Samples Of Different Molecular Weights Research Articles

Optical single molecule characterisation of natural and synthetic polymers through nanopores.

Nanopore techniques are now widely used to sequence DNA, RNA and even oligopeptide molecules at the base pair level by measuring the ionic current. In order to build a more versatile characterisation system, optical methods for the detection of a single molecule translocating through a nanopore have been developed, achieving very promising results. In this work, we developed a series of tools to interpret the optical signals in terms of the physical behaviour of various types of natural and synthetic polymers, with high throughput. We show that the measurement of the characteristic time of a translocation event gives access to the apparent molecular weight of an object, and allows us to quantify the concentration ratio of two DNA samples of different molecular weights in solution. Using the same tools for smaller synthetic polymers, we were able to obtain information about their molecular weight distribution depending on the synthesis method.

Emulsification characteristics of soy hull polysaccharides obtained by membrane separation

Membrane separation technology was used to separate and purify the microwave-assisted oxalic acid extraction of soy hull polysaccharides (MOSP) in order to obtain samples of different molecular weights. The emulsification characteristics of the MOSP were investigated including protein adsorption, polysaccharide adsorption, interfacial tension, emulsion index, and particle size; optical microscopy and Phenom electron microscopy were used to elucidate the emulsion structures. In addition, Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and high-performance gel-filtration chromatography (HPGFC) were used to study the differences in the components and structures of MOSP in different molecular weights. The molecular weight had several important effects on the emulsifying properties of MOSP. The adsorption capacities of the emulsion droplets containing low molecular weight MOSP (L-MOSP), middle molecular weight MOSP (M-MOSP), and high molecular weight MOSP (H-MOSP) were relatively low, and those of H-MOSP were slightly higher than those of L-MOSP. With extended storage time, the particle sizes of the emulsions rich in L-MOSP, M-MOSP, and H-MOSP increased. L-MOSP, M-MOSP, and H-MOSP were mainly composed of furans. The conformation of the molecular chain was spherical. The emulsions formed with H-MOSP were the most stable.

Thermal Properties of Poly(Methyl Methacrylate) Samples of Different Molecular Weights Impregnated with Single-Walled Carbon Nanotubes in Supercritical Carbon Dioxide

Thermal Properties of Poly(Methyl Methacrylate) Samples of Different Molecular Weights Impregnated with Single-Walled Carbon Nanotubes in Supercritical Carbon Dioxide

The effect of long-term natural aging on the iPB-1 structure and the II – I phase transformation rate

The long-term natural aging of isotactic polybutene-1 samples of different molecular weight has shown that the transformation rate from the initial phase II to the stable phase I significantly decreased after natural aging, ranging from 0 to 17 years. It was found that the total crystallinity decreased with aging time and a small amount of phase II remained untransformed for at least 17 years. The transformation rate of a lower molecular weight sample, DP 0400, was higher than the PB 0110 sample, even after repeated polymer melting of aged samples and their new melt crystallization. The major phenomenon of the iPB-1 aging is the change in a ratio of methyl/methylene functional groups; possibly because of a side chain splitting that reduces the geometric regularity of the molecular chain and consecutively slows down the proceeding phase transformation.

Inhibition of melanin synthesis and melanosome transfer by chitosan biomaterials.

Decreasing skin pigmentation is desirable for various medical or cosmetic conditions. Although numerous pharmaceutical agents are currently available, their depigmentation effects are still not satisfactory. In this study, we investigated the effects of chitosan, a natural marine product, on melanin synthesis and melanosome transfer. Treating B16F10 melanoma cells caused the inhibitory effect of chitosan on melanogenesis to be more prominent under α-melanocyte-stimulating hormone (α-MSH) stimulation. Chitosan samples of different molecular weights inhibited melanogenesis to a comparable extent, whereas increasing the deacetylation of chitosan enhanced its depigmentation effects. Chitosan was found to effectively reduce basal or α-MSH-stimulated melanogenesis by suppressing the expression of melanogenic-related proteins (microphthalmia transcription factor, tyrosinase, and tyrosinase-related protein-1 and protein-2) as well as inhibiting tyrosinase activity. Moreover, the inhibitory effect of chitosan on melanogenesis in human melanocytes was confirmed. A transwell coculture system using permeable inserts was designed to allow the contact of human melanocytes and human HaCaT keratinocytes through the tiny holes on the membrane. When chitosan was added to this melanocyte-keratinocyte coculture system, we observed decreased melanosome release from melanocytes. Reduced melanosome uptake by keratinocytes was also observed, and was probably mediated by inhibiting protease-activated receptor 2 expression. Many skin-whitening agents can modulate the process of melanogenesis, but few have been shown to inhibit the melanosome transfer and uptake process. We demonstrated that chitosan exhibits a robust effect on depigmentation by inhibiting melanogenesis as well as melanosome transfer and uptake. Therefore, chitosan represents a potential therapeutic agent for hyperpigmentation disorders.

