Effect Of Co-crystallization Research Articles

Polymorphic and Isomorphic Cocrystals of a N-Salicylidene-3-aminopyridine with Dicarboxylic Acids: Tuning of Solid-State Photo- and Thermochromism

The crystal structures and optical properties of (E)-2-methoxy-6-(pyridin-3-yliminomethyl)phenol (1), a N-salicylidene-3-aminopyridine, and its 2:1 dimorphic cocrystals with fumaric acid (2 and 3) and succinic acid (4 and 5) were studied at solid state in order to understand the effects of cocrystallization and molecular packing on their photo- and thermochromic behavior. New criteria for prediction of the chromic properties, based on the rationalization of the intermolecular interaction in the crystal, are also proposed. These results confirm once more the influence of the molecular packing on the chromic properties of solids and extend it to polymorphic and isomorphic cocrystals.

Effect of co-crystallization of ethanol, pyridine and 2,2′-bipyridine on molecular aggregation in bis(1,2,3,4-tetrahydroquinolinedithiocarbamato-S,S′)mercury(ii) and synthesis of HgS nanoparticles

Different structural motifs are obtained by co-crystallization of 2,2′-bipyridine, ethanol and pyridine with [Hg(thqdtc)2].

Solution Crystallization and Dissolution of Polyolefins as Monitored by a Unique Analytical Tool: Solution Crystallization Analysis by Laser Light Scattering

For the first time, the solution crystallization and dissolution behavior of polyolefins in a variety of solvents was investigated by using a recently developed crystallization based analysis technique, solution crystallization analysis by laser light scattering (SCALLS). SCALLS results provide clear evidence that crystallization and dissolution of linear polyethylene (PE) and isotactic polypropylene (iPP) are greatly influenced by the type of solvent used. It was demonstrated for a blend of PE and iPP that cocrystallization effects are minimal in solvents such as TCB and o-DCB and are significantly more pronounced in xylene and decalin. Surprisingly, in xylene, individual dissolution curves (bimodal SCALLS profile) for both PE and iPP with minimal codissolution effects were observed while in TCB, o-DCB, and decalin both components dissolve simultaneously. These findings provide a novel and facile approach to understand the effect of solvents on cocrystallization and codissolution of chemically dissimilar components in preparative fractionations such as prep TREF (which normally uses xylene), by using TCB as the crystallization solvent and xylene as the eluent.

Hydrochloride salt co-crystals: preparation, characterization and physicochemical studies

Co-crystallization approach for modification of physicochemical properties of hydrochloride salt is presented. The objective of this investigation was to study the effect of co-crystallization with different co-crystal formers on physicochemical properties of fluoxetine hydrochloride (FH). FH was screened for co-crystallization with a series of carboxylic acid co-formers by slow evaporation method. Photomicrographs and melting points of crystalline phases were determined. The co-crystals were characterized by FTIR, DSC and PXRD methods. Solubility of co-crystals was determined in water and buffer solutions. Powder and intrinsic dissolution profiles were assessed for co-crystals. Physical mixtures of drug and co-formers were used for comparisons at characterizations and physicochemical properties evaluation stages. Four co-crystals of FH viz. Fluoxetine hydrochloride-maleic acid (FH-MA), Fluoxetine hydrochloride-glutaric acid (FH-GA), Fluoxetine hydrochloride-L-tartaric acid (FH-LTA) and Fluoxetine hydrochloride-DL-tartaric acid (FH-DLTA) were obtained from screening experiments. Physical characterization showed that they have unique crystal morphology, thermal, spectroscopic and X-ray diffraction properties. Solubility and dissolution studies showed that Fluoxetine hydrochloride-maleic acid co-crystal possess high aqueous solubility in distilled water, pH 4.6, 7.0 buffer solutions and dissolution rate in distilled water than that of pure drug. Co-crystal formation approach can be used for ionic API to tailor its physical properties.

Study on high weld strength of impact propylene copolymer/high density polyethylene laminates

The impact propylene copolymer (IPC) and isotactic polypropylene (iPP) were separately selected to prepare laminates with high density polyethylene (HDPE) by hot press. The peel forces of IPC/HDPE and iPP/HDPE laminates were examined, and it was found that the welded joint strength in IPC/HDPE laminate was dramatically higher than that of iPP/HDPE laminate. According to the special microstructure of IPC, the co-crystallization of the ethylene segments in ethylene-propylene block copolymer (EbP) component of IPC and the PE chain in HDPE was proposed to explain the highstrength welding. The DSC results indicated that there indeed existed some interaction between IPC and HDPE, and the crystallizable PE component in IPC could affect the crystallization of HDPE. The scanning electron microscope (SEM) observations of IPC/HDPE blends demonstrated that HDPE tended to stay with the PE-rich EbP chains to form the dispersed phase, indicating the good miscibility between HDPE and EbP components of IPC. According to the above results, the effect of co-crystallization of the PE components of the IPC and HDPE on the high weld strength of IPC/HDPE laminate was confirmed.

