amphiphile polydimethylsiloxane-based networks reinforced with in situ generated silica

Amphiphile Polydimethylsiloxane-Based NetworksReinforced With In Situ Generated Silica

Mihaela Alexandru, Maria Cazacu, Carmen Racles, Cristian Grigoras‘‘Petru Poni’’ Institute of Macromolecular Chemistry, Iasi, Romania

Polydimethylsiloxanes, side functionalized in differentdegrees with chloromethyl groups, were reacted with4,40-bipyridyl and crosslinking occurred by the formationof ionic (bipyridinium) groups. The reactions were car-ried out in a silica sol–gel system, and thus, two net-works were generated simultaneously: amphiphile silox-ane-organic and silica networks. The samples, proc-essed as films, were characterized by Fourier transforminfrared spectroscopy to verify the occurrence of thecrosslinking reactions. Different techniques were alsoused to evaluate the properties: differential scanningcalorimetry for emphasizing the transitions, scanningelectron microscopy, and atomic force microscopy forthe evaluation of the morphology and surface topogra-phy. The modification of the film surface topography,which depends on the solvent polarity, was also empha-sized. The sorption capacities of the water vapors andof liquid solvents (water and chloroform) were investi-gated, and the obtained values proved to be a functionof the polar group’s content. POLYM. ENG. SCI., 51:78–86,2011. ª 2010 Society of Plastics Engineers

INTRODUCTION

For certain applications such as humidity sensors, the

hydrophilicity of the materials must be limited or con-

trolled. Thus, polymers containing hydrophilic groups, such

as ��COOH, SO3H, ��NþR3Cl, etc., are excellent materials

for sensing low humidity, but these cannot operate at high

humidity because of their solubility in water. Such draw-

backs can be avoided by blending them with a hydrophobic

polymer or by chemical modification of the hydrophobic

polymers to generate polar or ionic groups [1].

The hydrophobic character of the polysiloxanes is well

known and commonly used in water repellency. Polysilox-

anes may be modified by the introduction of various hydro-

philic functions to the attached organic radicals, which con-

siderably affect their properties. The great flexibility of pol-

ysiloxane chain makes these functions easy accessible. By

the siloxane modification with the proper groups, the highly

hydrophobic polysiloxanes can be converted in water to

strong swelling or soluble ones. Thus, hydroxyalkyl groups

and quaternary ammonium salt or ionizable tertiary amine

have been introduced in polysiloxanes of various topologies

to provide them hydrophilic properties [2].

Either linear or crosslinked polysiloxanes can be func-

tionalized with hydrophilic groups. The crosslinked struc-

tures can be functionalized with hydrophilic groups before

[3], during [4, 5], or after crosslinking process [6]. The

utilization of crosslinkable polymers able to generate

ionic sites in the crosslinked state is an interesting

approach [1]. Thus, the amination of the oligo(chloro-

methylsiloxane)s with either an excess or an insufficient

amount of 4,40-dipyridyl led to water-soluble or cross-

linked polymers, respectively, which proved to have elec-

trochromic and redox properties, to interact with divalent

metal chlorides, to act as catalysts, or to be useful for the

purification of hormones and antibiotics [5]. Oligo(chloro-

methylsiloxane)s have also been crosslinked with pipera-

zine to obtain materials useful in humidity sensors [4].

Mixed networks containing hydrophobic sequences with

ionic crosslinking points were formed. The reaction of the

halo-alkyl groups with amine was already used in the sur-

face modification of the silica gel [7].

To obtain more easily processable and handling prod-

ucts, we synthesized structures consisting of polysiloxane

crosslinked by ionic groups in a silica-generating sol–gel

system. In recent years, the sol–gel method has success-

fully led to the production of a significant number of

novel organic/inorganic frameworks with tunable design

and suitable properties. The combination of the appropri-

ate processing conditions with the adequate choice of the

organic and inorganic components dictates the morphol-

ogy, molecular structure, and features of the xerogels.

