A. Movahedi et al. / Reactive & Functional Polymers 82 (2014) 1–8
3
sodium triacetoxyborohydride (0.90 g, 4.2 mmol) was gradually
added. The mixture was stirred at room temperature for 5 h until
TLC analysis (silica, 80% ethyl acetate in heptane) showed no
remaining starting materials. Water (20 mL) was then added, fol-
lowed by addition of concentrated sulfuric acid (1.5 mL), stirring
for 10 min to quench the excess of NaBH(OAc)3. The solution was
neutralized with aqueous K2CO3. The organic phase was separated
and the aqueous phase was extracted with CH2Cl2 (3 Â 20 mL). The
combined organic phases were dried over MgSO4 and the solvent
was removed under reduced pressure. Flash chromatography on
silica gel (80% ethyl acetate in heptane) gave a white solid powder
(0.32 g,46%). 1H NMR (400 MHz,CDCl3) d 7.49 (s, 2H, triazoleAH),
7.40–7.36 (m, 4H, PhAH), 7.22–7.17 (m, 4H, PhAH), 5.46 (s, 4H,
PhACH2), 3.83 (s, 4H, NACH2Atriazole), 3.33 (s, 2H, N-CH2-CCH),
2.23 (s, 1H, alkynylAH), 1.31 (s, 18H, PhACACH3); 13C NMR
(400 MHz, CDCl3) d 151.8, 131.6, 127.9, 126.0, 123.0, 110.0, 54.4,
2.4.3. Poly(4-(tert-butyl)-triazole-co-TBTA) (5a) P(tBT-co-TBTA)
The product was obtained as a yellow powder (yield: 0.54 g). 1H
NMR (400 MHz, CDCl3) d 7.65 (s, triazoleAH), 7.24–6.00 (br m,
PhAH), 5.40 (br s, PhACH2), 3.65 (br s, NACH2Atriazole), 1.21 (br
m, PhACACH3 and backbone carbons); FTIR (KBr, cmÀ1
) m 3133,
2928, 2846, 1668, 1606, 1455, 1326, 1218, 1124, 1053, 799 and
721. Elemental analysis, Found: C, 67.77; H, 6.28; N, 22.11. Calcu-
lated loading for each of the functionalities: 0.63 mmol/g based on
N content, assuming a ligand ratio of 1:1 as determined by 1H
NMR.
2.4.4. Poly(4-(tert-butyl)-triazole-co-TtBBTA) (5b) P(tBT-co-TtBBTA)
The product was obtained as a pale yellow powder (yield:
0.62 g). 1H NMR (400 MHz, CDCl3) d 7.67 (s, triazoleAH), 7.24–
6.00 (br m, PhAH), 5.37 (br s, PhACH2), 3.66 (br s, NACH2Atria-
zole), 1.22 (br m, PhACACH3 and backbone carbons); FTIR (KBr,
47.8, 45.5, 34.7, 31.2; FTIR (KBr,cmÀ1
) m 3288, 2962, 2101, 1919,
cmÀ1
) m 3134, 2961, 2867, 1668, 1610, 1513, 1459, 1363, 1326,
1796, 1518, 1461, 1364, 1269, 1217, 1129, 1049, 1019, 963, 815,
and 558. Elemental analysis, calcd. for C31H39N7: C, 73.05; H,
7.71; N, 19.24. Found: C, 72.98; H, 7.74; N, 19.11.
1219, 1128, 1049, 815, 792, 703 and 559. Elemental analysis,
Found: C 69.54, H 7.14, N 19.21. Calculated loading for each of
the functionalities: 0.54 mmol/g based on N content, assuming a
ligand ratio of 1:1 as determined by 1H NMR.
2.4. General synthetic procedure for the one-pot functionalization of
polyvinylbenzyl chloride (PVBC)
3. Results and discussion
In a typical one-pot polymer functionalization reaction, a solu-
tion of PVBC (1.0 equiv, 0.31 g, 2.0 mmol chloride functionality),
the ligand precursors (1.5 equiv for the homo-polymers; 0.75 equiv
each of the ligand precursor and tert-butylacetylene for the co-
polymers) and sodium azide (1.5 equiv) in DMF (7.5 mL per mmol
of ligand precursor) was prepared at room temperature. To this
solution, a CuSO4 solution (10 mol%) was added whereupon the
solution became brown. Sodium ascorbate (30 mol%) and de-
ionized water (5 vol%) was added. At this point, the solution color
gradually changed back to cloudy yellow. The temperature was
then increased to 80 °C and the reaction was stirred for 48 h. The
reaction mixture was then added dropwise into water (reaction
solution:water, 1:10 v/v), after which the resulting suspension
was centrifuged to afford the crude polymer. These steps were then
repeated for purification, first with DMF and EDTA (1:10 of
DMF:0.05 M EDTA in H2O), and subsequently with CH2Cl2 and
methanol (1:10 v/v CH2Cl2:MeOH). After the final centrifugation,
the obtained product was dried under vacuum to afford the puri-
fied polymer as a powder.
