Doctoral Dissertations

Date of Award

8-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Mark D. Dadmun

Committee Members

Charles Feigerle, Roberto Benson, Jimmy Mays

Abstract

Polymer clay nanocomposites are a promising class of multicomponent systems where incorporation of small amount of clay results in dramatic improvement of mechanical, thermal and barrier properties. However, accomplishment of these properties necessitates molecular level dispersion of the clay platelets in the polymer matrix. This thesis presents the guidelines for obtaining thermodynamically stable nanocomposites where strong specific interactions such as hydrogen bonding between the polymer and the clay can be utilized to achieve the desired goal of nanoscale dispersion of clay sheets.

In first part of the dissertation, optimization of intermolecular hydrogen bonding between the polymer and clay is carried out by controlling the distribution of hydroxyl groups on the copolymer of styrene and 4-vinyl phenol. Copolymers ranging from 0- 100% vinyl phenol are synthesized by free radical polymerization. Nanocomposites containing 50 % poly(vinyl phenol) and 40 % poly(vinyl phenol) show optimum dispersion due to large extent of intermolecular hydrogen bonding with drastic improvement in glass transition temperature.

Furthermore, the effect of the nature of clay surfactant on the dispersion of clay sheets in the polymer matrix is also studied. Nanomer I.24 TL and Cloisite 25A show similar trends in dispersion for all the copolymer compositions. Increase in vinyl phenol content from 0-50% enhances the dispersion of clay platelets. However, Nanomer I.24 TL and Cloisite 25A show different morphological behavior than Cloisite Na+ towards the polymer containing 100% vinyl phenol. This behavior arises due to the fact that hydrophobic surfactants of Nanomer I.24 TL and Cloisite 25A do not find themselves very compatible with hydrophilic polymer, poly(vinyl phenol) thus giving rise to intercalated morphology in opposition to exfoliation observed for Cloisite Na+ nanocomposite with the same polymer. Cloisite Na+ is highly hydrophilic and therefore very miscible with 100% vinyl phenol, consequently a nanocomposite with improved dispersion is obtained.

Next, clay loading is also optimized in the nanocomposites to obtain the best morphological and thermal improvements. Clay loadings of 1, 3, 5 and 8 wt % are mixed with copolymers ranging from 0-100 % vinyl phenol. 3 and 5 % clay loadings with PVPh40 and PVPh50 nanocomposites exhibit optimum dispersion of clay platelets with drastic improvement in glass transition temperature.

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