The intense activity in this research domain is because of

the extraordinary implications that derive from the possi-

bility of tailoring multifunctional advanced compounds by

mixing, at nanosize level, both organic and inorganic

components in a single material. The synergy of such

combination and the particular role of the inner organic/

inorganic interfaces enlarge the scope of application of

nanohybrid materials in areas such as electrochemistry,

biology, mechanics, ceramics, electronics, and optics or

environmental protection.

Correspondence to: Maria Cazacu; e-mail: [email protected]

Contract grant sponsor: CNCSIS - UEFISCSU; contract grant number: 5,

PNII–IDEI 233/2007.

DOI 10.1002/pen.21781

Published online in Wiley Online Library (wileyonlinelibrary.com).

VVC 2010 Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—-2011

EXPERIMENTAL

Materials

(Chloromethyl)methyldichlorosilane (CMCl) (bp ¼121.5–1228C, d204 ¼ 1.2858) supplied by ABCR GmbH &

Co was used as received.

Octamethylcyclotetrasiloxane (D4) (purity [ 98%; mp

¼ 16–198C, bp ¼ 1758C/760 mm Hg; n20D ¼ 1.3960, d204¼ 0.955) supplied by Fluka was used as received.

Tetraethoxysilane (TEOS) purchased from Fluka (pu-

rity [98%, bp ¼ 163–167 oC, d204 ¼ 0.933) was used as

received.

Dibutyltin dilaurate (DBTDL) was received from

Merck-Schuchardt, d204 ¼ 1.055 and was used as received.

BiPy obtained from Fluka (purity [99%, mp ¼ 109–

1128C) was used as received.

Purolite CT-175, a styrene–divinylbenzene ion

exchanger with ��SO3H groups (4.1 mequiv g21), was

dehydrated by azeotropic distillation with toluene and

drying in vacuum at 1108C/10 mm Hg.

Poly[(chloromethyl)methylsiloxane]-a,x-diol (MCl)

was synthesized according to a modified procedure

described in Refs. 4 and 8: water (3.6 ml; 0.2 mol) was

slowly added to stirring solution containing 16.35-g (0.1

mol) CMCl in 40-ml diethyl ether (Scheme 1). The reac-

tion mixture was stirred for 4 h at room temperature, after

that the mixture was neutralized by repeated washing, first

with NaCO3 (5% solution in water) and then with water.

The etheric solution was dried by maintaining over CaCl2.

After filtration, the solvent was removed. Yield: 74%

polymer having an average number of molecular mass,

Mn, [determined by gel-permeation chromatographic anal-

ysis (GPC)] of about 2773.

Poly[(chloromethyl)methylsiloxane-co-dimethylsiloxane]-

a,x-diols having different average contents of (chlorome-

thyl)methylsiloxane units within the chain (determined by 1H

NMR spectrometry), according to Table 1, were obtained by

acid equilibration of the MCl with D4 in different ratios [9]

(Scheme 2). The cation exchanger, Purolite CT-175 was used

as a catalyst (2.5 wt% reported to the reaction mixture). The

equilibration was performed at 908C, 10 h after which, the

catalyst was removed by filtration. The reaction mixture was

devolatilized by heating at 1508C/5 mm Hg. The obtained

copolymers are slightly opaque viscous oils. The composi-

tions of the copolymers were estimated by 1H NMR spectra

based on the ratio between the signals assigned to protons

from dimethyl (at 0.60 ppm) and chloromethylsiloxane

(3.35–3.38 ppm) units (Fig. 1).

Measurements

Fourier transform infrared (FTIR) spectra were

recorded by using a Bruker Vertex 70 FTIR instrument.

Analyses were performed in the transmission mode in the

range 400–4000 cm21 at room temperature with a resolu-

tion of 2 cm21 and accumulation of 32 scans. The ground

samples were incorporated in dry KBr and processed as

pellets in order to be analyzed.

