Thermally activated, free-radical initiator-containing polymer compositions comprise a (i) free radical initiator, (ii) free radical crosslinkable polymer, (iii) scorch inhibiting amount and/or a cure-boosting amount of at least one of isocyanate, diiso-cyanate, e.g., MDI, or hydroxyalkyl(meth)acrylate compound, e.g., hydroxyethyl(meth)acrylate, and, optionally, (iv) other scorch retardants and/or cure boosters, e.g., a TEMPO compound, a hindered phenol, alpha-methyl styrene dimer, etc. The free radical initiator can be any thermally activated compound that is relatively unstable and easily breaks into at least two radicals, e.g., a peroxide or azo initiator. The crosslinkable polymer is a thermoplastic and/or elastomeric polymer that can be crosslinked (cured) through the action of a crosslinking agent, e.g., LDPE. The isocyanate, diisocyanate and (meth)acrylate scorch inhibitors and/or cure boosters can be used alone, or in combination with one another, or, optionally, in combination with a TEMPO compound, e.g., 4-hydroxy-TEMPO.