Strontium‐based initiator system for ring‐opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr‐PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring‐opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA). The Sr‐PO initiator demonstrated an effective initiating activity for the ROP of ε‐caprolactone (ε‐CL) and L‐lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr‐PO initiator. Block copolymer PCL‐b‐PLLA was prepared by sequential polymerization of ε‐CL and LLA, which was demonstrated by ¹H NMR, ¹³C NMR, and gel permeation chromatography. The chemical structure of Sr‐PO initiator was confirmed by elemental analysis of Sr and N, ¹H NMR analysis of the end groups in ε‐CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr‐PO initiator and model monomer γ‐butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination‐insertion mechanism, and cyclic esters exclusively inserted into the Sr–O bond. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1934–1941, 2003     

ON AN OPEN PROBLEM PRESENTED BY LADAS

ConsiderneutraldifferentialdiffereflceequatinwhereTE(0,co),ae[0,co),Q(t)EC[[t.,co),R ].In1988,G.Ladaspresentedanopenprobleminprivatecommuni(:ationandthenin[1].Theproblemisasfollowing:Assumethatfi:Q(s)ds=co,showthateverynonoscillatorysollltioTIot'equation(…     

LED大屏幕视频图象显示亮度校正的一种方法

在大屏幕视频显示的研究中,通常将侧重点放在显示驱动电路的优化上。本文从人眼的主观视觉理论出发,讨论了大屏幕视频图象显示与主观视觉之间的关系。并提出了一种很好的校正理论。经过实验检验,它能在图象列信息相同时,不管背景图象如何,均能使显示屏保持相同的亮度,使显示的视频图象的质量得以提高.     

轨迹成型法加工球面光学零件面形精度分析

分析了轨迹成型法加工球面时影响零面形精度的多种因素，其中包括：工件回转轴与摆动轴不共面误差，工件回转轴与砂轮轴不共面误差，工件回转轴径向跳动、摆动误差，轴向窜动工件摆动轴的径向跳动以及砂轮的振动等因素对工件面形精度的影响。为了提高工件面形精度，首先应提高各回转轴和移动件的制造精度和减少配合误差，使其静刚度和动刚度提高，这是保证面形精度的最重要和基本的条件。     

Pseudo almost periodic solutions of differential equations with piecewise constant arguments

In this paper, we give a definition of pseudo almost periodic sequence and study the existence of pseudo almost periodic sequence to difference equation. Based on these, we investigate the existence of pseudo almost periodic solutions to differential equations with piecewise constant arguments which was considered by K. L. Cooke & J. Wiener and found applications in certain biomedical problems.     

Straightforward synthesis of 4,5-bifunctionalized 1,2-oxazinanes via Lewis acid promoted regio- and stereo-selective nucleophilic ring-opening of 3,6-dihydro-1,2-oxazine oxides

Functionalized 1,2-oxazinanes are interesting and valuable heterocycles with potential applications in synthetic and medicinal chemistry. A straightforward strategy for quick access to unprecedented trans-4-hydroxyl-5-azido/cyano/amino 1,2-oxazinanes are developed: N-COR 3,6-dihydro- 1,2-oxazine oxides are prepared with ease from related dihydro- 1,2-oxazines and opened by nucleophiles TMSN₃, TMSCN and aryl/alkyl amines. Appropriate Lewis acid catalysts are found playing a vital role for both reaction rate and regioselectivity. The N-COR group can be removed under mild conditions to provide highly desirable NH 1,2-oxazinanes inaccessible via previous methods.     

Migration characteristics study of iodine in crushed Beishan granite column under dynamic flow condition

Journal of Radioanalytical and Nuclear Chemistry - The migration of iodine on Beishan granite was studied by the dynamic column method using an UV detector. Migration parameters, such as...     

Removal of iodate from aqueous solution using diatomite/nano titanium dioxide composite as adsorbent

Journal of Radioanalytical and Nuclear Chemistry - Highly deficient strontium cobaltite (SrCoOx), as a new nanomaterial that is thermally treated at low temperature...