Design of lamellar structured POSS/BPZ polybenzoxazine nanocomposites as a novel class of ultra low-k dielectric materials

Article abstract of DOI:10.1039/c4ra01905a

A novel class of lamellar structured polyhedral oligomeric silsesquioxane/bisphenol Z (POSS/BPZ) polybenzoxazine (PBz) nanocomposites was successfully designed by a facile one-step copolymerization technique. The chemical structures of the monomer and resulting polymer were characterized by Fourier transform infrared (FTIR) spectroscopy, ¹H, ¹³C, DEPT-135, ²⁹Si NMR (nuclear magnetic resonance) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The desired cross-linked lamellae structural arrangement of POSS/BPZ polybenzoxazine (PBz) nanocomposites was confirmed by transmission electron microscopy (TEM). The BPZ-PBz and POSS-PBz layers were self-assembled by intermolecular hydrogen bonding in such a way as to form the lamellar structure during ring opening polymerization. An advantage of this lamellar structure is that 30% POSS/BPZ polybenzoxazine composite exhibits an ultra low-k value of 1.7 at 1 MHz as well as high thermal stability. the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra01905a

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: S. K. R, A. M and
A. Muthukaruppan, RSC Adv., 2014, DOI: 10.1039/C4RA01905A.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
Design of lamellar structured POSS/BPZ polybenzoxazine nanocomposites as
the novel class of ultra low k dielectric material.
R. Sasi kumar, M. Ariraman and M. Alagar*
Polymer Composite Lab, Department of Chemical Engineering, A.C.Tech., Anna University,
Chennai-600 025, India.
Abstract
A novel class of lamellar structured polyhedraloligomericsilsesquioxne/bisphenol Z
(POSS/BPZ) polybenzoxazine nanocomposites was designed successfully via facile one step
copolymerization technique. The chemical structure of monomer and resulting polymer were
1
13
29
characterized by Fourier transform infrared (FTIR) spectroscopy, H, C, DEPTꢀ135, Si NMR
nuclear magnetic resonance) spectroscopy, Xꢀray diffraction (XRD), differential scanning
(
calorimetric (DSC) and Thermogravimetric analysis (TGA). Desired cross linked lamellae
structural arrangement of POSS/BPZ polybenzoxazine nanocomposites was confirmed with the
transmission electron microscope (TEM). The BPZꢀPBz and POSSꢀPBz layers were
selfꢀassembled by the intermolecular hydrogen bonding in such a way to form the lamellar
structure during ring opening polymerization. In advantages to this lamellar structure, 30%
POSS/BPZ polybenzoxazine composite exhibits ultra low k value of 1.7 at 1 MHz as well as
high thermal stability.
Keywords: polybenzoxazine, POSS, lamellar structure, bisphenol Z, dielectric constant.
Introduction
Design of smart and miniaturized microelectronic devices such as, integrated circuits,
memory devices etc., have been received enormous research interest owing to their negligible
1
time delay which are necessary for ultraꢀfast electronic devices. In general, the square of the
dielectric constant is inversely proportional to the propagation velocity of the signal.
Consequently, the high speed electronic device circuits require lowꢀk material to realize the
2
,3
faster signal transmission without cross talk. To achieve this, it is important to develop the

RSC Advances
Page 2 of 24
View Article Online
DOI: 10.1039/C4RA01905A
lowꢀk dielectric materials that are been needed for the efficient integrated circuits. It is well
established that the lowꢀk silica and other related materials can prevent the signal cross over with
4
low power consumption. In this view, many efforts have been taken to reduce the dielectric
5
,6,7
constant (<1.8) with the different kind of materials.
Especially, nanolevel porous inorganic
materials, variety of polymeric materials and their combinations are investigated for lowꢀk
dielectrics. At the same time, the low k composite materials should be compatible and have a
strong adhesion with the improved thermal and mechanical stability. Based on these aspects, the
composite materials of interconnected structures with air gaps and nanopores have been studied
extensively. Widely, the networked polymers such as polyimide, POSS, PEEK, and
8
ꢀ13
Polybenzoxazine were reported for ultra lowꢀk dielectric materials. Among those POSS is one
of the well known nanoporous inorganic material which contains eight organic groups with
cubical structural arrangement and has been demonstrated to be an excellent building blocks for
4
the high performance applications.
Recent years, benzoxazine based organicꢀinorganic hybrid network structures have
received a great research interest due to their unique structural, thermal and mechanical
properties. The heterocyclic benzoxazine ring can be synthesized by Mannich condensation from
phenolic derivatives, formaldehyde and primary amine. To the advantages of thermally induced
ring opening addition polymerization of benzoxazine does not require any catalyst and there was
no byproducts as well. In addition, the polybenzoxazine possesses an excellent thermal and
mechanical properties, low moisture absorption, high carbon residue, low shrinkage and
1
4
excellent electrical properties. More importantly, the polybenzoxazine exhibits both inter and
intra molecular hydrogen bonding in which the intermolecular hydrogen bonding could be
1
5
beneficial for the self assembly of polybenzoxazine. Hence, it is interesting to introduce the
benzoxazine group into the porous polyhedral oligomeric silsesquioxane (POSS) compound for
the preparation of self assembled polybenzoxazine nanocomposites to the benefit of reducing
their value of dielectric constant. The pristine polybenzoxazine shows the dielectric constant in
the range of ~3.5 and it can be used as an ideal dielectric material for microelectronics
1
6
applications. Meanwhile, the hybridization of benzoxazine with the ordered mesoporous
materials such as POSS, SBAꢀ15, SiO reduces their value of dielectric constant as low as to
2
1
7ꢀ20
~2.
In addition to the above, their easy compatibility with the organic functional materials

