2 research outputs found

    Syndiotactic Polyallyltrimethylsilane-Based Stereoregular Diblock Copolymers: Syntheses and Self-Assembled Nanostructures

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    Structurally well-defined stereoregular diblock copolymers composed of syndiotactic polyallyltrimethylsilane (sPATMS) and poly­(methyl methacrylate) (PMMA) were prepared by using an α-bromoester-terminated sPATMS macroinitiator, which was chain extended by MMA using a cuprous halide-based atom transfer radical polymerization (ATRP) system. The α-bromoester-terminated sPATMS macroinitiator was prepared via the esterfication of hydroxyl-capped sPATMS with α-bromoisobutyryl bromide. The hydroxyl-capped sPATMS was generated via a selective chain transfer reaction to triethylaluminum (TEA) during the syndiospecific polymerization of allyltrimethylsilane (ATMS) conducted in the presence of syndiospecific <i>ansa</i>-metallocene catalysts. The proposed synthetic route not only offers the high-yield production of stereoregular sPATMS-<i>b</i>-PMMA but also provides the linking of the stereoregular block (sPATMS) with PMMA through a controlled/living radical polymerization process. Moreover, the proposed method offers effective control over the block chain length, the molecular weight distribution (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub>) and the stereoregularity of sPATMS block. Thus, the self-assembly of the resultant diblock copolymers produces well-ordered nanostructures from microphase separation, as evidenced by transmission electron microscopy and small-angle X-ray scattering results

    Control of Nanostructural Dimension by Crystallization in a Double-Crystalline Syndiotactic Poly(4-methyl-1-pentene)-<i>block</i>-poly(l‑lactide) Block Copolymer

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    The control of nanostructural dimension by crystallization-induced chain stretching was investigated in a novel double-crystalline block copolymer, syndiotactic poly­(4-methyl-1-pentene)-<i>block</i>-poly­(l-lactide) (<i>s</i>PMP–PLLA), featuring a lamellar phase. Because of the similar glass transition temperatures of <i>s</i>PMP and PLLA, their blocks could crystallize under soft confinement (i.e., a crystallization temperature higher than the glass transition temperatures of the constituent blocks) in <i>s</i>PMP–PLLA. With the strong segregation of <i>s</i>PMP–PLLA, the first-crystallized <i>s</i>PMP block was templated by microphase separation to form confined crystalline <i>s</i>PMP lamellae within the microphase-separated lamellar texture. Most interestingly, the first-crystallized <i>s</i>PMP block may also induce significant stretching of the PLLA chains from the lamellar interface, resulting in the increase of microdomain thickness of the PLLA block. With the increase of crystallization temperature, this chain stretching may become more significant, resulting in a large increase (∼34%) of the lamellar long period. The double-crystalline lamellar morphologies having homeotropic orientation for both <i>s</i>PMP and PLLA crystals can be acquired in the shear-aligned <i>s</i>PMP–PLLA as evidenced by simultaneous 2D small-angle X-ray scattering and wide-angle X-ray diffraction, giving uniform birefringence under polarized light microscope with thermal reversibility. As a result, the switchable lamellar nanostructures having significant dimensional change can be carried out by simply controlling crystallization or melting of the crystallizable blocks
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