Fringed-micellar crystal

Fig. 11. Schematic representation of fringed-micellar crystals as junctions in a...

Polyolefin-based thermoplastic elastomers (TPEs) have received considerable attention due to their chemical inertness, low density, and low cost compared with other TPEs. Homogeneous ethylene-octene (EO) copolymers, synthesized via contemporary catalyst technology, with low crystallinity and low density (0.86-0.88g/cm ) exhibit the characteristics of thermoplastic elastomers. The elastomeric properties depend on the fringed micellar crystals which serve as network junctions. However, the low melting point of fringed micellar crystals have limited the application of elastic EO copolymers at higher temperatures. 

The spatial configurations proposed by Kratky [38] and Mark [39] repeat in principle the basic idea of the fringe micellar theory, according to which long cellulose chains lie lengthwise through the crystal and amorphous phases form the fibre (Fig. 80). 

Keywords Mesophase Crystallization Random coil Folded-chain fringed-micellar grains Flow... 

Fig. 24 Schematic pictures of flow-induced crystallization from the polymer melt (a) for the random coil model (b) using the folded-chain fringed-micellar grain model...

Fig. 26 Schematic picture of the growth front of a polymer crystal according to the folded-chain fringed-micellar grain model of the melt...

A fringed-micellar structure was proposed in 1930 for the sttuctures of colloids and gels [19]. By adding the possibility of chain-folded crystals, as illustrated in the center of Fig. 5.42, all three limiting macroconformations are combined. Semicrystalline polymers, thus, are a system consisting of folded-chain crystals, intercrystalline amorphous, and possibly extended-chain subsystems (see Fig. 2.80). The latter are expected particularly in fibers drawn to large extension. Most samples have a macroconformation somewhere within the triangle of Fig. 5.42. 

Keller et al. [86, 89,90] proposed the existence of two families of X-ray effects in stretched commercial poly(vinyl chloride) A-crystals with an orientation of the a-axis (i.e. in the direction of the polymer backbone) in the stretch direction and B-crystals with an orientation of the c-axis (i.e. perpendicular to the polymer backbone) in the stretch direction. The B-crystals are smaller and are supposed to form the network junctions (crosslinks) of fringed micellar crystallites, whereas the large A-crystals are supposed to be well developed... 

We must conclude from this set of typical data that the crystallite properties of the gel and that of the lamellae formed in dilute solution are the same. Hence, barring an unusual set of coincidences the basic crystallite characteristic of the gel should be of lamellar form for the linear polyethylenes when crystallized from homogeneous solutions. Thus we have at least one system where the crystaUization elation phenomenon does not involve a fringed micellar structure. 

Fig. 9. The basic polymer-crystal morphologies of (a) folded-chain, (b) fringed-micellar and (c) extended-chain crystals. The last is shown with fold-chain crystal overgrowth which results in the so-called shish-kebab...

Fig. 24. Schematic representation of a network structure formed by copolymer molecules consisting of non-crystalline sections and sections which crystallize to form fringed-micellar crystallite junctions.

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