AbstractPentachlorophenylethers (PCP‐ethers) of cellulose are prepared using cellulosetosylates as intermediates. The products release no measurable quantities of PCP into buffered solutions (pH 4, 7, and 9, resp.). However, the modified cellulose shows no fungicidal effect in agar plate tests with the usually cellulose‐metabolizing fungus,Trichoderma viride. The lack of biological activity is attributed to the stability of the cellulose pentachlorophenyl ether b