Thermochromism and solvatochromism of non-ionic polar polysilanes

Article abstract of DOI:10.1016/S0022-328X(00)00433-2

Polar polysilanes bearing ethereal side groups [{CH₃-Si-(CH₂)_m-O-(CH₂CH ₂O)_n-CH₃}_x, m = 3-5 and n = 0-3}] were prepared and were found to be soluble in a wide range of polar solvents. UV spectroscopic behavior is highly dependent on the nature of the solvents used but no simple relationship between λ_max and specific solvent parameter is found. Small molar absorbance (ε < 10 000/Si-Si bond) suggests that water-soluble polysilanes take highly entangled form in water. Solvatochromic redshift is induced by THF in aqueous solution of water-soluble polysilanes. This solvatochromism is ascribed to disentanglement the non-polar main chain by non-polar solvent. Another type of solvatochromic shift is also caused by (CF₃)₂CHOH (HFIP) in non-polar solvent (benzene, CH₂Cl₂) or even in (CH₃)₂CHOH solution, where higher HFIP concentration brings about longer wavelength absorption. This type of solvatochromism is originated by strong hydrogen bond formation between the ethereal side groups and HFIP. Because non-dissociative nature of HFIP-concerned hydrogen bonding, increased bulkiness of the side moieties brings about disentanglement. Polysilanes 1-5, though having long side chains, show thermochromism of continuous spectral shift on cooling. The same λ_max value in thermochromism and solvatochromism indicates that nearly the same degree of disentanglement is caused by HFIP and thermally.

Full text of DOI:10.1016/S0022-328X(00)00433-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 611 (2000) 45–51
Thermochromism and solvatochromism of non-ionic polar
polysilanes
Kunio Oka a,*, Naofumi Fujiue b, Saburo Nakanishi b, Toshikazu Takata b,
Robert West c, Takaaki Dohmaru a
a Research Institute for Ad6anced Science and Technology, Osaka Prefecture Uni6ersity, 1-2 Gakuencho, Sakai, Osaka 599-8570, Japan
b College of Engineering, Osaka Prefecture Uni6ersity, 1-1 Gakuencho, Sakai, Osaka 599-8570, Japan
c Department of Chemistry, Uni6ersity of Wisconsin, 1101 Uni6ersity A6enue, Madison, WI 53706, USA
Received 29 February 2000; accepted 30 March 2000
Abstract
Polar polysilanes bearing ethereal side groups [{CH3ꢀSiꢀ(CH2)mꢀOꢀ(CH2CH2O)nꢀCH3}x, m=3–5 and n=0–3}] were pre-
pared and were found to be soluble in a wide range of polar solvents. UV spectroscopic behavior is highly dependent on the
nature of the solvents used but no simple relationship between umax and specific solvent parameter is found. Small molar
absorbance (mB10 000/SiꢀSi bond) suggests that water-soluble polysilanes take highly entangled form in water. Solvatochromic
redshift is induced by THF in aqueous solution of water-soluble polysilanes. This solvatochromism is ascribed to disentanglement
the non-polar main chain by non-polar solvent. Another type of solvatochromic shift is also caused by (CF3)2CHOH (HFIP) in
non-polar solvent (benzene, CH2Cl2) or even in (CH3)2CHOH solution, where higher HFIP concentration brings about longer
wavelength absorption. This type of solvatochromism is originated by strong hydrogen bond formation between the ethereal side
groups and HFIP. Because non-dissociative nature of HFIP-concerned hydrogen bonding, increased bulkiness of the side moieties
brings about disentanglement. Polysilanes 1–5, though having long side chains, show thermochromism of continuous spectral shift
on cooling. The same umax value in thermochromism and solvatochromism indicates that nearly the same degree of disentangle-
ment is caused by HFIP and thermally. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Thermochromism; Solvatochromism; Polar polysilanes
ing a possible potential application for a photo-resist
[2], a non-linear optical material [3], a radical reaction
initiator [4], an electron-luminescence material [5] and
so on. Strong absorption in the UV region is one of the
most interesting physical properties among the diverse
properties that delocalized sigma electrons along a sili-
con backbone show. Degree of silicon catenation and
dihedral angle of silicon chains are the principal factors
to determine the UV characteristics of polysilanes [1,6].