The 1H NMR spectra of the CMCl copolymers were

recorded on a BRUKER Avance DRX 400 spectrometer,

using CDCl3 as a solvent.

GPC of the polymer and copolymers was carried out

on an evaporative mass detector instrument (PL-EMD

950) by using dimethylformamide (DMF) as eluant after

calibration with standard polystyrene samples.

Scanning electron microscopy (SEM) was performed

on a TESLA BS 301 SEM at 25 kV with a magnification

of 300–15,000. The images were recorded both on the

SCHEME 1. Obtaining of poly[(chloromethyl)methylsiloxane]-a,x-diol, MCl (m � 25).

TABLE 1. The main characteristics of the prepared copolymers.

Samples CMCl1 CMCl2 CMCl3

Composition, % MCla 18.2 51.2 60.0

Mn 36,300 33,500 21,400

Mw 65,200 64,300 43,500

I ¼ Mw/Mn 1.8 1.9 2.0

a % methylchloromethylsiloxane groups content ¼ 100y/(x þ y).

SCHEME 2. Reaction scheme for poly[(chloromethyl)methylsiloxane-

co-dimethylsiloxane]-a,x-diols synthesis.

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2011 79

film surface and on freeze-fractured surfaces deposed on

Al supports and coated by sputtering with Au thin films

using an EK 3135 EMITECH device.

A SOLVER PRO-M, NT-MDT was used to evaluate

the surface topography and morphology of the samples.

Water vapors’ sorption capacity of the samples has

been measured by using the fully automated gravimetric

analyzer IGAsorp supplied by Hiden Analytical (War-

rington, UK). An ultrasensitive microbalance measures

the weight change as the humidity is modified in the sam-

ple chamber at a constant regulated temperature. System

measurements are fully automated and controlled by a

user-friendly software package.

Differential scanning calorimetry (DSC) thermal analy-

sis was performed on a Pyrus Diamond DSC model

power-compensated differential calorimeter (Perkin

Elmer). The samples, of about 8–10 mg each, were her-

metically sealed in crimped Al pans. Helium was purged

both through the sample and reference cells with a flow

rate of 20 ml min21 to provide an inert atmosphere and a

good thermal conductivity. Before taking the measure-

ments, the differential calorimeter was calibrated within

for the temperature and energy scale. The scans were per-

formed in the temperature range 2150 to 2308C with

208C min21 heating rate. The glass-transition temperature,

Tg, was determined as the midpoint of the heat capacity

change in the second heating scan.

PROCEDURE

Model Reaction

BiPy and MCl, in stoichiometric amounts relative to

the functional (‡N and ��CH2��Cl) groups, were dis-

solved together in CHCl3:acetone (1:2 volume) for a solu-

tion 50% w/v. The reaction mixture was refluxed under

stirring for about 3 h, after which the solvents were

removed in rotavap. The product was successively washed

with chloroform and water and dried. The remained yel-

low-brown solid (M), insoluble in common solvents, was

analyzed by FTIR (Fig. 2a).

Networks Preparation

The chloromethyl side-functionalized polysiloxanes

(CMCl1–CMCl3), and BiPy, in stoichiometric ratio related

to the functional groups, were dissolved together in a

CHCl3:acetone (1:2 volume) mixture for a solution of about

50% w/v. TEOS in molar ratio TEOS: (chloromethyl)methyl-

siloxane units ¼ 2:1 and DBTDL as catalyst (1.5 wt%) were

also added. The reaction mixture was kept at 568C under

stirring for about 3 h, and then was poured in a Teflon dish

and left for the solvents to slowly evaporate and to complete

the crosslinking reactions. The formed colorless and trans-

parent films were peeled off from the substrate. The films

(0.8–1.0 mm) were then kept in the laboratory environment

about 2 months before investigations. The measurements

revealed that the mass of the samples is stabilized after this

time. The films were colored in slight yellow to brown. The

products were analyzed as such (samples P1, P2, and P3) or

after they were extracted in water and chloroform (labeled

as P1t, P2t, and P3t).

