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Chain Mobility (chain + mobility)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Distribution within Polymers and Materials Science

Polymer Science & Technology General	72%
General & Introductory Materials Science	18%

Selected Abstracts

Aging Effects on the Phase Composition and Chain Mobility of Isotactic Poly(propylene)

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2008
Cristian Hedesiu
Abstract Changes in phase composition and chain mobility in injection-molded isotactic poly(propylene), crystallized from the melt with slow cooling rate and subsequently quenched, associated with aging at temperature well above Tg for 150 and 1 000 h, are studied using time-domain 1H solid-state NMR and XRD. All sample exhibit physical aging when exposed to elevated temperatures, and the physical aging kinetics was observed to depend on the morphology of the homopolymer iPP and aging temperatures. The significant increase in the tensile modulus in time was observed for injection-molded iPP. The observed property changes induced by aging are attributed to microstructural changes within the semi-rigid and amorphous fractions. [source]

A Spring-Like Behavior of Chiral Block Copolymer with Helical Nanostructure Driven by Crystallization

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
Yeo-Wan Chiang
Abstract The crystallization of helical nanostructure resulting from the self-assembly of a chiral diblock copolymer, poly(styrene)- b -poly(L -lactide) (PS-PLLA), is studied. Various crystalline PS-PLLA nanostructures are obtained by controlling the crystallization temperature of PLLA (Tc,PLLA), at which crystalline helices and crystalline cylinders occur while Tc,PLLA,<,Tg,PS (the glass transition temperature of PS) and Tc,PLLA,,,Tg,PS, respectively. As evidenced by selected-area electron diffraction and two-dimensional X-ray diffraction results, the PLLA crystallites under confinement reveal a unique anisotropic character regardless of the crystallization temperature. On the basis of observed uniaxial scattering results the PLLA crystallites grown within the microdomains are identified as crystals with preferential growth directions either along the [100] or along the [110]-axes of the PLLA crystalline unit cell, at which the molecular chains and the growth direction are normal and parallel to the central axes of helices, respectively. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA,<,Tg,PS, owing to the directed crystallization by helical confinement, the preferential crystalline growth leads to the crystallization following a helical track with growth direction parallel to the central axes of helices through a twisting mechanism. Consequently, winding crystals with specific crystallographic orientation within the helical microdomains can be found. By contrast, while Tc,PLLA,,,Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices, resulting in crystalline cylinders that might be applicable to the design of switchable large-strain actuators. [source]

Low-Temperature Fusion of Polymeric Nanostructures Using Carbon Dioxide,

ADVANCED MATERIALS, Issue 2 2007
Y. Yang
A low-temperature fusion method for preparing polymeric nanostructures based on low-pressure CO2 -enhanced chain mobility at the nanoscale is presented. Characterization of the structures reveals a pressure-tunable rubbery layer on the surface. The successful fusion of polymeric nanostructures (see figure) at temperatures below the bulk glass-transition temperature of the polymer is demonstrated. The technique has potential for the assembly of 3D micro/nanoscale polymeric devices for biomedical applications. [source]

Impact of H+ ion beam irradiation on Matrimid®.

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007

Abstract Ion beam irradiation is an easily controlled method to modify the chemical structure and microstructure of polymers including the fractional free volume, free volume distribution and chain mobility, thus altering the gas transport properties of the irradiated polymers. The previous paper focused on the impact of H+ ion beam irradiation on chemical structural evolution of the polyimide Matrimid®. This paper focuses on the impact of H+ ion beam irradiation on microstructure and gas permeation properties of Matrimid®. Irradiation at low ion fluence resulted in slight decreases in permeabilities for five gases (i.e., He, CO2, O2, N2, and CH4) with increases in permselectivities for some gas pairs (e.g., He/CH4 and He/N2). In contrast, irradiation at relatively high ion fluences resulted in simultaneous increases in permeabilities and permselectivities for most gas pairs (e.g., He/CH4, He/N2, O2/N2, and CO2/CH4). While Matrimid® has bulk gas permeation properties that are below the range of commercially interesting polymers, samples irradiated at high ion fluences exhibited significant improvement in gas separation performances. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1670,1680, 2007 [source]

Synthesis, characterization, and cross-linking of a library of statistical copolymers based on 2-"soy alkyl"-2-oxazoline and 2-ethyl-2-oxazoline

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007
Richard Hoogenboom
Abstract The synthesis of statistical copolymers consisting of 2-ethyl-2-oxazoline (EtOx) and 2-"soy alkyl"-2-oxazoline (SoyOx) via a microwave-assisted cationic ring-opening polymerization procedure is described. The majority of the resulting copolymers revealed polydispersity indices below 1.30. The reactivity ratios (rEtOx 1.4 ± 0.3; rSoyOx = 1.7 ± 0.3) revealed a clustered monomer distribution throughout the polymer chains. The thermal and surface properties of the pEtOx- stat -SoyOx copolymers were analyzed before and after UV-curing demonstrating the decreased chain mobility after cross-linking. In addition, the cross-linked materials showed shape-persistent swelling upon absorption of water from the air, whereby as little as 5 mol % SoyOx was found to provide efficient cross-linking. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5371,,5379, 2007 [source]

