Glass Transition Of Poly Research Articles

Study of PVAc/EVA polymer series: Influence of the inter-/intra-molecular interaction ratio on the molecular mobility at the glass transition.

In this work, the molecular mobility at the glass transition of poly(vinyl acetate) (PVAc) and poly(ethylene-co-vinyl acetate) (EVA) amorphous sample series was investigated. The temperature and pressure dependences of the intermolecular interactions were studied from time-temperature-pressure superpositions and from the relaxation time dispersion of the segmental relaxation. The difference in terms of intermolecular interactions due to the lateral group ratio of vinyl acetate (VAc) was then estimated from the activation volume and related to the cooperative behavior. The isobaric fragility and its two contributions (thermal and volumetric) were estimated through high pressure broadband dielectric spectroscopy measurements. The volumetric and thermal contributions show different behaviors as a function of the VAc ratio and as a function of the pressure. Thus, the study of the PVAc/EVA series has allowed us to emphasize that the intramolecular and intermolecular interactions induced by the dipolar pendant groups directly influence the thermal and volumetric contributions to the isobaric fragility.

Divalent cation effects in the glass transition of poly(diallyldimethylammonium)-poly(styrene sulfonate) polyelectrolyte complexes.

The assembly and dynamics of polyelectrolyte complexes (PECs) and polyelectrolyte multilayers (PEMs) are influenced by water content, pH, and salt concentration. However, the influence of divalent salts on the assembly of polyelectrolyte complexes remains unclear. This work showcases that divalent chloride salts directly impact the glass transition temperature and the ion-ion interactions within PECs. Here, poly(diallyldimethylammonium)-poly(styrene sulfonate) (PDADMA-PSS) PECs are assembled in solutions containing MgCl2 and CaCl2 (following the Hofmeister series). These PECs are studied for the cations' influence on physicochemical properties (glass transition, polymer composition, ion pairing) at varying salt concentrations (0.03 M, 0.10 M, 0.15 M, and 0.20 M). Modulated differential scanning calorimetry (MDSC) experiments demonstrate that PECs assembled with CaCl2 have a significantly higher glass transition temperature when compared to PECs assembled with MgCl2. Neutron activation analysis (NAA) and nuclear magnetic resonance (NMR) spectroscopy demonstrate that this difference is due to strong ion-specific effects influencing the ratio of intrinsic and extrinsic ion pairings in the system. Furthermore, this study demonstrates a universal linear relationship between the thermal transition and the number of water molecules surrounding oppositely charged polyelectrolyte-polyelectrolyte intrinsic ion pairs, even when the salt contains divalent cations. Ion-specific trends have implications on the glass transition and composition of PDADMA-PSS PECs. Divalent salts not only follow the trend of the Hofmeister series but also introduce bridging into the polyelectrolyte complex; however, the structural relaxation of the PEC remains the same. This study offers a bridge between divalent cation behavior on polymer assembly properties and its transition to industrial applications such as controlled drug delivery, sensors, and water purification.

Effects of Ion Content on the Ion Aggregation Morphology and Glass Transition of Poly(styrene-ran-cinnamic acid) (SCA) Zn-Salt Ionomer

Poly(styrene-ran-cinnamic acid) (SCA) Zn-salt ionomers (SCA‒Zn) bearing increasing contents (0, 0.23, 0.55, 1.3, 3.0, and 5.5 mol%) of Zn2+ ions were successfully synthesized by solution neutralization of the SCA with Zn2+ ions at room temperature. As the ion content of the SCA‒Zn increased from 0 to 5.5 mol%, the size and the aggregation number of the ionic aggregates did not change significantly, because the increase in ion content led to a monotonic increase in the number density of ionic aggregates, while the number of ions participating in the aggregates to form ionic aggregates was essentially fixed. Furthermore, the T g values of the SCA‒Zn increased slowly as the Zn2+ ion content increased, and the linear increase rate with Zn2+ ion content was ∼0.8 °C mol−1, which was quite different from the reported increase rate in the T g values of the matrix phase with Na+ ion content of 3–6 °C mol−1. This appeared to be caused by the steric hindrance effect of the adjacent groups of –COO− ions in the SCA and the long-distance electrostatic attraction. In addition, the degree of ionization of the SCA‒Zn was too low to cause large changes in thermal stability.

