Title

Preparation of conductive composites by {\it in situ\/} polymerization of polypyrrole in ionomer-based matrices

Date of Completion

January 1996

Keywords

Engineering, Materials Science|Plastics Technology

Degree

Ph.D.

Abstract

In this research, the polymerization of pyrrole in various sulfonated thermoplastic and diblock matrices such as sulfonated polystyrene (SPS) and poly(ethylene-alt-propylene) (SEP) was studied. The pyrrole polymerization was a diffusion-controlled process in which both the pyrrole monomer and FeCl$\sb3$ oxidant aqueous solutions had to diffuse into a glassy SPS film for the reaction to occur. The amount and extent of penetration of the polypyrrole (PPy) into the film were functions of the immersion time in the pyrrole monomer and the sulfonation level of the ionomer matrix. The dependence of the polymerization yield on the sulfonate concentration may be attributed to the increased hydrophilicity of the ionomer as the extent of sulfonation increases, which provided a more favorable environment for absorption of the two aqueous solutions used in the polymerization reaction. The SPS/PPy composites were observed to be heterogeneous with the black PPy being deposited mostly at the surface of the SPS, and the surface morphology as studied by scanning electron microscopy (SEM) was observed to be composed of a distribution of PPy particles varying from 3-10 $\mu$m in diameter. A sharp increase in conductivity occurred within the first 10 hours of reaction, which indicated that a percolation threshold was achieved at the surface. Chlorine anion (Cl$\sp-$) was found to be the main counterion for the positively charged PPy, although some evidences indicated that the anions from sulfonated polystyrene were involved in a complex with PPy. Experimental techniques such as infrared (FTIR), UV/Vis, and x-ray photoelectron (XPS) spectroscopies were used to identify the interaction between the sulfonate groups from SPS and the N-H groups from PPy. The incorporation of PPy into the ionomer improved its mechanical properties specially above the glass transition temperature as shown by DMTA results. Improvements in Young's modulus and strength at break were also achieved by the incorporation of PPy. In order to better understand the possible interaction between SPS and PPy, model compound studies using pyrrole and p-toluene sulfonic acid were also performed.^ The in situ polymerization of PPy was also performed in an ionomer block copolymer matrix, poly(ethylene-alt-propylene). In this case, the block copolymer microstructure effectively served as a template for the polymerization and organization of pyrrole. Because of differences in hydrophilicity, the polypyrrole is expected to be preferentially deposited into the polystyrene phase of the block copolymer which provides a more favorable environment for the diffusion of the aqueous solutions of pyrrole monomer and FeCl$\sb3$ oxidant. The incorporation of PPy into HSEP did not affect the lamellar morphology of the diblock although it made the interface between the blocks much more diffuse as observed by transmission electron microscopy (TEM). Small angle x-ray scattering (SAXS) indicated a slight increase in the lamellae thickness of the styrene block after the incorporation of polypyrrole. ^