Crystallization and Homogeneous Nucleation Kinetics of Poly(ε-caprolactone) (PCL) with Different Molar Masses

Abstract

The crystallization and nucleation kinetics of poly(ε-caprolactones) (PCL) with molar masses between 1.4 and 6.1 kDa and negligible number of heterogeneous nuclei has been investigated by differential fast scanning calorimetry (DFSC) applying scanning rates up to 100 000 K/s. The samples were synthesized by ring-opening polymerization and chemically characterized by NMR spectroscopy, size exclusion chromatography (SEC), and multiangle laser light scattering (MALLS). For the smallest molar mass the chain length is comparable with the crystal thickness measured with small-angle X-ray scattering (SAXS), and extended chain like crystals may be formed. Because of the molar mass distribution (PDI ≈ 2), these crystals have a significant noncrystalline interface yielding nearly the same crystallinity for all molar masses. The critical cooling rate to obtain amorphous samples is below 1000 K/s and only for the lowest molar mass increased to 2000 K/s. The same trend holds for the about 1 order of magnitude higher critical heating rate to keep the samples amorphous on heating and for the analysis of isothermal nucleation and crystallization kinetics at 202 K. The samples which were shown not to contain heterogeneous nuclei active at a heating rate of >18 000 K/s were used for a study of the nucleation activity of ordered structures formed on annealing at low temperature. The analysis of the change of the thus-produced amorphous polymer samples on annealing from 202 to 272 K for times varying by a factor of more than 108 (0.1 ms to 8.3 h) revealed new details about the ordering processes (nucleation, poor crystal formation, crystallization, cold crystallization, and crystal perfection) and the accompanying changes in glass transition of the remaining amorphous phase (formation of rigid amorphous phases, RAF).

Vitrification and crystallization of poly(butylene-2,6-naphthalate)

“…PCL is a typical fast crystallizing polymer [8,27], but the critical cooling rate for full vitrification of the additive-free PCL is 10,000 K/s [8] as was mentioned in the introduction. Namely, the critical cooling rate of PBN is three times as large as that of PCL.…”

“…Furthermore, cooling at a rate faster than 1000 K/s also prevents the mesophase formation in iPP, which is initiated by the homogeneous nucleation, and consequently the glassy amorphous iPP is obtained [24,26]. For PCL, the cooling rate suppresses the formation of any nuclei that will be activated in the subsequent heating process [8,27]. However, in PBN, the mesophase formation could not be prevented by cooling faster than 1000 K/s [7].…”

Density of heterogeneous and homogeneous crystal nuclei in poly (butylene terephthalate)

“…Analysis of the crystallization behavior of vitrified samples of PCL [14,32], PA 6 [33] and isotactic polybutene-1 (iPB-1) [34] revealed furthermore that during annealing of the glass there is first observed enthalpy relaxation, and only after its completion there is detected crystal nucleation followed by crystal growth. The decrease of the enthalpy of the glass to the value of the liquid state corresponds to a densification of the glass, involving cooperative rearrangement of molecule segments on a lengthscale of few nanometers, eventually leading to formation of small clusters of parallel aligned chain segments, to be considered as homogeneous nuclei if being of supercritical size.…”

Effect of incongruent crystallization on glass–liquid transition features of a bulk metal glass

“…By using the technique of ultrafast calorimetry and q c and q h as high 10 4 K/s, they studied crystal nucleation and growth of rapidly crystallizing polymers, and reported the data for the heating scans. They stressed that steric hindrance from intra-molecular and inter-chain barriers prevents polymer chain segments from diffusing independently, and nucleation and crystal growth in polymers, therefore, requires chain folding [16]. Cold-crystallization of polymers differs from that of molecular materials, which have no such steric hindrance.…”

“…Cold-crystallization of polymers differs from that of molecular materials, which have no such steric hindrance. They also concluded that nucleation occurs in the nm-size regions of high molecular mobility in the glass structure [15][16][17].…”