			Home About us Contact

Polymer Decreased (polymer + decreased)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Synthesis and characterization of poly(ethylene oxide- co -ethylene carbonate) macromonomers and their use in the preparation of crosslinked polymer electrolytes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2006
Anette Munch Elmér
Abstract Methacrylate-functionalized poly(ethylene oxide- co -ethylene carbonate) macromonomers were prepared in two steps by the anionic ring-opening polymerization of ethylene carbonate at 180 °C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number-average molecular weight of 2650 g mol,1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self-supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 × 10,6 S cm,1 at 20 °C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195,2205, 2006 [source]

Efficient Molecular Weight Control with Trialkylaluminum in Ethylene/Norbornene Copolymerization by [Ph2C(Flu)(3-MeCp)]ZrCl2/Methylaluminoxane Catalyst

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19 2010
Tomoyuki Tada
Abstract Ethylene/norbornene copolymerizations were conducted with [Ph2C(Flu)(3-RCp)]ZrCl2 [R: Me (1) or Me3Si (2)], which give alternating EN copolymers. The activity of 1 in the absence of R3Al was approximately twice that of 2 and increased further upon addition of R3Al. Et3Al increased the activity most effectively, and the of the produced polymer decreased from 100 000 to 25 000,g,·,mol,1. On the other hand, the value increased upon addition of iBu3Al from 100 000 to 209 000,g,·,mol,1 accompanied by an ,2.5-fold increase of activity. Consequently, 1 was found to be one of the most promising complexes for the synthesis of alternating EN copolymers, of which value was efficiently controlled by the kind and the amount of R3Al added. [source]

Metallocene-Catalyzed Gas-Phase Ethylene Copolymerization: Kinetics and Polymer Properties

MACROMOLECULAR REACTION ENGINEERING, Issue 8 2009
Michiel F. Bergstra
Abstract The influence of 1-hexene is examined on the kinetics of ethylene copolymerization with a metallocene catalyst in gas phase. A model is derived, which is able to describe a large reaction rate increase due to a small amount of incorporated comonomer. This complexation model describes the measured reaction rates for ethylene and 1-hexene, and the co-monomer incorporation. Polymer properties were analyzed, such as comonomer weight fraction. The density, melting point, and molecular weight of the produced polymer decreased with increase in 1-hexene gas concentration. The in situ 1-hexene sorption is estimated and follows Henry's law, but seems much higher than reported in the literature. [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]

Ethylene and Propylene Polymerization Using In Situ Supported Me2Si(Ind)2ZrCl2 Catalyst: Experimental and Theoretical Study

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2006
Fernando C. Franceschini
Abstract Summary: Me2Si(Ind)2ZrCl2 was in situ immobilized onto SMAO and used for ethylene and propylene polymerization in the presence of TEA or TIBA as cocatalyst. The catalytic system Me2Si(Ind)2ZrCl2/SMAO exhibited different behavior depending on the amount and nature of the alkylaluminum employed and on the monomer type. The catalyst activity was nearly 0.4 kg polymer,·,g cat,1,·,h,1 with both cocatalysts for propylene polymerization. Similar activities were observed for ethylene polymerization in the presence of TIBA. When ethylene was polymerized using TEA at an Al/Zr molar ratio of 250, the activity was 10 times higher. Polyethylenes made by in situ supported or homogeneous catalyst systems had practically the same melting point (Tm). On the other hand, poly(propylenes) made using in situ supported catalyst systems had a slightly lower Tm than poly(propylenes) made using homogeneous catalyst systems. The nature and amount of the alkylaluminum also influenced the molar mass. The poly(propylene) molar mass was higher when TIBA was the cocatalyst. The opposite behavior was observed for the polyethylenes. Concerning the alkylaluminum concentration, the molar mass of the polymers decreased as the amount of TEA increased. In the presence of TIBA, the polyethylene's molar mass was almost the same, independent of the alkylaluminum concentration, and the poly(propylene) molar mass increased with increasing amounts of cocatalyst. The deconvolution of the GPC curves showed 2 peaks for the homogeneous system and 3 peaks for the heterogeneous in situ supported system. The only exception was observed when TEA was used at an Al/Zr molar ratio of 500, where the best fit was obtained with 2 peaks. Based on the GPC deconvolution results and on the theoretical modeling, a proposal for the active site structure was made. Molar mass distribution deconvolution of polyethylene prepared with the system Me2Si(Ind)2ZrCl2/SMAO/TIBA with 500 mol/mol of alkylaluminum as cocatalyst. [source]

Low Bandgap Polymers by Copolymerization of Thiophene with Benzothiadiazole

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2009
Youjun He
Abstract Three low bandgap copolymers of thiophene and benzothiadiazole with electron-donating and electron-withdrawing substituents, P1, P2, and P3, have been synthesized by Pd-catalyzed Stille-coupling. Electronic energy levels of the polymers are estimated by cyclic voltammetry. The polymer films show a broad absorption band in the wavelength range from 300 to 750 nm. Among the polymers, the polymer that contains the 5,6-dinitrobenzothiadiazole unit, P3, possesses the smallest bandgap of 1.55 eV calculated from its absorption band-edge at ,800 nm. With the increase of the electron-withdrawing ability of the substituents on the benzothiadiazole unit, the energy bandgap of the polymers decreased in the order P1,>,P2,>,P3. The results indicate that stronger electron-withdrawing substituents on the acceptor unit can effectively decrease the bandgap of the polymers. [source]