高顺式-1,4-聚丁二烯的结晶形态研究

用稀土催化剂得到的顺-1,4-聚丁二烯具有顺式含量高,支化度小及分子链结构规整性好等特点。在常温下为非晶态,但在低温下易于结晶,因而具有较高的力学性能。本文详细讨论了高顺式稀土顺丁生胶的低温结晶行为。用电子显微镜观察了在低温下球晶结构的形成及其分子结构规整性、结晶条件对结晶形态及结晶速率的影响。     

磁场影响聚合物本体结晶动力学的机理分析

在经典的热力学理论基础上,探讨了磁场对聚合物本体结晶过程的成核与生长的影响,建立了相关结晶动力学理论方程.初步认为,磁场产生的＂磁结晶效应＂可能是由于晶相与非晶相之间磁化率差异导致了两相之间磁化能的差异,也可能由于聚合物体系在结晶前会形成一种有序相,减小了体系的熵值,进而改变了结晶过程中的体系自由能,影响其成核与晶体生长,乃至整个结晶动力学方程.利用Matlab软件结合PLLA的各结晶参数值,绘制了结晶自由能与各成核临界参数之间的函数图像.结果表明,在低过冷度下,较小的自由能扰动可能导致较大的晶核临界参数变化.     

Morphology of solution crystallized trans-1,4-polyisoprene

The film formation method has been successfully used to grow single crystals and other complex morphological features of low melting form (LMF) and high melting form (HMF) of trans-1,4-polyisoprene (TPIP). Below 40 °C dilute amyl acetate solution gave hexagonal shaped LMF crystals. Thick and elongated hexagonal shaped morphology was shown by HMF crystals at temperatures above 40 °C. Straight faces and sharp corners of the single crystals, and also of complex crystals, acquired round shapes when highly polydispersed TPIP was used for crystallization.     

一个新颖三维配位聚合物Pb(1，4-napdc)(DMF)的合成、结构及热稳定性研究

A novel 3D metal-organic coordination polymer Pb(1,4-napdc)(DMF) (1,4-napdc=naphthalene-1,4-dicarboxylate) was synthesized at room temperature using slow vapor diffusion method to grow single crystal that has been analyzed by X-ray diffraction. The crystal belongs to orthorhombic with space group P2₁2₁2₁. The unit cell parameters are as fellows: a=0.701 3(2) nm, b=1.407 6(3) nm, c=1.521 5(4) nm, V=1.501 8(6) nm³ and Z=4. In the crystal structure of Pb(1,4-napdc)(DMF), the square grids constructed with paddle-wheel units of Pb(Ⅱ) and 1,4-napdc links stack over each other to generate infinite 3D network, which has square apertures (1.158×1.158 nm²) along the crystallographic a-axis. The thermal stability of compound was investigated by differential scanning calorimetry and thermogravimetric analysis. CCDC: 293617.     

Effects of Binding Energy of Bioinspired Sacrificial Bond on Mechanical Performance of cis-1,4-Polyisoprene with Dual-crosslink

Although bioinspired sacrificial bonds have been demonstrated to be efficient in improving the mechanical properties of polymer materials, the effect of binding energy of a specific dynamic bond on the ultimate mechanical performance of a polymer network with dual-crosslink remains unclear. In this contribution, diamine and sulfur curing package are introduced simultaneously into a sulfonated cis-1,4-polyisoprene to create dually-crosslinked cis-1,4-polyisoprene network with sulfonate-aminium ionic bonds as the sacrificial bonds. Three diamines(primary, secondary and tertiary) with the same spacer between the two nitrogen atoms are used to create the ionic bonds with different binding energies. Although the binding energy of ionic bond does not affect the glass transition temperature of cis-1,4-polyisoprene(IR), it exerts definite influences on strain-induced crystallization and mechanical performance. The capabilities of diamine in dissipating energy, promoting strain-induced crystallization and enhancing the mechanical performance are in the same order of secondary diamine primary diamine tertiary diamine. The variations in mechanical performances are correlated to the binding energy of the ionic bond, which is determined by p Ka values.     

