1D hypo-crystals: A novel concept for the crystallization of stereo-irregular polymers

Jae Hyun Sim, Sangwon Eom, Sangheon Lee, Changjun Oh, Minhwan Lee, Seulwoo Kim, Won Bo Lee, Jungju Ryu, Daewon Sohn, Hoeil Chung, Jinho Hyon, Cheolmin Park, Edwin L. Thomas, Youngjong Kang

Research output: Contribution to journalArticle

Abstract

It has been believed that stereo-irregular polymers hardly form crystalline structure because of the deficient ordering along the backbone direction. Here we show the crystallization of atactic polymers by rapid thermal quenching of polymers co-melted with a chain-stretching agent. To this end, crystalline PMMAs (hc-PMMAs) are prepared from stereo-irregular atactic-PMMAs (Mn = 35–1500 kg/mol) as well as stereo-regular isotactic- and syndiotactic-PMMAs by rapid quenching of molten PMMA/benzoic acid (BA) solutions. BA acts as a chain-stretching agent. PMMA chains are elongated up to 60% of their contour length when they are co-melted with BA. The preferential hydrogen bonding between PMMA and BA compensates the conformational entropy loss of PMMA chains in molten PMMA/BA solutions. Upon quenching, PMMA chains are further stretched because of the large tensile stress induced by the sudden temperature drop and because of mechanical squeezing by concomitant directional crystallization of anisotropic lath-like BA crystals. After sublimation of BA, the PMMA shows a clear melting transition: Tm = 276–283 °C for hc-s-PMMA and 293–306 °C for hc-a-PMMA. Unlike other conventional crystals having 3D crystallinity, hc-PMMAs exhibits 1D crystallinity due to ordered lateral packing between chains (d = ∼4.3 Å) which is independent on the tacticity while the packing is amorphous-like for the other two directions. For the reason of the reduced dimensionality in crystallinity, we named the crystalline PMMA as 1D hypo-crystalline PMMA (hc-PMMA). Because of their high 1D crystallinity (55–65%), hc-PMMAs exhibit the storage modulus (E′) enhanced by 20 times comparing with those of pristine PMMA.

Original languageEnglish
JournalMaterials Today
DOIs
StateAccepted/In press - 2020

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    Sim, J. H., Eom, S., Lee, S., Oh, C., Lee, M., Kim, S., Lee, W. B., Ryu, J., Sohn, D., Chung, H., Hyon, J., Park, C., Thomas, E. L., & Kang, Y. (Accepted/In press). 1D hypo-crystals: A novel concept for the crystallization of stereo-irregular polymers. Materials Today. https://doi.org/10.1016/j.mattod.2020.05.003