Page 3 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
like oxazole, fluorinated compounds, polyimide, etc, have increased their scope towards high
1
2,14,16,21ꢀ23
performance applications.
structural arrangement of functionalized polybenzoxazine reduces the dielectric constant greatly
Moreover, the characteristic polarization and favorable
1
2,24
as low value needed for practical applications.
Liu et al reported the methylmethacrylate
(MMA) and POSS hybrid composites with ordered lamellar structure and shows ultraꢀlow k
2
5
value of 1.47. Further they have found that the lamellar arrangement plays the vital role to
2
4ꢀ26
reduce the value of dielectric constant.
Similarly, Leu et al reported the POSS/Polyimide
nanocomposites at the optimum of 29% POSS exhibits the dielectric constant of 2.3 when
1
0
compared to that of neat Polyimide. To the best of our knowledge there are no reports have
been published till date with regard to lamellar structure based on POSS/BPZꢀPBz
nanocomposites. To the best of our knowledge there are no reports have been published till date with
regard to lamellar structure based on POSS/BPZꢀPBz nanocomposites. Specifically, 2ꢀallyl phenol
benzoxazine functionalized POSS with desired network structure have not been studied yet for low k
dielectric applications. Hence, in the present work, an attempt has been made to develop a novel
class of POSS/BPZꢀPBz nanocomposites with an ordered lamellar structure by the
copolymerization of polyhedral oligomeric silsesquioxane benzoxazine (POSSꢀBz) and
bisphenol Z benzoxazine (BPZꢀBz) in view to reduce the value of dielectric constant.
Experimental
Materials
Analytical grades of cyclohexanone, phenol, concentrated hydrochloric acid, acetic acid,
aniline, paraformaldehyde, chloroform and toluene, were purchased from SRL, India. High
purity tetraethylorthosilicate (TEOS), 2ꢀallyl phenol, tetramethyl ammonium hydroxide (40% in
methanol), chlorodimethylsilane, platinum (0)ꢀ1,3ꢀdivinylꢀ1,1,3,3ꢀtetramethyldisiloxane complex
solution in xylene [Pt (dvs)] catalyst were purchased from SigmaꢀAldrich and were used as
received without further purification.

RSC Advances
Page 4 of 24
View Article Online
DOI: 10.1039/C4RA01905A
Synthesis of 1,1ꢀBis(4ꢀhydroxyphenyl)ꢀcyclohexane (Bisphenol Z)
Typical synthesis of bisphenol Z (BPZ) are as follows; 10.37ml of cyclohexanone
0.22mol) was charged in to the mixture of concentrated hydrochloric acid and acetic acid
(
(
2:1 V/V), subsequently phenol (19.32ml, 0.1 M) was added dropwise to the reaction mixture
o
and stirred for 48 h at 55 C. The required amount of distilled water was added to the reaction
mixture and resulting pinkꢀcolored product was isolated by filtration and washed several times
o
with hot water to remove the excess phenol before dried at 70ꢀ80 C. Finally, the end product
was recrystallized using ethanol to obtain off white crystalline powder (Yield: 78%).
Scheme 1. Synthesis of BPZ (a) and BPZꢀBz (b).
Synthesis of bisphenol Z benzoxazine (BPZꢀBz)
To a solution of aniline (6.8ml, 0.075mol) in toluene, the formaldehyde (5g, 0.167mol)
o
was added and stirred for 30 minutes at 0 C. Followed by 10g of bisphenol Z (0.037mol) was
o
added to the reaction mixture and stirred for overnight at 80 C. After the completion of reaction
(monitored by TLC), the reaction mixture was extracted with ethyl acetate and washed with
2N NaOH, water, brine and concentrated the organic layer to yield 95% brownish semi solid.
Synthesis of 2ꢀallyl phenol benzoxazine (APꢀBz)
To a solution of aniline (5ml, 0.055mol) in chloroform, formaldehyde (3.3g, 0.11mol)
o
was added and stirred for 30 minutes at 0 C. Subsequently, 7.12 ml of 2ꢀallyl phenol (0.055mol)

