Morphological and Physical Properties of Triblock Copolymers of Methyl Methacrylate and 2‐Ethylhexyl Methacrylate
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AbstractSummary: Triblock copolymers of methyl methacrylate (MMA) and 2‐ethylhexyl methacrylate (EHMA) [that is, poly(MMA–EHMA–MMA)] were prepared by an emulsion atom‐transfer radical polymerization. The relationships of their structural, morphological, and physical properties were investigated. The latex particles had core‐shell morphologies and the block copolymers experienced phase separation. Small latex particles with a low number of cores could deform and wet silicon‐wafer surfaces, but the deformation of large latex particles was restricted by the internal two‐phase morphology of the particles. Latex casting produced continuous pinhole‐free films, in which hard poly(MMA) (PMMA) cores of different latex particles merged and provided interparticle connections. The morphology of solution‐cast films depended on block composition, solvent type, and film thickness. For all the prepared polymer samples, thick films cast in toluene had poly(EHMA) (PEHMA) materials at air surface, whereas those cast in tetrahydrofuran had a sponge‐like PMMA surface structure. Thin toluene‐cast films from P(MMA–EHMA–MMA) with the block degrees of polymerization ($\overline {DP}$) 200–930–200 showed spherical PMMA domains and those from 380–930–380 yielded a protruded worm‐like PMMA structure. The copolymer materials were coated on a glass surface for peeling tests. The films gave good hot‐melt adhesion properties when the $\overline {DP}$ of the PEHMA block was over 600. The peeling strength depended on the lengths of both PEHMA and PMMA blocks. The P(MMA–EHMA–MMA) sample with $\overline {DP} {\rm s}$ of 310–930–310 yielded the highest peeling strength of 7.4 kgf · inch−1. The developed material is demonstrated to be a good candidate for a solvent‐free, hot‐melt, pressure‐sensitive adhesives for special‐purpose applications such as medical tapes and labels.
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