Self-nucleation and crystallization kinetics of double crystalline poly(p-dioxanone)-b-poly(ε-caprolactone) diblock copolymers

Abstract

The crystallization kinetics of each constituent of poly(p-dioxanone)-b-poly(epsilon-caprolactone) diblock copolymers (PPDX-b-PCL) has been determined in a wide composition range by differential scanning calorimetry and compared to that of the equivalent homopolymers. Spherulitic growth rates were also measured by polarized optical microscopy while atomic force microscopy was employed to reveal the morphology of one selected diblock copolymer. It was found that crystallization drives structure formation and both components form lamellae within mixed spherulitic superstructures. The overall isothermal crystallization kinetics of the PPDX block at high temperatures, where the PCL is molten, was determined by accelerating the kinetics through a previous self-nucleation procedure. The application of the Lauritzen and Hoffman theory to overall growth rate data yielded successful results for PPDX and the diblock copolymers. The theory was applied to isothermal overall crystallization of previously self-nucleated PPDX (where growth should be the dominant factor if self-nucleation was effective) and the energetic parameters obtained were perfectly matched with those obtained from spherulitic growth rate data of neat PPDX. A quantitative estimate of the increase in the energy barrier for crystallization of the PPDX block, caused by the covalently bonded molten PCL as compared to homo-PPDX, was thus determined. This energy increase can dramatically reduce the crystallization rate of the PPDX block as compared to homo-PPDX. In the case of the PCL block, both the crystallization kinetics and the self-nucleation results indicate that the PPDX is able to nucleate the PCL within the copolymers and heterogeneous nucleation is always present regardless of composition. Finally, preliminary results on hydrolytic degradation showed that the presence of relatively small amounts of PCL within PPDX-b-PCL copolymers substantially retards hydrolytic degradation of the material in comparison to homo-PPDX. This increased resistance to hydrolysis is a complex function of composition and its knowledge may allow future prediction of the lifetime of the material for biomedical applications.

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

“…By the use of slower cooling rates, this overlap effect still cannot be overcome even at a cooling rate of 0.5°C/min, where a clear tailing area of crystallization was observed as shown in Figure 5. This may be related to the fact that, once the crystallization of PEG blocks started, it was quickly followed by the crystallization of the PTHF block which can be nucleated by PEG blocks, and this phenomenon was also reported in the literature by Müller et al [40]. Besides, the intensity of endothermic peak of PTHF block was much weaker than that of PEG blocks in Block4900, suggesting that the crystallizability of PTHF blocks was reduced following the increase in the molecular weight.…”

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.…”