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 (Lc) closer to the persistence length (Lp). As Lc approaches Lp, 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 Lp (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 ∼ Nv, 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.