Kinetics and Modeling of the Radical Polymerization of Acrylic Acid and of Methacrylic Acid in ...

295 Pages·2014·3.93 MB·English

Kinetics and Modeling of the Radical
Polymerization of Acrylic Acid and of
Methacrylic Acid in Aqueous Solution

Dissertation
zur Erlangung des mathematisch-naturwissenschaftlichen Doktorgrades
„Doctor rerum naturalium“
der Georg-August-Universität Göttingen
im Promotionsprogramm Chemie
der Georg-August University School of Science (GAUSS)

vorgelegt von
Nils Friedrich Gunter Wittenberg
aus Hamburg

Göttingen, 2013
Betreuungsausschuss
Prof. Dr. M. Buback, Technische und Makromolekulare Chemie, Institut für Physikalische
Chemie, Georg-August-Universität Göttingen
Prof. Dr. P. Vana, MBA, Makromolekulare Chemie, Institut für Physikalische Chemie,
Georg-August-Universität Göttingen

Mitglieder der Prüfungskommission
Referent: Prof. Dr. M. Buback, Technische und Makromolekulare Chemie, Institut für
Physikalische Chemie, Georg-August-Universität Göttingen
Korreferent: Prof. Dr. P. Vana, MBA, Makromolekulare Chemie, Institut für Physikalische
Chemie, Georg-August-Universität Göttingen

Weitere Mitglieder der Prüfungskommission:
Prof. Dr. G. Echold, Physikalische Chemie fester Körper, Institut für Physikalische Chemie,
Georg-August-Universität Göttingen
Prof. Dr. B. Geil, Biophysikalische Chemie, Institut für Physikalische Chemie, Georg-August-
Universität Göttingen
Jun.-Prof. Dr. R. Mata, Computerchemie und Biochemie,Institut für Physikalische Chemie,
Georg-August-Universität Göttingen
Prof. Dr. A. Wodtke, Physikalische Chemie I / Humboldt-Professur, Institut für Physikalische
Chemie, Georg-August-Universität Göttingen

Tag der mündlichen Prüfung: 24.10.2013
Meiner Familie

Table of Contents

Table of Contents

Abstract .......................................................................................................................... 1
1 Introduction ............................................................................................................ 3
2 Theoretical Background ......................................................................................... 7
2.1 General Aspects of Radical Stability and Reactivity ...................................... 7
2.2 Ideal Polymerization Kinetics of Radical Polymerization .............................. 9
2.2.1 Formation of Radicals and Initiation ..................................................... 10
2.2.2 Propagation ............................................................................................. 13
2.2.3 Termination ............................................................................................ 13
2.2.4 Steady State Kinetics ............................................................................. 14
2.3 Additional Reactions...................................................................................... 15
2.3.1 Transfer Reactions to Small Molecules .................................................. 15
2.3.2 Intermolecular Transfer to Polymer ...................................................... 19
2.3.3 Intramolecular Transfer to Polymer – Backbiting ................................ 20
2.3.1 β-Scission Reaction ................................................................................. 24
2.3.2 Retardation and Inhibition .................................................................... 26
2.4 Influences on Rate Coefficients ..................................................................... 27
2.4.1 Temperature and Pressure ..................................................................... 29
2.4.2 Concentration ......................................................................................... 30
2.4.3 Ionization ................................................................................................ 33
2.4.4 Chain Length .......................................................................................... 38
2.4.5 Conversion .............................................................................................. 45
2.5 Computer Modeling of Polymerizations ........................................................ 51
3 Materials, Experimental Procedures and Data Evaluation ................................ 55
3.1 Chemicals ....................................................................................................... 55
V
Table of Contents

