Nanostructured Thermosetting Blends of Phenolic Thermosets and Poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) Triblock Copolymer

The amphiphilic triblock copolymer, poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐b‐PPO‐b‐PEO) was incorporated into novolac resin to prepare thermosetting blends. The morphology of the thermosetting blends was investigated by means of atomic force microscopy (AFM) and small‐angle x‐ray scattering (SAXS) and the nanostructures were obtained. It was identified that the reaction‐induced phase separation occurred in the blends of phenolic thermosets with the model poly(propylene oxide) (PPO), whereas poly(ethylene oxide) (PEO) was miscible with novolac resin after and before the curing reaction. In terms of miscibility and phase behavior of the subchains of the triblock copolymer with novolac resin, it was demonstrated that the formation of nanostructures in the thermosets followed a mechanism of reaction‐induced microphase separation.     

牛血清白蛋白对Pluronic聚合物胶团形成的影响研究

用吡啶作为荧光探针研究了嵌段共聚物PluronicF108胶团形成以及牛血清白蛋白(BSA)对嵌段共聚物胶团形成的影响。研究表明,BSA阻碍嵌段共聚物的胶团形成,BSA与嵌段共聚物疏水链段的疏水相互作用是其阻碍嵌段共聚物胶团形成的主要原因。     

Tetramethylpolyarylate-polyarylate block copolymer: Synthesis and miscibility with polyarylate and poly(styrene-co-acrylonitrile)

Abstract

Tetramethylpolyarylate-polyarylate (TMPAr-PAr) block copolymers of various block lengths were synthesized by the coupling reaction of hydroxy-terminated TMPAr and hydroxy-terminated PAr using triphosgene. The phase behavior of these block copolymers are discussed based on the thermal properties observed by differential scanning calorimetry (DSC). The thermal properties of binary blends of these block copolymers with PAr homopolymer or poly(styrene-co-acrylonitrile) whose acrylonitrile content is 9.5 wt% (SAN 10) were observed by DSC. The compatibilizing effect of the microphase-separated TMPAr-PAr block copolymer in PAr/SAN 10 blends was observed from thermal properties and morphology.     

Fracture toughness of the epoxy/ATPEI-CTBN-ATPEI triblock copolymer/NMA blend system

The shortcoming of epoxy resin is the brittleness of this material though it shows excellent chemical, mechanical and electric properties. To improve fracture toughness of epoxy resin, rubbery materials that show high values in toughness but low values in glass transition temperature and mechanical properties, and thermoplastics that show high values in thermal and mechanical properties but relatively small increase in toughness were blended with epoxy. ATPEI-CTBN-ATPEI triblock copolymer, which consists of rubbery and thermoplastics blocks, was synthesized, and the triblock copolymer was blended with epoxy resin. The effects of parameters such as contents of the triblock copolymer, cure temperature, and contents of catalyst on the morphology of the blend systems were studied. From 30 wt% of the contents of the triblock copolymer, fracture toughness and impact energy absorption of the blend systems were increased significantly. This was due to the generation of nodular morphology in the system.     

Preparation and Properties of Novel Inherent Flame-Retardant Cyclotriphosphazene-Containing Epoxy Resins

A novel flame-retardant cyclotriphosphazene-based epoxy resin (CPEP) was successfully prepared by epoxidation of bis-(4-hydroxyphenylsulfonylphenoxy) tetraphenoxycyclotriphosphazene with epichlorohydrin, and was characterized by ¹H nuclear magnetic resonance (NMR), Fourier transform infrared, and gel permeation chromatography (GPC). Then the blends of CPEP and diglycidyl ether of bisphenol A (E51) with different mass ratios were cured using 4,4′-diaminodiphenylmethane as a curing agent. The curing behaviors and the glass transition temperatures of the resulting thermosets were studied by differential scanning calorimetry. The thermal stabilities and flame-retardant properties of the cured resins were studied by thermogravimetric analysis and UL94 tests, respectively. In addition, mechanical, hydrophobic, and electrical properties were also characterized. Compared to the corresponding E51-based thermosets, the cured resins with a mixture of CPEP and E51 showed better thermal stabilities, higher char yields, and greatly improved flame-retardant properties. Furthermore, relatively good mechanical properties, hydrophobicity, and electric resistance were maintained. The cured resins of CPEP/E51 (mass ratio 1:1) achieved UL94 V-0 rating, indicating that the epoxy resin prepared in this study could be used as a flame-retardant coating material.     

