Poly(Pentafluorostyrene)-b-Poly(Methacrylic acid) Amphiphilic Block Copolymers via Nitroxide Mediated Polymerization

Title: Poly(Pentafluorostyrene)-b-Poly(Methacrylic acid) Amphiphilic Block Copolymers via Nitroxide Mediated Polymerization
Authors: Kannan, Nirmal Balaji
Date: 2016
Abstract: 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.
URL: http://hdl.handle.net/10393/35294
CollectionThèses, 2011 - // Theses, 2011 -