Characterisation of spread monolayers of functionalised polyisobutylenes with various chain architectures

Abstract

Nine polyisobutylene (PIB) samples, consisting of three chain architectures (linear and branched), each of three molecular weights, were each derivatised at one, two or three chain ends with a hydrophilic head group based on diethyl azodicarboxylate. The surface pressure–area isotherms for spread monolayers of these polymers at the air/water interface were determined using a Langmuir trough, and the thicknesses of the films determined by ellipsometry. The isotherms showed that the area per molecule increased, whereas the collapse pressure decreased, with increasing molecular weight. The area per molecule and collapse pressures both increased with functionality, suggesting that the PIBs adsorb with all of the head groups at the interface. This was confirmed by the ellipsometry data which showed that the film thickness decreased with increasing functionality for similar molecular weight PIBs. Compared to other head groups which have been used to functionalise PIB, the azo head group has a much weaker affinity for water, leading to higher collapse areas and lower collapse pressures.