3.1.1 Monomers ............................................................................................... 55
3.1.2 Solvents .................................................................................................. 57
3.1.3 Initiators ................................................................................................. 58
3.1.4 Inhibitors ................................................................................................ 60
3.1.5 Substances used to prepare Buffer Solutions ........................................ 60
3.1.6 Others ..................................................................................................... 61
3.2 Purification Procedures ................................................................................. 63
3.3 NIR ................................................................................................................ 63
3.3.1 Setup ....................................................................................................... 63
3.3.2 Thermally initiated Polymerization in a Cuvette.................................. 64
3.3.3 Photoinitiated Polymerization in a Cuvette .......................................... 65
3.3.4 Degree of Monomer Conversion ............................................................. 65
3.4 EPR ................................................................................................................ 69
3.4.1 Setup ....................................................................................................... 69
3.4.2 Organic Samples .................................................................................... 69
3.4.3 Aqueous Samples ................................................................................... 70
3.4.1 Deconvolution of Spectra ........................................................................ 70
3.4.2 Calibration .............................................................................................. 70
3.5 NMR ............................................................................................................... 71
3.5.1 Quantitative 1H-NMR ............................................................................ 71
3.5.2 Quantitative 13C-NMR ........................................................................... 72
3.5.3 Polymerization in NMR Sample Tube ................................................... 77
3.6 Density Measurement ................................................................................... 78
3.7 Viscosity Measurement ................................................................................. 78
3.7.1 Important Features of Polymer Solutions ............................................. 79
3.7.2 Polymerization in Viscosity Measurement Capillary ............................ 80
3.8 Preparation of Buffer Solutions .................................................................... 80
3.9 SEC ................................................................................................................ 81
VI
Table of Contents

3.10 ESI-MS ........................................................................................................... 81
3.11 HPLC ............................................................................................................. 81
3.12 pH-Meter ........................................................................................................ 82
3.13 High-Temperature Polymerizations.............................................................. 83
3.13.1 Stopped-Flow experiments in High-Pressure Cell ................................. 84
3.13.2 Polymerization in a Tubular Reactor ..................................................... 84
3.14 Other Setups for Polymerization ................................................................... 88
3.14.1 1 L Automated Reactor ........................................................................... 88
3.14.2 Polymerization in a Heating Block ........................................................ 89
3.14.3 Polymerization in a Flask ...................................................................... 89
3.14.4 Polymerization in a Lined Flask ............................................................ 90
3.15 Computer Programs ...................................................................................... 90
3.15.1 Curve Fitting .......................................................................................... 90
3.15.2 Determination of Joint Confidence Regions .......................................... 90
3.15.3 Simulation .............................................................................................. 91
3.16 Error Estimate ............................................................................................... 91
4 Methacrylic Acid ................................................................................................... 95
4.1 Chain-Transfer to 2-Mercaptoethanol .......................................................... 96
4.1.1 Chain Transfer Constants deduced by the Mayo Method ..................... 97
4.1.2 Chain Transfer Constants deduced by the CLD Method .................... 101
4.1.3 Comparison of Mayo and CLD methods .............................................. 103
4.2 Model development for Non-ionized Methacrylic Acid ............................... 106
4.2.1 Modeling Polymerization at Medium initial Monomer Content ......... 110
4.2.2 Modeling Polymerization at Low initial Monomer Content ................ 123
5 Acrylic Acid ......................................................................................................... 141
5.1 Model development for Non-ionized Acrylic Acid ....................................... 142
5.1.1 Initiator Kinetics .................................................................................. 146
5.1.2 Evaluation of ks data ........................................................................... 149
p
VII
Table of Contents

5.1.3 Evaluation of k and Viscosity data ..................................................... 155
t
5.1.4 Determination k by 13C-NMR ............................................................ 159
bb
5.1.5 BA as a Model for AA to estimate C t by EPR .................................. 164
CTA
5.1.6 C s of ME with AA ............................................................................. 175
CTA
5.1.7 Determination of k for AA Macromonomers by 1H-NMR................... 178
p
5.1.8 Modeling Polymerization at 35 to 80 °C .............................................. 181
5.1.9 Modeling Polymerization at High Temperature .................................. 188
5.2 Model Development for Ionized Acrylic Acid .............................................. 197
5.2.1 k of Fully Ionized AA and dependence on Ionic Strength .................. 198
p
5.2.2 k at Full Ionization .............................................................................. 201
t
5.2.3 k at Full Ionization and dependence on Ionic Strength .................... 202
bb
5.2.4 Density .................................................................................................. 204
5.2.5 Modeling the Polymerization of Fully Ionized AA ............................... 208
5.2.6 The dependence of k on the Degree of Ionization ............................... 212
p
5.2.7 The dependence of k on the Degree of Ionization ............................... 214
t
5.2.8 The dependence of k on the Degree of Ionization.............................. 217
bb
5.2.9 β-Scission .............................................................................................. 219
5.2.10 The pK of pAA ..................................................................................... 220
A
5.2.11 Modeling the Polymerization of Partly Ionized AA ............................. 224
6 Acrylamide .......................................................................................................... 231
7 Closing Remarks................................................................................................. 243
Appendix .................................................................................................................... 251
Abbreviations and Symbols ....................................................................................... 263
References .................................................................................................................. 271

