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Nitroxide-mediated Controlled Degradation of Polypropylene <br /> Controlled-rheology polypropylene resins (CRPP) have been produced industrially for years using reactive extrusion processes employing peroxides as free radical initiators. The molecular weight characteristics of CRPP materials can be tailor-made depending on the final application in a very efficient and economic manner. <br /><br /> A PP-based nitroxide (NOR) with the trade name Irgatec CR76 has been recently developed by CIBA Chemicals, as a source of radicals and it is currently being evaluated for the production of CRPP. NORs are well-known as powerful stabilizers to protect plastics from the negative influence of light and heat, and easy in handling during processing. Preliminary experimental results exhibit a qualitative difference between Irgatec CR76 and other commonly used peroxides. <br /><br /> The purpose of this research work is to evaluate this new material as a potential replacement of commonly used peroxides in the production of CRPP. CRPP will be produced by reactive processing using varying amounts of Irgatec CR76 and the rheological properties of the materials produced will be investigated. By comparing results with Irgatec CR76 to those from other typical initiators, the effectiveness of Irgatec CR76 as an initiator will also be assessed. <br /><br /> The results of this research will have an impact not only on the potential extension of uses of the specific PP-based NOR (Irgatec CR76), but also, more generally, on the wider application of additives during degradation of PP. Potentially new materials can be produced with enhanced heat and light protection along with the other benefits inherent to standard CRPP.

Nitroxide-mediated Controlled Degradation of Polypropylene <br /> Controlled-rheology polypropylene resins (CRPP) have been produced industrially for years using reactive extrusion processes employing peroxides as free radical initiators. The molecular weight characteristics of CRPP materials can be tailor-made depending on the final application in a very efficient and economic manner. <br /><br /> A PP-based nitroxide (NOR) with the trade name Irgatec CR76 has been recently developed by CIBA Chemicals, as a source of radicals and it is currently being evaluated for the production of CRPP. NORs are well-known as powerful stabilizers to protect plastics from the negative influence of light and heat, and easy in handling during processing. Preliminary experimental results exhibit a qualitative difference between Irgatec CR76 and other commonly used peroxides. <br /><br /> The purpose of this research work is to evaluate this new material as a potential replacement of commonly used peroxides in the production of CRPP. CRPP will be produced by reactive processing using varying amounts of Irgatec CR76 and the rheological properties of the materials produced will be investigated. By comparing results with Irgatec CR76 to those from other typical initiators, the effectiveness of Irgatec CR76 as an initiator will also be assessed. <br /><br /> The results of this research will have an impact not only on the potential extension of uses of the specific PP-based NOR (Irgatec CR76), but also, more generally, on the wider application of additives during degradation of PP. Potentially new materials can be produced with enhanced heat and light protection along with the other benefits inherent to standard CRPP.

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.

This thesis presents the results of a study on the kinetics of nitroxide-mediated radical polymerization of styrene with a unimolecular initiator. The primary objective was to obtain a more comprehensive understanding of how a unimolecular-initiating system controls the polymerization process and to clarify the effects of various reaction parameters. Previous work in this field has met with some difficulties in the initiator synthesis, such as low yield and inconsistency of molecular weight. These problems were overcome by adjusting reaction conditions and procedures. Better yields of initiator with consistent molecular weight were produced by the improved methods. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and the initiator molecular weight on polymerization rate, molecular weight and polydispersity. Results indicated that increasing the initiator concentration had no effect on polymerization rate at low conversion, but led to lower polymerization rate at high conversion; higher initiator concentration led to lower molecular weight of the resulting polymer. It was also found that temperature significantly increased the polymerization rate, yet had no effect on number-average molecular weight, Mn, at low conversion, while it caused a plateau at high conversion levels; there was no effect on weight-average molecular weight, Mw, through the whole conversion range. In addition, increasing initiator molecular weight was found to have no effect on either polymerization rate or molecular weight. The experimental molecular weights of the unimolecular system were compared to theoretical molecular weights based on ideal controlled radical polymerization (CRP). The results were found to be close to the theoretical values. This confirmed the advantages of the unimolecular system, namely, the degree of control over molecular weight was nearly ideal (for certain conditions); and molecular weights could thus be predicted by simply following general rules relating to CRP mechanisms.

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.

This thesis presents the results of a study on the kinetics of nitroxide-mediated radical polymerization of styrene with a unimolecular initiator. The primary objective was to obtain a more comprehensive understanding of how a unimolecular-initiating system controls the polymerization process and to clarify the effects of various reaction parameters. Previous work in this field has met with some difficulties in the initiator synthesis, such as low yield and inconsistency of molecular weight. These problems were overcome by adjusting reaction conditions and procedures. Better yields of initiator with consistent molecular weight were produced by the improved methods. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and the initiator molecular weight on polymerization rate, molecular weight and polydispersity. Results indicated that increasing the initiator concentration had no effect on polymerization rate at low conversion, but led to lower polymerization rate at high conversion; higher initiator concentration led to lower molecular weight of the resulting polymer. It was also found that temperature significantly increased the polymerization rate, yet had no effect on number-average molecular weight, Mn, at low conversion, while it caused a plateau at high conversion levels; there was no effect on weight-average molecular weight, Mw, through the whole conversion range. In addition, increasing initiator molecular weight was found to have no effect on either polymerization rate or molecular weight. The experimental molecular weights of the unimolecular system were compared to theoretical molecular weights based on ideal controlled radical polymerization (CRP). The results were found to be close to the theoretical values. This confirmed the advantages of the unimolecular system, namely, the degree of control over molecular weight was nearly ideal (for certain conditions); and molecular weights could thus be predicted by simply following general rules relating to CRP mechanisms.

Nitroxide radical groups grafted on silica have been synthesized. The catalytic oxidation of alcohols to aldehydes and ketones using the nitroxide radical groups as a catalyst was also investigated. The results of scanning electron microscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy confirmed that the nitroxide radical groups are successfully grafted onto silica. The yield of the catalytic oxidation using the catalysts is higher than 99%. The catalysts are easily recovered. Furthermore, the reused catalysts still keep high performance in the catalytic oxidation.

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.