Glass Transition Temperature Of Poly Research Articles

Melamine as cross‐linking agent for mono‐cyclic benzoxazine with aldehyde groups: higher crosslinking density and thermal properties

AbstractBenzoxazine resin shows great potential as matrix for high performance composites, possessing good processabilty, dielectric property, mechanical property, and thermal properties, but its further application is limited by low crosslinking density and poor curing activity, especially for mono‐cyclic benzoxazines. In this work, melamine, a tertiary amine with a stable triazine structure, was introduced into the aldehyde‐containing mono‐cyclic benzoxazine, in order to achieve higher crosslinking density, higher curing activity, and better thermal properties. The chemical structure of prepolymers was verified by Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR) spectra, the curing behavior was investigated by differential scanning calorimetry, the thermal properties of polymers were studied by thermogravimetric analysis (TGA) and thermal mechanical analysis (TMA). It was found that the introduction of trifunctional melamine (MA) could lower curing temperature and promote the curing degree. Additionally, a proper amount of MA could increase the crosslinking density and thermal properties of the resultant polybenzoxazine. For example, poly(BZ‐3MA) showed the highest thermal stability with the temperature at 5% weight loss (Td5) of 415°C, carbon residue (Yc) of 67.7%, 23°C, and 2.9% higher than those of poly(BZ). Moreover, the glass transition temperature of poly(BZ‐5MA) reached 204.06°C, 36.51°C higher than that of poly(BZ).

Poly(cyclohexylsilsesquioxane)-Based Hydrophilic Thermoset-Resistant Deep-Ultraviolet-Transparent Glasses with Low Melting Temperatures.

Silsesquioxane (SQ)-based glasses with low melting temperatures were prepared by the cosolvent-free (solventless) hydrolytic polycondensation of organotrimethoxysilanes with cyclopentyl (c-Pe) and cyclohexyl (c-Hx) groups. Copolymers consisting of phenylsilsesquioxane (Ph-SQ) units and c-Pe-SQ units [poly(Ph-co-c-Pe-SQ)] or c-Hx-SQ units [poly(Ph-co-c-Hx-SQ)] were melted at 140 °C and formed clear glasses. The glasses prepared by this method contained many residual SiOH groups and exhibited high adhesive strength to microscope glass plates, metals, and several polymers. The glass-transition temperature of poly(c-Hx-SQ) was lower than that of poly(Ph-SQ) by only a small margin, whereas that of poly(c-Pe-SQ) was much lower. The poly(c-Hx-SQ)-based glasses were stiff at room temperature and transparent in the deep-ultraviolet spectral region (≲300 nm). They formed fragile melts with kinetic fragility parameters as high as ∼0.8. The melts of poly(c-Hx-SQ) and poly(c-Hx-co-Et-SQ) exhibited better resistance to thermal curing than that of poly(Ph-SQ) and maintained thermoplasticity even after heat treatment at 200 °C for 6 h.

Heterogeneities at the Onset of Reaction Acceleration during Bulk Polymerization of Methyl Methacrylate Investigated by Small-Angle Neutron Scattering

During bulk free-radical polymerization of methyl methacrylate below the glass-transition temperature of poly(methyl methacrylate), the relative fraction of monomer and polymer changes as the reaction proceeds. The liquid monomer is eventually converted to a solid glassy polymer. In other words, polymerization-induced vitrification or glass transition occurs. This process was traced by small-angle neutron scattering (SANS). The scattering profile discontinuously changes at the vicinity of vitrification. This discontinuous change was correlated with a sudden reaction acceleration known as the Trommsdorff effect. Ornstein–Zernike analysis revealed that the intensity at q = 0 (I(0)) and the correlation length of concentration fluctuation (ξ) suddenly increase at the discontinuous change of the scattering profile. The obtained data implies that the increased heterogeneity (i.e., microscopic concentration fluctuation) is intimately related to the Trommsdorff effect.

Influence of surfactant on glass transition temperature of poly(lactic-co-glycolic acid) nanoparticles.

