Abstract
An efficient synthesis strategy of a well-defined polylactide–dye conjugate in a controlled fashion is presented. The introduction of coloring species as end groups of polylactide (PLA) has been performed by using new homoleptic aminophenolate magnesium or zinc coordination compounds. The molecular structure of metal complexes has been determined in solution by NMR spectroscopy, and in the solid state by X-ray analysis. Lastingly colored polymers were obtained with 2-[4-(Nitrophenylazo)-N-ethylphenylamino]ethanol (Disperse Red 1) and 2-[4-(2-Chloro-4-nitrophenylazo)-N-ethylphenylamino]ethanol (Disperse Red 13) at very high lactide conversions, based on MALDI-ToF measurement, and the macromolecules were nearly fully chain end dye-functionalized. Based on 1H NMR, the DPn of conjugates was in the range of 10–300, which was consistent with the reaction setup. Various methods of gel-permeation chromatography (GPC) analysis were applied, and they demonstrated that the number-average molar mass (Mn) values (polystyrene (PS) standards) were a bit higher than calculated, the molar mass distribution index (ƉM) values were moderate to high, the TDA (triple detection array) system was inappropriate for analysis, measurements with PDA (photo diode array) detection at 470 nm gave nearly the same molar mass distributions such as the refractometer, and the relative absorbance of conjugates at 470 nm increased linearly versus (DPn)−1. The presented approach connects the gap between the current strategy of obtaining colored polymer fibers and the design of tailor-made initiators with eco polyesters designed for the targeted applications.
Highlights
Biodegradable polymers are considered as a green alternative to petropolymers and a long-term solution for the environmentally damaging factor of plastics pollution [1,2,3]
Dichloromethane (99.8% VWR), and n-hexane (HPLC, VWR) was dried and purified using the Solvents for synthesis were purified by standard methods: MeOH (HPLC, VWR)
It was used for the new homoleptic zinc and magnesium compounds syntheses by a clean reaction with commercially available metal precursors MR2 (e.g., Mg(n-Bu)2 or ZnEt2 )
Summary
Biodegradable polymers are considered as a green alternative to petropolymers and a long-term solution for the environmentally damaging factor of plastics pollution [1,2,3]. The industrial standard for the production of PLA is Sn(Oct) , which operates for lactide polymerization in bulk conditions at elevated temperatures (110–180 ◦ C) and, which is worth underlining, causes the number of transesterification reaction acts, so the distribution of molar masses is broad It is the most popular choice in conventional studies involving the ROP of cyclic esters. Even if the results obtained with Sn(Oct) are to be valued, new catalysts operating in solution under mild conditions are highly desirable to develop the further use of functional polyesters In this aspect, the rational alternative to commercial catalysts is the catalytic systems based on biometal coordination compounds that are suitable to a given targeted application.
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