Sub-5 nm Domains in Ordered Poly(cyclohexylethylene)-block-poly(methyl methacrylate) Block Polymers for Lithography

Abstract

A series of poly(cyclohexylethylene)-block-poly(methyl methacrylate) (PCHE–PMMA) diblock copolymers with varying molar mass (4.9 kg/mol ≤ Mn ≤ 30.6 kg/mol) and narrow molar mass distribution were synthesized through a combination of anionic and atom transfer radical polymerization (ATRP) techniques. Heterogeneous catalytic hydrogenation of α-(hydroxy)polystyrene (PS-OH) yielded α-(hydroxy)poly(cyclohexylethylene) (PCHE-OH) with little loss of hydroxyl functionality. PCHE-OH was reacted with α-bromoisobutyryl bromide (BiBB) to produce an ATRP macroinitiator used for the polymerization of methyl methacrylate. PCHE–PMMA is a glassy, thermally stable material with a large effective segment–segment interaction parameter, χeff = (144.4 ± 6.2)/T – (0.162 ± 0.013), determined by mean-field analysis of order-to-disorder transition temperatures (TODT) measured by dynamic mechanical analysis and differential scanning calorimetry. Ordered lamellar domain pitches (9 ≤ D ≤ 33 nm) were identified by small-angle X-ray scattering from neat BCPs containing 43–52 vol % PCHE (fPCHE). Atomic force microscopy was used to show ∼7.5 nm lamellar features (D = 14.8 nm) which are some of the smallest observed to date. The lowest molar mass sample (Mn = 4.9 kg/mol, fPCHE = 0.46) is characterized by TODT = 173 ± 3 °C and sub-5 nm nanodomains, which together with the sacrificial properties of PMMA and the high overall thermal stability place this material at the forefront of "high-χ" systems for advanced nanopatterning applications.