Effect of Molecular Architecture on Physical Properties of Tree-Shaped and Star-Shaped Poly(Methyl Methacrylate)-Based Copolymers

The synthesis of star-like A(B)_n copolymers based on the hydrophilic poly(ethylene glycol) monomethyl ether (m-PEG, block A) and the hydrophobic poly(methyl methacrylate) (PMMA, blocks B) is reported. We obtained copolymers made of one m-PEG chain and 2 or 4 PMMA blocks using a combined “arm first”—“core first” approach. Such structures were called tree-shaped copolymers where the m-PEG was considered as the trunk and PMMA arms as the branches. Star-like copolymers (B)_nA-A(B)_n built by two tree-shaped fragments with a poly(propylene oxide) (PPO) as the central junction, were also synthesized according to a previously reported procedure. The latter were called star-shaped structures and the synthesis was performed to obtain architectures different from the tree-shaped one but characterized by a similar length of the PMMA arms. Microstructural analysis was carried out through ¹H-NMR and GPC, and the thermal and transport properties (sorption and diffusion) to liquid water were investigated and correlated to the molecular architecture of the two classes of copolymers.     

Modification of Epoxy Resin with Cycloaliphatic-Epoxy Oligosiloxane for Light-Emitting Diode (LED) Encapsulation Application

A novel cycloaliphatic-epoxy oligosiloxane (EHDM) was incorporated into 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ERL-4221) for use as a light-emitting diode (LED) encapsulant. EHDM, with reactable epoxy groups and flexible Si-O-Si chains, was obtained by the hydrolytic condensation reaction between 2-(3,4-epoxycyclo-hexyl)ethyl-trimethoxysilane (EHETMS) and dimethyldiethoxylsilane (DMDES). The results of Fourier transform infrared spectroscopy, ²⁹Si nuclear magnetic resonance, and gel permeation chromatography indicated that EHDM had a narrow molecular weight distribution and high epoxy graft degree. The thermal and mechanical properties, morphologies, and light transmittance of the cured neat epoxy resin and EHDM-modified epoxy were investigated by differential scanning calorimetry, thermogravimetric analysis, tensile and impact testing, scanning electron microscopy, and ultraviolet-visible spectrophotometry. The experimental results demonstrated that the cured EHDM-10 hybrimer with 10 pph of EHDM relative to ERL-4221 maintained the neat ERL-4221 epoxy transmittance of 85% at 450 nm. With respect to the corresponding properties of the neat epoxy resin, EHDM-10 hybrimer possessed a higher glass transition temperature, better thermal stability, better fracture toughness, and lower water absorption ratio, indicating EHDM effectively improved the properties of ERL-4221 for LED packaging applications.     

共聚物Pluronic P103对牛血清白蛋白荧光光谱的猝灭

应用静态荧光光谱研究了嵌段共聚物PluronicP103对牛血清白蛋白(BSA)荧光光谱的猝灭。研究表明,PluronicP103对BSA的荧光有猝灭作用,动态猝灭是引起BSA荧光猝灭的主要原因。发现嵌段共聚物PluronicP103在水溶液中的蔟集状态影响其与BSA的相互作用,以胶团形式存在的PluronicP103对BSA的猝灭作用更强。     

Phase Separation in Poly(Methyl Methacrylate)-Epoxy Blend

Diglycidyl ether of bisphenol A (DGEBA) epoxy resin was modified with high molecular weight poly(methyl methacrylate) (PMMA). Morphological variations of a 2 wt% PMMA-modified epoxy mixture were studied by optical microscopy and scanning electron microscopy (SEM). A PMMA-epoxy blend cured at 100°C revealed that a secondary phase morphology was observed in both epoxy and PMMA phases from the early stages of the phase separation process. A morphology consisting of a rough striated continuous phase along with large smooth regions was observed by SEM, confirming the secondary phase separation. The dynamic mechanical thermal analysis showed that the PMMA modification of epoxy at such a low PMMA concentration of 2 wt% has no major influence on the glass transition temperature of the epoxy-rich phase. The PMMA-epoxy blend showed a slight increase in the flexural properties and the fracture toughness.     

