Diphenylsilane-containing linear and rigid whole aromatic poly(azomethine)s. Structural and physical characterization

Article abstract of DOI:10.1016/j.polymer.2018.07.038

Six new whole aromatic poly(azomethine)s with different rigidity were prepared from three diamines and two dialdehydes, all of them containing a diphenylsilane moiety as a central structural element. Two amines containing biphenyl moieties were obtained for the first time. Thus, the synthesized polymers contain two silicon atoms in the repeat unit, where methyl and/or phenyl groups bonded to them, complete the tetra-valence of the heteroatom. The new materials were structurally characterized by means of FT-IR, solid NMR and elemental analysis. Solubility was tested in several organic solvents at room temperature and 40 °C and the inherent viscosity was determined. GPC analysis showed oligomeric chains of five repetitive units for the tested samples. Additionally, thermal behavior was studied by TGA and DSC analysis, by evidencing materials highly stable and rigid. Band gaps values ranging between 2.71 and 3.14 eV were obtained from UV/Vis and DRS analysis. The spin-coating technique was used to prepare films from soluble samples in NMP and their thicknesses were determined by the ellipsometric method. From these samples, and using AFM and four-point techniques, the effect of the annealing time on the roughness and conductivity of the films was studied. In accordance with the appropriate thermal and conductivity properties of the new silylated materials (which has a whole aromatic structure), could be proposed as an alternative for applications in the optoelectronics field.

Full text of DOI:10.1016/j.polymer.2018.07.038

Polymer 150 (2018) 232e243
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Diphenylsilane-containing linear and rigid whole aromatic
poly(azomethine)s. Structural and physical characterization
A. Tundidor-Camba , C.M. Gonz aꢀ lez-Henríquez , M.A. Sarabia-Vallejos , L.H. Tagle a,
a
,
e
b
c, d
a
a
a
a
a, e, *
P.A. Sobarzo , A. Gonz aꢀ lez , R.A. Hauy oꢀ n , A.P. Mariman , C.A. Terraza
Research Laboratory for Organic Polymers (RLOP), Department of Organic Chemistry, Pontificia Universidad Cat oꢀ lica de Chile, P.O. Box. 306, Post 22,
a
Santiago, Chile
b
Laboratory of Nanotechnology and Advanced Materials (LNnMA), Chemistry Department, Universidad Tecnol oꢀ gica Metropolitana, P.O. Box 9845, Post 21,
Santiago, Chile
c
Departamento de Ingeniería Estructural y Geotecnia, Escuela de Ingeniería, Pontificia Universidad Cat oꢀ lica de Chile, Santiago, Chile
Instituto de Ingeniería Biol oꢀ gica y Medica, Escuela de Ingeniería, Pontificia Universidad Cat oꢀ lica de Chile, Santiago, Chile
UC Energy Research Center, Pontificia Universidad Cat oꢀ lica de Chile, Chile
d
e
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 April 2018
Received in revised form
Six new whole aromatic poly(azomethine)s with different rigidity were prepared from three diamines
and two dialdehydes, all of them containing a diphenylsilane moiety as a central structural element. Two
amines containing biphenyl moieties were obtained for the first time. Thus, the synthesized polymers
contain two silicon atoms in the repeat unit, where methyl and/or phenyl groups bonded to them,
complete the tetra-valence of the heteroatom. The new materials were structurally characterized by
means of FT-IR, solid NMR and elemental analysis. Solubility was tested in several organic solvents at
6
July 2018
Accepted 14 July 2018
Available online 17 July 2018
ꢀ
room temperature and 40 C and the inherent viscosity was determined. GPC analysis showed oligomeric
Keywords:
chains of five repetitive units for the tested samples. Additionally, thermal behavior was studied by TGA
and DSC analysis, by evidencing materials highly stable and rigid. Band gaps values ranging between 2.71
and 3.14 eV were obtained from UV/Vis and DRS analysis. The spin-coating technique was used to pre-
pare films from soluble samples in NMP and their thicknesses were determined by the ellipsometric
method. From these samples, and using AFM and four-point techniques, the effect of the annealing time
on the roughness and conductivity of the films was studied. In accordance with the appropriate thermal
and conductivity properties of the new silylated materials (which has a whole aromatic structure), could
be proposed as an alternative for applications in the optoelectronics field.
Silylated-poly(azomethine)s
p-conjugation
Band gap values
Thermal stability
Conductivity
©
2018 Elsevier Ltd. All rights reserved.
1
. Introduction
A common example of these materials are polymers which
contain an imine functional group (-C¼N-) in their structure, which
are generically named poly(Schiff base)s or poly(imine)s. A partic-
ular type of these poly(imides)s are the so-called poly(azomethine)
s (PAzMs), which are usually synthesized by condensation meth-
odologies of primary amines and aldehydes. PAzMs with aromatic
backbones are highly conducting polymers, which generates an
excellent electrical performance when are included as functional
Conjugated polymers based on C¼C bonds or isoelectronic ele-
ments have been widely investigated and used as a semiconductor,
LEDs (Light-emitting diodes) or photovoltaic cells in the last de-
cades due to their intrinsic electrical properties [1]. These com-
pounds are easy to process and their synthesis is low-cost
compared to those silicon-based materials, which also present
similar electrical properties. These advantages make this kind of
conjugated polymers into excellent candidates for this purpose.
components in material blends. Due to their extended
p-system,
they induce interesting properties to the whole material such as
high thermal stability [2], excellent mechanical strength [3], and
suitable optoelectronic properties for electrodes application [4]. At
the same time, these polymers have been explored and tested for
different applications in the field of organic electronic devices such
as LEDs [5] and acid-sensors [6], among others [7,8].
*
Corresponding author. Research Laboratory for Organic Polymers (RLOP),
Department of Organic Chemistry, Pontificia Universidad Cat oꢀ lica de Chile, P.O. Box.
306, Post 22, Santiago, Chile.
E-mail address: cterraza@uc.cl (C.A. Terraza).
https://doi.org/10.1016/j.polymer.2018.07.038
032-3861/© 2018 Elsevier Ltd. All rights reserved.
0