Poly(D,L-lactic-co-glycolic acid) (PLGA) is one of the most commonly used drug carriers in nanomedicines because of its biodegradability, biocompatibility and low toxicity. However, the physico-chemical characterization and study of drug release are often lacking the investigation of the glass transition temperature (Tg), which is an excellent indicator of drug release behavior. In addition, the residual surfactant used during the synthesis of nanoparticles will change the glass transition temperature. We thus prepared PLGA nanoparticles with polymeric (poly(vinyl alcohol) (PVA)) and ionic (didodecyldimethylammonium bromide (DMAB)) surfactant to investigate their influence on the glass transition temperature. Determination of Tg in dry and wet conditions were carried out. The use of concentrated surfactant during synthesis resulted in a larger amount of residual surfactant in the resulting particles. Increasing residual PVA content resulted in an increase in particle Tg for all but the most concentrated PVA concentrations, while increasing residual DMAB content resulted in no significant change in particle Tg. With the presence of residual surfactant, the Tg of particle and bulk samples measured in wet conditions is much lower than that in dry conditions, except for bulk PLGA containing the ionic surfactant, which may be related to the plasticizing effect of the DMAB molecules. Notably, the Tg of both particles in wet conditions is approaching physiological temperatures where subtle changes in Tg could have dramatic effects on drug release properties. In conclusion, the selection of surfactant and the remaining amount of surfactant are crucial parameters to utilize in designing the physico-chemical properties of PLGA particles.

Glass transition temperature of poly(d,l-lactic acid) of different molar mass

To evaluate the glass transition of poly(d,l-lactic acid)s (PDLLA), three PDLLA grades of different molar mass were analyzed by fast scanning calorimetry (FSC), on cooling at rates between 0.01 and 100,000 K/s. Poly(l-lactic acid) (PLLA) is used as a reference and measured at similar conditions as PDLLA, however, assuring the absence of crystallization. By using the Vogel–Fulcher–Tammann–Hesse (VFTH) equation to fit the glass-transition dynamics of PDLLA and PLLA, it is found that the Vogel temperatures of PDLLA and PLLA are essentially the same. In addition, the dependencies of the glass transition temperature on the molar mass of PDLLA and PLLA are evaluated. The glass transition temperatures of PDLLA and PLLA of infinite molar mass are the same, suggesting that the stereoisomerism does not influence the glass transition dynamics.

Enhancing Glass Transition Temperature of Poly(methylmethacrylate) by Incorporating Methacrylate-Functional Silane Grafted SiO2 Nanoparticles

Enhancing Glass Transition Temperature of Poly(methylmethacrylate) by Incorporating Methacrylate-Functional Silane Grafted SiO2 Nanoparticles

Synthesis, stereocomplex crystallization, homo-crystallization, and thermal properties and degradation of enantiomeric aromatic poly(lactic acid)s, poly(mandelic acid)s

