Glass Transition Temperature In Range Research Articles

A novel low colored and transparent shape memory copolyimide and its durability in space thermal cycling environments

Recently, shape memory polymers (SMPs) with high optical transmittance have been paid great attentions to endow the flexible optoelectronics with shape memory functions. Herein, a low colored and transparent shape memory copolyimide (SMcoPI) is obtained by suppressing the charge transfer complex interactions. The optical transmittance of the synthesized SMcoPI film could reach at ∼86% at the wavelength of 450 nm, far higher than the nearly zero optical transmittance of yellow and brown Kapton H. The better optical transparency could be attributed to the loose molecular chain arrangements induced by the meta-substituted groups and flexible ether linkages. The glass transition temperature (Tg) range of the synthesized SMcoPI films is from 179 °C to 220 °C, which is higher than that of reported optically transparent SMPs. The effective decomposition temperature at the weight loss of 5 wt% is 517 °C, showing excellent thermal stability. The SMcoPI also demonstrated good shape memory behaviors with high shape recovery ratio (Rr, >96%) and shape fixity ratio (Rf, >97%). In addition, the SMcoPI could maintain high optical transmittance, good thermostability and excellent shape memory behaviors after the ground-stimulated space thermal cycling test for 250 h. The synthesized SMcoPI has application potentials in high temperature areas or optoelectronic devices.

Nonmigratory internal plasticization of poly(vinyl chloride) via pendant triazoles bearing alkyl or polyether esters

ABSTRACTBranched and linear nonmigratory internal plasticizers attached to PVC by a pendant triazole linkage were synthesized and investigated. Copper‐free azide‐alkyne thermal cycloaddition was employed to covalently bind triazole‐based phthalate mimics to PVC. To systematically investigate the effect of plasticizer structure on glass transition temperature, several architectural motifs were explored. Free volume theory was considered when designing many of these internal plasticizers: hexyl‐tethers were utilized to generate additional space between the triazole‐phthalate mimic and the polymer backbone. Miscibility of these triazole‐plasticizers in PVC is important: variation of the ester moieties on the triazole possessing alkyl and/or poly(ethylene oxide) chains produced a wide range of glass transition temperatures (Tg): from anti‐plasticizing 96 °C, to highly efficient plasticized materials exhibiting Tg values as low as −42 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2397–2411

Preparation of Sound Absorption Material Based on Interpenetrating Polymer Network (PU/PMMA IPN)

Background: Polymer composites with interpenetrated polymer network (IPN) structure are widely used as sound and vibration damping materials due to their high viscoelastic properties within the glass transition temperature range. In this study, polyurethane (PU)/poly (methyl methacrylate) (PMMA)-based interpenetrating polymer network with different ratios of PU to PMMA (i.e. 85:15, 75:25, and 65:35) were prepared by in situ polymerization. Methods: The properties of as-prepared IPN and its components were evaluated by different scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and sound absorption. Tensile properties were also determined. As indicators of effective damping capability, viscoelastic parameters including loss factor (tan δ), glass transition temperature (Tg), and effective damping interval (tan δ > 0.3) were also determined. In order to determine the sound absorption coefficient in the prepared IPNs, a two-microphone impedance tube at the frequency of one octave was used. Results: The comparison of pure polymers (i.e. polyurethane and polymethyl methacrylate) and prepared IPNs indicated that the semi interpenetrated polymer network morphology was created through a broader range of tan δ in different IPNs. Incorporation of PMMA into polyurethane in the form of interpenetrating polymer networks enhanced the damping acoustic properties of the semi-IPNs due to the permeability of the two polymers. In the temperature range of -50 to 11 ˚C, both IPNs components showed high damping characteristics (tan δ ≥ 0.3). Conclusions: Evaluation of the results indicated that the blends are capable of exerting viscoelastic effects for damping and sound attenuation.

