Abstract:
In this article, we synthesize five poly(n-alkylene succinate)s, PnAS, with n = 2, 4, 6, 8 and 10 via multi-step polycondensation methods. In 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 mode), 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, 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 the changes in the semicrystalline morphology. We demonstrate that the structure/crystal memory is stronger for the lower n (shorter alkylene succinate monomers) due to 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-/intra- chain interactions, as well as the indirect ones, in CF and distribution of crystallites, were found 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 PnAS, the molecular dynamics mapping are 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 to spatial confinement 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, permeability), envisaging future biomedical, packaging and other applications for these PnAS.
Comments