Pieter Willot

Poly(3-alkylthiophene) with tuneable regioregularity: synthesis and self-assembling properties

This work reports a synthetic strategy to generate poly(3-alkylthiophene)s (P3ATs) with joint-simultaneous control of the molar mass and the regioregularity. A series of chiral P3ATs with different regioregularities is synthesized using a Pd(RuPhos)-catalyzed chain-growth polymerisation. All polymers have molar masses and polydispersities (PDI) that lie within a narrow region. Furthermore, it is shown that the Pd-catalyst forms all kinds of couplings [head-to-tail (HT), tail-to-tail (TT) and head-to-head (HH)] to a similar extent, which allows insertion of predictable amounts of regio-irregularities into the polymer chain. This enables a thorough study of the influence of the regioregularity on the properties of P3AT, which was performed using UV-vis and circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy (AFM) measurements. Unexpectedly, it is found that under “kinetic” conditions the highest crystallinity, π-stacking, supramolecular organisation and chiral expression are not obtained for fully regioregular P3AT with 100% HT couplings, but that a small amount of regio-irregularity increases these properties and the chiral expression. Under “thermodynamic” conditions (after annealing, very slow solvent evaporation or very slow cooling from the melt), this effect is less pronounced or not found. This behaviour can be explained by a higher degree of motional freedom within the non-perfect polymer chains due to the increased steric repulsion from the HH-couplings, which leads to a more easy stacking under “kinetic” conditions.

Heterobifunctional PEG Ligands for Bioconjugation Reactions on Iron Oxide Nanoparticles

Ever since iron oxide nanoparticles have been recognized as promising scaffolds for biomedical applications, their surface functionalization has become even more important. We report the synthesis of a novel polyethylene glycol-based ligand that combines multiple advantageous properties for these applications. The ligand is covalently bound to the surface via a siloxane group, while its polyethylene glycol backbone significantly improves the colloidal stability of the particle in complex environments. End-capping the molecule with a carboxylic acid introduces a variety of coupling chemistry possibilities. In this study an antibody targeting plasminogen activator inhibitor-1 was coupled to the surface and its presence and binding activity was assessed by enzyme-linked immunosorbent assay and surface plasmon resonance experiments. The results indicate that the ligand has high potential towards biomedical applications where colloidal stability and advanced functionality is crucial.

Direct visualization of microphase separation in block copoly(3-alkylthiophene)s

A poly(3-octylthiophene)-block-poly(3-butylthiophene) block copolymer was synthesized in a one-pot block copolymerization reaction, starting from a functional o-tolyl initiator in order to maximize A–B diblock copolymer formation. First, the composition of this block copolymer is extensively studied using gel permeation chromatography (GPC) and 1H NMR measurements. A complete block copolymer formation is obtained with almost equal block length; B–A–B block copolymer contamination is shown to be very limited. In a second part, the self-assembly was analysed through differential scanning calorimetry (DSC), atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) measurements, focusing on the microphase separation. A direct visualization of the different microphases can be obtained with STM.