Chemical Crosslinked And Metal Coordinated Shape Memory Polymers: Synthesis And Properties Studies

Shape Memory Polymer(SMP)is a new kind of smart material with shape changing abilities.The theory and experimental studies of SMP shows profound theory and practical significances.It is an urgent research task to study the design and synthesis method,the theoretical foundation,and space environmental adaptability of shape memory polymers having large deformation ability or good space environmental adaptability.Under this background,a chemical crosslinked shape memory cyanate and a transition metal coordinated shape memory elastomer were discussed from synthesis mechanism,performance control,the space environment adaptability and application prospects in this thesis.The microstructure and chemical composition of these materials were characterized by small angle X-ray scattering analysis,scanning electron microscope,and Fourier transform infrared spectroscopy.The mechanical properties of these materials were studied by rheological analysis,dynamic mechanical analysis,and tensile test.The thermal performance of these materials were investigated by differential scanning calorimetry and thermogravimetric analysis.The shape memory performance of these materials were investigated by bent-unfold and stretch-shrink test.The chemical crosslinked shape memory cyanate was prepared by introducing polyethylene glycol,a linear polymer chain into the three-dimensional crosslined network of cyanate.The optimized shape memory cyanate having good mechanical properties and tunable glass-transition temperature between 135.1 oC to 262.3 o C were obtained by adjusting the content of polyethylene glycol.The main effect of polyethylene glycol is through reducing the reactive chances of cyanate monomers to reduce the crosslink density.With the increase of polyethylene glycol,the initial thermal decomposition temperature of shape memory cyanate gradually declinied,but the values are all higher than 355 o C.Tensile strength distributed between 30~80MPa,and elastic modulus gradually dropped to 0.74 GPa from 2.95 GPa.The fracture strain increased from 3% to 36%.Modified shape memory cyanate could recovery its original shape in a free state within 30 s,and shape recovery rate is more than 95%.The novel thermosetting shape memory cyanate possessesing high glass-transition temperature,quick response ability,and high shape recovery rate are of great potential in space deployable structures.The space environmental adaptability of the shape memory cyanate with a glass transistion temperature 205.8 o C was studied by simulation experiments on the ground.The ground simulated space environment involved thermal cycling,ultraviolent ray,and atomic oxygen irradiation.The effects of the above space environment were investigated in terms of microscopic morphology,chemical composition,mechanical properties,glass transition temperature and thermal properties.The cyanate-based SMP shows 1.04% of total mass loss,0.01% of collected volatile condensable matter,and 0.80% of water vapour recovery,as determined by vacuum outgassing tests;The vacuum thermal cyclic test has a positive effect on all SMP properties.The initial decomposition temperature was increased by 10°C to 17°C,tensile strength by ~14.5%,Tg by 5°C to 10°C.The average elastic moduli were all above 1.83GPa;Vacuum UV radiation deepened the color of the surface,improved the thermal stability of the SMP sample and increased the initial decomposition temperature by 10°C to 16°C.The 1000 ESH and 2000 ESH of UV radiation resulted in minimal,if any,changes in chemical bonding.The 3000 ESH of irradiation induced some instability of the molecular structure within the material.However,UV radiation did not detectably change the mechanical properties of the cyanate-based SMP;the tensile strength and elastic modulus remained essentially constant at 65±2 MPa and 1.94±0.08 GPa,respectively;After exposed in atomic oxygen environment in vacuum,the SMPs' surfaces showed obvious local delamination.When the radiation dose achieved 1022O/cm2,the surface would be totally delaminated and result in a new uneven surface.However,the damage resulting from delamination was only on the surface,which have little effect on the mechanical p erformance.So the effect of sample thickness and depth of delamination should be comprehensively considered in practical application;The average shape fixity rate and average shape recovery rate before and after irradiation with thermal cycling,ultraviolent ray,and atomic oxygen irradiation were all above 97.6%,and the repeatability was good.A supramolecular shape memory elastomer was designed and synthesized using a blend of functionalized polybutadiene oligomers and functionalized poly(styrene-co-vinyl pyridine)(PSVP)where a physically crosslinked network was produced by a transition metal complex between Zn2+ ions from carboxylated telechelic polybutadiene and the pyridine group of the PSVP.The microstructure of the elastomeric blend consisted of microphase-separated glassy nanodomains of principally PSVP,which served as crosslink junctions that were connected with polybutadiene chains.Thus,the intermolecular metal-pyridine complex most likely resided at the interface between the nanodomains and the soft rubber phase.The elastomer had reasonably good mechanical properties and was thermoplastic.Shape memory was achieved by tuning the intermolecular complex and using the microphase separation as a permanent network.The shape memory elastomer exhibited good shape memory properties for large deformations.For example,for a strain of 212.8%,the shape fixing and recovery efficiencies were as high as 94.6% and 81.0%,respectively for the first shape memory cycle,and were 93.0% ±0.7% and 95.1%±1% respectively in the following seven cycles.In addition,the shape memory elastomer showed excellent triple-shape memory effect,which is applicable to variable deformations,inclouding stretching,twisting and rolling.The molecule structure of the cyanate-polyethylene glycol system was verified using molecular dynamic simulation.It shows that the linear polyethylene glycol could effectively adjust the Tg of the polymer system.From a macro perspective,this effect of polyethylene glycol makes the cyanate resin with ultra-high crosslink density easy to change its shape,and ended with shape memory behavior.The morphological structure of the metal coordinated shape memory elastomer was summarized as: in the blend of Zn PB and PSVP,PSVP takes the place of netpionts of the network,Zn PB takes the place of the flexible molecular chains of the network,and Zn PB and PSVP are linked by the metal coordination interaction between them.All these three parts construct the network that shape memory polymer needed.The rheology analysis also proofed that the metal coordination interaction was much stronger than hydrogen bonding in the polymer system.The chemical crosslinked and metal coordinated shape memorypolymer prepared in this work can be integrated by the principle and molecule level requirments of shape memory polymer.Taking the molecule level requirments as the start point,according to the reqiuments of service condition,the materials can be selected and designed appropriately.The thread and method of shape memory polymer research can be broaden based on this work.