Morphology and thermal properties of inorganic–organic hybrids involving epoxy resin and polyhedral oligomeric silsesquioxanes

Epoxy was modified by an incompletely condensed polyhedral oligomeric silsesquioxane (POSS), and the phenyltrisilanol POSS [Ph7Si7O9(OH)3, POSS-triol] was incorporated into the epoxy networks with the content of POSS up to 30 wt %. The organic−inorganic hybrid composites were prepared via in situ polymerization of epoxy monomers in the presence of POSS-triol, which started from the homogeneous solutions of POSS-triol and epoxy monomers. The nanocomposites of epoxy with POSS-triol can be prepared with the metal complex, aluminum triacetylacetonate ([Al]) being used as the catalyst for the reaction between POSS-triol and diglycidyl ether of bisphenol A (DGEBA). Otherwise, the phase separation induced by polymerization occurred, and the fine phase-separated structures were obtained, in which the spherical POSS-triol particles (0.3−0.5 μm in diameter) were dispersed in the continuous epoxy matrices. The hybrid composites with the different morphological structures displayed quite different thermomechanical pr...

Morphology and Thermomechanical Properties of Organic-Inorganic Hybrid Composites Involving Epoxy Resin and an Incompletely Condensed Polyhedral Oligomeric Silsesquioxane

Block copolymers with and without reactive functionalities can improve fracture resistance in brittle epoxies even when added in relatively small amounts (<5 wt %). At certain compositions, amphiphilic block copolymers spontaneously self-assemble into vesicles, spherical micelles, or wormlike micelles in thermoset resins, and these morphologies are retained with the full curing of the resins. The addition of such block copolymers leaves the glass-transition temperature of these blends relatively unchanged, whereas the fracture resistance increases up to a factor of 3.5 for the vesicle-modified blends. For epoxies modified with block copolymers self-assembled into a spherical geometry (vesicles or spherical micelles), the fracture resistance scales with the ratio of the interparticle distance to the average vesicle (or spherical micelle) diameter (D i /D p ) and increases as this quantity is reduced. Greater adhesion between the vesicle and epoxy resin improves the fracture resistance only at higher values of D i /D p , at which the materials are more brittle. Debonding and subsequent matrix plastic deformation are identified as the toughening mechanisms in these blends.

Mechanical properties of block copolymer vesicle and micelle modified epoxies

Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, worm-like micelles, and spherical micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched worm-like micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the worm-like micelle systems.

Jian Li

Papers

Miscibility, morphology and fracture toughness of epoxy resin/poly(styrene-co-acrylonitrile) blends