2.4. General Procedures for the Determination of Monomer Conversions by 1H NMR

¹H NMR spectra were recorded at 298 K using a Bruker HD 400 MHz BBO Probe or AVIII 400 MHz BBO Probe spectrometers. Chemical shifts for ¹H are reported in parts per million (δ); δ_H values are referenced to the residual solvent signal of DMSO-d₆ at 2.50 ppm. 1,2,4,5-tetramethylbenzene or 2-ethylnaphthalene were used as internal standards for quantitative ¹H NMR measurements. Spectra were processed using Bruker Topspin 4.0.1. Polymerization solutions used for the quantification of monomer conversions by ¹H NMR were prepared on a smaller scale in Wheaton™ bottles following the same procedure as described in Section 2.3, using DMSO-d₆ as the solvent. Two marginally different methods have been used for the quantification of monomer conversions.

Method A: Before sealing the Wheaton™ bottle, an internal standard was added to the pre-polymerization solution. A 500 µL aliquot of the mixture was transferred via microsyringe to an NMR tube, and a ¹H NMR spectrum was recorded (t = 0 spectrum). The Wheaton™ bottle containing the remaining polymerization solution was sealed, purged with N₂, and heated to an appropriate temperature for an appropriate time. After polymerization, another 500 μL aliquot of the mixture was transferred, and an ¹H NMR spectrum was recorded.

Method B: Before sealing the Wheaton™ bottle, a 500 µL aliquot of the mixture was transferred via microsyringe to an NMR tube. The remaining polymerization solution was sealed, purged with N₂, and heated to an appropriate temperature for an appropriate time. After polymerization, another 500 µL aliquot of the mixture was transferred to a different NMR tube. An appropriate volume of an internal standard stock solution in DMSO-d₆ was added to each tube and ¹H NMR spectra were recorded.

In both cases, the ¹H NMR spectra acquired were phased and integrated identically using an automated procedure. The concentration of monomers and crosslinker in the initial and final polymerization solutions were determined by comparing the intensities of monomer peaks at 6.58 ppm (4-VI), 5.51 ppm (AMPS), 5.55 ppm (NIPAM), 5.57 ppm (NPAM), 6.07 ppm (AM), 6.62 and 6.36 ppm (A–Pro–OH), and 4.56 or 5.63 ppm (MBA), against the intensities of peaks of the internal standard at 6.88 ppm (1,2,4,5-tetramethylbenzene) or 7.70 ppm (2-ethylnaphthalene). ¹H NMR spectra used to calculate monomer conversions and overall conversions of polymerizations N29, N36, and N42 are shown in Figures S1–S3 of the ESI, as representative examples for all ¹H NMR analyses.