Studies on the Thermal Properties of Epoxy Resins Modified with Two Kinds of Silanes

Dimethyldiethoxysilane (DMDES) and diphenyldimethoxysilane (DPDMS)-containing epoxy resins were synthesized by dehydration polycondensation. The chemical structures were determined by FT-IR, ¹H NMR, and ¹³C NMR. The cured samples, with 4, 4′-diaminodiphenylmethane (DDM) as curing agent, were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile and impact testing. Results showed that DMDES and DPDMS-modified epoxy resins possess higher glass transition temperatures, better thermal stability, and better fracture toughness than the neat epoxy resin.     

Properties of Compatibilized Nylon 6/ABS Polymer Blends

Nylon 6/poly(acrylonitrile‐butadiene‐styrene)(ABS) blends were prepared in the molten state by a twin‐screw extruder. Maleic anhydride‐grafted polypropylene (MAP) and solid epoxy resin (bisphenol type‐A) were used as compatibilizers for these blends. The effects of compatibilizer addition to the blends were studied via tensile, torque, impact properties and morphology tests. The results showed that the additions of epoxy and MA copolymer to nylon 6/ABS blends enhanced the compatibility between nylon 6 and ABS, and this lead to improvement of mechanical properties of their blends and in a size decrease of the ABS domains.     

Increased yield of immunogold labeling of epoxy sections by adding para-phenylendiamine in the tissue processing

The purpose of this study was to examine if the presence of para-phenylendiamine (PPD) in the tissue processing could increase the yield of immunogold labeling of the epoxy sections. Renal swine tissue with glomerular immune complex deposits with reactivity against IgG was embedded in epoxy resin. PPD was added (1) at the beginning of the dehydration, (2) in the first step with propylene oxide, (3) in the beginning of the dehydration and in all steps with propylene oxide included the infiltration step where propylene oxide and epoxy resin are mixed, or (4) PPD was totally avoided. The tissue was embedded with two different combinations of accelerator. Immunogold labeling with anti-IgG was performed on both non-heated and heated ultrathin sections. The immunogold labeling on the heated sections which were based on processing with PPD in all steps (3) was about 55–65% higher than the corresponding labeling for epoxy sections processed in total absence of PPD (4). The immunolabeling was not significantly increased when the tissue was processed with PPD only in the start of the dehydration (1) or in the first step with propylene oxide (2). We believe that tissue processing with sufficient PPD contributes to reduce the co-polymerization between the antigens and the epoxy polymer in the same way as excess of accelerator does (Brorson and Skjørten, 1996a). The practical significance of this study provides better opportunities for increasing the immunogold labeling of epoxy sections by adding PPD in the tissue processing, and our result may inspire other researchers to develop even more efficient methods for controlling the copolymerization between antigens and epoxy resin.     

Effects of Poly(Propylene Oxide)–Poly(Ethylene Oxide)–Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)–Poly(Propylene Oxide)–Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)–poly(ethylene oxide) ((EO)_n–(PO)_m–(EO)_n) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO–PPO–PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO–PEO–PPO into PEO–PPO–PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO₁₄–EO₂₄–PO₁₄ (17R4) was added to the Pluronics EO₂₀–PO₇₀–EO₂₀ (P123), EO₁₀₀–PO₆₅–EO₁₀₀ (F127), and EO₁₃₃–PO₅₀–EO₁₃₃ (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol–gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.     

