The synthesis of well defined functional homo- and block copolymers in aqueous media via Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization [Elektronische Ressource] / von Murat Mertoğlu

Murat

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• Publié par: universitat_potsdam
• Publié le: 01 janvier 2005
• Nombre de lectures: 29
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Universität Potsdam
Arbeitsgruppe Prof. Dr. Laschewsky




The Synthesis of Well-Defined Functional Homo- and Block Copolymers
in Aqueous Media
via Reversible Addition-Fragmentation Chain Transfer (RAFT)
Polymerization







Dissertation
zur Erlangung des akademischen Grades
"doctor rerum naturalium"
(Dr. rer. nat.)
in der Wissenschaftsdisziplin "Kolloid und Polymer Chemie"










eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam




von
Murat Merto ğlu
geboren am 18.07.1978 in İstanbul




Potsdam, im November 2004 ACKNOWLEDGEMENTS

I am indebted to many people who helped me during the preparation of this thesis. I
wish to express my gratitude to Prof. Dr. André Laschewsky for giving me the opportunity
to conduct research under his supervision. He was all the time available and open to
discuss about anything to support me. He encouraged and motivated me a lot, particularly,
when the things go wrong in research. Lastly I want to thank him for his intimate and
friendly manners both as an advisor and a person.

I am especially grateful to Dr. Joachim Storsberg and Dr. Jean-François Baussard
for their contribution to my thesis and particularly for their guidance in the laboratory to
develop my bench skills and learn better the modern synthetic methods.

I gratefully acknowledge the help of J.-L. Habib-Jiwan (Université catholique de
Louvain) for taking FAB mass spectra, to F. Malwitz (University of Potsdam) for helping
with IR measurements, to M. Kumke (University of Potsdam) for helping with
fluorescence measurements, to S. Bruzzano and C. Wieland (both Fraunhofer IAP) for
advices and measuremtns in ASEC of polycations, to H. Schlaad, G. Rother and M.
Gräwert (Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Potsdam) for
helping with ASEC for polyanions and SEC in NMP.

Special thanks to Christoph Wieland, Kamel Silmy, Katja Skrabania, Laurent
Wattebled, Nathalie Sieverling, Samira Nozari, Sébastien Garnier, Dr. Stefano Bruzzano,
Dr. Habil Veronika Strehmel and all members of the Fraunhofer Institute for Applied
Polymer Research in the science park of Golm for the friendly environment and their kind
support.

Finally I am extremely grateful to my parents and brothers who provide me
constant support and confidence however far they are.

iiABSTRACT


New chain transfer agents based on dithiobenzoate and trithiocarbonate for free
radical polymerization via Reversible Addition-Fragmentation chain Transfer (RAFT)
were synthesized. The new compounds bear permanently hydrophilic sulfonate moieties
which provide solubility in water independent of the pH. One of them bears a fluorophore,
enabling unsymmetrical double end group labelling as well as the preparation of
fluorescent labeled polymers. Their stability against hydrolysis in water was studied, and
compared with the most frequently employed water-soluble RAFT agent 4-cyano-4-
1thiobenzoylsulfanylpentanoic acid dithiobenzoate, using UV-Vis and H-NMR
spectroscopy. An improved resistance to hydrolysis was found for the new RAFT agents,
providing good stabilities in the pH range between 1 and 8, and up to temperatures of
70°C. Subsequently, a series of non-ionic, anionic and cationic water-soluble monomers
were polymerized via RAFT in water. In these experiments, polymerizations were
conducted either at 48ºC or 55ºC, that are lower than the conventionally employed
temperatures (>60ºC) for RAFT in organic solvents, in order to minimize hydrolysis of the
active chain ends (e.g. dithioester and trithiocarbonate), and thus to obtain good control
over the polymerization. Under these conditions, controlled polymerization in aqueous
solution was possible with styrenic, acrylic and methacrylic monomers: molar masses
increase with conversion, polydispersities are low, and the degree of end group
functionalization is high. But polymerizations of methacrylamides were slow at
temperatures below 60°C, and showed only moderate control. The RAFT process in water
was also proved to be a powerful method to synthesize di- and triblock copolymers
including the preparation of functional polymers with complex structure, such as
amphiphilic and stimuli-sensitive block copolymers. These include polymers containing
one or even two stimuli-sensitive hydrophilic blocks. The hydrophilic character of a single
or of several blocks was switched by changing the pH, the temperature or the salt content,
to demonstrate the variability of the molecular designs suited for stimuli-sensitive
polymeric amphiphiles, and to exemplify the concept of multiple-sensitive systems.
Furthermore, stable colloidal block ionomer complexes were prepared by mixing anionic
surfactants in aqueous media with a double hydrophilic block copolymer synthesized via
RAFT in water. The block copolymer is composed of a noncharged hydrophilic block
based on polyethyleneglycol and a cationic block. The complexes prepared with perfluoro
decanoate were found so stable that they even withstand dialysis; notably they do not
denaturate proteins. So, they are potentially useful for biomedical applications in vivo.
iiiTABLE OF CONTENTS

