Molecular Mobility Of Poly Research Articles

New contributions from thermal and dielectric techniques to the understanding of the dynamic properties of medium to long chain poly (propylene glycols)

AbstractThe molecular mobility of poly (propylene glycols) with molecular weights between 2000 and 18,200 g mol−1 was studied in the amorphous solid state, in the region of the glass transition and in the rubbery state; the experimental techniques used were differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). It was found that the glass transition temperature increases slightly with MW and tends to a limit value: TgDSC = −67°C, TgTSDC = −73°C.The different types of molecular mobility were analyzed: below Tg the secondary relaxations, and above this temperature the normal mode, were characterized in detail using TSDC; in the glassy transformation region, around Tg, the main relaxation was analyzed by both DSC and TSDC. It was found the dynamic fragility, m, behaves as independent of the molecular weight in the studied range: mDSC = 74 and mTSDC = 92. The TSDC results also show that, without influencing the kinetics of the segmental relaxation, the increase in molecular weight slows down the chain relaxation.

Effects of poly(hexylene succinate) amount on the crystallization and molecular mobility of poly(lactic acid) copolymers

Poly(lactic acid) (PLA), poly(hexylene succinate) (PHSu) and new block PLA-b-PHSu copolymers with mass ratios of 90/10 and 95/5 were synthesized. PHSu was chosen, as a proper agent to tune the crystallizability and to introduce biodegradability on PLA. Emphasis was given on crystallization behaviour, which is assessed by DSC, XRD and PLM. Also, to reveal any direct effects of the copolymer structure and composition on molecular mobility, TMDSC and BDS measurements were performed. FTIR was used as an accompanying technique. It was found that the slow crystallization rate of PLA becomes faster due to the presence of PHSu in the copolymers, while by XRD and DSC was proved that the degree of crystallinity decreases. Regarding molecular mobility of PLA at the presence of PHSu, the calorimetric (DSC) as well as the dynamic (α relaxation, BDS) glass transition, exhibit strong acceleration, weak enhancement in strength and suppressed cooperativity. These effects correlate well with the progressive decrease of molar mass in copolymers by increasing PHSu content. Local dynamics of PLA is not affected by PHSu, as expected.

Dielectric Relaxation of Nanocomposites Based on Poly(phenylene oxide) and Endometallofullerene

The molecular mobility of poly(phenylene oxide) nanocomposites with endometallofullerene at a concentration of 0.1, 0.5, and 1.0 wt % is studied by dielectric spectroscopy. Two processes of dipole polarization relaxation in the glassy state (β-process) and in the rubbery state (α-process) are found. It is shown that the molecular mobility of the β-process related to the presence of a nanoadditive does not change with concentration. Molecular mobility in the region of the α-process, which is associated with segmental mobility, shows a downward trend.

Relaxation Behavior of Thermoplastic Polyimide R-BAPB in the Amorphous State

The molecular mobility of poly(4,4'-bis(4-aminophenoxy)biphenyl)imido-1,3-bis(3,3'-4,4'-dicarboxyphenoxy)benzene) films is studied by the thermally stimulated depolarization current (TSDC) technique and dielectric spectroscopy. The existence of two dipolar polarization relaxation regions (β and α) related to the local mobility in the glassy state and the cooperative segmental mobility in the rubbery state, respectively, is revealed. The temperature dependences of the relaxation time for the β-process obey the Arrhenius equation; for the α-process, they obey the Vogel–Tammann–Hesse equation. Emergence of the third peak βI is related to relaxation of the space homocharge. The molecular mechanisms of all the observed processes are revealed.

Changes of the Molecular Mobility of Poly(ε-caprolactone) upon Drawing, Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation spectroscopy (DRS) of poly(e-caprolactone) with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases. The activation energy of the α process, which corresponds to the dynamic glass transition, increases upon drawing. The enlarged gap between the activation energies of the α process and the β process results in a change of continuity at the crossover between the high temperature a process and the α and β processes. At low drawing ratios the a process connects with the β process, while at the highest drawing ratio in our measurements, the a process is continuous with the α process. This is consistent with X-ray diffraction results that indicate that upon drawing the polymer chains in the amorphous part align and densify upon drawing. As the draw ratio increases, the α relaxation broadens and decreases its intensity, indicating an increasing heterogeneity. We observed slope changes in the α traces, when the temperature decreases below that at which τ α ≈ 1 s. This may indicate the glass transition from the ‘rubbery’ state to the non-equilibrium glassy state.

