Micro/Nano Structures Constructed Based On Hyperbranched Polymers

Hyperbranched polymers are a novel kind of three dimensional torispherical irregular macromolecules possessing highly branched architectures, many inner cavities and a large amount of terminal functional groups. Due to their unique molecular structures and properties, hyperbranched polymers have become the hot topics in many research fields. Up to now, great progresses have been made in the synthesis, characterization, modification, and application of hyperbranched polymers. On the basis of the previous works, this thesis focuses on the synthesis and modification of hyperbranched polymers through the reversible addition fragmentation chain transfer polymerization or a simple esterification to endow the hyperbranched polymers with new properties. The resulting hyperbranched polymers were applied to construct micro/nano structures, including the self-assembly of hyperbranched polymers into micelles, the construction of microporous films by the breath figure method and biomineralization mediated by hyperbranched polymers. The detailed results were described as follows.1. pH-responsive self-assembly of carboxyl-terminated hyperbranched polymers.The hydroxyl terminal groups of hyperbranched polymers (HBPO-OH) were replaced by carboxyl groups by a simple esterification and the obtained carboxyl-terminated hyperbranched polymers (HBPO-COOH) displayed a pH-responsive self-assembly behavior in solution. HBPO-COOH existed as unimolecular micelles at high pH (pH=12.21) due to the ionization of carboxyl groups, while the polymers aggregated into multimolecular micelles from 10 to 500 nm with the decrease of pH as a result of the partial protonation of the carboxyl groups. The size of the obtained micelles depended strongly on the solution pH, the lower the pH, the bigger the micelles. TEM, DLS, ATR-FT-IR, 1H NMR and AFM measurements substantiated that the multimolecular micelles were formed by the secondary aggregation of unimolecular micelles driven by the hydrogen bonding interaction depending on the solution pH.2. Honeycomb-structured microporous films made from hyperbranched polymers by the breath figure method.Honeycomb-structured microporous films were self-assembled from a new type of multiarm copolymer, hyperbranched poly(3-ethyl-3-oxetanemethanol)-star-polystyrene (HBPO-star-PS). The precursor consisting of an HBPO core and a number of PS arms was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The microporous film was prepared by the evaporation of a chloroform solution of the precursor in a humid atmosphere (the so-called breath figure method). Compared to our former work, the hexagonally packed pores in the film were not interpenetrated and isolated from one another by the walls. The size of the pores could be controlled easily by changing the casting volume of the solution, the molecular weight and the concentration of the polymer, and so forth. The water contact angle on the film surface indicated that the hydrophobicity of the film surface was significantly enhanced as a result of the formation of the porous structure.3. Bioinspired synthesis of calcium carbonate hollow spheres with a nacre-type laminated microstructure.We combine the characters of hyperbranched polymers and the concept of double-hydrophilic block copolymer (DHBC) to design a 3D crystal growth modifier, HPG-COOH. The novel modifier can efficiently control the crystallization of CaCO3 from amorphous nanoparticles, amorphous hollow spheres to vaterite hollow spheres by a nonclassical crystallization process. The obtained vaterite hollow spheres have a special puffy dandelion-like appearance; that is, the shell of the hollow spheres is constructed by platelet-like vaterite mesocrystals, perpendicular to the globe surface. The cross-section of the wall of a vaterite hollow sphere is similar to that of nacres in microstructure, in which platelet-like calcium carbonate mesocrystals pile up with one another. These results reveal the topology effect of the crystal growth modifier on biomineralization and the essential role of the nonclassical crystallization for constructing hierarchical microstructures.4. Control the CaCO3 crystallization in vitro through the molar ratio of the interacting/stabilizing portion (RI / S) in a hyperbranched polymer.Double hydrophilic block copolymers (DHBCs) often consists of one hydrophilic block designed to interact strongly with the appropriate inorganic minerals and surfaces, and another hydrophilic block that does not interact (or only weakly interacts), and mainly promotes solubilization in water. An effective DHBC should be an optimized molecular design combining the advantages of electrostatic particle stabilization with those of steric particle stabilization, so we changed the functionalization efficiency for the carboxyl groups coupled on the surface of HPG and synthesized a series of HPG-COOH with different ratios of the interacting to stabilizing portion (RI/S). We investigated the influence of the RI/S value on the morphology and crystal habit of the obtained CaCO3 by the one-pot precipitation and found that as the RI/S value increased from 0.1 to 0.9, the morphology of CaCO3 changed from pinecone-like, olive-like to highly monodisperse spheres and the phase transition occurred from pure calcite, a mixture of calcite and vaterite to pure vaterite. We also investigated the concentration effect of HPG-COOH with RI/S value 0.3, 0.6, 0.7 on CaCO3 crystallization. For HPG-COOH0.3, as the concentration increased from 0.5 mg/mL to 2 mg/mL, the morphology changed from peanut-like, olive-like to a mixture of sticks and spheres, the vaterite content also increased accordingly with the increasing of the concentration. For HPG-COOH0.6 and HPG-COOH0.7, the increasing of concentration resulted in the decreasing of the size of the highly monodisperse vaterite spheres.