Diblock Copolymers of Methacryloyloxyethyl Phosphorylcholine and Dopamine Methacrylamide: Synthesis and Real-Time Adsorption Dynamics by SEIRAS and RAIRS

Amphiphilic diblock copolymers containing a block of 2-methacryloyloxyethyl phosphorylcholine (MPC) with unique properties to prevent nonspecific protein adsorption and enhance lubrication in aqueous media and a block of dopamine methacrylamide (DOPMA) distinguished by excellent adhesion performance were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization for the first time. The DOPMA monomer with an acetonide-protected catechol group (acetonide-protected dopamine methacrylamide (ADOPMA)) was used, allowing the prevention of undesirable side reactions during polymerization and oxidation during storage. The adsorption behavior of the diblock copolymers with protected and unprotected catechol groups on gold surfaces was probed using attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy, surface-enhanced infrared absorption spectroscopy (SEIRAS), and reflection–absorption infrared spectroscopy (RAIRS). The copolymers pMPC-b-pADOPMA demonstrated physisorption with rapid adsorption and ultrasound-assisted desorption, while the copolymers pMPC-b-DOPMA exhibited chemical adsorption with slower dynamics but a stronger interaction with the gold surface. SEIRAS and RAIRS allowed proving the reorientation of the diblock copolymers during adsorption, demonstrating the exposure of the pMPC block toward the aqueous phase.

The cloudy yellow reaction mixture containing the formed sodium butyl carbonotrithionate was allowed to warm to room temperature.Later on, the mixture was 30 min purged with N 2 gas, then 5.08 g of iodine (20 mmol) were added in one portion, and the reaction mixture was stirred for 1 hour at room temperature.
The formed precipitate of insoluble NaI in diethyl ether were removed by filtration, and the filtrate was washed several times using 1 M Na 2 S 2 O 3 aqueous solution to remove unreacted iodine.The combined organic layers were dried with MgSO 4 , and the solvent was removed under reduced pressure giving 6.0 g of yellow viscous oil of bis-(butylsulphanylthiocarbonyl) disulfide.4,4-Azobis(4-cyanovaleric acid) (ACVA) (13.44 g, 48.0 mmol) was added into three-neck round-bottom flask containing 6.0 g of bis(butyltrithiocarbonate) dissolved in 150 mL of EtOAc, and the solution was stirred overnight under reflux in N 2 atmosphere.The solution was washed with water (3 × 100 mL) to remove unreacted ACVA, and concentrated using rotary evaporator.The product was purified using flash column chromatography (eluent hexanes:EtOAc:AcOH = 4:1:0.01(v/v), R f 0.2), and the solvent was removed resulting in yellow solid 4-(((butylthio)carbonothioyl)thio)-4-cyanopentanoic acid (BCPA).Overall yield 8.29 g (89%).

Removal of acetonide protective group
Removal of the acetonide protective groups from catechol moieties present in pADOMPA or diblock copolymers pMPC-b-pADOPMA was performed using TFA [1].In a round-bottomed flask, 0.2 g of the copolymer was dissolved in 7.4 mL of dichloromethane and 0.1 mL of deionized water, and the mixture was bubbled with nitrogen gas for 20 min.Then the mixture was cooled in an ice bath, and 2.5 mL of TFA was added under vigorous stirring.After 30 min the solution was left stirring for 60 min at room temperature.The copolymer was purified by dialysis through 3.5 kDa MWCO regenerated cellulose membrane against water, and the solid white powder was obtained by freeze-drying.3. Calculations

Calculation of copolymer composition from UV-Vis spectra
A series of pADOPMA absorption spectra in methanol showed typical benzene ring absorption peak at 289 nm (Figure S7).Solutions of pMPC showed wide but weaker than pADOPMA absorption peak ranging from 270 nm to 350 nm (maximum at 310 nm).Intensity of pADOPMA peak was corrected by subtracting intensity of pMPC absorption at 289 nm.The calibration graph absorption of ADOPMA versus concentration was used for determination of the amount of monomeric units carrying benzene ring in the copolymers pMPC-b-pADOPMA (Figure S9).Results of determination are summarized in Table S1.

Calculation of copolymer composition from 1H NMR spectra
Table S2.Composition of the diblock copolymers calculated from 1 H NMR and UV-VIS spectra.
4. Approval of copolymer structure using NMR spectra

Figure S3. 1 H
Figure S3. 1 H NMR spectrum of DOPMA in DMSO-d 6 at 22 o C

Figure S5. 1 H
Figure S5. 1 H NMR spectrum of ADOPMA in DMSO-d 6 at 22 o C

Figure S7 .
Figure S7.UV-VIS spectra of pADOPMA in MeOH.The data of polymer absorbance at 289 nm is used for calibration graph.

Figure S10. 1 H
Figure S10. 1 H NMR spectra of the diblock copolymer pMPC-b-pADOPMA in D 2 O, MeOD-d4/D 2 O mixture and MeOD-d4.The appearance of chemical shifts characteristic for pADOPMA block (marked in yellow) in MeOD-containing solutions proved diblock structure of the copolymer.

Figure S12. 1 H
Figure S12. 1 H NMR spectra of the diblock copolymers with unprotected catechol groups pMPC-b-pDOPMA (A) and with acetonide-protected catechol groups pMPC-b-pADOPMA (B) in D 2 O at various concentrations of the copolymers.
modelling of DOPMA adsorption onto Au 3 cluster Theoretical modelling of DOPMA fragment and DOPMA fragment with Au 3 cluster was performed using Gaussian 09 for Windows[2].Geometry optimization and vibrational frequency calculations were performed using the density functional theory (DFT) method and the B3LYP functional.Calculations were accomplished using the 6-311++G(2d,p) basis set for C, H, and O atoms and LANL2DZ with ECP for gold atoms.The cluster model built from 3 gold atoms represents the metal surface.Calculated vibrational frequencies and intensities were scaled according to the method described elsewhere[3].

Table S1 .
Copolymer composition calculation from UV-Vis data

Table S3 .
DOPMA (ADOPMA) content in the copolymers pMPC-b-pDOPMA and pMPC-b-pADOPMA determined from 1 H NMR spectra of the copolymers in D 2 O solutions of various concentrations.