Photopolymerization behavior in nanocomposites formed with thiol–acrylate and polymerizable organoclays

Because of the inherent characteristics of the thiol–ene step growth mechanism in preparation of thiol–ene photopolymer clay nanocomposites, the ratio between thiol and ene functional groups at and near the organoclay surfaces may have a significant effect on the polymerization behavior. This study investigates the influence of monomer composition and the type of polymerizable organoclay on thiol–acrylate photopolymerization behavior in preparation of photocurable clay nanocomposite systems. To this end, two types of polymerizable organoclays with acrylate or thiol functional group on the clay surfaces were compared in monomer compositions with different polarity and functionality. Real‐time infrared spectroscopy was used to characterize polymerization behavior in conjunction with photo‐DSC. The degree of clay exfoliation was evaluated using small angle X‐ray scattering and correlated with photopolymerization behavior. Higher chemical compatibility of components induced enhanced clay exfoliation resulting in increase in photopolymerization rate. By affecting the stoichiometric ratio of functional groups in the clay gallery, thiolated organoclays enhance thiol–ene reaction, whereas acrylated organoclays encourage acrylate homopolymerization. In addition, inducing more propagating thiyl radicals on the organoclay surfaces by increasing functionality of thiol monomer also facilitates thiol–ene copolymerization, whereas the increase of acrylate functionality reduces final thiol conversion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effects of organic modifications of clay on the ultraviolet‐curing behavior and structure of a polyester‐acrylate/clay nanocomposite system

A pristine clay (Na⁺‐montmorillonite (MMT) and three different organoclays (20A‐MMT, vinylbenzyl dimethyldodecyl ammonium (VDA)‐MMT, and siloxane diamine ammonium (SDA)‐MMT) that originated from the pristine clay were used to prepare polyester‐acrylate (PEA)/clay nanocomposites by in situ ultraviolet (UV)‐curing. Except for the commercial organoclay (20A‐MMT), VDA‐MMT, and SDA‐MMT were prepared in this study by ion exchange method. The effects of organic modifications of the pristine clay on the UV‐curing behavior and structure of the nanocomposite system were investigated. The organic modifications of the clay affected considerably the UV‐curing behavior and structure of the nanocomposite system. Copyright © 2008 John Wiley & Sons, Ltd.     

Organoclay/thermotropic liquid crystalline polymer nanocomposites. III. Effects of fully exfoliated organoclay on morphology,thermal, and rheological properties

A fully exfoliated organoclay in thermotropic liquid crystalline polymer (TLCP) based nanocomposite was prepared by a method combining ultrasonication, centrifugation, solution casting, and heat‐shearing separation. Morphological study showed that the organoclays of 15–25 nm in size dispersed uniformly in TLCP with fully exfoliated structures. The organoclays formed molecular level interactions with TLCP molecules. The interactions did not affect the liquid crystallinity and mesophase structure of TLCP, but they affected the thermal stability and thermal properties of TLCP, increasing the thermal stability and shifting the transition temperatures to the higher ends. Mechanical rheology investigations in the linear viscoelastic region showed that with the exfoliated organoclay in TLCP, more obvious pseudosolidlike behavior appeared in the terminal region. The rigidity of TLCP was enhanced by the presence of the exfoliated organoclay with percolated structures in the TLCP matrix. In steady shear tests, the nanocomposite had the similar shear viscosity and N1 (the first normal stress difference) to those of TLCP in the steady state condition. Percolated structures were easily destroyed by sufficient shear strain and the exfoliated organoclays were oriented along the shear direction, even assisting the neighboring TLCP molecules to align in the flow direction, resulting in a decrease of viscosity and an increase of the N1 slope. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 712–720, 2010     

气相生长碳纤维对环氧树脂固化反应的影响及其复合物固化动力学研究

用示差扫描量热方法研究了气相生长碳纤维作为填料对4,4′-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)/4,4′-二氨基二苯基砜(DDS)等温固化反应的影响.与纯环氧树脂一样,气相生长碳纤维复合物的固化反应也属于自催化反应类型.气相生长碳纤维对环氧树脂的固化反应动力学影响很小.固化反应的过程可以用一种修正过的自催化动力学模型来描述,在整个固化反应过程中纯TGDDM/DDS环氧树脂及其气相生长碳纤维复合物模型拟合得到的结果和实验数据相当一致.     

