Date

2015

Document Type

Thesis

Degree

Master of Science

Department

Materials Science and Engineering

First Adviser

Pearson, Raymond A.

Abstract

Block copolymers have been receiving considerable attention in tougheningepoxy due to their ability to form a wide variety of nanostructures. This study focuseson using both triblock and diblock copolymers to improve the fracture toughness ofan aromatic-amine cured epoxy system. The curing system consisted of 1,3-phenylenediamine (mPDA) as curing agent and aniline as a chain extender. Threetriblock copolymers and three diblock copolymers were incorporated in the samelightly crosslinked model epoxy system, which was chosen to mimic an underfillmaterial in flip-chip packaging for the microelectronics industry.In this research, rubber particles were formed in situ using self-assembling blockcopolymers. Mechanical, thermal and microscopic studies were conducted with themain goal to study the relationship between the block parameters and the finalmorphologies and their effects on static and dynamic mechanical properties of thetoughened resin, especially fracture toughness.In these block-copolymer-modified epoxies, spherical micelles and wormlikemicelles were obtained by varying block lengths, molecular weight, polarities andcompositions. It was found that miscibility of the epoxy-miscible block played acrucial role in the formation of different types of morphologies. At a low loadinglevel, diblock copolymers were able to toughen the model epoxy as effectively astriblock copolymers. The fracture toughness was improved to almost three times withrespect to that of the neat resin with addition of 10 phr AM*-27. At the same time,other mechanical properties, such as yield strength and modulus, were well retained.Incorporation of block copolymers did not have a significant effect on glass transitiontemperature but caused an increase in coefficient of thermal expansion (CTE) of themodified epoxy. Particle cavitation and matrix void growth were proved to be thetoughening mechanisms for SBM-Modified epoxies. However, these typicaltoughening mechanisms for rubber toughening were not identified in the AM*27-modified epoxies by examining the fracture surface and the subsurface damage.

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