Ring-opening polymerization of trimethylene carbonate (TMC) with a rare earth calixarene compound as catalysthas been studied for the first time. The effect of TMC/Nd (molar ratio) and polymerization conditions were investigated indetail. It was found that calix[8]arene-neodymium is a highly effective catalyst for the bulk polymerization of TMC and giveshigh molecular weight (M_v = 60,000) polymer. The optimum conditions of TMC polymerization were found to be asfollows:TMC/Nd (molar ratio) = 2,000, 80℃, 16 h. The polymers were characterized by NMR, GPC and DSC. Studying themechanism by NMR showed that the polymerization of TMC catalyzed by calix[8]arene-neodymium proceeds via a cationicmechanism. 相似文献
In this paper the laser-phase determination methods and transfer equations are
presented to directly reconstruct the detailed temporal structures
of ultra-short extreme ultraviolet (xuv) pulses from the measured
photoelectron energy spectra (PES). Each transfer equation
includes one of PID
(proportional-integral-differential) terms of PES. The
intensity and instantaneous frequency of attosecond xuv can be
retrieved from the integral term of PES. The
intensity profiles of narrow bandwidth atto- and femtosecond xuvs
can be rebuilt from the proportional and
differential terms of PES respectively. The
methods and equations may be used to improve time resolutions in
measuring ultrashort pulses. 相似文献
The BEPCⅡ project is for upgrading the Beijing Electron Positron Collider to reach a higher luminosity.BEPCⅡ is designed as micro-β plus multi-bunches with double rings and has adopted cryogenic superconducting technology. The BEPCⅡ control system is a distributed system based on EPICS. In the past few years, we went through the design stage, R&D stage, development stage and the system will be installated. The BEPCⅡ machine commissioning with beam will start in October 2006. This paper describes the BEPCⅡ~control system and the progress of its development. 相似文献
Summary: Heparin, a potent anticoagulant, has been used for the first time for the synthesis of PPy nanowires serving not only as an anion dopant but also as an effective morphology‐directing agent. The obtained PPy nanowires exhibit long and fine structures with smooth surface and the average diameter of the nanowires is about 90–100 nm and lengths are several hundred nanometers to micrometers. The possible formation mechanism of PPy nanowires may be related to the chain structure of heparin with functional groups ( SO and COO−) on the surface. The effect of concentrations of pyrrole monomers and heparin on the morphology and size of PPy nanowires has been investigated.
SEM image of PPy nanowires synthesized in the presence of heparin. 相似文献
Summary: With the proper selection of shear and thermal conditions, super‐hydrophobic polymeric surfaces (contact angle > 150°) with tunable sliding angles (from less than 1° to higher than 90°) can be prepared from pure isotactic poly(propylene) (iPP) without any further modification with low‐surface‐energy components under ambient atmosphere. The formed surfaces have naturally good thermal properties, chemical and moisture resistance, low density, and potentially low manufacturing cost.
SEM images of formed super‐hydrophobic surfaces and related two extreme sliding angles (contact angles of these surfaces are higher than 150°). 相似文献
This paper reports that the organic field-effect transistors with
hybrid contact geometry were fabricated, in which the top electrodes
and the bottom electrodes were combined in parallel resistances
within one transistor. With the facility of the novel structure, the
difference of contact resistance between the top contact geometry
and the bottom contact geometry was studied. The hybrid contact
devices showed similar characteristics with the top contact
configuration devices, which provide helpful evidence on the lower
contact resistance of the top contact configuration device. The
origin of the different contact resistance between the top contact
device and the bottom contact device was discussed. 相似文献