Synthesis And Characterization Of Branched Thermoresponsive Polymers Based On Oligo (Ethyl Oxide)

Thermpresponsive polymer has gained extensive attention in smart polymer due to its potential applications. However, most of the researchs were foucus on the flexible chain polymer or semi-rigid polymer in recent years. There is little work to discuss about the possibility of the critical state between these two structures. In this thesis, on the basis of our group's previous work on the semi-rigid thermoresponsive polymers, we reduced the size of the side groups, and synthesized a series of thermoresponsive polymers with different length of ethylene oxide chain. The structure–property relationships of these polymers were also studied. The main works are as follows:1. A series of oligo(ethylene oxide)-based monomers were synthesized successfully, i.e., 1,2,3-tris(2-methoxyethoxy)-5-vinylbenzene(STEO-1), 1,2,3-tris((2-methoxyethoxy)ethoxy)-5-vinylbenzene(STEO-2), 1,2,3-tris(((2-methoxyethoxy) ethoxy)ethoxy)-5-vinylbenzene(STEO-3). And the chemical structures of these monomers were confirmed by 1H NMR, 13 C NMR and MALDI-TOF-MS. The corresponding branched homopolymers PSTEO-n(n = 1, 2, 3) were synthesized through conventional radical polymerization. The chemical structure and molecular weight of these homopolymers were analyzed by 1H NMR and GPC. And the result showed that PSTEO-n(n = 1, 2, 3) had similar molecular weight and molecular weight distribution. Moreover, the bulk properties of polymers were measured by TGA, DSC, POM and 1D WAXD. The tests results indicated that the polymers had good thermal stability for their decomposition temperatures were above 360 oC. Secondly, the glass transition temperature of the polymers decreased from 5.44 oC to-48.03 oC with the increasing length of the ethylene oxide chains. Thirdly, neither crystal nor liquid crystalline structure was formed at the range of temperature from room temperature to 300 oC.2. The solution properties of the monomers STEO-n(n = 1, 2, 3) and their corresponding polymers PSTEO-n(n = 1, 2, 3) were measured by variable temperature UV-Vis spectroscopy. All of the monomers and polymers can solute in deionized water at low temperature, and exhibited the thermoresponsive behavior as the temperature increased. The hydrophilic of monomers and polymers enhanced while the length of ethylene oxide chain increased, and lead to the increasing of cloud point, that is Tcp-STEO-1 < Tcp-STEO-2 < Tcp-STEO-3 and Tcp-PSTEO-1 < Tcp-PSTEO-2 < Tcp-PSTEO-3. In addition, the cloud point of the monomers aqeous solutions showed great concentration dependence. For example, the temperature difference between 5 mg mL-1 and 20 mg mL-1 was up to 41.9 oC in STEO-1 aqueous solution system. The phenomenons of other monomer aqueous solution systems were similarly to that. However, the variation tendencies of cloud point of the polymer and monomer aqueous solutions with different concentrations were inconsistent. As the length of ethylene oxide chains increased, the concentration dependence of polymer solutions decreased. The temperature difference between 1 mg mL-1 and 20 mg mL-1 was only 1.7 oC in PSTEO-3 aqueous solution system. In another hand, the introduction of inorganic salts will cause varying degrees of salting-out or salting-in effect. The salting-out effect of PSTEO-3 was greater than PSTEO-2, while the salting-in effect of PSTEO-3 was less than PSTEO-2. Thirdly, acid and alkaline system would cause a lower cloud point of the polymers, and PSTEO-3 had greater effect than PSTEO-2.3. Three series of thermoresponsive branched polymers with well-defined molecular weight(PSTEO-n, n = 1, 2, 3) were prepared via Reversible Addition-Fragmentation chain Transfer(RAFT) polymerization, and the molecular weight effect on the solution properties was studied. The cloud point of polymer solution decreased with increasing of the molecular weight. And the molecular weight effect increased in low molecular weight region with the increasing length of ethylene oxide chains. Besides, the thermoresponsive behavior of PSTEO-2 and PSTEO-3 series with different concentration was studied. The cloud point of polymer with low molecular weight highly dependence on the concentration. The reliability of the cloud point on the concentration was reduced while the molecular weight increased.