High-temperature creep behaviors of polybutene-1 with different chain microstructure and molecular weight

Abstract

The creep resistance of polymer determines the dimensional stability of product under stress. The isotactic polybutene-1 (iPB) with outstanding high-temperature creep resistance and stress-crack resistance is applied widely in the field of hot-water pipes. Although the chain information including weight-average molecular weight (Mw) and aggregate structures of isotactic polybutene-1 (iPB) influence the creep resistance, the crucial factor affecting the creep behavior greatly is unclear. In this work, a series PB samples with varied Mw, isotacticity and configurational sequence were synthesized and characterized based on Gel Permeation Chromatography (GPC), solvent fractionation and Nuclear Magnetic Resonance Spectroscopy (NMR). The Differential Scanning Calorimetry (DSC), Wide-angle X-ray diffraction (WAXD) and Small angle X-ray scattering (SAXS) were used to characterize the aggregation structures of PB samples. The stress-strain behaviors and 95 °C creep deformation of these PB samples were testes by tensile test and Dynamic Mechanical Analysis (DMA), respectively. It was found that these PB samples showed different chain microstructures like 88–99 wt% high isotactic PB (HiPB) fractions, 90–97.6 mol% tetra-meso placements (mmmm) in HiPB fraction, and 50 × 104-160 × 104Mw. Increasing the molecular weight, isotacticity or configurational sequence mmmm enhanced the creep resistance of PB, while mmmm configurational sequence played more important role in creep resistance of PB through adjusting the aggregation structure (crystalline domains) of the final product greatly. Exploring the influencing factors of creep resistance provided guidance for the synthesis of high-performance PB for high-temperature pipe application.