P-125 is a heat-reactive, brominated octylphenol-formaldehyde resin that contains methylol groups. P-125 may be used with butyl rubber or other unsaturated elastomers with or without functionality. The presence of functionality allow for a faster cure. P-125 is unique in that it does not require a halogen donor. The use of brominated resins in compounding is especially effective when the rubber may be exposed to heat or repeated use. The rubber will not deteriorate as quickly as rubber crosslinked with other curing agents. P-125 exhibits good processing properties and offers an adequate scorch safety margin in a wide processing range. Rubbers compounded with P-125 exhibit exceptional scorch safety, high temperature stability and excellent dynamic properties. P-125 has a faster cure than P-124 due to a higher bromine content. P-125 has a faint halogen odor, and normal handling precautions should be followed.