Structure And Performance Design Of Polymalic Acid-based Polyester Functional Material

As people pay more and more attention to environmental and safety issues,biodegradable polymers have received widespread attention in the past few decades.So far,scientific researchers have successfully synthesized a large number of polymers with microbial or enzymatic degradability.Among them,biomass-derived polylactic acid(PLA)and polymalic acid(PLMA)are quite attractive.Taking PLMA as an example,its monomer L-malic acid is easily extracted from fresh fruits,and then it is polymerized into PLMA through ring-opening polymerization or direct condensation polymerization.However,the polymer has many ring-opening reaction steps and low yield,and direct polycondensation can only obtain polymers with lower molecular weights.Therefore,research on PLMA is mainly focused on aliphatic copolyesters with PLMA as the chain segment or main body,with the purpose of increasing its molecular weight and mechanical strength,so as to explore its possible applications in the field of biomedicine.In fact,there are a large number of active sites on the main chain of PLMA,not only for chain extension,crosslinking can also be an effective way to improve the overall performance of PLMA.At the same time,the design of the cross-linked network structure can also give it a wider range of applications,such as elastomers and smart materials.Therefore,establishing the relationship between structure and performance is essential for expanding the application of PLMA-based materials.Based on the structure and performance design of PLMA polyester functional material,this paper studies the influence of PLMA on the phase structure and performance of PLMA/PLA incompatible systems and the design of PLMA cross-linking network structure starting from the direct polycondensation of PLMA oligomers.The main conclusions on the influence of the final mechanical state and stimulus response of the material,as well as the influence of the light-heat conversion filler on the shape memory behavior of PLMA crosslinked materials,are as follows:(1)Using PLMA oligomer as the dispersed phase,a PLA/PLMA two-phase blend system was prepared.From the perspective of two-phase structure and interface interaction,the mechanical properties and degradation behavior of the blends and the effect of PLMA on the cold crystallization of PLA were studied.The phase behavior and viscoelastic response indicate that the two phases are thermodynamically incompatible,and the interfacial tension of the two phases is relatively high.Compared with PLA,PLMA's poor adhesion and lower quality result in a significant decrease in the mechanical properties of the blend.The dilution effect caused by the addition of PLMA promotes the cold crystallization of PLA.Therefore,solid-state annealing can well compensate for the loss of strength and modulus of the blend caused by the presence of the PLMA phase.In addition,the presence of the hydrophilic phase PLMA can also adjust the degradation rate of the blend.Therefore,a simple method for preparing green PLA/PLMA blends with customizable properties through controlled annealing is proposed,and an aliphatic polyester blend with comprehensive biomass sources,biodegradability,and comprehensive performance is developed.It also provides a new way to develop the application of PLMA.(2)Cross-linking can open up more possibilities of biodegradable PLMA as a functional material,and the network structure is the key to the mechanical state and final application of the cross-linking system.Diols with different chain lengths are used to construct a PLMA cross-linked network to establish the relationship between network structure-mechanical state-material function.When the molecular weight of the diol increased from 100 to 400,the sample experienced a significant transition from high-strength plastic to low-loss rubber,and finally to soft elastomer.Using elastoplasticity and dielectric relaxation as probes,the potential connection between the mechanical properties of the cross-linked sample and the network structure was explored,and the brittle-ductile transition process of the material was revealed.Using samples with different network structures as components,an asynchronous driver with good performance was fabricated.Because cross-linked PLMA has easy-to-adjust mechanical state and Tg,as well as good antibacterial activity and shape memory effect,it has broad application prospects in functional materials or smart materials.(3)By introducing carbon nanotubes(CNTs)into the cross-linked PLMA system,a light-absorbing nanocomposite with adjustable structure and performance is prepared.Through the in-situ polymerization of CNTs and PLMA,the uniform dispersion of CNTs is realized,and then a crosslinking agent is futher used for crosslinking to obtain a crosslinked PLMA-CNTs nanocomposite with good mechanical strength and biocompatibility.The mechanical properties and photothermal properties of the materials were studied from two aspects:the loading capacity of CNTs and the interaction between PLMA and CNTs.Using elastoplasticity as a probe,the relationship between the dispersion state of CNTs and the relaxation of the cross-linked network was explored.And through the photothermal conversion experiment,the light absorption efficiency and photothermal conversion stability of the crosslinked PLMA-CNTs nanocomposite were characterized,and the precise control of the shape memory recovery position of the crosslinked PLMA-CNTs nanocomposite was achieved.Using such biocomposite materials,smart devices with programmable photothermal response and adjustable material properties can be easily manufactured.