Environmentally Sensitive Luminescence Reveals Spatial Confinement, Dynamics, and Their Molecular Weight Dependence in a Polymer Glass.

Polymer glasses have an irregular structure. Among the causes for such complexity are the chemically distinct chain end groups that are the most abundant irregularities in any linear polymer. In this work, we demonstrate that chain end induced defects allow polymer glasses to create confined environments capable of hosting small emissive molecules. Using environmentally sensitive luminescent complexes, we show that the size of these confinements depends on molecular weight and can dramatically affect the photoluminescence of free or covalently bound emissive complexes. We confirm the impact of chain end confinement on the bulk glass transition in poly(methyl acrylate) (pMA) and show that commonly observed Tg changes induced by the chain ends should have a structural origin. Finally, we demonstrate that the size and placement of luminescent molecular probes in pMA can dramatically affect the probe luminescence and its temperature dependence, suggesting that polymer glass is a highly irregular and complex environment, marking its difference with conventional small molecule solvents. Considering the ubiquity of luminescent glassy materials, our work lays down a blueprint for designing them with structural considerations in mind, ones where packing density and chain end size are key factors.

Raman spectroscopic insights into the glass transition of poly(methyl methacrylate).

Poly(methyl methacrylate) (PMMA) is a very versatile polymer which is used as a glass substitute or as an economical alternative to polycarbonate for many types of important applications, due to its particular physical properties. In this study we deal with the Raman spectroscopic characterization of the glass transition of PMMA, the value of the glass transition temperature being generally a decisive parameter for determining the application of polymers. The information obtained by two-dimensional correlation spectroscopy (2DCOS) analysis and perturbation-correlation moving-windows spectroscopy (PCMW2D) analysis of the temperature dependent depolarized Raman spectra enabled us to recognize that the glass transition of PMMA is ruled by intermolecular interactions which influence the vibrational modes of the molecular groups associated with ν(C[double bond, length as m-dash]O), δa(C-H) of α-CH3 and/or O-CH3, ν(C-O-C), ν(C-COO), and ν(C-C-O). This information was employed for the temperature dependent study of the Raman shift and of the full width at half maximum of the Raman peaks obtained through anisotropic and isotropic Raman spectra, of the depolarization ratio, of the Raman spectroscopic noncoincidence effect, and of the Raman peak intensities represented by Arrhenius-type plots, all results supporting the outcomes of this work. The comparison with results obtained by differential scanning calorimetry and with published results in molecular dynamics studies was also part of this work. As the main result, one can highlight the peak associated with the ν(C-O-C) stretching mode at around 812 cm-1 as the one which presents the better outcome for explaining the glass transition from the molecular point of view.

Heat capacity spectroscopy by using stochastic temperature modulated calorimetry: Time-temperature superposition and fictive temperature at the glass transition of poly (vinyl acetate)

Complex heat capacity spectra were measured by stochastic temperature modulated calorimetry using a conventional differential scanning calorimeter on poly (vinyl acetate) in the glass transition region during cooling. It is shown, that the real and imaginary part of the complex heat capacity spectra measured above and below vitrification can be scaled to a master curve by use of the frequency-temperature superposition principle. After the transition from a structurally equilibrated state to the non-equilibrated glass (vitrification), the shift factors deviate from the Vogel-Fulcher-Tammann-Hesse equation. The vitrification is described in the concept of fictive temperature using the Adam-Gibbs-Scherer equation for the temperature dependence of the relaxation time.

