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

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, r_Str_FS = 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, r_Str_FS = 0.17 in bulk and r_Str_FS = 0.14 in toluene. For the copolymerization of styrene with 4FS, r_Str_FS = 0.69 at 25 °C under redox conditions and r_Str_FS = 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.