An Evahation of Molecular Weight Predictions in Emulsion Polymerization Under Conditions of Diffusion Limited Chain Transfer by Tricia Witty A thesis submitted to the Department of Chernical Engineering in conformity with the requirements for the degree of Master of Science (Engineering) Queen's University Kingston, Ontario, Canada April, 2001 Copyright O Tricia Witty, 2001 National Library Bibliothèque nationale ,,,a 1*1 ,,,a du Canada Acquisitions and Acquisitions et Bibliographie Services senices bibliographiques 395 Wellington Street 395, nie Wellington Ottawa ON K1A ON4 Ottawa ON K1A ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, disîribute or sefi reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/fllm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts ftom it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Abstract The rnoIecular weight (MW) and molecular weight distribution @IWO) of polymers are extremely important properties because many end-use properties are a function of the polymer's MW and W.Typically the MW and MWD are measured by on-line GPC, which can take up to 1 hour to generate a reading for a sample. From a control standpoint it would be desirable to be able to generate estimates on the molecular weight on the order a few minutes so that the process can be controlled more effectively. In homogenous polymerization systerns, kinetic rnodets are well estabiished. However, in emulsion system the heterogeneity of the system complicates the process. In this work the validity of integrating a kinetic model, proposed by Gilbert et al. (1995), and a diffusion model describing the transport of a chain-transfer agent (CTA) under conditions of difision limited chain transfer, (Nomura et al., 1994), in order to generate molecular weight predictions bas been investigated. The technology exists to obtain accurate estimates of the required mode1 parameters through techniques that make this approach amenable to on-line application. A series of styrene emulsion polyrnerizations were bedout with varying levels of CTA, surfactant, and initiator. The data collected ivas analyzed by the Malvern Mastersizer 2000 to determine the monomer droplet and polyrner particle size, by gas chromatography (GC) to determine the CTA concentration and by gel pemeation chromatography, (GPC) to determine the molecular weight. The results showed that our approach provides a reasonable estimate of the product's weight average molecular weight and molecular weight distribution, even under conditions of severely diffusion Iimited chain transfer. The results also demonstrate the model's sensitivity to accurate estimates of the monomer droplet size as well as the CTA partition coefficient. The data collected f?om the Malvem Mastersizer 2000 also demonstrates that in out system, monomer droplets do not disappear at the theoretid end of interval II. Ac knowledgments 1 would Iike to thank Dr. M. F. Cunningham for offering me the opportunity to work on this project. The guidance he has given me and the support he has shown has undoubtedly helped me to prepare for the many chaltenges that lie ahead. Thanks must be given to rny fellow members of the Cunningham !ab, Jodi Smith, Karine Tortosa and John Ma for al1 of their help support. Special thanks must also be given to John for the time he has spent helping with everything £iom getting things going in the lab, to interpreting the results, Steve Hogdeson also deserves thanks for the countless hours he has spent helping me with the analytics involved in this project. Without his help this project tvouId not have been possible. 1 would dso like to express my thanks to the Department of Chernical Enguieeruig for the financial support 1 received whiIe working on this project. Finally I would like to thank my fnends and fellow graduate students for providing me with the necessary distractions fiom my research and for making rny extended time at Queen's that rnuch more enjoyable. CHAPTER 1 1. Introduction 1.1 Objectives CHAPTER 2 2. Literature Revîew 2.1 OveMew of Emulsion Polyrnerization 2-2 Polymerizaîïon Kinetics 2.3 DBkion Limited Chain T-er 2.4 Molecular Weiglit Distributions 2.4.1 MWD ModeIs CHAPTER 3 3. Experimental 3.1 Materials 3.1.1 Monomer Purification 3 -2 Ex-perimental Apparatus 3 -3 Experïrnental Procedure 3 -3.1 Monomer Droplet Study Procedure 3 -3.2 Polymerization Procedure 3 -4 Anaiytical Procedures 3 -4.1 Gravimetric Analysis 3.4.2 Gas Chromatography 3 -4.2.1 Equipment 