Critical examination of chemically modified hybrid thermosets: Synthesis, characterization and mechanical behavior in the plateau regime of polyaminosiloxane-nitrile-DGEBA

Abstract

Poly(3-aminopropylmethylsiloxane) has been modified with acrylonitrile via aza Michael addition and a broad range of modified oligomers have been prepared with CN:NH 2 ratio ranging between 0.1 and 1. NMR and FTnIR analysis reveals that acrylonitrile modification proceeds without formation of tertiary amines. Modified oligomers have been characterized by DSC and analysis of Tg reveals that the adducts are self-associated probably due to weak hydrogen bonding and dipole interactions. The modified oligomers with a modification degree higher than 0.4 were miscible with DGEBA. The low and high temperature relaxations of the cured thermosets have been measured by DMTA. In addition to the commonly observed b 2 relaxation, a new b 1 process linked by an isosbestic point to b 2 has been found. b 1 is attributed to an extended segment comprising the pendant propionitrile group as well as the ami-nopropyl segment that connects tertiary amines to the polysiloxane backbone. Elastic modulus as well as the a relaxation can be tuned from high Tg and high rubbery modulus to low Tg and high damping thermosets changing the nitrile content. The experimental network structure obtained from elastic measurements and the Tg were related through well established structure-property relations.

Stretch-Induced Crystallization and Phase Transitions of Poly(dimethylsiloxane) at Low Temperatures: An in Situ Synchrotron Radiation Wide-Angle X-ray Scattering Study

“…Poly­(dimethylsiloxane) (PDMS) is an important rubber with a wide range of applications, which have unique properties such as heat resistance, electrical insulation, and chemical stability. − Because of weak intermolecular force and free intrachain rotation, PDMS has the lowest glass transition temperature ( T g ) of about −110 °C among current industrial rubbers, which thus exhibits excellent performance at low temperature. Over the past 60 years, due to these outstanding properties at low temperature and the rich variety of structures, PDMS has been widely used as high-performance products in the cold environments, such as sealed rings, press pads, and vibration mounts served in aerospace and thermal shielding material. − Actually, PDMS is a semicrystalline polymer, and its crystallization may be induced by either lowering temperature or imposing strain, which consequently affects the elasticity of PDMS at low temperature.…”