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11.
Adrian Boborodea Stephen O’Donohue 《International Journal of Polymer Analysis and Characterization》2017,22(7):631-638
A new evaporative light scattering detector (ELSD) for the analysis of polyolefins by high temperature gel permeation chromatography (GPC) was recently introduced by Agilent Technologies. For the first time, we investigated the possibility to use this detector to measure the molecular weight distributions (MWD) of different type of polyolefines (polypropylene, linear, and low-density polyethylene). These samples were previously characterized by GPC with a differential refractive index (DRI) detector by several companies, in an interlaboratory study conducted by International Union of Pure and Applied Chemistry.[1] The excellent baseline stability of ELSD as compared with DRI was reflected in a better reproducibility of the measured average molecular weights. More importantly, after applying required corrections to linearize the response of the ELSD as a function of concentration, we obtained similar results as previously obtained with DRI for the MWD of analyzed resins, covering typical applications of polyolefins. 相似文献
12.
Summary A method has been developed for the determination of trace levels of 32 pesticides, 19 explosives and 16 polycyclic aromatic
hydrocarbons (PAH) in water in three individual steps. Solid-phase enrichment (SPE) is coupled to high-performance liquid
chromatography (HPLC) with a fully automated system. The organic pollutants are enriched on reusable cartridges packed with
adsorbent materials: pesticides and explosives on a mixed bed of divinylbenzene-ethylvinylbenzene copolymers (LiChrolut EN?) and perfluorinated polyethylene (PolyF?), and polycyclic aromatic hydrocarbons on C18-modified silica (Zorbax? ODS1). Thermally assisted desorption (TAD) has been shown to increase the recovery of analytes significantly. As all enriched
analytes are transferred to the detector, only fifty millilitres of sample is needed for each single on-line analysis, compared
with at least a litre for conventional methods. The separation of the enriched organic analytes is performed on specialized
HPLC columns based on reversed-phase materials. The limits of detection of the system employed were found to be below 100
ng L−1. Use of fluorescence detection for the polycyclic aromatic hydrocarbons resulted in limits of detection in the upper pg L−1 range. Thek values, number of theoretical plates, the recovery rates and the limits of detection of this method for fast screening of
organic pollutants from three fifty-millilitre aqueous samples are described.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
13.
Mara K. Kuenen James A. Mullin Rachel A. Letteri 《Journal of polymer science. Part A, Polymer chemistry》2021,59(19):2212-2221
With a vast, synthetically accessible compositional space and highly tunable hydrolysis rates, poly(β-amino ester)s (PBAEs) are an attractive degradable polymer platform. Leveraging PBAEs in a wide range of applications hinges on the ability to program degradation, which, thus far, has been frustrated by multiple confounding phenomena contributing to the degradation of these charged polyesters. Basic conditions accelerate hydrolysis, yet reduce solubility, limiting water access to amines and esters. Further, the high buffering capacity of PBAEs can render buffers ineffective at controlling solution pH. To unify understanding of PBAE degradation and solution properties, this study examines PBAE hydrolysis as a function of pH and buffer concentration as well as polymer hydrophobicity. At low buffer concentrations, the PBAE amines and the acid produced during hydrolysis control solution pH. Meanwhile, at high buffer concentrations that afford relatively constant pH, hydrolysis rate increases with pH, despite the reduced PBAE solubility. Increasing the hydrophobic content of PBAEs eventually hinders the capacity of the polymer to accept protons from solution, limiting the pH increase and slowing hydrolysis. These studies showcase the role of buffering on the pH-dependent degradation and solution properties of PBAEs, providing guidance for programming degradation in applications ranging from drug delivery to thermosets. 相似文献
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The mechanical properties of glass bead filled low density polyethylene (LDPE) composites in tension have been investigated by using an Instron material testing machine. It is found that with increase of the glass bead weight fraction (φ) the tensile modulus (Ec) and the tensile yield stress (σyc) increase as a form of nonlinear function but contrary to the elongation strain at break; the correlation between Ec and φ accords with the logarithmic mixing rule and the relationship between σy and the volume fraction (φf) can be described by means of a second order equation; the effects of the glass bead diameter on the mechanical properties are not large; when φ and the bead size are suitable, the enhanced toughness effect of the filled-systems is more significant; the tensile strength of the glass bead filled system pretreated with a coupling agent are somewhat greater than those of the untreated system. In addition, the morphology of the samples is studied to explain the relationship between the micro-structure and the mechanical properties of the composites. 相似文献
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Samir Kumar Sarkar Meenakshi Pegu Santosh Kumar Behera Siva Krishna Narra Pakkirisamy Thilagar 《化学:亚洲杂志》2019,14(24):4431-4431
19.
Mechanical properties of copolymers of 2-hydroxyethyl methacrylate with methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate have been investigated using an Instron tensile tester. It was observed that the overall mechanical properties decrease as the ester alkyl group of alkyl methacrylate becomes bulkier. Biocompatibility of the copolymers was also investigated by implanting them subcutaneously in rats. 相似文献
20.
Dr. Shuangyan Hu Lijun Liu Dr. Heng Li Dr. David Pahovnik Prof. Dr. Nikos Hadjichristidis Prof. Dr. Xuechang Zhou Prof. Dr. Junpeng Zhao 《化学:亚洲杂志》2023,18(1):e202201097
A series of ester-ether copolymers were obtained via the reaction between α,ω-dihydroxyl poly(ϵ-caprolactone) (PCL) and ethylene oxide (EO) or monosubstituted epoxides catalyzed by strong phosphazene bases. The two types of monomeric units were distributed in highly random manners due to the concurrence of epoxide ring-opening and fast transesterification reactions. The substituent of epoxide showed an interesting bidirectional effect on the enzymatic degradability of the copolymer. Compared with PCL, copolymers derived from EO exhibited enhanced hydrophilicity and decreased crystallinity which then resulted in higher degradability. For the copolymers derived from propylene oxide and 1,2-butylene oxide, the hydrophobic alkyl pendant groups also allowed lower crystallinity of the copolymers thus higher degradation rates. However, further enlarging the pendant groups by using styrene oxide or 2-ethylhexyl glycidyl ether caused a decrease in the degradation rate, which might be ascribed to the higher bulkiness hindering the contact of ester groups with lipase. 相似文献