Investigating relaxation of glassy materials based on natural vibration of beam: A comparative study of borosilicate and chalcogenide glasses

The present work investigates the validity of using the frequency and decay rate of free-free beam vibration, which are measured by the impulse excitation technique (IET), to characterize the viscoelastic properties of glass in the temperature range of glass transition. Based first on the classical Burgers model, we show that the temperature-dependent flow viscosity of borosilicate glass, calculated from the measured frequency and amplitude decay rate of the flexural vibration, agrees very well with the existing data. While for chalcogenide glass, the same calculation approach does not render the similar agreement, and the reason probably lies in non-exponential effects. To comprehend the IET data in the temperature range of glass transition, we propose a simplified theoretical framework for describing the transition from the solid-like to liquid-like viscoelastic behavior and discuss the cause of difference of the rheology behaviors of these two types of glass based on the formulation of non-exponential relaxation.

Synthesis, characterization, and electroluminescent properties of indazole, pyrazole, and triazole/triphenylamine-based compounds

In this work, seven small molecular compounds named N,N-diphenyl-4-(2-phenylpyrimido [1,2-b]indazol-4-yl)aniline (1), N,N-diphenyl-4-(5-phenylpyrazolo [1,5-a]pyrimidin-7-yl)aniline (2), N,N-diphenyl-4-(5-phenyl- [1,2,4]triazolo [1,5-a]pyrimidin-7-yl)aniline (3), 4,4'-(pyrimido [1,2-b]indazole-2,4-diyl)bis (N,N-diphenylaniline) (4), 4,4'-(pyrazolo [1,5-a]pyrimidine-5,7-diyl)bis (N,N-diphenylaniline) (5), 4,4'-([1,2,4]triazolo [1,5-a]pyrimidine-5,7-diyl)bis (N,N-diphenylaniline) (6), N,N-diphenyl-4-(4-phenylpyrimido [1,2-b]indazol-2-yl)aniline (7) with donor-acceptor (D-A) structure were designed and synthesized by employing triphenylamine (TPA) as donor and indazole, pyrazole and/or triazole as acceptor. Systematic study and analysis on thermal, photophysical, electrochemical properties of all compounds were performed. All compounds exhibit good thermal and morphological stabilities with decomposition temperatures (Td) range from 270 to 462 °C, and glass transition temperatures (Tg) range from 78 to 127 °C. The investigation of photophysical properties of these compounds revealed that all these compounds are of high photoluminescence quantum yields (PLQY), particularly for compound 6, whose PLQY value was as high as 90.22%. To explore potential applications of these materials in organic light-emitting diodes (OLEDs), two devices with compounds 2 and 5 were fabricated. Both devices show excellent device performances with maximum current efficiency, maximum power efficiency and external quantum efficiency of 15.9 cd A−1, 10.4 l m W-1 and 8.4% for compound 2-based device and 10.1 cd A−1, 5.8 l m W-1 and 5.5% for compound 5-based device, respectively.

Thermopolarization Phenomena in the Temperature Range of Glass Transition of Amorphous Polydiethylsiloxane

The transition from the glass to the highly elastic state in polydiethylsiloxane (PDES) is not reflected on the temperature dependences of the relative permittivity, the dielectric loss tangent, and the specific volumetric electrical conductivity. But, the peak of the current of thermostimulated depolarization (TSD) is fixed in the temperature range of the transition to the highly elastic state. The peak of the TSD current at T ~ 130K indicates a continuous amorphous phase formation in the experimental conditions. The maximum value of the TSD current directly depends on the content of the amorphous phase in the polymer. The cooling of the polymer in an electric field reduces the magnitude of the peak. Exposure in the mesophase leads to an almost complete absence of thermopolarization effects near the glass transition temperature. This peak of the TSD current in the absence of preliminary polarization is characteristic, presumably, only for flexible-chain polymers where structural units have pyroelectric properties. Under certain conditions, PDES demonstrates itself as an active dielectric in the temperature range of 90 - 180K.

