Abstract
A large spherulite structure deteriorates the mechanical properties of crystalline polymers, and therefore various methods have been explored to increase primary nucleation density. Recently, chain-end modification has been proposed as an effective approach for regulating polymer crystal nucleation. However, the relevant nucleation mechanism still requires investigation. Therefore, in this work, 2-ureido-4[1H]-pyrimidinone (UPy) units, which can form stacks via quadruple hydrogen bonds with each other, are introduced as end groups for the preparation of interacting telechelic poly(butylene succinate) (PBS-UPy) oligomers with different molecular weights (Mns). The crystallization, especially the nucleation behavior of PBS-UPy, is studied in detail by comparing with the corresponding pre-polymer, the hydroxyl-terminal PBS (PBS-OH). The thermal properties of PBS-UPy exhibit similar Mn-dependent tendency to those of PBS-OH, but with weaker total crystallization rate. The spherulite growth rate is significantly reduced, whereas the primary nucleation density is highly promoted, after introducing UPy groups. Further investigation reveals that the mechanism of UPy stacks’ influence on nucleation ability changes from inhibition to promotion with respect to Mn. Even under an inhibition of nucleation ability, the final nucleation density is obviously increased because of a significant decline of the growth rate. In addition, the change in the impact of UPy stacks on nucleation ability is speculated to originate from the memory expression feasibility of ordered conformation in the melt during crystallization.
Highlights
Poly(butylene succinate) (PBS), as one of the promising and extensively investigated biodegradable aliphatic polyesters, exhibits a high melting point, excellent processing properties and thermal stability [1,2,3]
Telechelic PBS oligomers with different Mn were synthesized by introducing UPy units to the chain ends, and their crystallization behaviors—especially nucleation processes—were studied in detail
The UPy stacks formed via quadruple hydrogen bonding suppressed the total crystallization rate of PBS-UPy in comparison with PBS-OH
Summary
Poly(butylene succinate) (PBS), as one of the promising and extensively investigated biodegradable aliphatic polyesters, exhibits a high melting point, excellent processing properties and thermal stability [1,2,3]. It possesses comparable thermal and mechanical properties to polyolefin [4,5] but has some drawbacks, including large spherulite structure (i.e., poor primary nucleation density) and low melt strength, which limit its versatile application [6,7]. The use of UPy units as end groups of PLA with various molecular weights and architectures lowers the crystallization rate and decreases the nucleation density [18,19].
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