Influence concentration of modifying agent on properties of natural rubber/organoclay nanocomposites

Sodium-montmorillonite (Na-MMT) nanoclay was modified with different concentrations of octadecylamine organic modifying agent at 0.5, 1.0 and 1.5 times the CEC of Na-MMT. Influence of concentration of modifying agent on properties of the organoclays and natural rubber/organoclay nanocomposites was investigated. It was found that the optimum concentration of modifying agent was 1.5 times the CEC of Na-MMT. That is, at this concentration, larger d-spacing of organoclay particles and higher degree of clay dispersion in natural rubber matrix were observed. Larger interlayer d-spacing also caused enhancement of the mechanical properties of the NR/organoclay nanocomposites. Additionally, the NR/organoclay nanocomposites with higher concentration of modifying agent exhibited faster curing reaction with higher crosslink density. Furthermore, the organoclays with larger d-spacing and higher degree of dispersion in the natural rubber matrix exhibited enhancement of the mechanical and dynamic properties and thermal stability of natural rubber/organoclay nanocomposites.     

Synthesis and characterization of novel biodegradable epoxy‐modified polyurethane elastomers

Biodegradable polyurethane elastomers with the potential for applications in medical implants were synthesized from the reaction of epoxy‐terminated polyurethane prepolymers (EUPs) with 1,6‐hexamethylenediamine as a curing agent. EUPs were themselves prepared from the reaction of glycidol and isocyanate‐terminated polyurethanes made from different molecular weights of poly(ε‐caprolactone) (CAPA) and 1,6‐hexamethylene diisocyanate. All materials were characterized by spectroscopic methods. The curing conditions were optimized by gel content measurements. The curing kinetic and kinetic parameters were determined from differential scanning calorimetry measurements. The effects of changing the crosslink density and crystallinity of elastomers via the alteration of the CAPA polyol molecular weight on the physical, mechanical, and degradation properties of the final elastomeric polymers were examined fully. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2985‐2996, 2005     

A new thermoplastic vulcanizate (TPV)/organoclay nanocomposite: Preparation,characterization, and properties

The preparation, characterization, and properties of the new thermoplastic vulcanizate (TPV)/organoclay nanocomposites are reported in this article. The nanocomposites were prepared by the melt intercalation method. The organoclay was first treated with glycidyl methacrylate, which acts as a swelling agent for organoclays, as well as a grafting agent for TPV (in the presence of dicumyl peroxide) during the melt mixing. The nanocomposite was intercalated, as evidenced by X‐ray diffraction. The tensile modulus of the 5% TPV/organoclay nanocomposite was higher than that of the 20% talc‐filled microcomposite. The storage modulus of the nanocomposite was higher than that of the pristine TPV. The most important observation is obtained from dynamic mechanical analysis, which reveals that the glass‐transition temperature of the polypropylene phase of the nanocomposite increases (as compared to virgin TPV), whereas the ethylene–propylene–diene monomer phase remains almost the same. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2900–2908, 2004     

液晶环氧树脂/蒙脱土纳米复合材料的制备和固化反应动力学研究

用带有介晶基元的联苯二酚二缩水甘油醚 (BP)、4 氨基苯基磺酰胺 (SAA)和有机化蒙脱土 (93A)采用浇铸成模固化成型的方法制备出液晶环氧树脂 蒙脱土纳米复合材料 .WRXD结果表明 93A含量是 2 %时可形成剥离型纳米材料 ,而当 10 %时形成插层型纳米材料 ,5 %时则形成剥离和插层混合型的纳米材料 ;POM结果表明蒙脱土的存在能够破坏原有的扇形近晶相液晶织构 .DSC研究表明体系的固化反应动力学 ,可用变形的Kissinger Akahira Sunose法 (VKAS)表征 ,从求出的反应活化能和转化率关系 ,发现反应初期 ,蒙脱土使反应活化能降低 ,能够促进液晶环氧树脂的固化 .     

Kinetic study of the polymerization of aromatic polyurethane prepolymers by high‐throughput experimentation

In this contribution, high‐throughput screening experiments are reported to study the polymerization of different aromatic polyurethane (PU) prepolymers. The prepared prepolymers were synthesized from toluene diisocyanate (T80) with different molar mass polyether diols and polyether triols, respectively. The reactions were performed in solution using a Chemspeed Accelerator? SLT106 automated parallel synthesizer as well as in bulk to evaluate the high‐throughput approach for this kind of prepolymers. More than 100 samples were prepared and characterized by GPC within 1 week labor time to investigate the reaction kinetics and to compare the resulting trends obtained by high‐throughput experimentation (HTE) or by conventional, bulk prepolymerization. The synthesis of the prepared prepolymers with a linear (T80‐Diol) or a branched (T80‐Triol) structure followed a second‐order kinetic in solution but showed deviation from this phenomenon in bulk under the selected reaction conditions, although the same trends are observed in both cases. The calculation of the rate constants allowed comparing the reactivity of different prepolymer systems, which could have a significant influence on the industrial application and processing of these materials. As a result, the HTE approach was found to represent a powerful tool for the kinetic studies of PU prepolymers. Moreover, in spite of the complexity of the curing process, the results obtained by high‐throughput solution polymerization can be applied for evaluating the bulk polymerization. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 570–580, 2010     

