Synthesis of statistical PET/PEN random block copolymers and their crystallizability in the bulk and at the surface

Abstract

A series of PET/PEN copolyesters were synthesized by molten transesterification. The degree of randomness and the sequence length of the copolymers were determined by 1H NMR spectroscopy, and the changes in the bulk glass transition temperature (TgB), bulk crystallization temperature (TcB), and bulk melting temperature (TmB) were observed by DSC. A clear relationship was obtained between the observed enthalpy of melting (ΔHm) and degree of randomness (B), and TmB was suppressed for the midcompositions. As with their homopolymer counterparts, there was significant depression in crystallization temperature at the surface (TcS) of the random/block copolymers compared with the bulk, and so surface‐localized crystallization could be induced in spin‐coated thick films (thickness ranging from ca. 400 to 700 nm) by annealing at a temperature in which the surface region is mobile, but the bulk is not. The formation of these clear surface crystals allows the morphology to be directly imaged by AFM, and we observed that the crystallizability and the lamellar morphology of the surface crystals deviated from those of the original homopolymers, depending on the mixing ratio of PET/PEN and degree of randomness. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46515.

Crystalline morphologies at the surface of PET/PEN random copolymer films

“…L T of copolymer 10 is less than half (5.1) that of copolymer 4, while L N is nearly the same Table 2) are reduced from the homopolymer (PEN) as discussed in Shinotsuka. [20] The crystalline morphology of copolymer 9 is, however, basically similar to that of PEN ( Figure 4F1-F4), without the bristle-like protrusions on the crystals of thick films (F4).…”

“…On the other hand, the shortest sequence length for bulk crystallization is thought to be between 4.4 and 5.1. [20] According to the data reported by Jun et al, [7] the critical sequence length necessary for bulk crystallization of PET/PEN copolymers is thought to be ca. 4, which is consistent with this study.…”

“…This study is presented as a continuation of our previous work in which the synthesis and molecular characterization of a series of PET/PEN copolymers is reported in detail. [20] PET (Sigma-Aldrich) and PEN (kindly provided from Teijin Chemical Co., Ltd) at various ratios were codissolved in a mixed solvent of 70 wt% 2-chlorophenol (Fisher Scientific) and 30 wt% 1,1,1,3,3,3-hexafluoro-2-propanol (Sigma-Aldrich). Solutions were filtrated with 0.2 μm pore-sized poly(tetrafluoroethylene) (PTFE) syringe filters (Gelman), and coprecipitated by pouring the solution into acetone.…”

“…The series of synthesized copolymers were dissolved in deuteride 1,1,1,3,3,3-hexafluoro-2-propanol (Sigma-Aldrich) at 1.0 wt%, and 1 H NMR spectroscopy was carried out at 27 C with high resolution 500 MHz NMR (Bruker DRX 500, TBI probe, 16 scans, recycle delay = 1.0 second, acquisition time = 3.2 second) to determine the statistical sequence length and the degree of randomness of the copolymers. The sequence length and degree of randomness of the copolymers were obtained by the following calculations, [23] reported in our previous work [20] in detail. and 4) and bulk crystallinity (an example of which is given in Figure S2)…”

“…Copolymer 7 is a PEN-rich copolyester with the same composition as copolymer 9, but it has undergone a longer transesterification (PET/PEN = 10/90, 60 minute reacted), and therefore its sequence length L N is shorter (20). In the surface morphology diagram of Figure 3.…”