Reinforcing network structure: Analysis of the phase morphology and mechanical properties of polymer blends [poly(methyl methacrylate)/poly(ϵ‐caprolactone)] with the addition of a third polymer [poly(vinyl chloride)]

A thin matrix network structure of poly (vinyl chloride), poly(?‐caprolactone), and in situ formed poly(methyl methacrylate) (PMMA) was synthesized. The structure was observed with scanning electron microscopy. The dissolution test suggested that a simple method to generate high rates of crosslinking at a lower temperature was obtained. The relationship of the phase morphology and mechanical properties of the blends was studied, and a reinforced material of PMMA was obtained. The obvious increase in the mechanical properties and the reinforcing effect were attributed to the formation of crosslinking and the network structure in the blend. The glass‐transition temperatures, obtained by DSC, suggested confined thermal behavior of PMMA chains restricted by a crosslinking system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. I. Miscibility,curing behavior,and glass‐transition temperatures

The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride), with different chemical structures and MWs on the miscibility, cured‐sample morphology, curing kinetics, and glass‐transition temperatures for styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems were investigated by group contribution methods, scanning electron microscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis, respectively. Before curing at room temperature, the degree of phase separation for the ST/UP/LPA systems was generally explainable by the calculated polarity difference per unit volume between the UP resin and LPA. During curing at 110°C, the compatibility of the ST/UP/LPA systems, as revealed by cured‐sample morphology, was judged from the relative magnitude of the DSC peak reaction rate and the broadness of the peak. On the basis of Takayanagi's mechanical models, the effects of LPA on the final cure conversion and the glass‐transition temperature in the major continuous phase of ST‐crosslinked polyester for the ST/UP/LPA systems was also examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3369–3387, 2004     

Thermal and dynamic mechanical properties of γ‐ray‐cured poly(methyl methacrylate) used as a dental‐base material

In this study, γ rays were used for the first time to cure dental‐base material. The effect of the radiation dose on the thermal and rheological properties of poly(methyl methacrylate) (PMMA) used as a dental‐base material was investigated. The commercial powder and liquid material (heat‐curing‐grade) were mixed and polymerized at 60 and 70°C in a constant‐temperature water bath for 30 min and then were cured by γ rays, with total doses of 7.5, 15, 22.5, 30, 45, 52.5, 360, and 2160 krad. For each sample, the viscosity‐average molecular weights were measured, and no significant differences were observed of total dose on molecular weights. A thermal investigation with differential scanning calorimetry showed an exothermic peak in the thermograms of samples that were not completely polymerized and crosslinked. The rheological nature of the samples was studied with dynamic mechanical analysis. A comparison of properties of γ‐ray‐cured samples and those cured by other methods revealed γ curing to be a superior method for producing high‐molecular‐weight homogenous polymers with low porosity and crosslinking. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1291–1296, 2001     

Multifunctional formaldehyde resins as curing agent for epoxy resins

Formaldehyde resins (FR) at 1/1/2 molar ratios of monomers (Cl‐phenol/amino monomers/p‐formaldehyde) were synthesized under acid catalysis. The obtained resins were characterized using elemental analysis, FTIR and RMN spectroscopic methods, being used as crosslinking agents for epoxy resin formulations. The curing of epoxy resins with FR were investigated. The glass transition temperature (T_g) and decomposition behavior of crosslinked resins were studied by differential scanning calorimetry (DSC) and thermogravimetric (TGA) techniques. All DSC scans show two exothermic peaks, which implied the occurrence of cure reactions between epoxy ring and amine or carboxylic protons, in function of chemical structures of FR. The crosslinked products showed good thermal properties, high glass transitions, and low water absorption. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Differences in curing behavior of cocured and IPN materials

