Environmentally-responsive smart polymer gel

:2003―06―25 Fund Project: National Natural Science Fund Project (20174027); Tianjin Natural Science Fund (033610511) In the 21st century, smart materials will be the dominant material used in human production and life. In recent years, people's understanding, research and application of smart materials have developed rapidly. The so-called smart material or smart material refers to a new material that can coordinate the various functions within the material, be sensible and responsive to the environment, and has the capability of function discovery. Environmentally-responsive polymer gels are a type of smart polymer material that responds effectively to ambient environmental stimuli such as temperature, pH, ions, electric fields, magnetic fields, solvents, reactants, light, or stress. And its nature has also changed. In this paper, the author has introduced the research results of temperature-responsive polymer gel, light-responsive polymer gel and conductive polymer gel in recent years.

1 temperature response polymer gel temperature response Polymer gel can also be called temperature-sensitive hydrogel, which responds to changes in the temperature of the environment, that is, when the ambient temperature changes, the nature of the gel will follow change. At present, the most studied are gels that undergo volumetric phase transitions as a function of temperature, and can be classified into two types: high-temperature shrinkage and low-temperature shrinkage. There is also a temperature-responsive gel that has a temperature change without volume change.

11 Temperature change in response to volume change 1) The hydrogel is the most commonly used temperature sensitive polymer. PNIPAM has a low critical solution temperature (LCST) around 32C. Above this temperature, the swollen hydrogel shrinks and below this temperature swells again. Studies have shown that the hydrogel synthesized by the copolymerization of NIPAM and certain monomers not only has NIPAM-like and LCST properties, but also has better swelling and shrinkage properties. At present, it is common to synthesize hydrogels by copolymerization of anion-containing monomers with NIPAM, while the temperature-sensitive hydrogels containing cationic monomers are less studied. The authors synthesized a cationic cationic hydrogel containing three cationic ammonium chloride chloride, DMAPAAQ, and NIPAM. Compared to the NIPAM hydrogel, this cationic hydrogel has undergone great changes in its LCST, swelling properties, and adsorption behavior of the surfactant SDS, indicating that this copolymer hydrogel swell rate with temperature The result of the change. The temperature at which the change in the hydrogel swelling rate is most pronounced is defined as the LCST of the hydrogel, where x is the molar fraction of DMAPAA-Q. It can be seen that the LCST of the gel increases with increasing x; when x increases to 37.5%, the volume of the gel no longer changes with temperature and the LCST of the gel disappears. There is a hydrophilic/hydrophobic equilibrium process in PNIPAM, an acylamino group is a hydrophilic group, and an isopropyl group is a hydrophobic group. When the outside temperature is lower than LCST, the hydrophilic group on the polymer chain in the gel network binds to the water molecules through hydrogen bonds, which causes the hydrogel to swell and absorb water. As the temperature rises, this hydrogen bonding weakens, and the interaction between hydrophobic groups in the polymer chain is enhanced. When the temperature rises above the LCST, the hydrophobic interaction between macromolecule chains plays a leading role, and the molecular chains aggregate with each other through hydrophobic interactions. At this time, the hydrogel undergoes a phase transition and its swelling rate drops dramatically. Therefore, if hydrophilic groups are introduced into the backbone of the gel, the hydrophilic/hydrophobic ratio of the entire gel network is increased, and the number of hydrogen bonds formed with water molecules is increased, so that more energy is required to destroy these hydrogen bonds, then the water The temperature at which the gel undergoes a phase transition increases and its LCST increases accordingly. After the cationic monomer DMAPAA-Q was introduced into the molecular chain, the proportion of hydrophilic group was increased, and due to the electrostatic repulsion between ions, more energy was needed when the chain was crimped, so the LCST of NIPAM was increased. The cationic monomer content was increased. The more the proportion of hydrophilic groups is larger, the greater the electrostatic repulsive force is, and the more difficult the macromolecular chain is to curl. When enough cationic monomer is introduced, the increased electrostatic repulsive force can not shrink the NIPAM molecular chain into agglomerate, and the LCST of the copolymer disappears.

The swelling rate increases. The maximum amount of water that can be accommodated in hydrogels with different ratios at different temperatures is related to the content of cationic monomers. The number of water molecules near the hydrophilic groups in DMAPAA-Q increases, and the swelling ratio increases significantly, so DMAPAA- The more Q content, the greater the swelling rate of the gel. However, when x = 37.5%, the swelling rate of hydrogels decreases instead. This is because although the cationic monomer content is high, the electrostatic repulsive forces between the molecular chains are large, but due to the small content of PNIPAM, the range of gel volume changes can be limited, and the chain stretches quickly to reach equilibrium. Static repulsion and internal stress balance.

- It can also be seen that the -co-DMAPAA-Q) copolymer gel between DMAPAAQm and the h-surfactant on the hydrogel Shhg spacer is a novel polycationic electrolyte between its 2 charges There is a long carbon chain that shows some degree of hydrophobicity. For this reason, the author studied the adsorption behavior of the surfactant gel, sodium dodecyl sulfate (SDS). The mass change of the poly(NIPAM-co-DMAPAA~Q) copolymer gel in SDS solution. At room temperature, the quality of x=0 hydrogel did not change significantly before and after immersion; =2.75% hydrogel began to decrease with increasing SDS concentration, and gradually recovered after 8X14mol/L. The x=7.5% gel showed a significant trend of first decrease and then increase. With the increase of SDS concentration, the initial shrinkage of the gel was rapid. When the concentration of SDS reached 5×14 mol/L, the gel swelled again after the maximum shrinkage. Adsorption behavior is divided into two stages: the gel shrinkage contraction of the first stage is proportional to the concentration of SDS, indicating that SDS forms a 11: complex with cations on the macromolecular chain; during the second stage, the concentration of SDS in the system continues to increase. At that time, the contracted gel swells again, which is the result of the hydrophobic interaction of the copolymer with SDS. The amount of DMAPAA-Q in the copolymer is relatively small compared to NIPAM. Therefore, the copolymer corresponds to the insertion of several cations between the long chains of PNIPAM. The gel was soaked in an anionic surfactant SDS solution. The cations in the gel macromolecule first interacted with the anions in the SDS solution to form a 11 complex, and the macroscopic manifestation was gel dehydration shrinkage. The temperature-sensitive semi-interpenetrating network hydrogel polysulfonic acid N,N-dimethyl(methacryloyloxyethyl)propylene proanesulfonate, PDMAPS, due to the adjacent ions being divided by the long hydrophobic chain ) is an amphoteric polyelectrolyte, which contains both a quaternary amine cation and a sulfonic acid anion on its oxime chain. The aqueous solution of PDMAPS is temperature-sensitive, and when it has a high critical solution temperature, due to the intramolecular and intermolecular interactions of the aqueous PDMAPS solution, the PDMAPS aqueous solution phase separates, and when it is higher than this temperature Molecular heat movement plays a major role. The molecular chain changes from coil to stretch and the turbid PDMAPS solution dissolves. The UCST of PDMAPS aqueous solution is related to the concentration of the solution, molecular weight, ionic strength and other factors. The author's experiment shows. Applied Chemistry, 2003, 20(4):328-331.