Bimodality Criterion for the Chemical Composition Distribution of Ethylene/1‐Olefin Copolymers: Theoretical Development and Experimental Validation

AbstractEthylene/1‐olefin copolymers with controlled bimodal molecular weight distributions (MWDs) and chemical composition distributions (CCDs) have improved mechanical and rheological properties. In this work, the Stockmayer's distribution was used to develop a criterion for CCD bimodality. The proposed criterion was validated theoretically using simulation data and experimentally using crystallization analysis fractionation (CRYSTAF) and crystallization elution fractionation (CEF) of ethylene/1‐octene copolymer blends. The effect of mass fraction and number average molecular weight of copolymer produced with each metallocene catalyst on CCD bimodality was also examined. The proposed criterion was then used as a benchmark for describing cocrystallization effects in both CRYSTAF and CEF techniques. magnified image

A New Technique for Characterizing Comonomer Distribution in Polyolefins: High-Temperature Thermal Gradient Interaction Chromatography (HT-TGIC)

This paper documents a new polyolefin characterization technique, high-temperature thermal gradient interaction chromatography (HT-TGIC or TGIC), to quantify comonomer distribution. A set of homogeneous ethylene−octene homopolymers are used with a commercially available column having a graphitic substrate (HYPERCARB) to demonstrate this technique’s applicability to fractionating polyolefins. The separation mechanism appears to be based on the interaction of the polyolefin chains with the graphite surface upon a temperature change in an isocratic solvent. The TGIC technique overcomes the key issues encountered in crystallization based techniques and in high-temperature liquid chromatography with a solvent gradient (HT-LC). Crystallization based techniques cover only a narrow analysis range of 0−9 mol % comonomer content and suffer from potential error in the analysis caused by cocrystallization effects. HT-LC is limited in its capability because of the limited choice in detectors available. Conversely, TGI...

Crystal engineering to improve physicochemical properties of mefloquine hydrochloride

Background: Pharmaceutical cocrystallization is a promising alternative for improving the solubility and dissolution rate or manipulating other physical properties of active pharmaceutical ingredients. The objective of this investigation was to study the effect of cocrystallization with different cocrystal formers on physicochemical properties of mefloquine hydrochloride. Method: Cocrystals were prepared by solution crystallization method – mefloquine hydrochloride (414.8 mg, 1 mmol) and different cocrystal formers (1/2 mmol) were dissolved in 20 mL of ethanol with warming. Solution was cooled in ice bath for 6 hours. The crystals were isolated by filtration through a membrane (0.45 μm) and dried in the air. The pure drug and the prepared cocrystals were characterized in terms of saturation solubility, drug content, infrared spectroscopy, differential scanning calorimetry, powder X-ray diffraction, scanning electron microscopy, in vitro dissolution studies, and stability studies. Results: The cocrystals showed enhanced solubility and dissolution rate. The cocrystals were found to be stable over the period of 6 months confirmed from stability studies. Conclusion: Cocrystals resist the conversion of anhydrous form of drug into its hydrate which is responsible for the drugs less solubility and dissolution rate.

Comparison of thermal properties of crude by-product polyolefin wax, fractionated paraffin wax and their blend

The molecular weight and thermal properties of unfractionated by-product polyolefin wax (wax K) from a naphtha cracking unit, fractionated commercial paraffin wax (wax J) and their blend (wax M) were evaluated and were compared with each other using differential scanning calorimetry (DSC), normal and high-temperature gel per- meation chromatography (GPC), and wide-angle X-ray diffraction (WAXD). Such properties as molecular weight dis- tribution, melting temperature and degree of crystallization were altered by blending wax K with wax J. By blending with two parts of wax K and one part of wax J to prepare wax M, Mw of wax K was shifted, by half, to that of wax J in order to approach that of wax M, whereas the Mn of wax K remains almost unaltered to become that of wax M. In particular the effect of blending of wax K and wax J turned out co-crystallization for the sharper lower-melting-tem- perature endothermic peak of the blend, indicating narrower molecular distribution, than that of wax K at the melting temperature shifted even below that of wax J. The total degree of crystallinity for the blend, wax M, turns out less than that before blending wax K with wax J, which may be attributed to the effect of co-crystallization due to blending.