This study addressed the blending and cocuring of resole and epoxy, using NaOH and 4,4′‐diaminodiphenylmethane as curing agents. IR band shifts regarding the molecular interactions were investigated with FTIR. Exothermic peak shifts during cocuring reactions were studied with dynamic DSC. Viscosity increases were measured with a Brookfield LVT viscometer at 100°C. The dynamic mechanical properties of the cocured samples were investigated using rheometric dynamic spectroscopy (RDS). Experimental results revealed that the molecular interactions between resole and epoxy resulted in good compatibility as shown by the single damping peak in the RDS curve and the single glass transition for each cocured sample. Also apparent were accelerated curing rates, leading to shifts of the exothermic peaks to lower temperature and faster viscosity increases. Nevertheless, enhanced gel fractions and increased glass‐transition temperatures (T_g) of the samples were generally observed for this cocured system. The average molecular weight between crosslinked points calculated for the cocured materials also showed much less than the two components. These curing behaviors were quite different from those of the Interpenetrating Polymer Network (IPN) materials, which usually indicated lowered gel fractions, decreased T_g, and higher average molecular weight between crosslinkings than for components. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 963–969, 2001     

Synthesis and properties of a novel bismaleimide resin containing 1,3,4‐oxadiazole moiety and the blend systems thereof with epoxy resin

A new bismaleimide monomer, 2‐((4‐maleimidophenoxy)methyl)‐5‐(4‐maleimidophenyl)‐1,3,4‐oxadiazole (Mioxd), was designed and synthesized. The chemical structure of the monomer was confirmed by means of Fourier transform infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (¹H NMR) spectroscopy and elemental analysis, and its thermal properties were characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Mioxd as a reactive modifier was blended with epoxy resin based on bisphenol A diglycidyl ether (DGEBA) in weight ratio of 5, 10, and 15%, using 4,4′‐diaminodiphenyl sulfone (DDS) as hardener. The effect of Mioxd addition on the cure behavior and thermal properties of the blend resins was studied by DSC, TGA, and dynamic mechanical analysis (DMA). DSC investigations showed that the main exothermic peak temperature (T_p) of the blend systems did not obviously shift with increasing Mioxd content whereas a new shoulder appeared and gradually grew on the high temperature side of the exothermic peak. The results of DMA measurements exhibited the glassy storage modulus (G') and glass transition temperatures (T_g) increased as the Mioxd content was increased, the cured blends investigated were miscible and no phase separation occurred. Further, the thermal decomposition temperature first decreased and then increased, but the char yield at 600°C increased with an increase in Mioxd content. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Synthesis and properties of copolymer epoxy resins prepared from copolymerization of bisphenol A,epichlorohydrin, and liquefied Dendrocalamus latiflorus

Dendrocalamus latiflorus Munro (ma bamboo) was liquefied in phenol and polyhydric alcohol (polyethylene glycol/glycerol cosolvent) with H₂SO₄ as catalyst. Liquefied bamboos reacted with bisphenol A and epichlorohydrin were then employed to prepare copolymer epoxy resins. The curing property and thermal property of copolymer epoxy resins were investigated. The results showed that copolymer epoxy resins could cure at room temperature after the hardener was added, and its curing process was an exothermic reaction. Comparison showed that copolymer epoxy resins prepared with phenol‐liquefied bamboo as raw material had higher heat released than those prepared with polyhydric alcohol‐liquefied bamboo during curing. The DSC analysis showed that heat treatment could enhance the crosslinking of copolymer epoxy resins cured at room temperature. However, resins prepared with polyhydric alcohol‐liquefied bamboo had a lower glass transition temperature. The TGA analysis showed that resins prepared with phenol‐liquefied bamboo had better thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology and thermal properties of liquid crystal p‐PAEB/n‐propyl methacrylate copolymers

The copolymers of p‐phenylene di{4‐[2‐(allyloxy) ethoxy]benzoate} (p‐PAEB) with n‐propyl methacrylate (PMA) were synthesized. The liquid crystalline behavior and thermal properties of copolymers were studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X‐ray diffractometer (XRD), and torsional braid analysis (TBA). The results of XRD, POM, and DSC demonstrate that the phase texture of copolymers is affected by the composition of liquid crystal units in copolymers. The POM and XRD reveal that liquid crystal monomer (p‐PAEB) and copolymers of p‐PAEB with PMA are all smectic phase texture. The dynamic mechanical properties of copolymers are investigated with TBA. The results indicate that the phase transition temperatures and dynamic mechanical loss peak temperature T_p of copolymers are affected by the composition of copolymers and liquid crystal cross networks. The maximal mechanical loss T_p is 114°C and is decreased with added PMA. The behaviors of phase transition are affected by the crosslinking density, and it is revisable for lightly crosslinking LC polymer networks, but it is nonreversible for the densely crosslinking of LC polymer networks. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Energy Release in Isothermally Stretched Silicate Glass fibers

