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MW Distribution (mw + distribution)
Selected AbstractsIN VITRO DIGESTIBILITY OF CHINESE TARTARY BUCKWHEAT PROTEIN FRACTIONS: THE MICROSTRUCTURE AND MOLECULAR WEIGHT DISTRIBUTION OF THEIR HYDROLYSATESJOURNAL OF FOOD BIOCHEMISTRY, Issue 5 2006XIAONA GUO ABSTRACT Our previous study showed that in vitro pepsin digestibility of Chinese tartary buckwheat protein was relatively low compared to those of other edible seeds. In vitro pepsin digestibilities of four protein fractions of tartary buckwheat, microstructure and molecular weight (MW) distributions of hydrolysates were investigated. In vitro pepsin digestion assay showed that the digestibilities of tartary buckwheat protein fractions were albumin (81.20%), globulin (79.56%), prolamin (66.99%) and glutelin (58.09%). Scanning electron microscopy showed that albumin and globulin fractions were digested by pitting from the outer surface to the inner part and were more digestible, while prolamin and glutelin fractions resisted digestion because only the outer surfaces of their protein bodies were digested and the interior was protected. MW distribution of the hydrolysates from the four protein fractions was determined by high-performance liquid chromatography. The hydrolysates of albumin mainly consisted of polypeptides with lower MW. The hydrolysates of glutelin had larger polypeptides together with small and medium-sized peptide fractions. [source] Short chain branching profiles in polyethylene from the Phillips Cr/silica catalystJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2007Paul J. DesLauriers Abstract SEC and on-line Fourier transform infrared spectroscopy analysis have been combined to study branching profiles from the Phillips Cr/silica catalyst. For the first time, catalyst and reactor variables have been shown to affect the overall level and distribution of branches in polyethylene copolymers. Branching profiles from various chromium catalysts have been shown to vary from highly concentrated in the low MW end, to uniformly distributed over all of the MW range. Activation temperature and the presence of titania were highly influential. These observations, which have been used to gain insight into the chemistry of Cr/silica, explain much of the catalyst behavior that has for decades been used to optimize polymer properties. Trends in ESCR, impact resistance, and other physical characteristics, which were long attributed to changes in MW distribution, can now be seen to also be due in large part to changes in the branching profile. This knowledge should be of value in designing future resins. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3135,3149, 2007 [source] A comparative study of multimodal vs. bimodal polyethylene pipe resins for PE-100 applications,POLYMER ENGINEERING & SCIENCE, Issue 9 2005Paul 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] Branched polystyrene with abundant pendant vinyl functional groups from asymmetric divinyl monomerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2008Zhong-Min Dong Abstract Branched polystyrenes with abundant pendant vinyl functional groups were prepared via radical polymerization of an asymmetric divinyl monomer, which possesses a higher reactive styryl and a lower reactive butenyl. Employing a fast reversible addition fragmentation chain transfer (RAFT) equilibrium, the concentration of active propagation chains remained at a low value and thus crosslinking did not occur until a high level of monomer conversion. The combination of a higher reaction temperature (120 °C) and RAFT agent cumyl dithiobenzoate was demonstrated to be optimal for providing both a more highly branched architecture and a higher polymer yield. The molecular weights (Mws) increased with monomer conversions because of the controlled radical polymerization characteristic, whereas the Mw distributions broadened showing a result of the gradual increase of the degree of branching. The evolution of branched structure has been confirmed by a triple detection size exclusion chromatography (TRI-SEC) and NMR technique. Furthermore, the double bonds in the side chains were successfully used for chemical modification reactions. 1H NMR and FTIR measurements reveal that the great mass of pendant vinyl groups were converted to the corresponding objective end-groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6023,6034, 2008 [source] | ||||||||||