Synthesis And Characterization Of Well-controlled (fluoro)siloxane-containing Copolymers By Atom Transfer Radical Polymerization

The incorporation of （fluoro-） polysiloxane blocks into vinyl polymers couldgive block copolymers unique microphase separated structures to improve propertiesof copolymers, especially surface properties. However, the compositions andtopological structures of the copolymers influence the microstructures, which wouldhave effect on the surface properties of the copolymers. It needs to synthesizewell-defined polysiloxane-containing copolymers in order to investigate therelationship between the structure and property.In this work, a series of well-defined （fluoro）siloxane-containing comb-like graftcopolymers or trilock copolymer were synthesized based on the sequential atomtransfer radical polymerization （ATRP） of styrene （St） and tert-butyl acrylate （tBA）,using α-bromoisobutyryl-containing polysiloxane as the macroinitiators. And then,the structures, surface properties and morphologies of copolymer films wereinvestigated. The main results obtained are as follows:1. The comb-like graft copolymers consisting of polysiloxane, PS and PtBAblocks were successfully obtained based on the sequential ATRP of St and tBA, usingmultifunctional α-bromoisobutyryl-containing poly（dimethylsiloxane）（PDMS-Brn） asthe macroinitiators and CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine（PMDETA） as the catalyst system. The structures of the resulting copolymers withdifferent lengths of PS and PtBA moieties were examined by FTIR,1H-NMR, andDSC, which indicating a valuable method to the control of molecular architecture.2. The α-bromoisobutyryl-terminal poly[methyl（3,3,3-trifluoropropyl）siloxane]（PMTFPS-Br） were synthesized by a combination of anionic ring-openingpolymerization （ROP）, hydrosilylation and esterification.（1） Si-H functional poly[methyl（3,3,3-trifluoropropyl）siloxane]（PMTFPS-H） with narrow molecular weight distribution （MWD <1.10） was synthesized by theanionic ROP of1,3,5-trimethyl-1,3,5-trifluoropropyl cyclotrisiloxane （F3） intetrahydrofuran （THF） with n-butyllithium as the initiator and dimethylchlorosilane asthe capping agent.（2） Hydroxyl groups were introduced into PMTFPS chains via hydrosilylationwith allyl alcohol, using Pt as the catalyst. And then, α-bromoisobutyryl-terminalPMTFPS （PMTFPS-Br） were prepared by the esterification reaction ofα-bromoisobutyryl bromide with the hydroxyl-functional PMTFPS （PMTFPS-OH）.The characterization indicated that well-defined and lower MWD PMTFPS-Br wassuccessfully prepared for the following ATRP as macroinitiator.3. Well-architectured PMTFPS-b-PS diblock copolymers were obtained viaATRP of St from the PMTFPS-Br macroinitiators, using CuBr/PMDETA as a catalystsystem. The obtained M_n,PSlinearly increased with the conversion of monomers, andPMTFPS-b-PS diblock copolymers remains a PDI below1.5over the ATRP reaction.Morever, the linear dependence of ln（[M]₀/[M]） with time is consistent with acontrolled polymerization, even with a larger molecular weight PMTFPS-Br and alower monomer concentration. The¹H-NMR and GPC results indicated the ATRP ofSt has a typical characteristic of controlled/“living” polymerization.Then, a series of well-controlled PMTFPS-b-PS-b-PtBA triblock copolymers wresynthesized by the ATRP of tBA using PMTFPS-b-PS-Br as the macroinitiators, andCuBr/PMDETA as a catalyst system. A nearly complete conversion of tBA with lowMWD were achieved. Moreover, the kinetic plot was linearly increasing with thereaction time, indicating the polymerization was first-order with respect to themonomer. That is, the ATRP of tBA from PMTFPS-b-PS-Br macroinitiators is inagreement with a living process.4. The microstructures and surface properties of PMTFPS-b-PS-b-PtBA triblockcopolymers were investigated in this work.（1） The results of differential scanning calorimetry （DSC） measurementsrevealed that the length of PS and PtBA moieties in PMTFPS-b-PS-b-PtBA triblockcopolymers would influence the corresponding T_gof PS and PtBA blocks （T_g,PS, T_g,PtBA）. Moreover, when the molecular weights of blocks were large enough, theobtained PMTFPS-b-PS-b-PtBA triblock copolymers could exhibitmicrophase-separated structures, even some microstructure seemed to be morecomplicated.（2） Well water-, oil-or solvent-repellent efficiency of PMTFPS-b-PS-b-PtBAsurfaces could be found. The surface energies of PMTFPS-b-PS-b-PtBA films rangedbetween20.5and26.2mJ/m², which closed to the surface energy of21.4mJ/m²forpure PMTFPS. Moreover, the compositions of the triblock copolymers have importanteffect on the corresponding contact angle values.（3） The surface morphologies of PMTFPS-b-PS-b-PtBA films were investigatedby Tapping Mode Atomic Force Microscopy （TM-AFM）. The results showed that thedifference in wetting behavior of PMTFPS-b-PS-b-PtBA films was caused bydifferent macro-or nanoscale structures on the outmost layer of the copolymersurfaces. The films with high content of PtBA blocks exhibited almost no orderednanoscale structures on the outmost layer of the copolymer surfaces, even though theyhave microphase-separated structures in bulk.