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Highest Molecular Weight (highest + molecular_weight)
Selected AbstractsLiving carbocationic copolymerization of isobutylene with styreneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007Judit E. Puskas Abstract The carbocationic copolymerization of isobutylene (IB) and styrene (St), initiated by 2-chloro-2,4,4-trimethylpentane/TiCl4 in 60/40 (v/v) methyl chloride/hexane at ,90 °C, was investigated. At a low total concentration (0.5 mol/L), slow initiation and rapid monomer conversion were observed. At a high total comonomer concentration (3 mol/L), living conditions (a linear semilogarithmic rate and Mn,conversion plots) were found, provided that the St concentration was above a critical value ([St]0 , 0.6 mol/L). The breadth of the molecular weight distribution decreased with increasing IB concentration in the feed, reaching Mw/Mn , 1.1. St homopolymerization was also living at a high total concentration, yielding polystyrene with Mn = 82,000 g/mol, the highest molecular weight ever achieved in carbocationic St polymerization. An analysis of this system by both the traditional gravimetric,NMR copolymer composition method and FTIR demonstrated penultimate effects. IB enrichment was found in the copolymers at all feed compositions, with very little drift at a high total concentration and above the critical St concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1778,1787, 2007 [source] Pulsed field gradient (PFG) NMR spectroscopy: An effective tool for the analysis of mixtures of lubricating oil componentsLUBRICATION SCIENCE, Issue 4 2000G. S. Kapur Abstract In the presently reported work, the multinuclear two-dimensional (2D) diffusionordered nuclear magnetic resonance (NMR) spectroscopy (DOSY) technique based on the pulsed field gradient (PFG) has been used in experiments to analyse mixtures of lubricating oil components. One-dimensional (1D) PFG experiments have also been used to simplify and edit the NMR spectra of the mixtures. Such experiments provide a clean spectrum of the highest molecular weight (slower diffusing) component by eliminating the signals of lower molecular weight (faster diffusing) components, without any prior physical separation. These pulsed field gradient experiments not only facilitate the separation of resonance signals of different components, but also lead to their subsequent identification, and provide information about the number and structure of components in a mixture. Some examples of our initial efforts to establish 1D and 2D PFG-based NMR experiments for the analysis of mixtures of lubricating oil components are given and assessed to illustrate the potential applications of such techniques in the field of lubricating oils. [source] Anionic and ionic coordinative polymerization of ,-caprolactonePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2001Dr Cristina Stere Abstract The polymerization of ,-caprolactone initiated by two catalyst systems was studied: (1) carbazole-potassium in the presence of 18-crown-6 ether and (2) NdCl3/TBP/TIBA (neodymiumtrichloride/tri-n-butyl-phosphate/triisobutylaluminium) at the molar ratio 1/3/1. For both initiator systems conversion/time plots were determined and the polymers were characterized by IR, GPC and by 1H - and 13C,NMR spectroscopy. Polyesters with the highest molecular weight (Mn,44 000 g/mol) were obtained for the polymerizations initiated by the carbazole-potassium/18-crown-6 ether system. The features of the polymerization initiated by the carbazole-potassium/18-crown-6 ether system are discussed on the basis of a simple scheme. The nature of this polymerization is non-living. Copyright © 2000 John Wiley & Sons, Ltd. [source] New Polymer Syntheses, 112MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2003Hans R. Kricheldorf Abstract Bis(4-chlorophenyl)sebacate (BCPS) was polycondensed with 1,12-diamino-4,9-dioxadodecane or with its bistrimethylsilyl derivative in three different solvents with variation of time and temperature. The highest molecular weights were obtained in dimethylsulfoxide at 60,°C. The highest fraction of cyclic polyamides was detected by MALDI-TOF mass spectrometry in the samples with the highest molecular weights. Numerous polycondensations of BCPS and 1,13-diamino-4,7,10-trioxatridecane were performed with variation of solvent, time and temperature. Again the best results were obtained in dimethylsulfoxide at 60,°C. The fraction of cyclic polyamides increased with higher average molecular weights of the samples. The MALDI-TOF mass spectrum of the sample with the highest molar mass (Mn ca. 30,000 Da) exclusively displayed mass peaks of cycles (detected up to 13,000 Da). No side reactions were observed. MALDI-TOF mass spectrum (segment) of polyamide 1 prepared by polycondensation of DDD with BCPS in DMSO at 60,°C/48 h (no. 3, Table 1). [source] | ||||||||||