Metal-free Polycycloaddition Of Activated Azides And Alkynes Toward Functional Polytriazoles

Due to its remarkable features such as high efficiency,simple product isolation,tolerance to functional groups,regioselectivity,and mild reaction conditions,the Cu(I)-catalyzed azide-alkyne cycloaddition(C uAAC)has become the prime example of click reaction,being even used synonymously with click chemistry.Naturally,C uAAC has been used in polymer and materials sciences,which facilitates not only the preparation and modification of preformed polymers but also the generation of polymers with new structures.As a result,the click reaction has been nurtured into a new polymerization technique,i.e.Cu(I)-catalyzed azide-alkyne click polymerization(C uAACP).However,the use of Cu(I)catalysts for the click polymerization comes along with the problems that the products often tend to be insoluble in common organic solvents,and the metal residuals are difficult to be completely removed.While,the metal residues are toxic and destructive if the products are going to be used in biological and optoelectronic fields.This thorny copper residues problem could be thoroughly solved by the metal-free click polymerization of azides and alkynes(MFAACP).In this context,the development of MFAACP is particularly necessary.The key point of MFAACP is how to maintain the simplicity and e fficiency of the original CuAACP without the use of metal catalysts.O ne of the most facile and direct methods to achieve the MFAACP is using highly active alkyne or azide monomers.In this dissertation,we developed a new type of activated azide monomer and via systematically optimization,we successfully established a new MFAACP.Using this MFAACP,a series of linear and hyperbranched polytriazoles with different structures and properties were efficiently prepared,and their potential applications were also carefully studied.In C hapter 2,perfluorophenyl azides(PFPAs),a class of facilely available azides,was demonstrated to be activated monomers and was firstly introduced into polymer synthesis.MFAACP were then accomplished with various kinds of alkyne monomers.This new established polymerization can proceed without protection from oxygen and moisture to afford soluble polymers with high molecular weights(up to 170 000)in high yields(up to 93%)either in solvents or under neat conditions.Interestingly,the regioselectivity of the polymerization could be fine-tuned by the reaction solvents and diynes,and we proposed that arene-perfluoroarene(Ar-ArF)interaction is responsible for this phenomenon.This feature provides a powerful platform for regulating the structure and function of the target polymers.In Chapter 3,tetraphenylethene(TPE)and silole-containing linear polytriazoles with high molecular weights(up to 32000)were successfully synthesized in high yields(up to 90%)through we developed MFAACP in chapter 2.The resultant polytriazoles are completely soluble in commonly used organic sovents and possess good thermal stability.Thanks to the ir containing TPE and silole units as well as the spring-like alkyl spacers,the polytriazoles exhibit AIE instead of AEE features,and their nanoaggergates could be used to detect explosives with a superamplification quenching effect.Moreover,they also show high refractive indices and could be used to generate 2D fluorescent photopatten with high resolution.Thus,the multi-functionality of them enable to be applicalbe in diverse areas including chemosensors,optoelectronic and photonic devices,etc.In C hapter 4,trifunctional PFPAs were rationally designed and synthesized.Using the MFAACP established in C hapter 2,different hyperbranched polytriazoles with excellent solubility were prepared in high yields(up to 91%)via a A2 + B3 polymerization.Among the resultant polymers,the ones prepared from aromatic alkynes exhibited unique AIE properties,and their nanoaggergates could be used to detect diphenylamines(DPAs)with high selectivity and sensitivity,which could be reflected by the low detection limit of 54 nM.In addition,these hyperbranched polytrioles could also be adsorbed onto TLC plates to achieve rapid detection of trace DPAs in complicated samples.This demonstrates a prototype device for real-world application.Moreover,all hyperbranched polytrioles exhibited excellent thermal stability,and by further investigating their flammability properties,we found that they showed excellent flame retardant property.This will enormously improve their safe property in practical application.With such superior flame retardant property,these hyperbranched polytriazoles will undoubtedly find technology applications in diverse areas,for example flame-retardant coatings.During the exploitation of novel MFAACP basing on activated azides,we surprisingly observed that some PFPAs showed unique photochromic phenomenon.In C hapter 5,the structure-property relationships between different groups contained in PFPAs and photochromic properties were carefully studied and the structure of 4-azido-benzoyl was found to be responsible for this phenomenon.Aided by the nuclear magnetic resonance and electron spin resonance test,we think that the formation of free radicals in the UV irradiation process is the main reason of this phenomenon.The photochromic azide was successfully applied for UV strength sensors for direct eye detection of UV radiation pollution.