Heterogeneity Of Poly Research Articles

Structure and dynamics heterogeneity in poly(vinyl acetal)s: The effect of side group length

Understanding on the structure and dynamics of poly(vinyl acetal)s is insufficient due to the complicated chemical structure and amorphous nature of this type of polymers. In this work, we investigate the effect of side group length on structure and dynamics heterogeneity at different length scales spanning from side group, segment, and polymer network by combing dynamic mechanical analysis (DMA), dielectric relaxation spectroscopy (DRS), solid-state NMR, and differential scanning calorimetry analysis (DSC). By increasing the length of acetal side group, its intrinsic dynamics slows down. Taking into account the scale of segment and networks, with the increase of acetal group length, the formation of cross-linking sites formed by the hydroxyl-rich domain is suppressed, the relaxation distribution of the segment widens, and the volume fraction of rigid component decreases. The effect of side group length on the structure and dynamics heterogeneity of poly(vinyl acetal)s at different scales results in significant changes in material properties such as the non-monotonic change in loss factor value (tan δ) and a monotonous reduction in glass transition temperature (Tg).

Effects of Plasticizers on Structural Transitions and Heterogeneity of Poly(vinyl alcohol) Films as Studied via AIE Materials

Effects of Plasticizers on Structural Transitions and Heterogeneity of Poly(vinyl alcohol) Films as Studied via AIE Materials

Effect of Physical Aging on Heterogeneity of Poly(ε-caprolactone) Toughening Poly(lactic acid) Probed by Nanomechanical Mapping

Effect of Physical Aging on Heterogeneity of Poly(ε-caprolactone) Toughening Poly(lactic acid) Probed by Nanomechanical Mapping

Study of the Dynamic Heterogeneity in Poly(ethylene-ran-vinyl acetate) Copolymer by Using Broadband Dielectric Spectroscopy and Electrostatic Force Microscopy

Dynamic heterogeneities in ethylene–vinyl acetate (EVA) random copolymers were studied using broadband dielectric spectroscopy (BDS) over a broad frequency and temperature range. BDS data for EVA copolymers show relatively broad spectra extending over several frequency decades, which make interpretation of the data complicated. Thus, microscopic dielectric characterizations of the samples were done using single pass electrostatic force microscopy (SP-EFM) images. From these experiments two distinct dielectric contributions were found in the semicrystalline samples. Dielectric spectra of EVA copolymers were fitted using a model based on the SP-EFM images. According to this analysis, the broad dielectric responses of semicrystalline EVA copolymers were constituted from two dielectrically active phases, referred to as the constrained and nonconstrained phases, exhibiting different segmental relaxations. In the constrained phase, vinyl acetate (VA) motions were greatly restricted by crystalline microstructures, whereas in the nonconstrained phase, VA monomers were assumed to be completely free from crystalline effect. The glass transition temperature derived from the dynamics of the VA segments in the constrained phase was found to correspond well with that determined from DSC representing the overall amorphous phase in the more crystallized state. Moreover, crystallinity of the sample obtained using DSC was found to follow a similar variation with temperature to that of the dielectric relaxation strength of the constrained phase of the copolymers. However, at the earlier stage of crystallization, where crystallinity increases rapidly, the dielectric relaxation remains insensitive to it.

Asymmetrical flow field-flow fractionation as a novel technique for the analysis of PS-b-PI copolymers

Asymmetrical flow field-flow fractionation (AF4) was used as a fractionation technique to investigate the molecular heterogeneity of poly(styrene-b-isoprene) diblock copolymers synthesized by either sequential living anionic polymerization or coupling of living precursor blocks. AF4 coupled to multi-angle laser light scattering (MALLS), refractive index (RI), and ultraviolet (UV) detectors was used to separate the diblock copolymers from the homopolymers and coupling products, and the molar masses of the different components were analyzed. In order to get more information about the separated block copolymers, homopolymers, and coupling products, fractions were collected directly after the AF4 channel. The collected fractions were analyzed offline by (1)H NMR to provide identification of the different species and additional information on the true chemical composition, and the microstructure of the diblock copolymer was obtained.