Enantiomeric aromatic poly(lactic acid)s, i.e., poly(l-mandelic acid) (PLMA) and poly(d-mandelic acid) (PDMA), with different number-average molecular weight (Mn) values were synthesized by polycondensation and their stereocomplex (SC) crystallization and homo-crystallization by solvent-evaporation, as well as thermal properties and degradation were investigated in detail. The SC crystallization was confirmed by wide-angle X-ray diffraction and differential scanning calorimetry. However, Fourier-transfer infrared spectroscopy could not identify SC crystallization, excluding the lowered peak width of the carbonyl group. Predominant SC crystallization was observed for high molecular weight PLMA/PDMA (Mn = 1.7 × 104 and 1.5 × 104 g mol–1, respectively) blends and low molecular weight PLMA/PDMA (Mn = 5.8 × 103 and 7.2 × 103 g mol–1) blends, except for low molecular weight PLMA/PDMA blend with a PLMA fraction of 75%, where both SC crystallization and homo-crystallization occurred. This can be explained by the lower crystallizability of homo-crystallites at high Mn values compared to that of SC crystallites. The glass transition temperatures of poly(mandelic acid)s (87 °C − 112 °C) were higher than those previously reported for poly(lactic acid)s (PLAs) (approximately 60 °C), poly(2-hydroxybutanoic acid)s [P(2HB)s] (24 °C − 44 °C), and poly(phenyllactic acid) (32 °C − 47 °C). In marked contrast with the results previously reported for enantiomeric PLAs and P(2HB)s, melting temperatures of SC crystallites of PMAs (105 °C – 127 °C) were lower than those of homo-crystallites (162 °C − 180 °C). The thermal degradation temperatures at 10% weight loss for unblended PLMA, PDMA, and their (50/50) blend (290 °C − 313 °C) were much higher than those reported for unblended enantiomeric PLAs, and their (50/50) blend (218 °C − 243 °C) and similar to those reported for enantiomeric P(2HB)s, and their (50/50) blend (300 °C − 330 °C). The thermal degradation profiles and temperatures of unblended PLMA, PDMA, and their blend were similar with each other, whereas the activation energy for thermal degradation (ΔEtd) of PLMA/PDMA blend (136.7− 163.0 kJ mol–1) was between those of unblended PLMA (117.7 − 154.4 kJ mol–1) and unblended PDMA (196.3 − 226.6 kJ mol–1). These results contrast with those previously reported for enantiomeric PLAs and P(2HB)s, wherein ΔEtd values were increased by enantiomeric polymer blending. Furthermore, the crystallizability of aromatic poly(mandelic acid) and poly(phenyllactic acid) was compared.

Glass transition of nanometric polymer films probed by picosecond ultrasonics

The possibility to measure the glass transition temperature in poly(methyl methacrylate) (PMMA) films by picosecond ultrasonics with thicknesses ranging from 458 nm to 32 nm is demonstrated. A shift of the longitudinal acoustic eigenmodes towards lower frequencies with temperature is observed accompanied by a change in the temperature-frequency slopes at the glass transition temperature. The contributions to the frequency shift from changes in film thickness and sound velocity are discussed and the latter is extracted below the glass transition temperature. Finally, the advantages and disadvantages of the current approach in a comparison to other methods based on acoustic measurements in the GHz regime are reviewed.

Using the group contribution method and molecular dynamics to predict the glass transition temperatures and mechanical properties of poly-(p-phenylenediamine-alt-2, 6-diformyl multiphenyl)

This article reports the glass transition temperatures of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) predicted by both the group contribution method and the molecular dynamics simulations. The related modeling method and the degree of polymerization, density, specific volume, radius of volume, radius of rotation, and non-bonding energy terms with temperature are analyzed in depth. The bulk modulus, shear modulus, compressibility, Young’s modulus, and Poisson’s ratio of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) at room temperature are simulated by molecular dynamics. The results show that the simulated glass transition temperatures of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) are greater than 480 K, which indicates that poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) can be expected to be used as a high-temperature-resistant material. As the number of rigid benzene rings on the molecular side chain increases, the glass transition temperature decreases, with an average decrease of 10 K for each additional benzene ring. The free volume theory can explain the glass transitions of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl). The modulus and density of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) change accordingly with an increase of rigid benzene rings on the side chain, probably due to the fact that the flexibility of the polymers changes accordingly as the number of benzene rings on the side chain increases.

Spontaneous Patterning during Frontal Polymerization.

Complex patterns integral to the structure and function of biological materials arise spontaneously during morphogenesis. In contrast, functional patterns in synthetic materials are typically created through multistep manufacturing processes, limiting accessibility to spatially varying materials systems. Here, we harness rapid reaction-thermal transport during frontal polymerization to drive the emergence of spatially varying patterns during the synthesis of engineering polymers. Tuning of the reaction kinetics and thermal transport enables internal feedback control over thermal gradients to spontaneously pattern morphological, chemical, optical, and mechanical properties of structural materials. We achieve patterned regions with two orders of magnitude change in modulus in poly(cyclooctadiene) and 20 °C change in glass transition temperature in poly(dicyclopentadiene). Our results suggest a facile route to patterned structural materials with complex microstructures without the need for masks, molds, or printers utilized in conventional manufacturing. Moreover, we envision that more sophisticated control of reaction-transport driven fronts may enable spontaneous growth of structures and patterns in synthetic materials, inaccessible by traditional manufacturing approaches.