Page 5 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
o
was added to the reaction mixture and stirred for overnight at 70 C. After the completion of
reaction, the reaction mixture was extracted with ethyl acetate and washed with 2N NaOH,
water, brine and concentrated the organic layer to yield 97% pale yellow liquid.
APꢀBZ
Scheme 2. Synthesis of APꢀBz.
Synthesis of OHCꢀPOSS
The octahydridocubic polyhedral oligomeric silsesquioxane (OHCꢀPOSS) was
2
7,28
+
ꢀ
synthesized by the procedure as reported.
Octaanion solution [Me N ] [SiO ] was prepared
4 8 2.5 8
by mixing of tetraꢀmethyl ammonium hydroxide (8.04ml), methanol (3.91ml), and deꢀionized
water (2.93ml) followed by dropwise addition of tetraꢀethoxysilane (4.28ml) under nitrogen
atmosphere. OHCꢀPOSS [HMe SiOSiO ] , was made by the reaction of octanion solution
2
1.5 8
(18.5ml) with dimethylchlorosilane (10.6ml) to yield 38% of white crystalline powder.
TEOS
Octanion intermediate
OHCꢀPOSS
Scheme 3. Synthesis of OHCꢀPOSS.

RSC Advances
Page 6 of 24
View Article Online
DOI: 10.1039/C4RA01905A
Synthesis of POSSꢀBz
Finally, benzoxazine functionalized polyhedral oligomeric silsesquioxane (POSSꢀBz)
was synthesized by the addition of APꢀBz with OHCꢀPOSS using Pt(dvs) catalyst. To a solution
of OHCꢀPOSS (10g, 0.009mol) in chloroform, Pt(dvs) catalyst (8 drops) was added under
o
nitrogen atmosphere and stirred for 30 minutes at 30 C. Subsequently the solution of APꢀBz
(21g, 0.08mol) in chloroform was added to the reaction mixture and stirred for overnight at
o
o
1
10 C. After the completion of reaction reduced the temperature to 30 C and activated charcoal
was added to the reaction mixture and filtered through celite, the filtrate was concentrated by the
rotary evaporator to yield 91% of product as a pale yellow semi solid.
Scheme 4. Synthesis of POSSꢀBz.

Page 7 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
Preparation of neat polybenzoxazine matrix
In a glass mold, solutions of POSSꢀBz and BPZꢀBz in tetrahydrofuran (THF) was
separately heated at 100 °C for overnight to evaporate the solvent and then cured stepwise at
120, 140, 160, 180, 200, 220, 240 and 260 °C for 1h each to obtained dark brown film.
Preparation of POSS/PBz nanocomposites
The varying weight percentages of POSSꢀBz (10, 20, 30, 40 and 50 wt %) were added to
o
2
g of BPZꢀBz dissolved in 10 mL THF. The resulting solution was stirred for 30 min at 30 C.
The solutions were poured into respective glass molds and were heated at 100° C for 3h and then
cured stepwise at 120, 140, 160, 180, 200, 220, 240 and 260 °C for 1h each.
Characterization
1
13
29
H and C NMR spectra were recorded on a Bruckerꢀ300 NMR spectrometer. Si NMR
spectra were obtained from a Bruckerꢀ500 NMR spectrometer. Fourierꢀtransform infrared
FTIR) spectra of KBr disks were obtained using a Bruker Tensor 27 FTꢀIR spectrophotometer.
(
The Xꢀray diffraction analysis of the samples were carried out using a Rigaku, miniflux IIꢀC
Xꢀray diffractometer (30 kV, 20 mA) with a copper target (1.54 Å) at a scan rate of 4°/min.
Thermogravimetric and differential scanning calorimetric analyses of the polybenzoxazine films
were carried out with a Exstar 6300 at a heating rate of 10 °C/min under nitrogen atmosphere.
The surface overview of the composites was identified from FEI QUANTA 200F high resolution
scanning electron microscope (HRSEM). Samples for the high resolution transmission electron
microscopy (HRTEM) analysis were first prepared by putting POSSꢀBz/BPZꢀBz
nanocomposites films into epoxy capsules and cured at 70 °C for 24 h in a vacuum oven. After
that, the cured epoxy samples were microtone with a Leica Ultracut Uct into about 100 nm thick
slices and placed over the mesh of 200 copper nets. HRTEM images were captured using
TECNAI G SꢀTwin transmission electron microscope, with an acceleration voltage of 250 kV.
2