Electrogenerated Chemiluminescence and Fluorescence Lifetime Spatial Heterogeneity of Poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) in Presence of [6,6]-phenyl-C61-butyric Acid Methyl Ester

ABSTRACTWe present electrogenerated chemiluminescence (ECL) and fluorescence lifetime mapping of MEH-PPV/PCBM thin films. The ECL results show that the oxidation peak of MEH-PPV near 0.7 V (vs. SCE) and ECL response of films shifted positively towards 1.2 V in the presence of PCBM. At the same time, the oxidation current density of MEH-PPV increases along with the decrease of ECL intensity in the presence of PCBM. The fluorescence lifetime images clearly show that the lifetime spatial heterogeneities are affected by different substrates and MEH-PPV/PCBM ratios. Meanwhile, the lifetime of MEH-PPV decreases with the increasing of film thickness. The lifetimes of MEH-PPV films on TiO2 substrate are lower than films on glass.

Electrogenerated Chemiluminescence and Fluorescence Lifetime Spatial Heterogeneity of Poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) in Presence of [6,6]-phenyl-C61-butyric Acid Methyl Ester

Electrogenerated Chemiluminescence and Fluorescence Lifetime Spatial Heterogeneity of Poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) in Presence of [6,6]-phenyl-C61-butyric Acid Methyl Ester

Flow-cytometric assessment of cellular poly(ADP-ribosyl)ation capacity in peripheral blood lymphocytes

BackgroundPoly(ADP-ribosyl)ation is a posttranslational modification of nuclear proteins catalysed by poly(ADP-ribose) polymerases (PARPs), using NAD+ as a substrate. Activation of PARP-1 is in immediate response to DNA damage generated by endogenous and exogenous damaging agents. It has been implicated in several crucial cellular processes including DNA repair and maintenance of genomic stability, which are both intimately linked with the ageing process. The measurement of cellular poly(ADP-ribosyl)ation capacity, defined as the amount of poly(ADP-ribose) produced under maximal stimulation, is therefore relevant for research on ageing, as well as for a variety of other scientific questions.ResultsThis paper reports a new, robust protocol for the measurement of cellular poly(ADP-ribosyl)ation capacity in PBMC or Jurkat T-cells using flow cytometry, based on a previously established immuno-dot-blot assay. In order to validate the new assay, we determined the dose-response curve of 3-aminobenzamide, a well-known competitive PARP inhibitor, and we derived an IC50 that is very close to the published value. When testing a set of PBMC samples taken from fifteen healthy young human donors, we could confirm the presence of a substantial interindividual variation, as previously observed using a radiometric assay.ConclusionThe methodology described in this paper should be generally useful for the determination of cellular poly(ADP-ribosyl)ation capacity in a wide variety of settings, especially for the comparison of large sets of samples, such as population studies. In contrast to previously published radiometric or immuno-dot-blot assays, the new FACS-based method allows (i) selective analysis of mononuclear cells by gating and (ii) detection of a possible heterogeneity in poly(ADP-ribosyl)ation capacity between cells of the same type.

Dynamic Heterogeneity in Poly(vinyl methyl ether)/Poly(2-chlorostyrene) Blends

Dielectric spectroscopy was used to follow the component dynamics in the miscible blend of poly(vinyl methyl ether) (PVME) and poly(2-chlorosytrene) (P2CS). For the PVME component (which has the more intense loss peak due to its higher polarity), the shape of the segmental relaxation peak depends only on the relaxation time and is otherwise independent of thermodynamic conditions. This is in accord with the general behavior of neat materials. By measuring the spectra as a function of both temperature and pressure, the relative effect of temperature and volume on the segmental relaxation times was quantified from ratio of the isochoric and isobaric activation enthalpies. This ratio is essentially the same for the neat polymers, but blending has a disparate effect of the components: volume effects become stronger for the PVME but are diminished for P2CS. Similarly, the fragilities of the neat components are quite close but change markedly in the blend. The P2CS component has a fragility of 32, which is low...

Phase heterogeneity in poly(methyl acrylate)-polystyrene sequential interpenetrating polymer networks studied by thermally stimulated recovery

The aim of this work is to explore the ability of a mechanical thermal sampling (TS) technique to study the glass transition of heterogeneous polymer systems. Poly(methyl acrylate) and polystyrene are immiscible. Sequential interpenetrated polymer networks (IPNs) were prepared with these components with two varying cross-linking densities. The dynamic mechanical analysis shows, in the case of the loosely cross-linked IPN, two clearly separated main α-relaxations in a similar position as in the pure network components while in the highly cross-linked IPN the two peaks overlap. The thermally stimulated recovery (TSR) technique, using the TS procedure allows a more detailed analysis of the glass transition region. With this technique it is possible to determine the temperature dependence of the apparent activation energy of the conformational mobility in the range of the glass transition. A peak appears at a temperature very close to the glass transition temperature. The presence of differentiated peaks in the heterogeneous system allows one to reveal the phase separation or the presence of interphases with differentiated mechanical behaviour. More details related with phase heterogeneity are observable by the low-frequency TSR technique relatively to the conventional dynamic methods.

