Exploring the anionic sulfinyl precursor route towards tailor-made PPV block copolymer materials

Abstract

Tailor-made poly(p-phenylene vinylene)s (PPVs) are presented in this thesis with their ability to be polymerized in an anionic fashion starting from sulfinyl premonomers. For this sulfinyl precursor route, it is shown that with the use of lithium hexamethyldisilazide (LHMDS) as the base and THF as the solvent, the polymerization mechanism can be shifted towards a pure anionic pathway leading towards well-defined polymers. Further it is shown that this anionic mechanism can be applied to plain-PPV as well as different substituted premonomers (symmetrical and (ester-functionalized) unsymmetrical alkyloxyand cyano side groups incorporated on the aromatic core). The most studied polymer in this thesis is the symmetrically substituted poly[2,5-bis(2- ethylhexyloxy)p-phenylene vinylene] (BEH-PPV). With the use of anionic initiators, with a structure similar to the premonomer structure, efficient control is reached over molecular weight (between 15500 and 3000 g·mol-1 for conjugated material) and PDI (1.5 – 1.1). The high efficiency of incorporation of these units with different functionalities, is proven using electrospray ionization – mass spectrometry (ESI–MS). Because of the linear correlation that is found between molecular weight versus amount of initiator used, this high initiator efficiency is assumed to translate to all polymers synthesized using this method, underpinning the living nature of the polymerization. The ω-chain end cannot be controlled as confirmed via either ESI–MS or using a 13C-labeled end-capper. In further experiments the addition mode of the initiator to the reaction mixture and reaction temperature and time are explored. These experiments reveal that the polymerization reaction is very fast, even at reaction time “zero” and reaction temperature -78 °C high molecular weight (5900 g·mol-1) is reached for a polymerization reaction with addition of 0.1 eq of initiator, and thus no kinetics are studied for this system so far. In a last attempt to enhance the control over the anionic pathway, a specialized anionic polymerization setup – in collaboration with the University of Groningen – is used to perform the polymerization reactions. As is shown in this work, the obtained results are in good agreement with the results gained using the regular Schlenk lines (vacuum/N2). ...