Home About us Contact
|
Home About us Contact | ||
|
|
||
Vinyl Acetate Content (vinyl + acetate_content)
Selected AbstractsEnd-functionalized copolymers prepared by the addition,fragmentation chain-transfer method: Vinyl acetate/methacrylonitrile systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2001W. Ken Busfield Abstract Copolymers of vinyl acetate and methacrylonitrile were prepared by free-radical polymerization in the presence of the chain-transfer agent (CTA) ethyl-,- (t -butanethiomethyl)acrylate. Molecular weight measurements showed that the chain-transfer constants increased with the vinyl acetate content of the comonomer mixture, ranging from 0.42 for methacrylonitrile to 6.3 for the copolymerization of a vinyl acetate-rich monomer mix (89/11). The bulk copolymer composition was not appreciably affected by the amount of CTA used in the copolymerization. The efficiency of the addition,fragmentation mechanism in producing specifically end-functionalized copolymers was investigated with 1H NMR spectroscopy. Spectral peaks consistent with all the expected end groups were observed for all comonomer feeds. Peaks consistent with other end groups were also observed, and these were particularly prominent for copolymers made with lower CTA concentrations. At the highest concentrations used, quantitative measurements of end-group concentrations indicated that 70,80% of the end groups were those expected on the basis of the addition,fragmentation chain-transfer mechanism. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2911,2919, 2001 [source] Synthesis and Thermosensitive Properties of Poly[(N -vinylamide)- co -(vinyl acetate)]s and Their Hydrogels,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2003Kazuya Yamamoto Abstract Free radical copolymerization of water-soluble N -vinylamides such as N -vinylacetamide (NVA) and N -vinylformamide (NVF) with hydrophobic vinyl acetate (VAc) gave amphiphilic copolymers. The monomer reactivity ratios were determined as r1,=,5.8 and r2,=,0.68 (M1,=,NVA, M2,=,VAc) and r1,=,6.2 and r2,=,0.37 (M1,=,NVF, M2,=,VAc), respectively. The growing radical of the terminals of N -vinylamides propagates more favorably for N -vinylamide monomers than for VAc monomer, resulting in the possible formation of blocky copolymers. It is found that aqueous solutions of these amphiphilic copolymers exhibited a lower critical solution temperature (LCST), depending on their chemical composition, followed by coacervate formation above the LCST. Furthermore, thermosensitive hydrogels could be prepared by the free radical copolymerization of N -vinylamide and VAc in the presence of the crosslinker butylenebis(N -vinylacetamide) (Bis-NVA). The swelling ratios of these hydrogels decreased with an immediate increase in temperature from 20 to 80,°C, and then reversibly increased with decreasing temperature. These hydrogels showed the same thermosensitive properties as linear copolymers of NVF and VAc. Relationship between LCST and vinyl acetate content in poly(N -vinylamide- co -VAc)s. [source] Ethylene vinyl acetate/Mg-Al LDH nanocomposites by solution blendingPOLYMER COMPOSITES, Issue 4 2009T. Kuila Partially exfoliated ethylene vinyl acetate (EVA-40, 40% vinyl acetate content)/layered double hydroxide (LDH) nanocomposites using organically modified layered double hydroxide (DS-LDH) have been synthesized by solution intercalation method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies of nanocomposites shows the formation of exfoliated LDH nanolayers in EVA-40 matrix at lower DS-LDH contents and partially intercalated/exfoliated EVA-40/MgAl LDH nanocomposites at higher DS-LDH contents. These EVA-40/MgAl LDH nanocomposites demonstrate a significant improvement in tensile strength and elongation at break for 3 wt% of DS-LDH filler loading compare to neat EVA-40 matrix. Thermogravimetric analysis also shows that the thermal stability of the nanocomposites increases with DS-LDH content in EVA-40. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Metallocene based polyolefin: a potential candidate for the replacement of flexible poly (vinyl chloride) in the medical fieldPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2010M. C. Sunny Abstract A comparative assessment of the performance properties of metallocene polyolefin (m-PO) with those of plasticized poly (vinyl chloride) (pPVC) and ethylene vinyl acetate (EVA) copolymer having 18% vinyl acetate content (EVA-18), the two common polymers used for flexible medical products, is carried out. The preliminary evaluation of the processability, mechanical properties, and thermal stability of the new material, m-PO is described. The processability parameters like mixing torque and melt viscosity of m-PO are found to be comparable with those of pPVC and EVA-18. Mechanical properties such as tensile strength, elongation at break, and tear strength (TS) of m-PO are much higher than that of pPVC and EVA-18. Thermo gravimetric analysis (TGA) indicates that the thermal degradation of m-PO takes place only at temperatures above 340°C and can be processed at 170°C without much damage. Oxygen and carbon dioxide permeabilities of m-PO at three different temperatures (10, 25, and 40°C) are evaluated and compared with those of pPVC and EVA-18. It could be seen that the permeabilities of both the gases for m-PO at three temperatures were lower than those of pPVC and EVA. Biological evaluation of m-PO is carried out by assessing its cytotoxicity, hemolytic property, and blood clotting initiation. The cytotoxicity studies indicate that m-PO is non-toxic to the monolayer of L929 mammalian fibroblast cell lines on direct contact or the exposure of its extract. Non-hemolytic property of m-PO by direct contact as well as test on extract is revealed both in static and in dynamic conditions. Blood clotting time experiments indicate that the initiation of blood clotting due to m-PO is faster than that of pPVC and EVA-18. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||