Preparation And Properties Of Novel Semirigid Water-soluble Thermoresponsive Polymers

Thermoresponsive polymers, as a kind of smart polymers, which exhibit reversible property changes in response to temperature changes in environment, have attracted considerable research interest due to their promising potential. Recently, many kinds of thermoresponsive polymers have been synthesized. However, the remarkable character of these synthesized thermoresponsive polymers is that their main chains are mostly flexible. Of course, there is another class of interesting and important thermo-responsive polymers, such as polypeptide and alkyl-substituted celluloses, which have semirigid main chains. But the molecular design and synthetic process of these thermoresponsive natural polymer derivatives are still limited. It is well-known that mesogen-jacketed liquid crystal polymers (MJLCPs) have the typical semirigid chain structure. So far, the synthesized MJLCPs are hardly water-soluble and much less thermoresponsive. Here we designed some novel polymers in the light of the idea of combining MJLCPs with thermosensitive polymers. These new synthesized thermoresponsive polymers having both liquid crystal properties and thermoresponsive properties will be meaningful in academic research and practical applications.This dissertation gave a detailed discussion on the synthesis and characterization of two thermoresponsive monomers and corresponding polymers based on 2-vinylterephthalic acid. Three parts of works were stated as below:1. Two new mesogen-jacketed liquid crystal monomers bis(N-hydroxyethyl pyrrolidone) 2-vinylterephthalate (M1) and bis(N-hydroxypropyl pyrrolidone) 2-vinyl terephthalate (M2) were designed and synthesized. M1 and M2 both exhibited a thermoresponsive phase transition behavior in aqueous solution. The lower critical solution temperature (LCST) of M1 and M2 both decreased with increasing concentration and the rate of the phase transition became very fast at the high concentration. However, at the same concentration, the LCST of M2 was lower than M1, and M2 exhibited more sensitive thermoresponsive property.2. Corresponding polymers P1 and P2 were synthesized via free radical polymerization. Similar to previous MJLCPs, P1 exhibited a columnar nematic phase (ФN) and P2 exhibited a hexatic columnar nematic phase (ФHN). These polymers which were semirigid had been confirmed by solid-state NMR experiments. The lower critical solution temperature (LCST) of P1 in water exceeded the temperatures that could be measured. Subsequently, in order to decrease the cloud point, we designed and synthesized another new polymer P2 by introducing the more hydrophobic alkyl group. Just as expected, P2 polymer aqueous solution exhibited a sharp and rapid phase transition and no hysteresis phenomenon. The concentration and the deuterium isotope had great effect on the cloud point. The cloud point decreased with increasing concentration of the polymer solution. At the same concentration, the cloud point in D2O was lower than that in H2O.3. Narrow-disperse polymers P2 were prepared by atom transfer radical polymerization (ATRP). When the molecular weight reached 4.68×10⁴ g mol^-1, P2 exhibited the liquid crystal property. The cloud point of P2 polymer aqueous solution was strongly dependent on its molecular weight and concentration. The cloud point of P2 increased with increasing molecular weight, and when the molecular weight increased to a certain extent, the cloud point was slightly lower. As the concentration increased, their cloud points decreased.