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.
|Number of pages||12|
|Publication status||Published - 2020 Nov|
Bibliographical noteFunding Information:
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning ( 2018K1A3A1A32053991 and 2012R1A6A1029029 ), and by Samsung Research Funding Center of Samsung Electronics under Project Number SRFC-MA1401-05. X-ray experiments were conducted at 4C, 9A and 12D-IRS beamlines at Pohang Accelerator Laboratory (PAL), Korea. J.H.S. designed and analyzed the experiments. S.E., S.L., C.O., and J.R. assisted with SAXS and GIXD experiments. M.L., S.K. and W.B.L. performed the computational simulations. J.H. obtained the SEM images. D.S. and H.C. helped to analyze DMA and FT-IR data. C.P., and E.L.T. helped to analyze the data and revised the manuscript. Y.K. conceived and supervised the project. J.H.S. and Y.K. are inventors on a patent application (KR 10-2019-0113434) that is related to hc-PMMA.
© 2020 Elsevier Ltd
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering