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Structural Unit of Polymer Crystallization in Dilute Solution As Studied by Solid-State NMR and 13C Isotope Labeling
Macromolecules ( IF 5.1 ) Pub Date : 2018-10-26 00:00:00 , DOI: 10.1021/acs.macromol.8b01950
Shijun Wang 1 , Shichen Yuan 1 , Wei Chen 2 , Yang Zhou 1 , You-lee Hong 3 , Toshikazu Miyoshi 1
Affiliation  

The nucleation and growth mechanisms of semicrystalline polymers during crystallization in dilute solutions have been debated in the past decades. Wang et al. recently reported that 13C CH3 labeled poly(l-lactic acid) (PLLA), with small weight-average molecular weight ⟨Mw⟩ = 46K g/mol (s), adopted three-dimensional nanoclusters via adjacent re-entry folding in the solution-grown crystals, and its mean size was independent of crystallization temperature (Tc) [Macromolecules2017, 50, 6404–6414]. In this work, 13C CH3 labeled PLLA chains with middle and large ⟨Mw⟩ of 90K g/mol (m) and 326 K g/mol (l), respectively, were synthesized. Both ⟨Mw⟩ and kinetics effects on the chain-folding structures and crystal habits of the 13C CH3 labeled PLLA were systematically investigated by solid-state (ss) NMR and atomic force microscopy (AFM). s-, m-, and l-PLLAs commonly adopted faceted lozenge single crystals in dilute amyl acetate (AA) solution (0.05 wt %) under a very low supercooling, ΔT = 40 °C, but dendrites with multiple layers under a rapidly quenched condition, ΔT = ∼130 °C. By comparison of the experimental and simulated 13C–13C DQ buildup curves, it was indicated that (i) all s-, m-, l-PLLA adopted the same mean structure of the three-dimensional nanoclusters in multiple rows via adjacent re-entry structure in the lozenge shape and dendrite crystals and (ii) the mean size of the nanocluster was smaller than the nanocluster size expected from the smallest ⟨Mw⟩ used in this study. On the basis of the crystal habits as well as dimension and size of the nanoclusters, it was suggested that (i) the PLLA chains with different ⟨Mw⟩s initially adopted the same nanoclusters via folding (stage I) and (ii) the aggregation process of the nanoclusters, which was dominated by kinetics, resultantly led to the different morphological features as a function of ΔT (stage II).

中文翻译:

固态NMR和13 C同位素标记研究稀溶液中聚合物结晶的结构单元

在过去的几十年中,人们一直在争论在稀溶液中结晶过程中半结晶聚合物的成核和生长机理。Wang等。最近报道,13 ÇCH 3标记的聚(-乳酸)(PLLA),具有小重均分子量⟨中号瓦特⟩= 46K克/摩尔(小号),通过相邻的再入折叠采用三维纳米团簇在该溶液中生长的晶体,和其平均大小是独立结晶温度(的Ť ç)[大分子201750,6404-6414]。在这项工作中,13 C CH 3标记的PLLA链具有中,大⟨中号瓦特⟩90K的克/摩尔()和326ķ克/摩尔(),分别合成。既⟨中号瓦特⟩上链折叠结构和晶体习性和动力学的影响13 ÇCH 3标记的PLLA进行了系统的通过固态(SS)研究NMR和原子力显微镜(AFM)。s-m-l -PLLA通常在非常低的过冷度(ΔT = 40°C )下于稀乙酸戊酯(AA)溶液(0.05 wt%)中采用多面菱形单晶,但在快速冷却下会形成多层枝晶淬火条件,ΔT=〜130℃。通过实验的比较和模拟13条C- 13 ÇDQ恢复曲线,它表明,(i)所有小号- ,间- 1- PLLA经由相邻的再通过在多个行中的三维纳米簇相同的平均结构-菱形和枝晶晶体的进入结构,以及(ii)纳米团簇的平均尺寸小于本研究中使用的最小M w expected预期的纳米团簇尺寸。对晶体习性的基础以及尺寸和纳米团簇的大小,有人建议,(i)所述PLLA链具有不同⟨中号瓦特最初通过折叠(阶段I)和(ii)纳米簇的聚集过程采用了相同的纳米簇,而纳米簇的聚集过程受动力学支配,因此导致了不同的形态学特征随ΔT的变化(第二阶段)。
更新日期:2018-10-26
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