Activator Regenerated By Electron Transfer Atom Transfer Radical Polymerization In Meso-Confinement And Properties Study And Controllable Synthesis Of Azobenzene-Containing Polymers

Recently,polymerization in the mesoporous environment has received extensive attention.Under the influence of the mesopore-scale effect,the polymerization process generally has a higher selectivity and reaction efficiency than conventional polymerization,resulting in a polymer with quantum nano-effects or unique structure and properties.However,the mechanism of polymerization in mesoporous confinement is not clear,and the relationship between the structure and size of mesoporous template materials and the properties of products obtained in confined polymerization needs further study.In the new era of artificial intelligence,photoresponsive smart materials have unique advantages and broad application prospects in the fields of artificial muscles,flexible robots,and microfluidic manipulation.However,conventional photodeformation liquid crystal polymers or liquid crystal polymer actuators containing exchangeable dynamic covalent bonds are difficult to repair and reprocess due to their crosslinked networks and complicated alignment methods.In the field of polymer science,the most basic scientific question is the relationship between structure and performance.Designing a polymer with a controllable sequence structure and controllable molecular weight at the molecular level,achieving precise polymerization and customizing polymer materials is still a huge challenge.In view of the above problems,this thesis focuses on controlled/"living"radical polymerization,studies on mesoporous confinement polymerization and controllable synthesis and application of photoresponsive smart materials.Specific results and conclusions are as follows:（1）Before doing polymerization in confinement,optimizing conventional activators regenerated by electron transfer atom transfer radical polymerization（ARGET ATRP）solution polymerization of methyl methacrylate（MMA）was carried out.We found that ethyl2-bromopropionate（EBr P）was a high-efficiency initiator.Polymerization kinetics studies and chain extension reactions demonstrated the typical"living"/controlled radical polymerization characteristics during the polymerization process.The controllable preparation of the polymer can be further optimized by changing the types of reducing agents and the dosage amount,ligand types,catalyst concentration,temperature,etc.During the polymerization process,the reaction rate increases with increasing the dosage amount of reducing agent or catalyst concentration,the polydispersity is narrowed;the apparent rate constant of the polymerization increases with increasing the temperature,the monomer conversion increases with increasing the polymerization temperature and the dosage amount of reducing agent and catalyst.The molecular weight of the polymer increases with increasing of the monomer conversion,which is consistent with the theoretical molecular weight.For example,when the concentration of catalyst is 200 ppm and glucose/CuCl₂=15:1,the monomer conversion can reach to 97%after 4 hours,and the measured number average molecular weight(M_n,GPC)of the obtained PMMA is 48 700 g·mol^-1,the theoretical molecular weight(M_n,theo)is 48 500 g·mol^-1,and molecular weight distribution is 1.27.The ¹H-NMR analysis shows that the stereoregularity of the polymer is given priority over syndiotactic architecture and the effect of the type of ligand on the stereoregularity is very slight.（2）For ARGET ATRP solution polymerization of MMA in the confined space of the silane coupling agents modified SBA-15 mesoporous materials,the specific surface area,pore volume and pore diameter of the mesoporous materials decreased after MMA polymerization.The mesoporous channel of SBA-15 can be used as a nanoreactor and has a strong confinement effect on the ARGET ATRP of MMA.The morphology of PMMA obtained in confined polymerization replicates the intrinsic morphology of SBA-15.The modified SBA-15 can adsorb more monomer mixture solution than the unmodified SBA-15.Compared with C-PMMA obtained by conventional ARGET ATRP,the thermal stability,molecular weight,molecular weight distribution and isotactic ratio of PMMA obtained in confined polymerization were significantly increased,while the syndiotactic ratio was decreased.The glass transition temperature（T_g）of the PMMA obtained in the channel of modified SBA-15 is higher than that of obtained in the unmodified SBA-15 channel and the C-PMMA obtained by conventional polymerization.