Because of the flexible nature of an SiꢀSi single bond,
the backbone conformation is sensitive to external cir-
cumstances and thus results in various chromotropisms
[1,6]. Thermochromism [7] and piezochromism [8] are
among the most well known and have been studied
extensively in conjunction with structure of polysilanes.
Here, side chains on the silicon backbone are known to
play the important role on determining the type of
chromotropism. However, simple alkyl or aryl groups
1. Introduction
Polyorganosilanes are known to have unusual elec-
tronic and optical properties which arise from the delo-
calized sigma electrons along their backbones [1]. They
have been recognized as a new advanced material hav-
Scheme 1. Synthetic route for polysilanes 1–3.
* Corresponding author. Fax: +81-722-549935.
E-mail address: oka@riast.osakafu-u.ac.jp (K. Oka).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00433-2

46
K. Oka et al. / Journal of Organometallic Chemistry 611 (2000) 45–51
recently synthesized [16,17] and were found that these
polymers showed unusual polar characteristics. We
have, thus, studied the solvent dependent UV spectro-
scopic behavior of these polar polysilanes by comparing
thermochromic behavior.
Scheme 2. Synthetic route for polysilanes 4 and 5.
2. Results and discussion
Table 1
Yields, molecular weights, and solubilities a of polar polysilanes
2.1. Synthesis of polar polysilanes
Polysilane
n-Hexane
Toluene
THF
MeOH
H2O
Polar polysilanes 1–5 having ethereal side groups
were prepared by reactions depicted in Schemes 1 and
2. Monomers for polysilanes 1–3 were prepared by
hydrosilylation reactions of the corresponding allyl
ether with methyldichlorosilane. Those for polysilane 4
and 5 were prepared by Grignard reactions with corre-
sponding alkyltrichlorosilane. Yields, molecular
weights, and solubilities in representative solvents are
summarized in Table 1. Polysilanes 2–5 having more
than two oxygen atoms in the ethereal side group are
highly polar and are soluble in methanol or even in
water. Therefore, the ordinary procedure to isolate
and/or fractionate polysilanes was inapplicable to
polysilanes 2–5. Sodium chloride, after the reaction
was quenched with methanol and then water, was firstly
removed by dialysis using a cellulose acetate film. Re-
peated fractionations from dibutyl ether gave polysi-
lanes 2–5 with mono-modal pattern in GPC and good
polydispersity. Polysilanes 1–5 have more than 50 sili-
con atoms in their main chains and thus are suitable for
studying as polymeric materials.
1
2
3
4
5
X
X
ꢁ
X
X
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢁ
ꢀ
ꢀ
ꢀ
ꢀ
X
ꢁ
ꢀ
ꢀ
ꢀ
a ꢀ, soluble; ꢁ, partially soluble; X, insoluble.
Fig. 1. UV spectra of polysilane 3 in various states.
