Synthesis and characterization of polycarbonate-containing all-organic High-χ block copolymers for directed self-assembly

Abstract

To extend the scaling beyond the most widely used block copolymer (BCP), poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA), a new organic high-χ BCP based was developed. Polystyrene-b-polytrimethylene carbonate (PS-b-PTMC) BCP was synthesized using ring opening polymerization (ROP) of trimethylene carbonate from hydroxy-functional polystyrene (PS-OH) with diazabicyclo[5.4.0]undec-7-ene (DBU) as the base catalyst. The resulting BCP was characterized by 1H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) to confirm the complete chain extension of the polystyrene macroinitiator. For the DBU catalyzed BCP, the GPC trace revealed a trimodal distribution indicating the presence of coupling product and homo-PTMC impurity. Using purification techniques, homo-PTMC impurity was isolated to afford purified BCP. Thin-film morphologies of the non-purified and the purified BCPs on poly(methyl methacrylate) (PMMA) coated substrates followed by short thermal annealing were characterized using atomic force microscopy (AFM) analysis. The non-purified BCP showed island morphology with a step-height of 17 nm whereas the purified PS-b-PTMC showed a flat film with parallel cylinders of 16.4 nm pitch row-to-row distance. The ability for the PS-b-PTMC to self-assemble below 20-nm pitch resolution confirms the high interaction parameter, χ, between the PS and PTMC blocks and is a promising candidate as a high-χ BCP for directed self-assembly (DSA) application.