Swelling Experiments

The crosslinked samples previously dried in vacuum at

508C were used to determine, by gravimetric method, the

FIG. 1. Illustrative 1H NMR spectrum of the copolymer CMCl3.

FIG. 2. FTIR spectra for: (a) model compound M; (b) initial reaction

mixture for the sample P3 without catalyst and solvent; and (c) P3t.

80 POLYMER ENGINEERING AND SCIENCE—-2011 DOI 10.1002/pen

swelling capacity in two solvents: water and chloroform.

For this, each sample was soaked for 24 h in solvent, af-

ter which was taken out, tapped with filter paper to

remove the excess surface solvent, and weighted. The

weight-swelling percent (%W) was calculated with the

relationship: %W ¼ 100 (wet weight2dry weight)/dry

weight [10].

RESULTS AND DISCUSSIONS

Networks Preparation

Side chloromethyl-functionalized polysiloxanes were

reacted with BiPy (Menshutkin reaction) to obtain net-

works consisting of siloxane hydrophobic backbones

interconnected between them through hydrophilic bridges

with oppositely charged ion pairs [11, 12]. As previously

mentioned, we conducted the reaction in the presence of

silica-generating TEOS to process and handle the products

more easily. Thus, the crosslinking of the polysiloxanes

by their side-chloromethyl groups with the formation of

the bipyridinium salt occurred simultaneously with silica

network formation (Scheme 3). In addition, the polysilox-

ane’s Si��OH end groups can also react with TEOS or its

hydrolysis products, resulting in the interconnection of the

two networks by Si��O��Si groups.

Three polysiloxanes differing by the chloromethyl

groups content (CMCl1–CMCl3) were used to prepare the

samples as codified in Table 2.

Reactions occurred in solution using a CHCl3:acetone

solvent mixture in 1:2 volume ratio. BiPy acts as a nucle-

ophile agent forming bipyridinium salt with chloromethyl

groups side attached to polysiloxane chains. The cross-

linking of polysiloxanes through bipyridinium groups was

verified by a model reaction between BiPy and MCl in

the same conditions. FTIR spectrum of the purified prod-

uct reveals the presence at about 1652 cm21 of the band

assigned to pyridinium group [13], besides the bands at

1601 ([C¼¼N), 1034–1102 (Si��O��Si), 1271

(Si��CH3), 812 (Si��CH3) (Fig. 2a). These bands can

also be found in the spectra of polysiloxane/silica conet-

works at about the same wave numbers, but the bands

specific to BiPy moieties have a smaller intensity (Fig.

2c). The formation of the silica network is proved by the

SCHEME 3. The general scheme for the synthesis of the conetworks.

TABLE 2. The prepared networks.

Samples, Pi

Siloxane

precursor, CMCli Aspect of the product

P1 CMCl1 Colourless, transparent, flexible film

P2 CMCl2 Yellow, transparent, flexible film

P3 CMCl3 Brown, slight opaque, brittle film


fact that the bands at 1168, 1104, and 966 cm21, as well

as those at 2976 and 2890 cm21 (not shown here) belong-

ing to TEOS present in the initial reaction mixture, disap-

peared from the spectrum of the sample P3 (Fig. 2b and

c). The wide shoulder around 1220 cm21 in the spectra of

the sample P3 corresponds to Si��O��Si stretching of

crosslinked silica structures resulted by self-condensation

of Si��OH groups of hydrolyzed TEOS [14]. Also, the

bands group in the range 1023–1104 cm21 grows smother

and narrower at 1032–1092 cm21 in the samples P1–P3,

frequencies where Si��O��Si stretching vibration mani-

fest. The band at 454 cm21 in spectrum of the sample P3

is ascribed to the silica Si��O��Si bending vibration [15].

