Knotted polymers
[1][2][3][4][5][6] Such a structure was synthesized via the controlled polymerization of multivinyl monomers, which was first reported in Dr. Wenxin Wang's research lab.
These multiple intramolecular cyclized/knotted units mimic the characteristics of complex knots found in proteins and DNA which provide some elasticity to these structures.
meaning an average number of monomer units are added to a propagating chain end during each activation/deactivation cycle,[12] The resulting chain growth rate is slowed down to allow sufficient control over the reaction thus greatly increasing the percentage of multi-vinyl monomers in the reaction system (even up to 100 percent (homopolymerization)).
Typically, single chain cyclized/knotted polymers are synthesized by deactivation enhanced ATRP of multivinyl monomers via kinetically controlled strategy.
There are several main reactions during this polymerization process: initiation, activation, deactivation, chain propagation, intramolecular cyclization and intermolecular crosslinking.
In a similar way to normal ATRP, the polymerization is started by initiation to produce a free radical, followed by chain propagation and reversible activation/deactivation equilibrium.
It is worthy to note that due to the multiple reactive sites of the multivinyl monomers, plenty of unreacted pendent vinyl groups are introduced to linear primary polymer chains.
In this way, unlike what happens in free radical polymerization (FRP), the formation of huge polymer chains and large-scale combinations at early reaction stages is avoided.
Therefore, a small instantaneous kinetic chain length is the prerequisite for further manipulation of intramolecular cyclization or intermolecular crosslinking.
Once the monomers are converted to short chains, the intermolecular combination increases and allows the formation of hyperbranched structures with a high density of branching and vinyl functional groups.
[3] Single chain cyclized polymers consist of multiple cyclized rings which afford them some unique properties, including high density, low intrinsic viscosity, low translational friction coefficients, high glass transition temperatures,[13][14] and excellent elasticity of the formed network.
[15] In particular, an abundance of internal space makes the single chain cyclized polymers ideal candidates as efficient cargo-carriers.
The cyclized structure has been proven to reduce cytotoxicity and increase circulation time for drug and gene delivery applications.
