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Chain Architecture (chain + architecture)

Distribution by Scientific Domains

Polymers and Materials Science	80%

Selected Abstracts

Effect of chain architecture on biaxial orientation and oxygen permeability of polypropylene film

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008
P. Dias
Abstract Films of two isotactic propylene homopolymers prepared with different catalysts and a propylene/ethylene copolymer were biaxially oriented under conditions of temperature and strain rate that were similar to those encountered in a commercial film process. The draw temperature was varied in the range between the onset of melting and the peak melting temperature. It was found that the stress response during stretching depended on the residual crystallinity in the same way for all three polymers. Biaxial orientation reduced the oxygen permeability of the oriented films, however, the reduction did not correlate with the amount of orientation as measured by birefringence, with the fraction of amorphous phase as determined by density, or with free volume hole size as determined by PALS. Rather, the decrease in permeability was attributed to reduced mobility of amorphous tie molecules. A single one-to-one correlation between the oxygen permeability and the intensity of the dynamic mechanical ,-relaxation was demonstrated for all the polymers used in the study. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Novel Dynamic Viscoelastic Measurements of Polyurethane Copolymer Melts and Their Implication to Tack Results

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006
Sonia Florez
Abstract Summary: A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane-1,6-diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard-to-soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard-to-soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress-strain curves in tack experiments. The storage modulus of the adhesives as a function of frequency at 70,°C. [source]

Synthesis and characterization of semifluorinated polymers and block copolymers

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Doris Pospiech
Abstract The goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self-organization. The influence of the chain architecture on the self-organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self-organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains. [source]

A comparative study of multimodal vs. bimodal polyethylene pipe resins for PE-100 applications,

POLYMER ENGINEERING & SCIENCE, Issue 9 2005
Paul J. DesLauriers
In this paper several high density polyethylene pipe resins are compared to polyethylene resins made in the Phillips Loop-Slurry Process (single-reactor), using a catalyst of chromium on modified aluminophosphate (Cr/AlPO4). A brief description of the Cr/AlPO4 system is presented along with polymer chain architecture (i.e., topology) and other structural aspects of polymers made from these catalysts. The physical properties of these resins and their fabricated pipe processing/performance properties were compared to both PE80 and conventional bimodal type PE-100 resins. Results from this study show that high-density polyethylene resins made from Cr/AlPO4 catalysts possess primary structural attributes that are truly unique for chromium-catalyzed resins. These multimodal resins have very high molecular weights (MW; Mw > 400 kg/mol) and exceptionally broad MW distributions (MWD; Mw/Mn > 50). Topologically, these resins were found to have uniform short chain branching distributions across the MWD; as in polymers made from single site metallocene catalysts) and significantly reduced levels (10 times less) of long chain branching when compared to resins made using chromium catalysts on conventional supports. Furthermore, results from rheological, fabricated pipe processing, and performance studies suggest that these resins should be especially well suited for high performance pipe applications. Pipe samples made from these resins were found to meet PE-100 requirements including low temperature impact properties. POLYM. ENG. SCI., 45:1203,1213, 2005. © 2005 Society of Plastics Engineers [source]

Multicompartment Micelles From ,-Shaped ABC Block Copolymers

CHINESE JOURNAL OF CHEMISTRY, Issue 11 2007
Jun XIA
Abstract Dissipative particle dynamics simulations were performed on the morphology and structure of multicompartment micelles formed from ,-shaped ABC block copolymers in water. The influences of chain architectures were studied in a systematic way, and a rich variety of morphologies were observed, such as spherical, wormlike, X-shaped, Y-shaped, ribbon-like, layered rod-like, layered disk-like, as well as network morphologies. The simulations show that the distance between the two grafts plays an important role in control of the morphology. Since ,-shaped ABC block copolymers can be reduced to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self-assembly of complex block copolymers into micelles. The knowledge obtained in this work as well as the new morphologies identified provide useful information for future rational design and synthesis of novel multicompartment micelles. [source]