The role of 1-hexene comonomer content inthermal behavior of medium density polyethylene(MDPE) synthesized using Phillips catalyst

In this work, the role of comonomer content of 1-hexene-medium density polyethylene (MDPE) copolymer,synthesized using Phillips catalyst, on thermal behavior parameters such as: crystallization, melting temperatureand thermal degradation was investigated in detail. The copolymer was fractionated to homogenous short-chainbranching (SCB) fractions by preparative temperature rising elution fractionation (P-TREF) method and then itwas subjected to thermal analyses. A broad chemical composition distribution (CCD) in terms of SCB content andmolecular weight (Mw) was observed by P-TREF and gel permeation chromatography (GPC), respectively. Basedon P-TREF results, a parabolic relationship between methylene sequence length (MSL) and elution temperature(ET) was presented. Differential scanning calorimetry (DSC) showed distinct, well-defned melting peaks over a22 °C temperature range for SCB contents of about 3-12 (br/1000 C). The variations in physical characteristicssuch as melting temperature (Tm), crystallinity (Xc), crystallization temperature (Tc) and lamellae thickness (Lc)against SCB content were correlated. Thermogravimetric analysis (TGA) suggested linear relationships betweenthe temperature at maximum degradation rate (Tmax) as well as the degradation initiation temperature (T5%) versusSCB content. Moreover, the TGA curves exhibited distinct differences at both initiation and propagation stages ofthermal degradation at dissimilar comonomer contents. Polyolefns J (2014) 1: 117-129

Keywords:

ethylene/1-hexene copolymer , short-chain branching (SCB) , thermal degradation , Phillips catalyst , medium densitypolyethylene (MDPE)