Synthesis Of Well-defined Carbazole-containing Polymers Prepared Via ATRP For The Study Of Photoelectric Properties

Carbazole-containing polymers have special molecular structures with rigid fused rings and large ?-conjugated systems possessing strong intra-molecular electron transfer.The special structures endow carbazole-containing polymers various distinct photoelectric functions and properties such as high charge-carrier abilities,fluorescent and photoconductive features,as well as high thermal stability.Carbazole-containing star polymers are of branching architectures affording a more compact structure and higher segment density in comparison with linear polymeric counterparts,which have wide application prospect as organic photoelectric functional materials.Poly[(dimethylamino)ethyl methacrylate](PDMAEMA)is a typical so-called “stimuli-responsive” or “smart” polymer,due to the remarkable responsive behavior to the environmental stimuli such as temperature,pH and ionic strength.In thiswork,we synthesized block-copolymers with specific star architectures using carbazole-containing functional mononmer and DMAEMA via ATRP.The photoelectric function and the stimuli-responsive function were therefore combined together,and the coupling of the two functions was investigated.The main research work includes the following parts:Firstly,carbazole-containing star homopolymers with different number of arms and arm lengths were prepared in this work via ATRP through “core-first” approach by employing(9-(4-vinylbenzyl)-9H-carbazole(VBCz)as the monomer and 1,2,4,6-arm multifunctional initiators synthesized previously.All of the PVBCz star homopolymers absorb light in the range of 270-360 nm both in solution and as spin-coated film.The star polymers exhibit maximum fluorescent emission at 350 nm in THF solution,while at 406 nm as film,which prove them as blue-violet light-emitting materials.Using quinine sulfate solution as standard,the calculated values of quantum efficiency for VBCz is 43.1%,which ranges from 40.2% to 33.9% for the PVBCz star homopolymers.The HOMO energy levels of PVBCz star homopolymers range from-4.99 to-5.12 e V,while the LUMO from-1.53 to-1.67 eV.The high HOMO levels of PVBCz star homopolymers make low energy barriers from them to the common hole-transmission materials of PEDOT:PSS,leading to efficient hole injection.The band gap of the star homopolymers is around 3.45 eV.The decomposition temperature of the PVBCz star homopolymers is above 350?,showing good thermal stability.All the results indicate that the PVBCz star homopolymers are excellent organic optoelectronic functional materials which can be used in photoelectronic devices.Secondly,the PVBCz homopolymers with low degree of polymerization(degree of polymerization per arm is among 6-8)were obtained by reducing feed ratio of monomers to initiators and shortening the reaction time.Different PVBCz-b-PDMAEMA star block-copolymers were synthesized via ATRP using the PVBCz homopolymers with low degree of polymerization as macro-initiator and DMAEMA as the second monomer.The PDMAEMA block length of star block copolymers could be adjusted by controlling feed ratio of DMAEMA to the macro-initiator and reaction time.The degree of polymerization of PDMAEMA segment can be controlled in a relatively wide range(30-140)with relatively narrow molecular weight distribution(PDi<1.42).The block-copolymers exhibit good solubility in water.Moreover,the properties of different PVBCz-b-PDMAEMA star block-copolymers were investigated including ultraviolet-visible absorption,fluorescence emission,stimulus-response and fluorescence-stimulus-response.Both the structures of the block-copolymer and PDMAEMA block length have significant effects on the properties of the resulting polymers.The ultraviolet-visible absorption peaks of different block-copolymers shift compared with the homopoymers.The effects on fluorescence emission are mainly reflected by the changes of relative intensity of emission peak at 350 nm,365 nm and 405 nm.The block-copolymers have obvious temperature-and pH-responsive performance.The LCST of block-copolymers changes with respect to different pH values.Moreover,the LCST of different block-copolymers differ from each other.The fluorescence emission intensity and peak emission wavelength of block-copolymers in solutions change along with solvent,pH value and temperature.The structures of the block-copolymer and PDMAEMA block length also affect their special fluorescence-stimulus-response.To the best of our knowledge,scientific and applied research similar to this work has rarely been publicly reported before.The special multifunctions of the block copolymers endow them a wide application prospect,especially in the fields of sensors and intelligent photoelectric materials.Moreover,these functions could be easily adjusted to meet various specific practical demands by varying the structure and the block length,which is of great research and practical significance.