Kevin P. Chaffee

Polyhedral Oligomeric Silsesquioxanes (Poss): Silicon Based Monomers and their Use in the Preparation of Hybrid Polyurethanes

Abstract : A series of Polyhedral Oligomeric Silsesquioxane (POSS) monomers bearing reactive hydroxyl functionalities, suitable for incorporation into step-growth polymers, is described. These monomers are difunctional in nature and are particularly well suited for use as chain extenders in the synthesis of polyurethanes. This work describes the synthesis of these POSS and their incorporation into a series of polyurethanes. Preliminary thermal, mechanical and rheological data for the POSS containing polyurethanes will also be discussed.

Thermally crosslinkable thermotropic copolyesters : synthesis, characterization, and processing

The synthesis, characterization, and processing of thermotropic copolymers composed of hydroxybenzoic acid (HBA), hydroxynaphthoic acid (HNA), and systematically varying amounts of hydroquinone (HQ) and crosslinkable terephthalic acid (XTA) are described. The XTA monomer contains a benzocyclobutene (BCB) group that lies dormant during synthesis and initial steps of processing, but that can be thermally activated to introduce covalent crosslinking between laterally adjacent macromolecules. The XTA-containing HBA/HNA copolymers all remain thermotropically liquid crystalline, and can be processed into oriented fibres by melt spinning. Rheological characterization reveals an increase in the viscosity and transition from liquid-like to solid-like behaviour as the crosslinking proceeds. X-ray diffraction reveals the changes in local organization with increasing XTA content. The microstructures of the XTA-containing copolymers (up to 20% XTA) in the condensed state are similar to those seen in HBA/HNA copolymers.

Molecular and Textural Ordering of Thermotropic Polymers in Shear Flow

The texture and microstructural order present in mesomorphic polymers and their relation to their macroscopic behavior has been investigated using rheological, optical and dynamic scattering (WAXS and SALS) experiments. Shear orientation is observed under constant rate-of-deformation conditions where this orientation is always parallel to the flow direction. However, the high degree of orientation suggested by optical and SALS measurements is not reflected in the degree of molecular order observed in WAXS experiments. After cessation of flow, a rapid relaxation of stress is observed, while only little microstructural relaxation is found; i.e. , the state of orientation is very stable