Synthesis, micellar properties and application of amphiphilic linear block copolymers with different microstructure but same molecular weight

This dissertation is concerned with the synthesis and micellisation behaviour of linear block copolymers based on methacrylates by means of the modern controlled radical polymerisation technique, namely the atom transfer radical polymerisation (ATRP). The objective was the synthesis of linear block copolymers with different microstructure but same molecular weight. The chosen synthesis strategy should be applicable for various monomer pairs with different polarities and should include the use of macroinitiators due to a defined formation of the block copolymers. In selective solvents the amphiphilic structure induced self-aggregation of the block copolymers, ideally with the formation of spherical micelles. Thereby, micellisation behaviour was strongly dependent on the physical properties of the used monomer pair and the molecular weight and microstructure of the block copolymers. Symmetric diblock copolymers P(MAA)-b-P(MMA) and (P(MAA)-b-P(BMA)), and triblock copolymers, P(MAA)-b-P(MAA-co-MMA)-b-P(MMA) and P(MAA)-b-P(MAA-co-BMA)-b-P(BMA), were synthesised via ATRP of MMA and t BuMA as well as of BMA and t-BuMA with an overall molecular weight of max. 7000 g/mol, followed by acid catalysed cleavage of the P(t-BuMA) block. The association behaviour of the fully neutralised block copolymers was studied in water via polyelectrolyte titration, fluorescence spectroscopy, dynamic light scattering and scanning force microscopy. Due to the low molecular weight of the block copolymers an effect of the microstructure on the critical micelle concentration or the size of the micelle were hardly detectable. To intensify these effects, the synthesis was adapted to a final molecular weight of 40.000 g/mol. Symmetrical P(BMA)-b-P(MAA) di- and P(BMA)-b-P(BMA-co-MAA)-b-P(MAA) triblock copolymers were synthesised via ATRP and analysed by fluorescence spectroscopy, dynamic light scattering and scanning force microscopy concerning the critical micelle concentration, hydrodynamic radius and morphology of the micelles. Whereas no effect of the microstructure on the critical micelle concentration could be detected, the hydrodynamic radius decreased from di- to triblock copolymer The decrease of about 33% corresponds to the length of the random middle block within the triblock copolymer so that the reduction in hydrodynamic radius was caused by a complete orientation of the random middle block at the core corona interface. A further aim of this thesis was the extension of microstructures synthesised by ATRP. Therefore, gradient copolymers of t-BuMA / BMA with highly constant compositional gradients along the polymer chain were synthesised by means of semibatch atom transfer radical polymerisation using a pre-calculated monomer addition program. The addition program was based on the reactivity ratio of t BuMA / n-BMA and the effective rate constant function k(fn-BMA) determined in pilot experiments. The evolution of molecular weight and compositional gradient were determined via size exclusion chromatography and 1H-NMR spectroscopy for the gradient copolymers P(t BuMA160-grad-BMA100), P(t-BuMA162-grad-BMA73) and P(t-BuMA159-grad-BMA44), respectively. Besides block copolymers with a strong amphiphilic character, the same synthesis strategy was used to create double hydrophilic block copolymers, too. The chosen monomer pairs HEMA-TMS/t-BuMA and MEO2MA/t-BuMA should result in block copolymers with minimised hydrophobic character and direct solubility in water. The key reaction turned out to be the last reaction step, the deprotection of the t-BuMA segments. In case of the block copolymers out of HEMA-TMS/t-BuMA, it was impossible to deprotect the polymers without that cross-linking reactions ocurred, so that HEMA-TMS was exchanged by MEO2MA. Here, the deprotection reaction could be carried out without any problems so that well defined P(MEO2MA)-b-P(MAA) di- and P(MEO2MA)-b-P(MEO2MA-co-MAA)-b-P(MAA) triblock copolymers with a number average molecular weight of around 7000 g/mol were synthesised. Finally, the knowledge about the influence on the micellisation behaviour was used to generate switchable surfaces with changing wettability. The concept was based on the use of metastable micelles which should undergo inversion or break up of the micellar structure by temperature stimulus. This was achieved via decreasing the degree of neutralisation of the P(MAA) segments The rearrangement of the micelles by temperature stimulus was analysed via scanning force microscopy. It was demonstrated that no break up, but an inversion of the micellar structure occurred