are commonly adopted as the side chains and, thus,
they show limited types of interaction with their envi-
ronment. Thermochromic behavior of non-polar polysi-
lanes is explained as the result of dispersion interaction
of delocalized sigma electrons with surrounding polariz-
able medium including side groups or by co-operative
transition from one ordered form to other [9]. When
functional groups such as polar side groups are intro-
duced on silicon chains, extra function and interaction
can be added to sigma conjugation. Several polysilanes
with polar side chains including quarterly ammonium
[10], end-hydroxyl group [11], and ether groups [12]
have been reported so far. These polysilanes have
mostly been utilized to prepare LB films at water ꢀ air
interface. Miller [13] reported that polysilanes having
p-alkoxyphenyl side moieties showed solvent dependent
UV spectral behavior. On the other hand, oli-
go(ethyleneglycol) groups have been recognized as non-
ionic parts to induce polar interactions with ionic
species. Phosphazenec [14] and siloxane polymers [15]
bearing this side groups were synthesized recently and
showed the expected polar characteristics. Similarly,
several polysilanes bearing ethereal side groups were
2.2. UV spectral characteristics of water-soluble
polysilanes
Polysilane 3 gives clear aqueous solution and is also
soluble in various polar solvents. Thus, we have studied
UV spectral behavior of polysilane 3 as a representative
material. Fig. 1 shows UV spectra of polysilane 3 in
various states. Polysilane 3 gives broad absorption in
solid state and in aqueous solution compared with that
in THF. Because THF and water are freely miscible
each other, we have examined UV spectral behavior of
polysilane 3 in the mixed solution and found new
solvatochromism as shown in Fig. 2. Redshift is in-
duced as THF concentration is increased. This suggests
that polysilane 3 takes more extended form in THF
than in aqueous solution, and vise versa [18]. Because
of non-polar nature, the silicon main-chain must take
more extended form in non-polar solvent than in polar
solvent but takes shrunk form in water. The highly
polar side groups behave oppositely.
Since polysilane 3 was expected to have more polar
interaction s with polar species, spectral behavior was
further studied in aqueous solution. No spectral shift

K. Oka et al. / Journal of Organometallic Chemistry 611 (2000) 45–51
47
Fig. 2. Solvatochromism of polysilane 3 in THF–H2O system.
Fig. 3. UV spectra of polysilane 3 in alcoholic solvents.
was induced either by change of H+ or Li+ ion concen-
tration, suggesting that polysilane 3 does not form any
stable ionic complexes in aqueous solution. Blue shift
(ca. 5 nm) was, however, induced when europium chlo-
ride was added to aqueous solution of polysilane 3.
This indicates that complex formation with Eu3+ re-
sults in more shrunk form for polysilane 3.
UV spectral data of polysilane 3 are summarized in
Table 2 together with several solvent parameters. umax
value ranges from 299 to 322 nm and m/SiꢀSi from 4280
to 9520. No simple relationship between UV spectral
data and any solvent parameters was found. It is,
however, noticeable that halogenated solvents give
longer umax than others. 1,1,1,3,3,3-Hexafluoro-2-
propanol (HFIP) shows amongst the most remarkable
feature to give umax at long wavelength. m in HFIP is
almost the same value with that of poly(methylphenyl-
silane) or poly(methylhexylsilane) in hexane, indicating
that polysilane 3 takes similarly extended chain struc-
ture. Since this is out of expectation from the result in
Fig. 2, different mechanism from simple polar–non-po-
lar interaction as in Fig. 1 must be attributed to induce
the unusual spectral shift. Since HFIP is known to
make strong hydrogen bonding with ethereal oxygen
atoms [19], polysilane 3 forms strong hydrogen bonding
with HFIP at the ethereal side groups as shown by
H-NMR (vide infra). Other hydrogen bonding donors
are expected to induce similar spectral shift. Fig. 3
depicts the effect of hydroxyl group on UV spectral
behavior of polysilane 3. It is obvious that halogenated
alcohols induce red-shift more effectively than ordinary
alcohols, and HFIP is confirmed to be the strongest
Table 2
UV data for {CH3Oꢀ(CH2CH2O)3ꢀ(CH2)3ꢀSiꢀCH3}n and solvent parameters
b
d
e
Solvent
umax (nm)
m (O.D.) a
m
Is (eV) c
n
(n2−1)/(n2−2)Iav
H2O
THF
MeOH
CH3CH2OH
p-Dioxane
CH3CN
AcOAm
Diglyme
CHCl3
CH3CONHCH3
BuNH2
o-C6H4Cl2
Et2O
Toluene
Ethyl oxalate
C6H13OH
(CF3)2CHOH
CF3CH2OH
DMSO
299.6
310.4
306.2
305.6
309.4
306.2
305.5
307.4
315.8
305.2
308.4
314.9
304.8
311.4
304.2
306.2
322.4
317
4280
6110
5820
5660
6050
5950
6950
5700
6440
5090
5690
5550
5640
5530
5550
5160
9520
8930
4730
4670
72.39
7.58
32.7
24.55
2.209
37.5
12.59
9.54
10.85
10.48
9.13
12.22
10.01
9.70
11.42
8.90
1.33250
1.40496
1.32652
1.35941
1.42025
1.31416
1.4028
1.4043
1.4293
1.4286
1.3987
1.54911
1.34954
1.49413
1.41023
1.4161
1.435
0.989
0.859
0.923
1.002
0.868
1.005
0.995
1.197
1.340
0.939
1.256
0.868
1.136
4.75
4.806
191.3
4.88
9.93
4.335
2.379
1.8
8.71
9.07
9.53
8.822
13.3
1.2765
304.2
304.8
46.68
1.4773
1.4210
Propylene carbonate
a Molar absorbance per SiꢀSi bond.