Investigation of poly(trans-1,4-butadiene) crystals using the spin-probe method

The spin-probe technique has been employed to study the nature of the surface regions of poly(trans-1,4-butadiene) crystals grown from dilute heptane and toluene solutions. The narrowing of the ESR spectrum of the nitroxide radical probe added to the PTBD crystals and the activation energy for the rotational motion of the probes were found to very with the crystallization solvent and annealing temperature; in every case heptane-grown crystals showed a higher line narrowing temperature and activation energy than toluene grown crystals. Annealing at 80°C raised the narrowing temperature and the activation energy for crystal preparations from both solvents used, but annealing at high temperatures, near to but below the melting point, lowered both parameters again. These results support earlier assertions, based on infrared spectra, surface epoxidation, differential scanning calorimetry, broad-line nuclear magnetic resonance, and dynamic mechanical results concerning the nature and location of the amorphous regions in PTBD crystals.     

Study of crystallization kinetics of trans-1,4-polyisoprene

The concentrations and the growth rates of high- and low-melting type spherulites of trans-1,4-polyisoprene were measured in the temperature range 39–49°C. It was shown that above about 40°C., the crystallization rate of trans-1,4-polyisoprene is determined primarily by the radial growth rate of high-melting form (HMF) spherulites, whereas the predominance of the low-melting form (LMF) crystals below 40°C. can be attributed to the high rate of formation of LMF primary nuclei at lower crystallization temperatures. Temperature-independent rate parameters were calculated from optical and dilatometric measurements and were found to be in good agreement. Both the change in nucleation habit and spherulite growth rate with temperature can be explained on the basis of a lower end surface free energy of LMF crystals of trans-1,4-polyisoprene compared to that of the HMF crystals.     

A new class of liquid crystals: methylene-1,4-dihydropyridines

A group of liquid crystal materials which contain the novel methylene-1,4-dihydropyridine substructure were synthesized and their mesogenic properties examined. Three main classes of liquid crystal compounds which differ in the structure of the aromatic core group (phenyl, azobenzene and diphenylacetylene) attached to the nitrogen of the 1,4-dihydropyridine group were studied. The synthesis of the methylene-1,4-dihydropyridine group was accomplished in excellent yield by a Knoevenagel condensation of a 4-pyridone intermediate with an active methylene compound. The liquid crystal materials prepared thus far which contain this methylene-1,4-dihydropyridine structure all possess broad enantiotropic smectic A phases and one example also possesses a tilted smectic C phase. These mesogens may possess useful properties such as high birefringence.     

Studies on polyethylene crystallized at unusually high supercoolings: Fold length,habit, growth rate,epitaxy

The newly arisen possibility of crystallizing polyethylene at supercoolings much higher than were achievable previously has enabled the study of crystallization to be extended in several directions. Thus, fold length can be followed down to previously inaccessibly low crystallization temperatures, in the present case with sharp fractions, demonstrating the essential independence of the fold length of molecular weight. In this context the thinnest isolated crystal reported so far was obtained (ca. 6 nm). The faceted nature of crystals grown at such low temperatures and high rates has been noted, and is in line with new conceptions of polymer crystal growth. A previous observation of exceptionally high crystal growth rate (ca. 2 m/s) has been supplemented by measurements over a range of crystallization temperatures and the results found to be in good agreement with the predicated regime III behavior in the least theory of Hoffman. Observations of epitaxy on mica, while broadly in line with those by Lovinger, were revealing in several respects. Among these the observation that the substrate can influence the fold length when the chains are parallel to the substrate plane remains unexplained and puzzling.     

Coordination chemistry of 1,4-bis-carboxymethylcyclam, H(2)(1,4-bcc)

Zinc metal reduction of the cobalt(III) complex [Co(1,4-bcc)](+) (1,4-bcc = 1,4-bis-carboxymethylcyclam) produces the corresponding cobalt(II) complex which crystallises as the coordination polymer {[Co(1,4-bcc)]ZnCl(2)}(n). A method has been developed for removal of the cobalt(III) ion from [Co(1,4-bcc)](+) and isolation of the free ligand as its hydrochloride salt, H(2)(1,4-bcc).4HCl. This has been used for the preparation of new metal complexes, and the syntheses and characterisation of the copper(ii), nickel(ii), zinc(ii) and chromium(iii) complexes containing the 1,4-bcc ligand are described. X-Ray crystal structures of {[Co(1,4-bcc)]ZnCl(2)}(n).2.5H(2)O, {[Cu(1,4-bcc)]CuCl(2)}(n).0.25MeOH.H(2)O and [Cu(1,4-bcc)H]ClO(4) show the complexes to have the trans(O) geometry of the 1,4-bcc ligand, while the structure of [Cr(1,4-bcc)H(0.5)](ClO(4))(1.5).EtOH exhibits the cis(O) configuration.     

