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A. Altin et al. / Reactive & Functional Polymers 73 (2013) 1319–1326
monomers, similar levels of crosslinking density are attained at
much higher conversions because these reactive monomer are less
prone to affect crosslinking than TEGDMA.
FTIR (ATR): 3321 (NꢁH), 3060, 3062 (ArAH), 2960, 2928, 2890
(CAH), 1711 (C@O), 1628 (C@C), and 1587 (NAH) cmꢁ1
.
We propose that urea-containing monomers may be suitable
for this purpose. To test this hypothesis, we designed two new
urea-containing monomers functionalized with phosphonate
groups for improved biocompatibility and binding properties. A
previously reported [15], structurally similar monomer was also
investigated to test the correlation between the monomer struc-
ture and photopolymerization reactivity. Both homopolymeriza-
tions and copolymerizations with commercial dental monomers
were investigated.
2.3.1.2. Monomer 2. The pure product was obtained as a colorless
viscous liquid in 77% yield.
1H NMR (400 MHz, CDCl3, d): 1.25 (t, 6H, OCH2CH3), 1.87 (s, 3H,
CH3), 3.43 (t, 2H, OCH2CH2), 3.60 (m, 2H, CH2AP), 4.02 (m, 4H,
OCH2CH3), 4.13 (t, 2H, OCH2CH2), 5.80, 6.43 (s, 2H, C@CH2), 6.05,
6.25 (bs, 2H, NH) ppm.
13C NMR (400 MHz, CDCl3, d): 15.36 (OCH2CH3), 17.17 (CH3),
33.21, 34.95 (CH2AP), 38.15 (OCH2CH2), 61.60 (OCH2CH3), 63.31
(OCH2CH2), 124.76 (CH2@C), 135.14 (CH2@C), 157.59 (HNAC@O),
and 166.28 (OAC@O) ppm.
FTIR (ATR): 3349 (NAH), 2983, 2929, 2901 (CAH), 1716, 1686
(C@O), 1644 (C@C), 1561 (NAH), 1215 (P@O), 1019, 948
2. Experimental
(PAOAEt) cmꢁ1
.
2.1. Materials
31P NMR (CDCl3): 24.44 ppm.
Diethyl amino(phenyl)methylphosphonate and diethyl amin-
omethylphosphonate were prepared according to literature proce-
dures [20,21]. Chloroform was dried over activated molecular
sieves (4 A0). Diethyl phosphite, 2-isocyanatoethyl methacrylate
(IEM), Al(OTf)3, benzaldehyde, diethyl phthalimidomethylphosph-
onate, hydrazine hydrate, 2-hydroxyethyl methacrylate (HEMA),
triethylene glycol dimethacrylate (TEGDMA), hexyl acrylate (HA),
2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyloxy) phenyl] pro-
pane (Bis-GMA), 2,20-azobis(isobutyronitrile) (AIBN), 2,20-dime-
thoxy-2-phenyl acetophenone (DMPA), benzophenone (BP) and
all other reagents and solvents were obtained from Aldrich Chem-
ical Co. and used as received.
2.3.1.3. Monomer 3. The crude product was recrystallized from
diethyl ether and washed with hexane. The pure product was ob-
tained as a white solid in 70% yield (mp = 72 °C).
1H NMR (400 MHz, CDCl3, d): 1.01, 1.29 (t, 6H, OCH2CH3), 1.78
(s, 3H CH3), 3.35 (m, 2H, OCH2CH2), 3.59, 3.77, 4.01 (m and t, 4H,
OCH2CH3), 4.15 (m, 2H, OCH2CH2), 5.36, 5.91 (s, 2H, C@CH2), 5.41
(dd, 1H, CHAP), 5.99 and 7.09 (t and dd, 2H, NH), 7.20–7.41 (m,
5H, ArAH) ppm.
13C NMR (400 MHz, CDCl3, d): 16.16 (OCH2CH3), 18.05 (CH3),
38.73 (OCH2CH2), 49.87, 51.51 (CHAP), 63.18 (OCH2CH3), 64.01
(OCH2CH2), 125.44 (CH2@C), 136.03 (CH2@C), 127.81, 127.99,
128.34, 135.96 (ArAC), 157.77 (HNAC@O), and 167.13 (OAC@O)
ppm.
