Smart hydrogels based on trishydrophilic triblock terpolymers [Elektronische Ressource] / vorgelegt von Stefan Reinicke

Stefan Löfving

Informations

• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2010
• Nombre de lectures: 26
• Langue: Deutsch
• Poids de l'ouvrage: 9 Mo

Extrait

“Smart ” Hydrogels based on
Trishydrophilic Triblock
Terpolymers

DISSERTATION


zur Erlangung des akademischen Grades eines Doktors der
Naturwissenschaften (Dr. rer. nat.) im Fach Chemie der Fakultät für
Biologie, Chemie und Geowissenschaften der Universität Bayreuth





vorgelegt von
Stefan Reinicke
Geboren in Halle an der Saale

Bayreuth 2010 Die vorliegende Arbeit wurde in der Zeit von November 2006 bis September 2010 in
Bayreuth am Lehrstuhl Makromolekulare Chemie II unter Betreuung von Herrn Prof. Dr.
Axel H. E. Müller angefertigt.

Vollständiger Abdruck der von der Fakultät Biologie, Chemie und Geowissenschaften der
Universität Bayreuth genehmigten Dissertation zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften (Dr. rer. nat.).


Promotionsgesuch eingereicht am: 28.09.2010
Zulassung durch die Promotionskommission: 27.10.2010
Wissenschaftliches Kolloquium: 01.03.2011

Amtierender Dekan: Prof. Dr. Stephan Clemens

Prüfungsausschuss:
Prof. Dr. Axel H. E. Müller (Erstgutachter)
Prof. Dr. Thomas Hellweg (Zweitgutachter)
Prof. Dr. Andreas Fery (Vorsitzender)
Prof. Dr. Jürgen Senker
















I think perhaps the most important problem is that
we are trying to understand the fundamental
workings of the universe via a language devised for
telling one another when the best fruit is.
Terry Pratchett









Dedicated to Carina
and my family Table of Contents
Summary/ Zusammenfassung 1
1 Introduction 6
1.1 Stimuli-responsive polymers 6
1.1.1 Temperature- and pH-sensitivity 7
1.1.2 Additional stimuli 9
1.2 Magnetic nanoparticles 11
1.3 Structural definition and classification of gels 13
1.4 Stimuli-responsive (“smart”) hydrogels 16
1.4.1 Temperature- and pH-responsive hydrogels 17
1.4.2 Magneto-responsive hydrogels 19
1.4.3 Application fields for “smart” hydrogels 20
1.5 Experimental part 22
1.5.1 Block copolymer synthesis 22
1.5.2 Synthesis of magnetic nanoparticles and nanoparticle/
polymer hybrid structures 26
1.5.3 Rheology 27
1.5.4 Small angle neutron scattering (SANS) 32
1.5.5 Dynamic light scattering (DLS) 35
1.6 Objective of the thesis 37
1.7 References 39
2 Overview of the thesis 45
2.1 One-pot synthesis of polyglycidol-containing block copolymers with
alkyllithium initiators using the phosphazene base t-BuP 464
2.2 Smart hydrogels based on double responsive triblock terpolymers 48 Table of Contents
2.3 Flow induced ordering in cubic gels formed by P2VP-b-PEO-b-
P(GME-co-EGE) triblock terpolymer micelles: A rheo-SANS study 50
2.4 Combination of “living” anionic polymerization and ATRP via “click”
chemistry as a versatile route to multiple responsive triblock
terpolymers and corresponding hydrogels 52
2.5 Magneto-responsive hydrogels based on maghemite/triblock terpolymer
hybrid micelles 56
2.6 Individual contributions to joint publications 58
3 One-pot synthesis of polyglycidol-containing block copolymers with
alkyllithium initiators using the phosphazene base t-BuP 614
4 Smart hydrogels based on double responsive triblock terpolymers 77
5 Flow induced ordering in cubic gels formed by P2VP-b-PEO-b-
P(GME-co-EGE) triblock terpolymer micelles: A rheo-SANS study 107
6 Combination of “living” anionic polymerization and ATRP via “click”
chemistry as a versatile route to multiple responsive triblock terpolymers
and corresponding hydrogels 134
7 Magneto-responsive hydrogels based on maghemite/triblock terpolymer
hybrid micelles 167
8 Appendix 205
8.1 Thermo-sensitive polymers with tunable LCST based on modified
polyglycidol 205
8.2 List of publications 208
8.3 Contributions to national and international conferences 210
Glossary 212
Acknowledgements 216

