Viscoelastic behavior of the regular alternating terpolymers of ethene and propene with carbon monoxide

A series of the alternating terpolymers of ethene (Et) and propene (Pr) with carbon monoxide (CO), with different Et/CO contents, was characterized by storage and loss shear moduli (measured in a frequency window spanning about three decades) at several fixed temperatures in the interval from 120° to 220°C. The bell-like plot of the reduced (i.e., molar mass-independent) values of complex viscosity vs. Et/CO mass content was quantitatively reproduced by classical copolymerization theory assuming the strictly alternating Et/CO and Pr/CO copolymers as "virtual homopolymers" 11 and 22, and the strictly alternating (Et/CO)/(Pr/CO) terpolymer as an "alternating virtual copolymer" 12. Compared with other flexible-chain polymers, the apparent plateau moduli for the terpolymers were severalfold lower, suggesting an unusually loose structure of entanglement networks. Thus, the CO groups in the main chain of the terpolymers were ranked as the least effective entanglement formers, whereas the unlike dyads of the type (Et/CO)/(Pr/CO) were more effective than like dyads of the type (Et/CO)/(Et/CO) or (Pr/CO)/(Pr/CO). The systematic hysteresis viscosity effects during initial heating up to 220°C and subsequent cooling down to 120°C for samples Et/CO = 30.6 and Et/CO = 31.9 were regarded as experimental evidence for the existence of ordered nanodomains in the initial nanostructured state that served as reinforcing bridges for a continuous disordered matrix.