OEG-based Stimuli-responsive Dendronized Polymers

Dendronized polymers are constructed by densely rapping dendrons along a polymer backbone. This unique structure combination gives them various unique structural characteristics, and site isolation effect is among one of the most important. This isolation effect can alter the physical and chemical properties of the microenvironment encapsulated within the dendrons, and can weaken the influence of external factors to interiors. This effect is very important in controlled catalysis, photovoltaic and other application fields. Our previous work has demonstrated that oligoethylene glycol(OEG)-based dendronized polymers show unprecedented thermoresponsive behavior with fast phase transitions and small hysteresis. In present work, OEG dendrons were used to construct a series of novel thermoresponsive dendronized polymers, which show site isolation effect tunable by temperature. Herein, the research focus was shifted from the thermoresponsive behavior to the effect of temperature on the site isolation in the present thesis. The capabilities to weaken external influences by sites isolation effect were explored, aiming at understanding the temperature controlled mechanism. Along this line, the hydrolysis of dynamic covalent bond encapsulated within the microenvironment was investigated.Firstly, dendronized copolymers carrying dye moieties were investigated to examine the phase transition kinetics and fluorescence properties during the thermallyinduced aggregation processes. Site isolation effects from dendronized polymers can be controlled by thermally-induced collapse, and the alien moieties are forced to partly transfer from interior onto periphery of the aggregates. In addition, the p H indicator methyl red(MR) was introduced into the polymers to examine the site isolation effect. Results proved that this series of polymers can shield H+ in aqueous solutions, and the shielding can be enhanced by dendron generations and structural hydrophobicity. Neutralization experiments demonstrated that the microenvironment formed by site isolation can also be influenced by the external conditions. Fluorescence properties of BODIPY moieties within G1 copolymers were investigated, and the site isolation effect is found to enhance the fluorescence intensity which is also relevant to temperature. Releasing of DOX from G1 polymer under different conditions was investigated to prove that G1 polymer can control the release rate and amount of DOX. The nanospheres were formed through enamine crosslinking from different dendronized copolymers carrying aceto acetyl, and their morphologies can be controlled by p H and temperature. In the same time, the micro-membrane formed by dendronized polymers show shape memory behavior driven by temperature, which can be used as a media to convert the thermal energy into mechanical energy. Finally, the release test of Solvent Yellow 1(SY) from copolymer G2 A was tested, where SY was conjugated into the polymer through enamine bond. Here, G2 A polymer can control not only the release rate but also release quantity for SY.