Synthesis and characterization of polyelectrolyte brushes [Elektronische Ressource] : towards a synthetic model system for human cartilage / vorgelegt von Karen Lienkamp

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2006
• Nombre de lectures: 25
• Langue: English
• Poids de l'ouvrage: 24 Mo

Extrait

Dissertation zur Erlangung des Grades „Doktor der Naturwissenschaften“
am Fachbereich Chemie, Pharmazie und Geowissenschaften
der Johannes Gutenberg-Universität, Mainz
vorgelegt von
Dipl.-Chem. Karen Lienkamp
geboren in Freiburg im Breisgau
Synthesis and Characterization of Polyelectrolyte Brushes –
Towards a Synthetic Model System for Human CartilageContents
1 Motivation 1
1.1. Introduction 1
1.2. Objective 2
2 Polymerization Methods 3
2.1. General Comments 3
2.2. Free Radical Polymerization 3
2.3. Controlled Radical Polymerization 5
2.4. Anionic Polymerization 11
2.5. Cationic Polymerization 13
2.6. Suzuki Polycondensation 14
3 Characterization Methods 17
3.1. General Comments 17
3.2. Scattering Methods 17
3.3. Gel Permeation Chromatography (GPC) and Coupled Methods 25
3.4. Analytical Ultracentrifugation (AUC) 33
3.5. Imaging Techniques 35
3.6. MALDI-TOF Mass Spectrometry 40
4 Polymer and Polyelectrolyte Brushes 43
4.1. Polymer Brushes 43
4.2. Polyelectrolyte Brushes 47
5 Ionic Self-Assembly in Nature and Research 53
5.1. Synthetic Structures by Ionic Self-Assembly 53
5.2. Proteoglycan-Hyaluronic Acid Aggregates in Human Cartilage as 53
an Example for Ionic Self-Assembly in Nature
6 Synthetic Strategy 57
6.1. Synthesis of Poly(styrene sulfonate) Brushes in the Literature 57
6.2. Non-functionalized Polyelectrolyte Brushes as Model 59
Compounds
7 Macroinitiator Approach 63
7.1. ATRP Macroiniators for Polymer Brushes in the Literature 63
7.2. Macroinitiator Synthesis and Characterization 64
7.3. Synthesis of Polymer Brushes from Poly(styrene sulfonate 67
dodecyl ester)
7.4. Characterization of Polymer Brushes from Poly(styrene 71
sulfonate dodecyl ester)
7.5. Synthesis of Polymer Brushes from Poly(styrene sulfonate ethyl 87
ester)
7.6. Characterization of Polymer Brushes from Poly(styrene 89
sulfonate ethyl ester)
7.7. Polymer Brush Hydrolysis 977.8. Polyelectrolyte Brush Characterization 99
7.9. Conclusive Remarks 142
8 Synthesis of End-functionalized Polymer Brushes 147
8.1. Introduction 147
8.2. Synthesis of a Functionalized Macroinitiator 147
8.3. Synthesis of Functionalized Polymer Brushes 152
8.4. Synthesis of Functionalized Polyelectrolyte Brushes 154
8.5. Complexation Experiments 157
8.6. Conclusion 160
9 Macromonomer Approach 161
9.1. Macromonomers – General Synthetic Strategies 161
9.2. Styrene Sulfonic Acid Ethyl Esters 161
9.3. ATRP Initiator Synthesis 163
9.4. Synthesis of the AA Macromonomer via ATRP 164
9.5. Synthesis of the AB Macromonomer via ATRP 177
9.6. Macromonomer Hydrolysis 178
9.7. Further Macromonomer Characterization 180
9.8. Macromonomer Polymerization Attempts 180
9.9. Conclusion 181
10 Conclusion and Outlook 183
11 Summary 185
12 Experimental Part 187
12.1. Synthesis 187
12.2. Light Scattering Measurements 210
12.3. Small Angle Neutron Scattering 210
12.4. GPC and GPC-MALLS 211
12.5. Refractive Index Increment 211
12.6. Analytical Ultracentrifugation 211
12.7. Transmission Electron Microscopy 211
12.8. Scanning Electron Microscopy 212
12.9. Atomic Force Microscopy 212
112.10. H-NMR Measurements in Solution 212
112.11. H-NMR Measurements (Solid State) 213
12.12. MALDI-TOF Mass Spectrometry 213
12.13. Elemental Analysis 213
12.14. Chemicals 213
13 References 215
14 List of Abbreviations 221
15 Appendix 223
15.1. Sample Nomenclature 22315.2. Supporting Information 224Chapter 1
1. Motivation
1.1. Introduction
Self-organizing systems are ubiquitous in nature, the double-helix of DNA and the
folding of protein structures being common examples. Another important example of
self-organization in the human organism is the formation of proteoglycan aggregates
1with hyaluronic acid (Fig. 1.1.(left) ). These aggregates are found throughout all
extracellular compartments. Specifically, tissues which are subject to constant
mechanical strain, e.g. cartilage, contain large amounts. Being extremely resistant to
mechanical impacts, these tissues are at the same time highly flexible. The most
abundant proteoglycan-hyaluronic acid aggregate found in nature is the aggrecan-
hyaluronic acid aggregate. Aggrecan is a linear polypeptide chain carrying a large
number of anionic polysaccharide side chains, thus forming an anionic polymer brush.
In living organisms, aggrecan and hyaluronic acid are synthesized separately in
specialized cells of the cartilage and released into the extracellular compartment,
where about 100 aggrecan molecules self-assemble with one hyaluronic acid molecule.
The linker between aggrecan and hyaluronic acid is a positively charged, claw-shaped
protein, which is covalently attached to the aggrecan molecule. Thus the whole
aggregate is held together by electrostatic interaction of the positive link and the
1, 2negatively charged hyaluronic acid .
F