A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
233
Due to the presence of aromatic moieties, PAzMs are usually
infusible and partially insoluble in common organic solvents [8],
and several strategies have been applied to promote the process-
ability of the material. With the aims to improve both, solubility
and mechanical properties of PAzMs, the introduction of flexible
elements in their backbone such as aliphatic units, several func-
tional/pendant groups or structural irregularities, have been re-
ported in the literature in the last years [9,10].
spectra were recorded using KBr powder to manufacture sample
pellets on a Perkin-Elmer (Fremont CA, USA) 1310 spectropho-
ꢁ
1
tometer over the range 4000e450 cm . The melting points were
obtained with an SMP3 Stuart Scientific. Elemental analyses were
made on a Fisons EA 1108-CHNS-O equipment (Thermo Scientific,
Waltham/MA, USA). The inherent viscosity was measured in chlo-
roform (c ¼ 0.5 g/dL) in a Desreux-Bischof type dilution viscosim-
ꢀ
eter at 25 C. The weight- (Mw), number-average molecular weight
The aim of this research is the synthesis and the physical and
structural characterization of conjugated oligomeric aromatic pol-
y(azomethine)s. In order to overcome the solubility problems
associated to the whole aromatic materials, we incorporated, in the
(Mn), the degree of polymerization (DP) and polydispersity index
(PDI) of the oligomeric samples relative to polyethylene glycol
standards were determined at 40 C using a GPC system 150cv
ꢀ
(Waters, USA) equipped with a refractive index detector. For this,
repetitive unit, two silarylene moieties (-ArSi(R
1
,R
2
)Ar-) with
samples of PAzM dissolved in THF (c ¼ 0.5 mg/mL) were refined
methyl and/or phenyl groups as a lateral segment. Thus, the pres-
ence of silicon atom would promote a certain degree of flexibility to
the chains due to the longer C-Si bonds compared to C-C ones. This
fact and the nature of the R groups bonded to the heteroatom
would allow to increases the solubility of the polymers in common
organic solvents. Likewise, the silarylene units would promote
using micro-pore filters of 2 mm mesh, then 100 mL of the drain
solution was injected at 1 mL/min in
a MesoPore column
(300 ꢂ 75 mm), useful for samples up 25,000 molecular weight.
Thermal behavior was analyzed through the determination of glass
transition temperature (Tg) with a Mettler-Toledo (Greifensee,
ꢀ
Switzerland) DSC 821 calorimetric system (20 C/min under N
2
semi-conduction in the materials due to the presence of
d
ꢁ
p
flow). The Tg values were obtained during the first heating scan
conjugations in silicon internal orbital and also, due to the C¼C
neighboring conjugated system [11]. The polymers were charac-
terized by Nuclear Magnetic Resonance (NMR) and elemental
analysis. Material optical properties were measured via UV/Vis and
diffuse reflectance spectroscopies (DRS) (optical absorption). The
thermal properties of the PAzMs were studied using Differential
Scanning Calorimetry (DSC) and Thermogravimetric Analysis
under nitrogen gas atmosphere. Likewise, TGA measurements were
ꢀ
carried out with a heating rate of 20 C/min under N
2
flow on a
Mettler (Switzerland) TA-3000 calorimetric system equipped with
a TC-10A processor, and a TG-50 thermobalance with a Mettler MT5
microbalance. For this, 6e10 mg of the polymer were placed in an
alumina sample holder, and then, the TGA curves were performed
ꢀ
ꢀ
between 25 C and 800 C. The atomic percentage of carbon and
nitrogen were determined with an elemental analyzer (Elemental
Vario EL elemental analyzer; Elementar Analysensysteme, GmbH,
Hanau, Germany). The absorption spectra of the polymers were
recorded at room temperature, between 250 nm and 470 nm using
a UV/Vis spectrophotometer model Lambda 35 (Perkin Elmer, USA)
in NMP solutions (c ¼ 0.1 mg/mL) and a slit of 0.5. Diffusive
(
(
TGA). In particular, the samples soluble in N-methyl-2-pyrrolidone
NMP) were deposited by spin-coating onto a pre-treated silicon
wafer as substrate. Thicknesses of the deposited films were deter-
mined by ellipsometric methods, the refraction indexes of the
layers, which are mandatory for performing ellipsometry, were
obtained through an Abbe refractometer. The micro-topography of
the film surface was performed via Atomic Force Microscopy (AFM).
Besides, film conductivity values were also determined through
four-point methodology. Thus, according to their thermal and
electrical performance, the new synthesized silylated materials are
a contribution in the optoelectronics field.
4
reflectance measurement was carried out using a BaSO standard
white board in a UV-2450 UVevisible spectrophotometer. A spin
coater, model KW-4A from Chemat Scientific, coupled with an oil-
free vacuum pump (Rocker Chemker 410), was used for deposit the
solution (polymer in NMP) over the pre-treated silicon wafer. This
instrument possesses two spinning stages: (1) 500e2500 rpm
(2e18 s) and (2) 800e8000 rpm (3e60 s) with tunable acceleration
rate. The surface topography of the polymers was obtained by using
2
. Experimental
2
.1. Materials
an AFM model NTEGRA Prima, from NT-MDT Co., in intermittent
2
contact mode at different scan ranges (50 ꢂ 50
m
m ). Images were
Tetrakis(triphenylphosphine)
palladium(0),
bis(-
treated and analyzed using the off-line software Gwyddion. A
Multi-angle laser Ellipsometer, model SE 400adv, from SENTECH
Instrument GmbH, was used to perform optical measurements
triphenylphosphine) palladium(II) dichloride, 4-aminophenyl
boronic acid pinacol ester, 4-nitrophenyl boronic acid, anhydrous
N,N-dimethylacetamide (DMAc), p-toluenesulfonic acid mono-
hydrate (PTSA), anhydrous calcium sulfate, 10% w/w palladium on
activated carbon and hydrazine monohydrate 80% w/w were ob-
tained from Sigma Aldrich Chemical (Milwaukee, WI, USA). All
other solvents and reagents were purchased commercially as
analytical-grade (Sigma Aldrich Chemical, WI, USA or Merck,
Darmstadt, Germany).
ꢀ
ꢀ
ꢀ
with variable incidence angle from 30 to 90 in steps of 0.5 , the
equipment possesses an attached motorized goniometer, from
Hüber Diffraktionstechnik GmbH & Co. KG, for control incidence
angle variation. A stabilized He-Ne laser (
l
¼ 633 nm) permits a
precision of 0.1 Å in thin film thickness measurement. This equip-
ment was used to obtain the thickness of the polymeric films. The
four-point method was carried out using a digital multimeter from
GW Instek, model GDM-8255, which includes the 4 W test lead for
conduction measurement, as an optional accessory, used to obtain
the material resultant voltage with high resolution (0.012% rdg þ 5
digits). A DC power supply from GW Instek, model PLR 20e18, was
used for administrating a constant current to the system (6 A).
2
.2. Instrumentation and measurements
NMR spectra ( H, 13C, and 29Si) of the precursors and the new
1
diamines were carried out in solution on a 400 MHz instrument
Bruker AC-200, Germany) using CDCl as solvent and TMS as an
(
3
internal standard. A Bruker DSX 200 spectrometer was used to
2.3. Monomer synthesis
obtain solid-state 13C NMR spectra of the polymers at a frequency of
9
0.00 MHz with a commercial Bruker double air-bearing probe
Synthesis and characterization of the silylated dialdehyde
monomers (6 and 7) were reported in previous studies performed
by our research group [9]. Briefly, the precursor bis(4-
with 7 mm o.d. rotors. Chemical shifts were calibrated with glycine
and are reported relative to TMS. Additionally, NMR spectra in
CDCl
3
solution were recorded for the soluble polymers. FT-IR
bromophenyl)di-R-silane (R ¼ CH
3
or Ph) were obtained from the

