Crystal growth of the trigonal form of isotactic poly(butene-1) (it-PB1) was successfully observed in the melt at atmospheric pressure. The growth rate of trigonal crystals was obtained by in situ optical microscopy. It is one hundredth that of it-PB1 tetragonal crystals. The growth rate of trigonal crystals, as well as that of tetragonal crystals, shows supercooling dependence derived from the nucleation theory. The value of the kinetic constant K of tyigonal crystals is about 3.3 times larger than that of tetragonal crystals. The value of the pre-exponential factor G(o) of trigonal crystals was found to be 41 times as large as that of tetragonal crystals. The difference between these K values can be attributed to the conformational entropy of the ethyl side groups in a nucleating stem. The discrepancy found in the values of G(o) could be explained by introducing pinning and nucleation barriers, which originate from the crystal thickness delta l(c), which does not depend on the crystallization temperature. (c) 2007 Wiley Periodicals, Inc.