ACKNOWLEDGEMENT ..................................................................................................ii
ABSTRACT ........................................................................................................................iii
LIST OF SCHEMES ........................................................................................................vii
LIST OF TABLES ...........................................................................................................viii
LIST OF FIGURES ix
LIST OF ABBREVIATIONS .........................................................................................xiv
1. INTRODUCTION 1
1.1. Free Radical Polymerization............................................................................. 5
1.2. General Properties of Living Polymerization.................................................. 7
...........1.3. Comparison of Living Polymerization Systems with Free-radical
Polymerization ................................................................................................... 8
1.4. Controlled Radical Polymerization Methods (CRP) ......................................9
1.4.1. Nitroxyl Mediated Polymerization (NMP) ..........................................10
1.4.2. Atom Transfer Radical Polymerization (ATRP) .................................11
1.4.3. Reversible Addition Fragmentation Chain Transfer Polymerization
(RAFT) .................................................................................................11
1.5. A Closer Look to RAFT Polymerization ...................................................... 15
2. SYNTHESIS OF WATER-SOLUBLE RAFT AGENTS ........................................24
2.1. The most used reaction routes to dithioesters .............................................`25
2.1.1. Synthesis of dithiobenzoic acids ..........................................................25
2.1.2. Alkylation of dithiocarboxylates 25
2.1.3. Addition of dithiocarboxylic acids to olefins .......................................27
2.1.4. Synthesis of dithioesters using Pinner salts ........................................27
2.1.5. Conversion of thioesters to dithioester by using Lawesson’s reagent 27
2.1.6. Free radical coupling reaction between azo initiators and
bis(thiocarbonyl) disulfides .................................................................27
iv 2.1.7. Ester exchange reaction between dithiocarboxylates and thiols ........28
2.2 Synthetic routes to water-soluble RAFT agents .............................................. 28
2.2.1. Water-soluble RAFT agents via acidic addition of dithiocarboxylic
acids to olefins ......................................................................................30
2.2.2. Water-soluble RAFT agents via free radical coupling reaction between
azoinitiators and bis(thiocarbonyl) disulfides .....................................32
2.2.3. Water-soluble RAFT agents via alkylation of dithiocarboxylates .... 33
3. STABILITY OF RAFT AGENTS IN WATER ....................................................... 36
4. SYNTHESIS OF WATER-SOLUBLE HOMO- AND COPOLYMERS VIA RAFT
.............................................................................................................................................48
4.1. Usefulness of End Groups of Polymers Synthesized via RAFT ..................49
4.2. Presentation of Monomers Used .................................................................... 54
4.3. Homopolymerization Studies via RAFT ....................................................... 56
4.3.1. Polymerization of vinylbenzylchloride (M16) via RAFT ....................56
4.3.2. Aqueous RAFT polymerization of methacrylic monomers ................57