The band at about 3420 cm21 (not shown) and the

shoulder at 971 cm21 are associated with Si��OH groups

attached to the silica networks formed in the described

conditions. As expected, the pyridinium band increases in

intensity from P1 to P3.

The method used in this paper for the preparation of the

samples is based on the same principle of the method used

for the preparation of room-temperature vulcanization sili-

cones where the crosslinking of the polydimethylsiloxane-

a,x-diol with TEOS catalyzed by organometallic catalysts

occurs by polycondensation reactions requires a few days

for process ending. Both environmental humidity, which

can slowly diffuse deep in the film, and OH-end groups of

the polysiloxane chain constitute the proton providers for

the DBTDL-catalyzed hydrolysis/condensation reactions

involving TEOS. The alcohol generated as a condensation

low-molecular byproduct will migrate outside and as a

result, the equilibrium of the reaction shifts favoring the

formation of the silica. Therefore, the films were extracted

and investigated after long time enough (about 2 months),

when the masses of the samples were stabilized.

In fact, in the final network, the crosslinks by bipyridinium

bridges can coexist with dangling BiPy units bound at one of

the nitrogens only, and unreacted chloromethyl groups. How-

ever, it is difficult to determine the ratio between these spe-

cies because of the insolubility of the material.

Swelling Experiments

Because of the presence of the highly polar groups in

the siloxane network, it would be of interest from both

scientific and application potential to find how these

groups will influence the networks behavior in different

solvents. Both liquids and vapor sorption were investi-

gated.

The polysiloxanes crosslinked by bipyridinium groups

can be associated with recently defined amphiphile conet-

works (APCNs) [16]—two-component networks of inter-

connected hydrophilic/hydrophobic (HI/HO) phases with

co-continuous morphology. However, while in APCNs,

there are covalent bonds between HI and HO segments,

in our networks these are coulombic forces between two

oppositely charged ions. APCNs are considered smart net-

works, sensitive to the changes of the medium. Because

of the amphiphile character, APCNs swell both in water

and in hydrocarbons. Thus, they can be considered hydro-

gels that swell in hydrocarbons [16].

Therefore, we investigated the swelling capacity of the

prepared samples in two solvents having extremely polar-

ities (water and chloroform) by measuring the weight

TABLE 3. Comparative solvent uptake capacities of the networks.

Samples

Solvent uptake capacity, wt%a

Water Chloroform

P1t 0.5 123.8

P2t 6.5 18.0

P3t 58.5 0.8

a After 1 day immersion in solvent at room temperature, calculated

with relationship: %W ¼ 100 (wet weight2dry weight)/dry weight.

FIG. 3. Comparative representations of the rapid water vapors sorption isotherms for the prepared networks:

(a) M, P1t, P2t, and P3t; and (b) P1t, P2t, and P3t.


change due to solvent uptake, relative to the initial dry

mass of the sample (Table 3).

The swelling behavior of a polymer network depends

on a number of factors, like HI/HO ratio in the network,

the presence of ionic or ionizable groups in the polymeric

segments and crosslinking extent of the network [17, 18].

Unlike conventional gels where the amount of water

absorbed decreases with increasing degree of crosslinking,

in this case a reverse dependence can be seen. Thus, it

can be observed that highly crosslinked sample P3 (based

on a high-functionalized polysiloxane precursor, CMCl3)

has the higher water uptake ability (Table 1). This is dif-

ferent from the crosslinked pure polydimethylsiloxane

(PDMS), which has a negligible water sorption capacity

but uptakes chloroform in high amount [4]. Such behavior

is due to the fact that the crosslinker in sample P3 is a

hydrophilic one that favors the water sorption. In addition,

the presence of highly flexible siloxane between crosslink-

ing points permits mobility or relaxation of the macromo-

lecular chains in the matrix, providing enough space for

accommodation of water molecules in the network [17].

