Single crystals of syndiotactic poly[propene-co-(1-octene)] and syndiotactic polypropene crystallized in bulk

Single crystals grown in bulk samples of a syndiotactic random copolymer of propene and 1-octene with 4 wt.-% 1-octene are compared with single crystals of syndiotactic polypropene homopolymer. The random copolymer during isothermal crystallization at low supercoolings forms rectangular single crystals similar to syndiotactic polypropene. The single crystals of the random copolymer do not exhibit transverse cracks in contrast to neat syndiotactic polypropene. Both polymers have nearly the same linear thermal expansion coefficients along their crystallographic a- and b-axis, calculated from temperature-dependent wide-angle X-ray scattering (WAXS) measurements. Therefore, the absence of transverse cracks in single crystals of the random copolymer can only be explained by the relatively high disorder of the crystallite surface caused by the exclusion of 1-octene segments which leads to a more isotropic thermal expansion coefficient in this region.     

Improvement of supported catalysts for syndiotactic polymerization of styrene

The catalytic system Ti(OBu)₄ in combination with methylaluminoxane (MAO) was tested for the syndiospecific polymerization of styrene. A comparison was established between this homogeneous catalytic system and the same one supported on silica or alumina. An attempt was made to introduce a “tether” between the support and the active species to enhance both productivity and syndiospecificity. These tethers consisted of diols with different lengths. At last, the catalytic system Zr(OBu)₄ was supported on silica or alumina with MAO as a cocatalyst and was tested under the same conditions as other catalysts. This study reveals that Ti(OBu)₄ supported on silica enhances the productivity and leads to higher molecular weights, while the addition of a diol does not result in any enhancement compared to the silica-supported catalyst. On the contrary, alumina alone does not seem to be a good support for Ti(OBu)₄, while introducing a short diol such as ethylene glycol leads to a great enhancement of both productivity and syndiospecificity. As reported in the literature, Zr(OBu)₄ always leads to much lower productivities than Ti(OBu)₄.     

Microstructure of syndiotactic polypropylenes prepared with heterogeneous titanium-based Ziegler-Natta catalysts

Polypropylenes produced with various heterogeneous titanium-based Ziegler-Natta catalysts were fractionated by solvent extraction technique. The infrared analysis of the fractions indicates the presence of a crystalline syndiotactic sequence, soluble in xylene at 20°C, and boiling hexane soluble fractions of all samples examined. Highly syndiotactic polypropylene (proportion of rrrr pentad is 0,50), comparable in syndiotacticity to the syndiotactic polymer prepared at ?78°C with a homogeneous vanadium catalyst, was separated from the xylenesoluble fraction of the polymer prepared with the system TiCl₃-Al(C₂H₅)₂Cl by means of elution column fractionation. The steric irregularities are mainly rrrm and rrmr (ratio ≈ 1:1), suggesting that the propagation is controlled mainly by end-groups. Chemical inversions, i. e., head-to-head or tail-to-tail linkages of propylene units, are practically absent, though they are seen in syndiotactic polypropylenes prepared with vanadium catalysts.     

The influence of regio- and stereoirregularities on the crystallization behaviour of isotactic poly(propylene)s prepared with homogeneous group IVa metallocene/methylaluminoxane Ziegler-Natta catalysts

Poly(propylene)s with narrow molecular weight distributions were prepared with various methylaluminoxane-activated metallocene-based Ziegler-Natta catalysts to study the influence of randomly incorporated regio- and stereoirregularities on the crystallization behavior. As a function of the metallocene type and the polymerization temperature, the molecular weights varied between 11500 < M _n < 63 000, melting temperatures of annealed samples between 125 to 158°C, and the corresponding degrees of crystallinity, as measured by wide-angle X-ray scattering, between 49 and 67%. While the virgin poly(propylene)s exhibited exclusively the α-modification, annealing and melt crystallization favored the development of the γ-modification. The microstructure analysis by ¹³C NMR spectroscopy revealed a linear correlation between the content of the γ-modification and the average length of the isotactic segments.     

13C Nuclear magnetic resonance characterization of poly(propylene) prepared with homogeneous catalysts

The minor resonances in the ¹³C NMR spectrum of poly(propylene) prepared with soluble Group 4 metallocene/methylalumoxane catalysts are fully characterized. The ¹³C shifts for regioirregular sequences, chain-end structures, and 1,3-propylene adduct are obtained for both isotactic and atactic components. In both components the dominating mechanism is 1,2-insertion, with much lower amounts of 2,1-insertion and 1,3-insertion depending on the catalysts used. The isotactic component is stereoregular in all insertion modes. In the atactic components random stereosequences are observed. The regiostructures suggest that the propagation step is catalyticsite controlled even for the atactic component.     