Structural and biological evaluation of new chitosan membrane for dural closure

Objective: to study the structural and biological evaluation of chitin-chitosan based membrane for dura mater replacement. Materials and methods. Chitosan-based films were made out of 3% solution of chitosan for the research. We used 200, 500 and 700 kDa chitosan (deacetylation rate 80–90 %) to produce chitin-chitosan membrane by using solvent evaporation method. For enhancing mechanical properties and reducing the degradation, chitin particles were added to the chitosan solution. Chitosan and chitin ratio was 80/20. The chitin/chitosan solution in Petri dishes was dried out during 3 days at room temperature. To obtain information about the structure of membrane surface and cross-section scanning, electron microscopy was performed. Hydrolytic degradation was studied by pouring into SBF solution. To determine the rate of enzymatic degradation, trypsin solution was used. To determine the mass loss percentage, we measured the sample weight after 7, 14, 21, 30 and 60 days after being in the appropriate solutions. Relative elongation and strength were measured by digital dynamometer to study membranes mechanical properties such as the strength and elasticity. MLO-A5 cells were used to assess biocompatibility of new materials. Results. Macroscopic view of obtained samples has shown their relative transparency with impregnation of chitin particle that elevated over the membrane surface without any diversity between different chitosan molecular weight samples. Due to scanning electron microscopy, principal diversity between the samples of different molecular weight has being seen: rough pore surface at 200 and 500 kDa and flat with minimal roughness surface of 700 kDa membranes. Cross-section of 500 and 700 kDa membranes are dense with no pores, but 200 kDa membrane are sponge like and it can be prediction for fluid sorption and cell migration during healing process. Chitin-chitosan membranes are biocompatible and degrade in aqueous and enzymatic solutions. Due to polysaccharide nature of chitosan and chitin, enzymatic degradation has shown higher trend compare to the hydrolytic ones. 200 kDa membrane degrades faster with final mass loss 83.2 % and completely due to porous structure that allows fluid sorption. Membrane mechanical parameters strongly depend on their structure. 200 kDa membrane has shown 2-fold higher elongation compared to 500 kDa and 3-fold — compared to 700 kDa ones. The compensation of mechanical forces ensured by porous structure is better than in dense ones. Tensile strength was in 2-fold better in 200 kDa membranes than in 500 and 700 kDa ones. Cell culture experiment has shown the better adhesion at the 3 rd day for 200 kDa membrane and minimal cell adhesion for 700 kDa membrane, probably due to smooth surface. The reduction rate between all samples and PCT control differ a lot, except for 200 kDa membrane that has the same proliferation rate as TCP. Conclusion. Chitin-chitosan membranes, made from different molecular weight chitosan, are transparent and has appropriate structure for being used as a dura mater substitute. They are biocompatible and degrade in aqueous and enzymatic solutions. Due to porous structure, excellent mechanical properties as well as better cell adhesion and proliferation, 200 kDa chitosan membrane is more applicable for neurosurgical issues.

Chitosan-glutaraldehyde activated calcium pectinate beads as a covalent immobilization support

Chitosan (Chi) and glutaraldehyde (GA) were employed, for the first time, during the activation of calcium pectinate (CP) beads. The activated beads were able to covalently immobilize the model enzyme, β-D-galactosidase (β-gal). They also exhibited much higher mechanical stability than the unactivated CP beads. Different Chi samples of different molecular weights and degrees of deacetylation (DD) were tested for their efficiency as CP activators. Moreover, the Chi-GA activation process was optimized using the Box Behnken design which predicted that activating the CP beads with a 0.6% Chi solution of pH 3.41 and a 4.74% GA solution would allow for the attainment of 6.87 U/g gel of immobilized β-gal. The verification experiment, which was performed while employing the abovementioned conditions, confirmed this prediction as 6.77 ± 0.47 U/g gel of immobilized β-gal was attained. A reusability experiment was also performed, and it showed that the β-gal immobilized onto the optimally activated CP beads maintained 56.62% of its initial activity during the thirteenth reusability cycle.

