Preparation And Performance Of Thermosensitivity PNIPAM Hydrogels By Photo-frontal Polymerization

Photo-frontal polymerization（PFP）not only has energy-saving and hige advantages from thermal frontal polymerization but also has moderate and controllable advantages of photopolymerization.If the photobleachable photoinitiator was selected,then there is no need to add other thermal initiators to avoid the instability from the severe exotherm system.Therefore,the PFP method can be used to prepare thermosensitive hydrogels.Thermosensitive hydrogels have attracted much attention and research in the academic community because of its sensitive response to external temperature.But their inherent gel structure is relatively weak and lacks sufficient mechanical properties,making it difficult to use them stably in various fields.So it needs to be modified.The introduction of polyhedral oligomeric silsesquioxane（POSS）with an inorganic cage-like structure can increase the thermal stability and mechanical properties of the hydrogel.So long as POSS particles with suitable functional groups can be found,POSS can be added into the thermosensitive hydrogel by chemical crosslinking.The main work and results of the thesis are as follows:1.With using N-isopropylacrylamide（NIPAM）as a thermosensitive monomer and dimethyl sulfoxide（DMSO）as a solvent,using an armored K-type thermocouple to measure the highest temperature(T_max)of appointed position and calculate the rate of moving front in PFP system,to evaluate the kinetic effects of light intensity,type and amount of photoinitiator and crosslinking agent on the PFP process for preparation of thermosensitive PNIPAM hydrogel systems.It was found that the T_max of the appointed position and the rate of the PFP front both increase with increasing the light intensity.Both of T_max and PFP front rates of the appointted position increase with the amount of photoinitiator and crosslinking agent at the first step,and then they will decrease while the amount of photoinitiator and crosslinking agent is more than 0.5 mol%.Compared with photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide（TPO）and bis（2,4,6-trimethylbenzoyl）phenylphosphine oxide（Bis-TPO）,it is concluded that the photoinitiator TPO has a better effect in the PFP process.Compared with the crosslinking agent N,N’-methylenebisacrylamide（MBA）and tripropylene glycol diacrylate（TPGDA）,it was found that the lower the molecular weight between the double bonds of the the crosslinking agent,the lower the MBA has higher T_max and front rates of PFP.2.Selecting the appropriate light intensity and photoinitiator TPO,it can use infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）,weighing method,differential scanning calorimetry（DSC）,thermogravimetry（TG）,compressive testing and dynamic mechanical analyzer（DMA）to characterize the structure and properties of the thermo-sensitive hydrogel produced by the PFP method.The effect of the type and amount of the crosslinking agent on the structure and properties of the temperature-sensitive hydrogel was discussed.It is found that the molecular structure of the crosslinker has a certain influence on the structure and properties of the thermosensitive PNIPAM hydrogel.For example,because the crosslinking agent TPGDA has hydrophobic structure,the swelling rate of the PNIPAM hydrogel of this system is lower and the cross-linked network is tighter.However,its compression performance is slightly better than that of the MBA system.3.As a crosslinking agent,cage-like silsesquioxanes（MA-POSS）with eight acrylic acrylate groups were introduced into PNIPAM hydrogel.And it can use FT-IR,SEM,DSC,TG,compressive testing and DMA to characterize the effects of MA-POSS on the structure and properties of the organic-inorganic hybrid thermosensitive hydrogels prepared by the PFP method.Compared with commonly crosslinking agent,it found that the introduction of MA-POSS can increase the thermal stability and compression performance of PNIMAN hydrogel.