An experimental and modeling investigation of nitroxide-mediated radical polymerization (NMRP) of styrene using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as controller is presented. The objective was to examine the effect of temperature, controller to initiator molar ratio, and initiation mode on conversion, molecular weight and polydispersity development, and also to generate a source of reliable experimental data for parameter estimation and further model validation purposes. Polymerizations with a bimolecular initiator (Benzoyl Peroxide; BPO) were carried out at 120 and 130°C, with TEMPO/BPO molar ratios of 0.9 to 1.5. The effects of temperature and TEMPO/BPO ratio on polydispersity, molecular weight averages and conversion (rate) were studied. Results indicate that increasing temperature increases the rate of polymerization while the decrease in molecular weights is only slight. It was also observed that increasing the ratio of TEMPO/BPO decreased both the rate of polymerization and molecular weights. To investigate the contribution of thermal self-initiation in NMRP of styrene, thermal NMRP of styrene with TEMPO in the absence of initiator was carried out at 120 and 130°C. The results were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of BPO. It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide lower polydispersity polystyrene, the polymerization was never as controlled as that obtained by a BPO initiated NMRP. Additional experiments were conducted with a unimolecular initiator and compared to the corresponding bimolecular system with the same level of nitroxide at 120°C, to gain additional insight on the advantages and disadvantages of each system. In addition, the importance of diffusion-controlled (DC) effects on the bimolecular NMRP of styrene was assessed experimentally by creating conditions where DC effects may be present from the outset. The results were corroborated by mathematical modeling and it was concluded that DC-effects are weak in the NMRP of styrene, even in the presence of “worst case scenario” conditions created. Finally, a mathematical (mechanistic) model based on a detailed reaction mechanism for bimolecular NMRP of styrene was presented and the predicted profiles of monomer conversion, molecular weight averages and polydispersity were compared with experimental data. Comparisons suggest that the present understanding of the reaction system is still inconclusive, either because of inaccuracy in values of kinetic rate constants used or because of some possible side reactions taking place in the polymerization system that are not included in the model. This was somewhat surprising, given that papers on controlled radical polymerization, and NMRP in particular, have clearly dominated the scientific polymer literature in the last fifteen years or so.

An experimental and modeling investigation of nitroxide-mediated radical polymerization (NMRP) of styrene using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as controller is presented. The objective was to examine the effect of temperature, controller to initiator molar ratio, and initiation mode on conversion, molecular weight and polydispersity development, and also to generate a source of reliable experimental data for parameter estimation and further model validation purposes. Polymerizations with a bimolecular initiator (Benzoyl Peroxide; BPO) were carried out at 120 and 130°C, with TEMPO/BPO molar ratios of 0.9 to 1.5. The effects of temperature and TEMPO/BPO ratio on polydispersity, molecular weight averages and conversion (rate) were studied. Results indicate that increasing temperature increases the rate of polymerization while the decrease in molecular weights is only slight. It was also observed that increasing the ratio of TEMPO/BPO decreased both the rate of polymerization and molecular weights. To investigate the contribution of thermal self-initiation in NMRP of styrene, thermal NMRP of styrene with TEMPO in the absence of initiator was carried out at 120 and 130°C. The results were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of BPO. It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide lower polydispersity polystyrene, the polymerization was never as controlled as that obtained by a BPO initiated NMRP. Additional experiments were conducted with a unimolecular initiator and compared to the corresponding bimolecular system with the same level of nitroxide at 120°C, to gain additional insight on the advantages and disadvantages of each system. In addition, the importance of diffusion-controlled (DC) effects on the bimolecular NMRP of styrene was assessed experimentally by creating conditions where DC effects may be present from the outset. The results were corroborated by mathematical modeling and it was concluded that DC-effects are weak in the NMRP of styrene, even in the presence of “worst case scenario” conditions created. Finally, a mathematical (mechanistic) model based on a detailed reaction mechanism for bimolecular NMRP of styrene was presented and the predicted profiles of monomer conversion, molecular weight averages and polydispersity were compared with experimental data. Comparisons suggest that the present understanding of the reaction system is still inconclusive, either because of inaccuracy in values of kinetic rate constants used or because of some possible side reactions taking place in the polymerization system that are not included in the model. This was somewhat surprising, given that papers on controlled radical polymerization, and NMRP in particular, have clearly dominated the scientific polymer literature in the last fifteen years or so.

