Endo n hydroxy 5 norbornene 2 3 dicarboximide

Kraft lignin (total hydroxyl group content: 6.13 mmol g^–1 determined by ³¹P NMR spectroscopy^{37 (link)}), methacrylic
anhydride, triethylamine, 2,2′-(ethylenedioxy)bis(ethylamine)—EDBEA,
spermine, spermidine, lithium chloride, 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, endo-N-hydroxy-5-norbornene-2,3-dicarboximide,
pyridine, deuterated chloroform, and chromium(III)acetylacetonate,
tebuconazole, and boscalid were purchased from Sigma-Aldrich and used
as received. Azoxystrobin and pyraclostrobin were purchased from TRC,
Canada. Dimethylformamide (DMF) and isopropanol were obtained from
Merck. Kraft lignin and lithium chloride were dried overnight at 70
°C in a vacuum oven before use. The anionic surfactant sodium
dodecyl sulfate (SDS) was purchased from Alfa Aesar and used as received.

Softwood
kraft lignin was acquired from an industrial source in the southeastern
USA and was used after purification following a published methodology.^{31 (link)} That is, shortly, the received dry kraft lignin
was first suspended and stirred in the NaOH solution with EDTA-2Na⁺. The stirred mixture was then filtrated through a filter
paper (Whatman 1), and the filtrate was then gradually acidified to
pH = 3.0 with 2 M H₂SO₄ and then stored at −20
°C overnight. After thawing, the precipitates were collected
by centrifugation and washed thoroughly with deionized water. The
obtained air-dried powder was then used in the following 3D printing
procedure. The hydroxyl content on the softwood kraft lignin was characterized
by ³¹P NMR in the Supporting Information (Figure S2 and Table S1).
Photoreactive methacrylate
resins (product code: RS-F2-GPCL-04), including methacrylate monomer
and oligomer and initiator, were purchased from Formlabs, Inc. Acetone
(≥99.5%) and dimethyl sulfoxide (DMSO, ≥99.9%) were
supplied by Sigma-Aldrich Inc. 2-Chloro-4,4,5,5-tetramethyl-1,3,2
dioxaphospholane, endo-N-hydroxy-5-norbornene-2,3-dicarboximide,
pyridine, and deuterated chloroform and chromium acetylacetonate for
NMR were all of analytical grade and purchased from Sigma-Aldrich.
Isopropyl alcohol (≥99.5%) was provided by Fisher Chemical.
All chemicals were used as received.

³¹P NMR spectroscopic analysis was recorded on a Bruker Instrument
AVANCE400 spectrometer. Acquisition and data treatment were performed
with Bruker TopSpin 3.2 software. The spectra were collected at 29
°C with 4 s acquisition time, 5 s relaxation delay, and 256 scans.
Prior to analysis, samples were dried for 24 h under vacuum and then
derivatized according to a procedure described in the literature with
a few modifications.^{39 (link)} All chemical shifts
reported are related to the reaction product of the phosphorylating
agent with water which gives a signal at 132.2 ppm.
The lignin
sample (40 mg) was completely dissolved in 300 μL of N,N-dimethylformamide. To this solution,
the following components were added: 200 μL of dry pyridine,
100 μL of solution of internal standard (10 mg of endo-N-hydroxy-5-norbornene-2,3-dicarboximide (Sigma
226378) dissolved in 0.5 mL of a mixture of pyridine and CDCl₃ 1.6:1 v/v), 50 μL of solution of the relaxation agent
[5.7 mg of chromium(III)acetylacetonate (Sigma 574082) dissolved in
0.5 mL of a mixture of pyridine and CDCl₃ 1.6:1 v/v], 100
μL of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (Sigma
447536), and at the end, 130 μL of CDCl_3.

³¹P NMR; the content of functional groups in the lignin
samples was measured by ³¹P NMR.^{35 (link)} Approximately 20–30 mg of the lignin sample was weighed and
phosphitylated using 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane.
Endo-N-hydroxy-5-norbornene-2,3-dicarboximide (Sigma-Aldrich,
40 mg/mL) and chromium (III) acetylacetonate (Aldrich, 5 mg/mL) were
used as an internal standard and a relaxation reagent, respectively.
The derivatized sample was dissolved in CDCl₃ prior to
analysis. The ³¹P NMR experiment was performed with a 90°
pulse angle, inverse-gated proton decoupling, and a delay time of
10 s. For analysis, 256 scans with a time delay of 6 s and a total
runtime of 34 min were collected. Measurements were performed in duplicate.