EFFECT OF BIMODAL CHAIN-LENGTH DISTRIBUTION ON THE THERMAL-CHARACTERISTICS OF POLY(ETHYLENE OXIDE) END-LINKED NETWORKS

Poly(ethylene oxide) (PEO) end-linked networks have been prepared with bimodal distributions of molar masses between crosslinks (M(c)). The thermal characteristics of the PEO networks have been investigated in the unstretched state over the temperature range 173-373 K using differential scanning calorimetry. The elastomer with the lowest M(c) (205 g mol-1) showed a much higher glass transition temperature (T(g)) than the infinite molar mass value T(g)(infinity) for PEO. Although it is known that molecular topology affects T(g), this system involves incorporating bulky junction points, thus also causing a significant chemical change upon curing. The mechanical and swelling properties of the bimodal PEO networks have suggested that strain-induced crystallization may be facilitated by the relatively stiff short network chains acting as nucleation sites for crystallization in the stretched state. In the present study, however, it is seen that the extent of crystallization of the PEO networks decreases with an increase in short chain content in the unstretched state.