Ring-opening polymerization of emulsion-templated deep eutectic system monomer for macroporous polyesters with controlled degradability

Biodegradable polyesters with interconnected macroporosity, such as poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL), have gained significant importance in the fields of tissue engineering and separation. This study introduces functional macroinitiators, specifically polycaprolactone triol (PCLT) and polyethylene glycol (PEG), both OH-terminated, in the solventless ring-opening polymerization (ROP) of a liquid deep eutectic system monomer (DESm) composed of LLA and CL at a 30 : 70 molar ratio, respectively. The macroinitiators selectively initiate the organocatalyzed ROP of LLA in the DESm during the first polymerization stage, thereby modifying the PLLA architecture. This results in the formation of either branched or linear PLLA copolymers depending on the macroinitiator, PCLT and PEG, respectively. In the second stage, the ROP of the CL, which is a counterpart of the DESm, produces PCL that blends with the previously formed PLLA. The insights gained into the PLLA architectures during the first stage of the DESm ROP, along with the overall molecular weight and hydrophobicity of the resulting PLLA/PCL blend in bulk, were advantageously used to design polymerizable high internal phase emulsions (HIPEs) oil-in-DESm. By incorporating a liquid mixture of DESm and macroinitiators (PCLT or PEG), stable HIPE formulations were achieved. These emulsions sustained the efficient organocatalyzed ROP of the continuous phase at 37 °C with high conversions. The resulting polymer replicas of the HIPEs, characterized by macroporous and interconnected structures, were subjected to a degradation assay in PBS at pH 7.4 and 37 °C and remained mechanically stable for at least 30 days. Notably, they exhibited the capability to sorb crude oil in a proof-of-concept test, with a rate of 2 g g−1. The macroporous and interconnected features of the polyHIPEs, combined with their inherent degradation properties, position them as promising degradable polymeric sorbents for efficient separation of hydrophobic fluids from water.


Equations.
Mole fraction of monomers (Fi, were i = PLLA or PCL) was obtained by 1 H NMR.
Where ꞷ is the number of hydrogen atoms assigned to (-CH2-) group (Hb) corresponding at the three-arms units of PCLT with Mn ≈ 900 g mol -1 , and in this case, ꞷ = 48.Eqn.(S1) was exclusively used when the macroinitiator was PCLT, whereas Eqn.(S2) was utilized when PEG was employed.
Molecular weight of polyesters obtained by 1 H NMR.

𝑀 𝑛 ,𝑃𝐿𝐿𝐴 (𝑔𝑚𝑜𝑙
Where ꞷ is the number of hydrogen atoms assigned to (-CH2-) group (Hb) corresponding at the three-arms units of PCLT with Mn ≈ 900 g mol -1 , and in this case, ꞷ = 48.Eqn.(S5) was exclusively used when the macroinitiator was PCL T, whereas Eqn.(S6) was utilized when PEG was employed.°C with a mass loss of around 7.6%.The second decomposition temperature was observed at 362 °C with a mass loss of 30%.This decomposition is attributed to the degradation of PLLA in the blend, which is consistent with those reported for pure PLLA (361 °C). 1 The thermal degradation of PCL occurs at approximately 400 °C.Conversely, PEG block, in the linear PEGb-PLLA/PCL, was observed at 184 °C, as reported in the literature, 1   the presence of the characteristic functional groups of PLLA and PCL. Figure S6 shows the peaks at 2943 and 2864 cm -1 associated with (-CH3) and (-CH2-) groups present in PLLA and PCL. 1 The peak at 1757 cm -1 is attributed to (C=O) vibration in PLLA. 2 The intensity of this peak decreased in PEG-b-PLLA/PCL, suggesting the interaction of PEG counterpart of the block polymers with PLLA.The C=O peak attributed to PCL was observed at 1720 cm -1 . 3The peak at 1474 cm -1 is attributed to the C-H stretching of PEG. 4 The peaks of -C-O-and -COO-correspond to the presence of PLLA and PCL 3,5 in both PCLT-b-PLLA/PCL and PEG-b-PLLA/PCL. for LLA30-CL70 DESm at 37 °C in bulk varying PCLT or PEG as the macroinitiator of polyesters.
To study the role of initiators in PCLT-b-PLLA/PCL and PEG-b-PLLA/PCL polymerization, the reaction was followed by 1 H NMR spectroscopy (6, 12, and 24 h). Figure S9a shows the ROP of the DESm initiated by PCLT, where PLLA presence was confirmed by the appearance of the repeating unit peaks at 5.17  The presence of branched PLLA or linear PEG copolymers in blends with PLLA was reported to improve their properties, such as flow behavior or tensile strength, respectively.

