Synthesis And Solution Self-assembly Of Amphiphilic Block Copolymers Consisting Of Polysiloxane And Poly(Ethylene Oxide)

As a very potential method to prepare advanced materials of specific functionality,especially for the preparation of functional materials with desired structure and size(nanometers to micrometers),self-assembly behavior has attracted a lot research attention.Different from ordinary surfactants,amphiphilic copolymers behave in a much more complicated way in solution.Through proper choose of constituting blocks and appropriate control of the structure of block copolymers and the proportion of different blocks,the structure of self-assembled aggregates could be easily tuned.And meanwhile,the constituting blocks could be selected by one's will so that certain functionality introduced would qualify the applications of these copolymers in certain areas.In this dissertation,polysiloxane(and fluoro-containing polysiloxane) and poly(ethylene oxide) were chosen respectively as the hydrophobic and hydrophilic block.A series of amphiphilic block copolymers were constructed with different block composition and different structure by hydrosilation reactions between Si-H functional polysiloxane and ally terminated PEO homopolymers.The influence of block composition and block structure on the copolymer's solution property and self-assembly was studied.The detailed works were briefed as following:1.With the use of acid treated bentonite as the catalyst,we successfully prepared a series of functional polysiloxane hompolymers with relatively narrow molecular weight distribution.A discussion into the reaction mechanism was carried out.We thought that different from ordinary ring-opening polymerization of D4 with the catalysis of liquid acid,the current reaction system was constructed by two phases, the liquid monomer and the solid catalyst.Active sites for catalyzing are covalently bonded to the acid treated bentonite particles;therefore,the reaction system is free of free counter ions.Without the free counter ioins,the polymerization process is largely simplified.And meanwhile,because the bentonite particles serve as large counter ions,the steric hinderance provided would also influence the way the living chains grow and very probably force them to grow in a more disciplined way.By this catalysis system,we have successfully prepared functional polysiloxanes with relatively narrow molecular weight distribution(in the range of 1.2-1.4).2.In comparison,a series of mono-functional polysiloxanes with different molecular weight were synthesized.Reaction route for the anionic ring-opening polymerization of D₃ was designed and correspondent reactors for the polymerization were constructed.High vacuum techniques were used to prepare a series of monofunctional polysiloxane homopolymers with different molecular weight and narrow molecular weight distribution.Monofunctional polysiloxanes include two separate kinds,they are respectively polydimethylsiloxanes and polymethyltrifluoropropylsiloxanes.The prepared functional polymers were carefully characterized by ¹H-NMR,FT-IR and GPC characterizations.The results show a good support for the well-defined structure and good control of the molecular weight of prepared polymers.The polydispersity index is lower than1.1.Influence of different reaction conditions was also investigated.3.The suitability of Speier's catalyst for the hydrosilation reaction between Si-H terminated polysiloxane and aryl terminated poly(ethyleneoxide) was investigated. For the investigated hydrosilation reactions,speier's catalyst shows high selectivity and activity.The completeness of the hydrosilation reactions was proved with conversions higher than 99%.Through hydrosilation reactions between Si-H terminated polysiloxanes and ally terminated poly(ethylene oxide) homopolymers,we have successfully prepared five series of amphiphilic block copolymers,PDMS-b-PEO,PDMS-b-PEO-b-PDMS,PEO-b-PDMS-b-PEO, PMTFPS-b-PEO and PMTFPS-b-PEO-b-PMTFPS.The synthesized copolymers were shown to be well-defined through characterizations such as GPC,¹H-NMR and FT-IR measurements. 4.Solution properties of the copolymers synthesized were studied mainly by surface tensiometer.The possible influence of copolymer structure and composition on copolymer solution property was discussed and accordingly we proposed our understandings.5.Self-assembly behavior of different copolymers in aqueous solution was also investigated.Various morphologies of aggregates were found,including sphere, rod,vesicle and several others.Discussion into the factors which would influence the morphology of aggregates formed was carried out.And a discussion into specific shape transition was also provided,such as morphology transition from sphere-to-rod.The originality of this dissertation lies in:1.A more environmentally friendly synthesis route was proposed instead of traditional reaction route for the preparation of di-functional polydimethylsiloxane.With the use of insoluble acid treated bentonite,a series of narrow molecular weight distributed dihydrogen terminated polydimethylsiloxane were successfully prepared with polydispersity index ranging from 1.2-1.42.Effectively inhibits the "backbiting" and "redistribution" side reactions in the anionic ring-opening polymerization of D₃ and F₃.A series of mono-functional polysiloxanes were successfully prepared with polydispersity index ranging from 1.03-1.17.3.Two kinds of novel amphiphilic copolymers PMTFPS-b-PEO and PMTFPS-b-PEO-b-PMTFPS were synthesized and vesicle formations were found from solutions of these two kinds of copolymers.4.Structure of triblock copolymers was found to greatly influence the surface activities of correspondent copolymers.A plausible mechanism was proposed.5.In the solution self-assembly study of PDMS-b-PEO and PEO-b-PDMS-b-PEO copolymers,novel formation process of large compound micelle and novel "sphere-to-rod" morphology transition were observed.And correspondent plausible mechanisms were proposed.