Correlation of Free Radical Copolymerization Behavior and Copolymer Properties with the Strength of π−π Stacking Interactions between Aromatic Fluorocarbons and Aromatic Hydrocarbons: Copolymerization of Styrene and Fluorinated Styrenes at the Two Extreme Levels of Fluorination
journal contributionposted on 13.11.2007 by Coleen Pugh, Chau N. Tang, Marta Paz-Pazos, Om Samtani, Adam H. Dao
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In order to determine if the alternating tendency of styrene with fluorinated styrenes in free radical copolymerizations correlates with the strength and/or extent of π−π stacking interactions between aromatic fluorocarbons and aromatic hydrocarbons, styrene (St) was copolymerized with 2,3,4,5,6-pentafluorostyrene (PFS) and 4-fluorostyrene (4FS) under a variety of conditions. For the copolymerization of styrene with PFS at 25 °C, rStrFS = 0.048 and 0.069 in bulk and toluene, respectively, using tert-butylperoxy pivalate as the initiator. For the copolymerization of styrene with PFS at 70 °C using benzoyl peroxide as the initiator, rStrFS = 0.17 in bulk and rStrFS = 0.14 in toluene. For the copolymerization of styrene with 4FS, rStrFS = 0.69 at 25 °C under redox conditions and rStrFS = 0.62 at 70 °C in bulk. As confirmed by 1H, 13C, and 19F one-dimensional NMR and 1H−13C heteronuclear single quantum coherence and 1H−H nuclear Overhauser effect two-dimensional NMR spectroscopy results, St and 4FS tend to form random copolymers whereas the St-PFS copolymers tend to alternate with the alternating tendency increasing with decreasing temperature. The glass-transition temperatures determined by differential scanning calorimetry of the St-PFS copolymers are elevated relative to their mole-average values, whereas those of the corresponding homopolymer blends and the St-4FS copolymers occur at mole-average values. The water and ethylene glycol contact angles of both the St-PFS and St-4FS copolymer films occur at their mole-average values.