b Dielectric constant.
c Ionization potential.
d Refractive index.
e Schweizer’s solvent constant.

48
K. Oka et al. / Journal of Organometallic Chemistry 611 (2000) 45–51
To obtain more insight of the effect of HFIP on
inducing the red-shift, we have measured UV spectra of
polysilane 3 in benzene and dichloromethane. As shown
in Fig. 4, HFIP is found to induce continuous solva-
tochromic spectral shift in benzene. Similar feature is
also seen in CH2Cl2. Furthermore, HFIP is found to
induce solvatochromism even in alcoholic solution; Fig.
5 shows solvatochromism of polysilane 3 in 2-propanol-
HFIP system. This suggests that HFIP forms hydrogen
bonding more effectively with ethereal oxygen than
hydroxyl oxygen in alcohol groups. THF, known to
make distillable complex with HFIP, quenches this
solvatochromism when added into an HFIP-containing
benzene solution. Polysilanes 1, 2, 4, and 5 behave
similarly towards HFIP-induced solvatochromism and
shows umax around 322–324 nm in HFIP.
solvent to induce the red-shift among all solvents
examined.
H-NMR shows that hydroxyl proton of HFIP ap-
pears as a doublet at 1.43 ppm in C6D6 (Fig. 6),
supporting non-dissociative characteristics. It loses cou-
pling with the methine proton and shows downfield
shift to 2.62 ppm when polysilane 3 is added into the
C6D6 solution. Methine proton of HFIP also shows
downfield shift to around 3.0–3.4 ppm where the signal
become indistinguishable with ꢀOCH2-moieties. Three
signals of CH2ꢀOꢀ groups of polysilane 3 at 3.0–3.4
ppm change their intensity ratio. Other signals (0–2
ppm) of polysilane 3 stay unchanged by mixing with
HFIP. Therefore, HFIP makes strong hydrogen bond-
ing with the ethereal oxygen atoms in polar polysilanes,
suggesting that no direct interaction takes place with
the main chain. Therefore, hydrogen bonding with
HFIP must increase bulkiness of the side groups which
makes the main chain more disentangled form.
Fig. 4. Solvatochromism of polysilane 3 in HFIP–benzene.
Fig. 5. Solvatochromic shift and absorbance change of polysilane 3 in
HFIP–IPA.
2.3. Comparison of thermochromism and
sol6atochromism
Thermochromic behavior is known to be controlled
from continuous to discontinuous by adjusting the bal-
ance of alkyl side groups in poly(dialkylsilane)s,
(RꢀSiꢀR%)n [1,6]. In general, large size difference in the
side chain length, such as in poly(hexylmethysilane)
[20], induces continuous spectral shift in solution while
two long alkyl side chains, such as in polydihexylsilane,
brings about discontinuous spectral shift. However, this
widely accepted generalization is overthrown recently
by the fact that poly(hexylmethylsilane) in solid state
shows discontinuous thermochromic shift on cooling,
though polybutylmethylsilane and polypentylmethylsi-
lane show continuous spectral shift [21]. Therefore,
chromotropism of polysilanes is very sensitive to the
subtle change of environment as well as the balance of
the side chains. The ethereal side chains of polysilanes
1–5 are longer than hexyl group and it is interesting to
examine the type of their thermochromic behaviors. We
can also compare the effect of driving forces on ther-
mochromism and solvatochromism in polar polysilanes.