Thermal cis-trans isomerization and temperature-dependent phase behaviour of polyisoprene-polyacetylene solutions

Polyacetylene can be solubilized by making copolymers with polyisoprene via anionic polymerization of isoprene using BuLi as the initiator, followed by Ziegler-Natta copolymerization of acetylene onto the polyisoprenyllithium chains using either Ti(OBu)₄ or CoCl₂. In the present study, the effects of temperature on cis-trans isomerization of the polyacetylene blocks and the phase behaviour of the PI-PA copolymers in solution were investigated. We found that isomerization of the cis-polyacetylene blocks in a solution of the PI-PA copolymer is retarded by some intramolecular barriers, making the cis-isomer rather stable. Reducing the temperature below about 12°C was found to cause a phase transformation from the worm-like structure to spherical micelles in solution.     

The stereoregularity of poly(methyl methacrylate)s formed in the presence of highly syndiotactic poly(methyl methacrylate)s

Methyl methacrylate (MMA) was radically polymerized in the presence of highly syndiotactic deuterated or undeuterated poly(methyl methacrylate)s. In contrast to observations found in the literature no increase in isotacticity was observed. The stereoregularity of the polymers formed in the presence of an undeuterated PMMA as matrix was found by ¹H NMR spectroscopy to be about the same as that in polymers prepared without any matrix, except the polymers formed in the early stage of polymerization which show a little lower syndiotacticity. Determinations of triad tacticities of polymers formed in the presence of deuterated PMMA, gave values of syndiotacticity a little higher than in the case of undeuterated matrixes. The polymer formed in the graft copolymerization of MMA onto pre-irradiated syndiotactic PMMA was fractionated by GPC. The high molecular weight fraction showed a lower syndiotacticity than that of lower molecular weight.     

Propene polymerization in the presence of MgCl2-supported Ziegler-Natta catalysts, 5. Microstructural characterization of the “isotactic” (heptane-insoluble) polypropene fractions

The stereosequence distribution in the heptane-insoluble fraction of polypropene samples prepared with a number of MgCl₂-supported catalysts was analyzed in detail by means of ¹³CNMR. The results indicate that what is conventionally taken as “isotactic” polypropene is normally a stereoblock polymer, in which at least part of the macromolecules contain long isotactic blocks spaced by much shorter “syndiotactoid” sequences. This implies that the active sites responsible for the formation of the two types of stereosequences are able to interconvert reversibly on the surface of the MgCl₂ support in times which may be shorter than the average growth times of the polymer molecules. Possible models of active sites apt to explain the observed polymerization behavior are also briefly discussed.     

Characterization of the differences in the crystallinity from surface to bulk of compression-molded polypropene sheets using attenuated total reflection fourier-transform IR spectroscopy

The crystallinities of compression-molded polypropene sheets were investigated by applying Fourier-transform (FT)-IR and attenuated total reflection (ATR) FT-IR analyses. Two internal reflection elements, Ge and KRS-5, with an angle of incidence of 45°, were used to obtain the depth profiles of the crystallinity of polypropene sheets from the surface to bulk. The crystallinity in the region from the surface to about 0,7 μm depth was considerably lower than that in bulk. Polypropene sheets with higher comonomer content showed the same tendency, which was enhanced with decreasing molding temperature.     

Properties of homogeneous heat-labile enterotoxin from Escherichia coli.

Recently, the heat-labile enterotoxin (LT) of Escherichia coli has been purified to homogeneity and partially characterized (Clements and Finkelstein, Infect. Immun. 24:760-769, 1979). This study extends our observations on the physicochemical properties of LT. The toxin has an isoelectric point of pH 8.0, as compared with choleragen and choleragenoid, which have isoelectric points of pH 6.75 and 7.75, respectively. Sedimentation equilibrium measurements established an approximate molecular weight for LT of 91,440. LT had an even more marked affinity than choleragen for agarose-containing matrixes in gel filtration. Of several mono- and disaccharides tested, only galactose and lactose were highly efficient in removing 125I-labeled LT from agarose-containing columns. LT dissociated into subunits (designated A and B) during gel filtration in the presence of 5 M guanidine. These subunits were immunologically distinct and possessed unique and shared antigenic determinants to the corresponding A and B subunits of choleragen. During gel filtration of LT at pH 6.5 and room temperature, a spontaneously occurring toxoid of LT, analogous to choleragenoid, was discovered and designated "coligenoid." This product contains only the B subunits of the toxin. A partial amino acid sequence of the B subunit of LT revealed a remarkable homology to the primary structure of cholera toxin B. Within the first 20 amino acids of the two chains, only 5 differ, and these differences may be attributable to single base substitutions.     

