PCL‐ <i>b</i> ‐PnBA Additives Enable Flexible and Adhesive Photoresists through Microphase Separation

ABSTRACT Photoresists (PRs) are light‐sensitive polymers used in photolithography to fabricate micropatterns on substrates. This study proposes a microphase separation strategy to overcome the flexibility limitations associated with typical acrylic‐based PRs in patterning applications by incorporating poly(ε‐caprolactone)‐ b ‐poly(n‐butyl acrylate) (PCL‐ b ‐PnBA) block copolymer (BCP) additives. A BCP additive was prepared using a dual‐functional initiator, ethyl 2‐hydroxyethyl‐2‐bromoisobutyrate (HEBiB), which can efficiently combine two eco‐friendly polymerization techniques of ring‐opening polymerization (ROP) and supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) (i.e., ROP‐ Є ‐SARA ATRP), allowing for precise control over compositions and compatibility. For synthesizing the PRs, methyl methacrylate (MMA), acrylic acid (AA), and maleic anhydride (MAn) monomers were utilized to afford two randomly copolymerized pre‐polymers, namely, P(MMA‐ r ‐AA) and P(MMA‐ r ‐MAn). Following esterification with allyl bromide and hydroxyethyl methacrylate (HEMA), two PR systems (abbreviated as PMAV and PMMAnMA, respectively) were prepared. By mixing various amounts of the PCL 119 ‐ b ‐PnBA 96 ( M n,NMR = 26,080; Φ PCL = 0.49; Đ = 1.28) and two PRs following UV‐curing reactions, high transmission films can be obtained. Their photopatterning and mechanical properties were improved, owing to the occurrence of microphase separation within the matrix. Microstructure‐containing matrices were characterized by small‐angle X‐ray scattering (SAXS). The compatibility of the BCP additive with commercially available polyimide acrylate (PIA) and polyurethane acrylate (PUA) PRs was examined. Lithographic evaluations showed improved resolution, uniformity, and developer resistance, highlighting the potential of PCL‐ b ‐PnBA‐modified resins for high‐performance photoresists in flexible electronic fabrications and next‐generation lithography.