Steuerung funktioneller Materialeigenschaften eines Polybenzoxazin-Netzwerks über die Integration von Poly(caprolacton)-Oligomeren

The present dissertation deals with the specific control of the functional properties of a bisphenol A based polybenzoxazine (PBA-a). Therefore, the thermoset was combined with the thermoplastic oligomer poly(caprolactone) (PCL). The influence of covalently integrated versus unbound PCL on polybenzoxazines properties was the main focus of this cumulative work and for that reason systematically analyzed by varying the PCL content in the polymer mixtures. The polyester end groups were functionally modified with a tosyl leaving group. In contrast to the hydroxy-terminated basic structure, the modified PCL could be covalently integrated into benzoxazines network. The copolymers homogeneous morphology observed by scanning electron micrographs of PCL/PBA-a revealed that the covalent incorporation of the polyester chains could prevent phase separation of the components as occurred for the unmodified PCL/PBA-a blend-like structures. A slightly decreased network density, due to the incorporated PCL chains, reduced the brittleness of samples with low contents of modified PCL (wPCL 30 %). Thus, toughness values of up to 1.66 MPa were achieved compared to 0.48 MPa for neat PBA-a. By increasing the content of the tosylated PCL in the samples (wPCL = 30 - 50 %) network density was lowered accordingly, resulting highly flexibilized polymers with an almost 10 times increased elongation at break compared to PBA-a. Due to the macroscopic phase separation, a further increase of the amount of unmodified PCL led to samples with even higher brittleness. Polymers with high levels of tosyl-modified PCL (wPCL = 60 - 80 %) exhibited thermoresponsive shape memory properties, which could be attributed to the presence of both covalently incorporated and free PCL in these samples with mixed bonding mode. The combination of the widened network and increased crystallinity are key factors to the displayed shape memory effect. In this work, benzoxazine networks with variable and functional properties have been successfully prepared due to the covalent integration of PCL oligomers. The deeper understanding of the structure-property relationship will facilitate a broader application of polybenzoxazine based materials.