Preparation And Properties Of Smart Materials Based On Acrylic/Methacrylic (Easter)

In recent years,with the rapid development of medicine,electronics and information,traditional synthetic materials have been unable to meet the needs of related industries.The preparation of"smart materials"with special functions that can respond to changes in the external environment has become a hot topic for people to study.As a kind of smart polymer material,shape memory polymers（SMPs）can realize the transition between"initial form"and"temporary form"when they are subjected to external stimuli（such as heat,light and electricity,etc.）.Therefore,they are widely used in biomedical materials,textiles and industrial devices and other fields.Photochromic materials generally refer to materials that change color when exposed to ultraviolet light and are an integral part of optical adaptive lenses and smart windows.Acrylic acid/methacrylic acid（esters）are common monomers used in engineering polymers and can be used to prepare a series of functional materials through polymerization with various compounds,which have great potential in the production of multi-purpose chemical products.On the basis of summarizing the existing literatures,SMPs and photochromic WO₃organic/inorganic nanocomposites were prepared based on acrylic/methacrylic monomers.Firstly,a series of diblock polymers,polymethylmethacrylate-b-poly（butylacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid）（PMMA-b-P（BA-co-AMPS））with varying molecular weights and compositions were conveniently synthesized via the reversible addition-fragmentation chain-transfer（RAFT）polymerization.The selection of monomers and the design of molecular architecture lead to a strong Flory-Huggins interaction parameter（χ）between PMMA and P（BA-co-AMPS）segments,facilitating microphase separation for the materials,and therefore,segregated PMMA domains upon vitrification work as physical crosslinkers.Meanwhile,AMPS units are broadly applied in polymeric materials for their supramolecular interactions（dipole-dipole/ionic interactions）,which could offer the second crosslinkers.As such,the prepared PMMA-b-P（BA-co-AMPS）diblocks behave like typical SMPs with excellent shape memory characteristics:shape recovery ratio 95%.Notably,these materials are also endowed with superior mechanical properties,exhibiting breaking strain and tensile strength at about 500%and 10 MPa,respectively.These supramolecular block polymers are thermally processable due to the physical crosslinking and are facile to be melt compounded into any desired shape（dog-bone,disk,and film）.More importantly,the prepared SMPs also possess the self-healing capability under ambient conditions,benefited from the ionic interactions within the polymer network.In addition,in this paper,polymethylmethacrylate（PMMA）,polybutylacrylate（PBA）and inorganic photochromic tungsten trioxide（WO₃）were also combined to prepare organic/inorganic nanocomposites with excellent photochromic properties.Firstly,the surface of inorganic WO₃ was grafted to poly（methyl methacrylate-co-butyl acrylate）P（MMA-co-BA）by chemical grafting method.The photochromic properties of prepared nanocomposites with different proportions and compositions were qualitatively and quantitatively characterized.The study of photochromic properties showed that the percentage of WO₃ nanosheets had a dominant effect on the coloration and bleaching process of nanocomposites.When the percentage content of WO₃ was increased from 0.5 wt%to 2.0 wt%,the entire response time was drastically reduced from 4000 min to 80 min.The acrylate polymer components effectively contributed to the mechanical integrity and thermal processability of the product.Unlike the brittle and rigid WO₃ crystal,these WO₃-graft polymers showed extraordinary ductility with a breaking strain as high as 800%while maintaining a relatively high breaking strength（≈2 MPa）。Secondly,the preparation of WO₃ and random copolymer P（MMA-co-BA）was carried out separately.The photochromic organic/inorganic nanocomposites were prepared by simple mechanical blending.The effects of morphology,surface polarity and content of WO₃ on the photochromic properties and mechanical performance of the prepared nanocomposites were studied systematically.The miscibility of WO₃ and polymers was controlled by the polarity of WO₃ surface.The nanorod morphology was found to effectively reinforce the WO₃/P（MMA-co-BA）composites,while WO₃ nanosheets tended to deteriorate the mechanical performance.Compared with theσ_b of 32.1MPa andε_b of 175%for the pure random copolymer P（MMA-co-BA）,the addition of 0.5wt%of pristine WO₃ nanosheets decreasedσ_b to 29.5MPa andε_b to110%,however,WO₃-Rod（0.5%）exhibited an enhancedσ_b of 35.9 MPa andε_b of 200%.The morphology and loading level of WO₃ in the composites could strongly affect the photochromic behavior of the products,but the surface polarity did not.