High-Performance Silicone Poly(urea oxamide)-Based Clear Viscoelastic Film via Hierarchical Hydrogen Bonds for Foldable Displays

Clear viscoelastic films (CVFs) play a pivotal role in foldable display modules, requiring a delicate balance of viscoelasticity to meet multifaceted performance demands. Silicone pressure-sensitive adhesives (PSAs) exhibit significant potential for CVF applications due to their low modulus and thermal stability. However, previous studies of CVFs based on silicone polyureas (SPUs), which rely solely on strong hydrogen bonds from isocyanates, show superior elastic recovery but suffer from a suboptimal glass transition temperature (Tg), adhesion strength, and stress relaxation. Although synergistic hydrogen-bonding strategies offer a promising route to reconcile these trade-offs, current methods for introducing weak hydrogen bonds typically require harsh reaction conditions, such as elevated temperatures or catalysts. To overcome these limitations and achieve superior performance, we developed a facile room-temperature strategy to fabricate silicone poly(urea oxamide)s (SPUOs) featuring tunable strong/weak hydrogen bond ratios by adjusting the proportions of α, ω-bis(aminopropyl)polydimethylsiloxanes (A-PDMS), 4,4-methylene-bis(4-cyclohexylisocyanate) (HMDI), and diphenyl oxalate (DPO). Control SPU networks containing only strong hydrogen bonds were synthesized for comparison. Both SPUOs and SPUs were blended with silicone resin tackifier (1:1 mass ratio) to prepare CVFs. Critically, leveraging the hierarchical hydrogen bonds, the SPUO-based CVFs outperformed their SPU counterparts significantly. The optimized CVF-SPUO-6k-2 achieved exceptional properties: a Tg of −46.1 °C, peel force of 7.93 N/25 mm, stress-relaxation ratio of 82.1%, stretchability of 3300%, and creep recovery ratio of 85.2%. Notably, SPUO-based CVFs exhibited outstanding durability, surpassing SPU-based CVFs in a 200,000-cycle folding test. The comprehensive performance of SPUO-based CVFs not only exceeds that of previously reported foldable display-oriented silicone CVFs but also outperforms that of commercial counterparts. This study highlights the strategic introduction of oxamide-derived weak hydrogen bonds within a hierarchical bonding system to effectively decouple conflicting viscoelastic requirements, offering insights into the design of high-performance silicone materials for next-generation foldable electronics.