234
A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
reaction between 1,4-dibromobenzene and the respective
18 h, later cooling at room temperature, simultaneously, 50 mL of
water was added. After stirring the solution for 30 min, the solid
obtained was filtered and disgreged under reflux by using 50 mL of
methanol. The suspension was filtered and the grey solid was
diorgano-silane in presence of n-BuLi. Then, these derivatives
ꢀ
reacted at 85 C with 4-formylphenylboronic acid by using
Pd(PPh
ate (2 M) solution. Diamine 5 also has been previously reported
12,13]. However, the synthesis and characterization of the silylated
biphenylic diamines 3 and 4 have not been described yet.
3 2 2
) Cl as catalyst in a 1,4-dioxane-water potassium carbon-
ꢀ
exhaustively washed with cool methanol and dried at 60 C under
[
vacuum. The dry solid was treated with 100 mL of chloroform at r.t.
and filtered on celite/silica gel (2:1 w/w). The residue obtained after
removing the solvent under vacuum was purified by column
0
0
2
4
.3.1. Bis(4 -amino-[1,1 -biphenyl]-4-yl)di-R-silane (3: R ¼ phenyl,
: R ¼ methyl)
3
chromatography using n-hexane/CHCl (2:1 v/v) as mobile phase,
which allowed to obtain a white solid.
In
a 3-necked flask-bottom with nitrogen inlet bis(4-
bromophenyl)di-R-silane (1 or 2) (1.50 g, 3.03 mmol), 4-
aminophenyl boronic acid pinacol ester (1.59 g, 7.28 mmol), and
tetrakis(triphenylphosphine)palladium(0) (0.18 g, 0.16 mmol) were
dissolved in 90 mL of a toluene/ethanol (2:1 v/v) mixture. Then
1
8 mL of a 1 M K
mixture, which was heated at reflux for 5 h for the diamine 3 and
8 h for the 4, respectively.
2 3
CO aq. solution was added to the reaction
1
For the isolation of 3, the mixture was cooled and filtered by
using a mixture of celite/silica gel (5:1 w/w). The filtrate was
concentrated in vacuum and the residue was purified by column
chromatography using an acetone: n-hexane (1:2 v/v) mixture as
the mobile phase. The diamine 4 was isolated by solvent evapora-
tion from the reaction mixture. The residue obtained was purified
by column chromatography using an acetone: n-hexane (1:2 vol/
vol) mixture as the mobile phase. Both products (3 or 4) were ob-
tained as pale brown solid.
0
0
ꢀ
2.3.4. Bis(4 -nitro-[1,1 -biphenyl]-4-yl)diphenylsilane (8)
ꢁ1
Yield: 51%. M.p. ( C): 292e294. FT-IR (KBr powder,
n
, cm ):
3015 (C-H arom.), 1622, 1473 (C¼C), 1523, 1367 (NO
arom.), 811 (arom. p-disubst.), 712 (arom. monosubst.). H NMR
(CDCl
, ppm): 8.32 (d, J ¼ 8.8 Hz, 4H, H7), 7.77 (d, J ¼ 8.8 MHz, 4H,
H6), 7.69 (dd, J ¼ 28.5, 8.1 MHz 8H, H2, H3), 7.62 (m, 4H, H10), 7.45
2
), 1176 (Si-C,
1
3
, d
13
(dt, J ¼ 14.2, 7.0 MHz 6H, H11, H12). C NMR (CDCl
(C8), 147.38 (C5), 140.10 (C4), 137.29 (C2), 136.50 (C10), 135.20 (C9),
33.46 (C1), 130.18 (C12), 128.29 (C11), 128.01 (C3), 127.01 (C6),
3
, d, ppm): 147.46
1
1
2
9
24.35 (C7). Si NMR (CDCl
Si; (578.47): C, 74.74%; H, 4.49%; N, 4.84% Found: C,
4.69%; H, 4.41%; N, 3.73%.
For obtaining the diamine 3, the dinitro derivative 8 (1.07 g,
3
,
d
, ppm): ꢁ14.11. Elem. Anal. Calcd. For
36 26 2 4
C H N O
7
1,85 mmol) and 150 mg of 10% w/w palladium on activated carbon
were suspended in 100 mL of an ethanol:THF (1:1 v/v) mixture. The
mixture was heated at 40 C and then, 2.5 mL of hydrazine mono-
0
0
ꢀ
2
.3.2. Bis(4 -amino-[1,1 -biphenyl]-4-yl)diphenylsilane (3)
ꢀ
Yield: 73%. M.p. ( C): 225 (decomp.). FT-IR (KBr powder,
n
,
hydrate 80% w/w was added. The temperature was increased until
reflux by maintaining it for 12 h. Still warm, the mixture was
filtered and the solvent removed. The light grey solid obtained was
dissolved in 100 mL of chloroform and washed twice with 50 mL of
a saturated NaCl solution. The organic phase was dried with
ꢁ
1
cm ): 3462, 3378 (N-H), 3016 (C-H arom.), 1618, 1483, (C¼C), 1190
1
(
Si-C, arom.), 813 (arom. p-disubst.), 738 (arom. monosubst.). H
NMR (CDCl
3
,
d
, ppm): 7.61 (m, 8H, H3, H11), 7.55 (d, J ¼ 7.61 MHz,
H, H2), 7.41 (m, 10H, H6, H12, H13), 6.72 (d, J ¼ 7.95 Hz, 4H, H7),
.71 (m, 4H, H9). 13C NMR (CDCl
, ppm): 145.93 (C8), 142.10 (C4),
4
3
3
, d
anhydrous MgSO , filtered and the solvent removed under vacuum.
4
1
36.83 (C11), 136.42 (C2), 134.55 (C1), 131.65 (C10), 131.07 (C5),
The oily residue obtained was disgregated in n-hexane and the
2
9
129.53 (C13), 128.00 (C6), 127.86 (C12), 125.73 (C3), 115.38 (C7). Si
solid was purified by column chromatography using an acetone: n-
hexane (1:2 vol/vol) mixture as the mobile phase. The final product
was obtained as a white solid with 52% yield.
NMR (CDCl3,
d
, ppm): ꢁ14.51. Elem. Anal. Calcd. For C36
30 2
H N Si;
(
518.47): C, 83.39%; H, 5.79%; N, 5.40%. Found: C, 83.34%; H, 5.71%;
N, 5,31%.
2
.4. Silylated poly(azomethine)s synthesis
0
0
2
.3.3. Bis(4 -amino-[1,1 -biphenyl]-4-yl)dimethylsilane (4)
ꢀ
ꢁ1
Yield: 67%. M.p. ( C): 106e107. FT-IR (KBr powder,
472, 3361 (N-H), 3020 (C-H arom.), 2496 (C-H aliph.), 1613, 1517
n
, cm ):
The dialdehyde (1.0 mmol) was dissolved in 5.0 mL of anhydrous
ꢀ
3
(
DMAc at 80 C and then, 5.0 mL of a diamine solution (1.0 mmol) in
anhydrous DMAc were added. When the mixture reaches 100 C,
PTSA monohydrate (60 mg, 0.315 mmol) and 80 mg (0.501 mmol)
of anhydrous CaSO
ꢀ
C¼C), 1247 (Si-C, arom.), 1120 (Si-C, aliph.)785 (arom. p-dis-
1
ubst.). H NMR (CDCl
3
,
d
, ppm): 7.58 (d, J ¼ 7.66 Hz, 4H, H2), 7.53 (d,
J ¼ 7.79 Hz, 4H, H3), 7.42 (d, J ¼ 8.11 Hz, 4H, H6), 6.75 (d, J ¼ 8.11 Hz,
4
were incorporated. The mixture was stirred at
13
ꢀ
4
H, H7), 3.73 (s, 4H, H9), 0.58 (s, 6H, H10). C NMR (CDCl
3
,
d
, ppm):
100 C for 12 h and then poured over methanol under stirring. The
1
46.08 (C8), 141.85 (C4), 135.81 (C1), 134.70 (C2), 131.37 (C5), 128.09
solid obtained (PAzM-1/6) was filtered, washed exhaustively with
hot methanol and dried at 100 C under vacuum for 24 h.
2
9
ꢀ
(
C6), 125.85 (C3), 115.43 (C7), ꢁ2.58 (C10). Si NMR (CDCl
ppm): ꢁ8.30. Elem. Anal. Calcd. For C26 Si; (398.37): C, 78.38%;
H, 7.53%; N, 7.03 %Found: C, 78.29%; H, 7.46%; N, 6.94%.
3
,
d
,
26 2
H N
3. Results and discussion
An alternative route to prepare the diamine 3 was developed
through the synthesis of the respective dinitro derivative 8. For this,
dibromo derivative 1 (1.34 g, 2.70 mmol), 4-nitrophenyl boronic
acid (1.28 g, 6.75 mmol) and bis(triphenylphosphine) palladium(II)
dichloride (0.15 g, 0.21 mmol) were suspended in a mixture of
3.1. Synthesis and spectroscopic characterization of monomers
Two synthetic routes based on the Suzuki coupling reaction
were used to prepare the diamine 3 (Scheme 1). The route I allows
to obtain, in one step, the final monomer by using 4-aminophenyl
boronic acid pinacol ester as an amino-containing precursor and
1
2 mL of 1,4-dioxane and 12 mL of a 2 M potassium carbonate so-
ꢀ
lution and then stirred. The whole mixture was heated at 95 C for

