The multifarious self-assembly of triblock copolymers [Elektronische Ressource] : from multi-responsive polymers and multi-compartment micelles / von Katja Skrabania

Skrabania, Katja

Informations

• Publié par: universitat_potsdam
• Publié le: 01 janvier 2008
• Nombre de lectures: 25
• Langue: English
• Poids de l'ouvrage: 7 Mo

Extrait

Universität Potsdam
Arbeitsgruppe Prof. Dr. A. Laschewsky
The multifarious self-assembly of triblock copolymers:
From multi-responsive polymers and multi-compartment micelles
Dissertation zur Erlangung des akademischen Grades
„doctor rerum naturalium“ (Dr. rer. nat.)
in der Wissenschaftsdisziplin „Kolloid- und Polymerchemie“






























eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam
von Katja Skrabania, geboren am 9. Februar 1979 in Stralsund
Potsdam, im November 2008
This work is licensed under a Creative Commons License:
Attribution - Noncommercial - Share Alike 3.0 Germany
To view a copy of this license visit
http://creativecommons.org/licenses/by-nc-sa/3.0/de/










































Published online at the
Institutional Repository of the University of Potsdam:
http://opus.kobv.de/ubp/volltexte/2009/3076/
urn:nbn:de:kobv:517-opus-30764
[http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-30764] ACKNOWLEDGEMENTS
I wish to express my gratitude to all the people that contributed with their professional and
personal support to the successful completion of this PhD project.
I owe my greatest thanks to Prof. Dr. A. Laschewsky (University of Potsdam (UP) and Fraunhofer
Institute for Applied Polymer Research, Potsdam) for giving me the opportunity to prepare my PhD thesis
under his supervision working on this multifaceted and challenging research topic. At all times he has
been amenable to discussions and I am grateful to him for sharing his scientific knowledge and
experience and for his ongoing support. I greatly appreciate his confidence in me and the freedom he
gave me to follow my ideas. Finally, I am grateful for the opportunities to present the results of this PhD
thesis at conferences.
My sincere thanks go to all the members of the Fraunhofer Institute of Applied Polymer Research
in Potsdam-Golm for the friendly environment. In particular, I would like to thank Dr. H. P. Fink and
Dr. U. Buller who permitted me to conduct my research in the laboratories of the institute.
I gratefully acknowledge the help of Dr. V. Strehmel (UP) for TGA and DSC measurements,
Dr. M. Heydenreich and A. Krtitschka (UP) for NMR measurements, B. Hannemann (UP) for elemental
analyses and IR measurements and Dr. H. Wetzel (Fraunhofer IAP) for fluoride ion chromatography.
Moreover, I would like to thank Dr. H. Schlaad and M. Gräwert (Max-Planck-Institute of Colloids and
Interfaces) for their help with SEC measurements.
I am indebted to Dr. H. von Berlepsch and Dr. C. Böttcher (Research Center for Electron
Microscopy, Freie Universität, Berlin) for the cryo-TEM measurements and cryo-electron tomography
measurements that made the wealth of multi-compartment micelles visible.
I gratefully acknowledge J. Kristen (UP) for the synthesis of monomer N-acryloyl pyrrolidine (M3)
and A. M. Bivigou Koumba and D. Zehm (both UP) for the synthesis of the trithiocarbonates CTA3, CTA4,
CTA9 and CTA11. Many thanks go to S. Eidner (UP) for his valuable comments on the UV-vis
spectroscopic investigations of thiocarbonylthio compounds.
I would like to thank the scientists and technicians of the water-borne polymer systems
department (“FB4”) at the Fraunhofer IAP for the great atmosphere and their kind support. In particular, I
would like to thank Dr. J. Bohrisch, Dr. S. Bruzzano, V. Jentzen, Dr. A. Lieske and Dr. J. Storsberg for
their friendship and help - I could not have wished for better colleagues. I am deeply indebted to
Dr. M. Päch who not only provided me with valuable feedback and suggestions concerning my thesis but
became a great friend, too. Special thanks to Dr. M. Mertoglu, Dr. L. Wattebled, Dr. D. Schütt,
Dr. N. Sieverling, A. M. Bivigou Koumba, P. Ott and C. Wieland who have been wonderful office and lab
mates and friends.
Special thanks to F. Salles (Ecole Nationale Supérieure de Chimie, Montpellier, France) and Li
Wen (Master of Polymer Science program, Technische Universität, Berlin) for their practical help during
their internships at the Fraunhofer IAP and while preparing their master theses. Their placements for
several months not only gave me the great opportunity to learn more about their cultures but also to