Effect of different lengths of side groups on the thermal, crystallization and mechanical properties of novel biodegradable poly(ethylene succinate) copolymers

To explore the effect of different lengths of side groups, the thermal, crystallization, and mechanical properties were systematically investigated for three novel poly(ethylene succinate) (PES) based copolyesters containing methyl, butyl, and octyl as side groups, respectively, in this research. Relative to linear PES, the presence of side groups did not modify the crystal structure, while increasing the length of side groups slightly decreased the crystallinity of the copolymers. Despite the length of side groups, they all displayed high thermal decomposition temperatures. Increasing the length of side groups gradually decreased the melting point temperatures of PES copolymers. The glass transition temperature of poly(ethylene succinate-co-1,2-propylene succinate) slightly increased; however, those of poly(ethylene succinate-co-1,2-hexamethylene succinate) and poly(ethylene succinate-co-1,2-decamethylene succinate) gradually decreased with an increase in the length of side groups. PES and its copolymers displayed the same crystallization mechanism; however, the crystallization time increased as the length of side groups increased at the same degree of supercooling. The elongation at break increased while the Young's modulus decreased with increasing the length of side groups. The dynamic mechanical analysis results revealed that the storage modulus and tan δ gradually decreased as the length of side groups increased. In brief, the length of side groups significantly influenced the thermal, crystallization, and mechanical properties of PES based copolymers.

Chain flexibility and glass transition temperatures of poly(n-alkyl (meth)acrylate)s: Implications of tacticity and chain dynamics

The relationship between chain microstructure and glass transition temperature (Tg) is complicated for poly(alkyl methacrylate)s and poly(alkyl acrylate)s. Despite intensive studies, relationships between the structures of these polymers and their properties, including solution characteristics and Tg, are still controversial. Solution properties, chain conformations, including Flory's characteristic ratio (C∞), persistence length (lp), and chain diameters, and Tg are reported for series of poly(n-alkyl acrylate)s and poly(n-alkyl methacrylate)s having alkyl side chain lengths (n) ranging from 1 to 10 carbons in length, with uniform and well-characterized tacticities. Chain flexibilities of both series of polymers decrease as n increases, reflecting increased hindrances to rotation about backbone bonds as side chains become longer. Conversely, the Tgs for both series of polymers decrease substantially as n increases, reflecting the greater side chain mobilities of long alkyl substituents. For shorter alkyl chain lengths, Tgs for the poly(n-alkyl acrylate)s are much lower than for the corresponding poly(n-alkyl methacrylate)s, a difference which has been attributed in the past to the presumed reduced chain flexibility of polymethacrylates due to the presence of the α-methyl substituent. However, contrary to such expectations, C∞ and lp values for these two series of polymers are nearly identical at a given n value, except for the longest n-alkyl substituents. Instead, the differences in Tg may be attributed to the differences in tacticity of the two series – almost ideally atactic for the poly(n-alkyl acrylate)s but high in syndiotacticity for the poly(n-alkyl methacrylate)s. The Tgs for the two series of polymers approach that of polyethylene at longer alkyl chain lengths. In addition, the effects of tacticity and chain dynamics on C∞, lp, and Tg of poly(methyl methacrylate) is discussed.

In Situ Preparation of Polymer Nanocomposites Based on Sols of Surface-Modified Detonation Nanodiamonds by Classical and Controlled Radical Polymerization

The possibility of surface modification of detonation nanodiamonds to give them dispersability in methyl methacrylate is considered. In situ polymer composites are obtained by classical radical polymerization and reversible chain-transfer polymerization based on stable sols of detonation nanodiamonds in a monomer. Evidence that nanodiamonds are dispersed in a polymer matrix up to a size of units of nanometers is given. The effect of detonation nanodiamonds on the molecular weight characteristics and glass transition temperature of poly(methyl metacrylate) obtained in their presence is studied.

