Statistical Theory of Stable and Meta stable Transition for Crystallization and Fusion of Homopolymers ⅣStatistical Dynamics of Polymeric Crystallization by Molecular Segregation-Division of Crystal Grow-rate Regimes and Their Temperature and Grown Mechan

First a short review on the crystal growth theories and the experimental data was presented. Then a set of quantitative expressions for the size growth-rate of crystals produced by four different micro-growth mechanisms (folding, extending and two types of combination for folding and extending) was derived by a general evaluating method. A set of quantitative expressions for the correlations between the crystal size growth-rate and the product of crystalline temperature and super-cooling temperature at four different micro-growth mechanisms was obtained. Three growth-rate regimes were divided, the variations of the morphology for the crystals in the three types of regimes with the crystalline and super-cooling temperatures were discussed. They showed that these theoretical correlations between the morphology of crystals and the crystalline and super-cooling temperatures are in agreement with the later important observation on the lateral shape of crystals.     

Statistical Theory of Stable and Meta-stable Transition for Crystallization and Fusion of Homopolymers V Statistical Dynamics of Polymeric Crystallization by Molecular Segregation—Dependence of Growth-Rate for Crystals on the Grown Mechanism and Initial S

First a short review on the dependence of growth-rate for crystals on the grown mechanism and initial structure of polymers was presented. Based on the structural model of micro-nucleus and crystal-constituent chains and the feature of statistical dynamics for polymeric crystallization by molecular segregation, a general method for characteristics of the number growth-rate for micro-crystal-constituent chains and the size growth-rate for crystals was proposed. According to the method, a set of quantitative expressions for the correlation of the number growth-rate and the size growth-rate to the four types of growth was obtained (folding, extending and combination of folding and extending). Their dependences of the crystalline temperature and the initial structure of polymers were also derived, then the exponential parameters of H for molecular weight were combined with the fraction of conformation on segments, a new correlation of the exponential parameter to the temperature of crystallization and the flexibility of polymeric chain was theoretically obtained, and the dependence of H on the different types of growth was also studied. Finally the relationship between the growth-rate for crystals and the molecular weight of polymers of solution was verified by a great number of experimental data, and an excellent agreement between the theoretical prediction and experimental data was obtained.     

Synthesis and Crystallization of N-Benzoyl Tauryl Phenylalanine

HydrolysispePhdesatapboCularbondisvery~rtanincheIinStryandphannacology.Concehongonthestudyofcatalghcantithaes,althoughmpsuccessfiileXaInleshavbeenreportedinestershydrol}sis-therearestillgrcaanculhesinaInidehydrol}sis.CarboothaseA(CPA)isaproteinofbothesteraseandPephdaseachvihes,soweselectedthesubStratehippUrylphenylalamneofCPAasmodeltodesignandSynthesizenewhaPtenmoleculewhichcontalns-SOzNH-groupinsteadofco2NH-b}'bioisostericreplacement,andexPeCtedtopreParecatalyticantibodwithpePhdase…     

Kinetics of Nonisothermal and Isothermal Crystallization of Metallocene Polyethylene

Thedevelopmentofmetallocenecatalystsundoubtedlyrepresentsarevolutioninthepolyolefinbusiness.MetallocenePE(MPE)coverspolyethyleneswhichareproducedbymetallocenecatalysttechnology.EXXONChemicalCo.developedanewmeta-llocenepolyethylene-EXCEED'"PEin1991.Nowmoreandmoreeffortsarespentonthisinterestingproject.Uniformmolecularstructureandnarrowmoleculardistribution,makeMPEbetterphysicalpropertiesthanthoseofconventionalPE,andalsomakeitlowmeltstrengthandbadprocessability.Sotherelationshipbetween…     

