Free radical polymerization method

A radiation polymerizable composition comprising a photoinitiator coated on a substrate is irradiated with a monochromatic radiation. The photoinitiator and the radiation source wavelength are selected so that the extinction coefficient of the photoinitiator at the peak wavelength of the source is above 1000 M ->1>cm ->1>. The photoinitiator absorbs 2% or more of the incident actinic radiation. A substrate is coated with a mixture of a radiation polymerizable composition comprising an ethylenically unsaturated free radically polymerizable monomer, oligomer or their blends and a free radical initiator. The polymerizable composition is polymerized by irradiation with a monochromatic radiation having the appropriate wavelength to activate the photoinitiator. The photoinitiator and the wavelength of the radiation source are selected such that the extinction coefficient of the photoinitiator at the peak wavelength of the source is more than 1000 M ->1>cm ->1>. The photoinitiator absorbs 2% or more of the actinic radiation (emitted by the source) incident on the coating. An independent claim is also included for crosslinking a polymeric coating. A moving substrate is coated with a crosslinkable composition comprising a radiation crosslinkable polymer containing abstractable hydrogen atoms and a radiation activatable crosslinking agent. A monochromatic radiation source comprising one or more lamps, each lamp having an input power of less than 10 W/cm is provided. The radiation has sufficient wavelength to activate the crosslinking agent and the polymer is crosslinked.