Aging Effects on the Phase Composition and Chain Mobility of Isotactic Poly(propylene)

Use of Single-Walled Carbon Nanotubes as Reinforcing Fillers in UV-Curable Epoxy Systems

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2008
Marco Sangermano
Abstract CNT were dispersed in an epoxy matrix and cured by means of UV light. An increase on elastic modulus and Tg values was measured by DMTA analysis and attributed to the constraint effect of CNT on polymer chain mobility. Excellent scratch resistant coatings characterized by high critical load, small cracks and high recovery were obtained in the presence of a very low CNT content (0.025 wt.-%). TEM analysis showed some isolated CNT and some cluster agglomerations of size of about 250 nm. It was shown that it was possible to decrease the surface resistivity of the cured samples by three orders of magnitude in the presence of 0.1 wt.-% of SWCNT content. [source]

Synthesis of Well-Defined Figure-of-Eight-Shaped Polymers by a Combination of ATRP and Click Chemistry

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2008
Gang-Yin Shi
Abstract Well-defined figure-of-eight-shaped (8-shaped) polystyrene (PS) with controlled molecular weight and narrow polydispersities has been prepared by the combination of atom transfer radical polymerization (ATRP) and click chemistry. The synthesis involves two steps: 1) Preparation of a linear tetrafunctional PS with two azido groups, one at each end of the polymer chain, and two acetylene groups at the middle of the chain. 2) Intramolecular cyclization of the linear tetrafunctional PS at a very low concentration by a click reaction to produce the 8-shaped polystyrenes. The resulting intermediates and the target polymers were characterized by 1H NMR and FT-IR spectroscopy, and gel permeation chromatography. The glass transition temperatures (Tgs) were determined by differential scanning calorimetry and it was found that the decrease in chain mobility by cyclization resulted in higher Tgs for 8-shaped polystyrenes as compared to their corresponding precursors. [source]

Mechanical properties of Al2O3/polymethylmethacrylate nanocomposites

POLYMER COMPOSITES, Issue 6 2002
Benjamin J. Ash
Alumina/polymethylmethacrylate (PMMA) nanocomposites were produced by incorporating alumina nanoparticles, synthesized using the forced gas condensation method, into methylmethacrylate. The particles were dispersed using sonication and the composites were polymerized using free radical polymerization. At an optimum weight percent, the resulting nanocomposites showed, on average, a 600% increase in the strain-to-failure and the appearance of a well-defined yield point when tested in uniaxial tension. Concurrently, the glass transition temperature (Tg) of the nanocomposites dropped by as much as 25°C, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively. For comparison, composites containing micron size alumina particles were synthesized and displayed neither phenomenon. Solid-state deuterium NMR results showed enhanced chain mobility at room temperature in the nanocomposites and corroborate the observed Tg depression indicating considerable main chain motion at temperatures well below those observed in the neat polymer. A hypothesis is presented to relate the thermal and mechanical behavior observed in the composites to the higher chain mobility and Tg depression seen in recent ultrathin polymer film research. [source]

Crystallization and thermal behavior of multiwalled carbon nanotube/poly(butylenes terephthalate) composites

POLYMER ENGINEERING & SCIENCE, Issue 6 2008
Defeng Wu
Multiwalled carbon nanotube/poly(butylene terephthalate) composites (PCTs) were prepared by melt mixing. The nonisothermal crystallization and thermal behavior of PCTs were respectively investigated by X-ray diffractometer, polarized optical microscope, differential scanning calorimeter, dynamic mechanical thermal analyzer, and thermogravimetric analyzer. The presence of nanotubes has two disparate effects on the crystallization of PBT: the nucleation effect promotes kinetics, while the impeding effect reduces the chain mobility and retards crystallization. The kinetics was then analyzed using Ozawa, Mo, Kissinger, Lauritzen-Hoffman, and Ziabicki model, and the results reveal that the nucleation effect is always the dominant role on the crystallization of PBT matrix. Thus the crystallizability increases with increase of nanotube loadings. In addition, the presence of nanotubes nearly has no remarkable contribution to thermal stability because nanotubes also play two disparate roles on the degradation of PBT matrix: the Lewis acid sites to facilitate decomposition and the physical hindrance to retard decomposition. Hence the nanotubes act merely as inert-like filler to thermal stability. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

The effect of recycling on LDPE foamability: Elongational rheology

POLYMER ENGINEERING & SCIENCE, Issue 1 2008
Eddy Twite Kabamba
The purpose of this work was to investigate changes in the elongational rheology of low density polyethylene (LDPE) when recycled. Both foamed and unfoamed LDPE were submitted up to 10 generations in a closed loop using constant extrusion conditions and azodicarbonamide as a chemical blowing agent. For both foamed and unfoamed polymers, decreasing elongational properties in terms of strain hardening was observed, indicating progressive loss of foamability with the number of time the polymer is recycled. It was also found that the elongational properties of the foamed polymer decreased more rapidly than its unfoamed counterpart. It is believed that higher mechanical degradation of polymer may be the result of higher deformation rates (biaxial) associated with foaming and the accumulation of blowing agent residues limiting polymer chain mobility and entanglement. POLYM. ENG. SCI., 48:11,18, 2008. © 2007 Society of Plastics Engineers [source]