Immortal ring-opening polymerization of ε-caprolactone by a neat magnesium catalyst system: an approach to obtain block and amphiphilic star polymers in situ

Catalyst systems obtained from the inexpensive, ligand-free and commercially available (MgBu2)-Bu-n and alcohols were used for the ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) under mild conditions. The catalytic system of (MgBu2)-Bu-n/Ph2CHOH showed very high activity as compared with the system of (MgBu2)-Bu-n/Ph3COH, which applied a more bulky methanol derivative. Interestingly, in the presence of excess amount of alcohol (Ph2CHOH), i.e., varying the OH-to-Mg ratio in a wide range from 10 : 1 to 800 : 1, the system (MgBu2)-Bu-n/Ph2CHOH still remained highly active, and produced up to 800 polycaprolactone (PCL) chains per Mg center, suggesting a living immortal polymerization mode. The molecular weights of the obtained PCLs are accurately controlled when the ratio of [CL](0)/[Mg](0) changed from 500 to 8000 together with narrow molecular weight distributions. Moreover, diblock PCL-b-PLA copolymers with narrow PDIs have been facilely achieved. Furthermore, the allyl- and propargyl-functionalized diphenylmethanols could be employed as the chain transfer agents (CTA) in this system for in situ construction of allyl-and propargyl-functionalized PCLs that were facilely modified further to PCLs with multiple functionality as building blocks for amphiphilic and topological microstructured PCLs via coupling and click reactions.