The Constrained Crystallization of Nylon-6

Non-covalently bonded crystalline inclusion compounds (ICs) have been formed by threading host cyclic starches, cyclodextrins (CDs) onto guest nylon 6 (N6) chains. When excess N6 is employed, non-stoichiometric (n-s)-N6-CD-ICs with partially uncovered and dangling N6 chains result. While the crystalline CD lattice is stable to $\sim $300\r{ } C, the uncovered and dangling, yet constrained, N6 chains may crystallize below or, as shown below, be molten above $\sim $225\r{ } C. We have been studying the constrained crystallization of the dangling N6 chains in (n-S)-N6-CD-ICs, with comparison to bulk N6 samples, as a function of N6 molecular weights, lengths of uncovered N6 chains, and the CD host used. In the IC channels formed with host $\alpha $- and $\gamma $-CDs containing 6 and 8 glucose units, respectively, single and pairs of side-by-side N6 chains are threaded and included. In the $\alpha $-CD-ICs the $\sim $ 0.5 nm channels are separated by $\sim $ 1.4 nm, while in $\gamma $-CD-ICs the $\sim $ 1 nm channels are $\sim $ 1.7 nm apart, with each $\gamma $-CD channel including 2 N6 chains. N6 chains in the bulk and in the dense (n-s)-N6-CD-IC brushes show distinctly different kinetic and thermodynamic crystallization behaviors.