Miscibility and Crystallization of PHB/PMA Blends

BacterialPoly(5-hydroxybutyrate)(PHB)isabiodegradableandbioc0mpatiblethermo-plasticswithhighmeltingtemperatureandcrystallinity'.Theintrinsicbrittleness0fPHBpreventSitsdirectuseasac0mmoditypolymermaterial.ItisknownthatPHB,sbrittlenessisassociatedwiththecrackswithinthelargespherulitesofPHB2.Hence,itisconsideredthattopreparemiscibleblendsofPHBwithanamorph0usp0lymershouldbeago0dwaytodecreasethebrittleness0fPHBandproducePHBbasedmaterials3'4.PHBisknowntobendsciblewithPoly(vinylacetate)(P…     

Influence of Nucleation Agents Concentration on Crystallization Structure and Properties of Glass-ceramics

Deep color glass-ceramics is prepared by using gold tailings as the main raw material, and Cr2O3 is added as nucleation agent. Influence of different Cr2O3 additions on crystallization structure and properties of CaO-MgO-Al2O3-SiO2 glass-ceramics has been discussed so as to select optimum additions. DTA is employed to determine optimum crystallization and nucleation temperatures; XRD and SEM are used to characterize microstructure of each sample; and performance indexes, such as water absorption, bulk density, flexural strength and so on, are also determined. Experimental results show that when 3wt% Cr2O3 is introduced, fine glass-ceramics with diopside as the main crystal and Ca-Fe diopside as the second-crystal is obtained, and its corresponding performance indexes are as follows: water absorption 0.12%, bulk density 2.56 g/cm3, and flexural strength 70.01 Mpa.     

Effect of γ-Ray Irradiation on Chain Structure and Crystallization Rehavior of Isotactic Polypronylene

利用凝胶渗透色谱(GPC)、傅里叶变换红外光谱(FTIR)和示差扫描量热(DSC)等手段对不同剂量γ射线辐照后等规聚丙烯(iPP)的分子链结构及结晶行为的变化进行了研究.结果表明,γ射线辐照使iPP的分子量下降,并在其分子链中产生羟基和羰基等极性基团,从而影响其结晶行为.在非等温结晶过程中,当辐照剂量≤50 kGy时,iPP的热结晶温度略有升高;增大辐照剂量,iPP的热结晶温度明显降低.iPP的熔融温度则随辐照剂量的增大而降低,且分裂成双峰.利用Avrami方程研究了辐照前后iPP的等温结晶动力学,发现辐照前后样品的Avrami指数n都在3左右,表明iPP的结晶遵循异相成核机理,且不受辐照剂量和等温结晶温度的影响,但总结晶速率随等温结晶温度和辐照剂量的升高而逐渐减小.探讨了iPP经过γ射线辐照后,分子链断裂、链结构变化和结晶速率之间的关系.     

Crystallization and melting behaviors of polypropylene admixed by graphene and β-phase nucleating agent

In this work, the crystallization and melting behaviors of different polypropylene (PP) materials containing a certain amount of graphene, β-phase nucleating agent (β-NA), and their mixture, respectively, were comparatively investigated. The results showed that graphene exhibited the typical sheet structure in the PP matrix, and the presence of β-NA did not change the dispersion of graphene apparently. Both graphene and β-NA exhibited great nucleating effect for the crystallization of PP. However, the nucleation efficiency of β-NA was much larger than that of graphene. With the simultaneous presence of graphene and β-NA, the crystallization ability of PP matrix was greatly improved, which indicated that there was a synergistic effect between graphene and β-NA in accelerating crystallization of PP matrix. Furthermore, it was proved that the synergistic effect was greatly dependent upon the crystallization conditions. The higher the isothermal crystallization temperature or the bigger the cooling rate, the more apparent the synergistic effect was.     

