Σύνθεση, μοριακός και μορφολογικός χαρακτηρισμός μη γραμμικών τριπολυμερών μεγάλων μοριακών βαρών (μικτόκλωνα - δενδριμερή)

Abstract

The main purpose of this work was the synthesis of dendritic terpolymers consisting of poly(butadiene) with high 1,4 microstructure, poly(isoprene) enriched in 3,4 microstructure and polystyrene (PS) derived from the linking of identical or different molecular weight dendrons of the ABC type (miktoarm star terpolymers). The main aspect was the synthesis of polymers exhibiting high molecular and compositional homogeneity. The preparation of these materials was achieved via anionic polymerization techniques in combination with chlorosilane chemistry under high vacuum conditions. By adopting this approach unique control of all the reactions is handled due to lack of termination reactions. The method used for syntheisizing the final 2nd generation dendritic terpolymers was convergent, meaning that the dendrons were prepared initially followed by their linking with specific linking agents. The molecular characterization of the final dendritic materials was achieved via Size Exclusion Chromatography (SEC), Dilute Solution Viscometry (V), and 1H-Nuclear Magnetic Resonance (NMR) Spectroscopy, leading to the conclusion that they can be considered model polymers since both the dendrons and the final dendritic terpolymers exhibited high molecular and compositional homogeneity. Additionally, thermal analysis with Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) was also accomplished in order to study the behaviour during heating/cooling and to determine specific transitions (glass transition, crystallization and melting point) for the three chemically different blocks. The results were very encouraging since in most case three glass transition temperatures were observed, very close to those of the corresponding homopolymers, leading to a 3-phase separated system due to immiscibility between the blocks. The morphological characterization was conducted via Transmission Electron Microscopy (TEM) and Small Angle X-Ray Scattering for both the dendrons and the final 2nd generation dendritic terpolymers. The molecular characterization of the dendrons and the final dendritic materials concluded to the fact that both complex architecture materials exhibited high molecular and compositional homogeneity. The morphological results indicated that despite the complexity of the system in most cases microphase separation of the polydienes occurred leading to 3-phase systems. When the microstructure or geometric isomerism of the PB segments was increased in 1,2- percentage compared to 1,4- mixing of the polydienes occurred and 2-phase systems were observed. For all the results a comparison with other systems reported in the literature or with theoretical studies concerning such complex materials is included leading to interpretation of the results, conclusions and assumptions while there is, in all cases, a comparison study between the dendrons and the corresponding 2nd generation dendritic terpolymers.