European Polymer Journal 40 (2004) 57–62

www.elsevier.com/locate/europolj

Synthesis of new polysilane–crown ether

Liviu Sacarescu *, Rodinel Ardeleanu, Gabriela Sacarescu, Mihaela Simionescu

Institute of Macromolecular Chemistry ‘‘P.Poni’’, Aleea Gr.Ghica Voda 41A, 6600 Iasi, Romania

Received 16 July 2003; received in revised form 5 September 2003; accepted 16 September 2003

Abstract

This paper presents the synthesis of new polysilane with pendant crown ether groups. The polymer was obtained

through the addition reaction of 40-allylbenzo-15-crown-5 to poly[methyl(H)-co-methylphenylsilane] copolymer in

anhydrous toluene solution using hexachloroplatinic acid as a catalyst. The allyl functionalization of the crown ether

was achieved by the coupling of the crown ether bromide with allyl magnesium chloride. The availability of the crown

ether sites in complexation reactions with Cu(II) cations was tested.

The chemical structures of all products and intermediates were studied using spectral methods (IR, 1H-NMR,13C-NMR, UV), gel permeation chromatography (GPC) and thermogravimetric analysis (TGA).

� 2003 Elsevier Ltd. All rights reserved.

Keywords: Polysilane; crown ether; Polymer–metal complex; Hydrosilylation

1. Introduction

Conjugated polymers, which are intrinsic semi-con-

ductors because of their delocalized p-electrons, have

attracted much research effort in the last 15 years. Most

of the conjugated polymers studied today have a regular

alternation of single and double bonds like in the ori-

ginal model polymer polyacetylene.

A real current challenge for physicists and chemists is

the design of polymers which match the properties of

semi-conductors and metals for modern electronic ap-

pliances.

In contrast to the conjugated polymers, the redox

polymers possesses localized electroactive sites. These

polymers contain a redox-active transition metal based

pendant group covalently bound to the polymer back-

bone. Their specific electrochemical properties were

often used to obtain chemically modified electrodes.

Oligo- and polysilanes are a different class of mate-

rials which have been subjected to many investigations

[1–4]. The specific r-electron delocalization is similar to

* Corresponding author. Fax: +40-232-211299.

E-mail address: livius@icmpp.tuiasi.ro (L. Sacarescu).

0014-3057/$ - see front matter � 2003 Elsevier Ltd. All rights reserv

doi:10.1016/j.eurpolymj.2003.09.012

the alternating single and double bonds in polyenes and

gives polysilanes the character of conjugated polymers

[5–10]. Because of the spatially delocalized band-like

electronic structure, in this case the conductivity appears

as a result of the charged defects motion within the

conjugated framework [11–14].

New polymers which combine both mechanisms of

conductivity will be of great interest in the development

of new materials for electronic appliances. Therefore the

aim of this paper is to present a new conjugated-redox

hybrid polymer built onto a polysilane backbone. A

benzo-15-crown-5 ligand was selected as a redox- active

site and attached to the polymeric chain.

Studies relating to the synthesis and properties of

polysilane–crown ethers are rare but there are an im-

portant number of papers which present several experi-

mental approaches for enclosing crown ethers within

different polymeric supports. Therefore Chen and You

[15] transformed the crown ether into a silane monomer

through the hydrosilylation reaction of trichlorosilane

with 4-allylbenzo-15-crown-5. A subsequent hydrolysis

reaction led to the formation of polysiloxane-crown

ether. An unique series of compounds was built by Nolte

using the same method [16]. Starting with 4,5-dic-

yanobenzoethers he managed to obtain dichlorosilanes

ed.

58 L. Sacarescu et al. / European Polymer Journal 40 (2004) 57–62

with phthalocyanide structure. Some other reports pre-

sented the synthesis of crown ethers with unsaturated

hydrocarbon side groups. These were used in addition

reactions with polysiloxanes containing Si–H groups

[17–19].

To obtain these materials the proper functionaliza-

tion of both the polymer and crown ether must be car-

ried out. Therefore we have decided to start with the

halogenation reaction of the crown benzoethers. This

could be performed through N-bromsuccinimide [20] or

molecular iodide and bromide action over the appro-

priate unsubstituted ligands [21–23]. Further the func-

tional crown ether could be modified and used for the

catalytic addition reaction with the Si–H groups en-

closed within the polymer chain.