VIII
Abstract

Abstract

The radical polymerization of methacrylic acid, acrylic acid and acrylamide in
aqueous solution has been investigated. Detailed kinetic models for both acrylic acid,
AA, and methacrylic acid, MAA, have been developed applying the program
PREDICITM. Good representation of experimental conversion vs. time profiles and
molar mass distributions as well as, in case of AA, the branching level could be
achieved.
The polymerization of MAA has been studied at 35 and 50 °C with focus on the
influence of 2-mercaptoethanol, ME, as chain transfer agent, CTA, on reaction
kinetics. The rate coefficient of transfer to CTA, k , was measured for different
tr,CTA
monomer levels by the Mayo and the chain length distribution procedure. The ratio
of k to the propagation rate coefficient, k , is independent of monomer to water
tr,CTA p
ratio while both rate coefficients increase by approximately one order of magnitude
in passing from bulk to dilute aqueous solution.
It was found that addition of CTA reduces the rate of MAA polymerization by two
effects on k. At negligible monomer conversion, k increases towards higher
t t
content of CTA, because average chain length is reduced by the CTA. Chain-length
dependent termination may be represented by adopting the composite model, which
is a well-established theory to describe chain-length dependency of termination of
macroradicals of identical size. The composite model could be applied to average
chain length. The reduction of k towards higher degrees of monomer conversion
t
(Norrish–Trommsdorff or gel effect) becomes weaker towards higher levels of CTA,
which could be described by correlating the intensity of the gel effect to molar mass
of polymer in solution.
1
Abstract

The polymerization of non-ionized AA in aqueous solution has been studied between
35 and 80 °C with and without ME as CTA. Chain-length dependent termination
was taken into account for modeling as for MAA. During AA polymerization a 1,5-
hydrogen shift (backbiting) takes place transforming the secondary propagating
radical, SPR, into a tertiary midchain radical, MCR, the kinetics of which were
included into the model. The backbiting reaction was quantified via 13C-NMR, the
other MCR reactions were estimated from conversion vs. time profiles. By measuring
the MCR fraction during butyl acrylate, BA, polymerization via electron
paramagnetic resonance, EPR, it could be shown that the transfer of MCRs to CTA is
not an important reaction path. BA can be used as AA model compound so that the
same finding should also apply for AA polymerizations in aqueous phase. Chain
transfer of SPRs of AA was measured by the Mayo method.
The model was extended towards high-temperature polymerization of AA between 90
and 170 °C, where -scission and propagation of macromonomers need to be
considered. Moreover, a model for the polymerization of ionized AA was developed,
which takes numerous dependencies of rate coefficients on ionization and ionic
strength into account, e.g., propagation is reduced by ionization of monomer, but to a
higher extent for lower monomer concentration. Moreover, propagation of ionized
monomer augments towards higher ionic strength. MCRs were found during
acrylamide polymerization via EPR revealing the backbiting reaction to apply for
this monomer as well. Thus, the kinetic scheme is the same as for AA
polymerization.

Parts of this thesis have already been published:
Wittenberg, N. F. G.; Buback, M.; Stach, M.; Lacík, I. Macromol. Chem. Phys. 2012,
213, 2653–2658.
Wittenberg, N. F. G.; Buback, M.; Hutchinson, R. A. Macromol. React. Eng. 2013, 7,
267–276.

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