The AGMA1 polyamidoamine mediates the efficient delivery of siRNA

AGMA1, a prevailingly cationic, guanidine-bearing, linear, amphoteric polyamidoamine is an effective siRNA condensing agent. Here two AGMA1 samples of different molecular weight, i.e. AGMA1–5 and AGMA1–10 were evaluated as siRNA condensing agents and transfection promoters. AGMA1–10 formed stable polyplexes with a size lower than 50 nm and positive zeta potential. AGMA1–5 polyplexes were larger, about 100 nm in size. AGMA1–10 polyplexes, but not AGMA1–5 proved to be an effective intracellular siRNA carrier, able to trigger gene silencing in Hela and PC3 cell lines without eliciting cytotoxic effects. AGMA1–10 knocked down AKT-1 expression upon transfection with an AKT-1 specific siRNA. The polyplex entry mechanism was investigated and was mediated by macropinocytosis. In conclusion, AGMA1 has potential as an efficient, non-toxic tool for the intracellular delivery of siRNA and warrants further investigation.

Metallic-like thermal conductivity in a lightweight insulator: Solid-state processed Ultra High Molecular Weight Polyethylene tapes and films

Ultra High Molecular Weight Polyethylene with a reduced number of entanglements can be stretched in the solid state both uni- or biaxially to produce highly oriented tapes and films. The chain orientation, in combination with the reduced number of chain ends, is responsible for the high tensile modulus and tensile strength of the drawn materials, and, as we report here, also for the high thermal conductivity achieved through lattice movements. A property such as thermal conductivity in an electrical insulator makes UHMWPE tapes and films of great applicative interest. In-plane laser-flash thermal analysis has been applied to measure the thermal diffusivity of samples of different molecular weights stretched both uni- and biaxially, and a strong correlation has been found between the drawing ratio and the resulting in-plane thermal conductivity. Values of at least 40 W/m K have been achieved for UHMWPE having Mw comprised between 2 and 10 million, while higher values of 65 W/m K are observed for the higher Mw samples having relatively lesser number of chain ends. Surprisingly the biaxially stretched samples also show in-plane conductivity, with the highest value reaching 18 W/m K, comparable to stainless steel.

Kinetic Study of Thermal Degradation of Polydimethylsiloxane: The Effect of Molecular Weight on Thermal Stability in Inert Atmosphere

Thermal degradation of polydimethylsiloxane (PDMS) of different molecular weights in inert and oxygen atmosphere is studied and discussed in detail. PDMS samples of different molecular weights were prepared by anionically initiated ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion. The molecular weight of PDMS drastically affected the shape of TGA curve at higher temperatures when thermogravimetric (TGA) measurements were performed in the inert atmosphere. The thermal stability of PDMS decreased with increasing the average molecular weight of the sample, which could be explained by prevailing unzipping mechanism at lower molecular weights over intramolecular and intermolecular redistribution, which were more important at higher molecular weights. On the other hand, experiments in oxygen atmosphere showed zero effect of polydimethylsiloxane molecular weight on its thermal stability. In addition, a kinetic model describing the thermal degradation of PDMS in inert atmosphere as a function of PDMS molecular weight was proposed. The proposed kinetic model was composed of diffusion-limited kinetics step related to evaporation rates of the degradation products and of rate-determined step related to the formation of cyclic degradation products. As a result of mathematical modeling by fitting the calculated data to experimental data kinetic parameters were derived properly.

Molecular weight effects in interactions of guar gum with talc

Interactions between talc and four non-ionic guar gum samples of different molecular weights (from 160,000 to 1.40 million) were evaluated through adsorption, flotation, and stability measurements. It was found that the effect of molecular weight on adsorption was insignificant and all four guar gums produced similar adsorption densities on the talc particles. Turbidity data also showed that all four polymers were strong flocculants of fine talc particles. However, higher molecular weight samples were more powerful than lower molecular weight samples. Higher doses of the polymers led to steric re-dispersion of talc, and lower molecular weight polymers were more efficient in dispersing talc than higher molecular weight polymers. Finally, all four polymers were equally effective as depressants of talc flotation. Most interestingly, it was found that the strongest depression of talc flotation was accompanied by very strong flocculation of the fine talc particles. Implications of these phenomena to the entrainment of fine talc during the froth flotation process were also discussed.