However, this amphiphile network is reinforced with

silica, which limits the swelling capacity both in polar

(water) and in nonpolar (chloroform) solvents: 0.5–58.5

TABLE 4. Maximum water vapor sorption values.

Samples Total water sorption, wt% (db)a

P1t 0.998

P2t 1.246

P3t 1.293

M 15.856

a at RH ¼ 90%, T ¼ 258C, dry basis.

FIG. 4. SEM images of the unextracted films: (a) P1 surface; (b) P1 fracture; (c) P3 surface; and (d) P3

fracture.


and 123.8–0.8%, respectively. For simple comparison, for

networks based on the polybutadiene–polydiethylsiloxane

copolymers crosslinked by siloxane bonds, the reported

swelling capacity in toluene was in the range 310–1300%,

depending on the copolymer composition [19].

Water Vapor Sorption Capacity

Water vapors’ sorption capacity for the three samples

at 258C in the relative humidity range (RH) 0–90% was

investigated by using the IGAsorp equipment. The vapors

pressure was increased in 10% humidity steps, with a pre-

established equilibrium time between 30 and 40 min

(minimum time and time out, respectively). At each step,

the weight gained is measured by electromagnetic com-

pensation between tare and sample when equilibrium is

reached. An anticondensation system is available for

vapor pressure very close to saturation. The cycle was

ended by decreasing the vapor pressure in steps to also

obtain the desorption isotherms. The drying of the sam-

ples before sorption measurements was carried out at

258C in nitrogen flow (250 ml min21) until the weight of

the sample was in equilibrium at RH \1%. The sorption/

desorption isotherms registered in these conditions are

presented in Fig. 3.

While the model sample has a water vapor sorption

capacity relative high for a compound containing siloxane

[15.856 wt% (db)], the prepared materials consisting of

crosslinked polydiorganosiloxanes interconnected with

silica by Si��O��Si groups are mainly hydrophobic ones,

this being reflected in the sorption isotherm shapes. It is

presumed that a volumic sorption process consisting of

nonspecific dissolution of water in polymer matrix

(Henry’s law) occurs in such conditions (Fig. 3a). But the

presence of bipyridinium groups in crosslinking bridges

reduces the hydrophobicity, permitting the water vapors’

penetration. As the ionic group’s content increases, a dual

sorption mode can be noticed by the change of the iso-

therm shape (Fig. 3b). The presence of the hydrophilic

sites favors a sorption process governed by the Langmuir

equation [20, 21]. As a result, a slight increase of the total

water-vapor sorption capacity from 0.998 for P1t to

1.293% db for P3t can be noticed (Table 4). The hystere-

sis loops are insignificant.

The samples, processed as films, were investigated by

SEM. Examining the taken images, at first sight, it would

be believed that the domains visible on the surface of the

sample P1 are unreacted BiPy that acts as nucleation cen-

ters (Fig. 4a). However, taking into account that such

domains are not visible in fracture and based on the

known natural tendency of the polysiloxanes to segregate

on the surface, we believe that these are domains formed

by long dimethylsiloxane sequences between crosslinks.

When crosslinking degree increases, as in the case of

sample P3, these domains disappear, and a globular mor-

phology characteristic for the crosslinked structures is

developed both on surface and in fracture (Fig. 4b). The

presence of the globular structure also induces a certain

degree of porosity. The structure is also globular and po-

rous one in sample P2 but having smaller and disordered

domains as compared with P3.

The organization degree changes, depending on the

solvent polarity. When such a sample is swollen in a

selective solvent, the phase, that manifests affinity for

this, gains mobility and permits to the other phase to

arrange in a favorable mode leading to a specific mor-

phology. Two solvents were chosen to demonstrate this

presumption: water and chloroform. SEM images taken

on the film of the sample P2 swollen in these solvents

and subsequently dried are presented in Fig. 5.