Influence of synthesis conditions on glass formation, structure and thermal properties in the Na2O-CaO-P2O5 system doped with Si3N4 and Mg

Oxynitride phosphate glasses and glass-ceramics were prepared using new synthesis routes for phosphate glasses. Materials were melted from pre-prepared glass samples in the system Na-Ca-P-O with addition of Mg and/or Si3N4 powders under different preparation conditions. The melting process was conducted at 1000–1500 °C either under air or nitrogen atmosphere to obtain materials with different nitrogen content. Their topography and structure were characterized by Confocal Microscopy, Scanning Electron Microscopy, X-ray powder diffraction and Raman and infrared spectroscopy techniques, while their chemical compositions were examined by Energy Dispersive X-ray spectroscopy (EDS). All materials prepared under nitrogen atmosphere were found to contain a relative low quantity of nitrogen and high amount of Nb leached from the crucible. The reaction with the Nb crucible was not previously observed for silicon-based oxynitride glasses. The synthesized materials form two groups: glasses and glass-ceramics. The first ones, were prepared under air and nitrogen atmospheres at temperatures up to 1400 °C, and were found to be amorphous and homogeneous. Raman and infrared spectroscopy measurements confirm the presence of amorphous phosphates in the synthesized materials. The samples of the second group were prepared at temperatures above 1400 °C and were found to be translucent and partially crystallized. They contain nanocrystallites of calcium and sodium phosphates including hydroxyapatite (HAp). The thermal properties of samples were studied by Differential Scanning Calorimetry (DSC). The obtained glass transition temperatures range from about 360 °C to 640 °C and exhibit high values for glass-ceramic materials. Stability is improved in the studied glass-ceramics because of the increased degree of network polymerization of the remaining glassy matrix. The approximate fragility index decreases two times for oxynitride materials compared to the primary glass. The synthesized new materials may be competitive to well-known bioactive phosphate glasses thanks to their improved stability by Mg, Si, N and Nb doping.

Evolution of short range order in Ar: Liquid to glass and solid transitions–A computational study

The evolution of the short range order (SRO) as a function of temperature in a Lennard-Jones model liquid with Ar parameters was determined and juxtaposed with thermodynamic and kinetic properties obtained as the liquid was cooled (heated) and transformed between crystalline solid or glassy states and an undercooled liquid. The Lennard-Jones system was studied by non-equilibrium molecular dynamics simulations of large supercells (approximately 20000 atoms) rapidly cooled or heated at selected quenching rates and at constant pressure. The liquid to solid transition was identified by discontinuities in the atomic volume and molar enthalpy; the glass transition temperature range was identified from the temperature dependence of the self-diffusion. The SRO was studied within the quasi-crystalline model (QCM) framework and compared with the Steinhardt bond order parameters. Within the QCM it was found that the SRO evolves from a bcc-like order in the liquid through a bct-like short range order (c/a=1.2) in the supercooled liquid which persists into the glass and finally to a fcc-like ordering in the crystalline solid. The variation of the SRO that results from the QCM compares well with that obtained with Steinhardt’s bond order parameters. The hypothesis of icosahedral order in liquids and glasses is not supported by our results.

Examining the kinetics of the thermal polymerisation behaviour of epoxy resins initiated with a series of 1-ethyl-3-methylimidazolium based ionic liquids

An epoxy resin based on the difunctional diglycidyl ether of bisphenol A (DGEBA) is reacted thermally in the presence of a series of 1,3-dialkylimidazolium based ionic liquids comprising the common cation (1-ethyl-3-methylimidazolium) and an anion (acetate, dicyanamide, or thiocyanate). Dynamic differential scanning calorimetry was used to analyse the formulations comprising DGEBA and the ionic liquid where it was revealed that the lowest and highest temperature for the onset of reaction were observed for formulations with 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium dicyanamide respectively. Cured glass transition temperatures range from 151 to 175 °C, depending on the anion used. Gelation behaviour is also dependent on the nature of the anion, with the acetate promoting gelation most quickly, whereas the dicyanamide is least reactive. Kinetic analysis of the cure reactions yield consistent results (R2 > 0.99) using the Ozawa method (Ea = 74–98 kJ/mol) and are in good agreement with previous studies on imidazoles.

