The effect of controlled isothermal crystallization conditions on the final crystalline structure of a set of polyethylenes with precise Cl substitution on each and every 9th, 15th, 19th and 21st backbone carbons was assessed. Isothermally crystallized samples display a drastic change in their crystalline structure in a narrow range of crystallization temperatures. The structural change occurs within an undercooling difference of one degree and is revealed by a sharp increase in melting temperature, an increase in TG conformers and a decrease in SAXS periodicity. These changes are associated with a different distribution of Cl atoms in the crystallites. Under rapid crystallization conditions (Form I structure develops), the Cl distribution in the crystallites is disordered; whereas slower crystallization kinetics leads to staggering of chlorines and formation of a herringbone structure in the crystallites (Form II structure). Differences in nucleation mode between both types of structures were determined from the analysis of the crystallization kinetics according to nucleation theory. The drastic change in morphology correlates with the selection of the critical segment length required to form a stable nucleus. The length of the initial nucleus is governed by kinetics; when this length approaches the distance between halogens, Form II develops and folding is preferential at the substitution point. Shorter nuclei end in development of the Form I structure which has chains that fold at a random position along the methylenic chain. Controlling the crystallization kinetics in novel polyolefins of this nature allows strategies for producing materials with different properties attained by directing the crystallization process to preferentially Form I or rather to Form II structures. / A Thesis submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the requirements for the degree of Master of
Science. / Spring Semester, 2012. / November 29, 2011. / chlorine, crystallization, halogen, polyethylene, precise, substitution / Includes bibliographical references. / Rufina G. Alamo, Professor Directing Thesis; Subramanian Ramakrishnan, Committee Member; Theo M. Siegrist, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_183502 |
| Contributors | Kaner, Papatya (authoraut), Alamo, Rufina G. (professor directing thesis), Ramakrishnan, Subramanian (committee member), Siegrist, Theo M. (committee member), Department of Chemical and Biomedical Engineering (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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