Synthesis Of Functional Hyperbranched Poly(Triazole)s Via Click Polymerization

Click polymerization, a recently developed effective, mild, and functional group tolerant synthetic method, has now been wildly used in the preparation of various functional polymers. So far, a large number of linear polytriazoles have been prepared, but the research on hyperbranched systems is still rare. Hyperbranched polymers are highly branched macromolecules with some remarkable features, such as one-pot synthesis, low viscosity, high solubility, three dimensional structure and multiple end groups etc. Thanks to their unique structure and outstanding property, hyperbranched polymers could be good candidates in the applications of biomaterial and nano-technology, and thus have drawn growing attention.Aggregation-induced emission (AIE) is an unusual but interesting photophysical phenomenon observed by our group in2001:a series of propeller-shaped molecules are nonemission when molecularly dissolved but induced to emit intensely by aggregation. In this paper, a series of functional hyperbranched polytriazoles were designed and synthesized through the well combination of click polymerization and AIE materials. Furthermore, the properties and applications of these polymers were investigated in detail. The AIE mechanism of restriction of intramolecular rotation was also proven by study the tetraphenylethene (TPE)-based luminogens.By taking advantage of the innovative spring-like flexible spacers, we succeeded in synthesizing AIE-active hyperbranched polytriazoles, thus offered the AIE feature to hyperbranched systems. The polymers are soluble and thermally stable, and possess good film-forming ability and satisfactory light transmission. Photopattern could be generated via the photo-crosslinking reaction due to the remaining azide and ethynyl groups on the polymer periphery. Using the novel AIE effect, the polymers could act as chemosensors for the sensitive detection of explosives in their aggregate states with the superamplification quenching effect. The main mechanism for the detection of picric acid (PA) is ascribed to the energy transfer, while that for2,4,6-trinitroroluene (TNT) is the charge transfer. The difference in the quenching mechanism makes the polymer aggregates much more sensitive to PA than TNT. The concept of spring-like polymeric structures is of great value in terms of guiding the further development of hyperbranched polymers with AIE characteristics.Through rational structure design, we have successfully synthesized a pair of triazole-functionalized TPE derivatives and separated their pure conformers by the commonly used column chromatography technique. Both of the pure E and Z isomers show pronounced AIE effects. Using the precious pure stereoisomers, we have studied the AIE mechanism of TPE-based luminogens and found that no E/Z isomerization could be detected under the conditions of normal PL measurements, thus confirmed that the restriction of intramolecular rotation (RIR) is the main cause. The symmetric and asymmetric shapes of the E and Z isomers significantly affect their molecular packing, and the E isomer could self-organize into ordered microstructures, such as microfibers and nanorods, which exhibit obvious optical waveguiding effect. Both of the conformers undergo multiple chromisms, including mechano-, piezo-, thermo-, chrono-, and vapochromism, and because of its better organizability or crystallinity, the E isomer shows more marked chromic effects. The multiple chromic processes are all associated with changes in the modes of molecular packing which stem from the distinctive structural feature of the A/E luminogens.Soluble ethynyl-capped hyperbranched conjugated polytriazole with high molecular weight has been firstly constructed in high yield via the polymerization of TPE-containing diyne and tetrazide in equal concentration. This has been proven to be a repeatable and gel-free hyperbranched system. Thanks to the large amount of ethynyl groups on the periphery, this polytriazole could be facilely modified by alkyne-based click reactions. The PEG segment has been introduced onto the polymer via azide-alkyne click reaction in one pot; whereas pentanethiol could be efficiently reacted with the remained ethynyl groups through radical-mediated thiol-yne click reaction, and only one thiol coule be added to an ethynyl group. The obtained polytriazoles are all thermal stable and the char yield at800℃is up to74.8%. Due to the rigid structure, the polymers are aggregation-enhanced emission (AEE) active, and could form unimolecular nanoparticles from their dilute solutions with diameters around100nm. Thus, the polytriazole provides a novel clickable fluorescent platform, onto which various functional groups or biomolecules could be grafted efficiently, which will be surely to find broad applications in biological and optoelectronic fields.Soluble and thermally stable hyperbranched conjugated polymers containing triphenylamine (TPA) and TPE groups, which are linked by triazoles and triple bonds, respectively, were perepered. The PL measurement indicates that the triazole-linked polymer suffers from an aggregation-caused quenching (ACQ) effect, but the triple-bond linked one is AEE active. Meanwhile, their model compounds are all AIE active regardless the linkage and one of them could form white light emission solid under some special conditions. We thus consider that the ACQ effect of the obtained polytriazole is probably related to the existing large amount of polar triazoles, but the exact cause is still needed to be further investigated.Using the AIE-active hyperbranched polytriazole, we studied the pH effect on explosive detection in aqueous for the first time. The polymer aggregates are highly sensitive to explosive in acid to basic media, indicating that they are tolerant to various pH conditions. Improved quenching constant has been recorded in the acid THF/buffer mixture, suggesting a simple method to increase the detection efficiency of explosives. The prototype devices (test papers) of the polymer absorbed in filter papers could sense the PA in varying pH solutions. These advantages make the polymer be a good candidate for explosive detection in practical applications.