Crystallization cocrystallization

From the results discussed above, it is concluded that the crystallization behavior of HDPE/LDPE blends depends on the number, length, and distribution of branches in the LDPE component. In general, most HDPE/LDPE blends reveal a strong tendency to undergo separate crystallization. Cocrystallization is rarely observed in HDPE/LDPE blends. 

Recent studies (Defieuw 1989) indicate that the crystallization conditions, blend composition, chain rigidity and microstracture, and molecular weight of the components are important. Blends consisting of two crystallizable components (Sect. 3.2.2.2) can exhibit separate crystallization or concurrent crystallization (cocrystallization). 

When dealing with miscible blends containing two crystalline components, several modes of crystallization are possible separate crystallization, concurrent crystallization, cocrystallization, etc. Only those blends in which both components are miscible in the melt are considered here (Table 3.3). PET/PBT blends were reported to be an example of separate crystallization (Escala and Stein 1979 ... 

Two cocrystallization processes employ dibasic crystals as intermediates. The PPG process (199—202) is discussed under commercial processes. The PPC process (203) forms dibasic crystals from lime and recovered filtrates. The dibasic crystals are separated from thek mother liquor by decantation, slurried in caustic solution and chlorinated to produce a cocrystalline slurry of Ca(OCl)2 and NaCl. The slurry is sent to a flotation cell where the larger salt crystals settle out and the smaller hypochlorite crystals float to the top with the aid of ak and flotation agent. The hypochlorite slurry is centrifuged the cake going to a dryer and the centrate to the flotation cell. The salt-rich bottoms from the flotation cell are centrifuged and washed with dibasic mother Hquor. The centrates are recycled to the precipitation step. 

For instance, also the homopolymers PVF and PVDF have been described to crystallize in separate crystals in their blends [99] (Though constituted by isomorphous monomeric units which can cocrystallize in the copolymers in the whole range of composition, as seen in Sect. 4.1). Moreover, at least for the studied conditions, the polymorphic behavior of PVDF is not altered by the presence of PVF [99]. 

The reaction between Bul2Si(OH)2 and Cl4Sn affords, after workup and crystallization from CH2C12, the tin complex 51 containing a bridging But2Si(OH)2 molecule, which is cocrystallized with (H0Bu 2Si)20, the structure of which is described in Section IV,D,1 (272). 

TpAnt]Tl, and that the composition of the crystal studied was approximately [TpAnt](CoNCS)0.94TI0.06. As a consequence of the cocrystallization, the crystallographic site occupied by the CoNCS moiety was disordered with a thallium atom (Fig. 57). The ability of [TpAnt]CoNCS and [TpAnt]Tl, which differ substantially in the number of atoms at the disordered site, to cocrystallize is presumably due to the fact that the disordered site is enclosed within the pocket that is provided by the tris(pyrazolyl)hydroborato ligand. 

Compound 15 has an ill-defined structure 70) due to poor crystal quality. It is, however, interesting to note that 15 became resolved (space group 7 2,2, Z = 8) in an attempted cocrystallization experiment in the presence of optically pure 1. The two molecules of 15 in the asymmetric unit may be seen as a sort of a self inclusion , where molecules are again linked into infinite H-bond chains analogous to 13. 

Diphenylurea Crystallization. 1,3-hfsphenylurea (13) is the parent compound of a large family of derivatives, most of which do not cocrystallize with guest molecules (Etter et al. 1990). Even when put into solution with strong hydrogen bond acceptors, e.g., dimethyl sulfoxide (DMSO), triphenylphosphineoxide (TPPO) and tetrahydrofuran (THF), most diphenyl ureas crystallize with other molecules of the same kind in a connectivity pattern viewed as is shown below (14), instead of forming cocrystals (e.g., 15). 

Fe(Cp-C0NHCH2S03)2] anion have been identified (TTF)2[Fe(Cp-CONHCH2 S03)2] and the solvated (TTF)2[Fe(Cp-C0NHCH2S03)2]-2CH30H. Both crystal structures contain face-to-face dimers, with the main structural differences probably attributed to hydrogen bonding to the cocrystallized methanol. No physical properties of these salts have yet been published. 

Certain pairs of enantiomers, such as 25°C solutions of camphor in aqueous ethanol (Fig. 26a), 2,2,5,5-tetramethyl-l-pyrrolidinoxy-3-carboxylic acid in chloroform (Fig. 26b), or carvoxime in hexane (Fig. 26c), cocrystallize throughout the entire range of mole fractions. The crystals that are in equilibrium with the saturated liquid solution are solid solutions (mixed crystals), since they constitute a single phase. The racemic solid solution is termed a pseudoracemate [141]. 

There are six crystal structures reported in the Protein Data Bank two without ligand (ltqnand IwOe), one cocrystallized with progesterone (7) (IwOf), one with mytrapone (8) (IwOg), one with ketoconazole (9) (2j0c) and one with erythromycin (10) (2j0d). 

An interesting reactive mixed crystal was engineered on the basis of the observed packing of the 103 molecule having R1 = sec-butyl and R2 = ethyl (175). It was expected that the monomers in which 3-pentyl, 174, and 2-propyl, 175, replace the sec-butyl would cocrystallize in a chiral, polymerizable arrangement similar to that of 103. This was indeed what was found, and the resulting... 

Examples of solvent-mediated transformation monitoring include the conversion of anhydrous citric acid to the monohydrate form in water [235,236], CBZ with water [237] and ethanol-water mixtures [238,239], and cocrystallization studies of CBZ, caffeine, and theophylline with water [240]. Raman spectroscopy was used to monitor the crystallization rate and solute and solvent concentrations as griseofulvin was removed from an acetone solution using supercritical CO2 as an antisolvent [241]. Progesterone s crystallization profile was monitored as antisolvent was added [242]. 

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