Synthesis And Applications Of Novel Dendritic Polymers

Dendritic polymers have got much attention owing to their unique topology and features. And dendrimers and hyperbranched polymers are two major subclasses of dendritic polymers.Discovering novel and facile methods to prepare polymers with different topologies has become one of the focuses of polymer chemistry due to that the topology has significant influence on polymer properties. Owing to their compact structure and numerous functional groups, dendrimers have wide potential applications in many fields. Compared with dendrimers, dendritic-linear-dendritic copolymers have some special properties because the linear block can endow them some unique features, leading to numerous applications in delivery of gene and drug. Based on these dendritic-linear-dendritic copolymers reported, synthetic strategies can be generally divided into three categories. (1) Coupling method, linear polymer chain reacts with reactive dendron, which requires strict reaction conditions, and the uniform dendritic-linear-dendritic copolymer can’t be obtained because some unreacted dendrons remain in the product. (2) Macro reagent method, two dendrons are connected by a small molecular initiator or chain transfer reagent to form macro reagents, and the macro reagents were used in the controlled radical polymerizations to form dendritic-linear-dendritic copolymers. However, the formation of uniform macro reagent is very difficult because it is very hard to remove unreacted dendrons. (3) Divergent method, the linear polymer block with the dendritic blocks at both ends are prepared through iterative multistep reactions. We combined reversible addition-fragmentation chain transfer (RAFT) polymerization, and divergent method for the synthesis of temperature and pH-responsive dendritic-linear-dendritic PAMAM-PNIPAM-PAMAM. Due to each step having very high efficiency, the resulting PAMAM-PNIPAM-PAMAM is uniform.Responding to the stimulus changes of the environment, many tailored macromolecules synthesized by nature that can both assemble and disassemble. Though lots of macromolecules have been synthesized for a broad range of applications, few of them can self-degrade. In order to meet the demands of biomaterials, many macromolecules can self-degrade have been synthesized in recent years. We introduce a novel polymer that can not only self-immolate but also can self-cross-link via responding to the changes of the environment. This polymer bears disulfide bonds in the backbone,2-((2-nitrobenzyl)thio)ethanol and dimethylamine terminals. The dimethylamine unit is pH-and temperature-responsive. So the dimethylamine side unit can be used as the trigger to self-assembly. With the increased, the disulfide bonds in the backbone can exchange with each other which can cross-link the polymer. And the2-((2-nitrobenzyl)thio)ethanol units can in situ release mercaptoethanol via UV irradiation, which can break the disulfide bonds.