Alpha, Omega end group functionalization of RAFT polymers based on pentafluorophenyl esters and methane thiosulfonates

While polymers with different functional groups along the backbone have intensively been investigated, there is still a challenge in orthogonal functionalization of the end groups. Such well-defined systems are interesting for the preparation of multiblock (co) polymers or polymer networks, for bio-conjugation or as model systems for examining the end group separation of isolated polymer chains. rnHere, Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization was employed as method to investigate improved techniques for an a, w end group functionalization. RAFT produces polymers terminated in an R group and a dithioester-Z group, where R and Z stem from a suitable chain transfer agent (CTA). rnFor alpha end group functionalization, a CTA with an activated pentafluorophenyl (PFP) ester R group was designed and used for the polymerization of various methacrylate monomers, N-isopropylacrylamide and styrene yielding polymers with a PFP ester as a end group. This allowed the introduction of inert propyl amides, of light responsive diazo compounds, of the dyes NBD, Texas Red, or Oregon Green, of the hormone thyroxin and allowed the formation of multiblocks or peptide conjugates. rnFor w end group functionalization, problems of other techniques were overcome through an aminolysis of the dithioester in the presence of a functional methane thiosulfonate (MTS), yielding functional disulfides. These disulfides were stable under ambient conditions and could be cleaved on demand. Using MTS chemistry, terminal methyl disulfides (enabling self-assembly on planar gold surfaces and ligand substitution on gold and semiconductor nanoparticles), butynyl disulfide end groups (allowing the “clicking” of the polymers onto azide functionalized surfaces and the selective removal through reduction), the bio-target biotin, and the fluorescent dye Texas Red were introduced into polymers. rnThe alpha PFP amidation could be performed under mild conditions, without substantial loss of DTE. This way, a step-wise synthesis produced polymers with two functional end groups in very high yields. rnAs examples, polymers with an anchor group for both gold nanoparticles (AuNP) and CdSe / ZnS semi-conductor nanoparticles (QD) and with a fluorescent dye end group were synthesized. They allowed a NP decoration and enabled an energy transfer from QD to dye or from dye to AuNP. Water-soluble polymers were prepared with two different bio-target end groups, each capable of selectively recognizing and binding a certain protein. The immobilization of protein-polymer-protein layers on planar gold surfaces was monitored by surface plasmon resonance.Introducing two different fluorescent dye end groups enabled an energy transfer between the end groups of isolated polymer chains and created the possibility to monitor the behavior of single polymer chains during a chain collapse. rnThe versatility of the synthetic technique is very promising for applications beyond this work.

Während Polymere mit funktionellen Gruppen entlang des Polymer Rückgrates intensiv untersucht worden sind, gibt es noch immer eine Herausforderung, die Endgruppen orthogonal zu funktionalisieren. rnSolche wohl definierten Systeme sind interessant für die Darstellung von Multiblock (Co-) Polymeren oder Polymer-Netzwerken, für Bio-Konjugation oder als Modell-Systeme, um die Endgruppen Abstand an isolierten Polymerketten zu untersuchen. rnHier wurde „Reversible Addition Fragmentation Chain Transfer” (RAFT) Polymerisation als Methode verwendet, um verbesserte Techniken für eine ,  Endgruppenfunktionalisierung zu untersuchen. RAFT erzeugt Polymere, die mit einer R und einer Dithioester-Z Gruppe enden, wobei R und Z aus einem geeigneten Kettentransferagens (Chain Transfer Agent, CTA) stammen. rnFür Funktionalisierung der alpha Endgruppe wurde ein CTA mit einem aktivierten Pentafluorphenyl (PFP) Ester an der R-Gruppe entworfen und für die Polymerisation benutzt.rnFuer die Modifizierung der omega Endgruppe wurde die Aminiolyse in Gegenwart von funktionalen Methanthiosulfonaten durchgefuehrt. Diese Methoden erlaubten eine erfolgreiche Synthese von a, w functionalisierten Polymeren, z.B. mit zwei verschiedenen Farbstoff Endgruppen oder zwei verschienden Proteinen als Endgruppe.