Crystallization,melting and spherulitic structure of Β-nucleated random propylene copolymers

The characteristics of crystallization, melting and spherulitic growth of a random propylene copolymer (PRC) containing small amount of ethylene were studied in the presence of a selective -nucleating agent (calcium pimelate). It was established that the products of isothermal and non-isothermal crystallization are very rich in -modification but have mixed polymorphic composition. The formation of -modification may be attributed to -transition on the surface of growing -spherulites resulting in -twin-spherulites. During melting of PRC of -modification, the characteristics observed with -nucleated propylene homopolymers, namely, a -recrystallization of recooled samples and separated melting of non-recooled samples (i.e. the melting memory effect), as well as a -recrystallization leading to a perfection of the structure within the -modification, are also demonstrated. The disturbance of regularity of the polymer chain highly reduces the tendency to -crystallization. In contrast to the observations with propylene homopolymers, the growth rate of -modification (G ) is higher than that of -modification (G ) and no critical crossover temperature can be found (T()=413 K) below whichG >G . The experimental results show that a partial disturbance of chain regularity by incorporation of comonomer units considerably reduces the tendency to -crystallization.This research was supported by the National Scientific Research Fund (OTKA), the author is grateful for it. Thanks are due to Professor Géza Bodor for his help in X-ray diffractometric investigations and to Ms. Tünde Lócska for her prudential technical assistance in the optical experiments.     

Microemulsion‐Facilitated Crystallization of Carbamazepine

The crystallization patterns of carbamazepine precipitated from a confined microemulsion reservoir were studied by DSC, TGA, Powder XRD, single crystal XRD, SEM, and optical microscopy. The results suggest that interfacial fast nucleation and slow growth from O/W microemulsion leads to a selective, large, and better‐ordered single crystals of dihydrate form with primitive monoclinic unit cell with parameters a=10.16 Å, b=28.70 Å, c=4.93 Å, β=103.33°, cell volume of 1400.7 ų, and space group P21/c. The crystal structure, as well as the habit, are strongly influenced by the heat dissipation and prefered molecular orientation at the interface.     

Directing Role of Cage Structure for Crystallization of Zeolites

The directing mechanisms of liquid directing agents of zeolite Y and zeolite L were studied by means of light transmission, ultracentrifugation, NMR, XRD and “cross-exchange” experiments. It was discovered that not only microcfystals of zeolites, but also cage structures of zeolites play the directing role for crystallization of zeolites.     

Crystallization of polypropylenewith a minute amount of β-nucleator

Triammonium-N-dithiocarboxyiminodiacetate, (NH₄)₃L, a new dithiocarbamato derivative of iminodiacetate, has been synthesized. The coordination properties of the ligand were tested in reactions with copper(II), nickel(II) and palladium(II) salts in acidic solutions. Complexes with a general formula M(H₂L)₂ were obtained, with the coordination taking place through the sulfur atoms of the dithiocarbamate moiety. The new compounds were characterized by elemental analysis, UV/VIS and IR spectroscopy, thermal analysis and magnetic measurements. In addition, the ligand was characterized by ¹H- and ¹³C-NMR spectroscopy and molar conductivity measurements. The copper(II) complex is paramagnetic, while the nickel(II) and palladium(II) compounds are diamagnetic. The thermal decomposition of all compounds is continuous and the thermal stability of the complexes is higher than that of the ligand, as expected.     

Crystallization behavior of isotactic polypropylene induced by competition action of β nucleating agent and high pressure

Addition of β-form nucleating agent (β-NA) to isotactic polypropylene (iPP) can greatly induce the variation of the crystallization of matrix. Here, we introduce high pressure to the crystallization process of β-NA nucleated iPP. It is observed that there is a competition between the effect of high pressure and the nucleation effect of β-NA on crystallization of iPP. With the increasing of high pressure, both the contents of β-iPP and α-iPP decrease while the content of γ-iPP increases. A novel crystalline morphology of γ-iPP with the fragmentations of γ-spherulites regularly organized in a local region is observed. Namely, γ-spherulites grow on the lateral of β-NA needlelike structure. The dual nucleation effects of the special needlelike structure of β-NA towards β/α-iPP and the effect of high pressure which prevents the growth of β-iPP but promotes the growth of γ-iPP are the main mechanisms for the novel crystalline morphology of γ-iPP. Specifically, the mixed polymorphic β/γ-iPP can be achieved under a certain pressure. This possibly enlarges the application of iPP material.     