3.1. Synthesis of ligand precursors and functionalization of
polyvinylbenzyl chloride
A TBTA-ligand precursor (3a, Scheme 1) containing two triazole
unit and a pendant alkyne functionality was prepared in three
steps via intermediates 1a and 2a, starting from commercially
available benzyl azide and following a procedure reported by Chan
and Fokin [31]. Moreover, a tert-butyl substituted version of the
same precursor (3b, Scheme 1), with potentially higher solubility
in organic solvents, was also prepared using a similar but slightly
modified synthesis. The higher hydrophobicity of the tert-butyl
substituted ligand could translate into better compatibility with
oil-based paints, of importance for the ultimate goal of this project
which is to develop marine coatings with antifouling properties. To
access compound 3b, 4-(tert-butyl)benzyl chloride was converted
into the corresponding azide. Extensive purification of the interme-
diate azide was avoided in order to minimize risks involved with
the handling of this reactive compound. This intermediate aryl
azide was subsequently subjected to a CuAAC reaction with 3,3-
diethoxy-1-propyne to form triazole 1b in 70% yield. Deprotection
of the acetal functionality with trifluoroacetic acid then afforded
aldehyde 2b in 93% yield, of sufficiently high purity to be used
directly in the next step. Reductive amination with propargyl-
amine, using sodium triacetoxyborohydride as the reducing agent,
then provided the desired ligand precursor 3b as a white solid in a
moderate yield (46%).
2.4.1. Poly(tris[(1-benzyl-1,2,3-triazol-4-yl)methyl]amine) (4a)
P(TBTA)
The product was obtained as a yellow powder (yield: 0.70 g,
conversion ca. 60%). 1H NMR (400 MHz,CDCl3) d 7.64 (s,triazole-
H), 7.24–5.90 (br m, PhAH), 5.36 (br s, PhACH2), 3.62 (br s, NACH2-
Atriazole), 1.24 (br m, backbone carbons); FTIR (KBr,cmÀ1
) m 3133,
The alkyne handle provides an opportunity to ‘click’ precursors
3a and 3b onto an azide-functionalized polymer while simulta-
neously installing the third triazole ring needed to complete the
TBTA-structure of the ligand. To functionalize PVBC, a one-pot
two-step synthetic pathway was developed (Scheme 2). A solution
containing PVBC, the ligand, sodium azide and copper(II) sulfate
was prepared. Although CuAAC reactions in many cases proceed
at room temperature, a higher temperature (80 °C) was chosen in
order to facilitate the nucleophilic substitution of halide with
azide. In the first reaction step, PVBC was substituted with azide
ion to form polyvinylbenzyl azide (PVBAz). In the second step, a
CuAAC reaction between the supported azide functionality and
the pendant alkyne on the ligand both provides the third triazole
group needed for the formation of the TBTA-type structure, and
simultaneously attaches the ligand to the polymer backbone.
2927, 2842, 1666, 1496, 1455, 1326, 1217, 1125, 1049, 819 and
720. Elemental analysis, Found: C, 67.13; H, 6.11; N, 23.35. Calcu-
lated loading: 1.67 mmol/g based on N content.
2.4.2. Poly(tris((1-(4-(tert-butyl)benzyl)-1,2,3-triazol-4-
yl)methyl)amine) (4b) P(TtBBTA)
The product was obtained as a yellow powder (yield: 0.65 g,
conversion ca. 50%). 1H NMR (400 MHz, CDCl3) d 7.66 (s, 3H, tria-
zole-H), 7.24–6.00 (br m, 12H, PhAH), 5.33 (br s, 6H, PhACH2),
3.62 (br s, 6H, NACH2Atriazole), 1.18 (br m, 21H, PhACACH3 and
backbone carbons); FTIR (KBr,cmÀ1
) m 3135, 2961, 2867, 1666,
1514, 1459, 1326, 1268, 1218, 1128, 1049, 815, 717 and 559.
Elemental analysis, Found: C, 69.59; H, 6.91; N, 20.04. Calculated
loading: 1.43 mmol/g based on N content.