A new viscoplastic model and experimental characterization for thermosetting resins

Resins as matrix materials for structural composites show nonlinear rate-dependent mechanical behaviors. In the present work, a new viscoplastic constitutive equation based on a potential function is proposed to predict the mechanical response of an epoxy matrix to any three-dimensional loading condition. The proposed potential function is a combination of the second and third invariants of the deviatoric stress tensor as well as the first invariant of the stress tensor, i.e. the hydrostatic stress. Series of tensile and shear constant-rate straining tests were performed on epoxy resin specimens up to the fracture. Under shear loading, the nonlinearity of the stress-strain curve and the rate dependency of the initial modulus and strength are more significant than that under tensile loading. The viscoplastic model parameters are derived from the experimental data, and the fracture patterns of the specimens under tensile and shear loadings are studied. Further, the model predictions are compared with a known rate-dependent model to show the accuracy of the presented model.     

Design and synthesis of readily degradable acyloxysilane dendrimers

Two types of dendrimers with AB₂ branching, one with acyloxysilanes at the branching position (V type) and the other at the non-branching position (Y type), were synthesized using hydrosilylation with chlorosilanes followed by heterofunctional condensation with olefin-functional carboxylic acids, and examined as readily degradable template materials. The V type dendrimer was much more susceptible to ligand redistribution with chlorosilanes during preparation, whereas the Y type was less. The acyloxysilane linkages in these dendrimers could be cleaved readily by alcoholysis or hydrolysis on demand, making for suitable templates.     

Thermally reversible nanostructured thermosetting blends modified with poly(ethylene-b-ethylene oxide) diblock copolymer

The main aim of this research was the generation of new intelligent materials, in this case thermoreversible material, based on epoxy matrix modified with semi-crystalline block copolymers. In this study, the epoxy system based on a diglycidyl ether of bisphenol-A (DGEBA), was cured with a stoichiometric amount of an aromatic amine hardener, 4,4’-methylene bis (3-chloro-2,6-diethylaniline) (MCDEA). A diblock copolymer of polyethylene-b-poly(ethylene oxide) (PEOE) was used as self-assembly agent. Optical properties of the samples modified by addition of PEOE were studied by using transmission optical microscope (TOM) equipped with a hot stage. Additionally, morphology generated in the sample was studied by atomic force microscopy (AFM).     

Thermally degradable maleimides for reworkable adhesives

New thermosetting materials were developed for reworkable adhesive applications by introducing acetal ester groups as thermally degradable linkages into maleimide compounds. The synthesis of compounds containing maleimide functionality and acetal ester linkages was conducted by a one‐step neat reaction from commercially available materials. The polymerization process and thermal degradation of the synthesized materials were studied. It was found that the acetal ester linkage degraded rapidly above 225 °C, and introduction of this linkage into the adhesive formulation led to improved reworkability of adhesively bonded substrates. A mechanism for reworkability was proposed based on the insight provided by experimental and modeling work. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1073–1084, 2009     

Protein encapsulation and release from degradable sugar based hydrogels

Acid labile sugar based hydrogels have been synthesized using a commercially available acid sensitive cross-linker, 3,9-divinyl-2,4,8,10-tetraoxaspiro-[5,5]-undecane. The monomers used for polymerization are N-isopropylacrylamide (NIPAM) and d-gluconamidoethyl methacrylate (GAMA), which when polymerized in the presence of the acid labile cross-linker yield hydrogels that can swell and degrade under acidic conditions, making them ideal for drug delivery. The hydrogels are synthesized using either a photo-initiator, Irgacure-2959 or a conventional initiator, potassium persulfate. The hydrogels obtained by photo-polymerization exhibit defined and unique microstructures, when analyzed by scanning electron microscopy (SEM). The swelling capacity and protein release from the hydrogels as a function of pH is studied. The protein release from the hydrogels is found to be dependent upon the degree of cross-linking and the pH of the environment.     

Soluble and degradable polyimides with phenyl-2-pyridyl ether structure: Synthesis and characterization

A diamine monomer o-phenylenedioxybis(5-amino-2-pyridine) was synthesized via reduction of a dinitro compound o-phenylenedioxybis(5-nitro-2-pyridine), producing a series of new polyimides from this diamine and various commercially available aromatic dianhydrides via conventional two-stage processes. The resulting polyimides are able to form tough and transparent films, with decomposition temperatures in the range of 529–551 °C, and can be dissolved in organic polar solvents. Meanwhile, these polyimides can be degraded in a hydrazine hydrate medium, a degradation mechanism proposed by analyzing the degradation products suggests that the degradable properties could be attributed to the phenyl-2-pyridyl ether structure in the polymer. In addition, the transformation of the compound structure from dinitro compound to damine monomer in the synthetic process is discussed in respect to X-ray structure.     