A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
235
Scheme 1. Synthetic routes for the preparation of diamines.
tetrakis(triphenylphosphine) palladium(0) as a catalyst. Thus, a
purified pale brown product was obtained with 73% yield. On the
other hand, the route II involves the synthesis of the dinitro 8 as
intermediate from 4-nitrophenyl boronic acid and bis(-
triphenylphosphine) palladium(II) dichloride, which was reduced
through a classic methodology [14]. From precursor 1, this route has
a total yield of 26% for the monomer. Due to the high effectivity of
the boronic acid pinacol ester route (route I), this was used to
prepare the diamine 4, which was obtained in a 67% yield after
purification.
The phenyl- and methyl-diamine monomers were structurally
characterized by FT-IR and NMR techniques. From KBr powder,
pellets which contain the PAzM were manufactured and chemically
analyzed through FT-IR spectroscopy, these spectra showed the
Fig. 1. NMR spectra of the silylated biphenyl-diamines.
ꢁ1
characteristic stretching bands for the NH
2
group at 3470 cm and
ꢁ
1
as pale-yellow solids except for PAzM-5 which was green. Before
their characterization, the samples were treated with methanol to
remove the remaining monomers and structures of low molecular
weight.
3
370 cm . In particular, the spectrum of diamine 3 shows the Si-C
ꢁ
1
aromatic band between 1190 cm , while the spectrum of 4 evi-
dences both bands for the Si-C aromatic and Si-C aliphatic bonds at
ꢁ
1
ꢁ1
1247 cm
and 1120 cm , respectively. On the other hand, the
The samples were structurally characterized in solid state
spectrum of the diamine 3 obtained from reduction of the dinitro
derivative (route II) does not present any evidence about the bands
13
through elemental analysis, FT-IR and C NMR. Additionally, and
due to their solubility, only four polymers were characterized in
solution by using NMR technique.
associated with the remaining NO
2
group.
Fig. 1 shows the NMR signals for the diamines in CDCl
These result confirm the proposed structure. In both H NMR
3
solution.
1
The FT-IR spectra present common bands in each series (Fig. 2).
Thus, the stretching bands Si-C arom. and Si-C aliph. bonds at
spectra, a singlet at 3.7 ppm is observed, which is associated to the
ꢁ1
1
1290e1190 and 1100-990 cm , respectively and the imine band
NH
2
group. For diamine 4 (Fig. 1a), its H NMR spectrum shows a
ꢁ
1
(
C¼N) at a.c. 1620 cm , were recorded. In all cases, an absorption
narrow singlet associated to the magnetically equivalent methyl
groups, which, due to the bond with the silicon atom, is shifted to a
ꢁ1
band of variable intensity at 1700 cm was observed, which is
associated with the carbonyl stretching of the chain terminal
13
higher field (0.58 ppm). This effect is evidenced also in the C NMR
1
spectrum. The 29Si NMR spectra show the signal associated to each
aldehyde group. In Fig. 3 are depicted two H NMR spectra acquired
3
in CDCl solution which are representative of each series. At a low
silicon atom, where their chemical shift agrees with the magnetic
environment. Thus, for diamine 3 (Fig. 1b) this value is close to
magnetic field, the spectra show narrow singlets for the aldehyde
and imine hydrogens close to 10 ppm and 8.5 ppm, respectively,
while the aromatic hydrogens appear between 6.8 ppm and
.90 ppm as complex multipletes. The spectrum of PAzM-6 (Fig. 3a)
shows a singlet at 0.61 ppm associated with the methyl groups
bonded to the silicon atom of the dialdehyde moiety. In this spec-
14 ppm while the diamine 4 shows a chemical shift c.a. 8 ppm. This
behavior confirms the effect which generates the electronic density
granted by the silicon atom to the phenyl and methyl groups;
respectively.
7
2
trum, it is observed a small NH signal (4.80 ppm) associated with a
3
.2. Synthesis and spectroscopic characterizations of
29
chain terminal amine group. The Si NMR spectra evidence two
signals for each sample whose specific chemical shifts follow the
same pattern discussed for the diamines analysis. In the case of
PAzM-2 (Fig. 3b), it is not possible to assign these signals because
the magnetic environment of the heteroatoms is very similar.
poly(azomethine)s
Two series of PAzMs based on the nature of silylated-diamine
were prepared. Accordingly, the monomers reacted in a stoichio-
metric relation by using anhydrous DMAc as solvent, 4-
13
Some polymers were examined by solid-state C NMR (Fig. 4),
4
toluenesulfonic acid as catalyst and anhydrous CaSO as a desic-
and the results are in agreement with those obtained in solution.
The Fig. 4a (series II) revealed aldehyde signals at ~192 ppm,
assigned to the chain terminal groups. Additionally, the samples
exhibit non-protonated carbon atoms at 140 ppm, several aromatic
cant agent. Thus, the series I, composed by four polymers, is derived
from the condensation reactions of the dialdehydes 6 or 7 with the
diamines 3 or 4, while series II generates two polymers by involving
the diamine 5 (Scheme 2). Polymers were obtained in 94e98% yield

236
A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
4
Scheme 2. Synthesis of PAzMs by using 4-toluenesulfonic acid and anhydrous CaSO in anhydrous DMAc.
3.3. Elemental analysis
The samples were analyzed by elemental analysis in order to
establish the atomic percentage of C, N, and H. Table 1 shows the
experimental results and those calculated for each polymer series.
It is observed that the percentage of the elements is similar to the
calculated values from the proposed structure. Thus, these results
and those obtained from the spectroscopic analysis are in agree-
ment with the repetitive unit proposed for each sample.
3.4. Solubility and inherent viscosity od PAzMs
The solubility behavior of the samples was established using the
same concentration (5 mg/mL) in several common organic solvents
ꢀ
at room temperature (19 C). The partially soluble or insoluble
ꢀ
samples at this temperature were subsequently tested at 40 C. The
obtained results are shown in Table 2.
All solutions were yellow except those of PAzM-5, which were
green. In general, the series I shows lower solubility than series II,
probably due to the higher aromatic content promoted by diamine
moiety. In series I, the sample that showed the best solubility was
PAzM-2 with only phenyl groups bonded to the silicon atoms. The
volume of these lateral groups would decrease the packing forces
between the chains allowing the best contact with the solvent and
therefore, promoting their solubilization. The behavior was inver-
ted in series II, where PAzM-6 was more soluble than PAzM-5. In
this case, it is probable that the rigidity of the samples is modu-
lating their solubility. However, PAzM-6 was soluble at room
temperature, while PAzM-2 need heating to solubilize. This fact
could be explained by the lower aromatic content of the diamine 5.
Similarly PAzM-1, with small lateral groups bonded to the silicon
atoms, was insoluble in all solvents tested, even under heating. All
Fig. 2. FT-IR spectra of PAzMs.
carbon signals between 128 and 136 ppm and aliphatic carbon
signals at 47-37 ppm. The appearance of new resonances in the
spectrum of the polymers evidenced the formation of imine
connection. The carbon of imine group was detected at 158 ppm.
The signals observed at 226 and 218 ppm are “spin side-band” (ss,
not impurities). On the other hand, PAzM-6 shows a signal
at ꢁ2 ppm that is related to the methyl groups bonded to the silicon
atom.
ꢀ
samples showed partially soluble or insoluble behavior at 40 C in
THF.
Chloroform was chosen as a solvent for the inherent viscosity
measurements (Table 2). The obtained values are very similar to the
series and close to 0.30 (dL/g).
The Fig. 4b shows three samples from series I. In all cases, no
aldehyde signal was observed, in agreement with the assumption
that the reaction proceeds cleanly to form the eCH¼N- bonds. Two
peaks, at 161 and 153 ppm are related to the imine group carbon,
indicating two possible conformations. At high magnetic fields,
PAzM-1 evidences two peaks for the two methyl groups of the
3.5. GPC analysis
3 2
ePhSi(CH ) Ph-units, which are magnetically non-equivalent.
In agreement with the solubility results, diluted solutions of
PAzM-2 and PAzM-6 in THF (c ¼ 0.5 mg/mL) were prepared,

