Ch ical chemistr Reaction Kinetic Free-Radical polymerizations (a)Initiation k 2R● kill] R●+M knRM· ( fast) The rate-determining step is the formation of the radicals R (b) Propagation M+M,.-pl >oM M+M2·-2>M3 M+Mn_1·-·M The chain of reactions propagates quickly, 2k[ (1799 f is the yield of the initiation step, the fraction of radicals that R successfully initiate a chain 0.3<f<0.87 Free-Radical Polymerizations Physical Chemistry I ⎯⎯→ R• i k 2 R•+M ⎯⎯→RM • a k (a) Initiation (b) Propagation r k [I] = i (fast) 1 2 1 M M M p k + • ⎯⎯→• 2 3 2 M M M p k + • ⎯ ⎯→• n k M Mn M p n + • ⎯⎯⎯→• − − , 1 1  r k [M][ M] p = • The rate-determining step is the formation of the radicals R•. The chain of reactions propagates quickly, f is the yield of the initiation step, the fraction of radicals that R• successfully initiate a chain. 0.3  f  0.8 2 [ ] [ ] fk I dt d M = i • (17.99) Reaction Kinetics