Well-Defined Functional Polymer Network With Precise Macromolecular Structure Design And Synthesis

Functional polymer networks (hydrogels) have attracted wide spread attention as novel biomaterials due to their soft and variety functions. Many functional polymer networks such as amphiphilic polymer co-network (APCN), temperature responsive polymer network, pH responsive polymer network, electric field responsive polymer network, light responsive polymer network, magnetic polymer network and multi-responsive polymer network were developed in last twenty years. These functional polymer networks could be applied in drug controlled release, self-healing materials, biological scaffolds and smart sensors. Most of functional polymer networks were prepared by physical crosslinking reaction and chemical crosslinking reaction. Furthermore, chemical crosslinking reaction includes:traditional free radical polymerization, click reaction and living radical polymerization (Atom Transfer Radical Polymerization (ATRP) and Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT)). However, most of polymer networks are less structure integrity, many stress defects in the polymer networks and lead to their poor mechanical property, which limit their the further application as biomaterials, especially used in biomimic device. In this thesis, we synthesized macromolecules with controlled number of clickable functional groups and position, different molecular weight and topology molecular structure based on precisely macromolecules design and synthesis, by living radical polymerization and epoxy-amine ring opening reaction, respectively. Then, series of different functional topological polymer networks were prepared by "Click Chemistry". The main research of this essay as follows: (1) Well-defined amphiphilic copolymers and polymeric co-networks (APCNs) were prepared by precise controlled number of crosslinkings at the end of linear polymer. Firstly, linear polystyrene (PS) with well-defined molecular structure and accurate numbers of bromo groups on both ends were synthesized via multiple-step alternative reversible addition-fragmentation chain transfer polymerization (RAFT) of 3-bromopropyl maleimide and β-pinene monomers. The bromo end groups were transformed into the azido moieties via nucleophilic substitution. The reaction of as-synthesized linear PS having a named number of azide groups on ends ((N3)x-PS-(N3)x) with mono-and dialkynyl-terminated PEG (dA-PEG) via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) leads to the formation of the well-defined PS-PEG amphiphilic copolymers and polymeric co-networks (APCNs). The as-prepared APCNs exhibit unique ordered separated hydrophilic and hydrophobic phases, and a variable swelling capacity both in polar and non-polar solvents.(2) Well-defined amphiphilic polymer conetworks with precisely controlled number and position of cross-links were prepared by RAFT and CuAAC using linear polystyrene (PS) and poly(ethylene glycol) (PEG) as the building blocks. In this approach, linear polystyrene containing a specific number of bromo groups at a predetermined position of polymer chains was synthesized by multi-step RAFT polymerization and chain extension using styrene and 3-bromopropyl maleimide (PBMI) as the monomers. Subsequently, the bromo groups were transformed into the azido moieties via nucleophilic substitution. The well-defined linear multi-alkynyl PEG was prepared from PEG diglycidyl ether and propargylamine via epoxy-amine chain extension. The as-prepared PS-PEG amphiphilic polymer conetworks showed unique hydrophilic and hydrophobic phase separation with a variable swelling capacity and rheological behavior in both polar and nonpolar solvents and exhibited excellent mechanical properties with increased crosslinking density.(3) Well-defined multi-responsive poly(acrylic acid)-poly(ethylene glycol) (PAA-PEG) hydrogels with well-defined crosslinking structures were synthesized using atom transfer radical polymerization (ATRP) and CuAAC techniques. The well-defined PAA-PEG hydrogels with different degrees of crosslinking were produced from controlling the molecular weight of PAA and PEG chains. The prepared multi-responsive hydrogels exhibit regular physical and mechanical properties by adjusting the pH and Ca2+ ion secondary crosslinking. With increasing pH, the swelling ratio of the well-defined multi-responsive PAA-PEG hydrogels increased remarkably. Furthermore, the well-defined PAA-PEG hydrogels with Ca2+ secondary crosslinking possessed a significantly higher crosslinking density as reflected by the lower swelling ratio, higher storage modulus, higher electrical conductivity and thermal stability. An in vitro cell viability assay also indicated that well-defined multi-responsive PAA-PEG hydrogels are biocompatible and have potential for implantable biomaterials.(4) Antibacterial hydrogels containing quaternary ammonium (QA) groups were prepared via a facile thiol-ene "click" reaction using multifunctional poly(ethylene glycol) (PEG). The multifunctional PEG polymers were prepared by an epoxy-amine ring opening reaction. The chemical and physical properties of the hydrogels could be tuned with different crosslinking structures and crosslinking densities. The antibacterial hydrogel structures prepared from PEG Pendant QA were less well-defined than those from PEG Chain-End QA. Furthermore, functionalization of the PEG-type hydrogels with quaternary ammonium groups produced strong antibacterial abilities against Staphylococcus aureus, and therefore has the potential to be used as an anti-infective material for biomedical devices.The above four techniques of synthesizing functional polymer network with precise controlled molecular topology structure developed the new methods for preparing functional polymer network, furthermore, it also provides important means for the functional polymer networks applied in the bionic membrane in future.