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

Abstract

Monte Carlo simulation on the crystallization of double crystalline diblock copolymer unravels an intrinsic relationship between block asymmetry and crystallization behaviour.We model crystalline A-B diblock copolymer, wherein the melting temperature of A-block is higher than that of the B-block. We explore the composition dependent crystallization behaviour by varying the relative block length with weak and strong segregation strength between the blocks. In weak segregation limit, we observe that with increasing the composition of B-block, its crystallization temperature increases accompanying with higher crystallinity. In contrast, A-block crystallizes at a relatively low temperature along with the formation of thicker and larger crystallites with the increase in B-block composition. We attribute this non-intuitive crystallization trend to the dilution effect imposed by B-block.When the composition of the B-block is high enough, it acts like a "solvent" during the crystallization of A-block. A-block segments are more mobile and hence less facile to crystallize, resulting depression in crystallization temperature with the formation of thicker crystals. At strong segregation limit, crystallization and morphological development are governed by the confinement effect, rather than block asymmetry. Isothermal crystallization reveals that the crystallization follows a homogeneous nucleation mechanism with the formation of two dimensional crystals. Two-step, compared to one-step isothermal crystallization leads to the formation of thicker crystals of A-block due to the dilution effect of the B-block.

Novel Castor Oil‐Derived Block Copolymers as Promising Candidates for Biological Applications: Biorelevant and Biocompatible

“…In the case of diblock, TEHA‐ b ‐mPEG and triblock TEHA‐ b ‐PEG‐ b ‐TEHA copolymers only high melting block of TEHA crystallizes and a reduction in initial T c and Δ H c values is observed (Figure b,c). These results demonstrate that the crystallization of TEHA was suppressed by the presence of the low melting blocks mPEG and PEG . This is also an indication that the prepared copolymers have similar degrees of crystallinity.…”

“…Crystallization within semicrystalline block copolymers is an issue which has attracted increasing interest in recent years and several theories have been advanced to describe the structure development in the crystallizable block . In this study, the dendritic crystal growth attributed to TEHA ( Figure a) and typical spherulites of PCL, mPEG, and PEG spherulites with different diameters varying from 20 to 200 µm, could be directly observed (Figure b–d) during slow cooling of the melt (1 °C min −1 ) and through the polarizing microscope.…”

Phase separation and crystallization in double crystalline symmetric binary polymer blends

“…We define crystallinity as the ratio of number of crystalline bonds to the total number of bonds present in the system. A bond is defined as crystalline if it is surrounded by more than 5 nearest non-bonded parallel bonds [45,46]. Specific heat is calculated as equilibrium specific heat from the total energy fluctuations (for all the A-and B-type units in the simulation box), similar to that of Dasmahapatra et al [48].…”

“…Specific heat is calculated as equilibrium specific heat from the total energy fluctuations (for all the A-and B-type units in the simulation box), similar to that of Dasmahapatra et al [48]. To locate the macrophase separation point, we calculate C v for the A-B pair (C v_AB ) based on the de-mixing energy between A and B-polymers [45,46]. At the macrophase separation point, C v_AB shows a peak; peak value of U p decreases with increasing the value of λ.…”

“…In our work λ ≥ 0 and higher λ implies stronger segregation strength between the polymers. In terms of Flory's χ parameter, segregation strength is calculated as χN, which may be correlated to (q − 2) × U AB × N in our system, [44][45][46] where q is coordination number and N is the degree of polymerization. All the energies are normalized by k B T, where, k B is the Boltzmann constant and T is temperature in Kelvin; thus, U p~1 /T.…”