Fig. 6. 1H-NMR spectra of polysilane 3 in C6D6.

K. Oka et al. / Journal of Organometallic Chemistry 611 (2000) 45–51
49
trograde and obtained from Dojin Chemical Co. Ltd.
Platinum divinyltetramethyldisiloxane complex
(Karstead’s Catalyst) as hydrosilylation catalyst and
hexafluoro-2-propanol (HFIP) were obtained from
Toshiba Silicone Co. Ltd. and Central Glass Co. Ltd.,
respectively.
3.2. Synthesis of monomers
The synthetic route of polysilane 1 is depicted in
Scheme 1. The starting dichlorosilane was synthesized
according to Wang et al. [22].
Fig. 7. Thermochromism of polysilane 3 in THF.
Reaction of 4,7,10,13-tetraoxatetradecanol (84.1 g,
0.5 mol) with NaH (40.0 g, 1.0 mol) in THF (200 ml)
under argon atmosphere afforded the corresponding
alcoholate which was reacted with allyl bromide to
yield allyl derivatives. Unreacted NaH was quenched
with water and the product was extracted with diethyl
ether (200 ml). The ether layer was washed with water
three times and then distillation under reduced pressure
gave allyl 4,7,10,13-tetraoxatetradecyl ether (b.p.: 125–
126°C/6 torr, yield: 78%).
Hydrosilylation reaction of the allyl ether (60.9 g, 0.3
mol) with methyldichlorosilane (52.2 g, 0.45 mol) by
use of Karstead’s catalyst was carried out under argon
atmosphere at reflux temperature for 4 h. Vacuum
distillation gave [4,7,10,13-tetraoxatetradecyl]methyl-
dichlorosilane (b.p.: 120–121°C/0.1 torr, yield: 78%).
H-NMR (CDCl3): l 3.46–3.64 (14H, OCH2ꢀ), 3.35
(3H, OCH3), 1.76 (2H, SiꢀCH2ꢀCH2ꢀCH2ꢀ), 1.15 (2H,
SiꢀCH2ꢀ), 0.76 (3H,SiꢀCH3).
Homologous monomers were similarly prepared
from the corresponding alcohols. (4,7,10-Trioxaunde-
canyl)methyldichlorosilane: b.p.: 123°C/2 torr, yield:
77%). H-NMR (CDCl3): l 3.44–3.6 (10H, OCH2ꢀ),
3.35 (3H, OCH3), 1.76 (2H, SiꢀCH2ꢀCH2ꢀCH2ꢀ), 1.16
(2H, SiꢀCH2ꢀ), 0.76 (3H, SiꢀCH3).
(4,7-Dioxaoctyl)methyldichlorosilane: b.p.: 121°C/10
torr, yield: 77%). H-NMR (CDCl3): l 3.44–3.55 (6H,
OCH2ꢀ), 3.35 (3H, OCH3), 1.77 (2H, SiꢀCH2ꢀCH2ꢀ
CH2ꢀ), 1.15 (2H, SiꢀCH2ꢀ), 0.75 (3H,SiꢀCH3).
Thermochromic behavior of these polar polysilanes
in ethanol and THF has been studied. Polysilanes 1–3,
having three methylene chain between silicon atom and
the ethereal oxygen atom, show continuous redshift on
cooling and umax are 322 nm at 180 K (Fig. 7). In spite
of their having longer methylene chains on silicon
atoms, polysilanes 4 and 5 show only continuous ther-
mochromic spectral shift giving umax around 322–324
nm at 180 K in THF, ethanol, and dichloromethane.