The Mechanical Properties,Compatibility, and Thermal Stabilities of POE-Graft-Methyl Methacrylate and Acrylonitrile(POE-g-MAN)/ Styrene-Acrylonitrile Copolymer (SAN Resin) Blends

POE-graft-methyl methacrylate and acrylonitrile (POE-g-MAN) was prepared by graft copolymerization of methyl methacrylate (MMA) and acrylonitrile (AN) onto polyethylene-octene copolymers (POE) with suspension polymerization. POE-g-MAN/SAN resin blends (AOMS) were prepared by blending POE-g-MAN with styrene-acrylonitrile copolymer (SAN resin). The mechanical properties, compatibility, and thermal stabilities of AOMS were studied. The notched impact strength of the blends reached 54.0 kJ/m² when the AN/(MMA + AN) ratio (f_AN) of POE-g-MAN, benzoyl peroxide dosage, and POE content in AOMS were 15 wt%, 1.0 wt%, and 25 wt%, respectively. Transmission electron microscopy analysis showed that the highest toughness occurred when the size of POE-g-MAN particles and the surface-to-surface inter-particle distance were proper. Scanning electron microscopy analysis indicated that the AOMS fracture surface had plastic flow visible, which looked like a fibril morphology when the AN/(MMA + AN) ratio (f_AN) of POE-g-MAN was 15 wt%. The toughening mechanism of AOMS was shear yielding of the matrix, which endowed AOMS with remarkable toughness. Dynamic mechanical thermal analysis showed that the compatibility of the POE phase and SAN phase improved after graft copolymerization of MMA and AN onto POE. When the grafting chain polarity was appropriate, the miscibility between POE-g-MAN and SAN resin was the best. Thermogravimetry analysis showed that thermal stability of AOMS increased with increasing AN units in POE-g-MAN.     

Complex nanostructured materials from segmented copolymers prepared by ATRP

The development of new controlled/living radical polymerization processes, such as Atom Transfer Radical Polymerization (ATRP) and other techniques such as nitroxide mediated polymerization and degenerative transfer processes, including RAFT, opened the way to the use of radical polymerization for the synthesis of well-defined, complex functional nanostructures. The development of such nanostructures is primarily dependent on self-assembly of well-defined segmented copolymers. This article describes the fundamentals of ATRP, relevant to the synthesis of such systems. The self-assembly of block copolymers prepared by ATRP is illustrated by three examples. In the first, block copolymers of poly(butyl acrylate) with polyacrylonitrile phase separate, leading to spherical, cylindrical or lamellar morphologies, depending on the block copolymer composition. At a higher temperature, polyacrylonitrile block converts to nanostructured carbon clusters, whereas poly(butyl acrylate) block serves as a sacrificial block, aiding the development of designed nanostructures. In the second example, conductive nanoribbons of poly(n-hexylthiophene) surrounded by a matrix of organic polymers are formed from block copolymers prepared by ATRP. The third example describes an inorganic-organic hybrid system consisting of hard nanocolloidal silica particles (20 nm) grafted by ATRP with well-defined polystyrene-poly(benzyl acrylate) block copolymer chains (1000 chains per particle). Silica cores in this system are surrounded by a rigid polystyrene inner shell and softer polyacrylate outer shell. Received 9 July 2002 Published online: 11 March 2003     

Conductance study of poly(ethylene oxide)- and poly(propylene oxide)-based polyelectrolytes

The ionic conductivity of poly(ethylene oxide) and poly(propylene oxide) in pure solution form, individually complexed with salts of Na⁺ and Li⁺, with and without plasticizer (propylene carbonate) and in blended form with individual salt with and without plasticizer, was studied. The conductance measurements were made at various concentrations of salt polymer complexes and at different temperatures. The effects of temperature and plasticizer concentration were measured from Arrhenius conductance plots. It is shown that the addition of salts in pure PEO increases conductance many times. The plasticizer has also same effect. The blending of PEO with PPO gives enhanced conductivity as compared to pure PEO. The activation energies were determined for all the systems which gave higher values for pure PEO and the value decreases with the addition of Li and Na salts and further decreases with the addition of plasticizer. The blending has also lowered the activation energy values which mean that incorporation of PPO in PEO has decreased crystallinity and the amorphous region has increased the local mobility of polymer chains resulting in lower activation energies.     

