Properties of Epoxy Network Derived from the Reaction of Diglycidyl Ether of Bisphenol A with Polyhedral Oligomeric Silsesquioxanes Bearing OH-Functionalized Organic Substituents

S. A. PELLICE; D. P. FASCE; R. J. J. WILLIAMS.

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

Wiley Periodiclas, Inc.

Lugar: Nueva York; Año: 2003 vol. 41 p. 1451 - 1461

0887-6266

A polyhedral oligomeric silsesquioxane (POSS), consisting mainly on a mixture of octahedra (T8), nonahedra (T9), and decahedra (T10) with bulky and flexible organic substituents, with 3 secondary hydroxyls per organic group, was used to modify epoxy networks produced by the homopolymerization of diglycidylether of bisphenol A (DGEBA), in the presence of benzyldimethylamine. Several physical, thermal and mechanical properties of the cured materials containing 0, 10, 30 and 50 wt % POSS, were determined. The addition of POSS increased the elastic modulus and the yield stress measured in uniaxial compression tests, mainly due to the increase in the cohesive energy density produced by H-bonding through the hydroxyl groups. A constant yield stress / elastic modulus ratio equal to 0.03, was observed for different POSS concentrations and test temperatures. The glass transition temperature decreased with POSS addition due to the flexibility of organic branches present in the POSS structure and to the decrease in the crosslink density (determined from the rubbery modulus). Although a combination of reduction in glass transition temperature (plasticization) combined with an increase in the glassy modulus (antiplasticization), is a well-known phenomenon, what is original is the fact that it was not the consequence of the suppression (or reduction in intensity) of sub-glass relaxations, but produced by an increase in the cohesive energy density. An interesting property of the network containing 50 wt% POSS was the high temperature sensitivity of the mechanical behavior in the vicinity of the glass transition. Formulations containing 50 wt% POSS exhibited a sharp transition in the mechanical behavior observed in uniaxial compression, produced by a small change in temperature in the vicinity of the glass transition.