Synthesis and thermal properties of the thermosetting resin based on cyano functionalized benzoxazine

A novel thermosetting resin based on cyano functionalized benzoxazine (BZCN) has been synthesized from 2,6-bis(4-diaminobenzoxy)benzonitrile phenol and formaldehyde by solution reaction. The structure of the monomer is supported by FTIR, ¹H NMR and ¹³C NMR spectra, which have exhibited that the reactive benzoxazine rings and cyano group exist in the molecular structure of BZCN. The curing reactions of BZCN are monitored by the disappearance of the nitrile peak and the tri-substituted benzene ring that is attached with oxazine ring peak at 2231 and 930 cm⁻¹, respectively. The complete cured materials could achieve char yields up to 70% at 800 °C in nitrogen atmosphere, above 64% at 600 °C in air (20% oxygen) environments and the glass transition temperature up to 250 °C. The thermally activated curing polymerization reaction of BZCN follows multiple polymerization mechanisms via the ring-opening polymerization of oxazine rings and the triazine ring-formation of cyano groups, which contribute to the stability of the polymer.     

A pressure vessel for studying gas foaming of thermosetting polymers: sorption,synthesis and processing

We herein report the design of an apparatus for studying the concurrent chemo-physical processes occurring during gas foaming of thermosetting polymers. In particular, to address the recent interest in combining the gas (physical) foaming with the classical (chemical) polyurethane foaming, a novel instrumented pressure vessel was designed for investigating: i) gas sorption under high pressure on the different reactants, kept separate; ii) synthesis under high gas pressure, upon mixing and iii) foaming upon release of the pressure. The design of the new pressure vessel relies on two key features. From the processing side, we make use of a rubber impeller to keep the two reactants separate during gas sorption and to allow for an efficient mixing at the end of the sorption stage. From the analytic side, we utilized a sapphire window beneath the sample holder to use diffuse reflectance near-infrared spectroscopy to measure both the amount of sorbed gas and the reaction kinetics under gas pressure. Preliminary results are reported for the polyol-isocyanate/CO₂ system.     

Functionalization of polyhedral oligomeric silsesquioxanes with bis(hydroxyethyl) ester and preparation of the corresponding degradable nanohybrids

One novel difunctionalized polyhedral oligomeric silsesquioxanes（POSS） derivative was designed and synthesized by a convenient method with high yield.¹H NMR and FT-IR characterizations suggested that Michael addition reaction successfully took place between 2-hydroxyethyl acrylate（HEA） and aminopropylisobutyl POSS（POSS-NH₂） under mild conditions,which finally formed bi（hydroxyethyl） ester-functionalized POSS derivatives（BH-POSS）.Due to the similar functional groups and high reactivity,BH-POSS could be easily incorporated into the main-chain of biodegradable aliphatic-aromatic copolyesters PBTL via in situ melt polycondensation to prepare corresponding degradable nanohybrids with high mechanical properties.     

Strong interfacial modified aramid fabric reinforced degradable thermosetting composites: reinforcing and tribological effects

In this work, dense molybdenum disulfide (MoS₂) nanosheets were grown onto polydopamine (PDA) functionalized aramid fabric (AF) surface via a simple hydrothermal method to improve the wettability between AF surface and polyhexahydrotriazine (PHT) resin, thus resulting in stronger AF/resin interfacial bonding. The PDA-assisted surface modification on AF generated a high active interface allowing the nucleation and subsequent growth of MoS₂. Moreover, this nanosheet-coated reinforcement fiber enabled the viscous liquid of resin precursor to spread over and form intimate contact with its surface, which eventually promoted the formation of strong interfacial bonding between AF-MoS₂ and cured resin matrix. In addition, the enhanced interfacial bonding between the reinforcement and matrix generated stable mechanical interlock within the resulting AF-MoS₂/PHT composites, and thus, contributed better thermal stability, higher tensile strength, and tribological properties. Compared with AF/PHT composites, the tensile strength and elongation at break of the AF-MoS₂/PHT composites increased by 32.5% and 50%, and the average friction coefficient and wear rate of AF-MoS₂/PHT composites decreased by 43.9% and 86.3%, respectively. Furthermore, the composites realized the non-destructive recovery of expensive AF at 25 °C. Overall, our study demonstrates a dependable strategy to construct the recyclable AF-MoS₂/PHT composites, which exhibit valuable applications in tribology.     

