Synthesis and applications of novel dendritic polymers through chain walking polymerization.

摘要

Dendritic polymers have found many general applications due to their unique properties. Whereas perfect dendrimers have beautiful structural precision and uniformity, the multi-step syntheses involved in their preparations limit their general applications. We have been exploring a new strategy for controlling polymer topology through transition-metal catalysis. Instead of relying on step-wise synthesis; we achieved controlling polymer topologies by controlling the covalent linkage of simple monomers through transition-metal catalyzed chain walking polymerization (CWP). First, a simple and novel methodology for one-step synthesis of functional polymers with systematically tunable topologies, from linear to branch to hyperbranch to dendritic, was developed by using CWP. Copolymers containing a variety of functional groups, such as ester, ether, hydroxyl, aldehyde, expoxide, were synthesized in one step with various functional group incorporation ratios. Then, applying this methodology, facile synthesis of copolymers with dendritic topology was achieved. Dendritic polymers containing multivalent functional groups including hydroxyl, saccharides and siloxane was prepared for potential functional applications. Third, as one specific application, CWP was used for a one-pot synthesis of amphiphilic molecular dendritic nanocarriers. Nile Red encapsulation study showed that the copolymers behave like unimolecular micelle in aqueous solutions. Furthermore, dendritic polymer scaffold with NHS activated ester groups was prepared using hetero-difunctional PEG. Reactions of ovalbumin and the NHS activated scaffold successfully yielded protein conjugates. Finally, an efficient synthesis of NHS activated nanoparticles was developed through tandem CWP and ATRP. Dendritic macro-initiators bearing multiple radical initiation sites were prepared, which was subsequently used in Cu(I)-mediated ATRP with OEGMA and NAS monomer. Dendritic star polymer scaffolds with controllable molecular weight and size were obtained with 236 copies of NHS activated ester group ready for bioconjugation. The reactivity and availability of the NHS group was tested with a small fluorescein probe. Reactions with protein ovalbumin showed efficient conjugation between protein and the scaffolds. Conjugate of vaccinia virus antigen H3L was also prepared. Earlier immune response studies showed good antibody production boost.