Poly recrystallization

Other hand, when an equimolar mixture of 2,5-DSP and l OEt is recrystallized from benzene, yellow crystals, comprising 2,5-DSP and l OEt in a molar ratio of 1 2, deposit. In the DSC curve of this crystal, a single endothermic peak is observed at 166°C, which is different from the melting point of either 2,5-DSP (223°C) or l OEt (156°C). Furthermore, the X-ray powder diffraction pattern of the crystal is quite different from those of the homocrystals 2,5-DSP and l OEt. Upon irradiation the cocrystal 2,5-DSP-l OEt affords a crystalline polymer (77i h = 1.0 dl g in trifluoroacetic acid). The nmr spectrum of the polymer coincides perfectly with that of a 1 2 mixture of poly-2,5-DSP and poly-1 OEt. In the dimer, only 2,5-DSP-dimer and l OEt-dimer are detected by hplc analysis, but the corresponding cross-dimer consisting of 2,5-DSP and l OEt is not detected at all (Hasegawa et al., 1993). These observations by nmr and hplc indicate that the photoproduct obtained from the cocrystal 2,5-DSP-l OEt is not a copolymer but a mixture of poly-2,5-DSP and poly-l OEt in the ratio 1 2. 

All of the organohalogen compounds studied were commercial products obtained from various manufacturers and used as received. Only the DBDPO was purified further by recrystallization for some of the chromatography and thermal analysis experiments. Samples of antimony trioxide and antimony pentoxide were also obtained from commercial sources. The ultrapure antimony trioxide, bismuth trioxide, bismuth metal, antimony metal, dibenzofuran and diphenyl ether were all obtained from Aldrich Chemicals. The poly(propylene) (PP) resin was 0.7 mfi, food grade from Novamont and the poly(ethylene) was unstabilized, high molecular weight, HDPE from American Hoechst. 

Materials. Methylene 4,4 -diphenyldiisocyanate (MDI, Mobay) was recrystallized from cyclohexane. Toluenediisocyanate (TDI— represents mixture of 2,4- and 2,6-isomers in 80/20 ratio), p-toluidine (Aldrich) and aniline (Aldrich) were purified by vacuum distillation before use. Diphenylmethane, tert-butyl peroxide (TBP), 4-bromoaniline, butyl lithium in hexane, and ethyl chloroformate, were obtained from Aldrich and used as received. Spectrograde tetrahydrofuran (THF) and benzene from Burdick and Jackson were used as received. Poly(tetramethylene ether glycol) with MW 1000 was obtained from polysciences and dehydrated under a rough vacuum at 50 °C for 24 h. 

Richard, D. P., Weitz, E., Ouderkirk, A. J. and Dunn, D. S., Infared depth profiling studies of recrystallization in laser-amorphized poly(ethylene terephthalate), J. Phys. Chem., 97, 12061-12066 (1993). 

Anionic surfactant Sodium dodecyl sulfate (SDS, C] 2 25 3 supplied by Nihon Surfactant Industries Co., Ltd Tokyo, Japan. It was extracted with ether and recrystallized from ethanol. The purity was ascertained by surface tension measurement. Nonionic surfactant Alkyl poly(oxyethylene) ether (CjjPOEjj, CmH2nhPlO(CH2CH20)2oH, m=12, 14, 16, and 18 Ci6H330(CH2CH20) H, n=10, 20, 30, and 40) were supplied by Nihon Surfactant Industries Co., Ltd. These have a narrow molecular weight distribution. 

Finally, we have attempted to evaluate the possible impact of an intermediate liquid crystalline phase and the possibility of transfer of helical hand information from the melt to the crystal throughout this process. Assuming that the melt is structured, the melt of chiral but racemic polyolefins would be made of stretches of helical stems that are equally partitioned between left- and right-handed helices. Formation of antichiral structures (such as in a iPP) could be interpreted as indicating a possible transfer of information (but the problem of the sequence of helical hands would still remain). This analysis is, however, ruined by the observation that many of these polymers also form chiral structures (frustrated p phase of iPP, Form III of iPBul). For the achiral poly(5-methyl-pentene-l), the chiral, frustrated phase is actually the more stable one, and can be obtained by melting and recrystallization of a less stable antichiral phase. 