Effect of Disyndiotacticity on the Glass Transition Temperature of Poly(ethyl crotonate)s Synthesized by Group-Transfer Polymerization Catalyzed by Organic Acids

Poly(ethyl crotonate)s (PECs), possessing various disyndiotacticities, were synthesized by group-transfer polymerization using several silicon Lewis acid catalysts like N-(trialkylsilyl)bis(trifluo...

Synthesis of amphiphilic block copolymer using trimethylene carbonate bearing oligo(ethylene glycol) and investigation of thin film including cilostazol

AbstractTo prepare a thin film, the block copolymer poly(TMCM‐MOE3OM)‐b‐PTMC was prepared with different segment ratios of hydrophilic moiety. The glass transition temperature of poly(TMCM‐MOE3OM)‐b‐PTMC decreased as the content of TMCM‐MOE3OM increased as expected, and it was confirmed that the graft oligo(ethylene glycol) (OEG) affected intermolecular interaction. The polymers grafted with OEG showed a thermoresponsive property, which can be expected to be applied to materials triggered by temperature. A thin film was prepared by mixing block copolymer and cilostazol as a drug, and the distribution of cilostazol was observed. It was confirmed that cilostazol was uniformly distributed on the thin film and that local sustained release could be avoided at the time of elution. The eluting behavior of the thin film from the substrate was apparently affected on the segment ratio of the block copolymer. When the thin film was immersed in PBS, the eluting rate increased as the segment ratio of TMCM‐MOE3OM in the block copolymer increased. As a result, it is possible to control the eluting rate by changing the ratio of the hydrophilicity and the hydrophobicity of the block copolymer, contributing to the creation of a new coating material containing cilostazol.

Ceramic-Doped in Cross-Linked Solid Polymer Electrolyte for Solid-State Batteries

Replacing liquid electrolytes with solid-state Li-ion conductors is one way to achieve safe rechargeable batteries with high energy density. Semi-interpenetrating polymer network (s-IPN) was synthesized from the mixture of poly(propylene carbonate), poly(ethylene glycol) methyl ether acrylate, poly(ethylene glycol) diacrylate (PEGDA), and lithium bis(trifluoromethane)sulfonamide salt via one-pot thermal curing method. The crosslinker PEGDA content and salt concentration were optimized and the best result was abtained at a molar ratio of EO:Li ∼ 14:1. The electrolyte with higher salt concentration had lower ionic conductivity, consistent with higher glass transition temperature of poly(ethylene glycol) chain. Differential scanning calorimetry has shown a low degree of crystallinity when lithium lanthanum zirconate doped tantalum (LLZTO) was added to the s- IPN electrolyte which corresponds to an increase in ionic conductivity, 4.5 x 10-4 S/cm at 40°C. The resulting composite polymer electrolyte (CPE) showed high electrochemical stability up to 5.5 V. Lithium plating and stripping at 0.1 mA/cm2 at room temperature revealed a stable Li/electrolyte interface and no dendrite formation. Cycling performance of a full solid-state cell made with the CPE using LiFePO4 as the cathode will be discussed. Figure 1

Synthesis, Structural Characterization, Enzymatic and Oxidative Polymerization of 2,6-Diaminopyridine.

Enzymatic polymerization of 2,6-diaminopyridine (DAP) compound in the presence of HRP (Horse radish peroxidase) and H2O2 (hydrogen peroxide) with Poly(DAP-en) with the structures of two different types of polymers obtained by the oxidative polymerization of Poly(DAP-ox) using H2O2 in an aqueous basic environment was illuminated by 1H-NMR, 13C-NMR, FT-IR, UV-Vis spectral methods. GPC (gel permeation chromatography), TGA (thermal gravimetric analysis), DSC (differential scanning calorimetry), CV (cyclic voltammetry), fluorescence analysis and conductivity measurements to characterize the compounds and their electronic structure were examined. SEM analyzes were performed for the morphological properties of the compounds. As a result of the analysis, it was observed that the polymer obtained by enzymatic polymerization was better than the polymer obtained by oxidative method. It was observed that the results of the fluorescence measurements were better than Poly(DAP-en) in Poly(DAP-ox) emitting blue and green light. According to TGA analysis, the first decay temperatures for Poly (DAP-en) and Poly (DAP-ox) were calculated as 342°C and 181°C, respectively. The higher value of glass transition temperature for poly (DAP-en) confirms that the average molar mass is higher than 8650Da for Poly (DAP-en) according to GPC analysis.