Thermal behaviour of poly[imino(1-oxooctamethylene)], nylon 8

The thermal behaviour of nylon 8 was studied by differential scanning calorimetry (DSC). Glass transition temperatures (T_g) were measured over the molecular weight range 1,7·10³ – 3,4·10⁴ in order to determine a T_g-M_n dependence. A small decrease in the T_g values was observed for the lowest molecular weight samples which, however, were obtained by polymerization in presence of a chain terminator. The origin of multiple melting endotherms, found during DSC analysis of samples crystallized under different conditions, was also investigated. The effects of heating rate, of cooling rate from the melt, and of isothermal crystallization at various crystallization temperatures (T_c) on melting behaviour were consistent with the hypothesis of a meltrecrystallization process during heating.     

Structure and behaviour of SiO2/MgCl2 bisupported Ziegler-Natta catalysts for olefin polymerization

Bisupported catalysts for olefin polymerization were prepared by mixing a butyl alcoholate solution of MgCI₂ with pretreated SiO₂ in heptane, and further treating with TiCI₄ solution. The silica pretreating conditions and their effects on the composition of the catalysts were studied. The interaction mechanism of the two supports, MgCI₂ and SiO₂, is discussed. The effect of the composition and the structure of the catalyst on the behaviour of ethylene and propylene polymerization is described. The calcination temperature of SiO₂ has a significant effect on composition, structure and properties of the catalysts. There exist both chemical bonding and physical absorption between SiO₂ and MgCI₂ supports. The activities for propylene polymerization remarkably increase with increasing mole ratio Mg/Ti of the catalysts, while for ethylene polymerization, the activities mainly depend on the Ti content of the catalysts and the calcination temperature of SiO₂ used.     

Polymerization of propene with highly isospecific. SiO2-supported zirconocene catalysts activated with common alkylaluminiums

Several types of SiO₂-supported metallocene catalysts were prepared using chemically modified silica gel. Polymerization of propene was conducted with these catalysts combined with methylaluminoxane (MAO) or ordinary alkylaluminiums. Highly isotactic poly(propylene) with high molecular weight was obtained by the catalysts whose zirconocene ligands were chemically immobilized on SiO₂. The preparative methods of these catalysts and the results of propene polymerization, together with the analytical data of produced polymers, are reported in some detail.     

Thermal transition and frequency response of the dielectric behaviour of some cellulosic substances

The real part of the relative permittivity ?′_r of some cellulosic materials contaminated with commercial impurities and NaCl (determined as weight percent ash contents), and that of the purified fibres, as well as their hydrolysed residues, free of such contaminations, was measured in the frequency range 10² Hz ≤ f ≤ 10⁵ Hz and in the temperature range 283,15 K ≤ T ≤ 333,15 K. Additional measurements of the imaginary part of relative permittivity ?″_r have been carried out in the same frequency and temperature ranges for hydrocellulose samples free of inorganic impurities and contaminated with NaCl. The results obtained show that the variation with temperature of the relative permittivity of the samples examined exhibits a change in slope in the vicinity of 303,15 K except for hydrocellulose samples free of impurities. They further show that the presence of inorganic contaminations has a significant effect on the magnitude of the relative permittivity and its variation with temperature, particularly at low frequency. In the case of samples contaminated with inorganic impurities, interfacial polarization is responsible for the anomalous dielectric behaviour observed with the examined samples.     

