Synthesis And Characterization Of Diblock Copolymers Of Vinyl Monomers And Fluorosiloxane By Living Anionic Polymerization

Incorporation of polysiloxane blocks into conventional vinyl polymers would form block copolymers with different microphase separated structures and novel properties. Since the fluorinated polysiloxanes exhibit excellent properties of fluoropolymers and polysiloxanes, it is anticipated that the block copolymers of fluorinated polysiloxanes and vinyl polymers with well-defined structures will have unusual features and properties. And then, the novel polymeric materials with potential applications could be obtained. However, it was difficult for the controlled block copolymerization of fluorinated polysiloxane monomers and vinyl monomers.Living anionic polymerization is the most powerful synthetic tool for the preparation of block copolymers with controlled structures. Based on the living anionic polymerization method and the reliability of high-vacuum experimental techniques, high-vacuum apparatus and break-seal techniques for carrying out anionic polymerization were founded in this work, and a series of glass apparatus were designed or blown. Under the high-vacuum experimental techniques, the block copolymerizations of 1,3,5-trimethyl-1,3,5-tris(3',3',3'-trifluoropropyl)cyclotrisiloxane (F3) and vinyl monomers, such as styrene (St) or methyl methacrylate (MMA), were investigated in this work. The main results obtained are described as follows:1. A series of narrow molecular weight distribution (MWD) polystyrene-b-poly[methyl(3,3,3-trifluoropropyl)siloxane] (PS-b-PMTFPS) diblock copolymers were synthesized by sequential anionic polymerization of styrene and F3 in tetrahydrofuran (THF) with n-butyllithium as the initiator. The initiation of anionic ring-opening polymerization (ROP) of F₃ by living polystyryllithium was quite quick in THF, which would give benefit to the control of block copolymerization. However, the concentrations of styrene and F3 in the solution are essential to obtain high yields and narrow MWD PS-b-PMTFPS diblock copolymers. When high monomer concentrations were used, high polymer yields and good control of MWD diblock copolymers were obtained, which means the backbiting by the chain ends as well as the redistribution reactions between siloxane units of the PMTFPS block chains were suppressed. It was speculated that good control of the block copolymerization under the condition of high monomer concentrations was attributed to the slowdown of the anionic ROP rate of F₃ and the steric hindrance of the PS precursors. There was enough time to terminate the ROP of F₃ when the polymer yield is high, and good control of block copolymerization could be achieved thereafter.2. The morphologies of PS-6-PMTFPS diblock copolymers were investigated in detail. Transmission electron microscopy (TEM) images of the thin films of PS-6-PMTFPS showed spherical, cylindrical and lamellar microphase-separated structures depending on the molecular weight of the diblock copolymers, the volume fraction of PS, the annealing temperature and the casting solvent. Though THF, ethyl acetate (EA) and chloroform (CHC13) have the similar solubility parameters, they influenced the morphologies at room temperature when they were used as the casting solvents. According to the experimental results, the microphase behavior of PS-6-PMTFPS was predicted not to follow the strong segregation regime, and the Flory-Huggins segment-segment interaction parameter % between PS and PMTFPS was poorly described by regular solution theory because of the strong dipole in PMTFPS. Moreover, the phase diagram of the PS-6-PMTFPS diblock copolymers was quite complex and conformationally asymmetric.3. The properties of PS-6-PMTFPS diblock copolymers were investigated in detail. When the degree of polymerization of PMTFPS blocks (A^pmtfps) was sixteen, the glass transition was so weak that it was difficult to be clearly discerned. However, the glass transition of PMTFPS block became more clearly in the differential scanning calorimetry (DSC) thermograms with the increase of A^pmtfps* and the glass transition temperature stabilized at -69 °C when A^pmifps was large enough. The 5% weight loss temperatures of the diblock copolymers were all above 350 °C, which suggesting good thermal stability. The thermogravimetric analysis (TGA) results also showed that the thermal stability of the diblock copolymers could be better than Polystyrene when high content fluorosiloxane blocks