Microstructure and Damping Property of Polyurethane Composites Hybridized with Ultraviolet Absorbents

This article investigated the microstructure and damping property of TPU composites with different contents of ultraviolet absorbents. It can be found that the ultraviolet absorbents formed fiber‐shaped precipitations in the TPU matrix. The UV‐328 was randomly distributed in the matrix and exhibited a weak interfacial bonding with the matrix. In comparison, the UV‐329 was well embedded in the matrix and formed a relatively better interfacial bonding and compatibility with the TPU matrix. The damping factor tanδ of both 328‐composites and 329‐composites had been reduced gradually with increasing content of ultraviolet absorbents at the glass transition temperature range due to the fact that the ultraviolet absorbents were in the crystalline state which decreased the volume content of the viscoelastic TPU matrix. But the tanδ increased at the temperature range of higher than the glass transition temperature, which should be related to the dominance of interfacial frictions between the ultraviolet absorbents and the matrix on the energy absorption.

Predictive model for the composition dependence of glassy dynamics

AbstractThe problem of glass relaxation is traditionally known as one of the most challenging problems in condensed matter physics, with important implications for several high‐tech applications of glass. In this study, we present a predictive model for the temperature, thermal history, and composition dependence of glassy relaxation dynamics. Our model enables, for the first time, the quantitative prediction of relaxation behavior for new glass compositions. Using the commercial Corning EAGLE XG® alkaline earth aluminosilicate glass as a reference, the model gives accurate predictions of the nonequilibrium viscosity for 4 other aluminosilicate glasses, covering both alkali‐free and alkali‐containing compositions, without any free fitting parameters. Using the composition‐dependent nonequilibrium viscosity model, only the measured values of the glass transition temperature and fragility are required to predict the nonequilibrium viscosity as a function of both temperature and thermal history. The range of glass transition temperatures of the 4 verification glasses covers about 200°C, while that of fragility values is about 6. As such, this work gives insights into the structural origin of nonequilibrium viscosity and can enable the future design of glass compositions with tailored relaxation behavior.

Designing catechol‐end functionalized poly(DMAm‐co‐NIPAM) by RAFT with tunable LCSTs

ABSTRACTProviding catechol‐end functionality to controlled structure lower critical solution temperature (LCST) copolymers is attractive, given the versatility of catechol chemistry for tethering to nanostructures. Controlled polymer chain lengths with catechol RAFT end groups are of interest to provide tunable LCST behavior to nanoparticles, although these polymerizations are relatively unexplored. Herein, the reactivity ratios for the RAFT copolymerization of N,N‐dimethylacrylamide (DMAm) and N‐isopropylacrylamide (NIPAM) pairs based on catechol‐end RAFT agents using an in situ NMR technique were first determined. Several catechol‐end poly(DMAm‐co‐NIPAM) samples were then prepared using the RAFT agent to provide copolymer. The reactivity ratios for the DMAm‐NIPAM pair were rDMAm = 1.28–1.31 and rNIPAM = 0.48–0.51. All the poly(DMAm‐co‐NIPAM) samples were found to have Mn values ≤ 26 kDa and Ð < 1.08 with LCST values ranging from 31 to 92°C, while maintaining a short range of glass transition temperature (Tg = 118–137°C). The difference in LCST values for the catechol functionalized poly(DMAm‐co‐NIPAM) based on 0.5 wt% aqueous buffered solutions at pH 5.5 and 8.5 was found to be <3.0°C. These conditions are suitable for subsequent catechol‐induced coordination and nucleophilic addition chemistry for covalent and noncovalent linkages during subsequent post‐modification. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 4062–4070

Multiblock Inverse-Tapered Copolymers: Glass Transition Temperatures and Dynamic Heterogeneity as a Function of Chain Architecture

Systematic variation of the size and number of inverse-tapered blocks in styrene–butadiene copolymers results in a wide range of accessible glass-transition temperatures (Tg), including Tg’s approaching that predicted by the Fox equation. Composition-weighted average Tg’s are expected for miscible blends or random copolymers, but such behavior has not previously been reported for block copolymers made from immiscible styrene and butadiene segments. In this work, 50:50 wt % multiblock copolymers with Mn = 120 000 kg/mol were synthesized using an inverse-tapered block design for all blocks except the end blocks. The total composition and molecular weight were held constant, but the type and number of blocks were systematically varied in order to compare contributions from the inverse-tapered chain interfaces to the overall glass transition behavior. Discrete copolymers of similar block number and length were investigated as controls to help separate contributions from the inverse-tapered design and the mole...