Living radical polymerization has proved to be a powerful tool for the synthesis of polymers as it allows for a high degree of control over the polymer microstructure and the synthesis of tailored molecular architectures. Although it has great potential, its use on an industrial scale is limited due to environmental and economical aspects. Nitroxide mediated polymerization is explored to bring this technology closer to adoption in commercial applications. One of the obstacles encountered using nitroxide mediated polymerization in microemulsion systems is the difficulty in controlling both the particle size and target molecular weight. Due to the nature of the formulation, a decrease in the target molecular weight is coupled to an increase in the particle size. For many applications, it is important to be able to design polymer particles with both specifications independently. Strategies to decouple these two properties and processing conditions required for targeting a range of particle sizes and molecular weights for n butyl acrylate latexes are presented. Furthermore, in an attempt to reduce the large amounts of surfactant typically used in microemulsions, these methods were explored at low surfactant to monomer ratios (0.2 to 0.5 by wt.) in order to reduce the costs associated with excess surfactant and post processing steps for surfactant removal (high surfactant levels also give poor water-resistance in coatings). Stable nanolatexes with particle sizes <40 nm have been obtained by other groups using NMP in microemulsions with SG1 but have done so by using much higher surfactant to monomer ratios (~2.5 by wt.) and at much lower solids content (6 10 wt. %). In this work, molecular weights of 20,000 to 80,000 g∙mol-1 were targeted and stable, n-butyl acrylate microemulsions with particle sizes ranging from 20 120 nm were prepared at a solids content of 20 wt. % using much lower surfactant concentrations. Although numerous studies have shown the effects of process parameters on particle sizes and methods to control the molecular weight, the decoupling of the molecular weight and particle size effect in NMP microemulsions under these conditions has not been done to this extent. In copolymer systems, nitroxide mediated polymerization also provides an efficient method to synthesize well defined block copolymers. Random copolymers are widely used as protective colloids, but the use of block copolymers for these applications has not been well studied. It is unclear what effects do the importance of a narrow molecular weight distribution and purity of block copolymers have on their performance as protective colloids. In order to investigate this, a range of block copolymers with different properties would need to be synthesized for systematic analysis. The direct synthesis of polystyrene b poly(acrylic acid) copolymers of varying lengths and compositions was successful by use of nitroxide mediated polymerization in bulk and solution polymerization. The characterization of these amphiphilic block copolymers was explored by titration and nuclear magnetic resonance spectroscopy. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-09-28 15:43:00.513

Fluoropolymers are a versatile and attractive group of compounds having an interesting mix of properties that make them highly useful for various applications. Because of strong bonding between the carbon and fluorine atom, they exhibit unique physical and chemical properties such as high thermal stability, increased chemical resistance, low refractive index, enhanced inertness towards many solvents and hydro-compounds. These characteristics have led them to be widely used in aerospace, aeronautics, optics, microelectronics, paints and coatings, and engineering structures and as biomaterials. Amphiphilic copolymers possess unique solution and solid-state properties due to their well-defined molecular architecture. These properties arise as the result of covalently combining two thermodynamically different polymer blocks that phase separate on the nanoscale. Amphiphilic copolymers based on a fluoro-monomer will combine the favourable physiochemical properties of the desired fluorine segment in combination with complementary hydrophilic segments. Such fluorinated amphiphilic copolymers are potentially useful for drug delivery vehicles and membrane applications. This project is aimed at making fluorinated amphiphilic block copolymers of hydrophobic 2, 3, 4, 5, 6 –pentafluorostyrene (PFS) and hydrophilic methacrylic acid (MAA). A controlled radical polymerization mechanism, nitroxide mediated polymerization (NMP) using NHS-BlocBuilder as the initiator was employed. The advantage of using NMP is that it facilitates the synthesis of copolymers with well-controlled narrow molecular weight distribution. However, methacrylate homopolymerization by NMP is challenging due to the high dissociation equilibrium constant therefore, the use of PFS as a controlling comonomer was explored. We established that to obtain a controlled copolymerization, a minimum of 70 mol% PFS was required, which is significantly greater than other copolymerization systems such as using as little as 4.5-8 mol% styrene to control the copolymerization of MAA. We surmise that this lack of control is due to the unfavourable reactivity ratios (Appendix I) which favour the addition of MAA rather than PFS (rPFS = 0.012, rMAA = 8.12). However, these unique reactivity ratios suggest that a semi-batch approach can be utilized to synthesize almost pure block copolymers in one pot. Therefore, poly(PFS)–b-(PFS-ran-MAA) block copolymers were synthesized and characterized by a semi batch addition of MAA. While successful, the concentration of irreversibly terminated chains was evident and greater care in reducing these unwanted reactions needs to be addressed.

