Title:
Synthesis, Crystallization, Structure Memory Effects, and Molecular Dynamics of Biobased and Renewable Poly(n-alkylene succinate)s with n from 2 to 10
Abstract:
In this article, we synthesize five poly(n-alkylene succinate)s, PnASs, with n = 2, 4, 6, 8, and 10 via multi-step polycondensation methods. Next, we comparatively investigate these renewable and biobased polyesters from the points of view of structure, crystallinity, and molecular mobility, employing 1H nuclear magnetic resonance spectroscopy, size-exclusion chromatography, viscometry, X-ray diffraction, differential scanning calorimetry (DSC, conventional and temperature modulation modes), polarized optical microscopy (POM), and broadband dielectric relaxation spectroscopy (BDS). Next to the successful synthesis of the materials, we evaluate the characteristics of crystallization (temperature and fraction); moreover, we explore for the first time, on the same type of succinic polyesters, the impact of n on the structure memory related to crystal nucleation as well as the changes in the semicrystalline morphology. We demonstrate that the structure/crystal memory is stronger for the lower n (shorter alkylene succinate monomers) because of more chain-chain associations, the result being independent from the overall length of the polymer chain (molar mass, Mn 13-80 kg/mass). The crystalline fraction (CF ∼12-34%) increases with n, also independently from Mn; however, the chain length affects directly the nucleation rate as Tc increases with Mn. The direct effects of n, in the inter-/intrachain interactions, as well as the indirect ones, on the CF and distribution of crystallites were found to be responsible for the alternations in the static glass transition temperature in DSC (lowering of Tg with n) and the dynamic glass transition (α, αc relaxations in BDS). For the sum of these PnASs, the molecular dynamics mapping is shown here, also for the first time. With increasing n, segmental dynamics accelerates, whereas, interestingly, the cooperativity drops (elimination for n = 10). Comparing these results with the recorded alternations in the semicrystalline morphology (POM), we conclude spatial confinement to be imposed on the mobile amorphous polymer by the tightly distributed crystallites when n increases. Overall, these data provide proofs for the potential for tuning of the final polymer properties connected with crystallization (mechanical performance and permeability), envisaging future biomedical, packaging, and other application for these PnASs. © 2021 American Chemical Society.
Keywords:
Crystal structure; Crystallinity; Crystallites; Dielectric relaxation; Differential scanning calorimetry; Functional polymers; Glass; Glass transition; Mechanical permeability; Molecular dynamics; Morphology; Nanocrystalline materials; Nuclear magnetic resonance spectroscopy; Nucleation; Olefins; Polyesters; Size exclusion chromatography, 1H nuclear magnetic resonance spectroscopies; Broadband dielectric relaxation spectroscopy; Crystalline fractions; Dynamic glass transition; Mechanical performance; Polarized optical microscopy; Structure memory effects; Temperature modulation, Crystallization
