LIVING FREE RADICAL POLYMERIZATION IN MINIEMULSION

239 Pages·2008·10.64 MB·English

Research Collection
Doctoral Thesis
Living free radical polymerization in miniemulsion
Author(s):
Butté, Alessandro
Publication Date:
2000
Permanent Link:
https://doi.org/10.3929/ethz-a-004101826
Rights / License:
In Copyright - Non-Commercial Use Permitted
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ETH Library
Diss. ETH Nr. 13959
LIVING FREE RADICAL POLYMERIZATION
IN MINIEMULSION
A dissertation submitted to the
SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH (ETHZ)
for the degree of
Doctor of Technical Sciences
Presented by
Alessandro Butté
Dottore in Ingegneria Chimica, Politecnico di Milano,
born July 14, 1972
Citizen of Italy
Accepted on the recommendation of
Prof. Dr. M. Morbidelli, examiner
Prof. Dr. U. Suter, co-examiner
Dr. G. Storti, co-examiner
Zurich 2000
Contents
1 Introduction 1
1.1 From Classical to Living Free Radical Polymerization 1
1.2 Living Free Radical Polymerization in Miniemulsion 6
1.3 Structure of this work 8
2 Fractionation Techniques for the Solution of Molecular Weight Distri¬
bution Equations 11
2.1 Introduction 11
2.2 Kinetic Scheme and Molecular Weight Equations 14
2.3 Model Solution 15
2.3.1 Detailed Solution 16
2.3.2 Overall Method of Moments 16
2.3.3 Partitioning According to the Number of Branches (PANB) .... 17
2.3.4 Numerical Fractionation 18
2.4 Gel Weight Calculation 21
2.5 Results and Discussion 22
2.5.1 Base Cases 22
2.5.2 Bimolecular Termination by Disproportionation 23
2.5.3 Bimolecular Termination by Combination 33
2.6 Conclusions 40
2.7 Nomenclature 42
3 Application of the Kumar-Ramkrishna Discretization Method to MWD
Evaluation in Bulk FRP. 44
3.1 Introduction 44
CONTENTS il
3.2 Kinetic scheme and PBEs 47
3.3 Development of the KR method 48
3.4 Results and Discussion 55
3.4.1 Reconstruction of the CLD 57
3.4.2 Chain transfer to polymer 61
3.4.3 Cross-linking 67
3.4.4 Chain length dependent rate constants 72
3.4.5 Branching distribution 73
3.5 Conclusion 74
3.6 Nomenclature 77
4 Application of the Kumar-Ramkrishna Discretization Method to MWD
Evaluation in Emulsion FRP. 79
4.1 Introduction 79
4.2 Kinetic scheme 82
4.3 Development of the PBEs for Chain Lengths 83
4.4 Development of the Numerical Solution 85
4.5 Illustrative calculations 87
4.5.1 Linear Chain Distributions 88
4.5.2 Branched Chain Distributions 94
4.5.3 Application to a living
system in emulsion 99
4.6 Conclusion 105
4.7 Nomenclature 107
5 Comparative Analysis of the "Living" Free Radical Polymerization in
Homogeneous and Heterogeneous Systems. 109
5.1 Introduction 109
5.2 Kinetic Scheme and Model Equations 110
5.3 Living
process in bulk 112
5.3.1 LFRP by NMLP 112
5.3.2 LFRP by ATRP 122
5.3.3 LFRP by degenerative transfer 122
CONTENTS iii
5.4 Living
process in emulsion 126
5.4.1 The role of particle segregation 126
5.4.2 LFRP by NMLP and ATRP 130
5.4.3 Degenerative Transfer 139
5.4.4 Qualitative comparison with experimental data 142
5.5 Conclusions 144
5.6 Nomenclature 147
6 Bulk LFRP by RAFT 148
6.1 Introduction 148
6.2 Experimental Part 151
6.3 Application to
styrene 151
6.4 Application to other monomers 159
6.5 Influence of different reaction conditions 164
6.6 Formation of block copolymers 169
6.7 Conclusions 170
7 Miniemulsion LFRP by RAFT 172
7.1 Introduction 172
7.2 Previous work 174
7.3 Choice of the living mechanism 176
7.4 Experimental Part 182
7.5 Experimental results 184
7.6 Conclusions 193
A Overall Moment Equations for a FRP in Bulk 196
B Fractionated CLD Equations for a FRP in Bulk 198
C KR Equations for a Miniemulsion Polymerization in the Limiting Values
of the Indexes 200
D Application of KR Method to a Miniemulsion
Polymerization with De¬
generative Transfer 202
CONTENTS iv
E Overall Moment Equations for a Bulk LFRP 205
F
Analytical Polydispersity for Ideal Systems in LFRP 206
G S-E Equations for NMLP without Segregation of the Trapping Agent 208
H Application of the KR Method to a bulk LFRP with RAFT 210
I Formulation of a model for the Trommsdorff effect 212
J Diffusion Model for RAFT Agent in ab-initio Emulsion polymerization 215
Abstract
In this work, the
living free radical polymerization in emulsion has been developed.
