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Open Access Dissertation
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
Shaw Ling Hsu
Polymer and Organic Materials | Polymer Science
ABSTRACT THE ROLE OF CHAIN CONFIGURATION IN GOVERNING THE RATIONAL DESIGN OF POLYMERS FOR ADHESION
ONYENKACHI C. WAMUO, B.Eng., FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI (FUTO), NIGERIA M.S., UNIVERSITY OF MASSACHUSETTS AMHERST
Ph.D., UNIVERSITY OF MASSACHUSETTS AMHERST
Directed by: Professor Shaw Ling Hsu
The chain configurational control of polymers used in adhesion can be utilized as a means of tuning the cohesive properties of hot melt adhesives (HMAs). The cohesive properties control the solidification, strength, setting speed. Propylene-Ethylene copolymers (PP-co-PE) and thermoplastic polyurethanes (TPUs) were studied. In the first project, the effects of sequence distribution of the two types of the (PP-PE) copolymers, with propylene being the dominant component, on the associated crystallization behavior were analyzed. The average sequence lengths of the crystallizable propylene sequences in these copolymers are different, although the ethylene content was virtually identical. In one circumstance, the chain configuration was completely random with crystallizable propylene sequences following Bernouillian statistics. In the other case, we have used a bimodal distribution of crystallizable sequences. The crystallization kinetics, the crystallization temperature, and the degree of crystallinity were significantly higher for the latter sample as compared to the former. When crystallizing from the melt, the longest crystallizable propylene sequences crystallized first at any supercooling, thus controlling the segmental mobility of other segments in the distribution. This is especially evident in copolymers with the bimodal segmental distribution. The distribution of crystallizable polypropylene sequences also controls the size distribution and thermal stability of the crystallites formed. The elucidation of the crystallization behavior of these copolymers is crucial in defining the application driven setting speeds of hot melt adhesives, the principal application of interest in our laboratory. Due to its polarity and thermoplastic nature of its structure, TPUs can be used advantageously for binding a variety of substrates. The challenge with current polyurethanes based on conventional 1,4-butanediols is the long time dependency taken for their morphology and properties to set. These slow dynamics is unfavorable in HMAs where fast setting speeds are necessary and responsible for their widespread use in packaging applications. We hypothesize that the increased mobility and flexibility of the traditional 1,4-butanediol system enables slow morphology development in the traditional TPUs. We have therefore changed the mobility of the chain extenders by using a 1,2-propanediol chain extender which incorporates a methyl pendant group into the TPU structure. The presence of the pendant groups in this system incorporates rigidity to the chain extender and makes the HS made from it lack the mobility to move away from the SS matrix. We have shown this to be vital in creating stable domains whose properties do not change over time. Using DSC as well as LFNMR we established mobility differences between the symmetric and asymmetric chain extenders. Temporal DSC and FTIR were used to show the stable and time-independent morphologies associated with the 1,2-propanediol chain extender. In this study, we have achieved chain configurational control by changing the architecture of the chain extender. This concept of chain configurational control using chain extenders is highly useful in controlling the set speed for HMAs.
Wamuo, Onyenkachi, "THE ROLE OF CHAIN CONFIGURATION IN GOVERNING THE RATIONAL DESIGN OF POLYMERS FOR ADHESION" (2017). Doctoral Dissertations. 1134.