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In diblock copolymers, the constraining effects of different stereochemical structure of high-T m block on crystallization and melting behaviors of other constituent are supposed to be different. In this work, PEG-b-PDLLA and PEG-b-PLLA were synthesized, and crystallization kinetics, crystalline structure, melting behaviors of PEG blocks and morphology development in these systems were evaluated. Compared to those connected to PLLA, PEG-b-PDLLA exhibited lower crystallization rates, implying that connectivity of amorphous chain exerted more pronounced effect on crystallization rate of PEG than that of steric hindrance of PLLA crystallites. While all PEG-b-PDLLA samples showed a single endothermic peak during heating process, multiple melting peaks were observed in PEG-b-PLLA associated with composition, crystallization temperature and cooling rate of PLLA. A lamellar structure was formed by the crystallization of PEG in all PEG-b-PDLLA, however, when PEG-b-PLLA crystallized at room temperature directly, unexpected results occurred: lamellar for diblock copolymers with 31.5 and 48.0 wt% PLA or cylindrical structure for the diblock copolymers with 56.1 and 63.8 wt% PLA. Depending on composition, PEG-b-PLLA created one or two types of lamellar stacks after sequential crystallization of PLLA and PEG. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 455-465 KEYWORDS: block copolymer; confined crystallization; melting behavior; morphology; stereochemical structure observed of the banded spherulitic morphology before and after crystallization of PEG. Yang et al. found that the preceding crystallization of the PLLA determined the morphology and the crystal orientation of PEG block was affected by PLLA crystal when it crystallized epitaxially on PLLA crystal. 26 Afterward, the formation of alternating lamellar structure was proposed. 27 It was proposed that PEG blocks crystallized not Additional supporting information may be found in the online version of this article.

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The end group modification of hydrogen bonding units has a significant effect on physical properties of covalent linked polymers. In this study, telechelic poly(ethylene glycol)s (PEG) with various molecular weights were functionalized by thymine (Thy), which was able to form self-complementary double hydrogen bonding. The physical properties of Thy-functionalized PEGs, including viscosity in solution or melt state, crystallization behavior, crystalline structure as well as lamellar structure were systemically investigated by comparison with hydroxyl-terminated PEGs. Crystallinity and melting temperature of linked PEG chains were decreased by the presence of Thy groups and the depression effects were strengthened by increase of Thy content. Crystallization rate and temperatures at which crystallization occurred were more complicated. Lower crystallization rate was obtained for Thy-functionalized PEGs with highest Thy content, a signature for confined crystallization by covalent links to Thy groups. However, in the case of moderate Thy content, the trend of crystallization rate was shifted to lower temperature regions, where the maximum and minimum of crystallization rates were comparable with free polymer chains. For Thyfunctionalized PEGs with low Thy content, crystallization rates were similar with that of non-functionalized PEGs. The differences in supercoolings might give explanation on differences in crystallization behaviors among three conditions.

While stereocomplexable hydrogels composed of poly(l‐lactic acid) (PLLA)– poly(ethylene glycol) (PEG)–PLLA and poly(d‐lactic acid) (PDLA)–PEG–PDLA have been widely investigated, very few studies have reported the influence of salts on thermogelling behaviors in corresponding aqueous solutions. In this study, NaCl is selected as a model and stereocomplexable solutions with a wide range of salt concentrations (0–3 wt%) are prepared with the aim to tune Ts‐g. When polymer concentration is 8 wt%, the resulting hydrogels containing 1 wt% NaCl exhibits a notably lower Ts‐g of 34 °C, while salt‐free system shows a Ts‐g of 42 °C. The presence of NaCl leads to a higher content of stereocomplex crystallites, a larger size of micelle clusters, an amplified distance of interclusters and a smaller thickness of micelle shell, which is supposed to be ascribed to the salts effect on ion–water and water–PEG interactions and increased hydrophobicity of enantiomeric micelles by NaCl. For hydrogels governed by self‐assembly of micelles and stereocomplexation, this study provides a safe, practical, and feasible way to tune the thermogelling behaviors and physical properties by the addition of salts.