Model




1Fig. 1.1.: Cartoon representation of the proteoglycan-hyaluronic acid aggregates in
human cartilage (left) and a simplified synthetic model system for this
structure (right)


1 Motivation
In order to understand the unusual mechanical properties of these aggregates, which
act as biological lubricants, and to mirror them in synthetic products, the aim of this
work is to produce model compounds for the proteoglycan-hyaluronic acid complex
(see Fig. 1.1.).

1.2. Objective
As a model for the proteoglycan, anionic polyelectrolyte brushes from poly(styrene
sulfonic acid) will be synthesized (Fig. 1.2., left). This monomer has been chosen to
imitate the polyelectrolyte properties of the original proteoglycan molecule. Their
solution structure and aggregation behavior will be investigated. Ultimately, it is to be
attempted to end-functionalize the polyelectrolyte brush with a positively charged linker
(Fig. 1.1., right) and complex the resulting structure to negatively charged objects. The
structure of these materials would be investigated by microscopic methods (TEM,
SEM, AFM) and scattering techniques (static and dynamic light scattering, neutron
scattering).

H H
n

H
n

+
H N
m
+ N H
m

O S O

O
H O S O
O
H

Fig. 1.2.: Target structure, unfunctionalized (left) and functionalized (right)



2 Chapter 2
2. Polymerization Methods

2.1. General Comments
The literature available suggests for styrene-type monomers used in this work that
polymerization by radicals (free and controlled), living anionic polymerization and
cationic polymerization is possible. For the macromonomer polymerization, Suzuki
polycondensation is a promising method. The advantages and disadvantages of these
methods and their relevance for this work are discussed in the following sections.

2.2. Free Radical Polymerization
Free radical polymerization is by far the easiest polymerization method, as it does not
demand for extreme monomer or solvent purity, tolerating even water as an impurity as
well as many functional groups. Oxygen is to be excluded. In spite of this drawback,
radical polymerization is widely used in industry. Its disadvantage is the lack of precise
control over the reaction products, resulting in a broad molar mass distribution. This is
due to the fact that radicals are highly reactive and unselective intermediates and suffer
from termination reactions in a statistical fashion. Free radical polymerization consists
of three basic mechanistic steps: initiation, propagation and termination. Further
reaction steps such as inhibition and chain transfer complicate this simple picture. In
the initiation step, a suitable initiator radical attacks the double bond of a vinyl
monomer, resulting in a chain radical, as shown in Fig. 2.2.1..

The initiator radical can be generated by decomposition of a molecule containing a
thermally labile bond. Other possibilities include photolytic cleavage, redox reactions or
high energy radiation. In the propagation step, monomer molecules repeatedly react
with the chain end radical, forming a linear polymer. Further reaction channels, e.g.
termination reactions, limit the chain length of such a polymer. These include
disproportionation of two radicals into an alkane and an alkene terminated
macromolecule, as well as recombination of two radicals. The preferred termination
step depends on the monomer and temperature. From the rate laws for these three
reaction steps and application of the steady-state hypothesis for the concentration of
radicals, the following overall polymerization rate can be derived:

v = polymerization rate pf ⋅[I]⋅k k = reaction step rate constant d i [ ]ν = k ⋅ ⋅ M [I] = initiator concentration p p
k [M] = monomer concentration t f = initiator efficiency
3 Polymerization Methods

RInitiation: 1/2 R R
RR'
R'
R
R' R'
Propagation:
n R'
R R
R'
n
Termination:
R' R' R' R'
by recombination
R R
R' R'
n n
R by disprop