Branched and star copolymers based on poly(glycolic acid) and poly(lactic acid)

Abstract

The main objective of this thesis is the design and synthesis of poly(glycolide)-based polymers with various topologies. Dendritic and star-shaped topologies are of central interest to (i) overcome the fundamental drawback of insolubility and (ii) to provide access to an increased number of functional end groups at the aliphatic poly(ester) backbone. Different synthetic pathways toward branched poly(glycolide) copolymers will be explored with respect to the introduction of branching and also keeping in mind the ease of synthesis for possible industrial scale-up. Branching can be realized employing two different strategies: On the one hand, AB2 comonomers (e.g., bishydroxy acids) can be used, which serve as initiators in ring-opening polymerization (ROP) of glycolide and participate in subsequent polycondensation. On the other hand, the inimer strategy can be pursued to introduce branching sites via copolymerization of glycolide with a hydroxy-functional lactone. Besides material properties, the exploration of mild polymer modification reaction conditions considering the sensitive poly(ester) backbone is of great interest. The addressability of the functional end groups is proved using the dendritic copolymers as macroinitiators for the synthesis of multi-arm star polymers. Another important aspect of this thesis is the combination of PGA oligomers with hydrophilic and biocompatible building blocks to comb-like and multi-arm star copolymers, targeting amphiphilic poly(ester)-based materials with valuable features like self-aggregation in aqueous solution and partial degradability, which could be relevant in drug delivery systems. In general, different strategies are combined to provide easy access toward soluble PGA copolymers. The main task of the last part of this thesis is the synthesis of tailor-made poly(lactide) copolymers with flexible building blocks combining different polymerization methods, such as cationic/anionic ROP of cyclosiloxane or anionic ROP of propylene sulfide with lactide ROP. The copolymers benefit from poly(lactide)s’ unique property of stereocomplexation and its degradability. The investigation of the material properties, supramolecular structure formation and adsorption behavior is of central interest to establish new fields of application.