A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
237
Fig. 3. NMR spectra (400 MHz, CDCl
3
) of PAzMs. a) PAzM-6 and b) PAzM-2.
Fig. 4. Solid state 13C NMR of PAzMs from. a) series II and b) series I.
Table 1
polydispersity index is ca. 1.3, and it is in agreement with common
polycondensation reactions.
Chemical composition of the samples.
PAzMs
Experimental content (%)a
Calculated content
%)
The structures of the repetitive units are quite similar within the
series, therefore, the hydrodynamic volume should be comparable
in most of the cases. Accordingly, we propose that, for akin intrinsic
viscosity values, the molecular weight of the different structures
analyzed should be also similar. In this sense, the polymerization
degree of PAzM-2 and PAzM-5 would be located between 4 and 5.
(
C
H
N
C
H
N
1
2
3
4
82.94 ± 0.21
85.51 ± 0.29
83.99 ± 0.29
84.08 ± 0.07
5.44 ± 0.02
5.12 ± 0.06
5.27 ± 0.01
5.29 ± 0.05
3.47 ± 0.004
2.92 ± 0.08
2.87 ± 0.06
2.71 ± 0.02
83.28
86.54
85.14
85.14
5.91
5.26
5.54
5.54
3.60
2.73
3.10
3.10
3.6. Thermal analysis
6
5
81.75 ± 0.12
83.88 ± 0.11
5.09 ± 0.03
4.69 ± 0.01
3.15 ± 0.01
2.73 ± 0.04
83.19
85.12
5.59
5.26
3.73
3.20
All samples were analyzed according to their thermal proper-
a
Obtained from elemental analysis.
ties, under a nitrogen atmosphere. Fig. 5 shows the DSC curves. In
ꢀ
general, the Tg's are above 300 C, value normally found in wholly
ꢀ
aromatic samples. Thus, for series I (Fig. 5a), the obtained Tg values
maintain a difference of c.a. 100 C between the samples with the
lowest and the highest performance. PAzM-1, which contains
methyl groups as lateral elements bonded to the silicon atoms,
filtered and then analyzed at 40 C by GPC technique. The results
are shown in Table 3. These results show a similar polymerization
degree for the samples which possesses five repetitive units. The
ꢀ

238
A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
Table 2
PAzMs solubility behavior and their inherent viscosity.
CHCl
3
DMSO
NMP
DMF
DMAc
THF
h** (dL/g)
Series I
PAzM-1
PAzM-2
PAzM-3
PAzM-4
PAzM-5
PAzM-6
-/-
-/-
-/-
-/-
-/-
-/-
±/±
-/-
-/-
-/-
n.d.
0.29
n.d.
0.31
0.30
0.34
±/þ
±/þ
±/þ
-/þ
±/þ
±/±
-/±
-/±*
þ
-/-
-/-
-/-
-/-
±/þ
±/þ*
þ
±/±
-/±
þ
-/±
-/±*
þ
±/±
-/±*
þ
Series II
±/±
Results at room temperature (19 C)/40 ꢀC. þ: Soluble. ±: Partially soluble. -: Insoluble. n.d.: No determined.*: green solution.** Measured in chloroform (25 ꢀC, c ¼ 0.5 g/dL).
ꢀ
Table 3
3.7. UV/Vis spectroscopy analysis
Molecular weights, polymerization degree, and polydispersity index of the oligo-
mers measured by GPC.
The absorption spectra were carried out in NMP solutions
Mw (g/mol)
Mn (g/mol)
DPa
PDIb
(c ¼ 0.1 mg/mL) at 25 C between 250 nm and 470 nm (Fig. 7a and
ꢀ
c). The deconvolution of the UV/Vis curves reveals the presence of
PAzM-2
PAzM-6
6700
5800
5300
4200
5
5
1.26
1.38
two bands; an absorption located at 290e300 nm (Band I), attrib-
a
uted to the
a second broad absorption signal (Band II) between 330 and
60 nm, which could be assigned to n/ * transition of the imine
p/p* transition of the aromatic rings (main chain) and
Approximated polymerization degree: Mn/molecular weight of repetitive unit.
Polydispersity index: Mw/Mn.
b
3
p
groups (Fig. 7b and d) [15,16]. For PAzM-5, the second band was
deconvoluted as a broad and flattened band, in contrast to PAzM-2
which present an important contribution of this band to the whole
UV/Vis spectrum. The small difference between band peaks (Bands
I and II) from PAzM-2 and PAzM-5 could be attributed to the slight
chain planarity modifications due to the difference of phenyl
arrangement in the backbone of the sample for series I and II, i.e. the
conjugation of the compound is interrupted due to the presence of
the aromatic rings, inducing rigidity to the main chain (steric hin-
drance) due to the natural non-coplanarity acquired by the phenyl
groups.
shows the highest Tg value due to the rigidity associated with the
lower distance between chains, which promotes positive in-
teractions. On the contrary, the sample containing phenyl groups
ꢀ
bonded to silicon atoms evidences the lowest value (365 C). The Tg
recovered for the isomeric samples that contain phenyl and methyl
ꢀ
groups on the silicon atoms are similar and near 390 C.
Serie II shows lower Tg values in relation to samples of series I.
This result can be explained according to the absence of the
biphenyl units in the diamine moieties. According to the previous
discussion, the distance between the chains would be again the
parameter which controls the rigidity of the system.
Fig. 6 depicts the results obtained from TGA analysis and their
respective DTGA curves for series I and II. All samples evidence an
initiation of thermal degradation (ITD) near to 300 C with two
intense peaks in the DTGA curves associated with two maximum
degradation temperatures (MTD). On the other hand, the TDT10%, in
agreement with international standards, is indicative of sample
thermal stability and explains why the samples were evaluated
E
g
¼ 1242=
l
onset
(1)
ꢀ
Where onset is the onset wavelength which was determined by the
l
intersection of the two tangents on the absorption edges was used
to indicate the direct electronic transition of the sample. The
calculated optical band gaps are shown in Table 5.
ꢀ
ꢀ
Optical band gaps located between 2.71 and 3.14 eV were found
for some representative samples of both series and would be
associated with an organic semiconductor behavior [19]. The
samples of the series I (PAzM-2 and PAzM-4) showed the lowest
optical band gap values, probably due to the presence of the
biphenyl units in the diamine moiety which, in spite of their non-
planarity, promoted a longer electronic conjugation. Also, is
important to mention that the samples from series I present direct
band gap values located in the blue/violet region of the visible light
above 480 C for series I and above 400 C for series II. Regarding
this, samples of series I are more thermally stable than those from
series II, probably, due to the presence of biphenyl units in the
diamine moiety.
ꢀ
The residual weight at 800 C (Rw800) shows values above 50%,
which is common in samples containing silicon due to the forma-
tion of silicon oxides of high thermal stability and to carbon. Table 4
summarizes the obtained parameters.
Fig. 5. DSC curves under a nitrogen atmosphere (second scan) of PAzMs. a) series I and b) series II.

