Crystallization kinetics of isotactic polystyrene. II. Influence of thermal history on number of nuclei

Abstract

The influence of various thermal pretreatments on the nucleation of isotactic polystyrene has been studied quantitatively by dilatometry. A distinction can be made between nuclei still present above the melting point (“resistant” nuclei) and nuclei created by severe supercooling (“induced” nuclei). The number of spherulites formed has been determined for different combinations of supercooling and crystallization temperatures. The results are interpreted in a satisfactory manner by assuming that in severe supercooling induced nuclei are created, which may grow into effective nuclei at higher temperatures. The crystallization of a severely supercooled polymer is completely governed by these induced nuclei, because they outnumber the resistant nuclei by some orders of magnitude. The number of induced nuclei can be decreased by purifying the polymer (removing catalyst residues). When cooled polymer is heated to temperatures just above the melting point, the induced nuclei are destroyed (“reversible melting”), so that only the resistant nuclei, which are few in number, remain. These resistant nuclei govern the crystallization behavior of a polymer which has not previously been cooled. Their number decreases on heating to temperatures far above the melting point.

Influence of Solution Thermal and Structural History on the Nucleation of m-Hydroxybenzoic Acid Polymorphs

“…In 1907, Young and Burke 2 established qualitatively that both a prolonged time and an increased temperature of overheating led to a decreased tendency to crystallize during subsequent cooling, based on a large number of melt crystallizations of p-nitrotoluene. In work that followed, these findings were corroborated by observations reported for melts of organic compounds [3][4][5] , metals 6 and polymers 7,8 .…”

Influence of History of Solution in Crystal Nucleation of Fenoxycarb: Kinetics and Mechanisms

“…prior to being brought into a state of supersaturation, may influence the nucleation behaviour of the solute. First reported in 1902, 1 an effect on crystallization of thermal solution history has been demonstrated for melts of organic compounds, 2 metals 3 and polymers, 4 as well as for aqueous and organic solutions of inorganic salts 5 and organic molecules 6 including proteins. 7 Interesting results on this effect have also been presented for the nucleation of clathrate hydrates.…”

“…However, perhaps the most important aspect of history of solution is that this phenomenon most likely carries information about clustering of molecules in solution. Fenoxycarb has chemical formula C 17 H 19 NO 4 and systematic name 2-(p-phenoxyphenoxy)ethylcarbamate and is shown in Figure 1. It is a flexible organic molecule that exhibits conformational isomerism in its single reported crystal form.…”

Evidence of a Heterogeneous Nucleus in a Polypropylene Spherulite Using Electron Probe Microanalysis

“…Noblene w 101 produced by Sumitomo Chemical Co. Ltd. (M.=7X10 4 ) was used as base PP without further purification. AlB and NaB were used as nucleating agents for PP because both chemicals were reported as good 600 nucleating agents, 5 • 8 and both chemicals were reagent grade commercial materials used without further purification.…”

“…1 -3 Various Materials, such as catalyst residues, 4 organocarboxylic acid salts 5 and inorganic compounds 6 have been reported as heterogeneous nucleating agents for polymer crystallization. In most cases the function of the nucleating agent was assessed by measuring its effect on the polymer supercooling 5 ' 7 and the crystallization mechanism of the PP-nucleating agent compound was explained using the modified Avrami equation 8 on the assumption that nucleating agents act as heterogeneous nuclei for polymer crystallization.…”