Glucose-based Block Copolymers Via RAFT Polymerization:Synthesis,Properties And Application

With a growing voice of green chemistry in recent years,glycopolymers as a typical kind of green functional polymers have attracted an increasing attention.They are structurally derived from saccharide molecules and the combination of saccharides with other functional molecules via chemical bond or physical blend.These glycopolymers not only have the biocompatibility of saccharides,but also exhibit special functions of other molecules.To enrich the structures of glycopolymers and expand the application fields as well,in this thesis,employing glucose as the raw material,a series of glucose-based block copolymers were synthesized,and their applications were studied(a)serving as environmental stimuli-response smart material,(b)preparing 3D hierarchical structure of fluoride materials and(c)dispersing inorganic nanoscaled powders.Two kinds of glucose-based copolymers with A-B diblock and A-B-C triblock structures were prepared by sequential reversible addition-fragmentation transfer(RAFT)polymerization using glucosyl monomer as the biocompatible unit,N-isopropyl acrylamide(NIPAM)as the thermosensitive unit,and acrylic acid(AA)as the pH sensitive unit.This work was mainly focused on the following four research parts.(1)The synthesis of glycosyl monomer and the RAFT chain transfer agents.Synthesis of glucose monomers and chain transfer agents are the premise of the preparation of glucose-based copolymers.In order to accelerate the reaction rate of acetone with glucose on the surface of glucose particles,ultrasound reaction method was employed.The optimum reaction conditions were studied in detail.The yield of Diacetone-D-glucose(DAG)is up to 80.3%with a reaction time of 7 h at 60 ? using FeCl3 as a catalyst under ultrasound.3-O-allyl-1,2:5,6-di-O-isopropynylene-a-D-glucose(OAIG)and 3-O-acryloyl-1,2;5,6-di-O-isopropylidene-a-D-(-)-glucofuranose(ADIPG)were synthesized from DAG and allyl bromide,acryloyl chloride,respectively.Disulfide ester chain transfer agent cumyl dithiobenzoate(CDB)was prepared.The key step in this process is the quenching of the Grignard intermediate,to this end,we optimized the quenching method to end the process for 2,2'-Dithiodibenzoic acid(DTBA)which was the important intermediate to form CDB,and the DTBA yield increased from 20%to 85%.By a ketone reaction 2,2'-thiocarbonylbis(sulfanediyl)bis(2-methylpropanoic acid)(CMP)and 2-Dodecylsulfanyl-thiocar-bonyl-sulfanyl-2-methylpropionic acid(DMP)were one-pot synthesized with yield up to 85%and 63%,respectively.(2)The stimuli-response performance studies of glucose-based block copolymers as smart materials.To realize the structure controllability of the glycopolymers,diblock glucose-based copolymers,poly(N-isopropyl acrylamide)-block-poly(3-O-allyl-a-D-glucose)(PNIPAM-b-POAG)were prepared by RAFT polymerization.The structure and molecular weight of the as-obtained block copolymers were characterized and measured.These results showed that two steps of RAFT polymerization were well controllable.The relative molecular weight of the copolymer could be regulated by adjusting the dosage of the chain transfer agent(CTA).Sol-gel phase transition experiments demonstrated that PNIPAA-b-POAG hydrogel had a good temperature sensitive performance,and the gelation temperature decreased gradually with continuously increasing the relative molecular weight and concentration of the copolymer.Compared with the random copolymer,the diblock copolymer had a lower critical micelle concentration(CMC)value,indicating that it was easier to form micelles.The triblock copolymers poly(acryloyl glucofuranose)-block-poly(N-isopropyl acrylamide)-block-poly(acrylic acid)(PGNA)and poly(N-isopropyl acrylamide)-block-poly(acryloyl glucofuranose)-block-poly(acrylic acid)(PNAA)were prepared by five synthesis steps using CMP and DMP as the chain transfer agent,respectively.Every step reaction product was characterized by infrared spectroscopy(FT-IR),nuclear magnetic resonance hydrogen spectrum(1H NMR),gel permeation chromatography(GPC).The micelle structure of triblock copolymers were characterized by