The concept of living free radical polymerization (FRP) has been originally introduced by
Moad at the beginning of the '80, but it is only in the second half of the '90 that the first
applications and developments started to appear in the literature. Since then, many appli¬
cations of this technique in homogeneous system have been introduced. On the contrary
of a classical living
system, where all the chains grow simultaneously by starting all at
the beginning, this is impossible with free radical polymerization because of the
presence
of radical recombination, or bimolecular termination. The idea behind each living FRP
is to reversibly trap a large fraction of the chains by means of a chemical species. This
decreases the radical concentration and allows carrying out the
process with a negligi¬
ble amount of terminated chains. It is worth recalling, in fact, that, while bimolecular
termination rate exhibits a second order kinetics with respect to radical concentration,
propagation exhibits only a first order kinetics. Since terminations are only minimized
with respect to the growing chains and not avoided as in a classical living system, this
process is sometimes also referred to as pseudo-living FRP. The drawback of this approach
is clear. The reduction of the radical concentration leads to a corresponding reduction of
the polymerization rate, thus making this
process not attractive for industrial application.
A further
way to obtain a reduction of the number of termination is through the
segregation of the radical chains. This is best exploited in emulsion polymerization, where
the polymer particles provide a natural segregation for the growing radicals. Accordingly,
using living FRP in emulsion polymerization it is no more necessary to reduce the radical
concentration is order to minimize the final number of terminated chains, so to better
approach true living conditions.
In this work, the main aspects of
living FRP are first theoretically analyzed. In par¬
ticular, the attention is first focused on the living FRP in homogeneous systems, in order
to understand which are the main peculiarities and requirements to be fulfilled in order to
better approach living conditions. This is done with respect to all the living mechanisms
developed in the literature for FRP. The same analysis is then repeated for heterogeneous
system, i.e. to emulsion polymerization. At the end of this analysis, it will become appar¬
ent that not all the living mechanisms are suitable to be applied to emulsion in order to
obtain a reduction of the termination without
decreasing at the same time the polymer¬
ization rate. This
analysis represents the most important contribution and improvement
to the common knowledge of this work. This part of the work is preceded by a part where
suitable mathematical models to
correctly account for the molecular weight distribution in
emulsion are developed. This is done in order to select the
proper mathematical approach
to the solution of these problems. Finally, the correctness of all the theoretical
suppo¬
sitions
argued in the first part of the work is experimentally demonstrated both when
with and
dealing homogeneous heterogeneous systems.
Sommario
In questo lavoro é stata sviluppata la polimerizzazione radicalica
"living" in emulsione.
II concetto di polimerizzazione radicalica
"living" (PRL) é stato introdotto originariamente
da Moad all'inizio degli anni 80, ma é stato solo nella seconda meta degli anni 90 che le
prime applicazioni e sviluppi sono iniziati. Da allora, molte applicazioni di questa tecnica
sono state riportate in letteratura per sistemi omogenei. Al contrario dei sistemi living clas-
sici, dove tutte le catene possono crescere insieme partendo all'inizio del processo, questo
é impossibile in una polimerizzazione radicalica
per la presenza della terminazione per
combinazione tra radicah. L'idea che sta dietro la PRL é invece di "intrappolare" in modo
reversibile la
gran parte dei radicah per mezzo di una specie chimica. Questo provoca una
diminuzione della concentrazione di radicali e permette di portare a termine il
processo
con un numéro di terminazioni trascurabile. Vale la pena infatti di ricordare che mentre la
terminazione bimolecolare é del secondo ordine rispetto alia concentrazione di radicali, la
propagazione é solo del primo. Tuttavia, poiché le terminazioni sono solamente minimiz-
zate rispetto al numéro di catene dormienti e non sono eliminate come in un sistema living
classico, questa polimerizzazione é spesso chiamata polimerizzazione radicalica pseudo-
living. L'inconveniente di questa soluzione é chiaro. La riduzione della concentrazione
di radicali porta ad una corrispondente diminuzione della velocitâ di polimerizzazione,
rendendo il
processo poco attraente per sviluppi industriali.
Un modo ulteriore
per ottenere una riduzione del numéro di terminazioni puö essere
ottenuto attraverso la segregazione dei radicali. Questo meccanismo viene utilizzato nelle
polimerizzazioni in emulsione, dove le particelle di polimero contribuiscono a separare i
radicali. Per questo motivo, utilizzando la polimerizzazione living in emulsione non é piü
necessario diminuire la concentrazione di radicali
per ridurre il numéro di terminazioni
cosi da meglio avvicinare condizioni living.
In questo lavoro, i principali aspetti delle polimerizzazioni
living sono stati prima
analizzati da un punto di vista teorico. In particolare, si é prima focalizzata l'attenzione
sulla polimerizzazione in bulk in modo da capirne le peculiaritâ e quali sono i prerequisiti
da soddisfare in modo da ottenere una buona polimerizzazione living. Questo studio é
stato ampliato a tutti i meccanismi living riportati in letteratura per sistemi omogenei.
Quindi, la stessa analisi é stata ripetuta per i sistemi segregati, ovvero per l'emulsione.