Polypropylene epitaxial crystallization

Thin polymer films may also be investigated by TEM and high resolution images are obtained for e.g. thin films of liquid crystalline polymers [64]. Usually thin microtome cuts from bulk samples are investigated, but also epitaxial growth of polyoxymethylene on NaCl [152], chain folding of polyethylene crystals [153], epitaxial crystallization of polypropylene on polystyrene [154] or monomolecular polystyrene particles [155] are observed. The resolution is, however, in most cases not comparable to STM. 

Epitaxial Crystallization of Syndiotactic Polypropylene, Isochiral Form II. 28... 

The second and third illustrations of epitaxial crystallization deal with syndiotactic polypropylene (sPP). Syndiotactic polymers are by design susceptible to forming either right-handed or left-handed helices, and are therefore suitable materials in the present context of helical hand selection. 

Fig.6 (a) AFM image of the be contact face of sPP in its antichiral Form I, epitaxially crystallized on p-terphenyl. Note the strict alternation of right- and left-handed helices (helix axis at one o clock). Left-handed helices are better resolved than right-handed helices. Reproduced from [33] with permission (b) Fourier-filtered image of the upper left area of part (a) showing more clearly the right-handed helices that alternate with the left-handed ones. Reproduced from [33] with permission (c) The surface structure of p-terphenyl used as a substrate for the epitaxial crystallization of syndiotactic polypropylene (parts... 

Rickert, S., Baer, E., 1978. Epitaxial crystallization of iso tactic polypropylene on alkali halide surfaces. 

R. Su, K. Wang, Q. Zhang, F. Chen, Q. Fu, N. Hu, E, Chen, Epitaxial crystallization and oriented structure of linear low-density polyethylene/isotactic polypropylene blends obtained via dynamic packing injection molding. Polym. Adv. Technol. 22, 225-231 (2011)... 

F. Rybnikar, M. Kaszonyiova, Epitaxial crystallization of linear polyethylene in blends with Isotactic polypropylene. J. Macromol. Sci. Part B Phys. 53, 217-232 (2014)... 

Stocker, W Magonov, S. N. Cantow, H. J. Wittmann, J. C. Lotz, B. Contact faces of epitaxially crystallized a- and y-phase isotactic polypropylene observed by atomic force microscopy. Macromolecules 1993, 26, 5915-5923. 

Somani RH, Yang L, Zhu L, Hsiao BS (2005) Flow-induced shish-kebab precursor structures in entangled polymer melts. Polymer 46 8587-8623 Sorrentino A, De Santis F, Titomanlio G (2007) Polymer crystallization under high cooling rate and pressure a step towards polymer processing conditions. Lect Notes Phys 714 329-344 Stocker W, Magonov SN, Cantow HI, Wittmann JC, Lotz B (1993) Contact faces of epitaxially crystallized a- and y-phase isotactic polypropylene observed by atomic force microscopy. Macromolecules 26 5915-5923... 

Isotactic polypropylene displays a highly unusual ability to induce epitaxial crystallization of a number of different polymers with their chain axes tilted at large angles, 40—80°, relative to the helix axis direction of the polypropylene substrate. The same polymer shows an epitaxy, i.e. homoepitaxy, at an angle of 80° (Fig. 7.30). The homoepitaxy is responsible for crosshatching, a structure typical of the monoclinic a structure. This feature causes the lamellar branching and the optical complexity, with both positive and negative spherulites, typical of isotactic polypropylene (section 7.4). 

Xu Y, Asano T, Kawaguchi A, Rieck U, Petermann J. Epitaxial crystallization of polyoctenamer on uniaxiaUy oriented polypropylene films. J Mater Sci Lett 1989 8 675-677. 

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Sun Y, Li H, Huang Y, Chen E, Gan Z, Yan S. Epitaxial crystallization of poly (butylene adipate) on highly oriented isotactic polypropylene thin film. Polymer 2006 47 2455-2459. 

Zhang J, Yang D, Thierry A, Wittmann JC, Lotz B. Isochiral form II of syndiotactic polypropylene produced by epitaxial crystallization. Macromolecules 2001 34 6261-6267. 

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Figure 8.4 The packing of chains in the monochnic, a phase of isotactic polypropylene (odPP). Left as seen in chain axis projection, successive layers parallel to the ac plane (horizontal trace) are made of alternatively right-handed and left-handed helices. Middle and right the succession of different ac faces of odPP encountered as one travels along the +i>-axis direction. The helical hand (curved arrows) as weU as the pattern of methyl groups differs in the two distinct faces. Travelling along the -fo-axis direction, the mirror images of these faces would be observed. The less densely populated face (middle) is involved in epitaxial crystallization. Reproduced from Reference [27].

Polypropylene exhibits a distinctive bimodal orientation of the unit cells when crystallized from melts undergoing extension. There are crystals whose c-axis is oriented parallel with the fiber axis and a smaller population of crystals whose a-axis is oriented parallel with the fiber axis. For the H-0660 filaments at high stress, Nadella et al. [79] estimate that about 10-20% of the crystals have an n-axis orientation. Anderson and Carr [192] and Clark and Spruiell [198] concluded that the a-axis-oriented crystals were very small and were distributed throughout the sample and perhaps grew epitaxially to the c-axis-oriented crystals. 

The surface structure of pigments crystals enables the epitaxial growth of the polypropylene. 

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