Synthesis and characterisation of organic-inorganic hybrid block copolymers of polydimethylsiloxane and polystyrene

[摘要] Hybrid A-B type block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS)were synthesised. Three different synthetic routes, which allowed control over polymerstructure, were chosen to synthesise these block copolymers. The first technique, coupling offunctional prepolymers, involved using anionic polymerisation to produce PDMS and PSfunctional prepolymers of controlled structure. These prepolymers were functionalised witheither silane or allyl functionality and then coupled using a hydrosilylation reaction withKarstetds platinum catalyst. This technique was the least efficient in block synthesis due tothe incompatibility of the disparate prepolymers. The second technique under study,sequential anionic polymerisation, gave excellent block copolymer formation with goodcontrol over the chain architecture. The final technique employed atom transfer radicalpolymerisation (ATRP) of styrene using a bromoisobutyrate functionalised PDMSmacroinitiator. Silane functional PDMS molecules underwent a hydrosilylation reaction withallyl-2-bromo-2-methyl-propionate to produce the bromoisobutyrate functionalised polymer inexcellent yields. Subsequent ATRP with styrene allowed the successful synthesis of blockcopolymers of controlled structure. Chromatographic systems that allowed liquidchromatography at the critical conditions (LC-CC) of PS and gradient elution chromatography(GEC) of the products were developed. GEC was used successfully in the monitoring of thepresence and removal of PDMS homopolymer present in the block copolymer products. LCCCat the critical point of PS allowed successful chromatographic separation of PShomopolymer from the block material, as well as, the molecular weight distribution of theblock material according to the segmental length of the PDMS component. LC-CC coupled toFT-IR using a LC-transform device allowed successful characterisation of the blockcopolymer chemical composition. Corona treatment was used to modify the surface structureof the block copolymer films. Optical microscopy and slow positron beam studies highlightedthe formation of a thin silica like layer on the surface of the films after corona. The positronstudies enabled determination of the silica like layer's thickness. Contact angle studiesprovided the first evidence of hydrophobic loss and recovery for these PDMS containinghybrid polymer materials after corona treatment. A novel offline coupling technique wasdeveloped between LC-CC separation and transmission electron microscopy (TEM) analysis.This allowed easy sample preparation without the difficult bulk extraction procedures neededto remove homo-PS contaminants from the block copolymer. This technique also providedmorphological information as a function of PDMS segmental length.

[发布机构] Stellenbosch University