The basis for this research project is based on the discovery in the previous research that 2,2' ,5-trimethyl-3-( I-phenylethoxy)-4-tert-butyl-3-azahexane, (Styryl- TITNO) is able to control bulk polymerization of styrene at temperature as low as 70°C. The principle objective of this project was to evaluate the feasibility of using Styryl- TITNO to control radical solution and miniemulsion polymerizations at temperatures below 100°C. Styryl- TITNO was shown to effect solution polymerizations of both n-butyl acrylate (BA) and styrene below 100°C. Polymerization temperature was shown to be a crucial parameter for achieving control in Styryl- TITNO -mediated polymerizations. Good control of the number-average molecular weight (Mn) and molecular weight dispersity for the polymerization of BA was observed at 90°C. However, a lower temperature of 70 °C is required for good control of styrene polymerization. Living characteristics of polymer chains were demonstrated by a sequential chain extension of TITNO -terminated PBA with styrene at 90°C to form poly(n-butyl acrylate)- block-poly[(n-butyl acrylate)-co-styrene], [pBA-b-P(BA-co-PS)], block copolymers. An improvement in livingness in these reactions was observed when the second P(BAlstyrene) block was formed at 70°C after the first PBA block was produced at 90°C. Kinetics studies facilitated determination of the activation-deactivation equilibrium constant (K), which for styrene polymerization at 90°C (K = 4.1 x 10.9 mol L-J at 90°C and 3.0 x 10-9 mol L-J at 70 "C) is nearly an order of magnitude higher than that for BA polymerization at the same temperature (K = 8.5 x 10-11 mol L-I). This is the reason why BA polymerization shows better control than styrene polymerization at 90°C. The activation energy (Ea) for thermolysis of Stryl- TITNO is 104.1 kJ mol", which is relatively low compared to the literature values of Ea for various styryl alkoxymines. This explains why Styryl- TITNO is able to effect polymerization at temperatures as low as 70 "C. The studies of Styryl- TITNO-mediated miniemulsion polymerizations at 90 "C indicate that accumulation of free TITNO• in the particles is an issue for use of Styryl- TITNO in miniemulsion polymerizations. The use of L-ascorbic acid (L-AA) and L-ascorbic acid 6-palmitate (L-AAP) as nitroxide scavengers to reduce the level of free TITNO • in the polymerization was investigated. The best result was observed for the polymerization of BA in the presence of 5.35 mol% of L-AAP relative to Styryl- TITNO, which attained 48% conversion after 5 h. The chain extension of isolated TITNO -terminated PBA, TITNO -PBA, was used to examine the livingness of - polymer -chains before the rate of polymerization was severely retarded. The livingness of TITNO-PBA was evidenced by a shift of the staring PBA molecular weight distribution towards higher molecular weight, which provides solid evidence that the majority of polymer chains remained living. Thus, it can be concluded with certainty that the accumulation of free TITNO• was mainly responsible for the suppression of polymerization in miniemulsion polymerizations mediated by Styryl- TITNO.