A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
239
Fig. 6. TGA results under nitrogen atmosphere. a) TGA series I, b) DTGA series I, c) TGA series II and d) DTGA series II.
Table 4
Thermal parameters obtained from samples of series I and series II.
ITDa ( C)
ꢀ
TDT10% ( C)
b
ꢀ
MTD
c
( C)
ꢀ
MTD ( C)
c
ꢀ
Rw800 ( C)
d
ꢀ
Tge ( C)
ꢀ
1
2
Series I
PAzM-1
PAzM-2
PAzM-3
PAzM-4
PAzM-5
PAzM-6
304
304
303
301
293
264
490
515
497
486
412
406
500
519
500
506
446
499
577
587
578
573
571
576
55
59
62
55
52
50
464
365
389
397
238
306
Series II
a
Initiation of thermal degradation.
b
c
Thermal decomposition at which 10% weight loss.
Maximum degradation temperature.
d
e
ꢀ
Residual weight at 800 C.
Glass transition temperature.
(
2.90e2.71 eV), while PAzMs of series II were located in the violet/
3.9. Comparison with PAzMs references
ultra-violet sector (~3.10 eV). This fact suggests that all the poly-
mers of both series; I: PAzMs-2 and PAzMs-4, and II: PAzMs-5 and
PAzMs-6, could, in theory, generate electronic transitions in their
conducting bands when are exposed to sunlight. These results open
up the possibilities for future studies related to day-light opto-
electronic devices.
In order to compare the properties of the synthesized materials
with similar polymers, silarylene-containing-PAzMs from refer-
ences (PAzMs-ref) were used [9]. These polymers were already
synthesized and characterized by our research group. Its repetitive
units incorporate a phenoxy moiety between the biphenyl and
amino group (Fig. 9).
PAzM-1 and PAzM-3 show a lower solubility in DMSO, DMF, and
DMAc, which is clearly associated to the absence of the ether
linkages, a similar situation occurs in the reference samples (PAzM-
ref 1 and PAzM-ref 3; respectively). In general, TDT10%, values ob-
tained from reference samples, are similar to the values reported
3
.8. Diffuse reflectance spectroscopy (DRS)
Fig. 8 shows the curve obtained by DRS for the samples of series I
and II. Using the Kubelka-Munk (K-M) function the direct band gap
value of the polymer via Tauc plots analysis was obtained. All values
determined through this methodology were similar, ranging from
ꢀ
for the homologous PAzMs in this work (490e515 C and
ꢀ
4
86e515 C; respectively), while Tg values are higher for the last
~2.7 to 2.9 eV (~460-430 nm) (Table 5). Comparatively, the values
ꢀ
ones (
D
T average ¼ 165 C approximately). This phenomenon was
obtained via UV/Vis spectroscopy analysis were similar in all cases,
whose difference varied between 0.03 eV and 0.27 eV. It should be
mentioned that all the samples have an optical band gap in the
range of the visible spectrum, particularly in the blue-violet sector.
expected due to the increase in the chain structural rigidity. On the
other hand, the band gaps reported for the new silylated PAzMs
were lower than the data recovered for reference samples. Thus,

240
A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
Fig. 7. UV/Vis spectra of some polymers (a, c) with their respective fitted curves (b, d). From the UV/Vis spectra, the optical band gap values (E
1) [17,18].
g
) were obtained using the equation
(
Table 5
Band centers and optical band gaps obtained from UV/Vis NMP solution spectra and solid-state DRS.
Band I (nm)
Band II (nm)
lonset (nm)
E
g
(UV/Vis) (eV)
g
E (DRS) (eV)
PAzM-1
PAzM-2
PAzM-3
PAzM-4
PAzM-5
PAzM-6
2.83
2.70
2.84
2.83
2.89
2.87
298.7
362.7
427.4
2.90
298.9
297.6
293.1
363.4
330.3
343.3
458.6
398.8
395.5
2.71
3.11
3.14
o
Cut off: L NMP: 285 nm.
Fig. 8. Diffusive reflectivity curves for a) PAzM-5 and PAzM-6 (series I), b) full PAzM series II.
PAzM-ref 2 and PAzM-ref 4 showed band gap values closed to
.3 eV and 3.1 eV; respectively, while their homologs PAzM-2 and
PAzM-4 present values of 2.90 eV and 2.71 eV; respectively
Table 5). This decrease in ca. 0.4 eV showed by the new materials is
a consequence of the higher -conjugation in the main chain, and
therefore, as was suggested before, it could be used as base mate-
rials for day-light optoelectronic devices.
Poly(azomethine)s based on chains containing oxadiazole
moieties and silicon atoms bonded with four aliphatic carbon
atoms were synthesized by the group of Zaltariov et al. [20] These
3
(
p

