Approaches toward high oxygen barrier poly(ethylene terephthalate) and preparation of di-isocyanate infused clay aerogel composites

Louis Steven Somlai

Abstract

The first part of this dissertation discusses the synthesis and characterization of new poly(ethylene terephthalate) (PET) copolymers produced with 5-adamantylisophthalic acid monomer. Both monomer and copolymer syntheses are given in detail. Differential scanning calorimetry analyses of copolymers showed decreased melt transition temperatures with increased comonomer incorporation (0 to 5 mol-%), while copolymer glass transition temperatures increased slightly. Oxygen permeability was shown to increase with higher 5-adamantylisophthalic acid incorporation in the copolymers relative to virgin PET. The second part of this dissertation discusses PET-montmorillonite clay layered nanocomposites. Most commercially available, organically modified clays (OMCs) do not exhibit sufficient thermal stability for processing in commodity polymers such as poly(ethylene terephthalate). Surfactant degradation often leads to polymer discoloration and may be partially responsible for incomplete dispersion of the OMCs into PET. Our goal was to study the thermal stability of 4-(dimethylamino)pyridinium and 1,2-dimethylimidazolium surfactants, with a variety of long aliphatic hydrocarbon based tails on sodium exchanged montmorillonite, laponite, and fluoromica. Surfactant-sodium ion exchange resulted in increased onset of mass loss (OML) temperatures for surfactants on clays. Solvent extraction of unbound surfactant from OMC and lower percent surfactant-sodium ion exchange resulted in increased OML temperatures. Clay substrate also affects the OML temperature and mass loss profile. Preliminary experiments with these new OMCs and PET, at low incorporation via autoclave polymerization and melt-mixing, showed limited dispersion of silicate layers into the PET matrix and negligible changes to polymer thermal properties. The final part of this dissertation discusses diisocyanate infused montmorillonite aerogel composites. A process for the conversion of clay powder to organically modified clay aerogels (OMAs) is reported. The results show that stable OMAs are formed from stable clay-surfactant hydrogels. Isolated OMAs were then infused with diisocyanate monomers and cured to produce OMA composites. Rigid composites were formed with retained aerogel structure. The specific compression modulus of OMAs was improved with the infiltration and curing of diisocyanate monomer. Such aerogel structures and composites may be useful in polymer silicate layered composites, insulation applications and perhaps as supports for biologically active molecules.