Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
Micro-structural investigation of model polytetrahydrofuran networks
Abstract
Model networks of polytetrahydrofuran (PTHF) were prepared by end-linking reaction with the known functionality of cross-links, and the specific number of network chains of known molecular weight distribution. Bimodal networks are composed of stoichiometric amounts of short and long chain prepolymers. By selectively labeling either short or long chains with deuterium, one can simultaneously evaluate the local structure of each species by such methods as infrared (IR) and small-angle neutron scattering (SANS). The micro-structure of the bimodal networks were studied by these methods with an emphasis on the effect of spatial distribution of chain lengths between cross-links. IR results have revealed that the segmental orientation function for the long chains is almost equal to the one for the short species during the uniaxial deformation. There are two possible interpretations for the deformation mechanism from this equality according to the rubber elasticity theory of Kuhn and Grun. One is that the extension ratios of the two species are not equal as expected, therefore individual chain segments deform non-affinely. Another is that the bimodal network follows an affine deformation if it is treated as an "averaged unimodal" system consisting of the chain segments with the weight-averaged length between the long and short chains. SANS results have indicated spatial inhomogeneity in the bimodal network with a high mole fraction of short chains. The inhomogeneity is attributed to the formation of clusters of highly cross-linked domain of short chains in the media of sparsely cross-linked long chains. Size of a cluster increases in proportion to the increasing amount of short chains, while the average distance between clusters seems to be less dependent upon. The deformation ratios of the distance between clusters and that of the gyration radius of long chains were quantified. In all cases, it has observed that the bimodal network deforms locally in a non-affine manner, however, at the larger scale the effective functionality from the short chain clusters dominates and deforms close to affinely. These results suggest that theoretical developments incorporating the structural information are necessary to have a better understanding of the local behavior and to relate to macroscopic properties in real polymer networks.
Subject Area
Polymer chemistry
Recommended Citation
Hanyu, Aiko, "Micro-structural investigation of model polytetrahydrofuran networks" (1993). Doctoral Dissertations Available from Proquest. AAI9408285.
https://scholarworks.umass.edu/dissertations/AAI9408285