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. 2022 Nov 21;14(22):5040.
doi: 10.3390/polym14225040.

Ascorbic Acid-Modified Silicones: Crosslinking and Antioxidant Delivery

Guanhua Lu  1 , Akop Yepremyen  1 , Khaled Tamim  1 , Yang Chen  1 , Michael A Brook  1
Affiliations

Ascorbic Acid-Modified Silicones: Crosslinking and Antioxidant Delivery

Guanhua Lu et al. Polymers (Basel). .

Abstract

Vitamin C is widely used as an antioxidant in biological systems. The very high density of functional groups makes it challenging to selectively tether this molecule to other moieties. We report that, following protection of the enediol as benzyl ethers, the introduction of an acrylate ester at C1 is straightforward. Ascorbic acid-modified silicones were synthesized via aza-Michael reactions of aminoalkylsilicones with ascorbic acrylate. Viscous oils formed when the amine/acrylate ratios were <1. However, at higher amine/acrylate ratios with pendent silicones, a double reaction occurred to give robust elastomers whose modulus is readily tuned simply by controlling the ascorbic acid amine ratio that leads to crosslinks. Reduction with H2/Pd removed the benzyl ethers and led to increased crosslinking, and either liberated the antioxidant small molecule or produced antioxidant elastomers. These pro-antioxidant elastomers show the power of exploiting natural materials as co-constituents of silicone polymers.

Keywords: antioxidant activity; ascorbic acid; aza-Michael addition; reductive cleavage; silicone elastomer.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Synthesis of (A,B): benzyl protected, acrylated ascorbic acid and conversion to (C): mono or (D): dibutyl amine derivatives, or conversion to (E): pendent, or (F): telechelic ascorbic acid-modified silicone polymers.
Figure 2
Figure 2
(A): monofunctional modifier; (B): chain extender; (C): loop reagent; or, at higher concentrations, (D): crosslinker.
Figure 3
Figure 3
(A): Shore hardness data of benzylated ascorbic acid crosslinked aminoalkylsilicones for samples P22-20, P22-50, and P22-75 (B): DPPH assay results showing antioxidant activity of ascorbic acid and benzylated ascorbic acid control compared with different debenzylated ascorbic acids.
Figure 4
Figure 4
Reductive cleavage of benzyl ethers and the linking ester.
See this image and copyright information in PMC

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