For polymers and low-molecular-weight materials, crystallization mechanisms have been investigated through the morphology and growth rate of crystals. The nucleation theory of Hoffman¹ successfully explained the temperature dependence of polymer crystal growth rate by categorizing the growth mode into three distinct regimes, I, II and III, depending on the relative rates of formation of new surface nuclei on the growth front and the rate at which the nuclei once formed spread along the growth front. Regime I corresponds to single nucleation growth mode. At low supercoolings, the rate of spreading is so large compared with the rate of nucleation that a nucleus once formed spreads right across the growth front. Regime II is a growth mode of multiple nucleation. At higher supercoolings, several nuclei form and spread across the growth front together, the separation between them decreasing with increasing supercooling. Regime III corresponds to rough surface growth. At sufficient supercoolings, the separation is of the order of the molecular width and no more spreading takes place.

Between different growth regimes, transitions are observed in the temperature dependence of crystal growth rate. Regime I-II transition has been investigated in association with the morphological change of lateral growth shape of lamellar crystals. The most typical examples are change from lenticular shaped crystals into truncated-lozenge shaped ones reported for polyethylene by Toda et al². Regime II-III transition corresponds to a change from multiple nucleation mode into rough surface growth mode, and one can naturally associate it with kinetic roughening transition of lateral growth shape. However, reports of morphological change of lamellar crystals in association with regime II-III transition are very few^{3, 4}.

We have investigated the melt crystal growth of isotactic polybutene-1 (PB1) form I (trigonal phase)  and form II ( tetragonal phase) in order to elucidate the mechanisms of polymer crystal growth and to explain growth kinetics consistently with morphology change of crystal growth shape^5,6. Recently, PB1 is of growing interest because of its outstanding mechanical properties and its excellent thermal properties. Investigating PB1 crystal growth is also significant from a practical standpoint. In our previous work ^5,6, we observed the kinetic roughening transition of PB1 form II crystals. In this work, we are going to make a preliminary report of regime II-III transition of form II crystals in association with kinetic roughening transition.

¹ Hoffman, J. D.; Miller, R. L. Polymer 38, 315, 1997.

² Toda, A.; Faraday Discuss. Chem. Soc. 95, 129, 1993.

³ Abe, H.; Kikkawa, Y.;  Inoue Y.; Doi, Y.;  Biomacromolecules 2, 1007, 2001.

⁴ Abe, H.; Harigaya, M.; Kikkawa, Y.; Tsuge, T.; Doi, Y.; Biomacromolecules 6, 457, 2005.

⁵ Yamashita, M.; Miyaji, H.; Hoshino A.; Izumi, K.; Polymer J., 36, 226. 2004.

⁶ Yamashita, M.; Miyaji, H.; Hoshino A.; Izumi, K.; Polymer J., 41, 1152. 2009.

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1. Form I/II binary crystal phase morphology of melt grown isotactic polybutene-1
2. Formation and melting of high pressure rotator phase of n-tridecane, pentadecane and heptadecane studied by FT-IR
3. Defect population in the High pressure rotator phase of n-tridecane, pentadecane and heptadecane observed by FT-IR