Poly(ethylene glycol) cationization with alkali metals in matrix-assisted laser desorption ionization investigated with the solvent-free method

Matrix-assisted laser desorption ionization (MALDI) was applied to determine the relative efficiencies for attachment of alkali cations to poly(ethylene glycol) polymers. The solvent-free sample preparation method was employed in order to discriminate the gas-phase polymer-cation complex formation mechanism from solubility and co-crystallization effects. We show that the cohesion energy of the cation precursor has a strong influence on the outcome of the MALDI measurements. This potential drawback is circumvented by the simultaneous use of alkali salts of similar lattice energy. The experiments include chain polymers of different length (PEG600 and PEG1000) and alkali cations of different size (Na+, K+, Cs+). We found that the attachment efficiencies decrease with growing cation size. This decrease is significantly more rapid for the shorter PEG600 polymers. These results corroborate the general trends observed in earlier studies, but correct the dependence on alkali cation size assessed in previous MALDI experiments with the conventional dried-droplet sample preparation method.

Effect of operation parameters on temperature rising elution fractionation and crystallization analysis fractionation

AbstractCrystallization analysis fractionation and temperature rising elution fractionation are two techniques used to estimate the chemical composition distributions of semicrystalline copolymers. This study investigates the cooling rate and cocrystallization effects for both techniques with a series of ethylene/1‐olefin copolymers and their blends. Ideally, both techniques should operate in the vicinity of thermodynamic equilibrium so that crystallization kinetic effects are avoided. The results show that, in fact, crystallization kinetic effects play an important role at the typical cooling rate used with both techniques. Cocrystallization is significant when fast cooling rates are used. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1762–1778, 2003

Miscibility of linear and branched polyethylene blends by thermal fractionation: use of the successive self-nucleation and annealing (SSA) technique

In the present work, the recently developed thermal fractionation technique successive self-nucleation and annealing (SSA) was applied to blends of branched and linear polyethylenes (PEs), as a method to evaluate the phenomena of miscibility and segregation in PE blends. The melting behavior of the systems, after a controlled cooling and after the application of SSA was compared. The DSC scans corresponding to cooling of blend samples from the melt or subsequent heating displayed an overlap of the exotherms and endotherms, respectively, of the blend components that could lead to interpretations of partial miscibility. These effects were interpreted as arising from: a nucleation effect of the crystals formed by the more linear PE on the crystals of branched PE, a dilution effect of the molten branched chains on the crystals formed by the more linear PE and finally possible partial miscibility effects. However, after SSA, even when the nucleation and dilution effects are still present for some of the fractions produced, the thermal fractionation procedure helps to distinguish them from co-crystallization effects. This is mainly achieved by observing how the number of thermal fractions generated by SSA in the blends varies with composition and by comparing the relative amounts of the thermal fractions produced by SSA. The results indicate that only those PE fractions that are similar in chemical structure, as regards to content and distribution of short chain branches, are probably miscible in the melt and can oppose molecular segregation during SSA and therefore produce stable co-crystals in the solid state. The application of SSA to the study of PE blends can be a quick and convenient tool for making comparisons and ascertain miscibility of different types of PE blends.

Welding Behavior of Semicrystalline Polymers. 2. Effect of Cocrystallization on Autoadhesion

The effect of cocrystallization on the welding behavior of semicrystalline polymers was studied by means of T-peel testing at room temperature, using ultrahigh-molecular-weight polyethylene (UHMWPE) as a model polymer. Solution-cast films of UHMWPE have a very special morphology, consisting of regularly stacked, 107 A thick lamellae, which exactly double in thickness upon annealing for 15 min below the melting point at 125 °C. This lamellar doubling process was used to introduce a well-defined amount of cocrystallization across the interface, by annealing two stacked, completely wetted solution-cast films. It was found that doubling of the lamellae across the interface enhances the peel energy to such a level that the films could not be separated anymore. By contrast, reference samples, in which cocrystallization across the interface was prohibited by “preannealing” one side of the film, could still be separated easily. Therefore, it is concluded that cocrystallization across the interface is extremely ef...