RSC Advances
Page 8 of 24
View Article Online
DOI: 10.1039/C4RA01905A
Results and discussion
Scheme 1a represents the synthesis route of bisphenol Z (BPZ) and the corresponding
ꢀ1
ꢀ1
FTꢀIR spectrum is shown in Figure 1a. The appearance of peaks at 2931 cm , 2853 cm and 819
ꢀ1
cm are assigned to paraꢀsubstituted benzene ring, symmetric and asymmetric stretching CꢀH
2
8 1
bond respectively. H NMR spectra of BPZ (Figure 2a) shows the peaks at 8.25 ppm, 7.05ꢀ6.72
ppm and 2.17ꢀ1.46 ppm, associated to hydroxyl, aromatic and aliphatic cyclohexyl ring protons
which confirms the successful formation of BPZ.
The Mannich condensation of BPZ and aniline to form BPZ benzoxazine monomer has
been represented in Scheme 1b. From the FTꢀIR spectra as shown in Figure 1a, the bands related
ꢀ1
ꢀ1
to triꢀsubstituted benzene ring, (NꢀCꢀO), and (CꢀOꢀC) can be seen at 1508 cm , 948 cm and
ꢀ1
28,29
1
1
232 cm respectively.
The H NMR peaks at 5.31 ppm and 4.58 ppm in Figure 2b
corresponds to (OꢀCH ꢀN) and (ArꢀCH ꢀN) resonance of benzoxazine ring.
2
2
Figure 1. FTIR spectra of BPZ, BPZꢀBz, APꢀBz, OHCꢀPOSS and POSSꢀBz (1a) &
POSS/BPZꢀPBz polybenzoxazine nanocomposites (1b).

Page 9 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
The APꢀBz was synthesized by the condensation of 2ꢀallyl phenol with aniline as
ꢀ1
ꢀ1
represented in Scheme 2. The FTꢀIR bands (Figure 1a) at 941 cm (NꢀOꢀC) and 1221 cm
1
(
ArꢀCꢀN) confirms the formation of benzoxazine and it was further supported by the H NMR
peaks at 5.37 ppm (OꢀCH ꢀN) and 4.62 ppm (ArꢀCH ꢀN) in the spectra as shown in Figure 3.
2
2
1
Figure 2. H NMR spectra of BPZ (a) and BPZꢀBz (b).
The OHCꢀPOSS preparation was shown in Scheme 3 and the chemical structure of the
1
same was confirmed by FTꢀIR and H NMR spectra as shown in Figure 1a and Figure 4b
ꢀ1
ꢀ1
ꢀ1
respectively. The strong FTꢀIR bands are positioned at 1097 cm , 2145 cm and 902 cm
2
0
1
associated to the SiꢀOꢀSi, SiꢀH stretching and bending vibrations of OHCꢀPOSS. The H NMR

RSC Advances
Page 10 of 24
View Article Online
DOI: 10.1039/C4RA01905A
peaks appeared in the range of 4.74ꢀ4.72 ppm (SiꢀH), and 0.26ꢀ0.25 ppm [Si(CH ) ] as a
3
2
multiplet, indicates the successful formation of OHCꢀPOSS.
1
Figure 3. H NMR spectra of APꢀBz.
Scheme 4 shows the addition reaction between APꢀBz and OHCꢀPOSS. The appearance
ꢀ1
ꢀ1
of new FTꢀIR bands at 1166 cm (SiꢀCH ꢀCH ) and absence of SiꢀH at 2145 cm in Figure 1a
2
2
29
ascribes the addition reaction. The Si NMR spectra as sown in Figure 5a ascertain that the
30
presence of SiꢀOꢀSi (ꢀ102.95 ppm) and Siꢀ(CH ) (18.78 ppm) in POSSꢀBz. The corresponding
3
2
1
H NMR shifts in the region of 1.59ꢀ1.57 ppm and 0.65ꢀ0.61 ppm are related to SiꢀCH ꢀCH and
2
2
SiꢀCH in POSSꢀBz cages and are shown in Figure 5b. Herein the two way of addition is
2
13
possible as shown in Scheme 4. The precise addition reaction has been confirmed with the C
1
3
and DEPTꢀ135 NMR spectra and is illustrated in Figure 6 (a & b). The C NMR spectrum of
POSSꢀBz shows all carbon related (C, CH, CH CH ) peaks but in DEPTꢀ135 NMR shown only
2,
3
the CH and CH peaks that are appeared opposite to the CH peak except the C peak. In this case,
3
2
1
3
the C NMR peaks at 152.2, 148.5, 130.5 and 120.29, are attributed to respective aromatic C
peaks which are not been observed in DEPTꢀ135. Moreover, the DEPTꢀ135 NMR shows five