Nanocomposites of polyurethane with various organoclays: Thermomechanical properties,morphology, and gas permeability*

The properties of polyurethane (PU) nanocomposites with three different organoclays were compared in terms of their thermal stabilities, mechanical properties, morphologies, and gas permeabilities. Hexadecylamine–montmorillonite, dodecyltrimethyl ammonium–montmorillonite, and Cloisite 25A were used as organoclays for making PU hybrid films. The properties were examined as a function of the organoclay content in a matrix polymer. Transmission electron microscopy photographs showed that most clay layers were dispersed homogeneously into the matrix polymer on the nanoscale, although some particles of clay were agglomerated. Moreover, the addition of only a small amount of organoclay was enough to improve the thermal stabilities and mechanical properties of PU hybrid films, whereas gas permeability was reduced. Even polymers with low organoclay contents (3–4 wt %) showed much higher strength and modulus values than pure PU. Gas permeability was reduced linearly with an increasing amount of organoclay in the PU matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 670–677, 2002; DOI 10.1002/polb.10124     

Sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions as a route to well‐defined mono and bis end‐functionalized poly(N‐isopropylacrylamide)

Sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions have been used as a facile and quantitative method for modifying end‐groups on an N‐isopropylacrylamide (NIPAm) homopolymer. A well‐defined precursor of polyNIPAm (PNIPAm) was prepared via reversible addition‐fragmentation chain transfer (RAFT) polymerization in DMF at 70 °C using the 1‐cyano‐1‐methylethyl dithiobenzoate/2,2′‐azobis(2‐methylpropionitrile) chain transfer agent/initiator combination yielding a homopolymer with an absolute molecular weight of 5880 and polydispersity index of 1.18. The dithiobenzoate end‐groups were modified in a one‐pot process via primary amine cleavage followed by phosphine‐mediated nucleophilic thiol‐ene click reactions with either allyl methacrylate or propargyl acrylate yielding ene and yne terminal PNIPAm homopolymers quantitatively. The ene and yne groups were then modified, quantitatively as determined by ¹H NMR spectroscopy, via radical thiol‐ene and radical thiol‐yne reactions with three representative commercially available thiols yielding the mono and bis end functional NIPAm homopolymers. This is the first time such sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions have been used in polymer synthesis/end‐group modification. The lower critical solution temperatures (LCST) were then determined for all PNIPAm homopolymers using a combination of optical measurements and dynamic light scattering. It is shown that the LCST varies depending on the chemical nature of the end‐groups with measured values lying in the range 26–35 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3544–3557, 2009     

Synthesis,structure, and characterization of nematic liquid‐crystalline thermosets based on bisacrylates

Four bisacrylate mesogenic monomers and the corresponding liquid‐crystalline thermosets were synthesized. The chemical structures of the intermediate compounds and monomers obtained were confirmed by elemental analyses, Fourier transform infrared, and ¹H NMR and ¹³C NMR spectra. The mesomorphic properties and thermal stability were investigated with differential scanning calorimetry, thermogravimetric analysis, polarized optical microscopy, and X‐ray diffraction measurements. The influence of the curing temperatures and time on the phase behavior and thermal stability of the thermosets was discussed. All the monomers and thermosets exhibited a nematic schlieren texture. However, the monomers only showed the melting transition, and the thermosets displayed the glass transition. The experimental results demonstrated that the monomer structures strongly affected the phase behavior and the curing reaction rate, and the glass‐transition temperatures and thermal stability of the thermosets increased with the curing temperature and time. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4478–4485, 2005     

Combined effects of clay modifications and compatibilizers on the formation and physical properties of melt‐mixed polypropylene/clay nanocomposites

