Mercury plus 400 system

The 4,4′-methylene diphenyl diisocyanate (MDI) and a mixture (about 80:20) of 2,4- and 2,6-toluene diisocyanates (TDI) were provided by Elantas Europe S.r.l. and stored at − 18 °C. Reagent grade triethylamine (TEA), benzylamine (BA) and dibutylamine (DBA) were purchased from Sigma Aldrich. Acetone-d₆ was purchased from Sigma Aldrich.
HPLC water was purified using the Milli-Q system. HPLC grade acetonitrile was purchased from Sigma Aldrich. Technical grade acetonitrile and n-hexane were purchased from Carlo Erba. Technical grade dry tetrahydrofuran (THF) was purchased from Sigma Aldrich.
Three batches of PA were provided by Elantas Europe S.r.l. Samples have a mean viscosity of 1100 mPa s and a mean dry content of 22.9% (solvent used is NMP). Three samples were chosen corresponding to three batches produced over a year (Table 1). One batch was marked as anomalous as slightly greater quantities of MDI and TDI were added during the condensation step of the synthesis process to achieve final specifications.Table 1

PAs sample provided by Elantas Europe S.r.l.

Sample name	Production date	Abnormality
PA 1	August 2020	Yes
PA 2	January 2021	None
PA 3	April 2021	None

The molecular structures of the standards were confirmed by ¹H-NMR, recorded on a Varian Mercury plus 400 system at 400 MHz^{25 (link),26 (link)}.

PLGA-PEG-COOH polymer was synthesized using EDC/NHS chemistry. Briefly, 500 mg PLGA-COOH (0.071 mmol) and 109 mg EDC (0.7 mmol) were dissolved in 7 mL DCM, under magnetic stirring at room temperature for 10 min. Then, 160 mg NHS (1.4 mmol) was dissolved in 7 mL DCM, followed by dropwise addition into the above solution. The reaction was conducted overnight at room temperature. PLGA-NHS was washed with cold 1:1 methanol/diethyl ether mixture for three times, collected by centrifugation, and lyophilized. Then, 200 mg PLGA-NHS (0.028 mmol) was dissolved in 5 mL DCM under magnetic stirring at room temperature for 10 min. 30 mg NH₂-PEG-COOH (0.03 mmol) and 60 µL DIEA (0.28 mmol) were dissolved in 2 mL DCM, and dropwise added into the PLGA-NHS solution. The reaction was conducted overnight. The conjugated PLGA-b-PEG-COOH polymer was washed with cold, 1:1 v/v methanol/diethyl ether mixture for three times, collected by centrifugation, and lyophilized. The product was stored at – 20 °C. Chemical structure was confirmed by 1 H-NMR on a Varian Mercury Plus 400 system.

¹H nuclear magnetic resonance (NMR) spectra of the PLGC copolymer were measured using a Varian Mercury Plus 400 system with an internal standard of CDCl₃ in the presence of tetramethylsilane (TMS). Molecular weight distributions of the PLGC copolymer were measured using a YL-Clarity GPC system (YL 9170 RI detector) with three columns (Shodex K-802, K-803, and K-804 polystyrene gel columns) at 40 °C. For this measurement, polystyrene calibration was performed and CHCl₃ was used as an eluent at a flow rate of 1.0 mL/min. The melting temperature (T_m) of the PLGC copolymers was determined by differential scanning calorimetry (DSC; Q 1000, TA Instruments; Alzenau, Germany) from −80 to 200 °C at a heating rate of 5 °C/min under an atmosphere of nitrogen.