"Uncontrolled" Preparation of Disperse Poly(lactide)-block-poly(styrene)-block-poly(lactide) for Nanopatterning Applications

We report the facile synthesis of well-defined ABA poly(lactide)-block-poly(styrene)-block-poly(lactide) (LSL) triblock copolymers having a disperse poly(styrene) midblock (D= 1.27-2.24). The direct synthesis of telechelic α,-hydroxypoly(styrene) (HO-PS-OH) midblocks was achieved using a commercially available difunctional free radical diazo initiator 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]. Poly(lactide) (PLA) end blocks were subsequently grown from HO-PS-OH macroinitiators via ring-opening transesterification polymerization of (±)-lactide using the most common and prevalent catalyst system available, tin(II) 2-ethylhexanoate. Fourteen LSL triblock copolymers with total molar masses M_n,total = 24-181 kg/mol and PLA volume fractions f_PLA = 0.15-0.68 were synthesized and thoroughly characterized. The self-assembly of symmetric triblocks was analyzed in the bulk using small-angle X-ray scattering and in thin films using grazing incidence small-angle X-ray scattering and atomic force microscopy. We demonstrate both the bulk and thin film self-assembly of LSL disperse triblocks gave well-organized nanostructures with uniform domain sizes suitable for nanopatterning applications.