化学中考试题与课程标准一致性研究*——以聊城市化学中考试题为例

通过利用SEC“一致性”分析工具对聊城市2016-2018年化学中考试题与《义务教育化学课程标准(2011年版)》的一致性进行分析,得出2016-2018年的聊城市化学中考试题与课程标准不具有统计学意义上的一致性。在内容主题及认知层次分布上,3个年份的试题与课程标准均存在着明显的差异。     

Following the enzymatic digestion of chondroitin sulfate by a simple GPC analysis

We describe the use of gel permeation chromatography (GPC) setup with four size exclusion columns for analysis of enzymatically digested glycosaminoglycans (GAGs). This setup provides information about the molecular weight (Mw) and concentration of all species (low and high Mw) present in the digests in a single measurement. The data about the fraction with high Mw (often omitted in the analysis of GAG digests) provide direct evidence about the mechanisms of action of the enzymes. We proved the feasibility of this methodology by applying it to chondroitin sulfate (CS) substrates with different molecular weight and sulfation pattern and using different enzymes (hyaluronidase and chondroitinase). NMR analysis of the obtained digests fractionated by ultrafiltration confirmed the results obtained by GPC setup and reveal further details about the degradation mechanisms: (i) both enzymes preferentially attack 4-sulfated chondroitin and (ii) additionally to the well documented endolytic activity of hyaluronidase we also observed a low lyase activity for this enzyme reflected in the detected minor exolytic breakage. Finally, we demonstrate that CS with medium molecular weight (12–60 kDa) which is sulfated mainly at 6-position can be obtained in good yields by enzymatic digestion and following ultrafiltration.     

On the anionic homo‐ and copolymerization of ethyl‐ and butyl‐2‐cyanoacrylates

Ethyl‐(ECA) and butyl‐2‐cyanoacrylate (BCA) monomers of high purity and acidic stabilization were synthesized and anionically polymerized to homo‐ and copolymers in two different ways: by piperidine‐catalyzed bulk polymerization leading to transparent, brittle films (method A) and by polymerization in aqueous medium in the presence of sodium bicarbonate to obtain white powders (Method B). The molecular structure of the synthesized monomers, homopolymers and copolymers were corroborated by spectral methods. The polymers were studied further by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and proton nuclear magnetic resonance (¹H NMR). Controlling the composition of the monomer feed and the way the polymerization was performed, it was possible to obtain phase separated or homogeneous cyanoacrylate copolymers with glass transitions varying between the T_g of polyECA and that of polyBCA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5142–5156, 2008     

Comparison of the molecular dimensions of di-alkyl and aryl-alkyl-substituted polysilanes in solution using SEC/LS

Polysilanes provide an opportunity for exceptional control of the chain hindrances to rotation through the choice of substituents on each backbone silicon. Two alkyl substituents on each silicon result in a large characteristic ratio of at least 19 for poly (di-n-hexylsilane), determined by extrapolation of intrinsic viscosities. Bulky aromatic substituents provide even more hindrance to backbone rotations, and can be expected to result in a more extended polymer chain. Direct measurement of the dimensions of these polymers by scattering techniques has been limited by the small quantities available, and by the polydispersity of samples. The recent introduction of light-scattering detectors for size exclusion chromatography enables the simultaneous measurement of light scattered at as many as 15 scattering angles as the fractionated polymer elutes from the column. Determination of both M and the root-mean-square radius of gyration R_g of narrow fractions eluting from a column allows determination of the R_g M relation over as much as a decade in M with less than a milligram of sample. Values of R_g and M across the distribution have been determined for alkyl and aryl substituted polysilanes with this technique. Estimation of R_g,0/M unperturbed by long-range interactions is made by an extrapolation procedure. The dependence of R_g,0 on M across the distribution is compared among the different substituents and with other measurements reported for these polymers. © 1994 John Wiley & Sons, Inc.     