3 -4.2.2 Sample Preparation and Analysis 3.4.3 Gel Permeation Chromatography 3 -4.3.1 Equipment 3 -4.3 -2 GPC Calibration 3 -4.3 -3 Sample Preparation and Analysis 3 -4.3.4 Treatrnent of GPC Dam 3.4.4 Monorner Droplet and Particle Size Distributions 3-4.4.1 Equiprnent 3-4.4.2 Sample Preparation and Analysis CHAPTER 4 4. Particle Size Mcasurements 4.1 Monomer Droplet Analysis 4.1.1 Effect of Surfactant Concentration 4.1.2 Reactor RPM 4.1.3 Malvern RPM 4.1.4 Sampling Location 4.1.5 MingTime in the Reactor 4.1.6 Effect of the Scunple Injection Metliod 4.2 Polymerization Particle Size halysis 4.2.1 Understanding the Results 4.2.2 Polymerization Particle SizeResults 4.3 Summary CHAPTER 5 5. Eaperimentd Results 5,L Conversion Data 5-2 Dodecanethiol Consumption 5.3 Number and Weight Average MoIecular Weight CHAPTER 6 6. Resul ts 6.1 Two-Film Difhision Mode1 6.1.1 Mode1 Parameter Estimation 6-1.2 Comprison of [A,] Values 6.1.3 Twvo-Film DZhsion Mode1 Summaq 6.2 Kinetic Mode1 6.2.1 Muence of Diffiision Limitations of MW 6.2.2 Results 6.2-2-1 Evaluation of Weight Average MoIecuiar Weight Data 6.2.2.2 Cornparison of W(1ogMW) values 6.2-2.3 Filtering of Data to Improve Mode1 Predictions 6.2.2-4 Relative Peak Areas of Particles and Droplets 6.3 Summary CHAPTER 7 7. Conclusions CHAPTER 8 8. Recommendations for future work List of Tables Table 2.1: Parameters contained in the S2 term of Nomura's model-., .............................. 12 Table 3.1: The materials used in the project ............ ...,,,,... ........................................ 18 Table 3.2: A summary of the formuIations that were investigated-.. ............... .. ................21 Table 3 -3: The GC program setting used to analyze the latex samples .............................. 24 Table 3.4: The integration parameters used to detemine the integrated peak areas.. .......... -.-24 Table 3 -5: Molecular weight separation ranges for the GPC colum... ........................... ..25 Table 4.1: A surnmary of the distribution characteristic for systems with varying levels of surfactant concentration.. ...................................................... -31 Table 4.2: A surnmary-. of monomer droplet distributions subject to various rates of agitation.. .................................................................................. 32 TabIe 4-3: A sumrnary of the distribution charactenstics when the agitation speed of the Malvern is varied and the agitation speed of the reactor is constant (500rpm)............................................................... ..33 Table 4-4: A surnmary of the distribution characteristics when sarnples are withdrawn fiom three regions within the reactor .......................................... 34 Table 4.5: A surnmary of the particle size distribution information and its correspondïng conversion reported on a number basis .......................................................................................... -.39 Table 6-1: A surnmary of the constants used in diffùsion mode1 for a n-DDT water system at 50°C.. ............................................................. 37 Table 6.2: A cornparison of the number of particles calculated from Malvern and polymerization rate data for a run containing 3 wt%, 6.658 SDS, and 2.0 g KPS... ...................................................... ..-59 Table 6.3 (a)-(c) Monomer Droplets Observed in the Malvern Data compared to the Monomer Droplets Present in the Equilibnum Swelling Assumptioo ................................................................. 69 Figure 6-9: Comparison of W(1ogMW) for a nui containing 3wt% thiol: 3.0g SDS: 4.0g KPS at increasing conversion intervals .................................. 98 Figure 6.10. Cornparison of filtered and unfiltered data ............................................... 101 Figure 6.1 1: Monomer concentration in the polyrner particles ........................................ 102 Figure 6.12. MW Cornpan-son using Relative Peak Ares .............................................. 103 Figure 6.13. Cornparison of W(1ogMW) using relative peak areas ................................... 105 Figure 6.14. Cornparison of W(1ogMW) using relative peak areas ................................... 108 Nomenclature .l chah transfer agent concentration in the polymer particleç (moVdrn3) critical micelie concentration concentration of monomer in the polymer particles (moUdm3) chah transfer agent merconstant monomer droplet diameter polymer particle diameter