Three types of silicate glass fibers are annealed, simultaneously stretched in the glass transition region for certain time lengths, then slowly cooled to room temperature under load, and subsequently scanned by differential scanning calorimetry (DSC). During the DSC scanning, a broad exothermic peak (representing energy release) occurs in the stretched fibers well below the glass transition temperature, while it does not occur in the non-stretched fibers. The peak indicates that mechanical stretching can result in an energy enhancement in the fibers. It also confirms that the energy released during reheating of the fibers formed using an industrial continuous fiber drawing process originates not only from thermal quenching but also from mechanical stretching. However, the mechanical stretching-induced energy is much lower than the thermal hyperquenching-induced energy in glass fibers. The effect of annealing temperature and time on the energy release behavior is discussed in terms of viscoelasticity.     

Physical properties and structure of silk. III. The glass transition and conformational changes of tussah silk fibroin

The glass transition, crystallization, and α–β transition of the Tussah silk fibroin were studied by means of DSC (differential scanning calorimetry) and infrared spectroscopy. The endothermic shift due to the glass transition was observed at 162°C. The endothermic peak at 220°C was attributed to the α–β conformational transition from the infrared spectra. The exothermic peak due to the crystallization occurred at 230°C.     

Vulcanization of EPDM rubber compounds with and without blowing agents: Identification of reaction events and TTT‐diagram using DSC data

Vulcanization of industrial‐like ethylene propylene diene termonomer rubber compound is studied using a differential scanning calorimetry (DSC). The analysis starts with DSC information to obtain the total transformation heat, followed by an isothermal‐dynamic temperature ramp that captures diffusion‐controlled reaction kinetics. The vulcanization is modeled by an auto‐catalytic Kamal–Sourour model, complemented with a Kissinger model for the prediction of one energy of activation, DiBenedetto's equation for the glass transition temperature, and adjusted reaction constants to include diffusion mechanisms. Two rubber formulations, with and without blowing agents, containing crosslinking agents, primary and secondary accelerators, activators, promoters, and processing aids are studied. The identification and separation of multiple reaction events, occurring during crosslinking of the compound without a blowing agent, is done through a 2^k design of experiments. Time–temperature–transformation (TTT) diagrams are calculated, integrating the kinetic model, thereby delineating processability windows, providing avenues for optimization, design, and online processing control. According to the kinetics and the TTT diagrams, the blowing agent induces several differences to the vulcanization reaction: decreases reaction temperatures while increasing reaction heats. It eliminates the exothermic peak before vulcanization and decreases the fully cured resin's glass transition temperature. Therefore, the presence of the blowing agent drives a shift in the vitrification line, resulting in a reduced operational window. POLYM. ENG. SCI., 55:2073–2088, 2015. © 2014 Society of Plastics Engineers     

Characterization of poly(lactic acid) multifilament yarns. I. The structure and thermal behavior

The structure and thermal behavior of poly(lactic acid) (PLA) multifilament yarns were studied by complementary techniques of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide angle X‐ray diffraction (WAXD). As for PLA filaments, notable differences in the WAXD patterns, DSC curves, and FTIR spectra were observed. The combination of the WAXD and FTIR results showed that PLA samples with different crystallinity contain α‐form crystal structure. The FTIR spectra of the filaments were analyzed to study their crystallinity and crystal structure. The total crystallinity of the PLA filaments was obtained from the percent area loss of the skeletal amorphous band at 955 cm^?1. Crystalline fraction from FTIR and DSC were comparable with each other. The C?O stretching region, which is sensitive to crystallization and dipole–dipole interactions, was evaluated to provide information about chain conformers and crystallinity of the samples. Depending on the processing conditions, double melting peaks were observed in the DSC curves of the samples. This exhibited the structural reorganization of the crystal phase during heating affected by heating and cooling rate. In the DSC curves of the nearly amorphous multifilament yarn, the exothermic peak observed right above the glass transition temperature (T_g) indicated two relaxed and deformed amorphous regions. However, the multifilament yarn with higher crystallinity showed just endothermic melting peak after its glass transition. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and thermal properties of bismaleimide blends based on hydroxyphenyl maleimide