Characterization of chain dimensions of poly(ε-caprolactone) diols in THF by size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS)

In this work, we studied the chain dimensions, shape, and thermodynamic characteristics of poly(e-caprolactone) diols (HO-PCL-OH) in solution. PCL diol samples of different molecular weights and architectures were synthesized using immobilized Yarrowia lipolytica lipase as catalyst. Gel permeation chromatography (GPC) with online right-angle laser-light scattering (RALLS), differential viscometer (DV), and interferometric refractometer IRS detectors offered a proper way to obtain information on thermodynamic characteristics and chain flexibility. The weight-average molecular weights of the PCL diol samples (M w ) ranged from 2,750 to 13,120 uma. The z-average radius of hydrodynamic volume (<R h 2 > z 1/2 ) vs. z-average molecular weight curve (M z ) could be satisfactorily fitted to a power-law equation. Mark–Houwink–Sakurada parameters (K = 2.74 × 10−3 dL/g and a = 0.64) were derived from the plots of [η] w against M w . The overall results clearly suggest that a flexible geometry is present in tetrahydrofuran (THF) solution of PCL at 33 °C. Unlike other PCL systems, PCL diols are more hydrophilic and expected to form associated species. They behave differently from common hydrophobic polymers and do not strictly conform to thermodynamic relationships generally used in Polymer Science. A more compact geometry is present for Mn lower than 4,000 Da. For higher molecular weights, the chain expands and become more elongated. Plots of ln [η] w against ln M w (MHS equation) and of log R hz against log M z suggest that PCL diols behave as flexible chains in a good solvent.

Influence of Polymerization Conditions on Melting Kinetics of Low Entangled UHMWPE and Its Implications on Mechanical Properties

The synthesis of linear ultra high molecular weight polyethylene, with a “pseudoliving” catalyst in various conditions results in samples of different molecular weights (Mw ranging between 2 to 35 million g/mol), all having a reduced number of entanglements to an extent that allows the solid-state uniaxial deformation of such high molar masses without melting. The solid-state processing of these materials shows a clear relationship between mechanical properties and molecular weight. For the adopted polymerization conditions, stretching forces required for the uniaxial deformation increase with the increasing molar mass, ultimately limiting the achievable maximum draw ratio in the polymers having Mw > 10 million g/mol. The increase in the stretching force is attributed to the increasing number of entanglements between the crystals with the molar mass. The estimation of entanglements is established with the help of melting kinetics involved in the “disentangled” crystals, and rheological response of the polymer melt obtained just after melting of the crystals. In spite of the increase in the stretching forces with the increasing molar mass, tensile modulus increases with the increasing draw ratio and the molecular weight. However, above the molar mass of 10 million g/mol, the stretching force required increases to the level that the uniaxial deformation becomes difficult–thus limiting the tensile strength.

Chitosan-decorated polystyrene-b-poly(acrylic acid) polymersomes as novel carriers for topical delivery of finasteride

In view of the fact that the oral administration of finasteride (FIN) has resulted in various undesirable systemic side effects, the topical application of polystyrene and poly(acrylic acid)-based polymersomes (underexplored system) was investigated. Undecorated PS139-b-PAA17 and PS404-b-PAA63 vesicles (C3 and C7, respectively) or vesicles decorated with chitosan samples of different molecular weight (C3/CS-oligo, C7/CS-oligo, C3/CS-37 and C7/CS-37) were prepared by the co-solvent self-assembly method and characterized by small-angle X-ray scattering,transmission electron microscopy and dynamic light scattering techniques. In vitro release experiments and ex vivo permeation using Franz diffusion cells were carried out (through comparison with hydroethanolic finasteride solution). The ideal system should provide high finasteride retention in the dermis and epidermis while allowing some control of the drug release. The particle size and in vitro release were negatively correlated with the permeation coefficient and skin retention in both the epidermis and dermis. The findings that the longest lag time was obtained for the hydroethanolic drug solution and lowest permeation for the systems able to release the drug faster support the hypothesis that nanostructured systems may be required to enhance the penetration and permeation of the drug. Chitosan-decorated polymersomes interacted more strongly with the skin components than non-decorated samples, probably due to the positive surface charge, which increased the FIN retention and reduced the lag time. C7 polymersomes decorated with chitosan were more appropriate for topical applications (high retention in the dermis and epidermis and controlled drug delivery).

