Study On Properties Of Poly(Acrylonitrile) And Poly(Ethylene Glycol) Amphiphilic Block Copolymer And Their Application

A series of block copolymers poly(acrylonitrile)-b-poly(ethylene glycol)-b-poly(acrylonitrile) (PAN-b-PEG-b-PAN) (PAEA) and poly(acrylonitrile)-b- poly(ethylene glycol) (PAN-b-PEO) (PAE) were synthesized by ATRP method. The thermo stabilities, crystalline properties and self-assembly behaviors in selective solvent of these amphiphilic block copolymers were investigated. Silver nanoparticles with a cubic structure were synthesized by using amphiphilic block copolymer (PAE) based on the flexibility of the copolymer chains and the complex effect of -CN in the polyacrylonitrile with Ag~+ and Ag under ultrasonic irradiation.Firstly, a series of PAE and PAEA block copolymers were synthesized by using atom transfer radical polymerization (ATRP). This was achieved by using the esterification of poly (ethylene glycol) monomethyl ether and poly (ethylene glycol) with 2-Bromopropionyl bromide as macroinitiators respectively, acrylonitrile as monomer, CuBr/2,2'-bipyridine as the catalysts and ethylene carbonate (EC) as solvent at 70℃. The structure, the molecules weight, and the polydispersity of the products were characterized by using ~1H NMR, FTIR and GPC.Secondly, the self-assembling behavior of amphiphilic block copolymers in solution is one of the hottest topics of polymer science in recent years. It's well known that amphiphilic block copolymers can form micelles or colloidal size aggregates in solvent selective for one of the blocks. In this paper, the self-assembling behaviors of two styles amphiphilic block copolymers were studied. Through ~1H NMR, the micelles which were belonged to the amphiphilic block copolymers were formed in solvents. From the investigation of DLS and TEM, the morphology, size and stability of the aggregates are dependent on the composition and concentration of the block copolymers, the property of solvent and additives. The above results showed that the size of PAEA, PAE block copolymers micelles was increased as the molecular of PAEA and PAE increased. When the selective solvents of those copolymers were changed, the morphology of those micelles transformed from sphere to club-shaped. Based on the different additive to the copolymer, the structures of micelles can be distinguished: one is sphere micelle; the other is club-shaped micelle and vesicles.Thirdly, the thermo stabilities of these copolymers were investigated by TGA and FT-IR. Comparing the thermo stabilities of PEG; the thermo stabilities of PAEA were better and when the molecular of the amphiphilic copolymers increased, the thermo stabilities of PAEA improved. The crystalline properties of PAE and PAEA block copolymers were studied by XRD, DSC and POM. The results showed that component of PAE and PAEA had great influence on the crystallinizing properties ofPEG/PEO segments in the block copolymer. There was one PEG/PEO melting peak at high temperature in the DSC curves of crystallinized block copolymers with low content of PEG, and then two melting peaks were observed with increasing the PEG/PEO content, however, only one melting peak remained but at low temperature in the DSC curve of samples with higher content of PEG/PEO. The reason may be because of the fraction or second crystallization of imperfect PEG crystals in the PAEA. The crystallinity difference of PEG segment in PAEA and PAE two types block copolymer was studied. The experimental results indicated that the crystallization of PEG segments would decrease in the following order: PAE＞PAEA. The influence of PEG content on the crystallization mechanism was discussed. It was found that the crystallization mechanism of PEG/PEO segment in the block copolymer with low content of PEG/PEO is homogeneous nucleation. On the contrary, the mechanism is heterogeneous nucleation in higher content PEG of block copolymer. From POM observations, PAE(c) showed the similar spherulite morphology to that of PEO homopolymer, but PAE(a), PAE(b) and PAEA(a),PAEA(b),PAEA(c) couldn't form crystalline morphology, Such results indicate that the block length has significant influence on the crystalline morphology of the block copolymers.Lastly, silver nanoparticles with the average diameter of 20 nm were synthesized by using amphiphilic block copolymer PAE micelles based on the flexibility of the copolymer chains and the complex effect of -CN in the polyacrylonitrile with Ag~+ and Ag under ultrasonic irradiation. The product was characterized by XRD, FT-IR, TEM, UV-Vis spectrum, TGA and XPS. The FT-IR results revealed that the backbone of the PEA block copolymer was not been cleavage during the synthesis of the silver nanoparticles under ultrasonic irradiation. The results revealed that the silver nanoparticles were well protected by the amphiphilic copolymer micelles. Low initial silver ion concentration allowed for yielding silver nanoparticles with a small size and the size of the silver nanoparticles increased with the concentration of the silver ion solution increasing; when the molecular of the amphiphilic block copolymers decreased, the nanoparticles easily got together. The silver crystal was polycrystalline with a cubic structure, as confirmed by XRD.