Solubilization Behavior of Homopolymer in Its Blend with the Block Copolymer Displaying the Feature of Lower Critical Ordering Transition.

Yu-Hsuan Lin,Chang-Cheng Shiu,Hsin-Lung Chen,Jing-Cherng Tsai,Tien-Lin Chen

doi:10.3390/polym13193415

Yu-Hsuan Lin, Chang-Cheng Shiu + Show 3 more

Open Access

https://doi.org/10.3390/polym13193415

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Abstract

Blending with homopolymer offers a facile approach for tuning the microdomain morphology of block copolymer, provided that the homopolymer chains are uniformly solubilized in the corresponding microdomain to swell the junction point separation. Here we studied the solubilization behavior of poly(4-vinyl pyridine) homopolymer (h-P4VP) in the lamellar microdomain formed by its blends with a poly(ethylene oxide)-block-poly(4-vinyl pyridine) (PEO-b-P4VP) showing the feature of lower critical ordering transition (LCOT) in terms of weaker segregation strength at lower temperature. We revealed that, while the conventional criterion of homopolymer-to-block molecular weight ratio for attaining uniform solubilization was applicable to LCOT blend, there was an excess swelling of junction point separation upon the addition of homopolymer, leading to a decrease of interdomain distance with increasing homopolymer composition. This anomalous phenomenon was attributed to the reduction of interfacial free energy due to the incorporation of P4VP homopolymer into the microdomain interface.

Highlights

Microphase separation of the diblock copolymer, A-b-B, can generate a variety of long-range ordered microdomains, including one-dimensionally stacked lamellae (LAM), hexagonally packed cylinders (HEX), double gyroids and body-centered cubic (BCC)packed spheres [1,2]
We demonstrated that a lamellae-forming PEO-b-P4VP and its blends with h-P4VP showed the feature of lower critical ordering transition (LCOT) phase behavior, where the segregation strength reduced with decreasing temperature
When h-P4VP molecular weight was sufficiently low, excess swelling of the junction point separation was observed as compared to the theoretical prediction assuming unperturbed surface free energy

Summary

Introduction

Microphase separation of the diblock copolymer, A-b-B, can generate a variety of long-range ordered microdomains, including one-dimensionally stacked lamellae (LAM), hexagonally packed cylinders (HEX), double gyroids and body-centered cubic (BCC)packed spheres [1,2]. The free energy components of the copolymer blends displaying UCOT behavior compose the interfacial free energy, the conformational free energy of block and homopolymer chains, the free energy of mixing of h-A and A block, and the free energy associated with the translational entropy the junction points [5] This type of system is considered to follow the melt incompressibility condition, where the sum of the local number densities of A and B segments is constant when they mix in the disordered melt or in the microdomain interface [1,3,4]. The excess swelling of junction point separation constitutes another anomalous feature of LCOT block copolymer, besides the opposite temperature variation of segregation strength, compared with the UCOT system

Materials

Sample Preparation

Conclusions