were incorporated. Moreover, the TGA curves for PS-6-PMTFPS diblock copolymers involved two breaks that corresponded to the loss of PS and PMTFPS units in every case. The observed amount of weight loss is in good agreement with the amount calculated in the diblock copolymers.4. By measuring the contact angle of water and glycerol on the films of PS-b-PMTFPS diblock copolymers, good water and oil resistance was found. The surface tension of the diblock copolymers was as low as D^xlO^N-m"1, which was much lower than that of polystyrene-Z>-polydimethylsiloxane (PS-6-PDMS) diblock copolymers. The X-ray photoelectron spectroscopy (XPS) showed that the surface contents of fluorine and Si-0 chains of the diblock copolymer films were much higher than that in bulk. The surface composition of the film was nearly pure PMTFPS blocks, however, the -CF3 groups were not all orientated to the outer surface of thefilm.5. The surface activities of the blends of PS-6-PMTFPS diblock copolymers and PS were investigated by means of contact angle measurements. The results showed that only 1.0 wt% PS-6-PMTFPS (Mn=21.4xl03, 38.7 wt% PMTFPS) was added to PS (Mn= 21.4xlO3), the surface tension of the film approached 15.7*10"3 N-m"1. The annealing treatment could remarkably decrease the surface tensions of the films when CHCI3 was used as the casting solvent. Annealing temperature and annealing time also had effect on the surface activities. Moreover, different solvent would have different effect on the contact angles of the films of PS-6-PMTFPS/PS blends. It was found that the contact angles of the annealed films abnormally decreased when EA was used as casting solvent.6. The controlled block copolymerization of MMA and F3 was first carried out via living anionic polymerization, and a series of narrow MWD poly(methyl methacrylate)-6-poly[methyl(3,3,3-trifluoropropyl)siloxane] (PMMA-6-PMTFPS) diblock copolymers were first synthesized. The results showed that the heterofunctional linkage between chloromethylphenyl PMTFPS and living PMMA lithium could not happened even in the presence of Csl as the catalys. However, well-defined PMMA-6-PMTFPS diblock copolymers could be successfully synthesized by using an acetal-functionalized alkyllithium as the initiator. High monomer concentration conditions were also important to obtain high yields and narrow MWD PMMA-6-PMTFPS diblock copolymers.7. The thermal properties of PMMA-6-PMTFPS diblock copolymers were investigated in this work. DSC analysis results showed that the glass transition temperature of PMTFPS blocks was about -69- -70 °C when TV^pmtfps was large. At the same time, the glass transition temperature of PMMA blocks was 121- 136 °C, and was decreased with the increase of PMTFPS block length. The TGA curves showed that the diblock copolymers started to decompose at temperatures about 270-290 °C, and the 5% weight loss temperature of the diblock copolymers was all above 319 °C, which suggesting good thermal stability. The C-O-Si groups that connected the two blocks seemed to have little effect on the thermal stability of the diblock copolymers. Moreover, the thermal degradation of PMMA-6-PMTFPS diblock copolymers proceeded in three steps of weight loss: the first and second steps by the degradation of PMMA blocks, and the last by PMTFPS blocks.The main innovations in this work are presented as follows:1. A series of narrow molecular weight distribution (MWD) polystyrene-^-poly[methyl-(3,3,3-trifluoropropyl)siloxane] (PS-6-PMTFPS) diblock copolymers were first synthesized by sequential anionic polymerization of styrene and F3 in THF. Moreover, the mechanism of the block copolymerization was investigated in detail.2. The phase diagram of the PS-6-PMTFPS diblock copolymers was quite complicated and conformationally asymmetric. The Flory-Huggins segment-segment interaction parameter % between PS and PMTFPS was poorly described by regular solution theory because of the presence of 3,3,3-trifluoropropyl groups.3. It was found that the surface tension of PS-6-PMTFPS diblock copolymers was as low as D^xlO^N-m"1, which was much lower than that of PS-6-PDMS diblock copolymers. The surface composition of the film was nearly pure PMTFPS blocks, however, the -CF3 groups were not all orientated to the outer surface.4. Narrow MWD poly(methyl methacrylate)-&-poly[methyl(3,3,3- trifluoropropyl) siloxane](PMMA-6-PMTFPS) diblock copolymers were first synthesized, and the controlled block copolymerization of MMA and F3 was first carried out in this work.