Instability of styrene/polystyrene/polybutadiene/polystyrene‐b‐polybutadiene emulsions that emulate styrene polymerization in the presence of polybutadiene

AbstractThis article investigates the room temperature demixing of oil‐in‐oil emulsions containing styrene (St), polybutadiene (PB), a St‐butadiene star block copolymer (BC), and two polystyrene (PS) samples of different molecular weights and is a contribution toward a better understanding of the stability/instability of the reaction mixture in a bulk high‐impact polystyrene (HIPS) process close to the phase inversion. Twelve bulk prepolymerizations of St in the presence of PB were emulated, at 10%, 15%, and 20% conversion; and with constant grafting efficiencies. All the blends contained 6% in weight of butadiene units. After stirring the blends for 24 h, the decantation demixing process was monitored along 30 days, with daily measurement of the interface levels after appearance of a clear interface. For some of the isolated phases, their unswollen morphologies were observed by transmission electron microscopy. All the isolated phases exhibited macrophase separation into homopolymer‐ and copolymer‐rich macrodomains with lamellar microdomains. The BC showed a greater affinity toward the PS‐rich phase. The separation of an independent BC‐rich phase in the blends containing the high molar mass PS and at high grafting efficiencies, modifies the idea of the graft‐ or BC molecules located at the interface of large PS‐rich and PB‐rich phases. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers

Complexation of Lysozyme with Poly(sodium(sulfamate-carboxylate)isoprene)

The complexation between hen egg white lysozyme (HEWL) and a novel pH-sensitive and intrinsically hydrophobic polyelectrolyte poly(sodium(sulfamate-carboxylate)isoprene) (SCPI), was investigated by means of dynamic, static, and electrophoretic light scattering and isothermal titration calorimetry measurements. The complexation process was studied at both pH 7 and 3 (high and low charge density of the SCPI, respectively) and under low ionic strength conditions for two polyelectrolyte samples of different molecular weights. The solution behavior, structure, and effective charge of the formed complexes proved to be dependent on the pH, the [-]/[+] charge ratio, and the molecular weight of the polyelectrolyte. Increasing the ionic strength of the solution led to vast aggregation and eventually precipitation of the complexes. The interaction between HEWL and SCPI was found to be mainly electrostatic, associated with an exothermic enthalpy change. The structural investigation of the complexed protein by fluorescence, infrared, circular dichroism spectroscopic, and differential scanning calorimetric measurements revealed no signs of denaturation upon complexation.

UCST-type behavior of poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) in aliphatic alcohols: solvent, co-solvent, molecular weight, and end group dependences

Poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) is shown to possess insoluble–soluble transitions (UCST-type phase behavior) in a large variety of aliphatic alcohols. Samples of different molecular weights ranging from 5 kg mol−1 to 23 kg mol−1 prepared by the RAFT process and featuring different end groups at each end were analyzed by cloud point measurements. Transitions occurred sharply and were fully reversible. The UCST was found to increase with an increasing molecular weight. Hydrophobic (alkyl chain) end groups were found to lower the critical temperature in isopropanol, while rigid aromatic end groups raised the transition temperature. In ternary mixtures of isopropanol/chloroform/POEGMA, the UCST decreased with an increasing chloroform concentration, with 10 vol% of chloroform accounting for a 30 °C drop. In mixtures of isopropanol/hexane/POEGMA, the cloud point increased significantly only with hexane concentrations above 30 vol%, at which level a 2 °C transition temperature increase was found. Addition of water to isopropanol solutions had a strong effect, with 1 vol% of water causing a decrease of the transition temperature of 12.5 °C. With an increasing chain length of the solvent, the cloud point increased, while a branching of the hydrocarbon chains lowered the cloud point. Samples of 23 kg mol−1POEGMA were for instance found to have cloud points of 22.0 °C in ethanol, 35.7 °C in isopentanol, and 75.4 °C in dodecanol.

