Study On Preparation And Properties Of Polymer Hydrogel By Frontal Polymerization

With the rapid development of flexible electronics and biomedical materials and other fields,the demand for functional hydrogels has become more and more urgent.However,traditional hydrogel preparation methods have disadvantages such as time-consuming and energy-consuming,low conversion rate,and poor performance of single-component gels,which limit their applications in wearable electronic devices and biosensors,etc.Frontal polymerization(FP)is a novel method for the preparation of hydrogels,which has the advantages of fast reaction,low energy consumption,and high monomer conversion rate due to its self-propagating nature,and the reaction solvent of FP is generally a high-boiling organic solvent,which can be harmful to human body and the environment if not handled properly.Deep eutectic solvent(DES)is an emerging class of green liquids,which consists of hydrogen bond acceptor(HBA)and hydrogen bond donor(HBD)mixed and stirred at specific temperatures,and has excellent biocompatibility and stability.In this thesis,the mechanical properties,electrical conductivity,pH-responsive properties and self-healing properties of the composite hydrogels were investigated based on the rapid preparation of hydrogels and their composites by FP,mainly using DES as the reaction solvent,which provides relevant references for the further expansion of functional and application fields of hydrogels.(1)Ternary DES was prepared by using acrylic acid(AA)and acrylamide(AM)as HBD and choline chloride(Ch Cl)as HBA,and then nitrogen-doped carbon nanotubes(N-CNTs)with different mass fractions(0～1.0wt%)were dispersed in DES as fillers to prepare N-CNTs/P(AA-co-AM)composite hydrogels by FP.The interactions between N-CNTs and the composite hydrogels were investigated using analytical methods such as Fourier infrared spectroscopy(FTIR)and scanning electron microscopy(SEM),and the influence law of N-CNTs on the mechanical and electrical conductivity of the hydrogels was explored.The results showed that the mechanical properties of the hydrogels were significantly improved with the increase of N-CNTs content.Due to the dissociation of carboxyl groups in AA under alkaline environment,the composite hydrogels showed excellent pH-responsive properties under alkaline environment.Meanwhile,the increase of N-CNTs content had a significant enhancement effect on the conductivity of the hydrogels,and the conductivity of the hydrogels was enhanced by 4.2 times when the N-CNTs content was 1.0wt% compared with that of the hydrogels without the addition of N-CNTs,which provided great possibilities for their applications in electronic components and other fields.(2)DES was prepared with AA,AM and Ch Cl in the molar ratio of 1:1:1,and different contents(0～2.0wt%)of itaconic acid(IA)were added to the prepared DES with thorough stirring,the P(IA-co-AA-co-AM)composite hydrogels were prepared by thermal initiation frontal polymerization.It was observed using SEM scanning electron microscopy that the surfaces of the composite hydrogel samples all showed uniform porous structures,and it was also found that the variation of IA concentration affected their mechanical properties,swelling properties and pH responsiveness.The results showed that the elongation at break of P(IA-co-AA-coAM)hydrogels showed an increasing trend with the increase of IA content in the samples,with the highest elongation at break of FP5 samples reaching 167%.Since the addition of IA increased the number of hydrophilic groups,the equilibrium swelling of the composite hydrogels in distilled water increased.And it was found that the P(IA-co-AA-co-AM)composite hydrogels showed different swelling patterns under acidic and alkaline environmental conditions through testing,making them promising for applications such as acid-base indicators and biosensors.(3)P(AM-Urea)composite hydrogels were prepared by FP using Urea and AM as HBD and Ch Cl as HBA,and the three raw materials were mixed according to five groups of molar ratios(0.5/1.5/1～1.5/0.5/1)to obtain different DES.The effect of AM/Urea molar ratio on the behavior of FP was investigated,and the laws of AM/Urea molar ratio on the swelling properties,pH responsiveness and mechanical properties of the hydrogels were studied.The results showed that the FP5 sample with AM/Urea molar ratio of 1.5/0.5 took the shortest time to reach the swelling equilibrium and had the largest swelling ratio.In addition,the healing rate of FP3 samples reached 80% after 20 h of self-healing.The maximum tensile strength and maximum compressive strength of FP5 samples were increased by 7.5 and 4.55 times,respectively,compared with FP1 due to the increase of AM content,which led to the enhancement of hydrogen bonding between polymer molecules.The P(AM-Urea)composite hydrogel with good mechanical properties was prepared by FP,which could rapidly absorb water to reach the swelling equilibrium.