Anionic Synthesis, Modification, and Characterization of ABC Triblock Copolymers

Abstract

ABC triblock copolymers of poly(styrene)-b-poly(tert-butyl methacrylate)-b-poly(methyl methacrylate) (PS-PtBMA-PMMA) were anionically synthesized by sequential addition of styrene, tert-butyl methacrylate, and methyl methacrylate, respectively. Characterization of these triblock copolymers was done using nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and transmission electron microscopy (TEM). The gel permeation chromatograms were found to be somewhat broad (Mw/Mn ≈ 1.2) due to partial quenching of polystyryl anion upon switching to tert-butyl methacrylate. The actual polydispersity of these triblocks, not including PS homopolymer, was determined to be less than 1.1. TEM micrographs of these ABC triblocks indicated that the morphology is essentially lamellar. The long-range order of the microstructure, however, seems to decrease with decreasing spacer block length. The tert-butyl methacrylate middle block of these PS-PtBuMA-PMMA triblocks could be selectively modified to anhydride and carboxylic acid functionalities in the presence of the PMMA block. Thermal treatment of these ABC triblocks (230 °C for 30 min) quantitatively transformed the PtBMA middle block into poly(methacrylic anhydride) (PMAN). The PMAN block could then be quantitatively hydrolyzed to poly(methacrylic acid) (PMAA) under mild conditions (NaHCO3, 70 °C, 1 h).