Coil- to Worm-like Transition for Short Side chain Polymers: Impact on the Design of High-χ, Low-N Block Copolymers for High-Resolution Patterning

Abstract

As block copolymers (BCPs) are designed to self-assemble with smaller feature sizes, the requirement for a lower degree of polymerization (N) inevitably brings the contour length (L_c) closer to the persistence length (L_p). As L_c approaches L_p, even relatively short side groups on chain segments can drive the system away from flexible chain behavior toward worm-like and rod-like conformations. Here, we demonstrate that side groups consisting of only 8–12 carbon units induce worm-like chain (WLC) behavior at length scales relevant to 16–28 nm BCP domain spacings (L₀). We investigate thiol-modified poly(glycidyl methacrylate) (PGMA), a versatile platform for post-polymerization functionalization that has played a key role in the development of BCPs with A-b-(B-r-C) architectures for applications in directed self-assembly. Small-angle neutron scattering from PGMA-modified 4-methoxythiophenol (4MTP), trifluoroethanethiol (TFET), or mixtures of the thiols reveals rod-like scaling in the high-q regime and a relatively large L_p (2–3 nm), consistent with WLC behavior over block lengths relevant to these systems. All-atom simulation further corroborates reduced conformational flexibility with slower relaxation dynamics for the thiol-modified PGMA. These results provide fundamental insights into the onset of deviations in behavior compared to coil-coil BCPs as a function of N and side group lengths, including changes in scaling, with v > 2/3 for L₀ ∼ N^v, and narrower interfacial widths, and reveal chain stiffness as an additional design parameter for high-χ, low-N block copolymers in high-resolution patterning applications.