Observation of Compositional Heterogeneity in Poly(styrene sulfonate) Using Frontal Analysis Continuous Capillary Electrophoresis

Sulfonated polystyrene is frequently studied as a model polyelectrolyte because of its narrow molecular weight distribution, corresponding to that of the precursor, anionically polymerized polystyrene. Frontal analysis continuous capillary electrophoresis (FACCE) was carried out for polystyrenesulfonate (PSS) samples from various commercial sources. Whereas some of the electropherograms appeared as abrupt and discontinuous, indicating a single uniform mobility, others were sigmoidal, corresponding to a distribution of mobilities. This distribution must reflect sample heterogeneity, possibly due in part to the molecular weight distribution (MWD) for the low-MW samples, but only attributable to chemical heterogeneity for the higher-MW samples. Size-exclusion chromatography (SEC) was used to establish the possibility of some MWD contribution to the distribution of mobilities for the low-MW PSSs, but not for the high-MW ones. Because a high-MW sample with a broad MWD prepared by polymerization of styrenesulfonate did not show a mobility distribution, the only plausible explanation for those distributions is compositional heterogeneity, i.e., chain-to-chain variations in the degree of sulfonation.

Chemical Heterogeneity of Poly(ethylene terephthalate) As Revealed by Temperature Rising Elution Fractionation and Its Influence on Polymer Thermal Behavior: A Comparison with Poly(ethylene terephthalate-co-isophthalate)

The chemical heterogeneity of poly(ethylene terephthalate) (PET) and of poly(ethylene terephthalate-co-isophthalate) (PETI) was investigated using temperature rising elution fractionation (TREF). NMR and SEC results of the TREE fractions of the two polymers are compared. Both polymers show the same trend upon fractionation, confirming that diethylene glycol units (DEC;) can be considered as a statistical comonomer in PET which influences the crystallizability of PET. PET and PETI were finally analyzed by the stepwise isothermal segregation technique (SIST). The occurrence of multiple melting peaks for both polymers, when crystallized isothermally by step from the melt, is related to the statistical inclusion of the comonomers in the chains.

Structural Heterogeneity in Poly(methyl methacrylate) Glasses of Different Tacticity Studied by Thermally Stimulated Current Thermal Sampling Techniques

The thermally stimulated current thermal sampling (TSC-TS) technique was used to study the cooperative glass transition like relaxations in different tacticity poly(methyl methacrylates) (PMMAs) including iso- and syndiotactic forms. We use the high sensitivity of the TSC-TS method to study these weak and sometimes overlapping relaxations at a frequency of about 10 -3 Hz where one can resolve cooperative relaxations well below the main glass transition (Tg), even if the species are a minor fraction of the overall relaxing species. The magnitudes of the values of E a are compared with a theoretical prediction as a function of temperature, showing that the low-temperature tail of the glass transition in conventional atactic (e.g., 45% syndiotriads) extends down to 15 °C, while in our highest syndiocontent PMMA (80% syndiotriads), the glass-transition-like relaxations only extend down to about 80 °C. Results taken from the literature also substantiate the results obtained here for atactic PMMA. The results are contrasted to those for bisphenol-A polycarbonate and other polymers and suggest that compositional heterogeneity, more specifically the presence of low T g pockets of predominantly isotactic sequences, contributes to the broad glass transition extending almost 90 °C below the main glass transition in atactic PMMA.

Chemical heterogeneity in poly [styrene-co-(butyl methacrylate)] copolymer latexes prepared using different monomer addition modes. A study by isopycnic centrifugation in density gradient

