Melt-crystallized nylon-6 nucleated by the constrained chains of its non-stoichiometric cyclodextrin inclusion compounds and the nylon-6 coalesced from them

2014

Polymers

When non-covalently bonded crystalline inclusion compounds (ICs) are formed by threading the host cyclic starches, cyclodextrins (CDs), onto guest polymer chains, and excess polymer is employed, non-stoichiometric (n-s)-polymer-CD-ICs, with partially uncovered and "dangling" chains result. The crystalline host CD lattice is stable to ~300 °C, and the uncovered, yet constrained, portions of the guest chains emanating from the CD-IC crystal surfaces behave very distinctly from their neat bulk samples. In CD-IC crystals formed with α-and γ-CD hosts, each containing, respectively, six and eight 1,4-α-linked glucose units, the channels constraining the threaded portions of the guest polymer chains are ~0.5 and 1.0 nm in diameter and are separated by ~1.4 and 1.7 nm. This results in dense brushes with ~0.6 and 0.4 chains/nm 2 (or 0.8 if two guest chains are included in each γ-CD channel) of the un-included portions of guest polymers emanating from the host CD-IC crystal surfaces. In addition, at least some of the guest chains leaving from a crystalline CD-IC surface re-enter another CD-IC crystal creating a network structure that leads to shape-memory behavior for (n-s)-polymer-CD-ICs. To some extent, (n-s)-polymer-CD-ICs can be considered as dense polymer brushes with chains that are tethered on both ends. Not surprisingly, the behavior of the un-included portions of the guest polymer chains in (n-s)-polymer-CD-ICs are quite different from those of their neat bulk samples, with higher glass-transition and melt crystallization temperatures and crystallinities. Here we additionally compare their behaviors to samples coalesced from their stoichiometric ICs, and more importantly to dense polymer brushes formed by polymer chains chemically bonded to surfaces at only one end. Judging on the basis of their glass-transition, crystallization and melting temperatures, and crystallinities, we generally find the un-included portions of OPEN ACCESSPolymers 2014, 6 2167 chains in (n-s)-polymer-CD-ICs to be more constrained than those in neat bulk as-received and coalesced samples and in high density brushes. The last observation is likely because many of the un-included chain portions in (n-s)-polymer-CD-ICs are tethered/constrained at both ends, while the chains in their dense brushes are tethered at only one end.

Section: Introductionsupporting

confidence: 69%

Section: Methodsmentioning

confidence: 99%

Section: Semi-crystalline Polymers In (N-s)-cd-ics and Coalesced Frommentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Non-Stoichiometric Polymer-Cyclodextrin Inclusion Compounds: Constraints Placed on Un-Included Chain Portions Tethered at Both Ends and Their Relation to Polymer Brushes

2014

Polymers

Improving Poly(ethylene terephthalate) Through Self‐nucleation

Joijode

Hawkins

2013

Macro Materials & Eng

As‐received poly(ethylene terephthalate) (asr‐PET) may be reorganized by precipitation from trifluoroacetic acid upon gradual addition to a large excess of rapidly stirred acetone (p‐PET). Unlike asr‐PET, p‐PET repeatedly crystallizes rapidly from the melt, and can be used in small quantities (a few %) as an effective self‐nucleating agent to control and improve the bulk semi‐crystalline morphology and properties of asr‐PET. Nuc‐PET film has significantly increased hardness and Young's modulus and is much less permeable to CO2, while its un‐drawn fibers exhibit higher tenacities and moduli. Because nuc‐PET contains no incompatible additives, it may be readily recycled.

Enhancing the melt crystallization of polymers, especially slow crystallizing polymers like PLLA and PET

Polymer Crystallization

2020

Over 20 years ago we demonstrated that it is possible to control the melt crystallization of polymers via self‐nucleation. Non‐covalently bonded inclusion compounds (ICs) can be formed with cyclodextrins (CDs) or urea (U) when these small host molecules crystallize around guest polymers and form narrow parallel host channels, where the isolated and stretched guest polymer chains are included. Careful removal of the host crystalline lattice yields a neat coalesced (c) guest polymer sample with less entangled chains that are packed to a higher density than bulk samples of the same polymer obtained from its melt or solutions. Consequently, the reorganized c‐polymer samples behave distinctly, with higher glass‐transition temperatures for amorphous polymers and enhanced crystallizabilities for semi‐crystalline polymers. Remarkably, c‐polymer samples retain their distinct reorganized structures and behaviors even after extended periods of melt annealing. When a small amount of the rapidly crystallizable c‐polymer is homogeneously dispersed in a large quantity of the same as‐received (asr) polymer, and it is melted and then cooled, the c‐polymer chains crystallize first and nucleate the crystallization of the asr‐polymer chains, so that the entire sample (nuc‐polymer) crystallizes at nearly the same temperature as the neat nucleant (c‐polymer), including slow melt‐crystallizing polymers, such as PET and PLLA.