Di(p-tolyl)-1,10-phenanthroline 14 is synthesized in 70% yield from 1,10-phenanthroline 3 (1 equiv) and 4-lithiotoluene 13 (5 equiv), after hydrolysis, oxidation with Mn02 and recrystallization (Scheme 9.11). This reaction, detailed in Protocol 9, follows a literature procedure to make various poly-imines substituted by alkyl or aryl groups a to the nitrogen atoms.20... 

From studies on the polymerization behavior of four-center photopolymerizations in the crystalline state, several remarkable features have been found which suggest significant participation of the crystal lattice in polymerization. For example, the plate-like crystals of DSP (a) obtained by recrystallization from solution photopolymerize in the crystalline state whereas DSP crystals (y) obtained through sublimation are needle-like and do not undergo any photochemical change20. Moreover, plate-like crystals of DSP and P2 VB, and crystals of poly-DSP and poly-P2 VB respectively are very similar to each other in their major X-ray diffraction peaks (Fig. 9)8,40). X-Ray analyses of the crystal structures of several diolefinic compounds, including photostable DSP (y) crystals, have been performed mostly by Nakanishi and Sasada26,4151). 

The continuous change of the thermodiagram in polymerization has mainly been studied for DSP by means of differentially scanning calorimetry (DSC)10). DSC curves obtained in the course of photopolymerization of DSP crystals at the irradiation times of 20, 40, 50, and 70 min with a xenon lamp are shown in Fig, 15 together with those of DSP, as-polymerized, recrystallized, and amorphous poly-DSP s. 

Fig. 15. DSC curves of recrystallized, amorphous, and as-polymerized poly-DSP s and the curves obtained in the course of the photopolymerization of DSP crystals. Light source 500w xenon lamp, (source Ref. 10)...

Although no prominent differences have been found between the DSC curves of recrystallized and amorphous polymers, a slight endotherm, which may correspond to the crystal melting point or thermal depolymerization of the recrystallized poly-DSP, is seen at 310 °C in the former curve (Fig. 15)10). 

Inhomogeneous gold polycrystallites with compact structure and a broad range of orientations were formed after 45 min of ultrasonic treatment in a home-developed sonoreactor at the constant temperature. Sonication for additional 40 min recrystallized highly monodisperse platinum nanoparticles with smaller size. The fastest catalysis was enabled by platinum nanoparticles after sonication in the poly vinyl pyrrolidone solution for one hour, while the lowest activity was found for particles after the ultrasonic treatment for 20 min in the ethylene glycol solution. Amorphous and polycrystalline platinum nanoparticles before and after sonication in water have similar catalytic efficiencies. 

SCF technology has spread quickly from molecules such as naphthalene to more complex substances such as polymers, biomolecules, and surfactants. Supercritical fluids can be used to reduce the lower critical solution temperature of polymer solutions in order to remove polymers from liquid solvents(6.26 The technology has been extended to induce crystallization of other substances besides polymers from liquids, and has been named gas recrystallization(4). In other important applications, SCF carbon dioxide has been used to accomplish challenging fractionations of poly(ethylene glycols) selectively based on molecular weight as discussed in this symposium, and of other polymers(. ... 

Synthesis of Model Compounds. We have synthesized semi-rigid rod LC polyesters based on poly(methylphenylene bromoterephthalate-co-hexamethylene bromoterephthalate) (Fig. 1) by random copolymerization. The details of the synthesis of these polymers have been reported previously (fi), and are shown schematically in Fig. 1. All chemicals were purchased from Aldrich methyl hydroquinone, and 1,6-hexanediol were used as received. Bromoterephthalic arid (96%) was recrystallized with an 80/20 vol-% distilled water/ethanol solution. Pyridine (used a proton acceptor) was distilled and stored with desiccant. Solvents were used as received, and all glassware was oven dried. 

Bothun GD, White KL, Knutson BL. GAS antisolvent recrystallization of semicrystalline and amorphous poly(lactic acid) using compressed CO2. Polymer 2002 43 4445-4452. 

---