N‐(4‐hydroxyphenyl)maleimide was melt‐blended with the glycidyl ether of bisphenol‐A and various mole percentages of 4, 4′‐(diaminodiphenylsulfone) bismaleimide. The cure behaviour of the resins was evaluated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The blends showed distinct reductions in the onset of cure (T_o) and peak exothermic (T_exo) temperatures. The blends cured at low temperatures exhibited glass transition temperatures (T_gs) higher than the cure temperatures. The cured blends showed high moduli, glass transition temperatures in excess of 250 °C and good thermal stabilities up to 400 °C. Copyright © 2005 Society of Chemical Industry     

The effect of kevlar fiber reinforcement on the curing,thermal, and dynamic‐mechanical properties of an epoxy/anhydride system

Curing, thermal, and dynamic‐mechanical relaxational behavior of an epoxy/‐anhydride resin and a Kevlar‐fiber/epoxy composite were compared. Reinforcement by Kevlar fibers had a catalytic effect on the curing reaction. Reinforced formulations produced higher extents of reaction than neat formulations at the same curing time. Curing kinetics was also studied by means of DSC heating scans. When the Kevlar content increased, the heat flow curves and the exothermic peak temperature shifted significantly to lower temperatures. The glass transition temperature of the matrix also decreased as the Kevlar content increased. Postcuring reduced the differences between the neat and reinforced formulations. Loss tangent and storage modulus versus frequency master curves were obtained from isothermal dynamic‐mechanical measurements. The effect of fiber addition on the main dynamic‐mechanical relaxation was analyzed with a simple mechanical model.     

Preparation of a nanosilica‐modified negative‐type acrylate photoresist

A new type of negative photoresist, which incorporated nanosized silica into a photosensitive acrylic resin, was developed. First, free‐radical polymerization was employed to synthesize the acrylic resin, poly[methyl methacrylate/methacrylic acid/3‐(trimethoxysilyl) propyl methacrylate], and then a silica precursor, prepared by hydrolysis and condensation of tetraethoxysilane in a sol–gel process, was introduced into the as‐formed resin solution. After the addition of photosensitive monomers and photoinitiators, a negative‐type organic–inorganic photoresist was produced. The morphology of the UV‐cured photoresist, as observed by field emission scanning electron microscopy, indicated that the size of the silica domain in the material could be reduced from 300 to about 50 nm by appropriate dosage of 3‐(trimethoxysilyl) propyl methacrylate. Thermogravimetric analysis, dynamic mechanical analysis, differential scanning calorimetry, and thermal mechanical analysis were used to evaluate the thermal and dimensional stabilities of the cured photoresists. It was found that the thermal decomposition temperature and glass‐transition temperature increased, whereas the thermal expansion coefficients before and after the glass transition decreased, with increasing silica content. The incorporation of 3‐(trimethoxysilyl) propyl methacrylate also enhanced the thermal and dimensional stabilities; however, the level of enhancement was moderate for the thermal decomposition temperature and thermal expansion coefficient and low for the glass‐transition temperature. In addition, a photoresist coated on a copper substrate demonstrated high hardness (5H) and strong adhesion (100%) with a resolution of 30 μm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Polyoxyethylenic macromers from polyoxyethylene monomethyl ethers and isocyanatoethyl methacrylate. Synthesis and characterization of copolymers with styrene and methyl methacrylate, obtained through bulk, solution and soap-free emulsion polymerizations

Polyoxyethylenic (POE) macromers were prepared from polyoxyethylene methyl ethers and isocyanatoethyl methacrylate and characterized by ¹³C and ¹H nuclear magnetic resonance spectroscopy. Copolymers with styrene and methyl methacrylate (MMA) were obtained from these macromers upon free-radical initiation under various conditions (solution, bulk, soap-free emulsion) and some physical properties were studied (e.g. glass transition temperatures, stability of latex). Phase separation was observed in some copolymers with MMA as determined through dilatometry. Polystyrene latices, prepared without any emulsifying agent other than POE macromers themselves, were stable in the presence of high electrolyte concentrations.     

