To synthesize cyclic polymers with definite topological structure is always a challenging topic in polymer chemistry. Recently
Xie and coworkers at East China Normal University developed a blocking cyclization route to synthesize cyclic polymers with controllable topology
and synthesized a series of A(B
2
A)
n
(
n
= 1
2
and 3) type cyclic copolymers with well-defined ring size (the repeat unit was 40 − 400) and ring number (1 − 3)
mainly by successive ring-opening metathesis polymerization (ROMP) of alternating addition of di- and monofunctional norbornene monomers in a one-pot process. This blocking cyclization strategy
unlike the traditional ring-closure and ring-expansion techniques
can precede at high monomer concentration (0.02 mol L
−1
) producing very high cyclization efficiency
which has broken through the limitation of the previous two traditional cyclizing routes
and thus can be considered as the third route as a versatile platform to cyclic polymers by commercial Grubbs catalyst and conventional ROMP.