Gradient and block copolymer interfacial behavior: Examination of physical properties and the effects on compatibilization and micelle behavior of copolymer in polymer blends

The addition of copolymer to one or more homopolymers is one approach that can be used to develop novel materials with new or synergistic properties. This dissertation presents a study on the effects of copolymer sequence distribution and attractive interactions on the compatibilization of immiscible homopolymers and the effects of sequence distribution on the critical micelle concentrations (CMCs) of copolymer dispersed within homopolymer. Additionally, the first measurements on the glass transition temperature ( Tg) of polymer dissolved at trace levels within a second homopolymer and of polymer trapped within micelles were completed.;Dispersed-phase blends of polystyrene (PS) and polycaprolactone (PCL) were compatibilized by the addition of styrene-hydroxystyrene copolymer. By introducing a gradient in the copolymer sequence distribution, stable sub-micron diameter PCL domains were formed. Incorporating fewer hydrogen bonding units within the copolymer promotes compatibilization. Additionally, changing the sequence distribution of the copolymer affects its ability to hydrogen bond with PCL. By employing weaker dipole/dipole interactions, it is demonstrated that conventional melt mixing of two homopolymers (PS) and poly(ethylene oxide) (PEO) and a copolymer (styrene/methyl methacrylate (S/MMA) gradient copolymer) used as a compatibilizing agent can produce compatibilized nanostructured blends. Additionally, the effects of sequence distribution on the stabilization of a cocontinuous PS/PEO blend were examined. Opposite of the results found in the dispersed-phase blends, S/MMA block copolymer addition resulted in superior compatibilization effectiveness compared to S/MMA gradient copolymer addition.;The effects of copolymer architecture on the CMC were examined by employing a simple fluorescence technique. The CMCs of various copolymers dispersed within homopolymers were determined, and the following characteristics were tested to determine what greatly impacts the CMC: molecular weight, copolymer composition, sequence distribution, segregation strength, and attractive interactions. This fluorescence technique was then extended to examine Tgs of components within polymer blends. An increase or decrease in the Tg of polymer-A chains dispersed in a polymer-B matrix that depends on the Tg of the matrix was observed, consistent with theoretical predictions. It was also determined that the homopolymer matrix can impact the Tg of polymer chains trapped within the core of micelles.