Non-covalent interactions including nucleobase hydrogen bonding and ionic aggregation were studied in block and end-functional polymers synthesized via living polymerization techniques such as nitroxide mediated polymerization and anionic polymerization. The influence of non-covalent association on the structure/property relationships of these materials were studied in terms of physical properties (tensile, DMA, rheology) as well as morphological studies (AFM, SAXS). Hydrogen bonding, a dynamic interaction with intermediate enthalpies (10-40 kJ/mol) was introduced through complementary heterocyclic DNA nucleobases such as adenine, thymine and uracil. Hydrogen bonding uracil end-functionalized polystyrenes and poly(alkyl acrylate)s were synthesized via nitroxide mediated polymerization from novel uracil-functionalized alkoxyamine unimolecular initiators. Terminal functionalization of poly(alkyl acrylate)s with hydrogen bonding groups increased the melt viscosity, and as expected, the viscosity approached that of nonfunctional analogs as temperature increased. A novel difunctional alkoxyamine, DEPN2, was synthesized and utilized as an efficient initiator in nitroxide-mediated controlled radical polymerization of triblock copolymers. Complementary hydrogen bonding triblock copolymers containing adenine (A) and thymine (T) nucleobase-functionalized outer blocks were synthesized. Hydrogen bonding interactions were observed for blends of the complementary nucleobase-functionalized block copolymers in terms of increased specific viscosity as well as higher scaling exponents for viscosity with solution concentration. Multiple hydrogen bonding interactions were utilized to attach nucleobase-functional quaternary phosphonium ionic guests to complementary adenine-functionalized triblock copolymers. Ionic interactions, which possess stronger interaction energies than hydrogen bonds (~150 kJ/mol) were studied in the context of sulfonated poly(styrene-b-ethylene-co-propylene-b-styrene) block copolymers. Strong ionic interactions resulted in the development of a microphase separated physical network and greater extents for the rubbery plateau in DMA analysis compared to sulfonic acid groups, which exhibit weak hydrogen bonnding interactions. In contrast to the physical networks consisting of sulfonated or hydrogen bonding block copolymers, covalent networks were synthesized using carbon-Michael addition chemistry of acetoacetate functionalized telechelic oligomers to diacrylate Michael acceptors. The thermomechanical properties of the networks based on poly(propylene glycol) oligomers were analyzed with respect to the molecular weight between crosslink points (Mc) and the critical molecular weight for entanglement (Me). / Ph. D.

Polystyrene (PS) is an important commodity polymer. In its most commonly used form, PS is a high molecular weight linear polymer, typically produced through free-radical polymerization, which is a well understood and robust process. This process produces a high molecular weight, clear thermoplastic that is hard, rigid and has good thermal and melt flow properties for use in moldings, extrusions and films. However, polystyrene produced through the free radical process has a very broad molecular weight distribution, which can lead to poor performance in some applications. To this end, nitroxide-mediated radical polymerization (NMRP) can synthesize materials with a much more consistently defined molecular architecture as well as relatively low polydispersity than other methods. NMRP involves radical polymerization in the presence of a nitroxide mediator. This mediator is usually of the form of a stable radical which can bind to and disable the growing polymer chain. This will “tie up” some of the free radicals forming a dynamic equilibrium between active and dormant species, through a reversible coupling process. NMRP can be conducted through one of two different processes: (1) The bimolecular process, which can be initiated with a conventional peroxide initiator (i.e. BPO) but in the presence of a stable nitroxide radical (i.e. TEMPO), which is a stable radical that can reversibly bind with the growing polymer radical chain, and (2) The unimolecular process, where nitroxyl ether is introduced to the system, which then degrades to create both the initiator and mediator radicals. Based on previous research in the group, which included experimental investigations with both unimolecular and bimolecular NMRP under various conditions, it was possible to build on an earlier model and come up with an improved detailed mechanistic model. Additionally, it was seen that certain parameters in the model had little impact on the overall model performance, which suggested that their removal would be appropriate, also serving to reduce the complexity of the model. Comparisons of model predictions with experimental data both from within the group and the general literature were performed and trends verified. Further work was done on the development of an additionally reduced model, and on the testing of these different levels of model complexity with data. The aim of this analysis was to develop a model to capture the key process responses in a simple and easy to implement manner with comparable accuracy to the complete models. Due to its lower complexity, this substantially reduced model would me a much likelier candidate for use in on-line applications. Application of these different model levels to the model-based D-optimal design of experiments was then pursued, with results compared to those generated by a parallel Bayesian design project conducted within the group. Additional work was done using a different optimality criterion, targeted at reducing the amount of parameter correlation that may be seen in D-optimal designs. Finally, conclusions and recommendations for future work were made, including a detailed explanation of how a model similar to the ones described in this paper could be used in the optimal selection of sensors and design of experiments.

