Isothermal and nonisothermal transition kinetics of trans‐1,4‐polybutadiene

Abstract

Analysis of the isothermal and nonisothermal transitions of hexagonal crystal formation from the melt (transition 1) and of monoclinic crystal formation from hexagonal crystals (transition 2) for trans-1,4-polybutadiene (TPBD) was carefully carried out by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Isothermal transitions 1 and 2 are described by Avrami exponents (n) of Ϸ1, whereas nonisothermal transitions 1 and 2 are described by n Ϸ 4. These different n values indicate that different crystallization mechanisms took place for different crystallization driving forces under isothermal and nonisothermal crystallization. The Ozawa equation was also used to analyze the nonisothermal crystallization data. For transition 1 at lower temperature, the Ozawa equation fits the data well; however, at higher temperature, there is an inflection that shifts to lower crystallinity with increasing temperature. Inflections are also observed with the Ozawa analysis for transition 2. Furthermore, the crystallinities at the turning points are almost in the same range as those determined by Avrami analysis for nonisothermal transitions 1 and 2, which suggests that the Ozawa analysis inflections are due to secondary crystallization. However, TEM revealed no morphology discrepancy between the TPBD hexagonal crystals formed from melt by isothermal and nonisothermal crystallization. The agreement in activation energy (⌬E) values determined by the Arrhenius and Kissinger methods indicates that the Avrami equation can describe the initial stage of transitions 1 and 2 in the nonisothermal transition process quite well. The ⌬E values determined by the Arrhenius and Kissinger methods for transition 1 are 167.4 and 179.2 KJ/mol, respectively, and those for transition 2 are 186.1 and 196.3 KJ/mol; respectively.

An Enzymatic Approach to the Synthesis of Peptide Thioesters: Mechanism and Scope

“…Combining the two effects of a non‐negligible volume fraction of nuclei and changing crystal growth rate (Equations (9) and (11)), the last form of the modified Avrami equation can be written as follows: In the above, K + = gN 0 ν 0 n , where g is a geometrical factor (4π/3 for spheres), N 0 and ν 0 are the initial number of nuclei and linear growth rate, respectively: n ( m + 1) + a is known as an apparent coefficient. Both negative contributions ( m and a ) lead to a smaller value of the apparent coefficient, as observed from other studies 30, 32–34…”

Analysis of interfacial phenomena of aqueous solutions of polyethylene oxide and polyethylene glycol flowing in hydrophilic and hydrophobic capillary viscometers

“…The inner diameter of the PTFE capillary is measured to be 0.573 mm, and that of the glass capillary is 0.395 mm. The cleaning of the two types of capillary viscometers must be careful and has also been described in other papers [11,21]. The main procedures are below.…”

“…Up to now the method of combination of the literature-reported Mark-Houwink equation and the measured intrinsic viscosity under the same experimental conditions (same temperature and solvent or added salt aqueous solution) for evaluating the molar mass of polymers has been widely used for its convenience and economy [3,4]. However, adsorption phenomena frequently occur in viscosity measurements, due to the existence of hydroxyl groups on the inner surfaces of glass capillaries, which interferes with viscosity determination and leads to the usual occurrence of viscosity abnormalities, especially in the extremely dilute concentration region [5][6][7][8][9][10][11][12][13][14][15][16][17][18], and making invalid the usual method of linear extrapolation to zero concentration to obtain intrinsic viscosity.…”

Viscometric study of gelatin in dilute aqueous solutions

“…By the Poiseuille law of viscosity measurement, the viscosity of the pure solvent is related to its flow time in a clean viscometer with capillary radius R as follows: where the solute adsorption is absent, V is the volume of liquid flowing through a pipe, g is the acceleration of gravity, h is the height of the column of fluid, ρ 0 is the density of water, and L is the length of the pipe. If the viscometer capillary surface is fully covered with a layer of the adsorbed polymer, the flow time of the pure solvent is related to the viscosity of the solvent as follows: Combining eqs 3, 9, and 10, immediately we have According to the assumption that the Einstein viscosity law is valid for a nonassociable dilute polymer solution and any deviation from it is due to macromolecular self‐association or cluster formation, instead of the conventional Huggins equation (where K H is the Huggins coefficient) η r,true of a polymer solution can be represented by30–34 where K m is the apparent self‐association constant. It is related to the size and interactions between polymer chains in solution and numerically correlates with the Huggins coefficient ( K H ) and [η] as follows: With the combination of eqs 8 and 14, η r,exp of thepolymer solution should be expressed as follows: …”

“…Viscometry is the simplest, most convenient, and most sensitive way of investigating the conformational changes of macromolecules in solution 11–16. However, in the extremely dilute concentration region, the viscosity data usually show abnormalities, such as the upward‐bending phenomenon of a curve of the reduced viscosity versus the concentration,26–34 which has been attributed to the interference of the interfacial adsorption of polymer chains on the capillary wall surface and proved by lots of viscosity determination results for neutral polymer and polyelectrolyte solutions 28–33. This is the main reason that literature data for gelatin in this concentration region are lacking.…”