John M. Zielinski

Phase-separation studies of heat-cured ATU-flexibilized epoxies

Abstract Chemical incorporation of a flexible molecule into a heat-cured epoxy offers an important route by which to toughen the epoxy and tailor its ultimate material properties. Acrylate-terminated urethane (ATU) flexibilizers containing polypropylene glycol have been employed in the present work to modify epoxies composed of a diglycidyl ether of bisphenol-A and bis(4-aminocyclohexyl) methane. Differential scanning calorimetry, dynamic mechanical analysis and electron microscopy reveal that the flexibilizer and epoxy undergo phase separation during cure when the flexibilizer loading or molecular weight is sufficiently high. Partial phase miscibility, deduced from both glass transition temperature shifts and stress—relaxation behaviour, is interpreted here in light of thermodynamic and free-volume considerations.

Configurational studies of microphase-separated diblock copolymers in the solid state

Abstract Microphase separation occurs in block copolymers due to thermodynamic incompatibility between the blocks and is responsible for the formation of periodic microstructures, or domains, which are on the same size scale as the root-mean-square end-to-end distance of the domain-forming block ( 〈r 2 k 〉 1 2 ). Experimental evidence has shown that 〈r 2 k 〉 1 2 deviates significantly from its unperturbed analogue ( 〈r 2 k 〉 1 2 0 ), implying that each block in a microphase-separated block copolymer is either expanded or contracted owing to the presence of the other block. In this work, expansion coefficients for each block and for the entire copolymer molecule are predicted as functions of both molar composition and molecular weight in poly(styrene-butadiene) diblock copolymers exhibiting lamellar morphology with modified versions of the Leary-Henderson-Williams thermodynamic theory. A comparison of predictions obtained for each of these model variations, which reflect the extent of block interdependence, is also provided.