2. Experimental section

2.1. Materials

Benzo-15-crown-5 (99%, B15C5) and N-bromosuc-

cinimide (99%) were purchased from Fluka and used as

received. Allyl magnesium chloride––Grignard reagent

(2.0 M solution in tetrahydrofurane) was purchased

from Aldrich. 40-Bromobenzo-15-crown-5 was obtained

in laboratory through the following experimental pro-

cedure [24].

N-bromosuccinimide, 2 g was added under stirring to

the benzo-15-crown-5 (3 g, 0.01 mol) solution in 10 ml

CCl4. After refluxing for 1 h the reaction mixture was

cooled and filtered to remove the precipitate. The solvent

was removed through vacuum distillation and the re-

maining oily product was recrystallized from n-heptane.

Yield 1.8 g (56%) of white solid with mp¼ 66–68 �C.1H-NMR spectral analysis of the product (d ppm,

TMS, CDCl3): 3.75–4.10 (m, 16H, –O–CH2–CH2–O–);

6.61 (d, 1Har); 7.12 (d, 1Har); 7.19 (s, 1Har).

Scheme 1. Synthesis of 40-allylbenzo-15-crown-5.

2.2. Apparatus

Infrared spectrum was obtained using KBr pellets

with a SPECORD M80 spectrophotometer.1H-NMR and 13C-NMR spectra were obtained using

a Bruker AC-80 HL spectrometer.

Ultraviolet–visible absorption spectra were recorded

at room temperature on a Carl Zeiss Jena SPECORD

M42 spectrophotometer in 10 mm quartz cells.

Gel permeation chromatography (GPC) experiments

were carried out in tetrahydrofurane (THF) solution at

30 �C, at a flow rate 1 cm3/min. using a Spectra Physics

8800 gel permeation chromatograph with two PL-gel

packed columns (103 and 500 �AA). An UV116 spectro-

photometer and a R132 differential refractometer were

used as detectors. The calibration was made with 13

polystyrene etalons with narrow molecular weight dis-

tribution.

Thermogravimetric analysis was performed on a

MOM Paulik-Paulik-Erdey derivatograph at a 10�/min

heating rate, in air.

2.3. Synthesis of 40-allylbenzo-15-crown-5

40-Allylbenzo-15-crown-5 was synthesized through

the Grignard technique using allyl magnesium chloride

and 40-bromobenzo-15-crown- 5 (Scheme 1) [15].

A three-necked round-bottom reaction flask pro-

vided with mechanical stirrer, dropping funnel and

condenser were dried in an inert anhydrous argon at-

mosphere for 4 h. The reaction flask was charged with

50 ml of THF solution containing 3.47 g (0.01 mol) of 40-

bromobenzo-15-crown-5. Then 5.5 ml of allyl magne-

sium chloride solution was added, dropwise, and stirred

for 2 h at room temperature. After filtration of the

precipitate the clear THF solution was vacuum distilled

to remove the solvent. The resulting white solid product

was recrystallized from hexane. Yield¼ 77% (mp¼ 62–

64 �C).IR Spectrum (k, cm�1) shows the following charac-

teristic absorption bands: 3078–931, C–Har; 1638, C@C;

1592–667, polyether cycle; 1255, 1218, –H4C6–O–C;

1131, 1053, C–O.1H-NMR spectral analysis was presented in Fig. 1 (d

ppm, CDCl3): 3.22 (d, 2H); 3.6–4.2 (m,16H); 4.8 (d, 2H);

5.5–5.8 (m, 1H); 6.5–6.72 (m, 3H).13C-NMR spectral analysis (d ppm, CDCl3): 41.30

(C3); 69.02 (C8); 112.2 (C5;7); 120.1 (C6); 114.2 (C1);

134.8 (C4); 137.8 (C2); 148.7 (C9).

2.4. Synthesis of poly[methyl(H)-co-methylphenylsilane]

The synthesis of the poly(methylphenylsilane) co-

polymer with Si–H groups and narrow molecular

Fig. 1. H-NMR spectrum of 40-allylbenzo-15-crown-5.

