Prohibition Of Interchain Cross-Linking By H-Bonding Grafting Of The Polymer Chain

It is difficult to intramolcularly cross-link the relatively long middle block of the triblock copolymer to obtain pure polymeric single-chain particles at a relatively high concentration (i.e. 2.0 mg/mL). The polymer is prone to intermolecular cross-linking during the cross-linking process. Hence, developing an effective approach to suppress the intermolecular cross-linking of the polymer helps to obtain the high purity polymeric single-chain particles at a relatively high concentration. The triblock copolymer, polystyrene-b-poly(2-vinylpyridine)-bpolyethylene oxide (PS1596-b-P2VP(2895)-b-PEO726, the subscript is the corresponding degree of polymerization), was chosen, in which the polymer has a relatively long P2VP block. The single-chain particles were prepared by intramolecularly crosslinking the middle block using 1,4-dibromobutane in the common solvent, N,N-dimethylforamide. In order to efficiently suppress the interchain cross-linking, the cross-linking reaction conditions were firstly optimized, such as precursor concentration, amount of cross-linking agent, etc, to increase the preparation concentration of high purity single-chain particles to 0.5 mg/mL. Moreover, stearic acids (SA) were added to graft on the P2VP block via hydrogen bonding interaction before crosslinking. During the singlechain cross-linking procedure, the interchain cross-linking can be further suppressed and the preparation concentration of high purity single-chain particles can increase to 2.0 mg/mL. It is because the SA grafting on the P2VP blocks significantly reduced the contact probability between P2VP chains and thereby the occurrence of interchain cross-linking was inhibited. In addition, since the hydrogen bonding interaction is a noncovalent and reversible interaction, the existence of SA grafts will not have a significant influence on the structure and composition of the single-chain particles.