FTIR and Microscopy Analysis of the Effect of Chlorine on Polymorphism of Precision Halogen-Substituted Polyethylenes

• Other Authors: Zhang, Xiaoshi (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Chemical engineering; Biomedical engineering
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-9123

Polyethylenes with halogen substitution at a precise distance along the methylene backbone are unique models to study the effect of nano-structured chain-defects on folding and crystallization of polymers. Prior work has shown that the halogen is accommodated in the crystal disrupting the unit cell symmetry and crystallization proportionally to the halogen's size. Packing of the Chlorine units in the crystallites of polyethylene with Chlorine substitution on every 15th backbone carbon was found to undergo a transition which is kinetically controlled within one degree of undercooling. On crystallization from the melt at temperatures < 53 °C the chains pack in an all-trans planar conformation (Form I) with layered crystalline chlorines that present some longitudinal disorder as demonstrated by FTIR. The crystals formed at higher temperatures pack in a non-planar herringbone-like structure (Form II) with a TGGT....TG'G'T backbone conformation around the substitution, while conserving the trans packing of the methylene sequence. The analysis of the FTIR spectra for the rocking-twisting progression in a broad range of crystallization temperatures is extended here to a series of polyethylenes with Cl substitution every 9th, 19th and 21st carbons. The FTIR dispersion curves are analyzed in reference to the behavior of n-alkanes with length equivalent to the length of methylene sequence between Chlorines. The unique polymorphic transition found in the system with Chlorines between 15 carbons, is also found in all members of the series, making the planar and non-planar packing with respect to undercooling a general feature of crystallization of polyethylenes with Chlorine substitution. The polymorphic transition temperatures and temperature range of coexistence of both forms are analyzed as a function of increasing Chlorine in the series. === A Thesis submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the requirements for the degree of Master of Science. === Summer Semester, 2014. === June 16, 2014. === Crystallization, Ftir, Material, Polarized Optical Microscopy, Polymer === Includes bibliographical references. === Rufina G. Alamo, Professor Directing Thesis; Biwu Ma, Committee Member; Ravindran Chella, Committee Member.