Kinetic Partitioning of 1-Butene Defect in Random Propylene 1-Butene Copolymers by Time-Resolved FTIR

Two different types of regularity bands are identified in a time-resolved FTIR crystallization of a series of random isotactic propylene 1-butene copolymers with a concentration of 1-butene from 2 to 19 mol{\%}. The first type are bands associated with 31 helices of isotactic sequences of different n length (n, number of monomer units). The second are regularity bands at 830, 920, 1010 and 1240 cm-1 associated with continuous sequences of the chain that include the 1-butene comonomer. Conformational changes during the isothermal crystallization process were monitored with these regularity bands. The variation of the intensity of regularity band at 920 cm-1 with crystallinity content and a shift of the 841 cm-1 (n = 12) at lower frequencies correlate with the content of comonomer included in the crystal. Changes in frequency of the n = 12 band with varying crystallization temperature (Tc), and with crystallization time at a fixed Tc are associated with the kinetic partitioning of the comonomer units, that was quantified with data obtained from 13C NMR. The frequency shift is absent in copolymers with co-units that are excluded from the crystalline regions, such as the 1-octene comonomer.