monomer conversion, and their number‐average molecular weights (M_n's) and polydispersity ratios (M_w/M_n's) increased considerably just before the gelation occurred. On the contrary, the vinyl contents of the polymers obtained from the oligooxyethylene‐based divinyl ethers ( O‐3 , O‐4 , O‐5 , O‐6 , and O‐8 ) decreased steeply even in the early stage of the polymerizations and almost all the pendant vinyl ether groups were consumed in the soluble polymers at the final stage of the polymerizations. The oligooxyethylene spacer units adjacent to the pendant unreacted vinyl ether groups may solvate intramolecularly with the carbocationic active center to accelerate frequent occurrence of intramolecular crosslinking reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3729–3738, 2004     

Preparation and characterization of polymer electrolyte membrane from chloroacetate chitosan/chitosan blended with epoxidized natural rubber

Chitosan-based membranes are among the most effective and efficient PEMs for fuel cells, however their low proton conductivity needs to be improved. In this study, chitosan, chloroacetate chitosan (CCS), chitosan blend with epoxidized natural rubber (ENR), and CCS with ENR blend based membranes were prepared by solution casting, crosslinked with NaOH and H₂SO₄, and investigated for physical, chemical, electrical and ionic properties. The functional groups were identified by ATR-FTIR spectroscopy and the peaks matched improved membrane properties. The surface roughness of the membranes was determined by AFM, and it increased with the amount of ENR. The electrical properties measured with an LCR meter showed that the CCS, CS and CS-B had the highest conductance, conductivity, capacitance and dielectric constant, while the CCS10/ENR8, CS10/ENR8 and CS15/ENR3 showed the highest resistance and resistivity. Furthermore, the CCS gave the lowest dissipation factor, which indicates its suitability for use in a PEM. In addition, the contact angle was relatively high for CS-B, CS and CCS.     

Transport of benzene and methyl‐substituted benzenes through carbon black‐filled epoxidized natural rubber

Sorption and diffusion of benzene and methyl‐substituted benzenes were investigated through epoxidized natural rubber (ENR) reinforced with four types of carbon black: superabrasion furnace (SAF), intermediate superabrasion furnace (ISAF), high‐abrasion furnace (HAF), and semireinforcing furnace (SRF). Kraus equation has been used to investigate the extent of reinforcement for the different types of carbon black used in the experiments. Effect of the type and concentration of the carbon black on solvent uptake and mechanism of diffusion were studied in detail. The rate constant for diffusion of the solvents in epoxidized natural rubber vulcanizate based on different carbon black type, and loading was investigated. Diffusion constant was found to decrease with increase in the degree of reinforcement. The interaction constant values were experimentally determined. The sorption data were used to determine the activation energy for the diffusion process and the enthalpy and entropy of the sorption process. The experimental results were compared with theoretical predictions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 415–427, 1999