Molecular design of high dipole moment polyacrylates: achieving anti-plasticization and high moisture permeability
Junyao Ma1, Yilin Song1, Liang Fang1
1School of Pharmacy, Shenyang Pharmaceutical University, 103 Wenhua Road, Shenyang 110016, Liaoning, China.
Abstract:
This study addresses the challenges of cold flow and adhesion failure caused by plasticization or moisture accumulation by developing a high dipole moment polyacrylate pressure-sensitive adhesive (PSA), designated EO-AA, synthesized via free-radical polymerization using a combination of ethoxy and amide functional groups. EO-AA demonstrated exceptionally high skin peel adhesion strength (10.0 ± 1.1 N/25 mm) even after wetting with artificial sweat, alongside superior anti-plasticization performance, demonstrated by a 0% cold flow rate at 60 °C and under a 10% drug/permeation enhancer load. Rheological analysis revealed that EO-AA possessed rigid properties (G' = 62,555 Pa, G'' = 34,556 Pa) and maintained a stable phase angle (δ = 30°- 32°) during temperature scanning (25 °C - 45 °C). Furthermore, it demonstrated stable creep/recovery behavior after incorporation of 10% drug/permeation enhancer, confirming its exceptional resistance to plasticization. Importantly, EO-AA achieved a high water vapor transmission rate (1488.2 ± 21.1g/m2/day), a high water diffusion rate (2.66×10-10 m2/s), and hydrophilic characteristics (water contact angle θ = 81.5°), effectively preventing moisture accumulation. These properties arose from hydrogen bonding interactions between ethoxy and amide groups, which enabled EO-AA to achieve high dipole moment (8.89 D) and dielectric constant (κEO-AA = 8.78), significant surface space charge distribution (ρ = -9.81 C/m3), and large free volume (Tg = -41.61 °C). As a patch PSA, EO-AA exhibited superior drug miscibility (a 383% increase for drug-loading vs. commercial PSA), promising in vitro drug release/permeation profiles (>80%), and good biocompatibility. These combined properties position EO-AA as an ideal candidate PSA for long-term transdermal patches and wearable-device applications. STATEMENT OF SIGNIFICANCE: Transdermal patches and wearable skin-interfacing devices require pressure-sensitive adhesives that can simultaneously maintain adhesion, resist plasticization, and manage moisture, yet these properties are rarely achieved together. In this study, we developed a high-dipole-moment polyacrylate adhesive, EO-AA, by integrating ethoxy and amide groups. EO-AA showed resistance to cold flow, strong wet-state peel adhesion, high water vapor transmission, improved drug miscibility, and favorable release/permeation performance. These findings present a useful molecular design strategy for adhesive biomaterials that need to balance interfacial adhesion, mechanical stability, and moisture transport during long-term biomedical use.