The melt mixing technique was used to prepare various polypropylene (PP)‐based (nano)composites. Two commercial organoclays (denoted 20A and 30B) served as the fillers for the PP matrix, and two different maleated (so‐called) compatibilizers (denoted PP‐MA and SMA) were employed as the third component. The results from X‐ray diffraction (XRD) and transmission electron microscope (TEM) experiments revealed that 190 °C was an adequate temperature for preparing the nanocomposites. Nanocomposites were achieved only if specific pairs of organoclay and compatibilizer were simultaneously incorporated in the PP matrix. For example, PP/20A(5 wt %)/PP‐MA(10 wt %) and PP/30B(5 wt %)/SMA(5 wt %) composites exhibited nanoscaled dispersion of 20A or 30B in the PP matrix. Differential scanning calorimetry (DSC) results indicated that the organoclays served as nucleation agents for the PP matrix. Generally, their nucleation effectiveness increased with the addition of compatibilizers. The thermal stability enhancement of PP after adding 20A was confirmed with thermogravimetric analysis (TGA). The enhancement became more evident as a suitable compatibilizer was further added. However, for the 30B‐included composites, thermal stability enhancement was not evident. The dynamic mechanical properties (i.e., storage modulus and loss modulus) of PP increased as the nanocomposites were formed; the properties increment corresponded to the organoclay dispersion status in the matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4139–4150, 2004     

Polypropylene/organoclay nanocomposites compatibilized with hydroxyl‐functional polypropylenes

The properties of polypropylene composites can be tailored through the use of nanoclay fillers. The effectiveness of a metallocene‐catalyzed hydroxyl‐functional polypropylene in the compatibilization of polypropylene layered nanosilicate composites was studied, and the results were compared with those for a commercial maleic anhydride functionalized polypropylene. Polypropylene/organoclay nanocomposites were prepared by melt blending, and two polypropylene/compatibilizer/organoclay ratios, 90/5/5 and 70/20/10, were characterized. The organomodification of the clay was carried out with octadecylamine and N‐methylundecenylamine. The structure of the layered silicate was studied by transmission electron microscopy, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering. The fracture surfaces of the composites and thus the efficiency of the compatibilizers to penetrate the galleries of the organoclays were characterized by scanning electron microscopy, and the melt viscosity was studied by stress‐controlled rotational rheometry. The nanostructure was observed with both alkyl amines used for intercalation. The fillers facilitated the processability of all the composites, consisting of equal amounts of compatibilizer and organoclay filler and, in some of the composites, containing twice as much compatibilizer as organoclay filler. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1892–1903, 2005     

Study on intercalation and exfoliation behavior of organoclays in epoxy resin

Intercalation and exfoliation behavior of organoclays in epoxy resin has been studied through XRD and DSC. It was found that the organoclays were easily intercalated by epoxy oligomer to form a stable epoxy/clay intercalated hybrid. Under appropriate conditions the clays were able to be further exfoliated as the epoxy resin was cured; thus, a nanocomposite was obtained. It was also found that the exfoliating ability of the organoclays was basically determined by the nature of the clays and the curing agent used. The exfoliation mechanism is discussed in this paper. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 115–120, 2001     

Surface modification of clay and its effect on the intercalation behavior of the polymer/clay nanocomposites

Melt intercalation of the methylsilylated organoclays with polar polymers such as SAN was examined to verify the adhesive role of guest polymeric chains between hydrophilic clay layers, so-called “glue effect” on intercalation behavior. Once methylsilylated organoclay was melt-blended with SAN, it was found that the mixture presented significant retardation of increase of interlayer spacing, d₀₀₁ with heating time, and a noticeable decrease of d₀₀₁ after the methylsilylation of organoclay, implying that the diffusion of SAN was highly suppressed by the decrease of polar interaction force caused by conversion of OH to methylsiloxyl groups. However, when applying shear force for the methylsilylated organoclay/SAN nanocomposites during melt intercalation, a noticeable increase of d₀₀₁ was observed, expressing that intercalation of clay by SAN occurred much more effectively because of the reduction of gluing force between host clay and guest polymers, which was well supported by dramatic improvements of mechanical properties after methylsilylation of organoclays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2367–2372, 2004     

Functional off‐stoichiometry thiol‐ene‐epoxy thermosets featuring temporally controlled curing stages via an UV/UV dual cure process

We present a facile two‐stage UV/UV activation method for the polymerization of off‐stoichiometry thiol‐ene‐epoxy, OSTE+, networks. We show that the handling and processing of these epoxy‐based resins is made easier by introducing a material with a controlled curing technique based on two steps, where the first step offers excellent processing capabilities, and the second step yields a polymer with suitable end‐properties. We investigate the sequential thiol‐ene and thiol‐epoxy reactions during these steps by studying the mechanical properties, functional group conversion, water absorption, hydrolytic stability, and thermal stability in several different thiol‐ene‐epoxy formulations. Finally, we conclude that the curing stages can be separated for up to 24 h, which is promising for the usefulness of this technique in industrial applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2604‐2615     