Fig. 3. TGA trace for polysilane–crown ether.

L. Sacarescu et al. / European Polymer Journal 40 (2004) 57–62 59

weights distribution was performed through a homoge-

neous coupling technique of methylphenyldichlorosilane

with methyl(H)dichlorosilane [25].

30 cm3 of a 0.2 mol/dm3 THF solution of sodium/

potassium alloy complex with 18-crown-6 was titrated

with the THF solution (0.2 mol/dm3) of a CH3HSiCl2/

CH3C6H5SiCl2 equimolar mixture at )75 �C in an argon

atmosphere until discoloration of the blue metal solu-

tion occurred. Next the reaction was quenched with 2

cm3 of methanol. The solvent was then evaporated. The

remaining product was extracted two times with 5–10

cm3 of chloroform and combined chloroform extracts

were washed with water. Finally a white solid polymer

was obtained by precipitation from the chloroform so-

lution with 100 cm3 of methanol. Yield: 25%. After

separation of polymer, 15 cm3 of distilled water was

added to the filtrate and a second fraction was obtained.

Infrared spectrum of the polymer (Fig. 2) shows the

following characteristic absorption bands (k, cm�1):

3070–3000, C–Har; 2980, 2860 C–H; 2080, Si–H; 1455,

1100 Si–C6H5; 1250, 880 Si–CH3; 750, 705 Si–C; 460, Si–

Si.1H-NMR spectrum (d ppm, CDCl3): 0.18 (broad,

CH3); 3.64 (sharp, Si–H); 7.15 (broad, –C6H5).

GPC analysis was performed in solvent THF. The

Si–H functionalized polysilane shows an unimodal mo-

Fig. 2. IR Spectrum of poly[methy

lecular weights distribution with Mw ¼ 5280 and

Mw=Mn ¼ 1:20.Thermogravimetric analysis was performed in air

within a temperature range of 20–600 �C and a heating

rate of 10 �C/min (Fig. 3). The thermal decomposition of

the polyhydrosilane structure shows a single stage

starting at 350 �C. Ashes: 73%.

2.5. Synthesis of polysilane–crown ether

The polysilane–crown ether polymer (PSEC) was

obtained through the addition reaction of the allyl-

functional crown ether to the Si–H groups of the po-

lysilane (Scheme 2) [26].

A mixture of 40-alyllbenzo-15-crown-5 (4.8 g, 15.6

mmol), polyhydrosilane copolymer (2.64 g, 0.5 mmol),

and 0.2 ml hexachloroplatinic acid solution in isopro-

panol (0.1 mol/l) dissolved in freshly dried THF (20 ml)

was stirred at room temperature for 2 h and then ref-

luxed for another 20 h. The addition reaction was IR

monitored by measuring the intensity of the Si–H

l(H)-co-methylphenylsilane].

Scheme 2. Synthesis of polysilane–crown ether.

Fig. 5. GPC analysis of polysilane–crown ether.

Fig. 6. 13C-NMR Spectrum of polysilane–crown ether.

60 L. Sacarescu et al. / European Polymer Journal 40 (2004) 57–62

characteristic absorption band at 2150 cm�1. Finally the

solvent was removed through vacuum distillation and

the obtained solid product was washed several times

with n-hexane then dried. Yield: 67% (5.9 g).

IR Spectrum of polysilane–crown ether displays the

following characteristic absorption bands (k, cm�1):

3050–3000, C–Har; 2970–2910, C–H; 2150, Si–H; 1600,

1513 and 1458 Car; 1265, 805 Si–CH3; 1130, 935 C–O–

C; 495, Si–Si.1H-NMR Spectrum is shown in Fig. 4 (d ppm,

CDCl3): 0.15, Si–CH3; 1.5 and 2.65, –CH2–CH2–; 4.0, –

O–CH2–; 4.84, Si–H; 6.88–7.65, Har.

