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prepared via radical polymerization of N-vinylpyrrolidone.13 The
key property of PVP is its solubility in both organic and aqueous
solvents. Its solubility is due to the presence of the lactam amide
group which provides both hydrophobic and polar characteris-
tics. PVPs are mostly used as vesicle transporters,14,15 film for-
mers,16,17 binders,18 and detoxifiers19 in the pharmaceutical,
cosmetic, food, and adhesive industries. Recently, PVP has been
introduced on to cellulosic materials via NVP graft-
copolymerization in order to combine the properties of PVP and
cellulose. The resulting graft copolymers were shown to have
improved metal sorption,20 swelling,21 thermal stability,22 biode-
gradability resistance,23 and solubility.24
Synthesis and Characterization of Modified HECs
Functionalizing Agent: 1-(Hydroxymethyl)-2-Pyrrolidinone
The preparation of 1-(hydroxymethyl)-2-pyrrolidinone
followed a literature procedure25: In a one necked round bot-
tom flask carrying a condenser, 2-pyrrolidinone 1 (10.62 g,
0.125 mol, 1 eq.) and potassium hydroxide (0.03 g, 0.534
mmol) were mixed and heated at 80 ꢀC. Paraformaldehyde
(3.78 g, 0.125 mol, 1 eq.) was added slowly and the mixture
was stirred for 30 min at 80 ꢀC. After the mixture was
allowed to cool to room temperature, toluene was added, and
the mixture was heated to 80 ꢀC until complete dissolution
occurred. The solution was allowed to cool to room tempera-
ture and filtered. The solid product was then recryꢀstallized
from toluene, filtered, and dried under vacuum at 40 C over-
night to afford 1-(hydroxymethyl)-2-pyrrolidinone (11.78 g,
2
The functionalization of HEC via its three available hydroxyl
groups could lead to the development of novel materials with
the properties of synthetic polymers but which are produced,
in large part, from a renewable feedstock. The motivation of
our work was the coupling of HEC with lactam groups in order
to mimic the properties of PVP, leading to applications in new
areas of advanced materials science for cellulosic materials.
We aimed to lactam-functionalize HEC to give a unique bio-
based polymer, rather than graft copolymerize NVP onto HEC.
Our functionalization strategy is based on a low cost reaction
centered on short reaction times under solvent-free condi-
tions. Consequently, the lactam-functionalized HEC may com-
pete favorably with a grafted copolymer equivalent from an
industrial point of view. Like the graft copolymer, we hoped
that our lactam-functionalized HEC might display significantly
improved stability, swelling, solubility, and bacterial antiadhe-
sive properties over unfunctionalized HEC. These enhance-
ments, combined with straightforward synthesis, could
provide a new type of cellulose hybrid material that could be
produced economically on an industrial scale.
1
82%) as a white powder; mp. 78–80 ꢀC. H NMR (400 MHz,
DMSO-d6): dH (ppm) 5.75 (s, 1H, CH2AOH); 4.57 (s, 2H,
CH2AOH); 3.40 (t, J 5 7.2 Hz, 2H, CH2ACH2AN); 2.22 (t,
J 5 8.0 Hz, 2H, CH2ACO); 1.91 (app qn, J 5 7.6 Hz, 4H,
CH2ACH2ACH2); 13C NMR (100 MHz, DMSO-d6): dC (ppm)
174.2(C@O); 65.0(CH2AOH); 45.1 (CH2ACH2AN); 31.1
(CH2ACO); 17.6 (CH2ACH2ACH2); EA (calculated): 51.95%C;
7.85%H; 11.97%N; EA (found): 51.99%C; 7.76%H; 11.94%N.
Functionalization of HEC with
1-(Hydroxymethyl)-2-Pyrrolidinone
The functionalization reaction was inspired by the modifica-
tion of textiles with methylolated lactams.26 In a three necked
reactor
fitted
with
an
overhead
stirrer,
2-
hydroxyethylcellulose (HEC) 3 (Mw 5 250,000 g/mol, DS5 1,
MS5 2, 1.0 g, 4 mmol, 1 eq.), 1-(hydroxymethyl)22-pyrrolidi-
none (HMP) 2 (5.0 g, 43 mmol, 10 eq.), and 2-amino-2-
methyl-1-propanol hydrochloride (0.116 g, 0.923 mmol, 0.25
eq.) were mixed. The reactor was filled with nitrogen, closed
ꢀ
to air, and the reaction mixture was heated at 155 C for 30,
EXPERIMENTAL
60, 90, 120, 300, or 1020 min. Once the mixture had cooled
to room temperature, the product 4 was precipitated with
approximately 200 mL acetone and collected by filtration. The
recovered polymer was dissolved in water (10 mL) and dia-
lyzed for 2 days through a 3500 Da MWCO membrane against
milli-Q water. The precipitate was collected by filtration and
Materials
All chemicals were purchased from Sigma Aldrich and were
used as received. Solution state NMR spectroscopy was per-
formed using either a Varian VNMR-700 spectrometer at
699.73 MHz (1H) and 174.93 MHz (13C), or a Bruker Advance
400 spectrometer at 400.13 MHz (1H) and 100.60 MHz (13C).
For solid-state 13C NMR spectroscopy, a Varian VNMRS spec-
trometer with a 9.4 T magnet was used at 100.56 MHz
employing the cross-polarization method. Gel permeation
chromatography was undertaken with DMF as solvent at 70
ꢀC. 100 lL of solution agitated overnight to ensure complete
dissolution was injected at a flow rate of 1.00 mL min21 by a
Viscoteck SEC autochanger model. A Viscoteck TDA 301 unit
with triple detection (right angle laser scattering at 670 nm,
differential refractometer, and viscometer) was used. Analyses
were undertaken using OmniSEC 4.0 software. Elemental anal-
yses (C, H, N) were performed using an Exeter CE-400 Ele-
mental Analyzer. A Perkin Elmer Pyris 1 system was used for
thermogravimetric analysis (TGA). A Brookfield Digital Vis-
cometer model DV-I1 was used for measuring viscosities. A
PowerWaveTM XS Microplate Spectrophotometer was used for
measuring absorbance in 96-well microplates.
ꢀ
dried under vacuum at 50 C overnight to afford the modified
HEC as a pale yellow powder in yields ranging from 50 to
70% based on the estimation of DS by 13C NMR spectroscopy.
Samples from each reaction were characterized by solid-state
13C NMR spectroscopy using the cross-polarization method.
Samples were also dissolved in DMSO-d6 and were character-
ized using 1H (700 MHz), 13C (176 MHz), HMBC, and HSQC
NMR experiments; see Table 1 for summaries of DS.
Evaluation of Physical Properties of HMP-Functionalized HEC
Assessment of Solubility
The solubilities of HEC and HMP-functionalized HEC
(DSprimary alcohol 5 0.9) were evaluated. Solvent (1 mL) (see
Table 2) was added to cellulosic material (10 mg) in a vial. The
vials were allowed to stand overnight at room temperature
then the solutions were vortexed before determining visually
the solubility.
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JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2015, 53, 68–78
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