Macromolecular Nano-Carriers from Star Polymers produced via RAFT Polymerization
Final Report Abstract
In this project, the so called Z-RAFT star polymerization, which is a special type of the controlled radical RAFT polymerization and which can be used to generate well-defined star polymer, was studied in-depth with regard to its peculiar mechanism and was also used to synthesize novel types of functional nano-containers. For the mechanistic side of the project, we developed and explored several multifunctional starshaped RAFT agents, in which up to eight controlling dithioester- and trithiocarbonate-moieties, respectively, are irreversibly linked to the core via their so called Z-group. These systems were characterized in-depth both experimentally and by simulations with respect to their mechanism. The following key findings that are of immanent importance for the success of a Z-RAFT star polymerization were found during the project: Methods for obtaining absolute molar masses of star polymers via conventionally calibrated SEC and for tracing the initialization of arm growth via NMR spectroscopy using fully deuterated monomer revealed a significant impact of the pre-equilibrium, i.e. the choice of the leaving group of the used RAFT agent, on the star polymer topology. Monte Carlo simulations of the shielding effect occurring in the main equilibrium indicated that steric congestion is not affecting the process to a major extent and that performing Z-RAFT star polymerization in poor solvents enhances the polymerization control, hence the homogeneity of the material. Unexpected star-star coupling in Z-RAFT star polymerization of acrylates was identified to be a result of intermolecular chain transfer to polymer, which could be quantified with high precision using this effect. On the synthetic side of the project, we used Z-RAFT star polymerization to develop new core-shell structured nano-carriers having non-polar cores and polar shells or vice versa. This was achieved by a strategy that exploits the peculiar mechanism of Z-RAFT star polymerization and which rests on a complex sequence of macromolecular reactions, i.e. first developing star-block-copolymers in which every arm of the star is an amphiphilic block copolymer, then incorporating functionalized monomer to the outer block which provides reactive sites for crosslinking, then cross-linking the outer block to build up a stable shell-architecture, and finally remove the core in order to form a pocket for loading.
Publications
- Shielding Effects in Polymer-Polymer Reactions, 1. Z-RAFT Star Polymerization of 4-Arm Stars. Macromolecular Theory and Simulations, Vol. 16. 2007, Issue 6, pp. 610–618.
M. G. Fröhlich, P. Vana, G. Zifferer
(See online at https://dx.doi.org/10.1002/mats.200700026) - Shielding Effects in Polymer–Polymer Reactions, 2. Reactions between Linear and Star–Branched Chains with up to 6 Arms. The Journal of Chemical Physics, Vol. 127. 2007, Issue 16: 164906.
M. G. Fröhlich, P. Vana, G. Zifferer
(See online at https://dx.doi.org/10.1063/1.2780167) - Z-RAFT Star Polymerizations of Acrylates: Star Coupling via Intermolecular Chain Transfer to Polymer. Macromolecules, Vol. 40. 2007, Issue 8, pp. 2683–2693.
D. Boschmann, P. Vana
(See online at https://dx.doi.org/10.1021/ma0627626) - Tracing Arm-Growth Initiation in Z-RAFT Star Polymerization by NMR: The Impact of the Leaving R-Group on Star Topology. Journal of Polymer Science Part A: Polymer Chemistry, Vol. 46. 2008, Issue 21, pp. 7280–7286.
D. Boschmann, M. Mänz, A.-C. Pöppler, N. Sörensen, P. Vana
(See online at https://dx.doi.org/10.1002/pola.23032) - Z-RAFT Star Polymerizations of Styrene: a Comprehensive Characterization of Star Polymer via Size-Exclusion Chromatography. Polymer, Vol. 49. 2008, Issue 24, pp. 5199–5208.
D. Boschmann, R. Edam, P. J. Schoenmakers, P. Vana
(See online at https://dx.doi.org/10.1016/j.polymer.2008.09.048) - Characterization of Z-RAFT Star Polymerization of Butyl Acrylate by Size-Exclusion Chromatography. Macromolecular Symposia, Special Issue: Microstructural Control in Free-Radical Polymerization, Vol. 275/276. 2009, Issue 1, pp. 184–196.
D. Boschmann, R. Edam, P. J. Schoenmakers, P. Vana
(See online at https://dx.doi.org/10.1002/masy.200950121) - Mechanism of Z-RAFT Star Polymerization. In: Controlled/Living Radical Polymerization: Progress in RAFT, DT, NMP & OMRP. ACS Symposium Series, Vol. 1024, 2009, Chapter 14, pp 217–232.
D. Boschmann, M. Mänz, M. G. Fröhlich, G. Zifferer, P. Vana
(See online at https://dx.doi.org/10.1021/bk-2009-1024.ch014) - Shielding effects in polymer-polymer reactions, 3. Z-RAFT Star Polymerization under Various Solvent Conditions. Polymer, Vol. 51. 2010, Issue 22, pp. 5122–5134.
M. G. Fröhlich, M. M. Nardai, N. Förster, P. Vana, G. Zifferer
(See online at https://dx.doi.org/10.1016/j.polymer.2010.08.054) - Nano-Carrier Synthesis via Z-RAFT Star Polymerisation. Dissertation
Georg-August-Universität Göttingen, 2012,210 S.
N. Förster
- Photocrosslinkable Star Polymers via RAFT-Copolymerizations with N-Ethylacrylate-3,4-dimethylmaleimide. Polymers, Vol. 5. 2013, Issue 2, pp. 706-729.
N. Förster, P. Vana
(See online at https://doi.org/10.3390/polym5020706)