Synthesis and characterization of a novel isocoumarin derived polymer and its thermal decomposition kinetics

A novel isocumarin derived polymer poly(2-(isocoumarin-3-yl)-2-oxoethyl methacrylate) poly(ICEMA) was synthesized by free radical polymerization. The spectral characterization was performed with FTIR and 1H,13C-NMR techniques. The glass transition temperature of poly(ICEMA) was measured to be 161.69 °C by DSC technique. The initial decomposition temperatures obtained from TGA showed a change in the positive direction from 256.59 °C to 286.10 °C as the heating rate increased to 20 °C/min. Thermal decomposition activation energies of poly(ICEMA) in the conversion range of 7% - 19% were found to be 136.12 kJ/mol and 134.83 kJ/mol by Flynn–Wall–Ozawa and Kissinger’s models, respectively. In addition, various integral models such as Coats-Redfern, Tang, Madhusudanan and Van-Krevelen models were used to determine the thermal decomposition mechanism of poly(2-(isocoumarin-3-yl)-2-oxoethyl methacrylate)which showed that it proceeded at the optimum heating rate of 5 ºC/min over the D1 one-dimensional diffusion type deceleration mechanism

Glass-Transition Temperature and Characteristic Temperatures of α Transition in Amorphous Polymers Using the Example of Poly(methyl methacrylate)

The glass-transition temperatures of poly(methyl methacrylate) measured by 20 different physical methods are analyzed. At equal impact frequencies and heating rates of the samples, the values of glass-transition temperatures measured by different methods are equivalent. As follows from the analysis, for atactic PMMA with Mw > 1 × 105 without additives, crosslinking agents, and plasticizers at a standard heating rate of 10°С/min, the most probable values of the extrapolated onset temperature of the α transition Tf as a point of intersection of the first baseline and a line extrapolating linear decrease in heat flow in the region of the α transition are 105 ± 5°С; inflection temperatures corresponding to the temperature of a peak on the temperature derivative of heat flow in the region of the α transition Ti and the temperature of the midpoint determined at the half jump of normalized heat flow Tm are observed at 125 ± 5°С; and the values of the extrapolated end temperature of the α transition Te as the points of intersection of the line extrapolating the linear decrease in heat flow in the region of the α transition and the second baseline in the region of the rubbery state and the temperature of the last return to the second baseline Tr attain 140 ± 5°С.

Examining the Influence of Organophosphorus Flame Retardants on the Thermal Behavior of Aromatic Polybenzoxazines

Abstract2,2‐bis(3,4‐Dihydro‐3‐phenyl‐2H‐1,3‐benzoxazine)propane (BA‐a) is blended with three commercial organophosphorus compounds, bis(4‐ hydroxyphenyl)phenylphosphine oxide (BHPPO), diphenyl phosphorami‐date (DPPA), and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), at different loadings (1–10 wt%). Incorporation of all dopants results in a reduction in the initiation temperature for the curing mechanism (by some 30–60 K), but only the DOPO truly moves the curing into a lower temperature regime by decreasing the end temperature by 25 K (DPPA lowered this by 5 K). DPPA and DOPO are also shown to have a significant effect on the enthalpy of polymerization each decreasing the value by 50 J g−1. Differential scanning calorimetry rescan indicates all three additives have a positive impact on the glass transition temperature of poly(BA‐a) with increases of 9 K (BHPPO) and 14 K (DPPA, DOPO). Thermogravimetric analysis indicates that all additives have little effect on the magnitude of char formed (BHPPO and DPPA both increased the char yield by 3%, whereas DOPO reduces the nal char yield by 3%). However, importantly, the mechanism of thermal degradation for poly(BA‐a) differs for all three additives and is shown to change with increasing concentra‐ tion. DOPO has the greatest effect on promoting the formation of char at elevated temperatures.