To elucidate temperature change of intermolecular interactions and chain dimensions for poly(diallcylsilane)s with or without thermochromism, synchrotron-radiation small-angle X-ray scattering and UV-absorption measurements were carried out for relatively low-molar mass poly(n-hexylmethyl) silane (PSi-1), poly(n-decylmethyl)silane (PSi-2), and poly(n-hexylpropyl)silane (PSi-3) samples in isooctane over a wide temperature range down to -94 degrees C. While the dimensional properties for the three polysilanes were almost irrespective of temperature, the second virial coefficient for PSi-2 and PSi-3 significantly decreased and became negative below the thermochromic temperature at -60 degrees C and -50 degrees C, respectively. Analyses in terms of the quasi-two-parameter theory for the wormlike chain showed that conformational change detected by UV-absorption behavior does not cause appreciably the unperturbed chain dimensions of the polysilane samples. Furthermore, aggregates were detected by ultra-small-angle X-ray scattering measurements for high molar mass PSi-3 samples at low temperatures. These results indicate that intermolecular interactions between poly(dialkylsilane) molecules become attractive around the thermochromic temperature. (C) 2015 Elsevier Ltd. All rights reserved.