Backbone Flexibility On Conjugated Polymer's Crystallization Behavior and Thin Film Mechanical Stability

Authors

Zhiyuan Qian, University of Southern MississippiFollow
Luke A. Galuska, University of Southern MississippiFollow
Guorong Ma, University of Southern MississippiFollow
William W. McNutt, Purdue UniversityFollow
Song Zhang, University of Southern MississippiFollow
Jianguo Mei, Purdue UniversityFollow
Xiaodan Gu, University of Southern MississippiFollow

Document Type

Article

Publication Date

9-1-2021

School

Polymer Science and Engineering

Abstract

Extensive efforts have been made to develop flexible electronics with conjugated polymers that are intrinsically stretchable and soft. We recently systematically investigated the influence of conjugation break spacers (CBS) on the thermomechanical properties of a series n-type naphthalene diimide-based conjugated polymer and found that CBS can significantly reduce chain rigidity, melting point, as well as glass transition temperature. In the current work, we further examined the influence of CBS on the crystallization behaviors of PNDI-C3 to C6, including isothermal crystallization kinetics, crystal polymorphism and subsequently time-dependent modulus, in a holistic approach using differential scanning calorimetry, X-ray scattering, polarized optical microscopy, atomic force microscopy, and pseudo-free-standing tensile test. Results demonstrate that increasing the length of CBS increases the crystallization half-time by 1 order of magnitude from PNDI-C3 to PNDI-C6 from approximately 10³ to 10⁴ s. The crystallization rate shows a bimodal dependence on the temperature due to the presence of different polymorphs. In addition, crystallization significantly affects the mechanical response, a stiffening in the modulus of nearly three times is observed for PNDI-C5 when annealed at room temperature for 12 h. Crystallization kinetic is also influenced by molecular weight (MW). Higher MW PNDI-C3 crystallizes slower. In addition, an odd–even effect was observed below 50°C, odd-number PNDI-Cxs (C3 and C5) crystallize slower than the adjacent even-numbered PNDI-Cxs (C4 and C6). Our work provides an insight to design flexible electronics by systematically tuning the mechanical properties through control of polymer crystallization by tuning backbone rigidity.

Publication Title

Journal of Polymer Science

Recommended Citation

Qian, Z., Galuska, L., Ma, G., McNutt, W., Zhang, S., Mei, J., Gu, X. (2021). Backbone Flexibility On Conjugated Polymer's Crystallization Behavior and Thin Film Mechanical Stability. Journal of Polymer Science.
Available at: https://aquila.usm.edu/fac_pubs/19262