as the hard segment phase. Montana et al. [14] discovered that the block copolymer PMMA-PBA-PMMA could toughen PMMA up to an elongation at break about 17.5%, but decrease its tensile strength. It can be seen from the above-mentioned literatures that the toughness of PMMA can be greatly improved by introducing inorganic nanofillers, polymers with lower T g , or copolymerization units. However, the methods can cause relatively low strength of polyacrylate, and reduce its transparency at visible light deriving from the presence of phase separation structure. The incorporation of the third or more monomer units into binary polyacrylate can increase the compatibility of original polymers, that is, a narrower T g gap between the soft and hard phases, [16] thereby changing the phase separation structure. [17,18] The particle-brush and star polymers with the core-shell structure are prepared by atom transfer radical polymerization of BA with styrene and acrylonitrile, and then blended with PMMA. [19] The toughness of the blend prepared is better than PMMA, and its transparency is close to that of PMMA. The polymer films prepared by methyl methacrylate, butyl methacrylate, and glycidyl methacrylate exhibit different T g s with the increase of glycidyl methacrylate content, so the phase separation structure was modified and the latex film cast on the glass plate was transparent. [20] It can be seen that the copolyacrylate is still an elastomer and has good visible-light transmittance after the incorporation of the third or more monomer units.The transmittance of elastomer will be significantly reduced after damage, while the self-healing of transparent elastomer can improve its application performance and service life. The self-healing effect derived from dynamic non-covalent interactions, such as hydrogen bonding, [21][22][23] electrostatic, [7] dipoledipole, [3] host-guest, [24,25] intermolecular interactions, [26,27] and so on, can be applied to the transparent elastomer. The copolyacrylate is still an elastomer after the incorporation of the third or more monomer units, which will provide the mobility of molecular chain and contribute to intermolecular interactions, promoting self-healing, but will decrease the mechanical strength of copolyacrylate. So the healing of transparent copolyacrylate elastomer remains to be further studied. [28,29] The copolymerization of BA and MMA can improve the toughness of PMMA, but its transparency is reduced by the phase separation behavior. The glass transition temperature of HEA homopolymer is between those of PMMA and PBA. HEA will be incorporated into the copolymerization system as a third
Transparent ElastomersThe contradiction between mechanical properties, transparency, and healing effects for polyacrylate elastomers is not solved yet. The copolyacrylate elastomers are prepared based on the bulk copolymerization with methyl methacrylate (MMA) and butyl acrylate (BA), incorporating the β-hydroxyethyl acrylate (HEA) monomer. Compared with PMMA-co-PBA, with the incorporation of HEA...