Poly crystal lamella

It was shown that amorphous polymers certainly reside between crystal lamellae as a single phase mixture in poly(8-caprolactone) (PCL)/poly(vinyl chloride) (PVC) blends [Stein, 1978]. When the content of the amorphous polymer is high, its excess is excluded from interlamellar region to the outside of lamellar stacks in poly(etheretherketone)/ poly(etherimide) blends [Lee et ah, 1997]. 

In a 50/50 PP/hydrogenated poly(styrene-co-butadiene) (hSBR) blend, crystal lamellae were extremely fragmented to form the fringed-micelle type crystallites, as schematically shown in Figure... 

Figure 5-22. Interlamellar links between poly(ethylene) lamellae. Crystallization of mixtures of poly(ethylene) and paraffin wax (after H. D. Keith, F. J. Padden, and R. G. Vadimsky).

Crystallization of cis—1,4-polyisoprene from solution at -65 C has been carried out it is therefore possible that block copolymer preparation by epoxidation, bromination or some other reaction could be accomplished with lamellas of this polymer. Lamellar crystallization of cellulose, of amylose and of polyacrylic acid have been reported substitution reactions such as acetylation or ether formation with the hydroxyl groups and esterfication of the acid groups are possible reactions to carry out with lamellas of those polymers. The use of nonaqueous systems may be better suited to prevent swelling, and therefore, attack of the crystalline regions. It should also be possible to react poly(vinylalcohol) lamellas in suspension with acids or anhydrides to form vinyl-alcohol-vinyl ester block copolymers or with phosgene to obtain chloroformate groups which can undergo further reactions. 

The preferred conformation of poly(oxy methylene) is nearly all-gauche and the crystal structures reported are a trigonal form (I), which is the most stable, and a less stable orthorhombic (II). The chains in the unit cell are of the same handedness, and left- and right-handed molecules evidently appear in dif erent crystal lamellae. 

Poly(ethylene oxide) has been investigated in both a single-crystal form and in normal or commercial, partially crystalline form. Single crystals have been examined by X-ray analysis and have been shown to be flat platelets with the c-axis of the unit cell oriented normal to the basal plane (34). Electron microscopy has shown bulk crystallized polymer to have a lamellar structure (35, 36), and single-crystal lamellae have been grown from dilute solution (37, 38). 

Figure 8 Solution-crystallized lamellae of (a) poly(oxymethylene), (b) poly(4-methylpent-l-cne)...

Table 1 shows the crystallinity content of poly(2,6-dimethylphenylene oxide) using these methods. The SAXS analysis showed that the crystal lamellae were arranged in a superlattice with a high degree of order. Different crystalline structures formed are dependent upon the solvent used and the procedure followed in the drying of the crystals. 

Several studies have concerned the microstnicture of lamellae in materials such as the block copolymers polystyrene-h/oc/r-poly-l-vinylpyridine [139] and polystyrene-h/oc/r-polybutadiene [140], as well as single crystals of poly-para-xylylene [139], and reveal features (such as intersecting lamellae (figure Bl.19.29)) that had not been previously observed. 

First of all, these materials are ttractive "per se". In particular, poly(styrene-b-caprolac tone) is a semi-crystalline product displaying an amazing resistance to cold-fracture, and also macroscopically biodegradable at least when PCL represents the continuous phase. It can be "organized" into single crystals, wherein lamellae of PSt and PCL alternate with a periodicity of about 80 A. 

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