Solomon M. Kimani

Kinetic Control of Monomer Sequence Distribution in Living Anionic Copolymerisation

Sequence control in synthetic polymers is a subject that is sparsely reported with little research in the field of sequence control in chain growth polymerisation. We report herein preliminary investigations into anionic copolymerisation of diphenylethylene (DPE) and its derivatives with styrene. DPE is a monomer that will only copolymerise and can form alternating copolymers. However, by introducing electron donating or withdrawing substituents onto the phenyl rings of DPE it is possible to prepare new range of (alternating) copolymers and with careful choice of monomer combination and conditions, the kinetically controlled (simultaneous) copolymerisation of three or more monomers results in copolymers with a greater degree of monomer sequence control.

Surface modification of polyethylene with multi-end-functional polyethylene additives.

We have prepared and characterized a series of multifluorocarbon end-functional polyethylene additives, which when blended with polyethylene matrices increase surface hydrophobicity and lipophobicity. Water contact angles of >112° were observed on spin-cast blended film surfaces containing less than 1% fluorocarbon in the bulk, compared to ~98° in the absence of any additive. Crystallinity in these films gives rise to surface roughness that is an order of magnitude greater than is typical for amorphous spin-cast films but is too little to give rise to superhydrophobicity. X-ray photoelectron spectroscopy (XPS) confirms the enrichment of the multifluorocarbon additives at the air surface by up to 80 times the bulk concentration. Ion beam analysis was used to quantify the surface excess of the additives as a function of composition, functionality, and molecular weight of either blend component. In some cases, an excess of the additives was also found at the substrate interface, indicating phase separation into self-stratified layers. The combination of neutron reflectometry and ion beam analysis allowed the surface excess to be quantified above and below the melting point of the blended films. In these films, where the melting temperatures of the additive and matrix components are relatively similar (within 15 °C), the surface excess is almost independent of whether the blended film is semicrystalline or molten, suggesting that the additive undergoes cocrystallization with the matrix when the blended films are allowed to cool below the melting point.

Synthesis and surface activity of high and low surface energy multi-end functional polybutadiene additives

We report here the synthesis of well-defined, polybutadiene additives; chain-end functionalised with either multiple fluorocarbon or hydroxyl groups. Additives containing low surface energy fluorocarbon groups were made by end-capping polybutadienyllithium prepared via living anionic polymerisation while a combination of living anionic polymerisation and “click chemistry” was used to make high surface energy, hydroxyl functionalised additives. These synthetic methodologies resulted in a high degree of chain-end functionalisation as determined by 1H-NMR. The functionalised polybutadiene samples were then blended in low concentration with well-defined (unfunctionalised) perdeuterated polybutadiene to establish their effectiveness as surface modifying polymer additives. Elastic recoil detection analysis (ERDA) revealed that the functional polybutadiene additives were very surface active in spin-cast blended films on silicon substrates. The hydroxyl functionalised polymer segregated strongly to the polymer–silicon oxide interface, whereas the fluorocarbon functionalised additives were found to be in excess at the air interface of the polymer film. The wettability of pure additives on the surface of a silicon wafer and Teflon™ were also determined by static contact angle measurement. We anticipate that these additives could be utilised to disperse and stabilise nanoparticles in nanocomposites, and enhance the adhesion of polybutadiene onto low and high energy surfaces. Investigations into the application of the described additives are ongoing and will be reported at a future date.