In the polymerization of caprolactone to PCL, tin octanoate is usu used. Does it have adv over alkoxide ?
Answer:
Alkoxides will initiate polymerization of lactones, but the reactive site on the growing chain does not differentiate between monomer and polymer, resulting in high branching and uncontrolled molecular weights with high polydispersity. The rate of reaction is slow as well. Moreover, any water present will cause some hydrolysis and further lowering of the molecular weight.
The stannous alkoxide reactive center is much more selective between lactone carbonyl attack and polyester carbonyl attack, so much so that a ring-opening lactone polymerization using stannous salts are considered "living" in nature. This means that molecular weights and polydispersity are much more easily controlled. The resulting polymer is perfectly linear. The prepartion of block copolymers by sequential monomer addition is also possible in living polymerization systems. Living systems are only possible if the rate of polymerization is much faster than the rate of initiation, and there is an absence of termination reactions.
Yes, alkoxides are extremely reactive and easily give epoxides which are explosive by nature.
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