Synthesis of Macrocyclic Poly(ε-caprolactone) by Intramolecular Cross-Linking of Unsaturated End Groups of Chains Precyclic by the Initiation

摘要

Recent decades have witnessed steadily increasing progress in the area of so-called macromolecular engineering of the main families of synthetic polymers.[1] Ring-shaped copolymers show a unique topology as a result of the absence of any chain end and exhibit distinct properties to their linear counterparts, such as glass-transition temperatures, order-disorder transitions, reduced viscosities, and lower hydrodynamic volumes.[2] In the field of nanotechnology, macrocyclic polyesters are very promising for the production of heterophase materials with smaller size domains.[2] However, only a limited effort has been devoted to the purposeful synthesis of macrocycles and more complex architectures derived from them. The usual route towards macrocycles relies on the unimolecular coupling of the two identical chain ends (X) of linear chains by a difunctional agent, Y-Y.[2] The 1:1 molar ratio of the mutually reactive groups X and Y is of the utmost importance, as is the case for any coupling reaction. Under these conditions, the cyclization yield is expressed by Equation (1), where Cequal is the concentration at which the probability for the intra- and intermolecular reactions to occur is the same [Eq. (2)].[2]