Approaches To Prepare New Types Of Shape Memory Polymers Via RAFT Emulsion Polymerization

Shape memory polymers(SMPs)are an important class of stimuli-responsive materials.SMPs can achieve a predefined shape change spontaneously under specific environmental stimulus.The device prepared by SMPs can work as a programmable machine.Thus,SMPs are promising in the fields like biomedical,aerospace,flexible electronic applications.Until now numorous researches on theoritical basis have already clearly illustrated the physical mechanism of a SMP.The basic design methods have also been well established.However,there are still difficulties in designing SMPs with adjustable transition temperature,multi-SMPs and soft SMPs,which limit the development of shape memory polymers.From the view of multi-scale structure design,this thesis studied the controlled preparation of SMPs with adjustable transition temperature,multi-SMPs and soft SMPs by synthsizing a series of block copolymer latexes employing RAFT emulsion polymerization technique with styrene and acrylates as model monomers,constructing a multiphase system through latex blending methods and introducing 3D printing technique.The major studied topics and the key findings are listed in the following:1.The establishment of new technique to adjust the transition temperature of a SMP.Polymers with chain sequence structure as polystyrene-b-poly(styrene-random-meth acrylate)-b-polystyrene synthesized through RAFT emulsion polymerization technique had been synthsized.Glass transition temperature of the polymer can be adjusted by tuning the copolymerization ratio in the middle block.When the molecular weight of each block was 15 kg mol-1,100 kg·mol-1 and 15 kg mol"1,respectively,the polymer could self-assemble into "island-sea" structure.By tuning the copolymerization ratio of the middle block(7:1,1:1,3:7),the synthesized polymers had different Tg(45 ?,65 ?,80 ?)meanwhile owned excellent shape memory performance.2.The establishment of new method to prepare extrinsic multi-SMPs with the use of 3D printing technique.The synthesized polystyrene-b-poly(styrene-random-meth acrylate)-b-polystyrene copolymers with different Tg were sequentially processed through Fused Deposition modeling 3D printing to obtain a device with different SMPs in different locations,which could be used as an excellent extrinsic multi-SMP.When these polymers were processed at high temperature,the two outer polystyrene blocks could not only assemble into physical cross-links to provide outstanding shape recovery ability,but also form tough glassy zones in the interface between different polymers to improve the final material's strength.The method can produce multi-SMPs,which owned great superiority of convenience to set temporary shapes and design the arrangement of different parts,thus meeting the requirements in many applictaions.3.The establishment of new technique to prepare intrinsic multi-SMPs by core-shell nano-latex blending method.Latex particles with polymer chain sequence structure as polystyrene-b-poly(styrene-random-meth acrylate)-b-polystyrene were synthesized through RAFT emulsion polymerization technique.The blending of these latex particles led to very uniform distribution of different SMPs.In the following hot processing,the polystyrene shell layer broke and formed physical cross-links,which hindered the long-range movement of different phases and avoided the mixing of identical poly(styrene-random-meth acrylate)phases.This method could produce a multi-phase material with outstanding mechanical and shape memory properties wherein each phase owned around 100 nm phase size with excellent dispersion properties.Compared to latex blending method,the multi-phase material prepared by solution blending method had both micro-phase and macro-phase separation both inside,which was harmful to the final mechanical and shape memry properties.By using latex blending method,the well-dispersed-phase structure could be achieved then the blending ratio was adjusted in a large range,which helped the fixation of temporary shape under the condition of less hard phases.An optimized intrinsic multi-SMP with the shape fixity and recovery ratio higher than 80%between each two temporary shapes was achieved by tuning the blending composition.4.The establishment of new method to prepare soft SMPs through polymer chain design and latex blending technique.A high-modulus polystyrene-b-poly(styrene-random-meth acrylate)-b-polystyrene copolymer latex(SMMAS,the molecular weight of each block was 15 kg mol-1,120 kg mol-1 and 15 kg mol-1,respectively)and a low-modulus polystyrene-b-poly(n-butyl acrylate)-b-polystyrene copolymer latex(SBAS,the molecular weight of each block was 15 kg mol-1,120 kg·mol-1 and 15 kg mol-1,respectively)were designed and synthesized through RAFT emulsion polymerization.Different polymer composite could be produced by blending these copolymer latex particled and tuning the composition.When SSMAS content was 45%in the system,co-continuous structure could be formed inside the material.This material owned the Young's modulus of 40.9 MPa meanwhile its fixity ratio reached 90.8%.