The GPC analysis of the synthesized polysilane–

crown ether (Fig. 5) shows Mw ¼ 8200 corresponding to

a 35.6% content of organic segments. The amount of

B15C5 moieties within the polymeric chain calculated

from 1H-NMR resulted also in a 39.08% content of

crown ether segments (1:11 polysilane/crown ether mo-

lar ratio).13C-NMR Spectrum is shown in Fig. 6 (d ppm,

CDCl3): )2.5 (C10); 16.11 (C1); 28.37–36.65 (C2;3); 69.05

(C8); 111.2 (C5;7); 122.1–132.8 (C6;4;11); 148.7 (C9).

Thermogravimetric analysis was performed in air

within a temperature range of 20–600 �C and a heating

rate of 10 �C/min (Fig. 3). First stage: 200–350 �C de-

composition of the organic part; second stage: 350–500

�C decomposition of the polysilane structure. Ashes:

44%.

Fig. 4. 1H-NMR Spectrum of polysilane–crown ether.

The availability of the crown ether sites in com-

plexation reactions with Cu(II) cations was deter-

mined through UV–VIS spectral titration. A THF

solution of the polysilane–crown ether (9.5 · 10�5 M

in terms of B15C5) was treated with various amounts

of Cu2þ cations (Cu-acetate stock solution in ethanol,

1 · 10�3 mol/l) and maintained under gentle reflux for

2 h. UV spectral analysis was then performed re-

cording the absorbance change observed at 227 nm

(Fig. 6).

L. Sacarescu et al. / European Polymer Journal 40 (2004) 57–62 61

3. Results and discussion

A new polysilane–crown ether was synthesized

through the addition reaction of 40-allylbenzo-15-crown-

5 to polyhydrosilane in the presence of the hexachloro-

platinic acid catalyst.

The low molecular weight polyhydrosilane with a

narrow molecular weight distribution was obtained

through a homogeneous coupling process from

methyl(H)dichlorosilane and methyl(phenyl)dichlorosi-

lane [25].

40-Allylbenzo-15-crown-5 ether was obtained through

the coupling reaction of the allyl magnesium chloride

and 40-bromobenzo-15-crown-5.

IR, 1H- and 13C-NMR spectral analyses were per-

formed to investigate the chemical structure of the 40-

allylbenzo-15-crown-5. The IR spectrum showed little

changes especially in the 800–1400 cm�1 region. These

resulted from the superposition of the allyl group CH

absorption bands with the CH absorption band of the

ethereal ring.

More clearly the 1H-NMR spectrum shows the

presence of the allyl group protons at: 3.3 ppm for sat-

urated CH2; 4.81 and 5.9 ppm for unsaturated CH2 and

CH respectively. The crown ether’s –O–CH2– group

protons appeared around 4 ppm (Fig. 1).

The 13C-NMR spectral analysis confirmed the pro-

posed structure. The specific signals of the allyl group

appeared at 41.30 ppm (–CH2–), 114.2 ppm (ACH@)

and 137.8 ppm (@CH2). The chemical shifts of the O–

CH2– groups could be observed at 69.02 ppm.

The polysilane–crown ether was obtained through

the addition reaction of Si–H groups of polyhydrosilane

to the allyl groups of the 40-allylbenzo-15-crown-5 in the

presence of the hexachloroplatinic acid catalyst.

IR spectrum of the polysilane–crown ether shows

that some of Si–H groups remained unreacted probably

because of the sterical hindrances. This disadvantage of

the procedure could be useful meanwhile because ex-

posure to higher temperatures in a later stage should

lead to new kinds of thermally stable polycarbosilanes

with embedded crown ether segments. Also, residual Si–

H groups could be useful for supporting the polysilane–

crown ether thin layers onto solid porous materials.

The IR spectrum displays the specific absorption

bands of the Si–CH3 group at 805 and 1265 cm�1. Also,

the absorption bands of the aromatic ring carbon atoms

are present at 1458, 1513 and 1600 cm�1, and those of

the specific C–O–C bonds of the polyether ring at 935

and 1130 cm�1. The C–H bond absorption bands appear

in the same region as in the crown ether monomer, at

2910–2970 cm�1. The absorption band at 2150 cm�1

confirms the presence of Si–H groups.

Concerning the 1H- and 13C-NMR spectral analysis,

literature data indicate that polyhydrosilanes give broad

resonance peaks within the methyl groups region [27].