Effect of Mechanical Compression and Hydrostatic Pressure on the Molecular Mobility of Poly(lactic acid)

SummaryThe molecular mobility of an organic glass (PLA with 4.3% of D‐lactic acid content) was investigated by calculating the size of the Cooperative Rearranging Regions (CRR) at its glass transition. The samples were exposed to different external constraints – namely a large deformation by mechanical compression at T < Tg (prior to measurement) or different hydrostatic pressures (during the measurement). The measurements were performed by Differential Scanning Calorimetry (DSC) techniques: standard, temperature modulated (TM‐DSC) and high pressure (HP‐DSC). It was shown that mechanical deformations above the elastic limit increase the CRR size and shift the Tg value to higher temperatures, but have no effect on the value of ΔCp(Tg). On the other hand, increasing the hydrostatic pressure during the measurement (1 to 100 bar) decreases the CRR size, slightly influences Tg and does not change the value of ΔCp(Tg).

Gas permeability of thin dense films from polymer blend of thermoplastic elastomer and polyolefin

ABSTRACTStretched thin films composed of a thermoplastic elastomer, a polystyrene‐block‐poly(ethylene butylene)‐block‐polystyrene triblock copolymer (SEBS), and polyolefins, poly(ethylene‐co‐ethylacrylate) and poly(ethylene‐co‐propylene), were obtained by blow‐molding, uniaxial stretching, and cooling to room temperature and the gas permeability of the stretched films was investigated. When the as‐blown annealed film was subjected to uniaxial stretching in the machine direction, PO2 and PN2 increased with an increase in the stretching ratio K and approached a constant value at high stretching ratios. In addition, PO2/PN2 decreased gradually with K and approached a value of 2.95–3.0. The reason for this unique gas permeation behavior is that the molecular mobility of poly(ethylene butylene) chains in a direction normal to the film increases and reaches an equilibrium state at around K = 4.5. The change in gas permeability of the stretched films can be explained using a deformation model for the SEBS matrix. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39386.

10.1007/s11498-008-3004-9

The effect of uniaxial orientational drawing and subsequent isometric annealing on the molecular mobility of poly(vinylidene fluoride) was studied by dielectric spectroscopy and dynamic mechanical analysis. The influence of orientation, the polymorphic composition of the crystalline phase, and the structure of disordered regions on dielectric and mechanical relaxation in isotropic and oriented samples was investigated.

Molecular mobility of poly(methyl methacrylate) glass during uniaxial tensile creep deformation

AbstractAn optical photobleaching method has been used to measure the segmental dynamics of a poly(methyl methacrylate) (PMMA) glass during uniaxial creep deformation at temperatures between Tg − 9 K and Tg − 20 K. Up to 1000‐fold increases in mobility are observed during deformation, supporting the view that enhanced segmental mobility allows flow in polymer glasses. Although the Eyring model describes this mobility enhancement well at low stress, it fails to capture the dramatic mobility enhancement after flow onset, where in addition the shape of the relaxation time distribution narrows significantly. Regions of lower mobility accelerate their dynamics more in response to an external stress than do regions of high mobility. Thus, local environments in the sample become more dynamically homogeneous during flow. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1713–1727, 2009

Molecular mobility of poly(vinylidene fluoride) in the anisotropic state

The effect of uniaxial orientational drawing and subsequent isometric annealing on the molecular mobility of poly(vinylidene fluoride) was studied by dielectric spectroscopy and dynamic mechanical analysis. The influence of orientation, the polymorphic composition of the crystalline phase, and the structure of disordered regions on dielectric and mechanical relaxation in isotropic and oriented samples was investigated.

Solid‐state 19F MAS NMR study on the conformation and molecular mobility of poly(chlorotrifluoroethylene)

The temperature dependence of molecular mobility and conformational changes of poly(chlorotrifluoro- ethylene) (PCTFE) have been investigated by solid-state (19)F magic angle spinning (MAS) NMR spectroscopy. The pulse techniques of dipolar-filter and T(1rho)-filter allow selective observation of the amorphous and crystalline domains, respectively. The temperature dependence of T(1rho) (F) revealed that the segmental motion in the amorphous domain becomes vigorous above ca 80 degrees C, which is well above the glass transition (T(g)) temperature (52 degrees C) and more close to the beta-relaxation temperature (95 degrees C). On the other hand, vigorous molecular motions in the crystalline domain occur above 120 degrees C, which is much below the melting temperature (212 degrees C). This indicates that the polymer chains in the PCTFE crystallites are more mobile than those of typical semicrystalline fluoropolymers like poly(vinylidene fluoride) (PVDF), which can be associated with structural imperfections in the crystallites. In addition, the density functional theory (DFT) calculations of (19)F magnetic shielding suggest that the high-frequency shifts observed for the crystalline signals above 80 degrees C can be ascribed to the conformational change around meso diads toward more twisted and/or helical conformations in the main chain.

Neutron scattering study of the poly(butylmethacrylate) isomers

Molecular mobility of poly(butylmethacrylate) isomers, which differ in the length and microstructure of the side chain, is investigated with elastic temperature scans applying neutron backscattering. The onset of dynamics can be described by a distribution of rotation rate originating from the dynamics of the methyl groups in the sidechain which sense various local environments.

