Integer folding

Fig. 1 Integer folded (IF) forms observed in long n-alkanes C102H206 through C390H782. For a given alkane more folds per molecule are obtained with increasing supercooling AT (from [7] with permission of American Chemical Society)...

Fig. 4 Paths to integer folded forms in long alkanes. While solution crystallization gives integer forms (E, F2,...) directly, for melt crystallization this is true only for the E form. Below the melting point of F2, the transient non-integer form (NIF) appears and subsequently transforms isothermally either to the once-folded F2 form or the mixed-integer folded-extended (FE) form, based on layer triplets. Deuterium- labelled chain ends, prepared for neutron scattering experiments, are indicated with circles...

Fig. 6 The barrier factor, which is equal to Ao in LH theory, and the driving force , or survival factor (1 - B/A) of the growth rate as functions of stem length (schematic). Ao, A and B are rates of attachment of the first and subsequent stems, and rate of detachment, respectively. The (1 - B/A) factor is drawn for three temperatures T > T" > V". Vertical rectangles show growth rates for discrete integer folded forms E and F2 of a monodisperse oligomer...

A minimum in growth rate occurs as a function of either crystallization temperature or solution concentration at all growth transitions b etween successive integer folded forms. The latter results in negative-order kinetics, the dilution wave effect, and autocatalytic crystallization. 

Finally, it should be mentioned that self-poisoning due to erroneous integer folded depositions is only one manifestation of a productive reaction, which leads to thermodynamic stability, being retarded by a competing lower barrier reaction which almost leads to a stable product. The observations of a crystallization rate minimum in an aromatic polyketone [88], and recently an aromatic polyester [89], are further examples of such an occurrence. 

When either of the semicrystalline forms of the asymmetric alkane are cooled, they transform to a double-layer and a triple-layer crystalline structure, respectively. These 1-d superlattices are described as ABAB... and ABAABA... stacks of crystalline layers as depicted in Figure 25, panels c and e. Note that the structure in Figure 25e is related to the mixed integer folded-extended structure in some pure n-alkanes (Figure 7c) and in binary mixtures of long n-alkanes (Section II.J, Figure 30b). 

IF integer-fold IPT injected paint technology or in-mold... 

Ungar, G., Zeng, X., Brooke, G.M., and Mohammed, S. (1998) Structure and formation of noninteger and integer folded-chain crystals of linear and branched monodisperse ethylene oligomers. Macromolecules, 31,1875-1879. Wagener, K.B., Boncella, J.M., Nel, J.G. et al (1990) The key to successful acyclic diene metathesis polymerization... 

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