# Investigation of structure-property relationships of nylon 6-co-7 and linear alkyl model amide compounds and molecular modeling Quantitative Structure-Property Relationship (QSPR) for glass transition temperature predictions

#### Abstract

The research presented in this dissertation comes from two very different areas. The first area addresses the thermal and crystallographic properties of amide copolymers and n-alkyl amide model compounds. The amide copolymer research was set forth with the goal of exploiting the piezoelectric properties of nylon 7. Interest in these materials was focused on the disruptive nature of the interactions between the nylon 6, and the polar $\alpha$-nylon 7 crystallites (which are required for the piezoelectric properties). Through synthesis of various co-polymer compositions (ring-opening polymerizations) and use of various solid-state characterization methods (X-ray, FT-IR, NMR, DSC), the first reported room temperature stable pseudohexagonal phase for polyamides was observed. The effects on the piezoelectric properties are being investigated by the funding agency. A series of six linear alkyl amide molecules with 21 carbon atoms, 1 nitrogen atom, and 1 oxygen atom where the position of the amide group is varied along the chain were synthesized to elucidate the mechanism of the solid-solid phase transition observed in nylons. A premelt transition similar to nylons was observed for each analog. Through the combination of variable-temperature solid-state techniques (X-ray, FT-IR, NMR) that provide information at different molecular levels and about various molecular segments, it is demonstrated that the amide groups do not rotate (slight libration motions) and that the methylene segments undergo a large increase in amplitude of librational motions. This provides a route to molecular rearrangements resulting in the observation a pseudohexagonal-like crystal structure above the premelt transition. The second area of this dissertation addresses computer-aided molecular modeling. A molecular modeling quantitative structure-property relationship was derived to predict the thermal properties of polymers; specifically the glass transition temperatures (T$\sb{\rm g}$) for novel acrylate and methacrylate polymers. An original QSPR model called the EVM model (Energy, Volume, Mass) is described to calculate the T$\sb{\rm g}$ for aliphatic acrylate and methacrylate homopolymers with a standard deviation of 15 Kelvin using classical molecular mechanics and dynamics. The EVM QSPR relationship is based on an energy density function that describes molecular conformations and mobility.