Effect of crystallization conditions on single crystals of ladderlike polyphenylsilsesquioxane (PPSQ)

For the first time, formation of single crystals of ladderlike polyphenylsi lsesquioxane (PPSQ) is found from three kinds of solution (benzene, toluene or p-xylene) at different temperatures (room temperature, 55, 65, 75, 80, 85 or 100 degrees C) for some time (from 10 min to 257 h). Crystallization conditions, such as temperature, time and solvent, have a great effect on n umber, size and shapes of PPSQ single crystals. The black crystals with sha pes of square or rectangle have been prepared from benzene solution at 55 d egrees C for not less than 51 h. The single crystals with the shape of a pa rallelogram, whose acute angles are 70 and 60 degrees, have also been obtai ned from benzene solution, however, at 65 or 75 degrees C, while those para llelogram-like single crystals with acute angles of 39 and 26 degrees have been obtained from toluene or p-xylene solution at 75 or 80 degrees C. When PPSQ was crystallized at room temperature (about 20 degrees C) or as high as 85 degrees C (greater than or equal to 85 degrees C), only small irregul ar crystals are observed. The largest parallelogram-like single crystal wit h the size of 200 x 75 mu m(2) was formed from toluene solution at 75 degre es C for 199 h. The size or number of PPSQ single crystals increases with a n increase in the crystallization time. (C) 2000 Elsevier Science Ltd. All rights reserved.