Investigation on the accelerating effect of two-dimensional boron nitride on the phase transition from form II to I in isotactic polybutene-1

This work investigated the influence of two-dimensional boron nitride (BN) on the phase transformation kinetics of isotactic polybutene-1 (iPB-1) with differential scanning calorimetry, wide angle X-ray diffraction, and small angle X-ray scattering technique. The phase transition time (ttra) from form II to I largely decreases with the increasing content of BN nanosheets. Different from that in pure iPB-1, the phase transition is accomplished without residual form II in a relatively short time. It's speculated that the addition of BN leads to the irregular lamellae packing of form II (demonstrated by the SAXS result). The irregular packing can avoid the accumulation of negative stress that is induced by the lamellae deformation of the transformed form II, which may hider the chain movement of the residual un-transformed form II. The dispersion of the negative stress obviously accelerated phase transition kinetics from form II to I in iPB-1/BN blends. In addition, it's found that the thickness of form I in iPB-1/BN blends is thicker than that in pure iPB-1. By investigation on the melting temperature of partially transformed form II/I, it showed that the thickness of form I in iPB-1/blends increased continually during the whole phase transition process, which is different from that in pure iPB-1. The continuously lamellae thickening of form I during phase transition may be due to the dispersion of negative stress which benefits the chain movement.