Directional Entropy of Chain Folding Detected in Chain Folding Free Energies? Crystal Thickness Transition of isotactic Polybutene-1 Tetragonal Phase

Abstract

Lamellar crystal thickness l c of isotactic polybutene-1 (it-PB1) has been investigated for crystallization in the melt over a wide range of crystallization temperature T from 40 to 90 C by small angle X-ray scattering experiments and density measurements. The crystal thickness l c demonstrates two linear dependences on inverse supercooling and a transition from one dependence to the other has been observed around T ¼ 65 C. Each of the two dependences obeys the nucleation theory in the high and low supercooling ranges, respectively. Chain folding free energy q determined from the low supercooling range is larger than that determined from the high supercooling range. We discuss possible mechanisms for the transition taking account of entropy of chain folding directions and propose that the difference in the q values could be due to the change in directional entropy of chain folding caused by kinetic roughening.KEY WORDS: Isotactic Polybutene-1 / Tetragonal Phase / Melt Crystallization / Crystal Thickness / Chain Folding Direction / Small Angle X-ray Scattering /In the crystallization of polymers, polymer chains in the form of random coils develop into double layer structures composed of folded chain crystals (lamellar crystals) and amorphous layers. Lamellar crystal thickness is the most important quantity describing the morphology specific to polymer crystals. The nucleation theory by Hoffman et al.

Nucleation Mechanism for Form II to I Polymorphic Transformation in Polybutene-1

“…If we assume that the smaller value represents d c , the ratio of these values to d ac as the value of linear crystallinity (φ l × 100% = 25.6%) can be calculated. Obviously, linear crystallinity is lower than bulk crystallinity from WAXS (49.8%). , This does not make sense because it would suggest that lamellae fill up more than 100%. As shown in Figure c, it is interesting to see that φ l of Form II during the whole heating process was nearly constant.…”

“…Obviously, linear crystallinity is lower than bulk crystallinity from WAXS (49.8%). 24,80 This does not make sense because it would suggest that lamellae fill up more than 100%. As shown in Figure 3c, it is interesting to see that φ l of Form II during the whole heating process was nearly constant.…”

Kinetic roughening transition and missing regime transition of melt crystallized polybutene-1 tetragonal phase: growth kinetics analysis

“…In this work, we report another example of disagreement between temperature dependence of growth rate and morphology. We have investigated the crystallization of isotactic polybutene-1 (it-PB1) in the melt [7][8][9][10][11][12][13][14][15][16]. It-PB1 exhibits stable trigonal form ( I ) with 3/1 helical chains and metastable tetragonal form ( II ) with 11/3 helical chains as the most common structures as shown in Table 1.…”