Physical aging in strongly interacting blends
Youssef, Abdelsallam Ebrahim Abdelsallam
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Physical aging is the general term used to describe changes in the properties of glassy materials as a function of storage time, at a temperature below the glass transition, Tg. Extensive studies have been carried out on homopolymers and copolymers but fewer investigations have dealt with aging in polymer blends. This Thesis reports a detailed study of physical aging in polymer-polymer mixtures where strong intermolecular interactions are active between components. Miscible blends incorporating poly(4-hydroxystyrene) (P4HS) or styrene-co-4- hydroxystyrene (SHS) and poly(ethyl methacrylate) , poly(ethylene oxide) , poly(4- vinylpyridine) and poly(methyl methacrylate) were prepared. Fourier transform infrared spectroscopy was used to extract qualitative and quantitative information on the strength and number of hydrogen bonds. The effect of temperature and dilution of the hydrogen bonding sites is discussed and a comparison made between different systems. Enthalpic relaxation data for a series of homopolymers and copolymers, including poly(methyl methacrylate-co-ethyl methacrylate), and blends incorporating P4HS and SHS were collected and analysed using Cowie-Ferguson relaxation model. It is found that the enthalpic relaxation for all P4HS and SHS blends increases upon increasing hydrogen bonding strength between the components. The relaxation rate also increases with increasing strength of interaction as well as chain rigidity. Average activation energies were calculated of all homopolymers, copolymers and blends under study. This parameter is shown to be correlated to polymer structure and polymer-polymer interactions and it is therefore useful to compare the aging behaviour of different systems.