Isothermal cure kinetics of epoxy/phenol‐novolac resin blend system initiated by cationic latent thermal catalyst

The investigation of the cure kinetics of a diglycidyl ether of bisphenol A (DGEBA)/phenol‐novolac blend system with different phenolic contents initiated by a cationic latent thermal catalyst [N‐benzylpyrazinium hexafluoroantimonate (BPH)] was performed by means of the analysis of isothermal experiments using a differential scanning calorimetry (DSC). Latent properties were investigated by measuring the conversion as a function of curing temperature using a dynamic DSC method. The results indicated that the BPH in this system for cure is a significant thermal latent initiator and has good latent thermal properties. The cure reaction of the blend system using BPH as a curing agent was strongly dependent on the cure temperature and proceeded through an autocatalytic kinetic mechanism that was accelerated by the hydroxyl group produced through the reaction between DGEBA and BPH. At a specific conversion region, once vitrification took place, the cure reaction of the epoxy/phenol‐novolac/BPH blend system was controlled by a diffusion‐control cure reaction rather than by an autocatalytic reaction. The kinetic constants k₁ and k₂ and the cure activation energies E₁ and E₂ obtained by the Arrhenius temperature dependence equation of the epoxy/phenol‐novolac/BPH blend system were mainly discussed as increasing the content of the phenol‐novolac resin to the epoxy neat resin. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2945–2956, 2000     

Alder‐ene polymers derived from allyl aralkyl phenolic resin and bismaleimides: carbon fiber composites properties

The influence of structural variations in bismaleimides (BMIs) on Alder‐ene polymerization of O‐allyl aralkyl phenolic resin [O‐allyl Xylok (OAX)] was examined. Toward this, three BMI functional monomers, viz. 2,2′‐bis 4‐[(4′‐maleimido phenoxy) phenyl] propane (BMIP), 4,4′‐Bismaleimido diphenyl methane (BMPM), and Bis 4‐maleimidodiphenyl ether (BMPE), were blended with OAX in different molar ratios. The cure characterization revealed that the allyl‐dominated blends cure by three distinct reaction steps whereas the maleimide‐dominated blends exhibit a two‐step reaction invariable with the maleimide structure. Introduction of more maleimide functionalities increased the T_g and thermal stability of the co‐cured network. Differences in the storage modulus values and T_g of the BMI/OAX systems were correlated to the chemical structure of the BMI and crosslink density. Flexural, interlaminar shear strength (ILSS), and impact strength of the composites decreased systematically with the increase in maleimide content in the blend. Among the BMIs studied, T_g, thermal stability, and ILSS retention at elevated temperature were superior for BMPM/OAX blend owing to their high crosslink density and rigid backbone of the system. Allyl‐rich compositions exhibited improved mechanical properties owing to the better resin–reinforcement interaction as revealed from morphological analysis by scanning electron microscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of organoclays on morphology and thermal and rheological properties of polystyrene and poly(methyl methacrylate) blends

Morphology, thermal and rheological properties of polymer‐organoclay composites prepared by melt‐blending of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PS/PMMA blends with Cloisite® organoclays were examined by transmission electron microscopy, small‐angle X‐ray scattering, secondary ion mass spectroscopy, differential scanning calorimetry, and rheological techniques. Organoclay particles were finely dispersed and predominantly delaminated in PMMA‐clay composites, whereas organoclays formed micrometer‐sized aggregates in PS‐clay composites. In PS/PMMA blends, the majority of clay particles was concentrated in the PMMA phase and in the interfacial region between PS and PMMA. Although incompatible PS/PMMA blends remained phase‐separated after being melt‐blended with organoclays, the addition of organoclays resulted in a drastic reduction in the average microdomain sizes (from 1–1.5 μm to ca. 300–500 nm), indicating that organoclays partially compatibilized the immiscible PS/PMMA blends. The effect of surfactant (di‐methyl di‐octadecyl‐ammonia chloride), used in the preparation of organoclays, on the PS/PMMA miscibility was also investigated. The free surfactant was more compatible with PMMA than with PS; the surfactant was concentrated in PMMA and in the interfacial region of the blends. The microdomain size reduction resulting from the addition of organoclays was definitely more significant than that caused by adding the same amount of free surfactant without clay. The effect of organoclays on the rheological properties was insignificant in all tested systems, suggesting weak interactions between the clay particles and the polymer matrix. In the PS system, PMMA, and organoclay the extent of clay exfoliation and the resultant properties are controlled by the compatibility between the polymer matrix and the surfactant rather than by interactions between the polymer and the clay surface. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 44–54, 2003