Kinetics of Cross-Nucleation in Isotactic Poly(1-butene)

Abstract

During crystallization of polymorphic substances, a daughter phase may nucleate on the surface of a previously present polymorph: this crystallization scheme has been denoted as cross-nucleation. While several extensive studies exist for small organic molecules, analogous reports for semicrystalline polymers are scarce. Hereby we present the first determination of cross-nucleation kinetics for crystallizable macromolecules. The melt of isotactic poly(1-butene) was seeded with Form I spherulites through an in situ procedure. Measurements at different crystallization temperatures revealed a linear increase of Form II-on-Form I cross-nucleation density with time. In agreement with heterogeneous nucleation theories, the derived cross-nucleation rate shows an exponential dependence on undercooling.

Differential scanning calorimetry study of cross‐nucleation between polymorphs in isotactic poly(1‐butene)

“…it can be considered that the concentration of heterogeneous nuclei is constant at a given temperature within a certain time interval, cross-nucleation on Form I spherulites is 'pseudo-homogeneous', with the surface density of Form II nuclei linearly increasing with time. 24,27,28 Moreover, the amount of seed surface available for cross-nucleation is similarly time-dependent, being progressively occupied by Form II morphologies growing on the substrate or impinging from neighboring seeds. Therefore, the application of a simple crystallization model, such as the Avrami, is meaningless.…”

“…19,20 Cavallo and Alfonso have shown that many more overlooked examples exist in the polymer crystallization literature. [21][22][23] Moreover, systematic extension of a quantitative approach to cross-nucleation to different macromolecules (isotactic poly(1-butene), polypivalolactone and isotactic polypropylene) [23][24][25][26][27][28] allowed us to understand that the nucleation of one polymorph on another can be regarded as a special case of heterogeneous nucleation, unless the parent phase grows at rates comparable to those of the daughter polymorph. 24,28 All the wealth of information so far obtained on cross-nucleation has been exclusively gathered by optical microscopy analysis of the developing morphology.…”

Cross‐nucleation of polybutene‐1 Form II on Form I seeds with different morphology

“…Then the samples were quickly cooled down to room temperature and aged for more than 1 month in order to completely transform the original Form II crystals into Form I. It should be noted that, according to previously adopted procedures for cross‐nucleation studies in PB‐1, a dual morphology is produced . Indeed, low melting temperature crystals of Form I, formed during quenching to room temperature, are essential for having molten PB‐1 in contact with crystalline Form I seeds (with higher melting temperature) …”

“…It was found that nucleation rate at constant undercooling increased by 60 times with decreasing Δ σ/σ from 0.23 to 0.13, which confirms that Δ σ is extremely sensitive for detecting the nucleating ability of a substrate . For what concerns cross‐nucleation, although the kinetics of the process has already been studied for several systems, a detailed description based on Δ σ calculation was not extensively applied.…”

“…Given that the spherulitic seed of Form I in contact with PB‐1 melt has proven to efficiently cross‐nucleate the metastable polymorph, in this work we aim at gaining some insights on the role of the substrate type on cross‐nucleation. Therefore, substrates of Form I with different morphologies, namely spherulites, hedrites, or fibers, were employed to study cross‐nucleation kinetics by means of polarized optical microscopy.…”