（3）For the ARGET ATRP solution polymerization of MMA in the channels of modified halloysite nanotubes（HNTs）by the silane coupling agents,it was found that the HNTs skeleton structure was not destroyed after modification and MMA polymerization,and the crystal structure was still maintained.The specific structure,the specific surface area,the pore volume and the pore diameter decreased gradually,indicating that the modification of HNTs was successful and the polymerization was carried out in the confinement space.Compared with conventional polymerization of MMA,the PMMA in channels possessed higher molecular weight,thermostability,isotactic structure content,and narrower polydispersity,but decreased syndiotactic structure content.This is consistent with the results in the above-mentioned confinement polymerization in mesoporous materials.（4）For the ARGET ATRP bulk polymerization of styrene（St）in different types of mesoporous materials,compared with the conventional ARGET ATRP bulk polymerization of St,the ARGET ATRP bulk polymerization of St in three-dimensional cubic continuous structure MCM-48 channels shows a high potential isospecific polymerization.The polystyrene（PS）obtained in the rod-shaped SBA 15（2D）,spherical SBA-15 and MCM-41（1D）has a higher molecular weight and T_g,while the polydispersity is broadened.The PS obtained in the spherical MCM-48 not only increases the molecular weight,but also has a narrower polydispersity.Nitrogen adsorption-desorption results show that the specific surface area,pore volume and pore size of mesoporous materials decreased after St polymerization.For example,the MCM-41/PS displayed a reduction from 1236.0 to 601.9 m²·g^-1 of specific surface area and from 0.804 to 0.231 cm³·g^-1 of total volume,respectively.FT-IR results show that stretch vibration of PS in the pore channels of mesoporous materials is restricted.In addition,the morphologies of PS obtained in mesoporous silica templates replicates the morphology of the corresponding mesoporous silica templates.The above results indicate that the structure and morphology of different mesoporous materials have a strong and specific confinement effect on the ARGET ATRP bulk polymerization of styrene.（5）For the grafting method on the surface of mesoporous materials,the“grafting from” strategy was applied to immobilize the initiator 2-bromoisobutyryl bromide onto the pore walls of SBA-15 firstly.Then,the surface-initiated ARGET ATRP method was used to realize the controlled graft polymerization of a functional monomer glycidyl methacrylate（GMA）in a mixed solvent（cyclohexanone/DMF=1:2（v/v））,and the SBA-15-PGMA composite was obtained.The thickness（10-40 nm）and molecular weight(13 100-74 500 g·mol^-1)of the grafted polymer can be controlled by simply adjusting the polymerization time.The chain end functionality of SBA-15-PGMA was confirmed by using SBA-15-PGMA as a macroinitiator and added a second monomer MMA for further preparation of SBA-15-PGMA-PMMA hybrid.In addition,due to existence of abundant highly reactive epoxy groups,the PGMA brushes grafted SBA-15 could serve as a versatile reactive platform for further surface modification or functionalization.This work provides an efficient and facile strategy for the preparation of organic/inorganic hybrid materials within a mesoporous material by grafting a polymer brush with a predetermined structure,and controllable molecular weight.（6）In the last chapter of this thesis,a series of linear photoresponsive azopolymers with different molecular weights were synthesized.The high-molecular-weight azopolymer(M_n=80-100 kg·mol^-1)has more excellent mechanical properties and processing properties than the low-molecular-weight azopolymer(M_n=5-53 kg·mol^-1)due to the chain entanglement effect.Combined with polymer chain entanglement and photoinduced reversible solid-to-liquid transition,a healable and reprocessable photoactuator was prepared.The entangled azopolymer has excellent mechanical properties and flexibility.The entangled azopolymers can be prepared as free-standing films and used as photoactuators.The orientation alignment of the azobenzene mesogens in the actuator is achieved by stretching in its liquid crystal region（90°C）.Both oriented and unoriented azopolymer films exhibited photoinduced reversible deformation.The oriented film showed a faster response speed and a larger bending deformation.The oriented film bent 62°toward the light source after ultraviolet light irradiation for 10 minutes.The unstretched oriented film bent 26°toward the light source after ultraviolet light irradiation for 10 minutes.Photoinduced reversible solid-to-liquid transition of azopolymers contributes to photodeformation of unoriented azobenzene polymer films.Unlike traditional cross-linked liquid crystal elastomers（LCEs）,photoactuators prepared from linear azopolymers can be reprocessed by conventional solution or melt processes.Furthermore,based on the photoinduced reversible solid-to-liquid transition properties,it enables repairing cracks or reprocessing（photolithography microstructures）at high spatial resolution without the use of solvents or at room temperature.The combination of azopolymer chain entanglement and photoinduced reversible solid-to-liquid transition provides a new strategy for designing light-controlled flexible actuators with good reprocessability and healability.