No solvent dependence was so far found in ther-
mochromic behavior of these polar polysilanes. The
long ethereal side moieties of polysilanes 1–5 must be
too flexible and entangled, which restrict further con-
formational change. Therefore, there is no room to
induce drastic conformational change resulting in dis-
continuous spectral shift to polysilanes 1–5. The umax
value (322–324 nm) at low temperature and in HFIP is
almost the same value with umax value of polydialkylsi-
lanes at room temperature in solution. Thus, polysi-
lanes 1–5 must have still very irregular form even their
most disentangled shapes.
3. Experimental
3.1. Materials
Methyldichlorosilane was obtained from Shin-etsu
Chemical Co Ltd. and was used after distillation from
K2CO3. Sodium, sodium hydride, magnesium, and
potassium carbonate were obtained from Wako Pure
Chemical Co. Ltd. 2-Methoxyethanol, (2-methoxy-
ethoxy)ethoxy]ethanol (or 4,7,10-trioxaundecanol), [2-
(2-methoxyethoxy)ethoxy]ethanol(or4,7,10,13-tetraoxa-
tetradecanol), toluene, THF, dibutyl ether, diethyl
ether, 2-propanol (IPA), pentyl acetate, 2-fluoro-
ethanol, trifluoroacetic acid, 2,2,2-trifluoroethanol, tri-
ethylamine, and diethylamine were obtained from
Wako Pure Chemical Co Ltd. and used after distilla-
tion. Solvents for UV measurements (toluene, THF,
ethanol, methanol, acetonitrile, DMSO, DMF, diox-
ane, chloroform, dichloromethane, benzene) were Spec-
Monomers for polysilanes 4 (and 5) was prepared as
follows: Williamson reaction of the corresponding alco-
hol (168.2 g, 1.0 mol) with sodium (11.5 g, 0.5 mol) in
THF at 60–70°C for 24 h was carried out and 1,4-dib-
rimobutane (216 g, 1.0 mol) was added into the mixture
at room temperature. After filtering off the resultant
salt, desired product was extracted with diethyl ether,
washed with water. Vacuum distillation gave the corre-
sponding 4-bromobutyl ether in 39% yield (b.p.: 112–
115°C/0.15 torr). Grignard reagent obtained from the
4-bromobutyl ether was reacted with methyltrichlorosi-
lane to give [5,8,11,14-tetraoxapentadecyl]methyl-
dichlorosilane (b.p.: 133–141°C/0.1 tor, yield: 9.7).
H-NMR (CDCl3): l 3.29–3.50 (14H, OCH2ꢀ), 3.22
(3H, OCH3), 1.43–1.52 (4H, SiꢀCH2ꢀCH2ꢀCH2ꢀCH2ꢀ),

50
K. Oka et al. / Journal of Organometallic Chemistry 611 (2000) 45–51
0.99 (2H, SiꢀCH2ꢀ), 0.63 (3H,SiꢀCH3). 13C-NMR
(CDCl3): 72.2, 71.5, 70.9, 70.8, 70.4, 59.2, 32.5, 21.7,
19.5, 5.4 ppm. 29Si-NMR(CDCl3): l 32.7 ppm.
5-Bromopentyl ether was similarly prepared from
1,5-dibromopentane to give the 4-bromopentyl ether
(b.p.: 125–130°C/0.2, yield: 36%) and Grignard reac-
tion with methyltrichlorosilane gave [6,9,12,15-Tetraoxa-
hexadecyl]methyldichlorosilane (b.p.: 135–140°C/0.1
torr, yield: 16%). H-NMR (CDCl3): l 3.45–3.68 (14H,
OCH2ꢀ), 3.39 (3H, OCH3), 1.39–1.61 (6H, SiꢀCH2ꢀ
CH2ꢀCH2ꢀCH2ꢀCH2ꢀ), 1.12 (2H, SiꢀCH2ꢀ), 0.77
(3H,SiꢀCH3). 13C-NMR (CDCl3): 72.2, 71.5, 71.1, 70.9,
70.4, 59.2, 32.2, 21.0, 18.0, 5.5 ppm. 29Si NMR
(CDCl3): l 32.75 ppm.