Significant advances have been made in the understanding of living/controlled radical polymerization processes since their discovery in the early 1990’s. These processes enable an unprecedented degree of control over polymer architecture that was previously not possible using conventional radical polymerization processes, and this has made possible the synthesis of many new and interesting materials. However, there has been only limited success in commercializing these new methods. Recently there has been increased focus on the development of more industrially viable processes. Dispersed aqueous phase reactions have received much attention because these water-based processes have several technical, economic, and environmental benefits over the more common solution and bulk reactions that were originally developed. Likewise, there has been some investigation of using continuous reactors that have potential technical and economic benefits over the more commonly employed batch reactors. This thesis presents an in-depth study that combines the three aforementioned technologies: living/controlled radical polymerization, dispersed phase aqueous reactions, and continuous reactors. Specifically, the system of interest is a nitroxide-mediated miniemulsion polymerization reaction in a continuous tubular reactor to produce polymer latex. Design of the continuous tubular reactor is discussed in some detail with a focus on specific technical challenges that were faced in building a functional apparatus for this system. Scoping experiments are described which identified a significant effect of temperature ramping rate that is critical to understand when moving to larger scale reactors for this system. The unexpected phenomenon of room temperature polymerization initiated by ascorbic acid is also described. There is demonstration for the first time that bulk and miniemulsion polymers can be produced in a tubular reactor under controlled nitroxide-mediated polymerization conditions, and copolymers can be produced. A detailed residence time distribution study for the tubular reactor is also shown, and several interesting phenomena are discussed that have implications on the practical operating conditions of the tubular reactor. This particular study makes it clear that one should experimentally verify the residence time distribution within a continuous system with the reactants of interest, and that model systems may not give an accurate picture of the real system. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-12-20 12:00:37.974

Polystyrene (PS) is an important commodity polymer. In its most commonly used form, PS is a high molecular weight linear polymer, typically produced through free-radical polymerization, which is a well understood and robust process. This process produces a high molecular weight, clear thermoplastic that is hard, rigid and has good thermal and melt flow properties for use in moldings, extrusions and films. However, polystyrene produced through the free radical process has a very broad molecular weight distribution, which can lead to poor performance in some applications. To this end, nitroxide-mediated radical polymerization (NMRP) can synthesize materials with a much more consistently defined molecular architecture as well as relatively low polydispersity than other methods. NMRP involves radical polymerization in the presence of a nitroxide mediator. This mediator is usually of the form of a stable radical which can bind to and disable the growing polymer chain. This will “tie up” some of the free radicals forming a dynamic equilibrium between active and dormant species, through a reversible coupling process. NMRP can be conducted through one of two different processes: (1) The bimolecular process, which can be initiated with a conventional peroxide initiator (i.e. BPO) but in the presence of a stable nitroxide radical (i.e. TEMPO), which is a stable radical that can reversibly bind with the growing polymer radical chain, and (2) The unimolecular process, where nitroxyl ether is introduced to the system, which then degrades to create both the initiator and mediator radicals. Based on previous research in the group, which included experimental investigations with both unimolecular and bimolecular NMRP under various conditions, it was possible to build on an earlier model and come up with an improved detailed mechanistic model. Additionally, it was seen that certain parameters in the model had little impact on the overall model performance, which suggested that their removal would be appropriate, also serving to reduce the complexity of the model. Comparisons of model predictions with experimental data both from within the group and the general literature were performed and trends verified. Further work was done on the development of an additionally reduced model, and on the testing of these different levels of model complexity with data. The aim of this analysis was to develop a model to capture the key process responses in a simple and easy to implement manner with comparable accuracy to the complete models. Due to its lower complexity, this substantially reduced model would me a much likelier candidate for use in on-line applications. Application of these different model levels to the model-based D-optimal design of experiments was then pursued, with results compared to those generated by a parallel Bayesian design project conducted within the group. Additional work was done using a different optimality criterion, targeted at reducing the amount of parameter correlation that may be seen in D-optimal designs. Finally, conclusions and recommendations for future work were made, including a detailed explanation of how a model similar to the ones described in this paper could be used in the optimal selection of sensors and design of experiments.