One‐pot approach synthesizing and characterization of random copolymerization of ethyl acrylate‐co‐methyl methacrylate with broad range of glass transition temperature onto collagen

Collagen is a natural polymer that cannot be applied freely to specific end uses due to its inherent drawbacks. Grafting polymerization of methyl methacrylate‐co‐ethyl acrylate was applied to modify the surface of acid soluble collagen (ASC). The main objective of this work is not only reducing the hydrophilic behavior of collagen on which has been concentrated so far but also successfully showed that the introduced co‐monomers onto ASC can alter the thermal behavior of the resulted copolymer. The level of branched copolymer significantly influenced the initial viscosity in studied co‐monomer feed ratios. The graft polymerization of collagen demonstrated the meaningful change in conductivity value of branched copolymer, where the copolymer in side chain with low dielectric constant covalently bonded onto the ASC. The increase in the co‐monomer feed ratio had no significant effect on conductivity value of copolymer, afterwards. The novelty of this work was determined to achieve the new copolymer onto the backbone of collagen to be used in specific thermally stabled end uses that the sufficient chain entanglements improve the flexibility of final product. POLYM. ENG. SCI., 58:1261–1267, 2018. © 2017 Society of Plastics Engineers

Selection of healing agents for a vascular self-healing application

To increase the durability and reliability of thermosets, self-healing via a vascular network, is developed. A judicious choice of healing agents proves to be necessary to achieve the best recovery of properties. Four low viscosity two-component epoxy-amine healing systems were compared, to check which glass transition temperature range would be best to recover mechanical properties (Tg ranging from −8 to 68 °C). Interdiffusion experiments show that all systems react sufficiently slowly at room temperature to allow interdiffusion of epoxy and amine over more than 1 mm before the diffusion is stopped by vitrification. Swelling tests revealed that most of the selected healing agents diffuse into the surrounding matrix and swell it. This might be beneficial for crack closure and improved adhesion between healing system and matrix. Flexural tests demonstrated that, the higher the glass transition temperature of the fully cured healing system, the higher the healing capability.

The F···H Hydrogen Bonding Effect on the Dynamic Mechanical and Shape‐Memory Properties of a Fluorine‐Containing Polybenzoxazine

A fluorine‐containing difunctional benzoxazine is synthesized by hydrosilylation of a monofunctional benzoxazine based ono‐allylphenol andp‐fluoroaniline. Besides the intramolecular and intermolecular hydrogen bonding associated with the nitrogen and oxygen atoms in the oxazine ring, specific self‐complementary intermolecular ArF···HO hydrogen bonding is formed in the polymerization of the benzoxazine, which leads to the resultant polybenzoxazine possessing a broad glass transition temperature range and showing two not well‐separated transitions. Based on the two glass transition temperatures, the polybenzoxazine exhibits triple‐shape‐memory behaviors by manipulating temperature and strain in the shape fixing process under tensile and bending modes. The dynamic mechanical and shape‐memory properties of the polybenzoxazine are influenced by the combined effect of the cross‐linking density and the ArF···HO hydrogen bonding.image

Investigation of temperature sensitivity of actuation performance for piezoelectric fiber composites

Piezoelectric fiber composites (PFCs) suffer an extremely wide range of temperatures when used in various aerospace structures where temperature effects on the mechanical properties of PFCs are important. In this paper, the actuation performances of PFCs were studied when they were exposed to environmental temperatures from −15 °C to 80 °C. The results showed that the actuation performance of PFCs was greatly dependent on the environmental temperature. The free strain values and the calculated piezoelectric coefficients d33 and d31 were initially enhanced with the increase of temperature due to the restricted movement of epoxy molecule in the glassy state. The glass transition temperature range of the composite was broadened due to a large number of small pores on the surface of the Pb(Zr,Ti)O3 (PZT) fibers, when the epoxy molecules inside the pores had different transition behaviors compared with those outside the pores. The actuation performance including free strain performance and actuation capability, as well as the piezoelectric coefficients d33 and d31 decreased as the temperature increased above room temperature, since the deformation of epoxy molecules in the viscoelastic state was irreversible.