It is presumed that in chloroform, the diorganosiloxane

will be the preferred phase. During drying process, as the

FIG. 5. SEM images taken on the surfaces of the P2t films swollen in: (a) chloroform; and (b) water.


chloroform diffuses to the surface and evaporates, is

stimulated migration of the weakly or noncrosslinked

siloxane phase that covers the surface. Spherical forma-

tions with diameter of about 1 lm (probably formed by

low-crosslinked moieties) can be seen on an amorphous

surface (Fig. 5a). These formations migrated on surface

leaving perfectly spherical or semispherical pores in the

films as were emphasized by atomic force microscopy

(AFM) images, registered in semicontact mode compara-

tively on the raw and extracted films (Fig. 6a and b).

Thus, the water acts contrary that the surface morphology

is conferred by the polar organic moieties having a high

self-organization capacity (Fig. 5b).

As the functionalization degree of the siloxane precur-

sor increases, the structuration level of the film increases

such as, although the phase image of the sample P3

reveals the biphasic morphology, the domains are smaller

(Fig. 6c).

Generally, from DSC curves, it was noticed that the Tgvalues tend to increase with the increase in the presumed

crosslinking degree, starting from P1 to P3 (Fig. 7). The

crystallization process disappears during the scans of the

FIG. 6. AFM images of the film surfaces: (a) P2 (left, 3D image; right, 2D image), average roughness, Sa

¼ 1.29 nm; (b) extracted P2 (left, 3D image; right, 2D image), average roughness, Sa ¼ 10.07 nm; and (c)

P3 (left, 3D image; right, phase image), average roughness, Sa ¼ 3.77 nm.


samples P2 and P3. In the same time, it can be noticed a

decrease of Cp for the glass transition, which could be an

effect of the decrease of polymer chain, dynamics because

of the crosslinks (Table 5). From the DSC curves, it could

be noticed only for sample P1, the presence of an endo-

thermic peak around 2538C, assigned to the melting pro-

cess specific for polysiloxanes. A reorganizing of the

structure above its glass-transition temperature, which is

also a normal process for semicrystalline polysiloxanes,

precedes this melting. For the other samples (P2 and P3),

an increase in the Tg value was noticed, being because of

the decrease of the polymer chain mobility. It was noticed

that there were no major differences between the samples

extracted and unextracted, Pi (i ¼ 1–3) and Pit (i ¼ 1–3)

regarding their thermal behavior.

CONCLUSION

New structures consisting of poly[(chloromethyl)me-

thylsiloxane-co-dimethylsiloxane]-a,x-diols crosslinked

by bipyridinium bridges and by silica network were pre-

pared. The first is amphiphile one inducing specific

behaviors to the overall system. Thus, the prepared sam-

ples proved to uptake water or water vapors, but in lim-

ited amount because of the presence of the hydrophobic

segments, which instead permit the swelling in organic

solvents. The incompatible segments interconnected in the

APCNs can organize in domains having different shapes

depending on the solvent polarity as emphasized by SEM

and AFM. The transitions were also very sensible to the

presence of the crosslinking organic bridges. The con-

straints imposed by the coexistence of the silica network

diminish the stimuli-responsive behaviors. Instead, the

obtaining of freestanding reinforced films is permitted

because of the presence of the silica in system.

ACKNOWLEDGMENTS

The authors thank Dr. Aurelia Ioanid for taking SEM

images and help given in their interpretation.

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(2006).

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FIG. 7. DSC traces for the samples.

TABLE 5. The main parameters of the DSC curves registered for the

samples before and after extraction.

Sample Tg (8C)DCp

(J/g 8C)

Exo

(cold crystallization)

(J/g)

Endo

(melting)

(J/g) Tm (8C)

P1 2118.46 0.307 22.66 2.50 254.0

P1t 2120.41 0.189 22.30 1.95 252.7

P2 2118.25 0.140 — — —

P2t 2118.35 0.158 — — —

P3 289.12 0.096 — — —

P3t 289.21 0.100 — — —


amphiphile polydimethylsiloxane-based networks reinforced with in situ generated silica

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