Molecular weight control in emulsion polymerization by catalytic chain transfer : aspects of process development Citation for published version (APA): Smeets, N. M. B. (2009). Molecular weight control in emulsion polymerization by catalytic chain transfer : aspects of process development. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR642709 DOI: 10.6100/IR642709 Document status and date: Published: 01/01/2009 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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Smeets and Paul Verspaget Printed at the Universiteitsdrukkerij , Eindhoven University of Technology Molecular Weight Control in Emulsion Polymerization by Catalytic Chain Transfer Aspects of Process Development PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr.ir. C.J. van Duijn, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op vrijdag 3 juli 2009 om 16.00 uur door Niels Mathieu Barbara Smeets geboren te Ermelo Dit proefschrift is goedgekeurd door de promotoren: prof.dr. A.M. van Herk en prof.dr. J. Meuldijk Copromotor: dr.ir. J.P.A. Heuts “Je moet hoog mikken want de pijl daalt onder het vliegen” “Shoot for the moon and even if you miss you’ll land amongst the stars” † Huub Vromans Table of contents TABLE OF CONTENTS i SUMMARY iii SAMENVATTING v SAAMEVATTING vii CHAPTER 1: Introduction 2 Objective 3 Free radical polymerization 5 Emulsion polymerization 14 Process development in emulsion polymerization 20 Catalytic chain transfer 24 Scope of the thesis 36 References 37 CHAPTER 2: Catalyst partitioning in emulsion polymerization 42 Introduction 43 Results and Discussion 44 Conclusions 55 Experimental 56 Appendix 59 References 62 CHAPTER 3: Mass transport limitations in CCT emulsion polymerization 66 Introduction 67 Results and Discussion 69 Conclusions 81 Experimental 81 References 84 CHAPTER 4: Compartmentalization effects in CCT emulsion polymerization 88 Introduction 89 Results and Discussion 91 Conclusions 109 Experimental 109 References 112 i Table of contents CHAPTER 5: Effect of CCT on the emulsion polymerization kinetics 116 Introduction 117 Results and Discussion 118 Conclusions 137 Experimental 137 References 139 CHAPTER 6: Particle nucleation in batch and continuous CCT emulsion polymerization 144 Introduction 145 Results and discussion 147 Batch experiments 148 Continuous experiments in the PSPC 161 Conclusions 168 Experimental 169 References 173 CHAPTER 7: Process development in CCT emulsion polymerization 178 Introduction 179 Partitioning 182 Catalyst deactivation 185 Application in batch emulsion polymerization 192 Application in continuous emulsion polymerization 194 Concluding remarks 198 References 199 ACKNOWLEDGEMENTS 202 CURRICULUM VITAE 206 ii Molecular Weight Control in Emulsion Polymerization by Catalytic Chain Transfer Aspects of Process Development SUMMARY The molecular weight distribution (MWD), amongst others, governs the end use properties of polymeric materials, e.g., coatings. Robust molecular mass control is therefore a key issue in polymer production. Catalytic chain transfer (CCT) has proven to be a robust technique for the control of the MWD. In CCT the radical activity of a propagating polymer chain is transferred via the active cobalt complex to a monomer molecule. The catalytic nature of catalytic chain transfer agents (CCTA), combined with the high activity towards chain transfer allows for the use of very low amounts to achieve proper molecular weight control. This study aims at obtaining a thorough and fundamental understanding of the consequences of the heterogeneity of the emulsion polymerization reaction mixture for the application of CCT in a technical scale. The average molecular weight of the polymer formed can be predicted fairly accurately by the Mayo equation in bulk and solution polymerization, which relates the catalyst activity and the amount of catalytic chain transfer agent to the instantaneous number- average degree of polymerization. For emulsion polymerization an extended Mayo equation was derived which incorporates the effects of catalytic chain transfer agent partitioning. The lower apparent activity of these cobalt complexes observed in emulsion polymerization, when compared to bulk and solution polymerization, can be explained by the effects of partitioning. CCTA partitioning is a crucial parameter governing the performance of CCT in emulsion polymerization. The emulsion polymerization reaction system has some important consequences for the application of CCT. The absolute number of polymer particles in an emulsion polymerization very often exceeds the number of CCTA molecules, which implies that fast CCTA transport is required for proper molecular weight control. Partitioning of the CCTA in emulsion polymerization allows for fast transport via the aqueous phase. However, this is not the only transport mechanism in emulsion polymerization. This transport even occurs for a very sparingly water soluble CCTA, which also shows proper molecular weight control, suggesting that a CCTA (or other very hydrophobic species) iii can be transported by a shuttle mechanism. CCTA transport can be limited by the increasing viscosity of the polymer particles as the weight fraction of polymer is increasing. The high viscosity of the polymer particles can affect the rate of entry and exit of the CCTA. This results in compartmentalization behavior and a discrete distribution of CCTA molecules over the polymer particles, which is represented by a multimodal molecular weight distribution. The efficiency of chain transfer also severely changes throughout the course of an emulsion polymerization, which is governed by the polymer volume fraction in the polymer particles. The application of catalytic chain transfer also affects the course of the emulsion polymerization. Aqueous phase chain transfer, as a consequence of partitioning, affects the entry rate of radicals as well as the chemical nature of those radicals. This results in an extended nucleation period and as a consequence a broader particle size distribution, lower rates of polymerization throughout the entire course of the polymerization and possibly a loss of colloidal stability. Monomeric radicals, originating from the CCT process, can readily desorb from the polymer particles to the aqueous phase. This monomeric radical desoption, i.e. exit, results in a decrease in the rate of polymerization, relatively small polymer particles and a narrow particle size distribution. The reduced rate of entry in combination with the increased rate of exit results in a decrease of the average number of radicals per particle and consequently a decrease in the rate of polymerization. CCT mediated emulsion polymerizations obey Smith-Ewart Case 1 kinetics. Application of CCT in continuous emulsion polymerization was demonstrated in a pulsed sieve plate column (PSPC), which combines low net flow rates with limited axial mixing. For a very sparingly water soluble CCTA batch performance was approximately observed in the PSPC. For more water soluble CCTAs deviation from batch performance were observed. The observed differences could originate from CCTA backmixing. The results presented in this thesis illustrate the potential of CCT as a powerful technique for molecular weight control in emulsion polymerization. The