Abstract
A terpolymer of propylene with low amounts of ethylene and 1-butene comonomers was fraction- ated by temperature rising elution fractionation (TREF), and the effect of fractionation experiment was checked through crystallization analysis fractionation (Crystaf). Nuclear magnetic resonance ( 13 C NMR) spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were used to characterize the set of polymer frac- tions obtained. Each polymer fraction was composed of long isotactic propylene sequences and low amounts of ethylene and 1-butene comonomers, and had more uniform molecular weight distribution and narrower crystallization temperature distribution (σ, R) than the original sample. The macromolecular chains consisted mainly of PP, PB, and PE dyads with or without the presence of very low amounts of BB, EE, and EB dyads. The terpolymer could be considered a combination of a propylene-ethylene copolymer and a propylene-1-butene copolymer in analyzing the molecular chain microstructure of the terpolymer. The investigation concluded that with increase of elution temperature, ethylene and 1-butene content of the polymer fractions decreased, and the number average sequence length of ethylene (nE) and 1-butene (nB) decreased, whereas the number average molecular weight (Mn) and number average sequence length of propylene (nP) increased. It is ethylene, not 1-butene, that affects linearly the melting temperature at content lower 6.8 mol%. A linear relationship was found between reciprocal number average molecular weight (1/Mn) and reciprocal melting temperature (1000/T , 1/K) at number average molecular weight below 1.59 × 10 5 , in good agreement with Flory's theory. Molecular microstructure is of significance in its effect on the physical properties of propylene poly- mers such as melting crystallization, degree of crys-
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