Calixarene Rare Earth Complexes And Scandium Compounds Catalyzed Lactone, Cyclic Carbonate Ring-opening Polymerization Studies

Calixarenes are cyclic oligomers obtained from the condensation of formaldehyde with phenols. They are regarded as the third-generation host molecules after the crown ether and cyclodextrin due to their intrinsic cage-like architectures. The number of phenol units in a calixarene molecule and the substituent group in the opposite site of phenol hydroxyl are based on different synthesis methods. The calixarenes with four, six or eight p-tert-butylphenol units can be easily prepared according to Gutsche's "one-pot synthesis" method. In this paper, novel rare earth calixarene complexes were synthesized via the reaction between rare earth isopropoxides and p-tert-butylcalixarenes. This kind of rare earth calixarene complexes were firstly used as single component catalysts for the ring-opening homo-polymerization of 2,2-dimethyltrimethylene carbonate (DTC) and trimethylene carbonate (TMC) as well as their copolymerization with high activities. Mechanism study shows that the polymerizations of DTC and TMC initiated by rare earth calixarene complex proceed via acyl-oxygen bond cleavage and coordination-insertion mechanism. The reactivity ratios of TMC and DTC are measured to be r_TMC=4.68 and r_DTC=0.163, respectively under 80 ℃ with neodymium p-tert-butylcalix[6]arene complex as catalyst.A series of calixarene derivatives such as p-sulfocalix[6]arene, p-nitrocalix[6]arene and p-acetylcalix[6]arene were synthesized based on removing the p-t-butyl group of p-t-butylcalix[6]arene. Their potential applications in the host-guest chemistry is in progress. Star-shaped amphiphilic polymers with six hydrophilic poly(propylene oxide) (PPO) arms were firstly synthesized via anionic ring-opening polymerization of propylene oxide (PO) from a hydrophobic calix[6]arene core by means of the core-first method. Then, amphiphilic biodegradable star-shaped copolymer has been synthesized via the ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC) initiated by the above star-shaped polymer as macroinitiator, which have potential applications in the field of biodegradable materials and drug delivery micelles.Ring-opening polymerization of ε-caprolactone (CL) and TMC has been firstly achieved by a novel rare earth initiator of scandium tris(2,6-di-tert-butyl-4-methylphenolate) (Sc(OAr)₃) showing high activities under mild conditions. The kinetics equation of Sc(OAr)₃ initiating CLpolymerization could be written as -d[CL]/dt = k·[Sc(OAr)₃]·[CL}. The apparent activationenergy is 58.0 kJ/mol. Mechanism study reveals that the CL and TMC monomer rings are opened via acyl-oxygen bond cleavage leading to a Sc-O active center. The copolymerization of CL and TMC initiated by Sc(OAr)₃ could be well controlled by the reaction conditions to get copolymers with random and various block architectures.