Self-assembly and crystallization behavior of a double-crystalline polyethylene-block-poly(ethylene oxide) diblock copolymer
Self-assembly and crystallization behavior of a double-crystalline polyethylene-block-poly(ethylene oxide) diblock copolymer
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DOI：
10.1016/j.polymer.2004.09.063
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发表时间：
2004-11
期刊：
影响因子：
4.6
通讯作者：
Lu Sun;Yuxiu Liu;Lei Zhu;B. Hsiao;C. Ávila‐Orta
中科院分区：
文献类型：
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作者：
Lu Sun;Yuxiu Liu;Lei Zhu;B. Hsiao;C. Ávila‐Orta
研究了低分子量聚乙烯-聚环氧乙烷嵌段共聚物（PE-b-PEO）的自组装和结晶行为。PE和PEO嵌段的数均聚合度分别为29和20。通过尺寸排阻色谱法测定的分子量分布为1.04。PE-b-PEO样品表现出PEO和PE晶体分别在28.7 °C和97.4°C的两个熔点。PE块的结晶是无限制的，而PEO块的结晶被限制在预先存在的PE结晶薄片之间，如通过同时的小角X射线散射（SAXS）和广角X射线衍射（WAXD）研究所证明的。在完全结晶状态下，PE和PEO嵌段均形成延伸链晶体，PE链从片层法线倾斜约22°，PEO链平行于片层法线，如剪切取向样品的二维WAXD研究所证明的。无论PEO嵌段中羟基链端之间的氢键，PE和PEO晶体均观察到叉指型单晶层形态。部分结晶形态，其中PE结晶和PEO是无定形的，具有相同的整体d-间距作为完全结晶形态。基于傅里叶变换红外光谱的链构象研究，推断了夹在相邻的PE结晶层之间的双非晶PEO层。用差示扫描量热法研究了PEO嵌段的受限结晶动力学，并用非均相成核机理解释。PEO-嵌段中的结晶速率比相同分子量的均聚物慢，这归因于纳米限制和拴系到PE晶体的PEO链的影响。
The self-assembly and crystallization behavior of a well-defined low molecular weight polyethylene-block-poly(ethylene oxide) (PE-b-PEO) diblock copolymer was studied. The number-average degrees of polymerization for the PE and PEO blocks were 29 and 20, respectively. The molecular weight distribution was 1.04 as determined by size-exclusion chromatography. The PE-b-PEO sample exhibited two melting points at 28.7 and 97.4°C for the PEO and the PE crystals, respectively. The crystallization of the PE blocks was unconfined, while the crystallization of the PEO blocks was confined between pre-existing PE crystalline lamellae, as demonstrated by simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) studies. In the fully crystalline state, both PE and PEO blocks formed extended-chain crystals with PE chains tilted ∼22° from the lamellar normal and PEO chains parallel to the lamellar normal, as evidenced by two-dimensional WAXD study of shear-oriented samples. Regardless of hydrogen bonding among hydroxyl chain ends in the PEO blocks, interdigitated, single-crystalline layer morphology was observed for both PE and PEO crystals. The partial crystalline morphology, where the PE crystallizes and the PEO is amorphous, had the same overall d-spacing as the fully crystalline morphology. A double-amorphous PEO layer sandwiched between neighboring PE crystalline layers was deduced based on a chain conformation study using Fourier transform infrared. The confined crystallization kinetics for PEO blocks was investigated by differential scanning calorimetry, which could be explained by a heterogeneous nucleation mechanism. The slower crystallization rate in the PEO-block than the same molecular weight homopolymer was attributed to the effects of nanoconfinement and PEO chains tethered to the PE crystals.