Crystallization of segmented trans-1,4-polyisoprene/epoxidized trans-1,4-polyisoprene block copolymers from solution

The crystallization of segmented block copolymers of trans-1,4-polyisoprene (TPI)/expoxidized TPI from solution was investigated. One preparation with an average TPI block length of 14.5 and an average epoxidized TPI block length of 10 was crystallized from 2-pentanol at 20°C, 2-octanol at 20°C, and 2-pentanone at 0°C. A second preparation with an average TPI block length of 18 and the same average epoxidized TPI block length was crystallized from 2-octanol at 20°C and 2-pentanone at 0°C. The crystallization products were expoxidized in suspension a second time and then characterized by carbon-13 solution NMR to determine the average noncrystalline traverse length and the average crystalline stem length. The crystallized products were also studied by scanning electron microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry to determine the morphology, the crystal form and crystallinity, and the melting point, respectively. The average noncrystalline traverse length was found to be highly dependent on the crystallization conditions and the crystalline stem length of the parent TPI lamellas; the composition of these traverses is discussed.     

Effects of the oriented mesophase on the cold crystallization of syndiotactic polystyrene and its blend with poly(2,6‐dimethyl‐1,4‐phenylene oxide)

The effects of molecular orientation on the crystallization and polymorphic behaviors of syndiotactic polystyrene (sPS) and sPS/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) blends were studied with wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry. The oriented amorphous films of sPS and sPS/PPO blends were crystallized under constraint at crystallization temperatures ranging from 140 to 240°C. The degree of crystallinity was lower in the cold‐crystallized oriented film than in the cold‐crystallized isotropic film. This was in contrast to the case of the cold crystallization of other polymers such as poly(ethylene terephthalate) and isotactic polystyrene, in which the molecular orientation induced crystallization and accelerated crystal growth. It was thought that the oriented mesophase was obtained in drawn films of sPS and that the crystallization of sPS was suppressed in that phase. The WAXD measurements showed that the crystal phase was more ordered in an sPS/PPO blend than in pure sPS under the same annealing conditions. The crystalline order recovered in the cold‐crystallized sPS/PPO blends in comparison with the cold‐crystallized pure sPS because of the decrease in the mesophase content. The crystal forms depended on the crystallization temperature, blend composition, and molecular orientation. Only the α′‐crystalline form was obtained in cold‐crystallized pure sPS, regardless of molecular orientation, whereas α′, α″, and β′ forms coexisted in the cold‐crystallized sPS/PPO blends prepared at higher crystallization temperatures (200–240°C). The β′‐form content was much lower in the oriented sPS/PPO blend than in the isotropic blend sample at the same temperature and composition. It was concluded that the oriented mesophase suppressed the crystallization of the stable β′ form more than that of the metastable α′ and α″ forms during the cold crystallization of sPS/PPO blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1665–1675, 2003     

PREPARATION AND CHARACTERIZATION OF cis-,4-POLYBUTADIENE CONTAINING A FRACTION OF trans-1,4-POLYBUTADIENE

Polymerization of butadiene catalysed first with V(acac)_3-Al(i-Bu)_2Cl, then with Co(acac)_3-H_2O-Al(i-Bu)_2Cl has been studied. The polymer obtained was identified to be a new variety of cis-1,4-polybutadiene which contained a fraction of trans-1,4-polybutadiene chemically bonded to the cis-1,4-polybutadiene chains. Its molecular weight and trans-1,4 content can be regulated by varying the catalyst composition and concentration as well as other polymerization conditions. The trans-1,4 fraction, although it presents only in 9—16%, forms a crystalline phase in the matrix at room temperature and facilitates the crystallization of the polymer.     

顺式1,4-聚丁二烯的流变性质——Ⅱ.生胶的包辊性能

研究了四种催化体系的高顺式1,4-聚丁二烯生胶包辊性与温度及辊距的关系。流动曲线由连续变为不连续的临界温度可用作判断包辊性的一种依据,临界温度愈高,则2-3区转变温度也愈高即包辊性也愈好。但长链支化对包辊性,特别是在宽辊距时,有一定影响。对此现象的原因进行了推测。     

Confined crystallization of cylindrical diblock copolymers studied by dynamic Monte Carlo simulations

We report dynamic Monte Carlo simulations of polymer crystallization confined in the cylindrical microdomains of diblock copolymers. The microdomains were prepared via spontaneous microphase separation from homogeneous melt, and the major component was then frozen in a vitreous amorphous state to make a hard confinement to the crystallization of the minor component. We found that during the isothermal crystallization at high temperatures, crystal orientations are dominantly perpendicular to the cylinder axis at the early stage of crystal nucleation and remain to the final state; while if the block junctions are broken before crystallization, crystal orientations are dominantly parallel at the early stage of crystal nucleation, and eventually other orientations take the place of parallel preferences. Analysis of bond orientations in the heterogeneous melts demonstrates the microscopic origin of oriented crystal nucleation.     

