Nucleation and Crystallization in Double Crystalline Poly(p-dioxanone)-b-poly(ε-caprolactone) Diblock Copolymers

Abstract

The crystallization behavior of three double crystalline diblock copolymers containing poly-( -caprolactone) and poly(p-dioxanone) has been studied via differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray scattering (WAXS). Crystallization and melting temperatures and enthalpies are compared among copolymers and to those of the corresponding homopolymers. Only one crystallization exotherm was observed for the diblocks. DSC and WAXS indicated that during isothermal crystallization PPDX crystallized first, followed by PCL. POM revealed a transformation of crystalline morphologies at around 50 °C, from granular aggregates at high temperature (where only PPDX is crystalline) to banded spherulites at lower temperature, where both blocks were crystalline. The kinetics of crystallization were studied in detail via spherulite growth rates obtained from POM, and it was found that PPDX crystallization in the diblocks occurred much more slowly than in the homopolymers, this being responsible for the observed coincident crystallization of the two blocks during DSC cooling scans. On the other hand, the crystallized PPDX acts to nucleate the PCL block, so that heterogeneous crystallization was always observed even in copolymers containing a minority of this component (23%), for which "confined" crystallization might be expected. The crystallization kinetics of the PCL in the copolymers is accelerated by the presence of the crystalline PPDX block.

Crystalline and Spherulitic Morphology of Polymers Crystallized in Confined Systems

“…This makes the crystallizable block copolymers representative systems having confined crystallization behavior, especially in the strong segregation regime [52]. Confined crystallization has been widely observed in the diblock copolymers having double crystalline blocks, such as PEO-b-PCL [112][113][114][115][116], PLLA-b-PEO [117][118][119][120][121][122], PLLA-b-PCL [123][124][125], poly(p-dioxanone) (PPDX)-b-PCL [126][127][128], polyolefin-based block copolymers [129][130][131][132][133][134][135], and so on. The confined crystallization kinetics and crystalline morphology of such block copolymers have been extensively studied.…”

Effect of block asymmetry on the crystallization of double crystalline diblock copolymers

“…[21][22][23][24][26][27][28][29][30][31][32][33][34] However, depending on the nature of the blocks in diblock copolymer, they may crystallize simultaneously (viz., coincident crystallization). 28,32,[35][36][37][38] Primarily, the interplay between crystallization and microphase separation plays a crucial role in dictating the final crystal morphology of the semi crystalline materials.…”

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

“…Unfortunately, reports on this field are still inadequate till now. Recently, with the comprehensive investigations on crystallization process for block copolymers, the high order structures containing crystal lamellae were frequently discovered [6,[21][22][23][24][25], where several types of spherulites with unusual morphologies such as ring banded spherulite, spherical granular aggregates and double concentric spherulites have been reported [14,15,[26][27][28][29][30][31]. Especially, the double concentric spherulites were only found in poly(ethylene oxide)/poly(!-caprolactone) PEG/PCL block copolymer up to now [14,[26][27][28][29].…”