Studies on physical properties and structure of silk. Glass transition and crystallization of silk fibroin

Amorphous silk fibroin with random coil conformation shows endothermic and exothermic peaks and endothermic shift on the DSC (differential scanning calorimetry) curve. The endothermic shift observed at 175°C was due to the glass transition. The exothermic peak at 212°C is recognized to be the crystallization, which later was confirmed by x-ray diffraction pattern. The endothermic peak at 280°C is shown to be the degradation.     

Cyanuric Acid/Epichlorohydrin Energetic Prepolymers

In this work new energetic prepolymers are synthesised and characterised. The structure of the prepolymers exhibits the 1,3,5‐s‐triazine ring with lateral chains derived from the epichlorohydrin ring opening. The chlorine atoms in these precursors are here substituted by azido groups. The presence of these groups was confirmed by FTIR and ¹H NMR spectroscopy and elemental and thermal analysis. OH group content in the energetic prepolymers was found slightly lower than expected having in view the used inert precursors, while molar mass values were similar. Whereas the precursors show an endothermic thermal decomposition, the synthesised prepolymers show a clear exothermic thermal decomposition in DSC analyses. Due to the presence of the 1,3,5‐s‐triazine ring, the exothermic peaks were observed in a wide range of temperatures. The measured glass transition temperatures vary from −15.5 °C to −43.3 °C. High densities and a wide range of viscosities were found.     

Crosslinkable deoxidizing hybrid adhesive of epoxy–diacid for electrical interconnections in semiconductor packaging

For electrical interconnections in semiconductor packaging, epoxy‐based pastes have recently attracted considerable interest due to their excellent adhesion to various substrates and their reasonable electrical and mechanical properties, especially when combined with deoxidizing agents (to remove metallic oxides). Here, epoxy–diacid‐based hybrid pastes were examined to achieve a deoxidizing capability for eliminating Sn‐based solder oxides and adhesion between microchip and substrate as a one‐step process. Onset, exothermic peak and end temperatures of the reaction between epoxy and diacids were systematically probed using DSC, rheometry and Fourier transform infrared (FTIR) spectroscopy. The last moment of the adhesive reaction during heating substantially enhanced the thermal and mechanical properties of the epoxy–diacid adhesive despite the absence of exothermic enthalpy detected by DSC. The glass transition temperature (T_g) and Young's modulus gradually decreased as a function of aliphatic chain length of diacids except when the length was extremely short and voids were produced. Soldering (wetting) and deoxidizing capabilities of the hybrid adhesive were observed via optical microscopy and FTIR. The correlation between the reaction, T_g, conversion and viscosity was also investigated. Lastly, complete wetting and electrical interconnection with good mechanical robustness were achieved for a commercial chip/substrate set by flip‐chip bonding. © 2018 Society of Chemical Industry     

A pair of benzoxazine isomers from o-allylphenol and 4,4′-diaminodiphenyl ether: Synthesis,polymerization behavior,and thermal properties

An allyl-containing bifunctional benzoxazine is synthesized from o-allylphenol, 4,4′-diaminodiphenyl ether, and formaldehyde, followed by isomerization in the presence of chlorotris(triphenylphosphine)rhodium(I)/triethylsilane catalytic system yielding a propenyl-containing benzoxazine, and the chemical structures of the two isomers are confirmed. In the thermal activated polymerization, both isomers undergo the oxazine ring-opening polymerization and the radical olefin polymerization with the formation of the corresponding polybenzoxazines, but only one exothermic peak is shown on each of their dynamic differential scanning calorimetry (DSC) curves. After isomerization of allyl into propenyl, the onset and maximum polymerization temperatures decrease, but the temperature range covered by the DSC exothermic peak broadens. Consequently, the structures of the resultant polybenzoxazines are different, and some properties are obviously different, for example, the storage modulus decreases, but the glass transition temperature increases, and the thermal stability is slightly enhanced.