| Summary: | Cyclic <i>N</i>-halamines are highly antimicrobial, very stable, and not susceptible to bacterial resistance. A polysiloxane delivery vehicle was synthesized to deliver cyclic imide <i>N</i>-halamine onto cellulose via a benign and universal procedure that does not require a harmful solvent or chemical bonding. In brief, Knoevenagel condensation between barbituric acid and 4-hydroxybenzaldehyde furnished 5-(4-hydroxybenzylidene)pyrimidine-2,4,6-trione, whose phenolic O−H was subsequently reacted with the Si−H of poly(methylhydrosiloxane) (PMHS) via silane alcoholysis. The product of silane alcoholysis was interpenetrated into cellulose in supercritical CO<sub>2</sub> (scCO<sub>2</sub>) at 50 °C, to form a continuous modification layer. The thickness of the modification layer positively correlated with interpenetration pressure in the experimental range of 10 to 28 MPa and reached a maximum value of 76.5 nm, which demonstrates the ability for tunable delivery, to control the loading of the imide N−H bond originating from barbituric acid unit. The imide N−H bonds on cellulose with the thickest modifier were then chlorinated into N−Cl counterparts using <i>tert</i>-butyl hypochlorite, to exert a powerful biocidability, providing ~7 log reductions of both <i>S. aureus</i> and <i>E. coli</i> in 20 min. The stability and rechargeability of the biocidability were both very promising, suggesting that the polysiloxane modifier has a satisfactory chemical structure and interlocks firmly with cellulose via scCO<sub>2</sub> interpenetration.
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