A real-time study of homogeneous nucleation, growth, and phase transformations in nanodroplets of low molecular weight isotactic polypropylene using AFM

Macromolecules (Impact Factor: 5.93). 01/2007; 40:7223-7230. DOI: 10.1021/ma070861t
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    ABSTRACT: Isotactic polypropylene (iPP) nanodroplets were prepared by using the classical droplet method in this study. The formation of nanodroplets allowed the controlled observation of polymer nucleation as well as access to crystal growth at exceptionally high supercooling in iPP. Three cases including the heterogeneous nucleation and fast crystallization in iPP droplets, the formation of multiple independent homogeneous nuclei within a single droplet and a single nucleus within a single droplet were detected by using atomic force microscopy (AFM) during gradually cooling after remelting the nanodroplets. Moreover, it is found that when the volume of droplet is larger than the value of ca. 130000 nm3, the first case was observed. Otherwise, the latter two cases appeared. The temperature at which the onset of nucleation was observed in individual droplets was found to be mainly dependent on height of the droplets when the size scale of the droplet is comparable to the size of the critical nucleus in at least one dimension, which indicates the nucleation behavior under confinement.
    Chinese Journal of Polymer Science 31(9). · 1.27 Impact Factor
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    Polymer 07/2013; 54(16):4059-4077. · 3.77 Impact Factor
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    ABSTRACT: In this paper, two crystalline-coil diblock copolymers consisting of blocks of syndiotactic polypropylene (sPP) with different syndiotacticities ([rrrr]sPP1 = 0.78, [rrrr]sPP2 = 0.94) and poly(ethylene oxide) (PEO) were synthesized utilizing the click reaction of azide-terminated PEO (PEO–N3) with alkynyl-terminated sPP (sPP–C≡CH), which was obtained via the syndiospecific polymerization of propylene using fluorinated bis(phenoxyimine) titanium catalysts and further end-group transformation. All products and intermediates were characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). We probed the temperature-induced self-assembly of sPP-b-PEO in the solvent N,N′-dimethylformamide (DMF), which is selective for PEO. The self-assembly behavior and micellar morphology of each sPP-b-PEO were investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Before sPP crystallization, the crystalline-coil diblock copolymers self-assembled into spherical micelles with an amorphous sPP core and a soluble PEO corona. Platelet-like micelles with a crystallized sPP core sandwiched between two solvent-swollen PEO layers then formed upon the crystallization of the sPP block. Furthermore, the confined crystallization of sPP within nanosized micelle cores was investigated by differential scanning calorimetry (DSC). An enormous degree of supercooling was observed during crystallization due to the homogeneous nucleation.
    Journal of Polymer Research 20(2). · 2.02 Impact Factor


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May 26, 2014