Christoph Schüll

One-step synthesis of multi-alkyne functional hyperbranched polyglycerols by copolymerization of glycidyl propargyl ether and glycidol

By copolymerization of glycidol with the alkyne-containing oxirane monomer glycidyl propargyl ether (GPE), hyperbranched polyglycerol (hbPG) with a defined number of alkyne functionalities (up to 38%) can be obtained in a one-step procedure. The number of alkynes can be adjusted by the glycidol/GPE ratio to provide multi-alkyne functional hbPGs, maintaining the highly branched polyether structure. Interestingly, the acidic proton of the alkyne moiety does not interfere with the proton exchange mechanism during the polymerization of glycidol. By specific modification of the synthesis procedure, crosslinking reactions can be suppressed. The polymers exhibit molecular weights ranging from 1800 to 5500 g mol−1 (determined by 1H NMR spectroscopy and SEC) with moderate polydispersities (Mw/Mn < 2.0, mostly <1.7). Using inverse gated 13C NMR spectroscopy and two-dimensional NMR techniques, the different repeat units of the copolymers can be assigned. The degree of branching value (DB) ranges from 0.58 to 0.50 for increasing GPE content, which is caused by an increased number of linear repeat units with increasing GPE content. The alkyne functionalities are readily available for derivatization reactions by copper-catalyzed azide–alkyne “click”-type cycloaddition reactions. The convenient synthesis and the broad applicability of the alkyne functionalities render these copolymers interesting building blocks for the preparation of complex polymer architectures by “click”-chemistry. This is exemplified by the attachment of hydrophobic azide end-functional polystyrene to yield amphiphilic branched copolymers containing exactly one hbPG block.

Directing the self-assembly of semiconducting copolymers: the consequences of grafting linear or hyperbranched polyether side chains.

The synthesis and self-assembly of novel semiconducting rod-coil type graft block copolymers based on poly(para-phenylene vinylene) (PPV) copolymers is presented, focusing on the ordering effect of linear versus hyperbranched side chains. Using an additional reactive ester block, highly polar, linear poly(ethylene glycol), and hyperbranched polyglycerol side chains are attached in a grafting-to approach. Remarkably, the resulting novel semiconducting graft copolymers with polyether side chains show different solubility and side-chain directed self-assembly behavior in various solvents, e.g., cylindrical or spherical superstructures in the size range of 10 to 120 nm, as shown by TEM. By adjusting the molecular weight and the topology of the polyether segments, self-assembly into defined superstructures can be achieved, which is important for the efficient charge transport in potential electronic applications.

Nonlinear Macromolecules by Ring-Opening Polymerization

Ring-opening polymerization (ROP) is a well-established method for the controlled synthesis of linear polymers, which can be found in various everyday applications. However, during the past decades, there has been an increasing interest in the generation of nonlinear highly branched polymers, profiting from the fascination created by the structurally perfect dendrimers. The applicability of various heterocyclic monomers renders the ring-opening multibranching polymerization (ROMBP), a versatile tool for the generation of multifunctional hyperbranched polymers. First, the historical key steps leading to the development of ROMBP are described, which is the basis for the controlled synthesis of nonlinear macromolecules. Subsequently, specific concepts in ROMBP, namely cationic, anionic, and catalytic polymerizations, are detailed. In particular, anionic multibranching polymerizations are powerful tools for the controlled synthesis of hyperbranched polyether polyols, which are interesting candidates for applications ranging from the biomedical field to catalysis. In the last section, the recent trends in the generation of complex macromolecular architectures containing nonlinear polymers synthesized by ROMBP as building blocks, for example, linear-hyperbranched hybrid structures or conjugates with biologically relevant molecules, are discussed.