A composition comprising: a first anhydride-grafted polyethylene; and a cross-linking agent comprising: a first material selected from the group consisting of minoxidil, melatonin, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, and a derivative of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl; and a second anhydride selected from the group consisting of palmitic anhydride, caprylic anhydride, myristic anhydride, stearic anhydride, arachidic anhydride, capric anhydride, behenic anhydride, an alkyl or alkenyl succinic anhydride, lignoceric anhydride, cerotic anhydride, lauryl anhydride, citric anhydride, acetic anhydride, lactic anhydride, and a mixture of any two or more thereof; wherein: the composition is a master batch configured to cross-link a silane-grafted polyethylene material; and the composition is tin-free; and the derivative of (2,2,2,6,6-tetramethylpiperidin-1-yl)oxyl, when present, is selected from the group consisting of 4-acetamido-TEMPO; 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl; 4-amino-TEMPO; 2-azaadamantane-N-oxyl; 4-(2-bromoacetamido)-TEMPO; 4-carboxy-TEMPO; 4-cyano-TEMPO; 4-hydroxy-TEMPO; 4-hydroxy-TEMPO benzoate; 4-(2-iodoacetamido)-TEMPO; 4-isothiocyanato-TEMPO; 4-maleimido-TEMPO; 4-methoxy-TEMPO; 4-oxo-TEMPO; 4-phosphonooxy-TEMPO hydrate; and TEMPO methacrylate. a first anhydride-grafted polyethylene; and a cross-linking agent comprising: a first material selected from the group consisting of minoxidil, melatonin, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, and a derivative of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl; and a second anhydride selected from the group consisting of palmitic anhydride, caprylic anhydride, myristic anhydride, stearic anhydride, arachidic anhydride, capric anhydride, behenic anhydride, an alkyl or alkenyl succinic anhydride, lignoceric anhydride, cerotic anhydride, lauryl anhydride, citric anhydride, acetic anhydride, lactic anhydride, and a mixture of any two or more thereof; a first material selected from the group consisting of minoxidil, melatonin, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, and a derivative of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl; and a second anhydride selected from the group consisting of palmitic anhydride, caprylic anhydride, myristic anhydride, stearic anhydride, arachidic anhydride, capric anhydride, behenic anhydride, an alkyl or alkenyl succinic anhydride, lignoceric anhydride, cerotic anhydride, lauryl anhydride, citric anhydride, acetic anhydride, lactic anhydride, and a mixture of any two or more thereof; wherein: the composition is a master batch configured to cross-link a silane-grafted polyethylene material; and the composition is tin-free; and the derivative of (2,2,2,6,6-tetramethylpiperidin-1-yl)oxyl, when present, is selected from the group consisting of 4-acetamido-TEMPO; 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl; 4-amino-TEMPO; 2-azaadamantane-N-oxyl; 4-(2-bromoacetamido)-TEMPO; 4-carboxy-TEMPO; 4-cyano-TEMPO; 4-hydroxy-TEMPO; 4-hydroxy-TEMPO benzoate; 4-(2-iodoacetamido)-TEMPO; 4-isothiocyanato-TEMPO; 4-maleimido-TEMPO; 4-methoxy-TEMPO; 4-oxo-TEMPO; 4-phosphonooxy-TEMPO hydrate; and TEMPO methacrylate. the composition is a master batch configured to cross-link a silane-grafted polyethylene material; and the composition is tin-free; and the derivative of (2,2,2,6,6-tetramethylpiperidin-1-yl)oxyl, when present, is selected from the group consisting of 4-acetamido-TEMPO; 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl; 4-amino-TEMPO; 2-azaadamantane-N-oxyl; 4-(2-bromoacetamido)-TEMPO; 4-carboxy-TEMPO; 4-cyano-TEMPO; 4-hydroxy-TEMPO; 4-hydroxy-TEMPO benzoate; 4-(2-iodoacetamido)-TEMPO; 4-isothiocyanato-TEMPO; 4-maleimido-TEMPO; 4-methoxy-TEMPO; 4-oxo-TEMPO; 4-phosphonooxy-TEMPO hydrate; and TEMPO methacrylate.