Crystal perfection and triplet excitons in 1,4-dibromonaphthalene

The phosphorescent behaviour of 1,4-dibromonaphthalene single crystals at liquid-helium temperatures is strongly influenced by the crystal preparation techniques. Crystal unperfections appear to be essential for observing excitonic emission. A comparison is made between crystals grown from the melt, solution and vapour. Experiments on crystals doped with DBN-d₆ confirm the proposed model.     

Poly-N-methyliminotetrafluoro-1,4-phenylene

Poly-N-methyliminotetrafluoro-1,4-phenylene has been prepared. The polymer was insoluble in organic solvents, but dissolved in concentrated H₂SO₄. It started to melt at approximately 360°C with decomposition. The structure of the polymer is discussed on the basis of synthesized oligomers.     

Film formation from monodisperse acrylic lattices 1. Influence of concentration and layer thickness on particle ordering

The influence of concentration and layer thickness on particle ordering in polymer latex films, both open and closed, has been studied by means of rheology, microscopy and turbidimetry. Monodisperse acrylic lattices were synthesized by semicontinuous emulsion polymerization. The lattices exhibited a distinct thixotropy above a certain concentration, which is attributed to crystallization. Microscopy revealed a three-layer structure and a dependence of crystal size and crystal packing on layer thickness and layer concentration. Turbidimetry (i.e., analysis of light transmission and interference) was used to study the progress of ordering in open and closed systems. In closed films crystallization proceeds faster at higher concentrations and in thinner films. Above a sufficiently high concentration no crystallization was observed. Furthermore, an induction time was found below certain concentrations. The drying of open latex films at temperatures below the minimum film formation temperature (MFFT) was shown to proceed through five distinct stages. The drying of open films at temperatures below the MFFT was studied by analysis of the turbidity of rewetted films. A more compact structure was found in thinner films. The structure in lattices is discussed as a result of long-range and short-range ordering.     

Ab Initio and in-Crystal Geometry of trans-1,4-Dibromo1,4-dicarboxymethylcyclohexane

The structure of trans-1,4-dibromo-1,4-dicarboxymethylcyclohexane (I) has been determined by single crystal x-ray diffraction. The molecules, located on symmetry centers, are in the rigid chair conformation with the Br and COOCH₃ axial and equatorial, respectively. The molecular geometry observed in the crystal is similar to that calculated for the isolated molecule using ab initio calculations performed at the HF/6-31(d) level. A peculiar arrangement of the carboxymethyl substituents, along with short contacts involving the Br atoms, seem to play a role in the stabilization of the crystalline structure.     

Confinement Effects on the Crystallization of Poly(ethylene oxide) Nanotubes

In this work, we show the effects of nanoconfinement on the crystallization of poly(ethylene oxide) (PEO) nanotubes embedded in anodized aluminum oxide (AAO) templates. The morphological characteristics of the hollow 1D PEO nanostructures were evaluated by scanning electron microscopy (SEM). The crystallization of the PEO nanostructures and bulk was studied with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The crystallization of PEO nanotubes studied by DSC is strongly influenced by the confinement showing a strong reduction in the crystallization temperature of the polymer. X-ray diffraction (XRD) experiments confirmed the isothermal crystallization results obtained by DSC, and studies carried out at low temperatures showed the absence of crystallites oriented with the extended chains perpendicular to the pore wall within the PEO nanotubes, which has been shown to be the typical crystal orientation for one-dimensional polymer nanostructures. In contrast, only planes oriented 33, 45, and 90° with respect to the plane (120) are arranged parallel to the pore's main axis, indicating preferential crystal growth in the direction of the radial component. Calculations based on classical nucleation theory suggest that heterogeneous nucleation prevails in the bulk PEO whereas for the PEO nanotubes a surface nucleation mechanism is more consistent with the obtained results.