Industrial & Engineering Chemistry Research, Vol.58, No.36, 16869-16876, 2019
Preparative Temperature Rising Elution Fractionation of One Poly(1-butene) Copolymer and Its Chain Microstructure Characterization
Generally, commercial P-TREF (preparative temperature rising elution fractionation) equipment carries out an experiment for polyolefin samples between room temperature (or the lowest temperature at 20 degrees C) and 150 degrees C. Although we have applied the traditional TREF method in polyethylene and propylene resin in our previous studies, it failed to fractionate poly(1-butene) with a polymorph structure. Up to now, it has been a challenge to realize an effective P-TREF separation procedure for poly(1-butene) resins. Based on the analysis and experiments, it was found that a low temperature was important for poly(1-butene) resin. Herein, a novel P-TREF instrument with a broad temperature range from -80 to 150 degrees C is designed and fabricated. By applying this equipment, one poly(1-butene) copolymer, i.e., 1-butene/ethylene random copolymer, is first effectively fractionated according to its crystallizability by the TREF principle. The main fractions are eluted at 30, 42, and 46 degrees C, corresponding to the weight percent of 12.81%, 18.05%, and 39.52%, respectively. Chain microstructures of the original resin and its fractions are further characterized by high-temperature gel permeation chromatography coupled with triple detectors (refractive index-laser light scattering-viscometer), C-13-nuclear magnetic resonance spectroscopy (C-13 NMR), and differential scanning calorimetry (DSC). With an increasing elution temperature from -30 to 46 degrees C, the ethylene content of the fractions decreases from 12.6 to 2.9 mol %; meanwhile, the isotacticity increases from 41.2% to 83.6%, and the crystallinity increases gradually. From these results, the TREF technique can be extended to resins (for example, poly(1-butene) copolymer) with slow crystallization kinetics, and the chain microstructure of polymorphic poly(1-butene) copolymer can be analyzed in detail. This will lay a foundation for both basic research and industry applications.