Glass transition of poly (methyl methacrylate) filled with nanosilica and core-shell structured silica

Core-shell (CS) nanocomposite particles with 53.4 wt% cross-linked poly (methyl methacrylate) (PMMA) shell of 11.6 nm in thickness were fabricated via miniemulsion polymerization of methyl methacrylate in the presence of modified nanosilica. The influence of nanosilica and CS nanoparticles on glass transition and segmental dynamics of PMMA in the nanocomposites prepared via solution casting was compared. The remarkable depression (≥10 °C) of glass transition temperature (Tg) induced by the incorporation of SiO2 and CS was both observed at low loadings. Here, different mechanisms were responsible for the effect of SiO2 and CS on the segmental acceleration of PMMA matrix. The formation of rigid amorphous fraction (RAF) layer around SiO2 with the thickness of 16.4 nm led to the adjacent molecular packing frustration, while the “lubrication” effect of nonwetting interface between the grafted crosslinked chains and matrix chains resulted in the segmental acceleration and the reduction of dynamic fragility.

Glass transition dynamics and cooperativity length of poly(ethylene 2,5-furandicarboxylate) compared to poly(ethylene terephthalate)

The glass transition of poly(ethylene 2,5-furandicarboxylate) (PEF), an emergent bio-based polyester, was investigated in comparison to one of its chemical analogues: poly(ethylene terephthalate) (PET). These investigations were conducted at different crystallinities by means of stochastic modulated differential scanning calorimetry (stochastic TMDSC) and dynamic mechanical analysis (DMA). Amorphous PEF presents a higher ΔCp at the glass transition and a broader relaxation spectrum attributed to a higher free volume. The higher Tg of PEF is then purely related to segmental mobility and specific interactions in PEF. The length of cooperative rearranging regions (CRR) was similar for both materials. Additionally, the variations of the effective activation energy E of PEF and PET at glass transitions were determined by isoconversional kinetic analysis. The rate of decrease in E was similar for the two amorphous polyesters. Upon crystallization, the glass transition of PEF is broadened but its temperature range is not increased as with PET. The creation of the rigid amorphous fraction (RAF) with crystallinity is lower in PEF than in PET. The difference in free volume also explains the lower coupling between the crystalline phase and the amorphous phase in PEF.

Segmental mobility and glass transition of poly(ethylene-vinyl acetate) copolymers: Is there a continuum in the dynamic glass transitions from PVAc to PE?

The segmental dynamics of amorphous poly(ethylene-vinyl acetate) copolymers (from PVAc to EVA50) were studied. In that sample set with similar backbone stiffness and different amount of dipoles, the dynamic glass transition was investigated by Modulated Temperature Differential Scanning Calorimetry and Broadband Dielectric Spectroscopy measurements. A decrease of the cooperativity length scale was obtained with the vinyl acetate (VAc) content decreasing. On the other hand, there was no modification of the temperature dependence of the relaxation time. Thus, the fragility value is quite constant whatever the VAc content. These results show that fragility and cooperativity have two different origins. An extrapolation to nonconstrained polyethylene amorphous phase was proposed and new glass transition temperature and fragility values were determined.

Glass transitions of poly(methyl methacrylate) confined in nanopores: conversion of three- and two-layer models.

The glass transitions of poly(methyl methacrylate) (PMMA) oligomer confined in alumina nanopores with diameters much larger than the polymer chain dimension were investigated. Compared with the case of 80 nm nanopores, PMMA oligomer confined in 300 nm nanopores shows three glass transition temperatures (from from low to high, denoted as Tg,lo, Tg,inter, and Tg,hi). Such phenomenon can be interpreted by a three-layer model: there exists an interphase between the adsorbed layer and core volume called the interlayer, which has an intermediate Tg. The behavior of multi-Tg parameters is ascribed to the propagation of the interfacial interaction during vitrifaction process. Besides, because of the nonequilibrium effect in the adsorbed layer, the cooling rate plays an important role in the glass transitions: the fast cooling rate generates a single Tg; the intermediate cooling rate induces three Tg values, while the ultraslow cooling rate results in two Tg values. With decreasing the cooling rate, the thickness of interlayer would continually decrease, while those of the adsorbed layer and core volume gradually increase; meanwhile, the Tg,lo gradually increases, Tg,inter almost stays constant, and the Tg,hi value keeps decreasing. In such a process, the dynamic exchanges between the interlayer and adsorbed layer, core volume should be dominant.