Novel biobased and food contact epoxy coatings for glass toughening applications

Three series of novel food contact approved and low-toxic coatings for glass toughening applications were successfully prepared based on dicyandiamide and biobased epoxy compounds, e.g. epoxidized cardanol (NC514), diglycidyl ether of vanillin (DGEVA), triglycidyl ether of phloroglucinol (TGEP). Processability of formulations in bulk and in aqueous phase, and optimum materials were carefully investigated. The cure temperature of these epoxide:amine systems ranged from 160 to 250 °C, for which TGEP showed the highest reactivity. The developed materials exhibited excellent thermal stability and a wide range of glass transition temperature (Tg) was achieved, from 29 to 187 °C. The glass adhesion and mechanical properties were characterized by adhesion test and by mechanical ring test, respectively. The results revealed excellent glass adhesion properties without adhesion promotor addition and enhanced glass mechanical properties with all materials. These food contact and lowly-toxic materials are promising alternatives for DGEBA-based materials in widespread applications.

Reverse Engineering Eighth Century C.E. Window Glass Processing at Sardis, Turkey

ABSTRACTFrom the early eighth century CE Byzantine shops next to the Synagogue and Bath-Gymnasium Complex at Sardis, Turkey, were excavated from 1958 to 1969 more than 50 pounds, or about 350 panes of transparent flat glass sheets interpreted as window glass. Examination using optical microscopy showed little variation in size, shape, thickness, edge shape, tool marks, bubble and cord elongation and alignment. Microstructural and compositional variation of weathered surfaces and unweathered cross sections were studied using scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDS). Differential thermal analysis (DTA) was used to determine glass transition temperature range. Three traditional window-forming methods have been described in the glass technology literature: crown, plate and cylinder. The Sardis glass is most similar to criteria expected for cylinder glass, but significant differences were documented. Consistently patterned characteristics evidence a developed technological practice. Replicative tests were conducted using various forming sequences. Wooden and ceramic two-piece molds were made to overblow one or both ends, and hot glass threads were used to thermal shock the cylinder ends and to make a vertical crack that allowed opening during a reheating and slumping operation. These reconstructed methods fit the observed microstructural and macrostructural characteristics of the glass sheets. Analysis of glass manufacturing methods in antiquity contribute to the historical knowledge of craft practices and to the interpretation of industrial debris excavated at markets and industrial workshops.

Tuning nanophase separation behavior in segmented polyhydroxyurethane via judicious choice of soft segment

Polyhydroxyurethane (PHU) is of major research interest because it is a non-isocyanate polyurethane-like (NIPU) polymer. Here, we demonstrate the ability to tune nanophase separation in linear, segmented PHU copolymers via the soft segment. PHUs were synthesized from polytetramethylene oxide (PTMO)- and polybutadiene-co-acrylonitrile (PBN)-based soft segments, with divinyl benzene dicyclocarbonate and Dytek-A as hard segment and chain extender, respectively. These NIPU polymers were characterized by small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and tensile testing. SAXS reveals that the NIPUs with 30–40 wt% hard segment are nanophase separated with interdomain spacings of 9–16 nm. DMA reveals that PTMO-based PHUs have broad interphases with a range of local compositions and glass transition temperatures (Tgs), with tan δ ≥ 0.3 over temperature ranges exceeding 70 °C in breadth. In contrast, PBN-based PHUs have sharper interphases, evidenced by narrow tan δ peaks near soft-segment and hard-segment Tgs as well as by DSC and AFM data. FTIR shows that the ratio of hydrogen-bonded carbonyl to free carbonyl is higher in PBN-based PHU than in PTMO-based PHU, consistent with the absence and presence of intersegment hydrogen bonding in PBN-based PHU and PTMO-based PHU, respectively.