Chemoenzymatic Preparation Of Amphiphilic Functional Block Copolymer And Study Of Self-assembly And Drug Delivery Behavior

Over the previous decade, enzyme-mediated polymerization has emerged as a new and important method of preparing polymers. While traditional catalysts often contain toxic and environmentally damaging metal species, enzyme catalysis is often seen as an eco-friendly alternative. Indeed, enzymatic catalysts often exhibit considerable benefits over their chemical analogues; enzymes as catalysts for polymerizations show high activity and chemoselectivity. Lipases alone have been shown to effectively catalyze ring-opening polymerization of lactones, lactides, and cyclic carbonates to the corresponding polyesters and polycarbonates. More importantly, these polymerization catalysts can operate under much milder conditions than metal catalysts and are considered biocompatible alternatives.In this work, we have shown that enzymatic ring-opening polymerization eROP ofε-caprolactone (ε-CL) was successfully combined with atom transfer radical polymerization (ATRP) to yield copolymers with well-defined molecular weight and polydispersity. A series of functional multiblock copolymer with different structure were carried out in this strategy, such as penta-, H-shaped, star like and brush block copolymer. Moreover, the self-assembly behavior of copolymers in aqueous media were investigated. In vitro release kinetics of folic acid and paclitaxel from the diblock copolymer PCL-b-PDMAEMA micelles were also studied respectively.In Chapter 2, a symmetric linear ABCBA-type pentablock copolymer consisting of polyethyleneglycol (PEG), poly(ε-caprolactone) ( PCL ) , and poly N-isopropylacrylamide (PNIPAM) was synthesized by the combination of eROP and atom transfer radical polymerization (ATRP). Dihydroxy-capped PEG first initiated eROP of CL in the presence of Novozym435. Subsequently, the resulting dihydroxy-terminated copolymer PCL-b-PEG-b-PCL was converted to a bromine- ended triblock macroinitiator by esterification with a-bromopropionyl bromide. The pentablock copolymer PNIPAM-b-PCL-b-PEG-b-PCL-b-PNIPAM was obtained via a subsequent ATRP of nipam. Temperature dependence of hydrodynamic diameter of amphiphilic pentablock copolymer was characterized by DLS. When temperature rises, the hydrodynamic diameter slowly increase, at 35℃the hydrodynamic diameter increases to 125nm, this temperature is also known as the LCST,PNIPAM undergoes a coil-to-globule phase transition in dilute aqueous solution at its LCST. At temperatures below the LCST, PNIPAM chains adopt a random-coil conformation, while at temperatures above the LCST, the structure of the resultant core-shell-corona micelles with temperature increasing. The aggregates of various morphologies, such as normal spherical micelles, rodlike micelles and linear micelles, were observed by self-assemblies of the pentablock copolymer in aqueous media, and crystals morphologies were observed, The resulting crystals of PEG and PCL were characterized by XRD and TEM. The work in this chapter demonstrated that solutions of pentablock copolymer in THF or DMF present an excellent model system for the study of the interplay between aggregation and crystallization.In chapter 3,We describe the first account of the synthesis and intriguing micellization properties of nonlinear block copolymers of the B2AB2 and C2BABC2 type. Atom transfer radical polymerization (ATRP) macroinitiators with four initiating sites at ends of polyethyleneglycol (PEG) and BAB typed copolymer PCL-b-PEG-b-PCL were synthesized via by esterification with excess 2,2-dichloro acetyl chloride (DCAC) respectively. Well-defined H-shaped block copolymer (PVP)2-b-PEG-b-(PVP)2 and (PVP)2-b-PCL-b-PEG-b-PCL-b-(PVP)2 were then prepared by polymerizing 4-vinylpyridine(4VP) via ATRP in which CuCl/HMTETA was used as the catalyst system using the prepared macroinitiators. The pH responsive micellization behavior of (PVP)2-b-PEG-b-(PVP)2 and (PVP)2-b-PCL-b-PEG-b-PCL-b-(PVP)2 was then investigated by a combination of dynamic laser light scattering(DLS), atomic force microscopy (AFM) and transmission electron microscope(TEM). Due to P4VP is a pH-sensitive polymer,pH dependence of the hydrodynamic diameter of H-shaped triblock copolymer (PVP)2-b-PEG-b-(PVP)2 and copolymer (PVP)2-b-PCL-b-PEG-b-PCL-b-(PVP)2 were characterized by DLS, the hydrodynamic diameter of the triblock copolymer micelle was sharp decrease when the PH decrease,however,pentaiblock copolymer micelle were cross-linked.An amphiphilic star block copolymer comprised of a hydrophobic PCL block and a hydrophilic hexaarm poly(glycidyl methacrylate) (PGMA) block was synthesized by copolymerization of GMA, CuCl/bpy as a catalyst system. The star copolymer undergoes self-assembly to the micellar nanoparticles with a well-defined core–shell structure. The sizes of the nanoparticles with different chain ratio were charactered by DLS, AFM and TEM. The PCL/PGMA ratio in the star block copolymers had a significant effect on the micellization properties; the aggregation of micelles appeared with the increasing length of the PGMA block. In the second section of chapter 4, grafting of hydrophilic poly(glycidyl methacrylate) (PGMA) block brushes was carried out from the polystyrene(PSt) synthesized with star macroinitiators, TMP-(PCL-b-PSt2-Br)3, which was performed through a bromination reaction between pendant allylic groups of the PSt and N-bromosuccinimide (NBS). This method is a novel route to synthesize star-combtype polymer. Amphiphilic star block copolymer could self-assemble sphere type micelle and the diameter of star-combtype polymer was decrease contrast to star block copolymer.In chapter 5, a novel biodegradable amphiphilic copolymer with hydrophobic poly(e-caprolactone) and a hydrophilic poly(N,N-dimethylamino-2-ethyl methacrylate) chain was synthesized by combined eROP and ATRP. The copolymer was characterized by FTIR, 1H NMR, gel permeation chromatography (GPC). The amphiphilic copolymer could self-assemble into micelles in an aqueous solution. The critical micelle concentration (CMC) of the amphiphilic copolymer with different chain ratio was determined by fluorescence spectroscopy. The CMC value was increased with the PDMAEMA increase. The characteristic in response to the change in environmental temperature and pH were investigated by the dynamic light scattering (DLS). The results showed that the Dh of the micelles were decreased as the temperature increase and increased as the pH decrease. Nanoparticle drug delivery system with a regularly spherical shape was prepared with high encapsulation efficiency. The in vitro drug release from the drug loaded polymeric nanoparticles was investigated with a series PH and temperature and the drug release rate was affected by the thermo-trigger at pH 7.4, as well as the pH-trigger at 37 ?C...