Influence of Teflon Substrate on Crystallization and Enzymatic Degradation of Polymorphic Poly（butylene adipate）

Oriented and non-oriented Teflon films, which were found to have the same crystalline structure, but different surface morphologies, were used to sandwich poly(butylene adipate)(PBA) films during isothermal crystallization. It was found that both the Teflon surface structure and the PBA polymorphic structure are the determining factors to induce epitaxial crystallization. The oriented Teflon film was able to induce epitaxial crystallization of PBA α crystal, while the non-oriented Teflon did not induce any epitaxial crystallization of PBA. Epitaxial crystallization did not occurred for PBA β crystals between neither the oriented nor the non-oriented Teflon films. The enzymatic degradation rate of PBA films was not determined by the epitaxial crystallization, in fact it was still dependent on the polymorphic crystal structure of PBA. The morphological changes of PBA films after enzymatic degradation confirmed again that the epitaxial crystallization only occurred for the PBA film with α crystal structure which was produced by being sandwiched between oriented Teflon films, and it happened only on the surface of PBA films.     

Statistical quantification of the influence of material properties on the oxidation and ignition of activated carbons

The influence of material properties on the reactivities of activated carbon materials have been studied on a laboratory scale. Carbon samples having diversified origin and properties were characterized using a thermogravimetry (TG) coupled with a differential scanning calorimetry (DSC). Reactivity parameters like the Point of Initial Oxidation (PIO) representing the beginning of the oxidation reactions and the Spontaneous Ignition Temperature (SIT) where the bed combustion takes place in a self sustaining manner were experimentally determined. The intrinsic properties of the activated carbons influencing oxidation and ignition were examined qualitatively followed by quantitative statistical correlations. Results from both qualitative and statistical correlations showed that increase in the oxygen content in the form of surface oxygenated groups increased the reactivity of activated carbons. It was by far the single most influential property discriminated from the analysis. The porosity characteristics like the specific surface area and pore volume did show some vague trends but could not be validated like that of the oxygen content. The effects of these individual properties on the oxidation and ignition reactivity are discussed.     

Crystallization and polymorphic transition behavior of chloramphenicol palmitate in 2-hydroxypropyl-β-cyclodextrin matrix

Chloramphenicol palmitate (CPP) was converted to an amorphous complex when spray-dried with 2-hydroxypropyl--cyclodextrin (HP--CyD), and no crystallization of CPP was observed for at least 2 months under the storage condition of 50°C and 50% relative humidity. The dissolution rate of CPP/HP--CyD complex in aqueous HCO-60 solution was much faster than CPP polymorphs (complex > metastable forms (B and subB) > stable form (A)), which was reflected in thein-vivo absorption behavior of CPP following oral administration in dogs.     

Crystalline Morphology and Crystallization Characteristics of In-situ Blends of Anionic Polyamide 6 with Noncrystallizable Semiaromatic Polyamide Copolymer

A noncrystallizable semiaromatic polyamide copolymer(NSAP) was dissolved in molten caprolactam, and PA6/NSAP blends were produced in-situ via the anionic ring-opening polymerization of caprolactam. The presence of a single loss tangent(tanδ) peak measured by means of dynamic mechanical analysis(DMA) proves the miscibility between PA6 and NSAP in the blends. It was found that there existed drastic changes in the crystallographic form and crystallization kinetics for the in-situ blends, e.g., when 20% NSAP was added, nearly all crystallites existed in the γ form and the crystallization could hardly occur upon cooling even at a rate of 2.5 ℃/min. Moreover, cold crystallization appears during the subsequent heating, and its melting point is 40 ℃ lower than that of the virgin system. On the other hand, the size of the spherulites only decreases modestly. It is suggested that the introduction of irregular stiff segments originated from NSAP into PA6 macromolecule chain, which resulted from transamidation during the polymerization play a dominant role in the drastic change of crystallization kinetics and the resultant morphology of the in-situ blends.     

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene γ Form

The crystallization behavior of syndiotactic polystyrene(s PS) γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl's crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering(SAXS) measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes: lamellae stable region(25-90 °C), melt-recrystallization region(90-185 °C) and pre-phase transition region(185-195 °C). As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the s PS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting(phase transition) temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the s PS γ form.