A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
241
Fig. 9. Silylated poly(azomethine)s used as a reference [9].
2
þ
2þ
materials were used to capture several metals (Cu , Zn , and
out in order to obtain smoother surfaces and to evaporate the
solvent. The thickness of the polymeric film was determined by
ellipsometric measurements (Table 6). The initial thicknesses of the
neat films were similar, indicating the success in the methodology
used for the silicon wafer pre-treatment and the deposition pa-
rameters were highly influent in film thickness. On the contrary,
the films keep their thicknesses according to the sample annealing
times, which evidences the absence of solvent after deposition.
2
þ
Co ) through their N atoms. The obtained polymer-metal com-
opt
plexes were chemically and electrically characterized. The E
reported values for those materials are located between 3.10 and
.12 eV, while the polymer without metal atoms depicts values
around ~3.03 eV. All those values are higher than those reported for
g
3
PAzMs (series I) in this work and quite similar to the E
PAzM-5 and PAzM-6 (series II).
g
reported for
3.10. Preparation of polymeric films and determination of their
thicknesses
3.11. Atomic force microscopy (AFM)
Two polymers of each series were employed to prepare thin
films using spin coating technique, then the thicknesses of them
were established. The remaining samples (PAzM-1 and PAzM-3)
were insoluble in NMP and therefore could not be deposited by this
technique.
It is important to note that NMP was selected as deposition
solvent due to three main reasons. The first one is derived from
solubility tests, which shows that NMP, DMAc, DMF, and DMSO was
the best solvents in this case for almost all the studied samples. The
second one is related to the polarity of the solvents used for solu-
bility tests, as was mentioned in the last paragraph. All organic
The roughness of the four films previously described was
studied by AFM, and their micro-topographies are depicted in
Fig. 10. For PAzM-6, a homogeneous film with small isolated clus-
ters was observed, probably related to the high solubility of the
polymer in NMP. On the other hand, PAzM-2, which presents a
lower solubility, leads to a heterogeneous deposition by forming
larger clusters, by leaving large spaces with no film deposition. The
roughness of the polymeric films and their evolution, according to
the annealing time, was also evaluated via AFM micrographs
analysis (Fig. 10a). From these results, it is with the annealing time
increase.
solvents used are polar aprotic except for CHCl
3
, which is an apolar
Two tendencies are clearly observed in accordance with the
nature of the polymer series analyzed. Thus, PAzM-2 and PAzM-4
(series I) presented a slight decrease in the roughness during the
first annealing lapsus (from 0 to 3 h), but a higher decrease was
observed once concluded the second annealing cycle (from 3 to
6 h). On the other hand, PAzM-5 and PAzM-6 (series II) present a
different behavior respect to annealing treatment. In this case, the
first annealing lapsus depicts a significant decrease in the rough-
ness, more accentuated in the case of PAzM-6, while the second
step of annealing, only produces a slight decrease in the resulted
roughness.
Surprisingly, the roughness was higher for samples of series II
evidencing the best solubility in NMP (Table 2). This is indicative
fact, that the structural rigidity of the chains represents an impor-
tant factor to evaluate. Thus, it is possible to establish a clear
relationship between the structure of the repetitive unit of the
chains and their capacity of changing their conformation during the
annealing process.
solvent and does not allow to deposit the samples over hydrophilic
substrates. The third reason was related to the evaporation of the
solvent from the obtained surfaces, where NMP has the highest
boiling point (b.p.) of among the tested solvents (b.p.:
NMP > DMSO > DMAc > DMF > THF > CHCl
3
).
A
higher boiling
point generates a lower evaporation rate during deposition, which
is a crucial parameter to form homogeneous films. Thus, samples
dissolved in NMP, a polar aprotic solvent which has a hydrophilic
nature, will generate homogeneous films.
As the first step and in order to improve the hydrophilicity of
substrate surface and, so, the adherence of the polymer film, silicon
wafer pieces were submitted to a cleaning treatment. For this, the
original native silicon oxide film was removed from the surface by
the immersion of the substrate in a piranha solution (H
2
SO
4
:H
2
O
2
;
ꢀ
7
:3 vol/vol) during 30 min at 80 C [21]. Afterward, the wafer was
washed with HPLC water, slightly sonicated and exposed to an
ultra-pure nitrogen gas flow. Contact angle measurements were
performed on the silicon wafers in order to corroborate the effec-
ꢀ
tiveness of the process. The results show that angles lower than 10
Table 6
(
highly hydrophilic) was achieved after piranha treatment, in
ꢀ
Films thickness in function of the annealing time at 200 C.
ꢀ
contrast to the initial angles, which were founded close to 30e40 .
Thicknessa (nm)
After the drying process, 10
mL of a solution composed by 9.5 mg
of polymer and 500 L of NMP was deposited, on the cleaned silicon
m
0 h
3 h
6 h
2
wafer (1 ꢂ 1 cm ) surface, using the following procedure: 500 rpm
PAzM-2
PAzM-4
PAzM-5
PAzM-6
498.3 ± 1.1
495.4 ± 1.0
503.2 ± 0.8
512.0 ± 0.9
508.8 ± 1.0
495.5 ± 1.2
500.6 ± 0.7
512.9 ± 0.8
494.8 ± 0.4
496.3 ± 0.7
502.0 ± 0.6
514.4 ± 1.1
per 18 s, 1000 rpm per 18 s (twice), 1500 rpm per 18 s (twice),
1
700 rpm per 18 s and the 2000 rpm per 18 s. The modified silicon
ꢀ
wafers were submitted to an annealing treatment (200 C during
3
ꢁ
4
a
h or 6 h), under vacuum (10 torr). This annealing was carried
Obtained by ellipsometry.

242
A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
Fig. 10. a) Roughness of the films at different annealing time at 200 ꢀC (0, 3 and 6 h) and b) AFM topographic images (50 ꢂ 50
m
m ) obtained from spin-coated films.
2
3.12. Conductivity
The four-point probe was used to establish the resistivity of
different PAzMs films, which was performed by dissolving the
polymer in NMP. The set-up consists of four points collinear probes,
in which a constant current is applied between the two outer
probes, while the voltage variation is measured in the inner probes.
The surface resistivity can be determined via the Equations (2) and
(
3) [22,23] (Tabulated data).
ꢀ
ꢁ
V
I
r
¼
*CFðt; w; sÞ
(2)
(3)
p
ðt þ wÞ
CFðt; w; sÞ ¼
ꢀ
ꢁ
w
s
sinh
ln
ðtþwÞ
sinh
2
s
Fig. 11. Model for the four probe resistivity measurements.
Where V is the voltage measured between the probes, I is the
current applied to the system, t and w are the film and substrate
thicknesses, respectively, and s is the separation between probes
Table 7
Results of the resistivity of the PAzMs films.
(
Fig. 11). CF corresponds to a corrector factor based on physical
dimensions related to the sample and the probes (t, w, s) (Equation
3)). The experiments were carried out by using the following pa-
Resistivitya
(U cm)
(
0
h
3 h
6 h
Mean
rameters: I ¼ 6 A; t ¼ from Table 6; w ¼ 0.0525 cm (silicon wafer
thickness) and s ¼ 0.1 cm. Clean silicon wafers were used as a
calibration standard. Table 7 shows the resistivity of the polymers,
which are related to the structure of each one of them. A common
structural factor is the presence of imine groups, which have a
donor element (N-atom) and therefore an increase in the distri-
bution of the electron density along the chain [24].
PAzM-2
PAzM-4
PAzM-5
PAzM-6
60.02
63.10
70.80
64.64 ± 5.55
136.98
141.60
174.84
147.75
158.53
224.71
152.37
155.76
214.86
145.70 ± 7.90
151.96 ± 9.08
204.81 ± 26.41
Silicon wafer substrate
10.77
a
Obtained by using the four-point probe technique after a heating treatment at
ꢀ
2
00 C at different annealing time.
The samples prepared without thermal annealing were first
analyzed. It was observed that PAzM-2, with only phenyl groups
linked to the silicon atoms, evidences the highest conductivity due
to its high symmetry and electronic conjugation in relation to its
structural homologous of series II; PAzM-5. On the other hand,
PAzM-4 and PAzM-5 have similar results, while than PAzM-6
shows the highest resistivity due to the loss of symmetry, which
would decrease the density of carriers.
4
. Conclusions
Two series of new conjugated poly(azomethine)s, containing
diphenylsilane as a central unit, were synthesized from three di-
amines and two dialdehydes. Both monomers and polymers were
characterized by FT-IR, NMR, and elemental analysis. Chloroform
polymeric solutions showed similar values of inherent viscosity for
all samples. GPC data for PAzM-2 and PAzM-6 were obtained using
THF as a solvent, evidencing the presence of chains with five re-
petitive units and a narrow polydispersity index. Due to their high
aromatic content and structural rigidity, PAzMs showed a low
solubility in common organic solvents, especially those samples
ꢀ
When the samples were treated at 200 C for 3 h or 6 h before
the analysis, the tendency in the resistivity was the same. This
behavior could be associated with the high Tg value observed in all
ꢀ
cases (Tg > 230 C) which would indicate that the annealed poly-
mers films do not relax into identical isotropic disordered states
[
25]. It is important to mention that, in general, the annealing times
tend to increase the resistivity of the samples.