14.7, 4.4 ppm. 29Si NMR (C6Cl3): l −31.7 ppm.
Polysilane 5: (yield; 4.9%). GPC: Mw/Mn=36 000/
14 000. Tg=194 K. 1H-NMR (C6Cl3): l 3.50–3.60
(12H, OCH2ꢀ), 3.41 (2H, SiꢀCH2ꢀCH2ꢀCH2ꢀ), 3.19
(3H, OCH3), 1.80–1.58 (6H, SiꢀCH2CH2ꢀCH2ꢀ
CH2ꢀCH2ꢀ), 1.15 (2H, SiꢀCH2ꢀ), 0.59 (3H, SiꢀCH3).
13C-NMR (C6Cl3)): l 71.7, 71.0, 70.4, 70.2, 70.0, 58.0,
30.7, 29.5, 27.0, 14.9, 4.5 ppm. 29Si NMR (C6Cl3): l
−31.7 ppm.
Polysilane 2: (yield; 9.7%). GPC: Mw/Mn=19 000/
12 000. Tg=193 K. 1H-NMR (C6Cl3): l 3.60–3.68
(8H, OCH2ꢀ), 3.47 (2H, SiꢀCH2ꢀCH2ꢀCH2ꢀ), 3.23 (3H,
OCH3), 1.95 (2H, SiꢀCH2ꢀCH2ꢀCH2ꢀ), 1.20 (2H,
SiꢀCH2ꢀ), 0.59 (3H,SiꢀCH3). 13C-NMR (C6Cl3): l 74.0,
71.8, 70.5, 70.4, 70.1, 58.1, 27.0, 10.6, 4.3 ppm. 29Si
NMR (C6Cl3): l −31.6 ppm.
3.3. Polymerization
In the cases of polysilane 1, toluene layer involving
crude product was separated from water layer by a
separating funnel. The toluene layer was washed with
water several times to remove ionic species. After evap-
oration of toluene, the residual crude material is dis-
solved in defined amount of toluene and then was
subjected to fractionation with methanol to give polysi-
lane 1 (yield; 9.7%). (1.46 g, 7.2%). GPC: Mw/Mn=
21 000/12 000. Tg=193 K. 1H-NMR (C6Cl3):
1H-NMR (CDCl3): l 3.60–3.68 (12H, OCH2ꢀ), 3.47
(2H, SiꢀCH2ꢀCH2ꢀCH2ꢀ), 3.24 (3H, OCH3), 1.94 (2H,
SiꢀCH2ꢀCH2ꢀCH2ꢀ), 1.20 (2H, SiꢀCH2ꢀ), 0.65
(3H,SiꢀCH3). 13C-NMR (C6Cl3): l=73.9, 71.8, 70.5,
70.3, 70.1, 58.0, 26.3, 10.0, 4.9 ppm. 29Si-NMR (C6Cl3):
l=32.1 ppm.
Representative polymerization procedure for polar
polysilanes 2–6 is described. To a 0.5 l four necked
round bottom flask equipped with a pressure equili-
brated dropping funnel which was connected to an
argon inlet, a stirring rod, a condenser, a thermometer
were placed toluene (50 ml) and sodium (2.2 g, 0.01
atom). After sodium was finely dispersed at reflux
temperature,
[4,7,10,13-tetraoxatetradecyl]methyl-
dichlorosilane (13.9 g, 0.0435 mol) was introduced
quickly into the flask through the dropping funnel.
