Behavior of Poly(ε-caprolactone)s (PCLs) Coalesced from Their Stoichiometric Urea Inclusion Compounds and Their Use as Nucleants for Crystallizing PCL Melts: Dependence on PCL Molecular Weights

Abstract

We have formed noncovalent inclusion compounds (ICs) between guest poly(ε-caprolactone) (PCL) chains, with molecular weights ranging from ∼2000 to 80 000 g/mol, and host urea (U). Upon careful removal of the U host, each of the guest PCL chains were coalesced from their U-IC crystals to produce coalesced samples (c-PCLs). As previously observed for PCL and other polymer guests when coalesced from their ICs formed with host cyclodextrins (CDs), upon cooling from their melts, PCLs coalesced from their U-ICs also show enhanced abilities to crystallize, regardless of their molecular weight. Also consistent with polymer guests, including PCL, that were coalesced from their CD-ICs, c-PCLs obtained from their U-ICs retain their enhanced abilities to crystallize even after spending long times (weeks or more) in the melt. Because, unlike CD hosts, U does not thread over guest polymer chains in their ICs, we conclude that the enhanced ability of c-PCLs to crystallize from their melts upon removal of either host from their ICs is solely a consequence of their coalesced conformations/structures/morphologies, which are stable to prolonged melt-annealing. Furthermore, because c-PCLs with chain lengths well below and well above those corresponding to the entanglement molecular weight of PCL behave similarly, we conclude that their enhanced ability to crystallize from the melt is likely an exclusive consequence of the extended and unentangled arrangement of their coalesced chains. In addition, c-PCLs obtained from their U-ICs are observed to effectively act as self-nucleants, when added in small amounts to as-received PCLs, to produce nuc-PCLs, which like neat c-PCLs exhibit an enhanced ability to melt-crystallize.

Single-polymer composites (SPCs): Status and future trends

“…The guest macromolecules coalesced and appeared in aligned form after appropriate removal of the host. They acted subsequently as strong self-nucleants and generated a reinforcing crystalline superstructure during the bulk melt crystallization of the same polymer [48,49].…”

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

“…Behaviors of amorphous polymers threaded through and coalesced from their (n-s)-CD-ICs and stoichiometric CD-and U-ICs (see Figure 7) have also been blended/mixed and examined [32][33][34]. In general, the glass transition temperatures, T g s, of amorphous guest polymers coalesced from their stoichiometric CD-and U-ICs and (n-s)-CD-ICs and those un-included chain portions in the (n-s)-CD-ICs exhibit significantly elevated T g s. This is demonstrated [34] for atactic PVAc and PMMA in Figure 8.…”

“…PMMA/PVAc can also be partially blended using γ-CD as a compatibilizer through formation of their common non-stoichiometric (n-s)-c-CD-ICs [32], as shown in Figure 12. We prepared (n-s)-γ-CD-ICs with 2:1, 3:1, and 6:1 ratios of the polymer pair to γ-CD and 1:1 and 1:2 PMMA:PVA stoichimetries, which were confirmed with DSC results for the common 3:1 (n-s)-PVAc/PMMA-Υ-CD-IC blends are shown in Figure 13 and summarized in the Table 4.…”

Coalesced Poly(ε-caprolactone) Fibers Are Stronger

“…IC formation and coalescence processes have been explained in detail elsewhere. 8 Briefly, urea can be removed from PCL−U−IC in two ways: (1) by simply stirring the PCL−U−IC in methanol or (2) stirring in excess water for 1 day, followed by filtering and drying the resulting material, and then stirring in methanol. In both methods, the coalesced PCL samples were vacuum-dried for 1 day.…”

“…8,9 CDs are cyclic molecules with a cavity size varying from 0.5−1 nm. CDs can form noncovalently bonded inclusion compounds with small molecules and polymers via inclusion of these guest molecules in their small cavities.…”