2.2. Characterization
FTIR (ATR): 3379, 3317 (NAH), 3060, 3032 (ArAH), 2987, 2929,
2907 (CAH), 1722, 1684 (C@O), 1638 (C@C), 1545 (NAH), 1216
1H, 13C and 31P NMR spectra were obtained on Varian Gemini
(400 MHz) spectrometer. IR spectra were obtained on a Nicolet
6700 FTIR spectrometer. Elemental analyses were obtained on a
Thermo Electron SpA FlashEA 1112 elemental analyzer (CHNS sep-
aration column, PTFE; 2 m; 6 ꢂ 5 mm). Photopolymerizations were
performed using a TA Instruments Q100 differential photocalorim-
eter (DPC). Dynamic mechanical analysis (DMA) was performed on
a Perkin Elmer Pyris Diamond DMA.
(P@O), 1014, 980 (PAOAEt) cmꢁ1
.
31P NMR (CDCl3): 23.22 ppm.
ELEM. ANAL., Calcd. for C18H27N2O6P: C, 54.27%; H, 6.83%; N,
7.03%; O, 24.10%; P, 7.77%. Found: C, 54.54%; H, 7.31%; N, 7.31%.
2.4. Photopolymerization
Photopolymerizations were conducted using a DSC equipped
with a mercury arc lamp. The samples (3–4 mg) containing
2.0 mol% initiator were irradiated for 10 min at either 40 °C or
72 °C with an incident light intensity of 20 mW/cm2 and a nitrogen
flow of 20 mL minꢁ1. Polymerization rates were calculated using
the following formula:
2.3. Synthesis of monomers
2.3.1. General procedure for the synthesis of monomers 1–3
To an ice-cold solution of the desired amine (2.8 mmol) in
10.2 mL of dry chloroform under a stream of nitrogen, 2-isocyanat-
oethyl methacrylate (2.9 mmol,0.41 mL) was added dropwise. The
solution was stirred at room temperature overnight under nitrogen
and then extracted with 1 wt% NaOH (3 ꢂ 42 mL), 1 wt% HCl
(3 ꢂ 42 mL), and brine (3 ꢂ 42 mL). The organic layer was dried
over anhydrous sodium sulfate, filtered and evaporated under re-
duced pressure to leave the crude product.
ðQ=sÞM
Rate :
nDHpm
where Q/s is the heat flow per second, M the molar mass of the
monomer, n the number of double bonds per monomer molecule,
DHp the heat released per mole of double bonds reacted, and m is
the mass of monomer in the sample. The value used for the
of a methacrylate double bond was 13.12 kcal/mol [22].
DHp
2.3.1.1. Monomer 1. The crude product was recrystallized from
diethyl ether and dried under vacuum. The pure product was ob-
tained as a white solid in 75% yield (mp = 70 °C).
2.5. Calculation of dipole moments
1H NMR (400 MHz,CDCl3,d): 1.82 (s,3H,CH3), 3.33 (t,2H,OCH2-
CH2), 4.07 (t,2H, OCH2 CH2), 4.21 (s, 2H, CH2AAr), 5.12, 5.26 (bs,
2H, NH), 5.46, 5.98 (s, 2H, C@CH2), and 7.16–7.24 (m, 5H, ArAH).
13C NMR (400 Mz, CDCl3, d): 18.34 (CH3), 39.58 (OCH2CH2),
44.47 (NHACH2), 64.08 (OCH2CH2), 125.96 (CH2@C), 135.96 (CH2-
@C), 127.30, 127.36, 128.60, 139.10 (ArAC), 158.21 (HNAC@O),
and 167.53 (OAC@O) ppm.
Boltzmann-averaged dipole moments were calculated with
PM3 for all the monomers. In this procedure, all possible rotations
around single bonds were considered for a given acrylate to gener-
ate all the conformations corresponding to stationary points. Min-
imization, followed by the calculation of the Boltzmann-averaged
dipole moments for all the conformations, was carried out with
PM3 in the Spartan ’06 program [23]. The unique structures were