Melt rheology and structure of silicone resins

Rheological investigation and X-ray analysis of silicone resins have been p erformed to get a fundamental understanding of the relationship between mel t rheology and structure. Rheological properties of the melts of silicone r esins were characterized by dynamic shear measurements. Samples were a seri es of silicone resins having different side groups, such as methyl, phenyl, methylphenyl, and propylphenyl. A time-temperature superposition based on the WLF rule was successfully applicable. The free volume fraction at the g lass transition temperature and the free volume expansion coefficient were estimated from the C-1 and C-2 values of the WLF-equation. The loss modulus G " was found to be proportional to the angular frequency in a double-loga rithmic plot over a wide frequency range. However, the storage modulus G ' exhibited a bending in a intermediate frequency region for all silicone res ins. The shape of the G ' curve is unexpected from the results of gel perme ation chromatography (GPC) and differential scanning calorimeter (DSC), whi ch demonstrate that the silicone resins are amorphous polymers of relativel y low molecular weight. To get more insight into the rheological properties of the silicone resins which indicate a heterogeneous structure, X-ray ana lysis was carried out. The X-ray measurement displayed two peaks, one broad peak around 4.5 Angstrom of d-spacing which corresponds to a random amorph ous structure, and the other higher intensity peak from 8.5 Angstrom to 12 Angstrom. This peak strongly depends on the size of organic side groups. Fr om the rheological characterization and the X-ray analysis, it can be concl uded that the silicone resins consist of two components; one of them shows a random amorphous and the other a regular structure even in the molten sta ge.