Several minutes took for initiation of the polymeriza-
tion reaction, which was detected by the characteristic
blue coloration of the reaction system. After refluxing
for 2 h and then cooled to room temperature by use of
an ice bath, 40 ml of ethanol and 100 ml of water were
added to quench the reaction. Organic layer was ex-
tracted by 160 ml of toluene and evaporation gave
pasty material. To remove residual NaCl, the resultant
crude material was dissolved in water and subjected to
dialysis using a cellulose acetate membrane for one
week. Evaporation of water gave oily material which
was dissolved in toluene and insoluble materials were
filtered off. The oily product obtained after evaporation
of toluene layer was subjected to repeated precipitation
from dibutyl ether. Centrifugation and subsequent vac-
uum drying at 70°C yielded a colorless, pasty polymer
(1.46 g, 7.2%). GPC: Mw/Mn=21 000/12 000. 1H-
NMR (C6Cl3): l 3.60–3.68 (12H, OCH2ꢀ), 3.47 (2H,
SiꢀCH2ꢀCH2ꢀCH2ꢀ), 3.24 (3H, OCH3), 1.94 (2H,
SiꢀCH2ꢀCH2ꢀCH2ꢀ), 1.20 (2H, SiꢀCH2ꢀ), 0.65 (3H,
SiꢀCH3). 13C-NMR (C6Cl3): l 73.9, 71.8, 70.5, 70.3,
70.1, 58.0, 26.3, 10.0, 4.9 ppm. 29Si-NMR (C6Cl3): l
−32.1 ppm. Tg=193 K.
3.4. Instruments and measurement
IR spectra of polysilanes were measured as neat films
on KBr plate by a Horiba FT-210 Spectrophotometer.
NMR spectra were obtained in DCCl3 or C6D6 solu-
tions with a Varian Unity 300 Spectrometer (300 MHz
for H and 75.5 MHz for C). Mass spectra were ob-
tained by a Shimadzu QP-5000 Mass Spectrometer.
Thermal analysis (DSC) was performed by a Rigaku
TAS 200. Molecular weight was obtained by gel perme-
ation chromatography (GPC) using a set of Waters
Ultrastyragel columns of 103, 104, 105, 106 referring to
polystyrene standards. THF (0.8 ml min−1) was em-
ployed as the eluent using a Toyo Soda HCL-800D
pump. Yanaco M-315 SpectroMonitor (measured at
254 nm) was used to monitor the chromatogram.
UV spectra were measured with a Shimadzu UV-PC
3100 Spectrophotometer by dissolving polysilanes in a
solvent (ca. 1.54×10−3 mol l−1) at ambient tempera-
ture. Variable temperature spectra were obtained by use
of an Oxford 39498 type Cryostat with an ITC 502
temperature controller. Fluorescence spectra were ob-
tained by a Shimadzu FP-1600 spectrophotometer.
Polysilane 4: (yield; 6.8%). GPC: Mw/Mn=36 000/
14 000. Tg=193 K. 1H-NMR (C6Cl3): l 3.54–3.60
(12H, OCH2ꢀ), 3.42 (2H, SiꢀCH2ꢀCH2ꢀCH2ꢀCH2ꢀ),
3.20 (3H, OCH3), 1.75 (4H, SiꢀCH2ꢀCH2ꢀCH2ꢀCH2ꢀ),
1.15 (2H, SiꢀCH2ꢀ), 0.62 (3H,SiꢀCH3). 13C-NMR
(C6Cl3)): l 71.7, 71.0, 70.4, 70.2, 70.0, 58.0, 34.2, 23.3,

K. Oka et al. / Journal of Organometallic Chemistry 611 (2000) 45–51
51
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Acknowledgements
[8] K. Song, R.D. Miller, G.M. Wallraff, J.F. Rabolt, Macro-
molecules 25 (1992) 3629.
This work was partly supported from grants-in-aid
for Scientific Research nos. 11120249 and 10640564
from Ministry of Education, Science and Culture. We
are also grateful to Central Glass Co. Ltd., Shin-etsu
Chemical Co. Ltd., and Toshiba Silicone Co. Ltd. for
generous gifts of 1,1,1,3,3,3-hexafluoropropa-2-ol,
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Karstead’s
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