Introductory remarks for symposium on transitions and relaxations in polymers

Abstract

AbstractMost organic polymers show a complex array of transition and/or multiple relaxation phenomena in addition to the classical glass transition and the melting point. An amorphous hydrocarbon backbone polymer such as an equimolar, random copolymer of ethylene and propylene, can exhibit, four types of relaxation regions: (1) motion of the entire chain as a unit; (2) motion of a chain segment of perhaps 50–100 carbon atoms, i.e., the glass transition; (3) motion of a 2, 3, or 4 carbon atom moiety about the chain axis, i.e., the γ transition: (4) motion of a side group, such as CH3 in a propylene unit. A moderately crystalline hydrocarbon backbone polymer, i.e., polypropylene, can show all of the loss peaks noted above but in addition may exhibit peaks as follows: (1) melting point; (2) a first‐order transition from one crystal type to another; (3) motion of side groups such as CH3 within the crystallites; (4) interactions between crystallites and amorphous regions; (5) frictional losses within crystallites. Single crystals of linear polyethylene show several loss peaks related to loss peaks in partially crystalline polyethylene. Additional types of loss mechanisms arise in polymers such as polyethylene glycol terephthalate, polycarbonates, cellulose derivatives, and nylon, in which different types of moieties alternate along the chain. Different teat methods varying in specificity toward molecular groups in frequency and in sensitivity are needed to elucidate the full spectrum of loss mechanisms. Brief comment is made on the dielectric data of Kheir showing two clearly resolved loss peaks for 5% cellulose acetate in dioxane.