梳状形状的高聚物梳在二氧化硅纳米颗粒的表面上 毕业论文外文翻译.doc
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1、MacromoleculesCommunications to the EditorVolume 38, Number 26 December 27, 2005 Copyright 2005 by the American Chemical SocietyComb-Coil Polymer Brushes on the Surface of Silica Nan particlesHanding Zhao,* Xiao Kang, and Li Leakey Laboratory of Functional Polymer Materials, Ministry of Education, D
2、epartment of Chemistry, Nankai University, Tianjin 300071, P. R. China Received August 17, 2005Revised Manuscript Received November 4, 2005During the past decade, surface modification of inorganic Nan particles by attachment of polymer brushes has attracted much interest due to the improvement of th
3、e properties of the Nan particles, especially the dispersion and stability of the particles in various solvents.Recently, many groups reported preparation of polymer brushes on the surface of gold nanoparticles,1magneticnanoparticles,2and silica nanoparticles.3There are two principal techniques to g
4、raft polymer brushes on the surface of the inorganic particles: (1) the “grafting to” method, where the end-functionalized polymers react with the functional groups on the inorganic particle surface, and (2) the “grafting from” method, where the polymer chains grow from the initiator-modified inorga
5、nic particle surface. Because of the satiric hindrance imposed by the grafted polymer chains, it is difficult to prepare polymer brushes with high graft density on the particle surface using the “grafting to” method. How-ever, in the “grafting from” method polymer chains grow from the initiators tha
6、t have been initially anchored to the particle surface, and the grafted chains will not hinder the diffusion of the small molecular monomers to the reaction sites, so the polymer brushes with higher graft density can be obtained. In recent years, there have been increasing research activities in the
7、 use of various polymerization methods to grow polymer chains on the silica particle surface. These methods include anionic polymerization,3bcat-Ni ionic polymerization,3dring-opening polymerization,3cradical polymerization,3eand atom transfer radical polymerization (ATRP).4-8Because ATRP allows bet
8、ter control over the molecular weight and distribution of the target polymer, much attention has been paid to these of this polymerization method in the synthesis ofpolymer brushes from a surface. Recently, Matyjasze-wskis group reported an improved ATRP method, activators generated by electron tran
9、sfer (AGET) ATRP.9In a typical AGET ATRP system, an alkyl halide is used as initiator, and a transition metal complex in its ox datively stable state (e.g., Cu2+/ligand) is used as catalyst. The activator is generated by using an electron transfer to reduce the higher oxidation state transition meta
10、l. In their experiments tin(II) 2-ethylhexanoate and ascorbic acid were used as the reducing agents. The AGET ATRP method has all benefits of normal ATRP and remains tolerant to air during sanitation, so it will be very useful in the preparation of polymer brushes on the silica nanoparticles surface
11、 .In this paper we report the first synthesis of comb -coil polymer brushes on the surface of silica nanoparticles. In this approach two steps are involved. At the first step, poly(2-hydroxyethyl methacrylate) (PHEMA)brushes on the surface of ATRP-initiator-anchored silicananoparticles were prepared
12、 using ATRP. At the second step using a combination of ring-opening polymerization and AGET ATRP, poly(DL-lactate) -poly(n-butyl acryl-late) (PLA -PBA) comb-coil polymer brushes were synthesized from the backbone and the terminal site morpheme brushes, respectively. This process is illus-traded in S
13、cheme 1. To synthesize PHEMA polymer brushes, ATRP-initiator-anchored silica nanoparticleswere prepared by a reaction of original silica particles with 3-(triethoxysilyl)polyamine and followed by an-other reaction with 2-bromoisobutyryl bromide. PHEMAbrushes were synthesized by ATRP. PLA comb and Pa
14、colet were synthesized by a combination of ring-opening polymerization and AGET ATRP (Scheme 1). The hydroxyl groups on PHEMA chains can be used in the ring-opening polymerization of LA, and the bromide Scheme 1. Schematic Representation for the Preparation of Comb-Coil Polymer Brushes on the Surfac
15、e of Silica Nanoparticles groups at the end of PHEMA chains can be used as initiators in AGET ATRP of BA. In this polymerization system, the Cu2+/bipyridine complex was used as catalyst for AGET ATRP, and tin(II) 2-ethylhexanoate was used as a reducing agent. Meanwhile, tin(II) 2-ethylhexanoate was
16、also used as catalyst for the ring-opening polymerization of DL-lactate (LA). So the ring-opening polymerization of LA at the backbone of PHEMA chains and AGET ATRP of BA at the end of PHEMA chains were taken place in the same polymerization system (Scheme 1). In this case each monomer should indepe
17、ndently propagate via two different mechanisms (ring opening and radical) and form different structures (comb structure at the backbone of PHEMA and coil structure at the end of PHEMA chain).The primary amino groups were introduced onto particle surface by a reaction with 3-(triethoxysilyl)-polyamin
18、e (Scheme 1). The elemental analysis result shows that the nitrogen content is about 0.93%, which means the concentration of amino groups on the surface is about 0.66 mol/g. This result keeps consistent with the literature report.3a ATRP-initiator-anchored silica particles were prepared after a reac
19、tion of laminated silica particles with 2-bromoisobutyryl bromide. The elemental analysis result shows that the bromide content on the silica particle surface is about 6%. This result indicates that on the particle surface the amount of ATRP initiator is roughly the same as that of amino group.Therm
20、o gravimetric analysis (TGA) result indicated that the weight retention of ATRP-initiator-anchored silica nanoparticles at 800 C was about 90%. But it has to be pointed out that part of the weight loss of the modified silica particles is due to the continued condensation reaction and associated wate
21、r loss.8,10 If the weight retention of the residue at 800 C is used as the reference, the weight retention of PHEMA brushes on the surface is about 76%, and that of the comb-coil polymer brushes is about 50%.Comb-coil polymer/silica composite was etched by HF acid, and the polymer was measured by 1H
22、 NMR. Figure 2 shows the 1H NMR spectrum of the comb-coil polymer. In Figure 2 the peak at 3.8 ppm indicates the successful ring-opening reaction of LA by -OH group on PHEMA backbone. In the spectrum the peaks at 5.16 ppm (d) and at 2.28 pap (e) represent the signed to ethylene protons adjacent to t
23、he -OH group in PHEMA basically disappears, which methane protons in PLA and PBA backbone, respectively.11 Using these two peaks it can be calculated that the molar ratio.Figure 1. Thermo gravimetric analysis of (a) ATRP-initiator anchored silica nanoparticles, (b) PHEMA brushes on the surface of si
24、lica nanoparticles, and (c) PLA-PBA comb-coil polymer brushes on the surface of silica nanoparticles.Figure 2. 1H NMR spectrum of PLA-PBA comb-coil polymer of LA to BA is about 1:0.36. The peak at 4.36 ppm (b) is attributed to the ethylene group of PHEMA. Using this peak and the peak at 5.16 ppm (d)
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