Speaker: David Pahovnik
Time: 10:00, Oct. 30th, 2019
Venue: Room 346, Building 25, Wushan Campus
Abstract: Ring-opening polymerization (ROP) of heterocyclic monomers such as lactones, lactides, epoxides and α-amino acid N-carboxyanhydrides (NCA) is an invaluable tool for the preparation of biocompatible and (bio)degradable polymers as well as hybrid copolymers in a controlled manner. Since polyesters/polyethers prepared by ROP propagate through hydroxyl group, which is slow initiating group for ROP of NCA, the synthesis of polypeptide-based hybrid block copolymers commonly demands multistep reactions with expensive and time-consuming intermediate steps needed for end-group transformation. To overcome the issue of slow NCA initiation by the hydroxyl group, we developed the procedure where initiation is separated from the propagation step, and instead they were performed in a successive manner. By using simple alcohol initiators and hydroxyl-terminated macroinitiators we have been able to prepare both the homopolypeptides and polypeptide-based block copolymers, respectively. This approach was further developed to allow for one-pot sequential ROP, where cyclic esters/carbonates are first polymerized, followed by NCA polymerization.
In the second part, several examples of porous polymers prepared by employing ROP will be discussed. Since ROP and free-radical polymerizations are orthogonal they have been performed in situ simultaneously to prepare the PCL/PS semi-interpenetrating polymer networks. By selective removal of degradable polyester component, the porous non-degradable polystyrene monoliths were prepared, where the final morphology of the porous network was controlled by tuning the relative polymerization rate of both monomers. On the other hand, fully degradable scaffolds were synthesized by ROP within the oil-in-oil high internal phase emulsions (HIPE). In this way, the macroporous cross-linked PCL polyHIPE foams were synthesized, which demonstrate cross-linking degree dependant shape memory behaviour. HIPE templating was extended to ROP of NCA to prepare HIPE templated synthetic polypeptide scaffolds, where experimental conditions were carefully tuned to prevent foaming of the scaffold due to CO2 evolution during polymerization.
The last part of the presentation will focus on comprehensive characterization of complex macromolecular structures, which presents a challenge since no single analytical technique provides adequate information on all distribution properties that complex polymers have. It will be shown that hyphenated techniques like AF4 or SEC coupled to a multi-detection system (MALS, DLS, UV, RI) can provide detailed insight into such structures.
Biography:Dr. David Pahovnik received his B.S. in Organic chemistry at the Faculty of Chemistry and Chemical Technology, University of Ljubljana, Slovenia, in 2007, and his Ph.D. in Polymer Chemistry in 2012 at the Department of Polymer Chemistry and Technology, National Institute of Chemistry, Slovenia. Between 2013 and 2014 he was a postdoctoral fellow at prof. Nikos Hadjichristidis group in the Polymer Synthesis Laboratory, King Abdullah University of Science and Technology (KAUST), Saudi Arabia. After his postdoc he returned to National Institute of Chemistry, where he is currently a Research fellow. His main research interests are synthesis and characterization of polymers, with special focus on ring-opening polymerization of NCAs for preparation of synthetic polypeptide-based materials.
