Effect of crystallisation conditions on physical structures and mechanical properties of isotactic polybutene-1

The relationship between the physical structures and mechanical properties of isotactic polybutene-1 (iPB-1) with a crystal-fixed form I was investigated using a combination of uniaxial tensile testing, dynamic mechanical analysis (DMA), and time-domain 1 H NMR T 2 relaxometry. Two samples with different crystallinity, the long-range periodicity of the lamellar structure and the density of physical network junctions in the amorphous phase were prepared by slow isothermal melt-crystallisation and by quenching of the polymer melt in ice water. The relative difference in the density of physical network junctions, which are caused by chain anchoring to crystallites and form tie molecules in amorphous domains between crystalline lamellae, was determined from the T 2 relaxation time of the amorphous phase. Despite low crystallinity, the number of tie molecules was larger for the quenched sample than for the slowly-crystallised one due to two times smaller long-range period of the lamellar structure, as determined by SAXS. The population-weight-average T 2 relaxation rate (1/ T 2 PWAR ) was introduced for estimating the contribution of crystalline (rigid) and amorphous (soft) domains to the volume-average macroscopic storage ( G ′) and shear ( G ) moduli. PWAR values for the entire sample (1/ T 2 PWAR/all ), for rigid (1/ T 2 PWAR/rigid ) and soft (1/ T 2 PWAR/soft ) domains were determined in a wide temperature range and compared with G ′ and G values. A linear relationship was observed between 1/ T 2 PWAR/all and G for both samples. The quenched sample displays a lower G value due to more disordered rigid domains and lower crystallinity. The effect of temperature on G ′ and 1/ T 2 PWAR values for rigid and soft domains is very similar. This study suggests that the temperature dependence of G ′ and G depends on four physical structure characteristics: (1) crystallinity, (2) molecular mobility in rigid domains composed of crystal lamellae with the interfacial layer on their surface, (3) molecular mobility in soft domains, and (4) the density of network chains in the amorphous domains – tie molecules. The results of the present study are of interest for a better understanding of the role of different phases in the deformation properties of semicrystalline polymers. • iPB-1 with form I crystals was studied by NMR relaxometry, SAXS and mechanical tests. • iPB-1 with different phase compositions and physical network junctions was studied. • Crystallisation temperature largely affects the stiffness of rigid and soft domains. • The Population-Weight-Average T 2 relaxation Rates characterize relative stiffness. • A good relationship between PWAR and mechanical moduli is observed.