SECTION 1 .
Characterization of the final products of the ROP LLA30-CL70 DESm at 37 °C varying PCLT or PEG as the macroinitiator of polyesters.
Figure S2.13 C NMR spectra of the final products of the ROP of LLA30-CL70 DESm at 37 °C varying PCLT or PEG as the macroinitiator of polyesters: (a) PCLT-b-PLLA/PCL, and (b) PEG-b-PLLA/PCL.

Figure S3 .
Figure S3.Mn of the PCL produced by adding the MSA organocatalyst at different times after the completion of PLLA ROP (1 min).The Mn was calculated by 1 H NMR spectroscopy using the Eqn.(S6).

Figure S4 .
Figure S4.SEC traces of molar mass distribution of branched PCLT-b-PLLA/PCL and linear PEGb-PLLA/PCL polyesters.The thermal stability of both products, branched PCLT-b-PLLA/PCL and linear PEG-b-PLLA/PCL polyesters, was studied by TGA.Branched PCLT-b-PLLA/PCL shows the first degradation at 293 followed by the total decomposition of PLLA at 351 °C.The proportion of PLLA in the blend corresponded to ca. 30%.Finally, the PCL degradation occurred at ca. 408 °C.The degradation temperature of PLLA in the branched PCLT-b-PLLA/PCL increased ca. 10 °C compared with linear PLLA in PEGb-PLLA/PCL.This can be attributed to the presence of branched PLLA in the PCLT-b-PLLA/PCL sample allowed for entanglement with the linear PCL homopolymer.This, in turn, increased the thermal stability of the copolymer.(Figure S5b).

Figure S8 .
Figure S8.Evolution of the conversion profiles of PCLT-b-PLLA/PCL and PEG-b-PLLA/PCL polyesters at 37 °C (Dashed lines denote tendencies, and solid lines are the linear regressions).

6
Size exclusion chromatography (SEC) was performed on PLLA, PLLA/PCL, branched PCLT-b-PLLA/PCL and linear PEG-b-PLLA/PCL.Figure S10 shows the unimodal SEC traces of PLLA.PCL and PLLA homopolymer mixtures show a bimodal curve representing PCL and PLLA.The SEC of the branched PCLT-b-PLLA/PCL and linear PEG-b-PLLA/PCL show unimodal peaks at a lower retention volume compared to the PLLA/PCL blend.No peak was observed at the same elution time of neat PLLA, which suggested that PLLA obtained in PCLT-b-PLLA/PCL and PEG-b-PLLA/PCL have higher molecular weight due to PCLT and PEG-initiated ROP, and are associated with the other polyesters (including the macroinitiators) as discussed in the main manuscript after the NMR and DOSY results.

Table S1 .
Estimation of  , 1 8,9We compared the chromatographic profile of branched PCLT-b-PLLA/PCL and linear PEG-b-PLLA/PCL with PLLA/PCL homopolymer blends and pure PLLA homopolymer by SEC.PLLA/PCL and PLLA were obtained from the method reported by Pérez García et al. initiated by BnOH.

Table S3 .
Biodegradable and non-biodegradable materials-based sorbents used for oil adsorption.