The preparation of t-butyl acrylate, methyl acrylate, and styrene block copolymers by atom transfer radical polymerization: Precursors to amphiphilicand hydrophilic block copolymers and conversion to complex nanostructured materials

Atom transfer radical polymerization conditions with copper(I) bromide/pent amethyldiethylenetriamine (CuBr/PMDETA) as the catalyst system were employe d for the polymerization of tert-butyl acrylate, methyl acrylate, and styre ne to generate well-defined homopolymers, diblock copolymers, and triblock copolymers. Temperature studies indicated that the polymerizations occurred smoothly in bulk at 50 degreesC. The kinetics of tert-butyl acrylate polym erization under these conditions are reported. Well-defined poly(tert-butyl acrylate) (PtBA; polydispersity index = 1.14) and poly(methyl acrylate) (P MA; polydispersity index = 1.03) homopolymers were synthesized and then use d as macroinitiators for the preparation of PtBA-b-PMA and PMA-b-PtBA diblo ck copolymers in bulk at 50 degreesC or in toluene at 60 or 90 degreesC. In toluene, the amount of CuBr/PMDETA relative to the macroinitiator was impo rtant; at least 1 equiv of CuBr/PMDETA was required for complete initiation . Typical block lengths were composed of 100-150 repeat units per segment. A triblock copolymer, composed of PtBA-b-PMA-b-PS (PS = polystyrene), was a lso synthesized with a well-defined composition and a narrow molecular weig ht dispersity. The tert-butyl esters of PtBA-b-PMA and PtBA-b-PMA-b-PS were selectively cleaved to form the amphiphilic block copolymers PAA-b-PMA [PA A = poly(acrylic acid)] and PAA-b-PMA-b-PS, respectively, via reaction with anhydrous trifluoroacetic acid in dichloromethane at room temperature for 3 h. Characterization data are reported from analyses by gel permeation chr omatography; infrared, H-1 NMR, and C-13: NMR spectroscopies; differential scanning calorimetry; and matrix-assisted, laser desorption/ionization time -of-flight mass spectrometry. The assembly of the amphiphilic triblock copo lymer PAA(90)-b-PMA(80)-b-PS98 within an aqueous solution, followed by conv ersion into stable complex nanostructures via crosslinking reactions betwee n the hydrophilic PAA chains comprising the peripheral layers, produced mix tures of spherical and cylindrical topologies. The visualization and size d etermination of the resulting nanostructures were performed by atomic force microscopy, which revealed very interesting segregation phenomena. (C) 200 0 John Wiley & Sons, Inc.