Use of a mixed triisobutylaluminum/1,1-diphenylhexyllithium intiator enabled the anionic polymerization of methyl methacrylate at room temperature, resulting in narrow molecular weight distributions and syndiorich structures. Polymerizations were controlled above Al:Li = 2, and control significantly decreased at elevated temperatures above 25 °C. A significant increase in Tg with increasing control of syndiotacticity demonstrated the ability to tailor polymer properties using this technique. Analysis with MALDI-TOF/TOF spectroscopy revealed the dominance of a back-biting side reaction at elevated temperatures. Hydroxy-functional random and block copolymers of n-butyl acrylate (nBA) and 2-hydroxyethyl acrylate were synthesized using nitroxide mediated polymerization. Controlled polymerization was demonstrated, resulting in narrow polydispersities and linear molecular weight vs. conversion plots. In situ FTIR spectroscopy monitored the polymerizations and revealed pseudo first order rate kinetics for random copolymerizations. Protection of the hydroxyl using trimethylsilyl chloride alleviated isolation issues of amphiphilic polymer products. For the first time zwitterion-containing copolymers were electrospun to form nanoscale fibers with diameters as low as 100 nm. Free radical copolymerization of nBA and sulfobetaine methacrylamide produced zwitterionic copolymers with 6-13 mol % betaine. Dynamic mechanical analysis revealed a rubbery plateau and biphasic morphology similar to ionomers. Electrospinning from chloroform/ethanol solutions (80/20 v/v) at 2-7 wt % afforded polymeric fibers at viscosities below 0.02 Pa™s, which is the lowest viscosity observed for fiber formation in our laboratories. We hypothesized that intermolecular interactions rather than chain entanglements dominated the electrospinning process. Solution rheology of zwitterionic copolymers containing 6 and 9 mol % sulfobetaine methacrylate functionality revealed two concentration regimes with a boundary at ~1.5 – 2.0 wt %, regardless of molecular weight. This transition occurred at an order of magnitude lower specific viscosity than the entanglement concentration (Ce) for poly(nBA), and correlated to the onset of fiber formation in electrospinning. Comparison to existing models for polymer solution dynamics showed closest agreement to Rubinstein's theory for associating polymers, in support of our hypothesis that zwitterionic interactions dominate solution dynamics. The effect of ionic liquid (IL) uptake on mechanical properties and morphology of zwitterionic copolymers was explored using 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES). Dynamic mechanical analysis and impedance spectroscopy revealed a significant change in properties above a critical uptake of ~10 wt % IL. X-ray scattering revealed a significant swelling of the ionic domains at 15 wt % IL, with a 0.3 nm-1 shift in the ionomer peak to lower scattering vector. Results indicated the water-miscible IL preferentially swelled ionic domains of zwitterionic copolymers. / Ph. D.