45853-AC7
Electropolymerizable Dendrons in Reversible Addition Fragmentation Chain-Transfer (RAFT) Polymerizations: Electrochemical Behavior and Macromolecular Assemblies
This Project involved the exploration of various electropolymerizable linear-dendron macromolecular architectures for controlled surface modification and phase separation with electrografting. We have recently described a series of well-defined dendritic-linear block copolymer architectures via the reversible addition fragmentation chain transfer (RAFT) polymerization technique. Using dendritic chain transfer agents (CTA)s possessing a single dithioester moiety at the focal point, RAFT polymerization was carried out to attach polystyrene (PS) and polymethylmethacrylate (PMMA) chains of controlled lengths by kinetic control. To provide electrochemical functionality, the dendritic CTAs were designed with carbazole moieties at the periphery of the structures. The results on the electrochemical polymerization of the carbazole moieties at the periphery of the dendritic component of the block copolymers reveal quantitative cyclic depositions with changes in viscoelastic properties of the deposited films as monitored by the electrochemical quartz crystal microbalance (E-QCM) technique. The electro-active dendritic blocks proved to be an effective electrochemically active macromonomer for the electrodeposition of these structures on conducting substrates. A complementary approach is the electrografting of dendron-CTAs on surfaces based on the above dendrons followed by surface initiated polymerization. Whereas the method described above is a type of “grafting onto” approach of a preformed polymer, the complementary method is a type of “grafting from” approach. Possible complications of the methods may be unwarranted decay of the CTA with anodic electrodeposition and the limitations on the formation of thin film or monolayer like array of the initiators. The initial results have so far shown the viability of electrodeposition of the CTA’s while preserving the functionality for RAFT polymerization. It should be noted that the other possible direction involves the use of ATRP methods to control the MW and dispersity with pre-formed synthesis and or SIP by ATRP. We are currently exploring the synthesis and characterization of protein-resistant polymers via RAFT polymerization based on PEGylated carbazole dendron. Our initial results showed that a PEG oligomer and be directly attached at the focal point of a dendron via esterification. For the RAFT application, the PEG mathacrylate polymerization followed a linear growth of the molecular weight and low molecular weight distribution values, which signified highly controlled parameters for this method. The homopolymers were also successfully electrografted on gold surfaces as characterized by ellipsometry, AFM, contact angle and XPS. Preliminary studies were done for protein adsorption using ellipsometry and AFM. Thicker films were observed to be more protein resistant than the thinner films produced. We have also synthesized terthiophene functionalized dendritic CTAs for the formation of polythiophene films during Electrografting. Other related work included the surface initiated polymerization of polyvinylcarbazole (PVK) brushes on ITO and dual-responsive polymer brushes from combined layer-by-layer and SIP approaches with a macroinitiator.