Effect of cocrystallization on kinetic parameters of high-density polyethylene/linear low-density polyethylene blend

The isothermal crystallization kinetics of a binary melt blend of high-density polyethylene (HDPE)/linear low-density polyethylene (LLDPE) is presented. An effort was made to understand the phenomenon of cocrystallization between these two constituting components of the blend with the help of kinetic parameters. The analysis based on the Avrami exponent entails that both HDPE and LLDPE undergo individual seeding of nuclei and they merge with each other in the growth process to form cocrystallites. The incorporation of the LLDPE segment in the HDPE crystallites progressively dilutes the properties of HDPE in the blend. The half-time of crystallization (t1/2) shows variation in three distinct stages: The t1/2 increases slowly in the region of 0–30% LLDPE content (HDPE-rich blend), remains constant in the 30–70% LLDPE-containing region (middle region of blend composition), and increases sharply thereafter. These variations of t1/2 quite appreciably explain the change in % crystallinity, the Avrami exponent, and crystallite-size distribution. These observations were further supported by the small-angle light-scattering experiment. © 1996 John Wiley & Sons, Inc.

Flexural and impact properties of high‐density polyethylene/linear low‐density polythylene blend

AbstractIn this article, a study of flexural and impact properties of binary blends of high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE), over a full range of blending ratios, is presented. The property distinctions in the three ranges of composition (viz., HDPE‐rich blend, LLDPE‐rich blend, and the middle region) are remarkable and consistent with the different effects of cocrystallization in the respective concentration ranges. Furthermore, the analysis of flexural yield properties data, in terms of the Ree‐Eyring equation, and the correlation of results with variation of x‐ray crystallinity are presented, which suggests the existence of two types (i.e., mobile and immobile) of segments in the amorphous phase of the blend. The relative variation of these two types of amorphous phase in the three different composition ranges of the blend are discussed. The impact strength variation of this blend is also found to correlate with the variation of the fraction of amorphous phase in the blend. © 1993 John Wiley & Sons, Inc.

Mechanical properties and morphology of high‐density polyethylene/linear low‐density polyethylene blend

AbstractThe binary blend of high‐density polyethylene (HDPE) and linear low‐density polyethylene (LLDPE) in the range of composition from 100% HDPE to 100% LLDPE has been investigated for tensile and flexural properties and the morphology in the deformed state on tensile fracture. Tensile properties (initial modulus, yield stress, and elongation‐at‐yield, ultimate tensile strength and elongation‐at‐break, and work of yield and work of rupture) and flexural properties (flexural modulus and flexural yield stress) are studied as a function of blend composition. Behavior, in terms of these properties, is distinguishable in three zones of blend composition, viz. (i) HDPE‐rich blend, (ii) LLDPE‐rich blend, and (iii) the middle zone. In zones (i) and (ii), the variations of these properties are more or less linear, whereas in the middle region [i.e., zone (iii)], there is a reversal of trends in variation or sometimes a behavior opposite to the expected one. The results are explained on the basis of the effects of cocrystallization and the presence of octene‐containing segments in the amorphous phase. Scanning electron micrographs of the tensile fracture surfaces are presented to illustrate the occurrence of transverse bands interconnecting the fibrils.

Conformations of the Pyranoid Sugars. II. Infrared Absorption Spectra of Some Aldopyranosides.

The conformations of twenty-four aldopyranosides have been studied by analysis of their infrared absorption spectra. The most stable conformations of twelve of the glycosides had previously been assigned by Reeves from a study of their instability factors; these conformations were assumed to apply to the crystalline state, for which the spectra had been recorded. The compounds were classified into (a) configurationally and (b) structurally related groups, and the spectra were intercompared. The analysis revealed groups of absorption bands which showed a concerted shift on change of anomeric disposition.With these groups of absorption bands thus identified, intercomparison with nine of the remaining spectra afforded evidence that the anomeric group (1) is axial in methyl d-glycero-α-l-gluco-heptopyranoside, methyl d-glycero-α-l-manno-heptopyranoside, and methyl d-glycero-α-d-gulo-heptopyranoside; (2) is equatorial in methyl 6-deoxy-β-l-mannopyranoside, methyl d-glycero-β-d-gulo-heptopyranoside, and cyclohexyl d-glycero-β-d-gulo-heptopyrnoside; and (3) either is quasi or occurs as different (or mixed) axial and equatorial forms in methyl α-d-lyxopranoside, methyl β-d-lyxopranoside, and (possibly) α-d-methylgulopyranoside.Three of the glycosides were available as their crystalline complexes with calcium chloride. The spectra of these complexes were also examined, and the effect of co-crystallization with calcium chloride is pointed out.