Synthesis And Luminescence Properties Of Amphiphilic Fluorescent Polymer

Fluorescent polymers (FPs) have recently attracted much research attention for their promising applications in the area of chemosensor and bioassays. The FPs available nowadays are usually hydrophobic aromatic conjugated polymers with lipophilic alkyl substituents. And there are also few hydrophilic species with ionic moieties. However, the biocompatibility of these two kinds of FPs still needs to be improved. The essences of the present work are to design and synthesize amphiphilic FPs by the conjugation of biocompatible poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene glycol) (PEG) segments with fluorophores, to investigate their fluorescence properties, and to contribute fundamental data for their potential applications in chemosensor and bioassays.Firstly, a series of novel PNIPAM derivatives containing tetraphenylethene (TPE) fluorophores with Aggregation-induced emission (AIE) characteristic, (PNIPAM-TPEs) were design and synthesized via introducing TPE moieties into PNIPAM. The PNIPAM-TPEs not only shows the intrinsic temperature-responsive performance of PNIPAM segments and AIE behavior of TPE moieties, but also demonstrates unprecedented features. Thanks to the highly responsive to local-environment of molecular conformation and the ultra-sensitivity of fluorescence, the primary-folding and quasi-collapse of polymer chains before Lower Critical Solution Temperature (LCST) were observed. This observation contributes a new technique to monitoring the LCST feature of temperature-responsive polymers and motion behaviors of macromolecular chains in complement to the traditional methods such as Dynamic Light Scattering (DLS) and turbid point measurement. In addition, by tuning the content of TPE moieties, the polymers exhibites unique temperature-regions in which the fluorescence intensity was evidently enhanced. This property offers a potential fluorescence probe to detect the subtle temperature changes that occurrs in micro-domain of bio-systems and is induced by bioactivities (e.g.) hyperpyrexia.Secondly, fluorescent hyperbranched polymers (PEG@hb) were constructed by Click reaction of azide-functionalized PEG chains with an acetyl-terminated hyperbranched polymer containing triphenylamine (TPA) fluorophores (hb-TPAs). PEG@hb possesses fluorescent hydrophobic core and biocompatible hydrophilic shell. The peripheral modification with PEG chains prominently changes the hydrophilicity of the hb-TPAs and longer PEG chains showed higher hydrophilic effect than shorter ones. These were confirmed by static contact angle measurement results. Colloidal particles of PEG@hb were fabricated through dialysis technique; the obtained particles demonstrated uniform size and clear core-shell structure, as observed in TEM images. These results are instructive to develop novel biocompatible materials for bioassays based on hydrophobic hyperbranched fluorescent polymers.