We describe the synthesis of diblock and triblock copolymers by sequential atom transfer radical polymerization of styrene and acetoxymethylstyrene. Contrary to the usual block copolymerization involving isolation of the macroinitiator, a convenient one-pot procedure is developed. This is possible because of the preferential polymerization of acetoxymethylstyrene, even in the presence of residual styrene, as inferred from characterization of the intermediate polystyrenes and the block copolymers by size exclusion chromatography, 1 H NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, and GPEC techniques. The latent acetoxy functionalities in these block copolymers are shown to be easily unmasked to OOH and OBr functionalities, with the potential for block ionomers and dense graft architectures.
High molecular weight dumbbell shaped polymers were prepared by atom transfer radical polymerization (ATRP) to grow branches from repeat units of end blocks of a symmetric triblock copolymer. The triblock copolymer itself was prepared by polymer-polymer coupling of a commercially obtained R,ω-end functionalized polystyrene as central block with end-functionalized poly(chloromethylstyrene) that we synthesized by nitroxide-mediated polymerization. Temperature gradient interaction chromatography (TGIC) enabled the estimation of the terminal hydroxyl functionality of the high molecular weight R,ω-difunctional polystyrene as 75%. Size exclusion chromatography (SEC) and 1 H NMR enabled the determination of molecular weights and verification of the structures of the intermediate and the cleaved products. Size exclusion chromatography coupled with light scattering (SEC-LS) and scanning force microscopy (SFM) were used to confirm that the desired dumbbell architecture was obtained.
Carboxyl-terminated polystyrene was esterified with 2,2,2-trifluoroethanol using a carbodiimide-mediated room temperature reaction, and hydroxyl-terminated polystyrene was fluoro-derivatized with trifluoroacetic anhydride. The soformed fluorine-containing esters were then quantitatively determined with 19F NMR, using α,α,α-trifluorotoluene as secondary standard. This provides a technique for the reliable determination of carboxylic acid and hydroxyl groups in small samples of polymers.
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