transmission electron microscopy(TEM)and dynamic light scattering(DLC).The effects of solution concentration,molecular weight,pH value on sol-gel phase transition behavior were investigated.The results showed that the PGNA and PNAA smart hydrogels had good temperature and pH response behaviors,and presented a reversible sol-gel-syneresis phase transition behavior.The content of the glycosyl segments significantly influenced the size of the micelles and CMC values.In vitro drug release experiments demonstrated that three triblock gylcopolymers can effectively control the drug release under physiological conditions.The cumulative release amount depends on the proportion of hydrophilic and hydrophobic chain segments and the content of glucosyl segment.In vitro cytotoxicity tests and in vivo biocompatibility tests showed that the three triblock gylcopolymers had good biocompatibility.Experimental results revealed that the as-prepared stimuli-response glucose-based copolymers had a good potential application prospect in the fields of tissue engineering and drug sustained release.Compared with other temperature-response glycopolymers derived from isopropylacrylamide reported so far whose structures are usually grafting,random,and blend,our block glucose-based copolymer enriches the kinds of stimuli-response glycopolymers.(3)The application of glucosyl block copolymer in the preparation of 3D hierarchical structured fluoride materials.Due to the rare report on polymers assisting preparation of hierarchical structured materials and the structural feature of triblock glucose-based copolymer which resembles the structure of small surfactants,with the aid of PGNA,well-dispersed hierarchical ZnOHF and EuF3 microstructures were prepared via a simple solution-based method.The purity and morphological properties of as-prepared EuF3 were characterized by FTIR,XRD,TEM and SEM.The role of PGNA in the preparation of 3D hierarchical micro/nanostructures was investigated.The SEM and TEM results indicated that the hierarchical ZnOHF architectures were microflowers with porous structures and the obtained EuF3 architectures were microspheres that organized by nanodisks-assembled.As complexing agent and dispersing stabilizer,the amount of PGNA and reaction time played crucial roles in the formation of hierarchical ZnOHF and EuF3 architectures.N2 adsorption-stripping experiment further evidenced that the 3D ZnOHF and EuF3 were mesoporous materials and had bigger BET surface area.After calcination,ZnOHF was completely transformed into ZnO while the flower structures were perfectly retained.The as-obtained ZnOHF and ZnO hierarchical flowers exhibited excellent UV light photocatalytic activities for photodegradation of Rhodamine B.The photoluminescent spectrum of hierarchical EuF3 displayed enhanced red emission compared with that of EuF3 nanodisks,suggesting a promising application in optical fields.Compared with other methods reported in the literatures for the preparation of EuF3 and ZnOHF,our approach has many advantages such as novel structure,milder reaction conditions,lower reaction temperature,shorter reaction time,more regular uniform,larger surface area,better photocatalysis and better photoluminescence performance.(4)The application of glucosyl block copolymer for dispersing inorganic nano powders.To improve the biocompatibility of dispersing system of inorganic nano particles,the glucosyl triblock copolymer PGNA was used to disperse nano TiO2.The results showed that it was an excellent dispersant.FTIR and SEM results indicated that PGNA was absorbed on the surface of nanosized TiO2.Isotherm revealed that,being a dispersant,PGNA was monolayer adsorption when it was dispersing TiO2 nanoparticles.It was consistent with Langmuir adsorption isotherm.PGNA with a molecular weight of 14346 Da displayed the best dispersing performance,and the maximum amount of adsorption on the nano-TiO2 surface was 5.35 mg/g with mean diameter of 120 nm.The application of glucosyl block copolymers with good water solubility and biocompatibility will enrich dispersing methods for inorganic nano powder in specific areas such as sunscreen cosmetics,and so on.