“Uncontrolled” Preparation of Disperse\nPoly(lactide)-<i>block</i>-poly(styrene)-<i>block</i>-poly(lactide) for Nanopatterning Applications

Abstract

We report the facile\nsynthesis of well-defined ABA poly­(lactide)-<i>block</i>-poly­(styrene)-<i>block</i>-poly­(lactide)\n(LSL) triblock copolymers having a disperse poly­(styrene) midblock\n(<i>Đ</i> = 1.27–2.24). The direct synthesis\nof telechelic α,ω-hydroxy­poly­(styrene) (HO-PS-OH)\nmidblocks was achieved using a commercially available difunctional\nfree radical diazo initiator 2,2′-azobis­[2-methyl-<i>N</i>-(2-hydroxy­ethyl)­propionamide]. Poly­(lactide) (PLA) end blocks\nwere subsequently grown from HO-PS-OH macroinitiators via ring-opening\ntransesterification polymerization of (±)-lactide using the most\ncommon and prevalent catalyst system available, tin­(II) 2-ethylhexanoate.\nFourteen LSL triblock copolymers with total molar masses <i>M</i>_n,total = 24–181 kg/mol and PLA volume fractions <i>f</i>_PLA = 0.15–0.68 were synthesized and\nthoroughly characterized. The self-assembly of symmetric triblocks\nwas analyzed in the bulk using small-angle X-ray scattering and in\nthin films using grazing incidence small-angle X-ray scattering and\natomic force microscopy. We demonstrate both the bulk and thin film\nself-assembly of LSL disperse triblocks gave well-organized nanostructures\nwith uniform domain sizes suitable for nanopatterning applications.