Detection of Glass Transition in Poly(vinyl butyral) Thin Films with a Quartz Crystal Resonator on Different Overtones

We demonstrate that that a quartz crystal resonator (QCR) is applicable to investigate the glass transition of the Poly (vinyl butyral) (PVB) thin films by the simultaneous measurement of both resonant frequency and bandwidths on several overtones. The response of resonant frequency and bandwidths of film coated quartz crystal directly reflects the information about surface mass and film shear modulus. This enable us to explicitly deduce the glass transition temperature and the shear modulus parameter of PVB thin films on different overtones from the frequency shift and the bandwidths shift. These results indicate the feasibility of using QCR technique to characterize glass transition temperature and viscoelastic properties of the PVB thin films.

Combined effect of relative humidity and temperature on dynamic viscoelastic properties and glass transition of poly(vinyl alcohol)

ABSTRACTOn the basis of the experimental studies on viscoelastic properties of poly vinyl alcohol (PVA) films at various relative humidity (RH) and temperature conditions by dynamic mechanical analysis (DMA), the influence of both temperature and RH on the glass transition are discussed and an improved property model is developed to relate the dynamic modulus to RH and temperature. The results indicate that (1) with increasing the RH, the storage modulus of PVA decrease remarkably, while both loss modulus and tanδ sharply increase to reach the peak and then markedly drops. The intensity of this variation is highly dependent upon temperature. (2) Moisture increase will cause the glass transition of PVA at isothermal condition and the transition point can be detected by glass transition relative humidity (RHg) that obtained by isothermal RH scans. (3) Similar to the relationship between Tg and RH, the RHg of PVA vary linearly with temperature. The state diagram of RHg versus temperatures is nearly consistent with that of Tg versus RH. (4)The present equation based on model of Mahieux and Reifsnider (Mahieux and Reifsnider, Polymer 2001, 42, 3281) can predict well the dynamic modulus of PVA at various RHs and temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3161–3167, 2013

A Temperature Modulated DSC Study of Glass Transition in Poly(ethylene terephthalate)

A dynamic heat capacity of poly(ethylene terephthalate) in the temperature range of glass transition has been examined by a new technique of temperature modulated differential scanning calorimetry. The shift of glass transition temperature caused by the desorption of water could be monitored by the change in the dynamic heat capacity. Under quasi-isothermal condition, the increase in the glass transition temperature causes the decrease in the magnitude of the dynamic heat capacity and a negative or positive change in the phase, depending on temperature.

Atomistic simulation based prediction of the solvent effect on the molecular mobility and glass transition of poly (methyl methacrylate)

We present an investigation of the retained solvent effect on the glass transition temperature (Tg) of poly(methyl methacrylate) (PMMA) through all-atom molecular dynamics simulations. Addition of a weakly interactive solvent, tetrahydrofuran (THF), causes a depression of the PMMA Tg that can be identified through an analysis of the mean squared displacement of the polymer chains from atomistic trajectories. Our results are in very good agreement with an atomistically informed theoretical model based on free volume theory and demonstrate the applicability of molecular simulation to discern solvent effects on polymer thermomechanical behavior in silico.

Glass transition of poly(ethylmethacrylate) admixed and bound to nanoparticles

The chain dynamics at the glass transition of poly(ethylmethacrylate) in the bulk is compared to that of mixtures of the polymer with nanoparticles by advanced NMR methods. In order to make the two components compatible, the particles were functionalized with the polymer itself. Particular emphasis is placed on the extended local chain conformations of this polymer accessible by (13)C NMR spectroscopy. The isotropization dynamics of these extended conformations is only slightly changed in the mixtures, but is significantly slowed down by attachment of the chains to the nanoparticles themselves. The slowing down is studied at various distances from the nanoparticle and is observed for most of the attached chains segments except for the chain ends. The results are put into perspective to the glass transition in polymers attached to surfaces, thin polymer layers, and the chain dynamics of star polymers.