以纤维素材料为基质的降解塑料的研究进展

本文详述了以天然高分子纤维素材料为基质的降解塑料的发展。纤维素材料由于其来源丰富,有良好的反应性,优异的生物降解性,无毒性等,因而可用来制备降解塑料．其开发和应用是解决目前世界范围内的“白色污染”的一条理想途径．     

Thermally Responsive Materials for Bioimaging

The last decade has witnessed multiple thermally responsive materials emerge as a significant class of stimuli‐responsive materials. These materials are elaborately designed and exert interesting properties. Herein, an overview of thermally responsive materials with respect to design strategies, fabrication procedures, and their applications is presented. Recently reported thermally responsive materials are highlighted. Then, applications of thermally responsive materials in bioimaging are summarized.     

高分子载体材料在药用微球中的应用及进展

微球给药系统可实现药物的靶向给药,其在药物的缓控释放等方面表现出良好的应用前景,因而成为近年来药剂学领域的研究热点之一。高分子载体材料（Polymer Carriers）是随着药物学研究、生物材料科学和临床医学的发展而新兴起来的,是一类具有优良生物相容性、生物可降解性、可加工性,经过安全性评价并应用于药物制剂的高分子辅...     

Adhesion of an aromatic thermosetting copolyester with copper foils

Copper foils have been widely used in microelectronic devices. Adequate adhesion between copper foils to various substrates, such as Si, SiO₂, polyimide, is crucial to high performance of these devices. The adhesion between a new high temperature adhesive, aromatic thermosetting copolyester (ATSP), and various copper foils, namely, zinc(Zn)‐coated copper foil, copper foil and nickel (Ni)‐coated copper foil was characterized by a 90° peel strength test. It was found that the peel strength of Zn‐coated copper foil to ATSP was 1050 N/m, which was more than three times higher than copper foil and five times that of Ni‐coated copper foil. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS) studies indicated that this higher adhesion results from the stronger mechanical interlocking due to the rougher surface of Zn‐coated copper foil, and from chemical reactions at the interface which occur during the curing process of ATSP on the Zn‐coated copper surface. In contract to the adhesive failure at the ATSP/Cu and ATSP/Ni interfaces, the failure mechanism of ATSP/Zn is both cohesive and adhesive. Copyright © 2004 John Wiley & Sons, Ltd.     

Polyethersulfone‐epoxy terminated materials as thermosetting resins for microelectronic devices

A totally aromatic polyether/sulfone resin (PES‐E) was synthesized and tested as an insulating glue in the construction of a Chip‐on‐Chip (CoC) device. PES‐E, essentially constituted of open‐chain macromolecules of low molecular mass (M _n of about 3000 Da) with hydroxy and/or epoxy end‐groups, has a glass transition temperature of about 150 °C and is subject to crosslinking at temperatures higher than 320 °C. A CoC device was assembled using a five‐step process by interposing a layer of PES‐E between two chips. After curing, SEM cross section images showed a homogeneous crosslinked resin layer well stuck (flick and shear tests) to both chips. The chemical structure of the chains and the hydroxy/epoxy end‐groups ratio were optimized to obtain a crosslinked material with good adhesion and sufficient flexibility to avoid cracking during assembly and use. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5682–5689, 2009     

Synthesis of Thermally Stable MCM-41 at Ambient Temperature

A new process to synthesize thermally stable mesoporous molecular sieves of MCM-41 structure based on delayed neutralization at ambient temperature was investigated. All samples synthesized by this new method have BET surface areas of about 1100m²/g and possess high thermal stability up to 900°C. Higher crystallinity and less lattice constriction after calcination were observed for samples with a longer aging period. Those samples with aging time longer than 10 days exhibited four characteristic XRD peaks of MCM-41 both before and after calcination at 560°C. The N₂ adsorption-desorption isotherms of the calcined samples showed larger average pore size and more homogenous pore size distribution. The method was also successfully applied to the synthesis of MCM-41 with different surfactants of hydrocarbon length with 10–18 carbons and proves to be a simple route for obtaining thermally stable MCM-41 at room temperature.     

Polycyclic phosphonate resins: Thermally cross-linkable intermediates for flame-retardant materials

Two series of polycyclic phosphonates were synthesized by reacting p-substituted phenol–formaldehyde resins with excess phosphonic dichlorides under dilute conditions in a polar aprotic solvent. MALDI–TOF was used to detect the absolute masses of different species formed under these conditions. The presence of phosphorus-containing species was also confirmed by ³¹P-NMR. The polycyclics were subjected to ring-opening polymerization simultaneously with a transesterification reaction with commercial polycarbonates in order to cross-link the polymers and to impart flame retardancy to the final thermosetting materials. Thermal properties of the polycarbonates containing phosphonate moieties were determined by thermogravimetric analysis and differential scanning calorimetry techniques. Percent char yields of the final thermosetting materials were considerably higher than that of the linear polycarbonates. Polycyclic phosphonates, therefore, can potentially be used to impart flame retardance to polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1911–1918, 1998