Previous studies reported a unique direction of lamellar twist in banded spherulites of polymers with main-chain chirality, which lead to the suggestion that a correlation exists between the handedness of the helical chain and the twist direction. However, these proposals were presented without identifying underlying reasons for such a correlation. Hence, the goal of this thesis was to identify morphological features that could be ascribed to main-chain chirality, which, in turn, would provide insight concerning the transmission of chirality to asymmetries in various levels of crystalline morphology. / Studies at the molecular level, based on chain-packing simulations showed that main-chain chirality leads to the formation of helices of a given handedness but indicated that the helix handedness does not have the ability to generate asymmetric habits at the next higher dimensional level, which is the chain-folded lamella. This was confirmed by the TEM studies of solution-grown single crystals of the R and S polyenantiomers of poly(epichlorohydrin) (PECH), poly(propylene oxide) (PPrO) and poly(3-hydroxyvalerate) (PHV). / Electron diffraction studies established that chain tilting (considered a root cause of lamellar twisting) is absent in these single crystals. However, this does not eliminate the possibility of an induced chain tilting in stems at growth fronts during fast crystallization from the melt. Indeed, optical microscopy studies of the behavior of spherulites grown from the melt established that the lamellae (fibrils) twist, uniquely in either a right- or left-handed fashion, depending on the chiral identity (R or S) of the polyenantiomer. Although the handedness of the lamellar twist of the R and S polyenantiomers of PECH and PPrO both showed a direct correlation with the handedness of the helical chain, this correlation is not universal. While poly(3-hydroxybutyrate) (PHB) and PHV both form left-handed helices, the directions of lamellar twist are left- and right-handed, respectively. It was also demonstrated that the handedness of spiral patterns developed in banded spherulites of chiral polymers is not rigorously related to the molecular chirality. The overall conclusion is that determination of the ultimate origin(s) of lamellar twisting in banding of polyenantiomers requires further investigations.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36702 |
| Date | January 1999 |
| Creators | Saracovan, Ilie. |
| Contributors | Brown, G. Ronald (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001747397, proquestno: NQ64662, Theses scanned by UMI/ProQuest. |
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