Ketopinyl peroxide (KPO) was synthesized by the reaction of ketopinyl chloride with Na2O2 in the presence of 15-crown-5.The reaction of KPO with Cr(II) formed radicals

anions and Cr(III)s. The radicals existed as “free” radicals and in the form complexes which consisted of radicals

anions and Cr(III)s. After aging of the redox system

the “free” radicals were terminated by the coupling reaction

but radicals in the complexes were relatively stable due to the β-keto group and steric effect

and initiated methyl (meth).acrylae to polymerize with "living"characteristics

when polymerization was carried out bellow 30℃.Other monomers

vinyl acetate

hydroxyethylene methacrylate and acrylic acid (AA) could be polymerized using this initiator system and crosslinked PAA was obtained in several minutes.The initiator efficiency (f) of the aged KPO and Cr2+ was intensively affected by the aging temperature

and varied from 30% at 0℃ to 5℃ at 20℃.