Toward the Development of a Chemo-Enzymatic Process for the Production of Next-Generation Taxol Analogs

Discovered over fifty years ago, the shear piezoelectric effect occurs in biopolymers that possess chirality due to asymmetric backbone carbon atoms.

This dissertation focuses on the mechanisms responsible for shear piezoelectricity, as well as methods to improve the multifunctionality of these materials without degrading their shear piezoelectricity.

Previous research has determined that shear piezoelectricity is a function of polymer crystallinity and orientation.

At the present time, investigations concerning the effects of these parameters are incomplete since previous studies have relied exclusively on using orientation to alter crystallinity.

In this research, polylactic acid (PLA) samples were fabricated by a twofold drawing/annealing process to investigate further the relationship between crystallinity, orientation, and shear piezoelectricity.

The results of this study reveal that the product of crystallinity and orientation determines shear piezoelectricity regardless of either parameter's individual magnitude.

Methods to prepare these typically weak biopolymers for potential applications were also examined.

Single-wall carbon nanotubes (SWCNTs) have previously been incorporated into polymers to introduce multifunctionality, but their effects on shear piezoelectricity are unknown.

In order to achieve thorough dispersion in these materials, the copolypeptide poly (leucine-ran-phenylalanine) (polyLF) was engineered to exhibit favorable interactions with SWCNTs.

The enthalpic and entropic penalties of mixing between these molecules were reduced due to the copolypeptide's aromatic sidechains and their similar size/shape, respectively.

This study is the first to demonstrate the dual enthalpic/entropic approach in mixtures of SWCNTs and a high molecular weight polypeptide.

The enhanced interactions result in a well-dispersed SWCNT/polyLF nanocomposite with improved multifunctionality.

A third polymer, poly (gamma-benzyl-L-glutamate) (PBLG), which exhibits similar dispersion-aiding attributes as polyLF, was chosen to study the effects of SWCNTs on shear piezoelectricity.

In addition to introducing multifunctionality, SWCNTs did not degrade PBLG's shear piezoelectricity (at concentrations below the percolation threshold), a finding previously not observed.

This research shows that SWCNTs do not interfere with the dipole rotations responsible for generating shear piezoelectricity.

The findings of this dissertation provide critical contributions for the potential development of shear piezoelectric materials.

At appropriate SWCNT concentrations, highly drawn biopolymers with dispersion-enhancing structural components will produce a homogenous, multifunctional material with enhanced shear piezoelectricity.