Kinetics of crystallization and a crystal‐crystal transition in poly‐1‐butene

Abstract

The formation and melting of the two crystalline modifications of poly‐1‐butene have been studied by the techniques of differential thermal analysis, infrared spectroscopy, dilatometry, and polarizing microscopy. On cooling the melt, modification 2 (Tm = 120–126°C.) appears within minutes. This form is unstable and gradually transforms to modification 1 (Tm = 135–142°C.). A density change of over 4% accompanies this latter transformation. As torsional damping experiments have shown the amorphous content to decrease by only about 5%, the stable modification must be much more dense than the unstable form. The kinetics of the crystallization of modification 2 from the melt were studied primarily dilatometrically at several temperatures. The data generally followed the Avrami equation with n equal to 4. This crystallization shows a high negative temperature coefficient (T1/2 = 380 min. at 110°C. and 2 min. at 90°C.) and becomes too rapid to measure by this technique at lower temperatures. The kinetics of the transformation of modification 2 to modification 1 were followed in infrared spectral, density gradient tube, and dilatometric studies. At room temperature, halftimes ranging from 250 to 1600 min. were observed, depending on the mechanical and thermal history of the sample. The observed discrepancies have been shown to be due, at least in part, to orientation effects. In dilatometric studies of the temperature dependence, the transition rate showed a pronounced maximum in the region of 15°C. Large increases in the torsional modulus and offset yield point of the specimen were observed to accompany the transition.

High pressure dilatometry on polybutene-1

“…This discrepancy can be attributed to incorrect crystallinities. Although the transformation II --~ I itself does not change the crystallinity [9,25], a slow crystallization into modification II is superposed on this transformation [24] so that a sample after full transformation into modification I has a higher crystallinity than a sample before the transformation, the crystallization of which has not yet finished (see also ref. [26]).…”

“…This transition is fastest near room temperature at 1 bar [9][10][11]6] and has a half-time of more than one day, but can be accelerated by some orders of magnitude by the application of mechanical stress [12,13] or hydrostatic pressure [6]. By the second method the temperature of minimum half-time is increased slightly.…”

Effect of polymorphism of isotactic polybutene‐1 on peel behavior of polyethylene/polybutene‐1 peel systems

“…10 Melt-crystallization, at ambient pressure, triggers formation of form II crystals. 11,12 In the presence of special nucleating agents, melt-crystallization can also lead to form III crystals. 8,9 Furthermore, melt-crystallization at elevated pressure higher than about 100 MPa, 7,10 on defined substrates 9 or of a strained melt results in formation of form I 0 crystals.…”

“…Melt-crystallization at ambient pressure yields primary formation of tetragonal form II crystals, which convert at ambient temperature to stable trigonal form I crystals. 3,12,16,[18][19][20][21][22][23] The crystalcrystal transformation occurs via nucleation at crystal sites which locally are under stress, despite the exact mechanism at molecular scale is not fully identified. 16 The kinetics of the phase transformation depends on one side on the chemical structure of the macromolecule, i.e., on the molecular weight, tacticity, or presence of comonomers, and on the physical superstructure which is controlled by the condition of processing/primary solidification.…”

Rheo-Optical Studies of High Polymers. XXI. The Deformation Process and Crystal Transformation in Polybutene-1

“…1) when a fresh sample of this material is allowed to stand after preparation. 1 Accordingly physical properties related to crystalline structure, such as birefringence, change with time. Yang (Yee) and Stein 2 ' 3 have investigated the deformation of fresh and aged polybutene-I, and found notable differences between the fresh and the aged samples.…”