Short chain branching profiles in polyethylene from the Phillips Cr/silica catalyst

SEC and on‐line Fourier transform infrared spectroscopy analysis have been combined to study branching profiles from the Phillips Cr/silica catalyst. For the first time, catalyst and reactor variables have been shown to affect the overall level and distribution of branches in polyethylene copolymers. Branching profiles from various chromium catalysts have been shown to vary from highly concentrated in the low MW end, to uniformly distributed over all of the MW range. Activation temperature and the presence of titania were highly influential. These observations, which have been used to gain insight into the chemistry of Cr/silica, explain much of the catalyst behavior that has for decades been used to optimize polymer properties. Trends in ESCR, impact resistance, and other physical characteristics, which were long attributed to changes in MW distribution, can now be seen to also be due in large part to changes in the branching profile. This knowledge should be of value in designing future resins. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3135–3149, 2007     

多检测GPC/SEC技术在高分子表征中的应用 II.C_(70)/PS共聚物的表征

用ＳＥＣ／ＲＩ／ＲＡＬＬＳ／ＤＶ 三检测技术表征了Ｃ７０／ＰＳ 共聚物。解决了用传统ＳＥＣ／ＲＩ不能解释的现象，提出了Ｃ７０ － ＰＳ共聚物的大致结构。结果表明Ｃ７０ － ＰＳ共聚物／ＴＨＦ体系不符合普适标定。     

On-line measurement of the RMS radius of gyration and molecular weight of polyimide precursor fractions eluting from a size-exclusion chromatograph

The recent introduction of multiangle light-scattering detectors for size-exclusion chromatography has made possible the measurement of the root mean square radius of gyration (R_g) and molecular weight (M) of polymer fractions eluting from a size-exclusion chromatography column. The characterization of the dimensions of a polymer may be accomplished with only a few milligrams. The dimensions of a polyimide precursor prepared by the condensation of the meta-diethyl ester of pyromellitic dianhydride with para-phenylene diamine have been measured with this technique. The dependence of R_g on M across the distribution is compared with that predicted for a freely rotating chain, and with other similar polymers measured with hydrodynamic techniques.     

Equilibration of mixtures of polyamic acids studied using size-exclusion chromatography and light scattering

The transamidation reaction in a polyamic acid solution has been investigated using size-exclusion chromatography and low-angle light scattering. Mixtures of a high-molecular weight (DP = 150) and a low-molecular weight (DP = 10) polymer and of the high-molecular weight polymer with monomer were studied. Mixtures were made at high and low concentrations. The polyamic acid studied is the product of the polycondensation of 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) with oxydianiline (ODA). In all cases the molecular weight distribution equilibrated with time to a most-probable distribution with a DP consistent with the stoichiometry of the mixture. Equilibration required about 2 weeks for mixtures of 10% by weight at ambient temperatures. The effect of addition of a small amount (5%) of low-molecular weight material to sample of high-molecular weight is dramatic; for DP = 150 the molecular weight is decreased by more than one-half. In an entangled solution or melt, this would reduce the viscosity by an order of magnitude.     

Molecular weight characterization of soluble high performance polyimides. 2. Validity of universal SEC calibration and absolute molecular weight calculation

Six different soluble high-performance aromatic polyimides, each prepared by solution imidization to three controlled average molecular weights, were analyzed by size exclusion chromatography (SEC) using on-line parallel coupled refractometric and viscometric detectors. N-methylpyrrolidone (NMP) with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phase for four of the polyimides; NMP with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phases for four of the polyimides; NMP with 0.06 M LiBr tetrahydrofuran (THF) and chloroform served as mobile phases for the other two polyimides. For all the samples the stationary phase in the SEC columns was cross-linked polystyrene beads. Molecular weight averages of the polyimides were calculated using universal SEC calibration with polystyrene standards in each solvent. The agreement of the calculated molecular weight averages in the different solvents confirms that the universal SEC calibrations are valid for these semiflexible polymers. There was good agreement with weightaverage molecular weights obtained by low-angle laser light scattering (LALLS) performed in pure NMP. Intrinsic viscosity and molecular weight data for a series of nine samples of one polyimide covering a M_w = 20,000–70,000 g mol^–1 interval were treated to obtain Mark-Houwink-Sakurada constants. Unperturbed chain dimensions of this polyimide were obtained by application of the Stockmayer-Fixman extrapolation procedure to these data. ©1995 John Wiley & Sons, Inc.     

Chromatographic methods for the analysis of crude tall-oil

Chromatographic methods currently used for isolation, separation, and identification of the components of crude tall-oil have been reviewed, and their resolution and analytical methodology compared. Sample introduction by cold on-column, rather than vaporizing, injection provides good reproducibility and operational convenience for capillary GC analysis. Size exclusion chromatography for isolation followed by capillary GC-MS for identification, gave the best performance for analysis of acidic and dimeric compounds.