Solution Behavior of Poly(sodium(sulfamate-carboxylate)isoprene), a pH Sensitive and Intrinsically Hydrophobic Polyelectrolyte

The solution properties of a novel pH sensitive and intrinsically hydrophobic polyelectrolyte poly(sodium(sulfamate-carboxylate)isoprene) (SCPI) were investigated by means of dynamic, static, and electrophoretic light-scattering and fluorescence spectroscopy techniques. Because of the pH dependent charge density of the polyelectrolyte chain, the dynamics and structure of the solution were studied at both pH 7 (high charge density) and pH 3 (low charge density) and at low ionic strength conditions for two samples of different molecular weights. In all cases, a fast and a slow diffusive mode were observed. The fast mode is attributed to the diffusion of isolated polyelectrolyte chains, while the slow mode denotes the presence of multichain domains in solution, formed by electrostatic and/or hydrophobic interactions. The size and density of the multichain domains were reduced with decreasing charge density and molecular weight. Effective charge of the particles does not depend appreciably on solution pH, while fluorescence spectroscopy revealed the presence of hydrophobic domains in the studied systems. It was found that increasing temperature resulted in the compaction of both isolated chains and multichain domains due to the hydrophobic effect. Furthermore the increase of the ionic strength of the solution led to a partial dissociation of the multichain domains at short times and at pH 7, while it led to increased aggregation and precipitation at pH 3 and long times. The performed experiments allowed for a separation of the electrostatic and hydrophobic contributions to the self-assembly of the particular polyelectrolyte systems.

Interaction between Poly(9,9-bis(6′-N,N,N-trimethylammonium)hexyl)fluorene phenylene) Bromide and DNA as Seen by Spectroscopy, Viscosity, and Conductivity: Effect of Molecular Weights and DNA Secondary Structure

The interaction between three poly(9,9-bis(6-N,N,N-trimethylammonium)hexyl)fluorene phenylene) bromide (HTMA-PFP) samples of different molecular weights (Mn=14.5, 30.1 and 61.3 kg/mol) and both dsDNA and ssDNA secondary structures has been studied using UV-visible absorption and fluorescence spectroscopies (including steady-state, time-resolved, and anisotropy measurements for the latter), viscosity, and electrical conductivity in 4% (v/v) DMSO-water mixtures. At low nucleic acid concentrations, formation of a 1:1 complex in terms of HTMA-PFP repeat units and DNA bases occurs. This interaction results in quenching of polymer emission. For higher molar ratios of DNA to HTMA-PFP, corresponding to charge neutralization, a second process is observed that is attributed to aggregate formation. From the changes in the absorption spectra, the polymer aggregation constant and the aggregate absorption spectra were calculated by applying an iterative method. Polymer aggregation dramatically quenches HTMA-PFP fluorescence in the region of the electroneutrality point. Under these conditions, the ratio of the emission intensity at 412 nm (maximum) to that at 434 nm (I412/I434) reaches a minimum, the electrical conductivity decreases, and the viscosity of the solution remains constant, showing that the DNA concentration can be determined through various HTMA-PFP physicochemical properties. With respect to the photophysical parameters (emission quantum yield, shape and shift of emission spectra), no significant differences were observed between dsDNA and ssDNA or with conjugated polymer or DNA molecular weight. The two short-lived components in the fluorescence decays are attributed to the presence of aggregates. Aggregates are also suggested to be responsible for the decrease in the fluorescence anisotropy through interchain exciton migration.

RHEOLOGICAL PROPERTIES OF POLY(VINYLIDENE FLUORIDE) IN MOLTEN STATE

The rheological behavior of poly(vinylidene fluoride) (PVDF) samples of different molecular weights was investigated by means of high pressure capillary rheometer and rotational rheometer. Information on the rheological properties of such materials above melt temperatures is of interest as this can lead to an improved understanding of polymer behavior in processing and fabrication technologies. Shift factors derived from time-temperature superposition showed good fit to the Arrhenius equation with a flow activation energy E of almost 74 kJ/mol, which was essentially independent of polymer molecular weight suggesting the unit of flow was a collective motion of chain segments rather than the whole chain itself.