Page 11 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
CH peaks in the aliphatic upꢀfield region and six CH peaks in the aromatic downꢀfield region.
2
The absence of CH peak in aliphatic region indicates the formation of POSSꢀBz (b) [Scheme 4].
3
1
Figure 4. XRD pattern (a) and H NMR spectra (b) of OHCꢀPOSS.
The formation of polybenzoxazine nanocomposites were confirmed by FTꢀIR spectra.
Figure 1b shows the FTꢀIR spectra of polybenzoxazine nano composites. The characteristic
ꢀ1
ꢀ1
absorption bands at 945 cm (out of plane bending vibration of C−H) and 1463 cm
(triꢀsubstituted benzene ring) were gradually disappeared. Meanwhile, a new absorption band
ꢀ1
appeared at 1412 cm is attributed to tetraꢀsubstituted benzene ring, indicates the ringꢀopening
2
8
polymerization of benzoxazine. It is further evidenced by the DSC analysis and described in
detail at the thermal analysis section.
The stepwise structural modifications of POSSꢀBz copolymer has been investigated by
low angle Xꢀray diffraction pattern. Figure 8 shows the XRD patterns of respective
POSSꢀBz monomers and their conjugated polymers. From the pattern it can be seen that
OHCꢀPOSS exhibits (Figure 4a) highly crystalline features. It is that the peak positions and
o
o
o
o
o
corresponding dꢀspace values are found to 8.01 , 10.72 , 11.86 , 18.61 , 24.1 and 10.5Å,
8.0 Å, 7.2 Å, 4.6 Å, 3.6 Å respectively. These values can be indexed to rhombohedral crystal
1
0
structure and are in good agreement with the earlier reports as well. In contrast, the
benzoxazine monomer shows the predominant amorphous phase (Figure 8). Also, there is no

RSC Advances
Page 12 of 24
View Article Online
DOI: 10.1039/C4RA01905A
evidence for any crystalline phase for POSSꢀBz monomer. This result further confirms the
functionalization of APꢀBz with OHCꢀPOSS which disrupts the crystallinity of OHCꢀPOSS to a
significant extent. However, copolymerization of POSSꢀBz with BPZꢀBz shows different
2
9
1
Figure 5. Si (a) and H NMR (b) spectra of POSSꢀBz.
diffraction pattern as can be seen in Figure 8. With the concentration of POSSꢀBz their
crystallinity enhances, in particular 30% of POSSꢀBz hybridized polymer composites have
shown the higher crystallinity that may lower its dielectric constant to an extremely low value by

Page 13 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
the benefit of their desired structural arrangements. This observation is in consistent with the
1
0,12
earlier reports.
When increases the POSSꢀBz concentration to above 30%, the crystallinity of
the composites falls down towards amorphous due to the aggregation of POSSꢀPBz.
1
3
Figure 6. C (a) and DEPTꢀ135 NMR (b) spectra of POSSꢀBz.
In order to understand the surface over view and the incorporation of POSSꢀBz in the
polymer network, the samples were analyzed by scanning electron microscope (SEM).
Figure (9aꢀd) represents the SEM micrograph of neat BPZꢀBz (Figure 9a), 30% POSS/BPZꢀPBz

RSC Advances
Page 14 of 24
View Article Online
DOI: 10.1039/C4RA01905A
(Figure 9b), the corresponding Si mapping (Figure 9c) and 100% POSSꢀPBz (Figure 9d). As can
be seen that the dense morphology with large number of voids in the SEM micrograph of pristine
BPZꢀPBz film. It is mainly arises from the ring opening polymerization of cyclohexyl ring
functionalized BPZꢀBz that enhances the external porosity of the neat as well as composite
polymers. After the copolymerization process, the SEM image designates the uniformly
distributed crystallite aggregates of POSSꢀBz, in addition to the voids created by the BPZꢀBz.
Moreover, the visible (Figure 9) open pores with dark background at 30% POSSꢀBz composite
3
2,33
film further increases the free volume space which also reduces the dielectric constant.
Conversely, the 100% POSSꢀPBz film have shown the large amount of crystallite aggregates are
discernible when compared to that of 30% POSSꢀBz composite. Figure 9c describes the results
of Siꢀmapping for the 30% POSSꢀBz composite and demonstrates that the uniform distribution
of POSSꢀBz over the surface.
Figure 7. Schematic representation of BPZ/POSS Polybenzoxazine nanocomposites with
cross linked lamellae and its photograph of film.
The internal microstructure of the 30% POSSꢀBz composite film has been observed with
the HRTEM analysis and the captured images are shown in Figure (10a, b & c). The TEM
images are clearly indicating the ordered lamellae structure with multilayers. From the high
magnification TEM as shown in Figure (10b & c) it can be seen that the well separated
unidirectional multilayer’s arrangement with large number of cross links. It could be
understandable that the observed dark layers are associated to the POSSꢀPBz and the less intense
layer corresponds to the BPZꢀPBz. In this order the layers have been arranged and form the

