A study on the isothermal crystallization of poly(3-methylbutene-1)

Poly(3-methylbutene-1) (P3MB1) is a polyolefin with a high melting temperature T-m (approximate to 305 degrees C). We investigated the structural evolution of P3MB1 during isothermal crystallization from the melt by synchrotron radiation X-ray scattering and polarizing optical microscopy. At crystallization temperatures (T-c) of 297 and 290 degrees C or shallow quench conditions (Delta T =T-m(0)-T-c = 26 and 33 degrees C), needle-like crystals comprising lamellae were formed and flowed during their growth in the molten portion. To clarify the origin of the wide temperature region of the needle-like crystals in P3MB1, we estimated the critical lamellar width lambda*, which is a parameter characterizing the suppression of lamellar branching, of P3MB1 and polyethylene (PE). The lambda* of P3MB1 was larger than that of PE at the same Delta T, owing to the low viscosity of P3MB1. However, the range of lambda* in the temperature region of the needle-like crystals of P3MB1 was 0.41 < lambda* < 7.4 mu m; PE formed spherulites in this range. Thus, suppression is not only the origin of the needle-like crystals in P3MB1, but may also be responsible for the flow of the needle-like crystals in melts.