A. Tundidor-Camba et al. / Polymer 150 (2018) 232e243
243
that only contain biphenyl moieties in their backbone. In this sense,
assembly and charge carrier mobility, Chem. Mater. 16 (2004) 4765e4771.
[
4] G. Zotti, A. Randi, S. Destri, W. Porzio, G. Schiavon, Polyconjugated azomethine
the substituents, linked to the silicon atoms (Me, Ph) allowed to
modulate, the solubility behavior of the samples. TGA analyses
showed that the materials possess high thermal stability in all
0
layers by sequential condensation of
4
a
,
a
-dialdehyde-oligothiophenes and
0
,4 -diamino-diphenylenes on ITO/glass electrodes, Chem. Mater. 14 (2002)
4550e4557.
[5] A. Kimoto, K. Masachika, J.-S. Cho, M. Higuchi, K. Yamamoto, Synthesis and
electroluminescence properties of novel main chain poly(p-
ꢀ
ꢀ
cases, with a TDT10% between 406 C and 515 C. Particularly, the
samples from series I evidenced higher values than series II. Like-
wise, the higher Tg value of these last polymers was associated with
the increases of the structural rigidity.
phenylenevinylene)s possessing pendant phenylazomethine dendrons as
metal ligation sites, Chem. Mater. 16 (2004) 5706e5712.
6] M.K. Choi, H.L. Kim, D.H. Suh, Changes of fluorescence color in novel poly(-
[
azomethine) by the acidity variation, J. Appl. Polym. Sci. 101 (2006)
For samples soluble in NMP, optical properties were measured
by using UV/Vis spectroscopy from which band gaps between
1228e1233.
[7] M. Cazacu, M. Marcu, A. Vlad, A. T oꢀ th, C. Racles, Chelate Polymers. III. New
0
polyazomethines of 5,5 -methylene-bissalicylaldehyde with siloxane di-
2
.71 eV and 3.14 eV were observed. Similar bandgap results were
amines and their divalent metal complexes, J. Polym. Sci. Part A Polym. Chem.
obtained via DRS in all the samples analyzed. Most of the prepared
polymers presented a band gap in the visible region (blue-violet
sector), thus becoming it into potential materials for sunlight op-
toelectronic applications, however, more research about the spe-
cific structural modifications are needed to propose silylated
poly(azomethine)s with better optoelectronic performance.
41 (2003) 3169e3179.
[8] A. Iwan, D. Sek, Processible polyazomethines and polyketanils: from aerospace
to light-emitting diodes and other advanced applications, Prog. Polym. Sci. 33
(2008) 289e345.
[
9] A. Tundidor-Camba, C.M. Gonz ꢀa lez-Henríquez, M.A. Sarabia-Vallejos,
L.H. Tagle, R.A. Hauy oꢀ n, P.A. Sobarzo, A. Gonz ꢀa lez, P.A. Ortiz, E.M. Maya,
C.A. Terraza, Silylated oligomeric poly(ether-azomethine)s from biphenyl
moieties-containing monomers. Synthesis and characterization, RSC Adv. 8
In the final part of the study, two selected samples of each series
were deposited as films using NMP as solvent via the spin-coating
technique. Subsequently, topographical and electric conductance
studies were performed to the films through AFM and four-probe
method, respectively. Parallelly, annealing cycles were applied to
the samples in order to increase surface smoothing, demonstrating
that the film thickness is not seems affected by the annealing time.
However, the surface morphology of the films was affected by
either, the structure of each polymer and the annealing time.
Consequently, the surface roughness of the samples tends to
decrease with the annealing time. From the conductivity studies, it
was verified that the symmetry of the polymer main chain affects
its electrical conductance. In this sense, the conductivity increases
in accordance with the symmetry of the chain. Finally, it was
(
2018) 1296e1312.
[
[
10] P.K. Dutta, P. Jain, P. Sen, R. Trivedi, P.K. Sen, J. Dutta, Synthesis and charac-
terization of a novel polyazomethine ether for NLO application, Eur. Polym. J.
3
9 (2003) 1007e1011.
11] M. Bruma, B. Schulz, Silicon-containing aromatic polymers, J. Macromol. Sci.
Part C 41 (1e2) (2001) 1e40.
[12] L.H. Tagle, F.R. Díaz, D. Radic, A. Opazo, J.M. Espinoza, Synthesis and charac-
terization of poly(amides) derived from diamines with germanium and sili-
con, J. Inorg. Organomet. Polym. 2 (2000) 73e79.
13] J. Pratt, S.F. Thames, Organosilicon compounds. XVIII. Silicon-containing dia-
nhydrides, J. Org. Chem. 38 (1973) 4271e4274.
14] A. Tundidor-Camba, L.H. Tagle, C.M. Gonz ꢀa lez-Henríquez, D. Coll, R. Hauy oꢀ n,
P.A. Sobarzo, I.A. Jessop, C.A. Terraza, New oligomeric poly(ether-imide)s
containing diphenylsilane and dibenzofuran moieties. Synthesis and charac-
terization, J. Maromol. Sci. Part A Pure Appl. Chem. 55 (2018) 234e331.
15] F. Do gꢁ an, I. Kaya, Thermal decomposition kinetics of poly(5-
[
[
[
hydroxyquinoline) synthesized by oxidative polycondensation, Mater. Focus
3
[16] D. S¸ enol, I. Kaya, Synthesis and characterization of azomethine polymers
(2014) 310e317.
ꢀ
observed that the annealing process developed at 200 C slightly
affects the resistivity of the material by increasing it according to
the annealing time.
containing ether and ester groups, J. Saudi Chem. Soc. 21 (2017) 505e516.
[
17] M.M. Ahmida, S.H. Eichhorn, Measurements and prediction of electronic
properties of discotic liquid crystalline triphenylenes and phthalocyanines, in:
ECS Trans., 2010, pp. 1e10.
Acknowledgments
[18] T. Daimon, E. Nihei, Fabrication of organic electrochemiluminescence devices
with -conjugated polymer materials, J. Mater. Chem. C 1 (2013) 2826e2833.
p
[
19] P. Liu, Y.L. Wu, H.L. Pan, Y.N. Li, S. Gardner, B.S. Ong, S.P. Zhu, Novel high-
performance liquid-crystalline organic semiconductors for thin-film transis-
tors, Chem. Mater. 21 (2009) 2727e2732.
The authors acknowledge Fondo Nacional de Desarrollo Cientí-
fico y Tecnol oꢀ gico, FONDECYT (1150157 and 1170209) and FON-
[
[
20] M.-F. Zaltariov, M. Cazacu, S. Shova, C.-D. Varganici, L. Vacareanu, V. Musteata,
A. Airinei, Des. Monomers Polym. 17 (2014) 668e683.
21] I.M. Tidswell, B.M. Ocko, P.S. Pershan, S.R. Wasserman, G.M. Whitesides,
J.D. Axe, X-ray specular reflection studies of silicon coated by organic
monolayers (alkylsiloxanes), Phys. Rev. B 41 (1990) 1111e1128.
DEQUIP (EQM120021). P.A. Sobarzo thanks CONICYT for
fellowship No 21151317.
a
References
[
[
[
22] L.B. Valdes, Resistivity measurements on germanium for transistors, Proc. IRE
42 (1954) 420e427.
[
1] A. Peron, P. Rannou, Processile conjugated polymers: from organic semi-
conductors to organic metals and superconductors, Prog. Polym. Sci. 27 (2002)
35e190.
23] F.M. Smits, Measurements of sheet resistivity with the four-point probe, Bell.
Syst. Tech. J. 37 (1958) 711e718.
24] D. Senol, I. Kaya, Synthesis and characterization of aromatic compounds
containing imine and amine groups via oxidative polycondensation, Des.
Monomers Polym. 17 (2014) 557e575.
1
[
2] S. Matsumura, A.R. Hlil, C. Lepiller, J. Gaudet, D. Guay, Z. Shi, S. Holdcroft,
A.S. Hay, Ionomers for protein exchange membrane fuel cell with sulfonic acid
groups on the end-groups: nobel branched poly(ether-ketone)s, Polym. Prepr.
[25] G.R. Strobl, The Physics of Polymers. Concepts for Understanding Their
(
Am. Chem. Soc. Div. Polym. Chem.) 49 (2008) 511e512.
Structures and Behavior, Springer, Berlin, 2007.
[
3] N. Kiriy, V. Bocharova, A. Kiriy, M. Stamm, F.C. Krebs, H.J. Adler, Designing
thiophene-based azomethine oligomers with tailored properties: self-