Three different styrene-butyl methacrylate copolymer latexes were prepared by a uniform procedure but introducing styrene (S), butyl methacrylate (BMA), and minor amounts of acrylic acid (AA), in three different orders: i) simultaneous monomers addition, which yielded P(SBMA); ii) addition of S (and half of the AA) followed by BMA (and the remaining AA), yielding PS/PBMA and iii) the inverse order, PBMA/PS. Product characterization was done by centrifugation in density gradients coupled to scattered light scanning photometry of the centrifugation tubes. IR and NMR spectra were obtained from bulk polymer as well as from isopycnic centrifugation fractions. In agreement with findings of other authors, the particles produced by simultaneous monomer addition P(SBMA) are made out of the statistical copolymer, whereas sequential monomer addition leads to the formation of latex with homopolymer domains. IR and NMR spectra of PS/PBMA and PBMA/PS are identical but isopycnic density band profiles of all three samples are distinct. Acrylic acid residues are not detected in the dialyzed latex, using both IR and NMR. Spectra of latex isopycnic fractions do also show significant differences arising from their monomer chemical compositions, but isopycnic centrifugation and spectral data do not reveal any correlation between particle density and monomer composition. Isopycnic centrifugation can thus solve two problems on latex characterization: first, it is a high-resolution preparative technique, unmatched by any other separation method. Second, it yields latex particle fingerprints, which are dependent on particle chemical characteristics, rather than on particle diameters.

Molecular Level Structural Heterogeneity in Poly(ether−ester)/Poly(vinyl chloride) Blend Characterized by Cross-Polarization/Magic Angle Spinning 13C Nuclear Magnetic Resonance Spectroscopy

A blend of poly(ether-ester) and poly(vinyl chloride) (PVC) was examined by dynamic mechanical analysis and cross-polarization/magic angle spinning (CP/MAS) 13 C NMR spectroscopy. The presence of structural heterogeneity in the solid blend was identified by the temperature dependence of its frequency-swept viscoelastic behavior. In the CP/MAS 13 C NMR experiment, analysis of the magnetization decay of specific carbons as a function of delay time determined the proton spin-lattice relaxation times in the laboratory frame, T 1 , and the rotating frame, T 1ρ , for the two polymers in their respective pure states and in the 50/50 blend. This analysis provided more precise information pertaining to the microheterogeneity and the molecular state of mixing in the blend. The single-exponential decay of T 1 relaxation of the blend confirmed a homogeneity on a characteristic length of 26 nm estimated from the spin diffusion process. The double decompositions in the T 1ρ relaxation of component polymers in the blend indicated a coexistence ofa mixed and two structurally heterogeneous phases which corresponded to poly(ether-ester) hard segments and PVC microcrystallites. The maximum size of the microheterogeneous phases was estimated to be ca. 24 A.

Heterogeneity of poly(I) x poly(C)-induced human fibroblast interferon mRNA species.

Three classes of human interferons (IFNs) have been defined on the basis of their immunological properties: the 'Le' or 'alpha' IFN, mainly derived from leukocyte or lymphoblastoid cells; the 'F' or 'beta' IFN, mainly derived from fibroblast cultures; and the 'T', 'immune' or 'gamma' IFN, mainly derived from mitogen- or antigen-stimulated lymphoid cells. Whereas several individual species of Le IFN have been purified to homogeneity, it is generally considered that F IFN represents a single protein. Thus current efforts to clone human fibroblast IFN mRNA sequences are based on the observation that F IFN mRNA sediments in sucrose gradients as a single RNA species of size corresponding to 12-14 S (refs 7-10). We show here, using gel electrohporesis of mRNA, that two populations of translationally active human fibroblast IFN mRNA molecules exist--an abundant '14 S' species and a scarce '11 S' species. Microinjection of either species of mRNA into Xenopus oocytes leads to the synthesis of biologically active F-type human IFN. These data agree with and complement recent RNA hybridization studies of Weissenbach et al.

Molecular modifications associated with Aging of globin messenger RNA in vitro.

Using polyacrylamide gel elution-electrophoresis in aqueous medium, highly purified rabbit globin mRNA can be fractionated into several populations of molecules differing by their mean poly(A) content. Both alpha and beta globin mRNA are heterogenous with respect to their electrophoretic mobilities. With the conditions used no separation of alpha and beta globin mRNA occurs during electrophoresis. From the specific radioactivity distribution in the different mRNA fractions one can conclude that the polyadenylate sequence at the 3' end of globin mRNA molecules becomes shorter with aging. This shortening occurs on alpha as well as beta, globin mRNAs and the extent of heterogeneity in poly(A) content is similar for both globin mRNAs. Furthermore, using two different methods of mRNA fractionation (polyacrylamide gel elution-electrophoresis and elution of poly (U)-Sepharose-bound mRNA at increasing temperatures) it is shown that old mRNA molecules differ from relatively young messages in their ability to direct cell-free globin synthesis. Modifications reducing template activity in vitro thus seem to take place during globin mRNA aging.