Maintenance of highly interfacial shear strength by diblock copolymer between carbon fiber and epoxy resin in hostile environment

The environmental resistance properties of carbon fiber (CF), with various surface modifications, reinforcing epoxy resin composites have been studied by a microbond test. The results of cooling–heating cycling between ?40 and 95?°C indicate that the introduction of the flexible poly(n-butyl acrylate) (PnBA) blocks into the interface can effectively decrease the interfacial degradation rate, induced by interfacial thermal stress. After 50 cooling–heating cycles, the interfacial shear strength between CF and epoxy resin was still as high as 32.69?±?2.13?MPa. The results of hygrothermal treatment by immersing the composites in hot water show that assembly morphology of the diblock copolymer hydroxyl-terminated poly(n-butyl acrylate-b-glycidyl methacrylate) (OH-PnBA-b-GMA) at the interface can decrease the interfacial water absorption and thus increase the hygrothermal resistance of the composite. Besides, the length of PnBA block in the diblock copolymer influenced the interfacial properties of the composite in a hygrothermal environment.     

Nanofilled Polypropylene/Poly(trimethylene terephthalate) Blends: A Morphological and Mechanical Properties Study

Polypropylene (PP) /poly(trimethylene terephthalate), (PTT), binary blends in the presence of two interfacial modifier as well as two organically modified nanoclay additives were studied in terms of mechanical and morphological characteristics. Scanning electron microscopy confirmed the incompatibility of the system which was solved to some extent through incorporating the nanoclay as well as functional compatibilizers. An evaluation of the specimens via static mechanical tests in tensile mode gave credence to the assumption that the higher the PTT content, the higher the mechanical performance would be. Furthermore, the compatibilizer-containing blends not only exhibited higher toughness, but also possessed enhanced stiffness when a maleated compatibilizer was added. The tensile modulus was promoted further in the presence of clay nanoparticles; however, toughness was somewhat sacrificed. The Barentsen as well as Halpin-Tsai models were found to describe the binary blends modulus. The reinforcing impact of the nanoclay was exploited to a greater degree in the presence of the compatibilizer.     

Stimuli-responsive poly(ethylene oxide)-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) triblock copolymers and complexation with poly(acrylic acid) at low pH

The self-organization of the double hydrophilic triblock copolymer poly(ethylene oxide)-b-poly(2-vinylpyridine)-b-poly(ethylene oxide), PEO-b-P2VP-b-PEO, was investigated in dilute aqueous solution under several experimental conditions using turbidimetry, as well as static and dynamic light scattering. As a result of the temperature-sensitive properties of the end PEO blocks and the p H-responsive properties of the middle P2VP block, the formation of large star-like micellar nanostructures is observed at high p H, while at low p H, but in the presence of salt and at high temperature, flower-like micelles are formed. Moreover, the viscosimetric and dynamic light scattering studies at low p H revealed that micelle-like nanostructures are formed upon mixing the triblock copolymer with poly(acrylic acid), PAA, due to hydrogen bonding interpolymer complexation.     

SIMS depth profiling of polymer blends with protein based drugs

We report the results of the surface and in-depth characterization of two component blend films of poly(l-lactic acid) (PLLA) and Pluronic surfactant [poly(ethylene oxide) (A) poly(propylene oxide) (B) ABA block copolymer]. These blend systems are of particular importance for protein drug delivery, where it is expected that the Pluronic surfactant will retain the activity of the protein drug and enhance the biocompatibility of the device. Angle dependant X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) employing an SF₅⁺ polyatomic primary ion source were both used for monitoring the surfactant's concentration as a function of depth. The results show an increased concentration of surfactant at the surface, where the surface segregation initially increases with increasing bulk concentration and then remains constant above 5% (w/w) Pluronic. This surface segregated region is immediately followed by a depletion region with a homogeneous mixture in the bulk of the film. These results suggest the selection of the surfactant bulk concentration of the thin film matrices for drugs/proteins delivery should achieve a relatively homogeneous distribution of stabilizer/protein in the PLLA matrix. Analysis of three component blends of PLLA, Pluronic and insulin are also investigated. In the three component blends, ToF-SIMS imaging shows the spatial distribution of surfactant/protein mixtures. These data are reported also as depth profiles.