Stearyl poly(ethylene oxide) grafted surfaces for preferential adsorption of albumin Part 2. The effect of molecular mobility on protein adsorption

The adsorption of plasma proteins (fibrinogen and albumin) from buffer onto polystyrene-graft-(stearyl-poly(ethylene oxide)) (PS- g-SPEO) was investigated by radioiodine labeling of proteins using the iodine monochloride method. The molecular mobility of poly(ethylene oxide) grafts was determined by ESR spectroscopy, and the effects of PEO mobility on the ability of PS- g-SPEO to resist the non-specific protein adsorption have been studied. The non-specific adsorption of fibrinogen was found to decrease with increasing PEO mobility, whereas the interfacial energies lack significant correlation to the protein adsorption. The elastic restoring force seems much more important than hydrophobic interaction in PS- g-SPEO/protein interfaces. The high molecular mobility of PEO side chain is supposed to be the key effect on the protein-resistant properties of PS- g-SPEO. The protein adsorption results also reveal that the molecular mobility of PEO has a quite important role in developing albumin preferential materials. A high albumin preferential adsorption layer has been developed by immobilizing the stearyl end groups onto high mobile PEO chains.

ESR spectroscopy to determine the molecular mobility of poly(ethylene oxide) grafts in amphiphilic graft copolymers

ESR spectroscopy to determine the molecular mobility of poly(ethylene oxide) grafts in amphiphilic graft copolymers

Carbon-13 high resolution solid state NMR study of poly(vinyl chloride)

From a nuclear magnetic resonance (NMR) study, a difference in the molecular mobility of poly(vinyl chloride) (PVC) was characterized, which is related to the polymerization process. In this work it is shown that, in accordance with the polymerization process, the arrangement of the chain sequence along the role molecule affects the NMR parameter such as proton spin-lattice relaxation time in the rotating frame. This influence can be interpreted as a configurational sequence distribution in the macromolecular structure.

Molecular mobility of poly(methyl methacrylate): a time-resolved electron spin resonance study with photoexcited triplet-state phenazine as a probe

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMolecular mobility of poly(methyl methacrylate): a time-resolved electron spin resonance study with photoexcited triplet-state phenazine as a probeSoon Sam. Kim, Fun Dow. Tsay, and Amitava. GuptaCite this: J. Phys. Chem. 1987, 91, 18, 4851–4856Publication Date (Print):August 27, 1987Publication History Published online1 May 2002Published inissue 27 August 1987https://doi.org/10.1021/j100302a039RIGHTS & PERMISSIONSArticle Views72Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts

Relaxation behavior of poly(acrylic acid) and its copolymers with 2-hydroxyethyl methacrylate

Abstract The molecular mobility of poly(acrylic acid) (PAAc) and its copolymers with 2-hydroxyethyl methacrylate (HEMA) was investigated by means of dynamic mechanical measurements carried out with a freely oscillating torsional pendulum (∼1 Hz). An increase in the content of AAc in the copolymers leads to reduction and eventually to complete disappearance of both the low-temperature (−135°C) and secondary (28°C) dispersion, while the glass transition temperature passes through slight maximum. In the temperature range under investigation (from −196 to 140°), PAAc exhibits only the glass transition at Ca 108°C (1 Hz). The sorbed water markedly decreases the glass transition temperature of PAAc and gives rise to a secondary dispersion near −80°C; with increasing water content, the dispersion is shifted towards lower temperatures, and its intensity increases. The effect of AAc on the temperature and intensity of the low-temperature dispersion of PHEMA was compared with that of six other comonomers; it was fo...

Relaxation Behaviour of Poly(2-Hydroxyethyl Acrylate) and of Its Copolymers with 2-Hydroxyethyl Methacrylate

Abstract The molecular mobility of poly(2-hydroxyethyl acrylate) (PHEA) and of its copolymers with 2-hydroxyethyl methacrylate (H EM A) was determined by means of dynamic mechanical measurements with a torsional pendulum. The low-temperature dispersion assigned to the motion of the hydroxyethyl groups of the side chains was observed at -133°C (1 Hz) for all polymers; its intensity increased with the content of HEMA. Another secondary dispersion of PHEA detected at -95°C(1 Hz) was ascribed to the motion of the side chains including oxycarbonyl groups. With the incorporation of HEMA the temperature of the latter dispersion remained virtually unchanged, but its intensity rapidly decreased. The main transition temperature of PHEA, Ta = 9°C (1 Hz) is lower than Ta of PHEMA by approximately 94°C; the effect of the copolymer composition on Ta could be described by means of a one-parameter equation. The sorption of water led to a significant decrease in the Ta of PHEA and to an intensification of the secondary re...