Summary/ Zusammenfassung
Summary
The work presented in this thesis focuses on the synthesis of double stimuli-responsive,
trishydrophilic triblock terpolymers and their utilization for the construction of “smart”
hydrogel systems, responding to a variety of external stimuli. The central focus was put on
ABC triblock terpolymers composed of a pH-sensitive A block, a water soluble B block and a
thermo-sensitive or multi-responsive C block. This concept was used for the construction of
hydrogels responding independently to pH, temperature, and UV light. It was further applied
to the formation of polymer/nanoparticle hybrid micelles suitable for the formation of
magneto-responsive hydrogels (ferrogels).
At first, a new route for the synthesis of block copolymers, containing ethylene oxide and
glycidol derivatives, was developed. The crucial aspect of this procedure, based on sequential
anionic polymerization, was the utilization of the phosphazene base t-BuP , enabling the 4
anionic polymerization of epoxide monomers in the presence of lithium counterions. It was
shown, that ethoxyethyl glycidyl ether polymerizes easily under the established
polymerization conditions without unwanted termination. Hence, we were able to synthesize
well-defined block copolymers containing vinyl and epoxide monomers in a one-pot reaction,
without performing additional intermediate steps.
This new synthetic route was then utilized to synthesize a series of poly(2-vinylpyridine)-
block-poly(ethylene oxide)-block-poly(glycidyl methyl ether-co-ethyl glycidyl ether) (P2VP-
b-PEO-b-P(GME-co-EGE)) triblock terpolymers suitable for pH and temperature dependent
hydrogel formation. The reversible gelation for this particular system relies on two distinct
mechanisms. Under conditions, where only one outer block is insoluble, core-shell-corona
(CSC) micelles are formed, resulting in gelation via close cubic packing of the micelles. On
the other hand, the micelles are also able to crosslink through their corona when both outer
blocks are insoluble. As a direct consequence, a temperature triggered gel-sol-gel transition
occurred at pH = 7, accompanied by a unique gel strengthening. Solubility and gelation
studies were performed by DLS, rheology and SANS. The influence of polymer
concentrations and block lengths on the gelation behavior and gel properties was studied.
In order to derive information about the exact structure of the cubic lattice formed in the low
temperature gel phase (simple cubic or body centered cubic), a 19 wt% aqueous solution of
P2VP -b-PEO -b-P(GME -co-EGE ) at pH = 7 was further investigated using SANS 56 410 48 48
1
Summary/ Zusammenfassung
under steady shear. By application of shear stress, the irregularly arranged polydomains of the
sample oriented macroscopically along a preferred direction, which led to highly defined,
strongly anisotropic 2D scattering patterns. The interpretation of these patterns confirmed the
presence of a body centered cubic packing. The gel-sol transition upon temperature increase
can be explained by a shrinkage of the shell of the CSC micelles.
To increase the versatility of the established hydrogel concept, we further synthesized ABC
triblock terpolymers with different responsive polymers as C blocks. This required an
alternative synthetic route, combining anionic polymerization and ATRP via “click”
chemistry. After optimization of each synthetic step, exemplary poly(2-vinylpyridine)-block-
poly(ethylene oxide)-block-poly(oligo(ethylene glycol) methacrylate) (P2VP-b-PEO-b-
POEGMA) and poly(2-vinylpyridine)-block-poly(ethylene oxide)-block-poly(dimethyl-
aminoethyl methacrylate) (P2VP-b-PEO-b-PDMAEMA) triblock terpolymers were
synthesized, respectively, and characterized regarding their solubility and gelation behavior.
At pH > 5, P2VP -b-PEO -b-PDMAEMA forms CSC micelles with a P2VP core, and a 56 370 70
pH- as well as thermo-sensitive PDMAEMA corona. This particular structure represents a
hydrogel, whose temperature dependent response can be easily changed from a gel-sol to a
sol-gel transition by increasing the pH from 8 to 9. At pH = 7.5 on the other hand, gel
3-formation is induced by the addition of hexacyanocobaltate(III) ([Co(CN) ] ) ions due to 6
3- electrostatic interactions between the [Co(CN) ] ions and the charged DMAEMA units, 6
causing a physical crosslinking of the CSC micelles. The gel can subsequently be
disintegrated by an exposure to UV-light, based on a UV-catalyzed aquation of the
3- 2-[Co(CN) ] ions to [Co(CN) H O] . 6 5 2
In the last part, a new approach was developed to create a novel type of magnetic field-
responsive hydrogels (ferrogels), in which the nanoparticles are tightly bound to the polymer
matrix. The P2VP block of the previously synthesized P2VP-b-PEO-b-P(GME-co-EGE)
triblock terpolymers was quaternized to a low extent and complexed with negatively charged,
citrate stabilized maghemite (γ-Fe O ) nanoparticles. Using different analytical methods it 2 3
was shown that well-defined CSC hybrid micelles were obtained with cores formed by a
complex of P2VP and 3-4 nanoparticles per core. Concentrated sol