This particularity is present also in the case of the syn-

thesized polysilane–crown ether and could be the result

of a conformational effect combined with the shielding

of the neighboring phenyl groups [28].

The 1H-NMR spectral analysis of the polysilane–

crown ether confirmed the proposed chemical structure

(Fig. 4). The aromatic protons H5;6;7 of the benzene

nuclei attached to the polyether ring and those of the

phenyl groups substituents at the silicon atoms give a

multiplet signal within 6.88–7.65 ppm. The unreacted

Si–H groups’ protons give a specific singlet peak at 4.84

ppm. The protons of the –O–CH2– ring and the –CH2–

protons of the propyl bridge show an overlapping

chemical shift around 4.2 ppm. The H2;3 protons of the

propylene bridge could be noted at 0.8 and 1.85 ppm.

The methyl protons of the Si-CH3 group give a broad

specific peak at 0.15 ppm.

In the 13C-NMR spectrum (Fig. 6) the characteristic

chemical shifts of the ethereal ethylene group appear at

69.05 ppm. The propyl group gives specific signals at

16.11 ppm (–Si–CH2–) and within 28–36 ppm (–CH2–

CH2–Car).

The GPC analysis of the synthesized polysilane–

crown ether shows an unimodal molecular weights

distribution with Mw ¼ 8200 (Fig. 5). The synthesis

procedure of polyhydrosilanes leads to the formation of

small amounts of cyclic oligomers which could be no-

ticed in the low molecular weight region. These cyclic

byproducts appeared mainly at the beginning of the

reaction because of the competition between the end-

biting reactions and the two-electron transfer one [25].

The polysilane–crown ether thermal decomposition

presents two differential peaks (Fig. 3): the first one

(within 200 �C–350 �C) was assigned to the organic

segment destruction process. Within this period about

27% of the sample weight is loss. This indicates that the

ethylene bridge scission take place first affecting

the crown ether cyclic structure. The second stage of the

thermal decomposition starts over 350 �C and represents

the transformation process of the polysilane mainly into

SiO2 (44%). Comparing the weight losses in both stages

it is possible to estimate that the organic part content

within the polymeric chain is close to 30% and therefore

corresponds to the 1:11 polysilane/crown ether molar

ratio.

A UV–VIS spectral titration of the polysilane–crown

ether with Cu (II) cations was performed to estimate the

availability of B15C5 moieties in complexation reactions.

The UV/VIS spectrum of both the polymer–metal

complex and free ligand is shown in Fig. 7. The ab-

sorption bands at 227 nm and 273 nm were assigned to

ligand to metal charge transfers (B15C5fiCu). The 320

nm absorption band resulted from both the conjugative

interactions between phenyl substituent and the silicon

backbone which acts as a r–r� or r–p chromophore

and the conformational strain.

Fig. 7. UV absorption spectra of free ligand (– – –) and B15C5

Cu(II) complex (––).

Fig. 8. Absorbance change measured at 227 nm for PSEC

(9.5· 10�5 M in terms of B15C5 concentration) with various

amounts of Cu(II) ion.

62 L. Sacarescu et al. / European Polymer Journal 40 (2004) 57–62

Because B15C5 is randomly attached to the polysi-

lane chain, complexation of two or more crown ether

moieties to one metal ion is not likely because of the

conformational strain imposed by the polymer back-

bone. The spectral titration data presented in Fig. 8 re-

veals that the B15C5 groups form a 1:1- type complex

with Cu(II) cations. From the equivalence point it was

calculated that a maximum amount of 54% of the crown

ether moieties within the polysilane backbone could

participate to the complexation process.

4. Conclusion

A new hybrid conjugated-redox polymer was ob-

tained through attachment of benzo-15-crown-5 moieties

onto a polysilane copolymer backbone. Experimental

data on the synthetic procedure and characterization of

intermediates and product were presented and discussed.

The complexation ability and availability of the crown

ether moieties within the polysilane chain was studied

through UV spectral titration with Cu(II) cations.

The novel polysilane–crown ether could be used to

develop new organic semi-conductors for electronic ap-

pliances. Further work will explore the electrochemical

properties of the material.

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