Fractionation and Characterization for a Propylene–Ethylene Random Copolymer

Abstract

ABSTRACT:A random copolymer of propylene with 3.5 mol% ethylene comonomer is firstly fractionated by temperature rising elution fractionation (TREF). Techniques including 13 C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), gel-permeation chromatography (GPC), crystallization analysis fractionation (Crystaf) and differential scanning calorimetry (DSC) are used to characterize the obtained fraction polymers. The results show that each fraction polymer is composed mainly of isotactic propylene sequence plus a small amount of ethylene comonomer and has uniform molecular weight and ethylene content. The PPP, PPE, and PEP are main part of triad sequence unit. As the elution temperature increasing, ethylene content of the fraction polymers decreases, number average molecular weight increases, and meanwhile number average sequence length of propylene, n P , increases, while that of ethylene, n E , decreases, close to 1. The results show that ethylene content affects linearly the melting temperature (T m ) in a range of ethylene content being as low as less than 10.23 mol%; there is a linear relationship between the reciprocal melting temperature (1000/T m , K −1 ) and reciprocal number average molecular weight (M Polypropylene is a common semi-crystalline synthetic polymer, and its macromolecular chain structure is an important factor to affect such properties of propylene polymers as crystallization behavior, morphologies, melting temperature, degree of crystallization, toughness, and rheological and optical properties. By the way of introducing some comonomers (e.g., ethylene) into its macromolecular chain, the performance of propylene polymers can be improved purposefully and effectively. Because propylene tacticity and ethylene comonomer complicate the macromolecular chain structure, and can farther lead to complex crystallization behaviors and morphologies, it is very important to firstly characterize the macromolecular chain structure well. In order to investigate thoroughly the relationship between performance and macromolecular chain structure, it is necessary to make samples uniform. Temperature rising elution fractionation (TREF) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has been shown to be a powerful technique to make crystal polyolefins uniform on the basis of their crystallizability and molecular weight. Through TREF experiments, a set of fraction polymers with uniform molecular weight and content of ethylene comonomer can be obtained; hereafter crystallization analysis fractionation (Crystaf) will be used to check the effect of fractionation by analyzing such parameters as σ and R, 16 which can define the broadness of the crystallization temperature distribution of the fraction polymers. [16][17][18][19][20][21][22] Up to now most samples of propylene copolymers on investigation are the impact propylene-ethylene copolymers, a very complex blend. Even though after they have been fractionated by TREF, 3-11 each fraction polymer also consists of PE, ...

13C NMR, GPC, and DSC Study on a Propylene-ethylene-1-butene Terpolymer Fractionated by Temperature Rising Elution Fractionation

“…Therefore, according to Monrabal 11 and Brull, 4 the classical Flory eq 1 21 simplified to eq 2, formerly applied to explain the relationship between melting temperature and ethylene content for propylene-ethylene random copolymer. 2 This study extends the application of eq 2 from copolymers to terpolymers. To analyze the effect of comonomer of terpolymer on melting temperature, we first considered this comonomer as a defective comonomer.…”

“…Eq 4 has been applied to explain the T m − M n relationship of random copolymers of propylene with low amounts of ethylene (<10.23 mol%) by assuming weight of the ethylene comonomer identical to that of propylene. 2 For terpolymers of propylene with low amounts of ethylene and 1-butene, the same method was used to analyze the T m − M n relationship. The macromolecular chain of the terpolymer was assumed identical to that of propylene homopolymer.…”

Preparative TREF ‐ HT‐HPLC ‐ HPer DSC: Linking Molecular Characteristics and Thermal Properties of an Impact Poly(propylene) Copolymer

“…These two factors, the CCD (the chain structure, polymer type, and chain branching) and MMD, primarily influence the thermal properties (melting and crystallization behaviour) of such semi‐crystalline polymers. A variety of techniques has been reported to correlate the molecular characteristics of IPCs with their thermal and mechanical properties . Fractionation of the bulk sample by preparative TREF and further analysis of the separated fraction by conventional analytical techniques such as HT SEC, FTIR, 13 C NMR, and DSC has been found to be an effective method for the detailed analysis of such copolymer system .…”

Effect of copolymerized ethylene unit on the crystallization behavior of poly(propylene-co-ethylene)s

“…Although investigation of the latter is not as wide as that of the former, recently, more and more attention has been drawn to the studies on the propylene-rich copolymers. Reports on thermal behavior [12][13][14][15], crystal structure [16][17][18][19], morphology [20][21][22][23], crystallization kinetics [13,14,[22][23][24][25] and polymorphism [19,24,[26][27][28][29][30][31][32][33] of propylene-ethylene copolymers (PPE) with minor ethylene contents have been published. However, the relationships between the chain structure and the crystalline morphology of the PPE have not been studied in detail.…”

“…The temperature rising elution fraction technique (TREF) [34,35], which has shown to be a powerful technique for studies of the compositional heterogeneity of polyolefin, provides a feasible way to investigate the relationships between the chain structure and the crystalline morphology because the PPE can be fractionated according to the comonomer composition and sequence distribution [12,13,28,30,36]. As for PPE, the chain structure is closely related to the distribution of the comonomer.…”