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101.
C. Garrett Campbell Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2017,55(12):1991-1997
Lewis‐acid catalyzed degradation of poly(isobutylene‐co‐isoprene) (butyl rubber) in the presence of an alkoxybenzene compound was studied as a new route toward low molecular weight multifunctional polyisobutylenes. Simultaneous cleavage and functionalization of butyl rubber was conducted at ?70 °C and ?40 °C under TiCl4 or AlCl3 catalysis in 60/40 hexane/methylene chloride cosolvents in the presence of (3‐bromopropoxy)benzene (BPB) for various times up to 24 h. The butyl rubber (EXXON? Butyl 365) possessed M n = 1.91 × 105 g/mol, PDI = 1.66 (GPC/MALLS), and 2.30 mol % isoprene units (nearly exclusively trans ?1,4). At ?70 °C with TiCl4, molecular weight was reduced to various values within the range 7 to 11 × 103 g/mol depending on conditions; lower BPB concentration produced lower molecular weight. However, the ratio of isobutylene repeat units to BPB units (IB/Q ) remained constant at about 43:1, which is approximately the same as the ratio of isobutylene to isoprene repeat units (IB/IP) in the starting butyl rubber (42.5:1). At ?40 °C with TiCl4, molecular weight was reduced to about 5 × 103 g/mol, and IB/Q was reduced below IB/IP, indicating nearly a difunctional telechelic structure. AlCl3 was a more active catalyst and produced results similar to TiCl4 at ?40 °C, even when used at seven times lower concentration. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1991–1997 相似文献
102.
Gillon AL Davey RJ Storey R Feeder N Nichols G Dent G Apperley DC 《The journal of physical chemistry. B》2005,109(11):5341-5347
The solid state dehydration of inosine dihydrate has been investigated using powder X-ray diffraction, differential scanning calorimetry, thermal gravimetric analysis, dynamic vapor sorption, hot stage microscopy, 13C solid state NMR, and variable temperature Fourier transform infrared spectroscopy. The information obtained from these experiments has been combined with an analysis of the crystallographic packing of inosine dihydrate and its two anhydrous polymorphs to yield mechanistic insights into the modes of water loss. The results allow an understanding of why, surprisingly, the dehydration of the dihydrate is always found to give the anhydrous, metastable, alpha-form. 相似文献
103.
In Part 1 of this paper (Ref. 1), a new, generalized conjugate gradient algorithm was proposed and its convergence investigated. In this second part, the new algorithm is compared numerically with other modified conjugate gradient methods and with limited-memory quasi-Newton methods. 相似文献
104.
In this paper, low-order Newton methods are proposed that make use of previously obtained second-derivative information by suitable preconditioning. When applied to a particular 2-dimensional Newton method (the LS method), it is shown that a member of the Broyden family of quasi-Newton methods is obtained. Algorithms based on this preconditioned LS model are tested against some variations of the BFGS method and shown to be much superior in terms of number of iterations and function evaluations, but not so effective in terms of number of gradient evaluations. 相似文献
105.
106.
107.
An algorithm for unconstrained minimization is developed which uses a rational function model, rather than a quadratic, as a basis for conjugate directions. The algorithm is similar to one previously proposed by the authors, but inexact linear searches are investigated in the present paper. 相似文献
108.
Efficient hybrid conjugate gradient techniques 总被引:23,自引:0,他引:23
Descent property and global convergence proofs are given for a new hybrid conjugate gradient algorithm. Computational results for this algorithm are also given and compared with those of the Fletcher-Reeves method and the Polak-Ribière method, showing a considerable improvement over the latter two methods. We also give new criteria for restarting conjugate gradient algorithms that prove to be computationally very efficient. These criteria provide a descent property and global convergence for any conjugate gradient algorithm using a nonnegative update . 相似文献
109.
The simple thermal addition product of N,N-dimethyltrimethylsilylamine with 2,2,2-trifluoroacetophenone provides a shelf-stable reagent for nucleophilic trifluoromethylation of both the carbonyl and the imine group. 相似文献
110.
A.E. Beezer W.H. Hunter R.P. Lipscombe R.D. Newell D.E. Storey 《Thermochimica Acta》1982,55(3):345-349
A twin, automatic microtitration assembly suitable for use with an LKB Batch Microcalorimeter is described. The apparatus, which can accurately and reproducibly deliver volumes as low as 1 μl, permits up to 20 titration additions to be made. It has been tested by the determination of the heat of ionisation of water at 303.15±0.01 K. The value determined compares favourably with the “best” value reported in the literature. 相似文献