Phase transition from a C-centered to a B-centered orthorhombic crystalline form of syndiotactic poly(propylene)

Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered orthorhombic form are here characterized through high resolution solid state ¹³C NMR sepctroscopy and wide angle X-ray diffraction. The ¹³C NMR CP MAS (cross-polarization, magic angle spinning) spectra of highly disordered quench-precipitated s-PP samples (with a structure very close to a C-pseudo-centered orthrohombic form) yield additional resonances beside those already reported in the literature for s-PP samples crystallized with the chains in a fully helical $ \rlap{--} (TTGG\rlap{--} )_n $ conformation (T: trans; G: gauche). From the correlation of ¹³C NMR CP MAS spectra with the X-ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C- to the B-pseudo-centered orthorhombic form starts to occur. Correspondingly, the aforementioned additional resonances in the ¹³C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the ¹³C NMR CP MAS spectrum of samles crystallized in the B-pseudo-centered structure. NMR and X-ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon; at temperatures below 140°C for our samples, the variously sized C-pseudo-centered orthorhombic crystallites melt and readily re-crystallize in the B-pseudocentered orthorhombic form.     

沙门菌属外膜蛋白的抗原同源性分析

目的 分析沙门菌属外膜蛋白（outer membrane protein，OMP）的抗原同源性。方法 十二烷基肌氨酸钠法提取甲型副伤寒沙门菌、伤寒沙门菌、鼠伤寒沙门菌、大肠埃希菌、福氏志贺菌、肺炎克雷伯菌、阴沟肠杆菌和粘质沙雷菌的OMP。用甲型副伤寒沙门菌的OMP与完全佐剂制成乳油状，多次多部位免疫日本大耳兔，获得抗OMP抗体血清。35％饱和硫酸铵沉淀并纯化IgG，用HRP标记。SDS-PAGE法分离检测上述8种细菌的OMP。Western blot测定兔抗甲型副伤寒沙门菌OMP抗体与上述其他细菌OMP抗原的反应特异性。斑点印迹．酶联免疫吸附试验（Dot blot-ELISA）测定兔抗甲型副伤寒沙门菌OMP抗体与肠炎沙门菌、费氏枸橼酸杆菌、变形杆菌、铜绿假单胞菌、蜂房哈夫尼亚菌、棒状杆菌、嗜麦芽窄食假单胞菌、金黄色葡萄球菌、摩根摩根菌、屎链球菌、肺炎链球菌、新型隐球菌、热带念珠菌、光滑念珠菌和白色念珠菌提取物的反应性。结果 沙门菌属成员的OMP可与兔抗甲型副伤寒沙门菌OMP抗体血清发生特异性反应；其他革兰阴性菌OMP与之无反应；革兰阳性菌和真菌亦不发生反应。结论 沙门菌属OMP具有高度的抗原同源性，有别于其他细菌。     

Evaluation of cardiac output from a tidally ventilated homogeneous lung model

We used the direct Fick measurements to validate a method for estimating cardiac output by iteratively fitting at the mouth to lung model values. This model was run using a series of 50, 30 and 10 breaths to test sensitivity to number of breaths used for fitting. The lung was treated as a catenary two-compartment lung model consisting of a dead space compartment connected with a single alveolar space compartment, perfused with constant pulmonary blood flow. The implemented mathematical modeling described variations in O₂ and CO₂ compartmental fractions and alveolar volume. This model also included pulmonary capillary gas exchange. Experimental data were collected from measurements performed on six healthy subjects at rest and during 20, 40, 60 and 85–90% of peak The correlation between the two methods was highest and the average agreement between the methods was best using 50 breaths The mean difference and lower to upper limits of agreement between measured and estimated data were 0.7 l/min (–2.7 to 4.1 l/min) for cardiac output; –0.9 ml/100 ml (–1.3 to –0.5 ml/100 ml) for arterial O₂ content; –0.8 ml/100 ml (–3.8 to 2.2 ml/100 ml) for mixed venous O₂ content and –0.1 ml/100 ml (–2.9 to 2.7 ml/100 ml) for arteriovenous difference O₂ content. The cardiac output estimated by the lung model was in good agreement with the direct Fick measurements in young healthy subjects.     

Thermal degradation of polybutadiene, 2. Overall thermal behaviour of polymers with different microstructures

The thermal decomposition at volatilization temperatures of polybutadiene samples with different initial microstructures was investigated i. vac. and under nitrogen atmosphere by thermogravimetry, differential scanning calorimetry, thermal volatilization analysis and infrared spectroscopy. The decomposition of cis-1,4-, trans-1,4- and random polybutadienes occurs in two stages, whereas only one stage is shown by 1,2-polybutadiene. Chemical changes and amounts of weight loss in the first degradation stage are dependent on the sample heating rates. The volatile degradation products were collected, fractionated and compared for the different polymers.