Surface free energies of isotactic polybutene-1 tetragonal and trigonal crystals: the role of conformational entropy of side chains

Lateral and end surface free energies of melt-crystallized isotactic polybutene-1 (it-PB1) trigonal and tetragonal crystals have been determined by small-angle X-ray scattering and in situ observation of the crystal growth kinetics. The lateral surface free energy σ of the trigonal phase is about seven times as large as the value σHoff calculated according to Hoffman's equation [Hoffman (1992). Polymer, 33, 2643–2644], while that of the tetragonal phase is roughly in agreement with the estimation. The discrepancy between the values of σ and σHoff for the trigonal phase can be attributed to the loss of conformational entropy of the ethyl side chains of it-PB1.