Application Of C-S And C-Se Weak Bond In Design And Syntlhesis Of Polymer With Well-defined Structure

Free radical polymerization is an important method for sythesis polymeric materials.But the intrinsic of unreversable thain transfer and termination properties of conventional radical polymerization limited their application in synthesis polymer with controlled structure.At the same time,there are more and more requirements for the versatile nature of polymeric materials with the development of society and economy which resulted in the requirement of polymers with controlled composition and structure.The development of living radical polymerization,which has the advantages of high efficiency structure regulation,mild polymerization conditions and wide monomers range,has provided convenience for the design and synthesis of polymers,especially functional polymers.It has become a hotpot in the field of polymer chemistry in the past more than 20 years.Among them,the methods for the construction of well-defined polymers based on carbon sulfur and carbon selenium weak bonds include initiator-transfer agent-terminator(iniferter),Reversible Addition-Freamentation Chain Transfer(RAFT),and organoselenium-mediated living radical polymerization(SeRP).This thesis is based on the C-S/C-Se weak bonds whose bond energy were lower than that of C-C.This meant that C-S and C-Se were easy to be cracked under the light and generating carbon free radicals and relatively stable sulfur(selenium)radicals.Carbon free radicals can be used to induce polymerization,while sulfur(selenium)radical can be acted as radical capture agent,which is idealed for contructing living radical polymerization process.Thus,novel living radical polymerization system was constructed and performed through the simplification of components,the adjustment of light wavelength and the usability of monomers.Furthermore,based on the above research,phenylselenyl polycaprolactone was synthesized using the flexible selenium chemistry and the application of C-Se weak bond in the modification of polycaprolactone was explored.The specific research contents are as follows:(1)Five diaryl diselenide compounds with different sunstitution groups on the benzene ring including bis(2,6-dimethylphenyl)diselenide(DmXDS),bis(2,6-diethylphenyl)diselenide(DEPDS),bis(2,6-diisopropylphenyl)diselenide(DiPPDS)and bis(2,6-di-tert-butylphenyl)diselenide(DtBuPDS)were synthesized.The polymerization behavior of styrene under 50 ? was studied under visible light with these diselenides as the mediators.The results showed that DmXDS with two methyl groups on every benzene ring was the most efficient mediator for preparing polystyrene,while the other diselenides were poor mediators,and even not polymerized.It is found that the different substituents on the benzene ring in the diselenide lead to the different degrees of deflection of the molecular orbits of the free radical formed by its fracture.The rotated molecular orbital results in a high steric hindrance for these radicals adding to that of styrene,which resulted in different polymerization behavior.Subsequently,the polymerization of styrene in the presence of DmXDS was further studied,and the effect of DmXDS concentration on the polymerization was investigated.~1H NMR,MALDI-To F MS and successful chain extension confirmed the existence of an arylseleno and high fidelity.The kinetic of chain extension using PS as macromolecular initiator was studied.The induction period of polymerization was very short,which provide evidence for the study of polymerization mechanism.In addition,with the treatment of 30%hydrogen peroxide,the phenyl selenide group at the end of the polymer was transformed into carbon carbon double bonds,which provides a route for the synthesis of“macromonomers”with a narrow molecular weight distribution.(2)Polymerization of VAc with 2-(ethoxycarbonothioyl)sulfanyl propanoate(EXEP)as initiator and mediator was studied under visible light and room temperature.This system was simple and no catalyst.The polymerization behavior with different EXEP concentration was studied.The results showed controlled molecular weight and narrow molecular weight distribution.And sunlight also was used as an external light source in this system.The polymerization system has a high responsiveness to illumination.And the polymerization process can be started and stopped through"ON"and"OFF"the light.~1H NMR,MALDI-To F MS and successful chain extension confirmed high fidelity(over 99%)of polymer chain-end.Furthermore,xanthate containing functional groups such as carboxylic acid(EXAP)and alkyne(EXSD)were synthesized for controlled polymerization of VAc.It can be used for the synthesis of PVAc with functional end group.The simplest polymerization system for living polymerization of VAc has been developed.(3)Lanthanide-doped upconversion nanoparticles(UCNPs)can convert NIR light into visible light by adsorbing NIR photons.In this system,UCNPs was used as internal light polymerization of butyl acrylate(BA),VAc and methyl methacrylate(MMA)under NIR laser and room temperature were achieved.The polymerization kinetic was studied with BA as a template.It was found that polymerization of BA was well controlled for the molecular weight and molecular weight distribution.And after 5 h,the monomer conversion was nearly 100%.High end-group fidelity(>99%)was verified by ~1H NMR and MALDI-TOF MS.Moreover,successful chain extension suggested that the terminal of polymer is still“living”.In addition,the polymerization conditions are mild and highly tolerant to functional groups.Infrared analysis shows that azido groups of small molecules remain in polymers.The deep penetration power of NIR and the good design imply a latent application for biomedicines and biomaterials.(4)Phenylselenyl caprolactone was synthesized as a monomer for the ring opening polymerization with ethylene glycol as an initiator and stannous octanate as a catalyst at 100 ?.The polymerization wa goog controlled.The molecular weight increased linearly with the increasing of monomer conversion,and the molecular weight distribution was narrow.The polymer(unsaturated polymer),which contains carbon carbon double bonds,can be synthesized by the oxidation of 3-chloroperbenzoic acid(mCPBA)by the oxidation of the phenyl selenide group in the polymer repeating unit.Utilizing the double bonds,the fluorescent group pyrene and epoxy groups were successfully attachment to the polymer through the Michael addition and epoxidation reaction,respectively.Moreover,the content of phenylselenyl group in the polymer could be regulated by the copolymerization of CLSePh and CL with different molar ratio.It can be used to realize the regulation of the number of functional groups.The glass transition temperature of the copolymer is between PCL(-60 ?)and PCLSePh(-9.08 ?).By changing the ratio of these two monomers,the T_g value of the random copolymer can be adjusted.Furthermore,the degradation experiments showed that the degradation rate of PCLSePh was significantly slower than that of PCL.So,the degradation rate of copolymer can also be adjusted by the composition of copolymer.The system provides a versatile platform for the synthesis of functional polycaprolactone.