Polyester-inorganic nanocomposite materials via sol-gel reactions: Synthesis and characterization of fundamental properties

A scheme was developed for producing poly(ethylene terephthalate (PET) ionomer)/silicate hybrid materials via polymer-in situ sol-gel reactions for tetraethylorthosilicate (TEOS) using different solvents. Scanning electron microscopy/EDAX studies revealed that silicate structures can be grown deep within PET ionomer films that were melt pressed from silicate-incorporated resin pellets. 29Si solid-state NMR spectroscopy revealed considerable, successful Si-O-Si bond formation, but also a significant fraction of uncondensed SiOH groups. 23Na solid-state NMR spectra suggested the presence of ionic aggregates within the unfilled PET ionomer and that these aggregates do not suffer major structural re-arrangements by silicate incorporation. For an ionomer treated with TEOS using MeCl₂ solvent, Na + ions are less self-associated than in the unfilled control, suggesting silicate intrusion between PET-SO₃− Na + ion pair associations. The ionomer treated with TEOS + tetrachloroethane had more poorly formed ionic aggregates, which illustrates the influence of solvent type on ionic aggregation. First-scan DSC thermograms for the ionomers demonstrate an increase in crystallinity after the incorporation of silicates, but solvent induced crystallization also appears to be operative. Second-scan DSC thermograms also suggest that the addition of silicate particles is not the only factor implicated in re-crystallization, and that solvent type is important even in second scan behavior. Silicate incorporation does not profoundly affect the second scan T_g vs. solvent type, i.e., chain mobility in the amorphous regions is not severely restricted by silicate incorporation. Re-crystallization and melting in these hybrids appears to be due to an interplay between a solvent induced crystallization that strongly depends on solvent type, and interactions between PET chains and in situ-grown, sol-gel-derived silicate particles.; Isothermal studies confirmed that the crystallization rate and melting behavior of PET 5% Na+ ionomers depend on processing conditions.; PET ionomer/ORMOSIL composites were formed via in situ sol-gel reactions using the ionic regions of PET as preferential reaction sites. TGA analysis revealed successful uptake for all three different solvents and TEOS:MTES composition ratios. TGA derivative curves suggest that for the THF and MeCl₂ carrier solvent systems the MTES-generated network interacts more with the PET ionomer matrix. In the case of TCE, the TEOS-generated network interaction appears to be more operative. First scan DSC traces reveal that the in situ sol-gel processing of ORMOSIL phases induces PET ionomer crystallinity, although systems with higher silicate uptake have reduced induced crystallinity. Second scan DSC traces show that T_g is not effected by the incorporation of silicates into the PET ionomer. Also, for the ORMOSIL phases generated using THF and MeCl₂ as the swelling solvent, only the pure silicate networks (synthesized using only TEOS) allow recrystallization and melting during the quick scan timeframe. It is thought that the presence of semi-organic MTES silicate networks do not allow fast nucleation onto the inorganic nuclei. (Abstract shortened by UMI.)...