Crystallisation, solvent-induced

Most of the poly(etherketone-carborane)s so far prepared are non-crystalline and thus readily soluble in organic solvents such as chloroform or NMP, from which tough, coherent films and coatings can be obtained by solvent evaporation. However, we have found two polymers of this type, both derivatives of p-carborane, which display significant levels of crystallinity.8 Thus, the semi-aliphatic polymer derived from bis(4-phenoxyphenyl)-p-carborane (3) and hexadecanedioic acid (6) undergoes solvent-induced crystallisation on contact with NMP, and then shows a crystal melting point of 122 °C. 

Bisphenol-A polycarbonate 15 is normally amorphous (and clear) but is subject to solvent-induced crystallisation in the presence of some low-molecular-weight solvents [125]. 

Solvents that can induce crystallisation - A large number of papers [10-16] report the solvent-induced crystallisation of amorphous PEEK. Most of these solvents operate by reducing of the PEEK to below ambient temperature which then allows crystallisation. They typically have an H-C-X fimctionality, where X is electron withdrawing. Examples include chloroform, methylene chloride, tetrahydrofuran and chlorotoluene. Such solvents tend to have an enhanced ability to cause ESC in crystalline PEEK. Solvent crystallisation is an interesting phenomenon but, so far, has limited industrial application. 

The glass transition of PETP samples which were subjected to solvent induced crystallisation (SINC) was investigated by modulated differential scanning calorimetry (MDSC) and density measurements. The differential heat capacity signal from MDSC was used to monitor the SINC process. 16 refs. 

The method of procedure is to add the solvent used as diluent drop by drop to the cold or hot concentrated solution until turbidity is just produced crystallisation is then induced by leaving the liquid to stand or by scratching with a sharp-edged glass rod. When crystallisation has begun the solution is cautiously diluted further. It is a mistake to precipitate the dissolved substance at one stroke with large amounts of the diluent. 

Note. (1) The Schiff base may be prepared by heating the components in the absence of solvent at 100 °C for 15 minutes, cooling, and then stirring the product with methanol to induce crystallisation. 

Often it is possible to use a mixture of miscible solvents where the substance to be recrystallised is soluble in one of the solvents but relatively insoluble in the other. The solute can be dissolved hot in a suitable solvent mixture, which is then allowed to cool. Alternatively, the solute can be dissolved in the solvent in which it is more soluble either at elevated or at room temperature the other solvent is then added until crystallisation just begins, and the resulting mixture is cooled to further induce recrystallisation. 

SAXSAVAXS/RAMAN is especially useful when dealing with chemically induced phase transitions. The example shown in Figure 2(e) is the polymerisation of solvent styrene into polystyrene in which polyethylene is in solution. Polyethylene is soluble in styrene but insoluble in polystyrene. RAMAN allows the determination of the reaction kinetics of polystyrene formation and monitors the crystallisation of the polyethylene. The SAXS monitors the liquid-liquid phase separation followed by the liquid-solid phase transition, whilst the WAXS also observes the liquid solid phase by monitoring the appearance of peaks due to the crystallisation of polyethylene. These are very valuable parameters when trying to define any new manufacturing process. ... 

---