Page 15 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
1
0,12
desired lamellae structure.
During the ring opening copolymerization process, there is the
more probability for the formation of hydrogen bonding which may self assemble the BPZꢀPBz
and POSSꢀPBz layers together, consecutively it forms the ordered lamellae.
Figure 8. XRD pattern of pristine and POSSꢀBz copolymerized nanocomposites.
Thermal stability is one of the important factors for the inter layer dielectric materials.
Herein, the thermal stability of BPZꢀBz and POSSꢀBz polymer nanocomposites has been studied
with thermogravimetric analysis. Typical TGA curves of pristine and composite films are shown
in Figure 11. As expected the BPZꢀBz copolymerized with POSSꢀBz exhibits high thermal
stability than the pristine. It is directly associated to the presence of POSS network strengthens
the BPZꢀBz chains during copolymerization. When increases the POSS concentration it is
observed that the gradual increment of thermal stability for the resulting composites. Although,
the maximum thermal stability for POSSꢀPBz was obtained, this may be attributed to the
1
4
formation complete stable POSS network. In detail, the initial weight loss in the range of
o
o
2
40ꢀ300 C probably by the removal of solvent residues. The major weight loss beyond 300 C is
associated to the degradation of polymer network which is in consistent with the earlier

RSC Advances
Page 16 of 24
View Article Online
DOI: 10.1039/C4RA01905A
3
4
investigation. Typical DSC profile of the monomer shows (Figure 12a & b) the broad
exothermic peak at above 175 °C as the indication of BPZꢀPBz curing temperature. With the
30% POSS, only a single exothermic peak maximum at 224 °C was observed which indicates the
1
4,35
coꢀreaction between the oxazine rings of POSSꢀBz and BPZꢀBz.
Figure 9. SEM images of BPZꢀPBz (a), 30% POSS/BPZꢀPBz (b), Si mapping of 30%
POSS/BPZꢀPBz (c) and POSSꢀPBz (d) nanocomposites.
In microelectronics applications the material with extremely low dielectric constant is
more desirable and it warrants the development such novel materials. The extensive efforts are
made by several researchers in order to reduce the dielectric constant nearly equivalent to air
2
5,36
(1).
Generally, the polymer systems which offers the low k value should scarifies the other
structural, chemical and thermal properties. Therefore it needs more concern to use the materials
in full potential for commercial appliances. It is well established that the dielectric constant is a

Page 17 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
Figure 10. HRTEM micrographs for 30% POSSꢀBz/BPZꢀBz polymer nanocomposites (aꢀ
ꢁm & b, cꢀ200nm).
1
Figure 11. TGA curve of BPZꢀPBz and POSSꢀPBz nanocomposites.
tunable factor and it can be possible by the introduction of mesopores in the polymer matrix
which results lowering the value of dielectric constant at the extreme level upto ~1.7. Similarly,
it can also be possible to reduce the dielectric constant by altering the chemical and physical
1
4,16,21
structures of the polymer matrix using functionalization processes.
The former method lead
by the mesoporous materials such as POSS, SBAꢀ15 etc., which creates the pores in the polymer

RSC Advances
Page 18 of 24
View Article Online
DOI: 10.1039/C4RA01905A
10,20
matrix thus lowering the dielectric constant to a significant extent.
the tedious synthesis process to alter the structure.
The later method requires
Figure 12. DSC profile of BPZꢀBz and 30%POSS/BPZꢀBz nanocomposite before (a) and
after (b) polymerization.
According to the earlier reports on benzoxazine based nanocomposites exhibits the
3
7
dielectric constant of about ~1.8 and it needed to be improved for better applications. In this
study, we designed a novel POSS/BPZꢀPBz composite film with layered microstructure and has
achieved the ultra low dielectric constant value of 1.7±0.01 at the optimum concentration of
30% POSS/BPZꢀPBz nanocomposites (Table 1). To the best of our knowledge this is the lowest
value for ever reported in the case of POSS/BPZꢀPBz hybrid nanocomposites. This is the lowest
value for ever reported in the case of POSS/BPZꢀPBz hybrid nanocomposites. The novel type of 2ꢀallyl
phenol benzoxazine functionalized POSS plays the crucial role to impart desired lamellar structure which
inturn contributes to result Ultra lowꢀk value of the hybrid composites. An interestingly, the neat
polymer shows the relatively low k value of 3.49 which is also comparatively lower when
1
6,17,38
compared to that of the values reported earlier.
This may be due to the presence of larger
voids that enhances the external porosity which in turn reduces the kꢀ value considerably. In the
present composite systems, when an increase in the concentration of POSSꢀBz, the
corresponding kꢀvalue decreases upto 30 weight% further it increases with increase in

Page 19 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
concentrations. The neat POSSꢀPBz exhibits the higher value of dielectric constant of 2.9 than
that of concentrations due to large aggregates of POSS crystallites and completely packed voids.
Figure 13. The frequency dependence of dielectric constants of BPZꢀPBz and POSSꢀPBz
nanocomposites.
The observed ultra low k (Figure 13) for the POSS/BPZꢀPBz composites can be explained by the
following structural features; first, the self assembled layered structure with unidirectional
orientation is responsible for reducing the polarization by increasing an inter and intra layer
1
2,24ꢀ26
distances.
In particular, the layer thickness for the dark region (POSSꢀPBz) is higher when
compared to that of the BPZꢀPBz layer and it is almost two order magnitude that increases the
internal porosity due to the high volume fraction of POSS density in the film. Therefore, the
reduction in dielectric constant is strongly influenced by POSS portion in composites. At 30%
POSSꢀBz concentration imparts the desired lamellae structure with enhanced crystallinity which
in turn results the ultra low k value at this concentration.