Dynamic crossover of the sub-Rouse modes in the glass–rubber transition region in poly(n-alkyl methacrylates) with different side chain lengths

The dynamic crossover of the sub-Rouse modes (a transition from one Vogel–Fulcher–Tamman law to another in relaxation map) above glass transition in poly(n-alkyl methacrylates) (PnAMA) was observed and compared for the first time. The α and α′ relaxations become better resolved from each other with increasing side chain length, while the crossover relaxation time is 10−0.5±0.5s, essentially independent of side chain length of the PnAMA, indicating the universal presence of the sub-Rouse modes in PnAMA. Analysis of the mechanical spectra shows that the crossover originates from change of intermolecular coupling of the sub-Rouse modes when temperature crosses TB.

Determination of the transition phenomena of poly(α-n-alkyl) methacrylates adsorbed on silica by inverse gas chromatography (IGC)

Inverse gas chromatography (IGC) at infinite dilution is a powerful technique to characterise the superficial and interfacial properties of solid substrates as oxides, polymers or polymers adsorbed on oxides and to determine the transition phenomena of polymers. This technique was applied in earlier studies in order to determine the change, as related to temperature, of the properties and the second order transitions of some polymers adsorbed on oxides, and particularly to study the transition phenomena in PMMA and poly(α-n-propyl) methacrylate (P3) adsorbed on silica or in their bulk phases. In this paper, the superficial properties and glass transitions of poly(α-n-pentyl) methacrylate (P5) and poly(α-n-octyl) methacrylate (P8) were studied when adsorbed on silica or in their bulk phases. The study of the evolution of RTlnVn, as a function of 1/T for different n-alkanes adsorbed on poly(α-n-alkyl) methacrylates (Pn), proved that IGC technique allowed a fairly accurate determination of their transition temperature (Tg). Moreover, the glass transition temperature Tg was observed to vary from 110 °C for PMMA (P1) to 10 °C for poly(α-n-octyl) methacrylate. Results obtained in this study proved an important shift in the value of Tg, due to the adsorption of various Pn on silica and the more spread chains of the adsorbed polymers. A reduction in Tg value was observed when the length of the side chain increases that leads to an internal plastification effect in poly(α-n-alkyl)methacrylates.

A study of the glass transition in the amorphous interlamellar phase of highly crystallized poly(ethylene terephthalate)

The glass transition of poly(ethylene terephthalate) (PET) crystallized for 4 h at temperatures between 413 and 453 K was studied. Secondary crystallization processes were monitored by differential scanning calorimetry and the glass transition of the remaining interlamellar amorphous phase was studied by thermally stimulated depolarization currents measurements. Non-isothermal window polarization is employed to resolve the relaxation in modes with a well-defined relaxation time that is subsequently adjusted to several standard models. An analysis of experimental results reveals that cooperativity can be disregarded in the modelization of data. The evolution of modes during secondary crystallization, once primary crystallization has been completed, gives more weight to lower energy modes. As a consequence, secondary crystallization tends to lower the glass transition temperature of the amorphous interlamellar phase, although remaining noticeably higher than in amorphous samples. The evolution of calorimetric scans of the glass transition is simulated from the obtained results and shows the same behaviour. Regarding the glass transition temperature of the material, it can be concluded that primary and secondary crystallization act in opposite directions even though the effect of secondary crystallization is much smaller. The interpretation of these results in terms of current views about secondary crystallization is discussed.

Smectic structure and glass transition in poly(butylene terephthalate)

Smectic structure and glass transition in poly(butylene terephthalate)

Acetone Influence on Glass Transition of Poly(methyl methacrylate) and Polystyrene in Compressed Carbon Dioxide

In this work, the glass transitions of poly(methyl methacrylate) and polystyrene in compressed gaseous acetone/carbon dioxide were measured by an in situ creep compliance method at pressures lower than 7.0 MPa and at 318−338 K. When a small amount of acetone (x = 0.01−0.02) was added to a polymer-compressed carbon dioxide system, the glass transition pressure of polymer was further depressed by 1.0−4.0 MPa. The observed glass transition pressure depression increased with the acetone concentration in carbon dioxide and decreased with the temperature rise. A simple model was used to estimate the glass transition temperature depressions for the polymers in compressed gaseous acetone/carbon dioxide solution. The calculated results were in good agreement with the determined ones, except for the retrograde vitrification region.