Biobased Hyperbranched Polyesters as Effective Non-Leachable UV Blockers for Sunscreens

There is a strong societal demand for the development of effective and eco-friendly UV blocking substances for sunscreen applications. In this work, three AB₂-type monomers with 0-2 methoxy groups are synthesized using three corresponding lignin-based monomeric aromatics and a potentially biobased hydandoin. The obtained AB₂-type monomers are conveniently polymerized via conventional bulk polycondensation to yield three UV-active hyperbranched polyesters. The molecular and thermal characteristics of the obtained hyperbranched polyesters are characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), high resolution mass spectrometry (HRMS), gel permeation chromatography (GPC), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The monomers with 0 and 2 methoxy groups and their corresponding polymers provide protection in the UV B region, while the monomer with 1 methoxy group and its corresponding polymer provide protection in both UV A and UV B regions. All the obtained polymers exhibited strong UV absorption with molar extinction coefficient (ε) of ≈15600 to 21000 L mol⁻¹ cm⁻¹. The obtained polymers can be conveniently blended into creams, which exhibited desirable photostability after 4 h of exposure to direct sun light. Finally, these hyperbranched polyesters showed negligible leakage into fresh or salt water during 76 h from their blended creams, which indicated their potentially low environmental impacts as new UV blockers for sunscreens.