Characterization of copolymers of polycarbonate and polydimethylsiloxane by 2D chromatographic separation,MALDI-TOF mass spectrometry,and FTIR spectroscopy

Abstract

The structure and composition of polycarbonate polydimethylsiloxane copolymer (PC-co-PDMS) was investigated by applying various analytical approaches including chromatographic separation methods, spectrometric, and spectroscopic detection techniques. In particular, size exclusion chromatography (SEC) and liquid adsorption chromatography operating at different conditions (e.g. using gradient solvent systems) were used to achieve separations according to molar mass and functionality distribution. The coupling of both techniques resulted in fingerprint two-dimensional plots, which could be used to easily compare different copolymer batches. Matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry was applied for structural investigations. The different ionization behavior of both comonomers, however, strongly limited the applicability of this technique. In contrast to that, Fourier-transform Infrared (FTIR) spectroscopy could be used to quantify the amount of PDMS in the copolymer at different points in the chromatogram. The resulting methodology was capable of distinguishing PC-co-PDMS copolymer from PC homopolymer chains present in the material.     

Statistical molecular design of peptoid libraries

Statistical experimental design provides an efficient approach for selecting the building blocks to span the structural space and increase the information content in a combinatorial library. A set of renin-inhibitors, hexapeptoids, is used to illustrate the approach. Multivariate quantitative structure-activity relationships (MQSARs) were developed relating renin inhibition to the peptoid sequences variation, parametrized by the z-scales. By using the information from the models, the number of building block sets could be reduced from six to three. Using a statistical molecular design (SMD) reduces the number of compounds from more than 100 000 down to 90. A second SMD was used for comparison, based on less prior knowledge. This gave a reduction from over 2 billion to 120 compounds.     

Optical analysis of dichroism measurements in polymer science

The polarization properties of an optical system, source–interferometer–polarizer–polymer film–detector, have been calculated. Using Mueller matrices, the intensity has been obtained as a function of polarizer angle. It is shown in some detail how polarization of the beam in both interferometer and detector optics distort the spectra. The contributions from the finite extinction ratio of the polarizer are also calculated and intensity variations caused by beam-wandering are discussed. It is shown that the commonly used procedure for correcting the spectra is wrong. Better methods for correcting the spectra are proposed. The influence of a uniaxial refractive index on the data is discussed, and experimental methods that can deal with refraction effects are presented. © 1993 John Wiley & Sons, Inc.     

Effect of γ-radiation on radionuclide retention in compacted bentonite

Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ) under anoxic conditions. Because of this, the effects of γ-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs⁺ and Co²⁺ were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co²⁺ than for Cs⁺, which generally showed no significant differences between irradiated and unirradiated clay samples. For Co²⁺ however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that γ-radiation may alter the surface characteristics contributing to surface complexation of Co²⁺. With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained D_a values.     

Design of polarization-maintaining retro-reflector for folded-path applications

A design of polarization-maintaining retro-reflectors(PMRRs) for folded-path applications is proposed and analyzed.The prism-based scheme enables the output light,which is parallel to the input,to have an identical state of polarization.The principle of the design is theoretically verified,and the related error is analyzed due to possible manufacturing imperfection.The maximum spatial angle error is ±2.75°.The effect on the extinction ratio and insertion loss is also discussed,which further proves the design’s feasibility in practical applications.     

关于n+k相多体系(k≥4)封闭网的构造

本文证明了n+k多体系(k≥4)的全部可能的封闭网均可以通过若干相应的子n+3相多体系的拼合运算得出,从而为具体构造n+k相多体系(k≥4)的全部合理的封闭网,提供了基本方法。     

超导临界温度理论(Ⅱ)

在文献[1]中,我们导出了超导临界温度T-c的一个严格级数表式.本文讨论这个级数的收敛范围,以及通过解析延拓来扩展收敛范围的可能性.结论是:我们的T_c级数(指文献[1]原来的级数,或者经过延拓后的级数)在∞>λ>λ₀的整个范围内,都是收敛的.这里λ₀是Matsubara表象中使决定T_c的方程具有正实数解的最小的λ值.它实际上就是库伦赝势.因此,也许除了少数非常弱耦合的超导体以外,我们的T_c级数能适用于一切超导体.     

多光束共振光压作用下钠原子束的偏转

本文报道了多光束共振光压作用下钠原子束偏转的实验研究结果。文中提出了用多光束与原子束相互作用以增大原子束的偏转量,并可大大降低对激光功率的要求。用一台染料激光器照射钠原子束得到1×10^-2rad的偏转角,偏转距离约7.2mm,并用激光诱导原子束荧光的方法检测原子束的偏转。     

Electroreflectance and reflectance study of 2H-MoSe2

We report the first electrolyte electroreflectance (EER) study of 2HMoSe₂ in the energy range 0.7 to 6 eV. The reflectivity (R) was also measured in the range of 0.7 to 9.5 eV and the real and imaginary parts of the dielectric constant were determined using the Kramers-Kronig relations. All the measurements were done at room temperature. Single crystals of 2H-MoSe₂ were grown using the direct combination of the elements in a sealed silica tube combined with chemical vapor transport using Br as the transport agent. The EER spectrum exhibits sharp structure in the vicinity of the excitonic transitions A, A′, B and B′ as well as higher lying interband transitions; the transition energies are determined with better accuracy than has been possible to date. A comparison of the R and EER spectra helped identify the various features in the EER spectrum.