Rubber-elasticity of hybrid organic-inorganic composites evaluated using dynamic mechanical spectroscopy and equilibrium swelling

Abstract

Estimations of the average molar mass between crosslinks for sol-gel-derived poly(tetramethylene oxide) (PTMO)–polysilicate hybrid composites have been made using both dynamic tensile modulus and equilibrium swelling techniques. Modulus-based calculations have been performed using storage modulus values obtained from dynamic mechanical spectroscopy at frequencies ranging from 0.1 to 10 Hz. The analysis revealed that gels containing either 4 or 19% polysilicate (by volume) had an average molar mass between crosslinks significantly less than that predicted by a PTMO and SiO2 rule of mixtures. Thus, the analysis indicates that there is extensive restriction of PTMO chain mobility in these gels. Aging of the 19% polysilicate-loaded gels in a basic ethylamine and water solution for 25 h, which has previously been shown to enhance phase separation without loss of optical transparency, results in increasing average chain length. To verify this approach, the values obtained using the dynamic mechanical spectroscopy-based technique were compared with those calculated using the Flory-Rehner equation. Somewhat surprisingly, the analyses by both techniques were in excellent agreement, thereby suggesting that, in the absence of chemical change, elementary rubber elasticity theory is a good tool for investigating the phase interactions in these seemingly nonideal hybrid composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 947–957, 1998