RSC Advances
Page 20 of 24
View Article Online
DOI: 10.1039/C4RA01905A
o
o
Sample
T5 ( C)
T10 ( C)
Yc (%)
11.2
Dielectric constant (k)
3.49±0.01
BPZꢀPBz
186.2
184.0
204.6
229.3
345.7
301.2
242.8
294.0
322.5
423.7
1
2
3
0%POSSꢀBz/BPZꢀBz
0%POSSꢀBz/BPZꢀBz
0%POSSꢀBz/BPZꢀBz
POSSꢀPBz
32.8
2.03±0.01
34.7
1.86±0.01
36.1
1.70±0.01
63.8
2.89±0.01
Table 1. The weight loss, char yield (Yc) and dielectric constant (k) of neat BPZꢀPBz and
POSS/BPZꢀPBz nanocomposites.
Figure 14. The frequency dependence of dielectric loss of BPZꢀPBz and POSSꢀPBz
nanocomposites.
In addition, the cyclohexyl functionalized benzoxazine monomer (BPZꢀBz) offers the
external voids to enhance the free volume of the composite that also play the significant role to
reduce the value of dielectric constant. Further an increasing the percentage of POSS

Page 21 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
concentration upto 100%, the larger aggregation and lower crystalline features enhances the
value of dielectric constant due to reduction of voids and dense packing. Dielectric loss is a one
of the key factor to understand the utilization of dielectric material in microelectronics. Typical
frequency versus dielectric loss curves of the POSS/BPZ polybenzoxazine nanocomposites are
shown in Figure 14. It is found that the observed dielectric loss is ultimately very low in the
value of 0.0019 at 1MHz for lamellar structured 30% POSSꢀBz composites which shows the
ultra low k value as well. From this investigation it is suggested that the design and introduction
of lamellar structure in to the POSS/BPZꢀPBz hybrid nanocomposites could be effectively used
as an interesting candidate for the microelectronic devices.
Conclusion
In view to reduce the dielectric constant, we successfully designed the novel hybrid
POSS/BPZ polybenzoxazine nanocomposite systems. As expected the composite with
30% POSS exhibits the ultra low k value of 1.7±0.01 at 1MHz. The observed low k value mainly
attributed to the highly ordered lamellar network with distinct cross links. Meanwhile, the
thermal stability and dielectric constant has been tuned by varying the POSS concentration
without loss of their transparency. This kind of hybrid composites can expect to find potential
application in advanced microelectronic devices.
Supplementary Information: Data’s of FTIR and NMR spectra are provided for more
information.
Acknowledgement:
The authors thank DST Nanomission, (SR/NM/NSꢀ18/2010), New Delhi, Govt. of India., for the
financial support. The authors thank Dr. K. Gunasekaran and Mr. M. Kesavan, Dept. of
Crystallography and Biophysics, University of Madras, for providing the NMR facility.

RSC Advances
Page 22 of 24
View Article Online
DOI: 10.1039/C4RA01905A
References
1
2
3
4
. Y. Huang and J. Economy, Macromolecules, 2006, 39, 1850ꢀ1853.
. Y. Watanabe, Y. Shibasaki, S. Ando and M. Ueda, Polymer Journal, 2006, 38, 79–84.
. G. Maier, Prog. Polym. Sci., 2001, 26, 3ꢀ65.
. C. Zhang, S. Guang, X. Zhu, H. Xu, X. Liu and M. Jiang, J. Phys. Chem. C., 2010, 114,
2
2455–22461.
5
. K. Su, D. R. Bujalski, K. Eguchi, G. V. Gordon, D. Li Ou, P. Chevalier, S. Hu and
R. P. Boisvert, Chem. Mater., 2005, 17, 2520ꢀ2529.
6
. G. D. Fu, Y. Zhang, E. T. Kang and K. G. Neoh, Adv. Mater., 2004, 16, 839ꢀ842.
7
. S. Nunomura, K. Kog, M. Shiratani, Y. Watanabe, Y. Morisada1, N. Matsukil and
S. Ikedal, Jpn. J. Appl. Phys., 2005, 44, 1509ꢀ1511.
8
. Z. Geng, J. Ba, S. Zhang, J. Luan, X. Jiang, P. Huo and G. Wang, J. Mater. Chem., 2012,
2
2, 23534–23540.
9
. S. Nagendiran, M. Alagar and I. Hamerton, Acta Materialia, 2010, 58, 3345–3356.
1
0. ChyiꢀMing Leu, YaoꢀTe Chang and KungꢀHwa Wei, Macromolecules., 2003, 36, 9122ꢀ
9
127.
1
1. Md Abdul Wahab, Khine Yi Mya and Chaobin He, J. Polym. Sci., Part A: Polym.Chem,
008, 46, 5887–5896.
2
1
2. ChyiꢀMing Leu, G. Mahesh Reddy, KungꢀHwa Wei and ChingꢀFong Shu, Chem. Mater.,
003, 15, 2261ꢀ2265.
2
1
3. Y. Chen, L. Chen, H. Nie and E.T. Kang, J. Appl. Polym. Sci., 2006, 99, 2226–2232.
1
4. K. Zhang, Q. Zhuang, X. Liu, G. Yang, R. Cai and Z. Han, Macromolecules., 2013, 46,
2
696−2704.
1
5. ChuꢀHua Lu, ShiaoꢀWei Kuo, WenꢀTeng Chang and FengꢀChih Chang, Macromol.
Rapid Commun., 2009, 30, 2121–2127.
1
1
6. YiꢀChe Su and FengꢀChih Chang, Polymer, 2003, 44, 7989–7996.
7. M. R. Vengatesan, S. Devaraju, K. Dinakaran and M. Alagar, J. Mater. Chem, 2012, 22,
7
559–7566.