develop my skills as supervisor.
Finally, I wish to express my heartfelt thanks to M. Steude and K. Okulla (Fraunhofer IAP) for
their friendship and for providing me with insights into PR and marketing.
Last, but by no means least, I am grateful to the support, patience, and understanding of my
family.
ii ABSTRACT
New ABC triblock copolymers were synthesized by controlled free-radical polymerization via
Reversible Addition-Fragmentation chain Transfer (RAFT). Compared to amphiphilic diblock copolymers,
the prepared materials formed more complex self-assembled structures in water due to three different
functional units. Two strategies were followed: The first approach relied on double-thermoresponsive
triblock copolymers exhibiting Lower Critical Solution Temperature (LCST) behavior in water. While the
first phase transition triggers the self-assembly of triblock copolymers upon heating, the second one
allows to modify the self-assembled state. The stepwise self-assembly was followed by turbidimetry,
1dynamic light scattering (DLS) and H NMR spectroscopy as these methods reflect the behavior on the
macroscopic, mesoscopic and molecular scale. Although the first phase transition could be easily
monitored due to the onset of self-assembly, it was difficult to identify the second phase transition
unambiguously as the changes are either marginal or coincide with the slow response of the self-
assembled system to relatively fast changes of temperature.
The second approach towards advanced polymeric micelles exploited the thermodynamic
incompatibility of “triphilic” block copolymers – namely polymers bearing a hydrophilic, a lipophilic and a
fluorophilic block – as the driving force for self-assembly in water. The self-assembly of these polymers in
water produced polymeric micelles comprising a hydrophilic corona and a microphase-separated micellar
core with lipophilic and fluorophilic domains – so called multi-compartment micelles. The association of
1triblock copolymers in water was studied by H NMR spectroscopy, DLS and cryogenic transmission
electron microscopy (cryo-TEM). Direct imaging of the polymeric micelles in solution by cryo-TEM
revealed different morphologies depending on the block sequence and the preparation conditions. While
polymers with the sequence hydrophilic-lipophilic-fluorophilic built core-shell-corona micelles with the core
being the fluorinated compartment, block copolymers with the hydrophilic block in the middle formed
spherical micelles where single or multiple fluorinated domains “float” as disks on the surface of the
lipophilic core. Increasing the temperature during micelle preparation or annealing of the aqueous
solutions after preparation at higher temperatures induced occasionally a change of the micelle
morphology or the particle size distribution.
By RAFT polymerization not only the desired polymeric architectures could be realized, but the
technique provided in addition a precious tool for molar mass characterization. The thiocarbonylthio
moieties, which are present at the chain ends of polymers prepared by RAFT, absorb light in the UV and
visible range and were employed for end-group analysis by UV-vis spectroscopy. A variety of
dithiobenzoate and trithiocarbonate RAFT agents with differently substituted initiating R groups were
synthesized. The investigation of their absorption characteristics showed that the intensity of the
absorptions depends sensitively on the substitution pattern next to the thiocarbonylthio moiety and on the
solvent polarity. According to these results, the conditions for a reliable and convenient end-group
analysis by UV-vis spectroscopy were optimized. As end-group analysis by UV-vis spectroscopy is
insensitive to the potential association of polymers in solution, it was advantageously exploited for the
molar mass characterization of the prepared amphiphilic block copolymers.

iii CONTENTS
Abreviatons vi
1 Introduction 1
1.1 Block copolymers in selective solvents 2
1.1.1 Micellization of block copolymers
1.1.2 Applications amphiphilic block copolymers 4
1.2 Increasing the complexity of block copolymer micelles 7
1.2.1 ABC triblock copolymers 7
1.2.2 Stimuli-responsive block copolymers 8
1.2.3 Multi-compartment micelles - A new class of polymeric micelles 10
1.3 Methods of controlled radical polymerization (CRP) 13
1.3.1 Introduction to CRP methods 13
1.3.2 Nitroxyl-mediated polymerization (NMP) 14
1.3.3 Atom transfer radical polymerization (ATRP) 15
1.3.4 Polymerization by revers