Page 23 of 24
RSC Advances
View Article Online
DOI: 10.1039/C4RA01905A
1
1
2
2
8. A. Chandramohan, K. Dinkaran, A. Ashok Kumar and M. Alagar, High Perform. Polym.,
2
012, 24, 405–417.
9. S. Devaraju, M. R. Vengatesan, M. Selvi, A. Ashok Kumar, I. Hamerton, J. S. God and
M. Alagar, RSC Adv. 2013, 3, 12915–12921.
0. Benꢀhong Yang, Hongꢀyao Xu, Zhenꢀzhong Yangc and Xiangꢀyang Liu, J. Mater.
Chem., 2009, 19, 9038–9044.
1. K. Zhang, Q. Zhuang, X. Liu, R. Cai, G. Yang and Z. Han, RSC Adv., 2013, 3, 5261–
5
270.
2
2. J. Lin and X. Wang, Polymer, 2007, 48, 318ꢀ329.
2
3. K. R. Carter, R. A. DiPietro, M. I. Sanchez and S. A. Swanson, Chem. Mater., 2001, 13,
2
13ꢀ221.
2
4. HungꢀCheng Liu, WenꢀChiung Sub and YingꢀLing Liu, J. Mater. Chem., 2011, 21,
182–7187.
7
2
2
2
5. YingꢀLing Liu and MengꢀHan Fangchiang, J. Mater. Chem., 2009, 19, 3643–3647.
6. MinꢀChi Tseng and YingꢀLing Liu, Polymer., 2010, 51, 5567ꢀ5575.
7. J. Choi, J. Harcup, A. F. Yee, Q. Zhu and R. M. Laine, J. Am. Chem. Soc., 2001, 123,
1
1420ꢀ11430.
2
2
3
8. M. R. Vengatesan, S. Devaraju, K. Dinakaran and M. Alagar, Polym. Compos., 2011, 32,
1
701ꢀ1711.
9. T. Agag, C. R. Arza, F. H. J. Maurer and H. Ishida, J. poly. Sci. part a: poly. chem., 2011,
9, 4335–4342.
4
0. J. Rathore, Q. Dai, B. Davis, M. Sherwood, R. D. Miller, Q. Linb and A. Nelson,
J.
Mater. Chem., 2011, 21, 14254–14258.
3
3
3
1. ShiaoꢀWei Kuoa and FengꢀChih Chang, Prog. Polym. Sci., 2011, 36, 1649–1696.
2. Yiwang Chena and EnꢀTang Kang, Materials Letters., 2004, 58, 3716–3719.
3. YuanꢀJyh Leea, JiehꢀMing Huangb, ShiaoꢀWei Kuoa, JianꢀShing Lua and FengꢀChih
Chang, Polymer., 2005, 46, 173–181.
3
4. YingꢀLing Liu and YiꢀWen Chen, Macromol. Chem. Phys., 2007, 208, 224–232.
3
5. WenꢀYi Chen, Ko Shan Ho, TarꢀHwa Hsieh, FengꢀChih Chang and YenꢀZen Wang,
Macromol. Rapid Commun., 2006, 27, 452–457.

RSC Advances
Page 24 of 24
View Article Online
DOI: 10.1039/C4RA01905A
3
3
6. H. Chen, L. Xie, H. Lu and Y. Yang, J. Mater. Chem., 2007, 17, 1258–1261.
7. G. D. Fu, Z. Yuan, E. T. Kang, K. G. Neoh, D. M. Lai and A. C. H. Huan, Adv. Funct.
Mater., 2005, 15, 315ꢀ322.
3
8. C. H. Lin, S. J. Huang, P. J. Wang, H. T. Lin and S. A. Dai, Macromolecules, 2012, 45,
7
461−7466.