Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 94~01480
21~ 9 6 71 PCl~EPg3/01587
NON-LINEAR OPTICALLY ACTIVE POLYURETHANES HAVING HIGH GLASS TRANSITION
TEMPERATURES
The invention relates to a non-linear optically active polyurethane
comprising a polymeric main chain and a donor-~-acceptor sidegroup.
Such non-linear optically active polyurethanes are known from
EP O 350 112, which discloses non-linear optically active
polyurethanes comprising a donor-~-acceptor group of which the donor
group comprises an oxygen atom or nitrogen atom coupled di~ectly to a
benzene ring of the ~-acceptor system, with the ~-system being a
stilbene group.
When polymeric non-linear optically active material is poled, non-
linear polarisation will be effected in it under the influence of an
external field of force (such as an electric field of force). Non-
linear electric polarisation may give rise to a number of optically
non-linear phenomena, such as frequency doubling and Pockels effect.
By utilising these phenomena it is possible to employ this material in
optically active waveguiding structures such as optical switches,
frequency daublers, etc. in the form of a poled film.
,
- While the stability of poled films made of the present non-linear
optically active polymers is excellent at room temperature, it leaves
something to be desired at elevated temperature: relaxation results in
lower values of the Pockels coefficients (r33 an~ r13, in this
description it is assumed that r33 = 3 x r13). The Pockels coefficient
' (r33) is indicative of the non-linear optical behaviour of the film.
The poor thermal stability of poled films of known non-linear
optically active polymers gives rise to problems especially when the
polymer is briefly heated to 200-300C during soldering. Neither are
~~ the present non-linear optically active polymers suitable for constant
use at elevated operating temperatures in the range of 60 to 120C.
To enhance thermal stability efforts have been made, int. al., to
WO 94/01480 PCI'/EP93/01587
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render non-linear optically active polyacrylates less flexible by
omitting the conventional spacers between the main chain and the
donor-~-acceptor sidegroup. However, it was found that such
polyacrylates could not be poled.
The present invention has for its object to obviate these drawbacks
and provide a non-linear optically active polymer of which the poled
film is thermally stable without the polability being negated. To this
end the invention consists in that the sidegroup of the non-linear
optically active polyurethane comprises a rigid donor group which is
also part of the polymeric main chain.
- Polyurethanes do not require spacers. When rigid donor groups are
employed, these are in effect incorporated into the main chain, thus
giving a rigid bond between the donor-~-acceptor sidechain and the
main chain. For further elucidation a schematic depiction is provided
in Figure 1.
: ~ ~ 20 ` . :
~,
- . - ~
-- - _
Figure 1
WO 94~01480 PCr/EP93/01587
2139671
wherein D represents a donor group, n stands for a ~-system, A is an
acceptor group, and H is the main chain of the polyurethane.
The result of this is a higher glass transition temperature (Tg above
170C) and hence a higher thermal stability also. It was found that
such polyurethanes could be poled. Since polable non-linear optically
active polyurethanes of such a high Tg were hitherto unknown, the
invention also relates to non-linear optically active polyurethanes
having a Tg above 170C. Among the many donor groups enumerated in
EP-A2-0 358 476 is a rigid donor group which may be used in the donor-
~-acceptor sldegroups of a polymer, e.g., in the donor-~-acceptor
sidegroups of polyurethanes. However, this publication makes no
mention of the fact that the use of such rigid donor groups will
result in non-linear optically active polymers having high Tgs. In
fact, this document fails to so much as mention Tgs.
Suitable rigid donor groups include alicyclic groups containing
nitrogen or sulphur. These groups were found to render the bond
between the donor-~-acceptor sidegroup and the main chain so rigid as
to give a polyurethane of high Tg without the polability of the
polymeric material being negated. Examples of such donor groups are
shown in formulae 1-5 below, ln which FG represents a functional
group. These functional groups may be the same or different.
_ .
,
FG
j ~ G iO~FG
formula 1formula 2 formula 3
WO 94/014B0 PCI/EP93/01587
2139671
-G ~c FC .c
5 /~
fonmula 4 : formula 5
Pyrrolidine groups (according to formula 2) in which the nitrogen atom
is coupled direc~ly to the ~-acceptor group and dithiafulvene groups
(according to formula 1) in particular were found to be highly
suitable for obtaining optically non-linear ac~ive polyurethanes of
good thermal stability and polability.
It is possi~le in principle for any n-acceptor group to be coupled to
the donor groups according to the invention. As examples may be
mentioned: substituted stilbene groups, such as nitrostilbene groups,
-cyanostilbene groups, sulphonate stilbene groups, and sùlphonyl
stilbene groups, substituted azo compounds, such ~as paranitro
azobenzene, cyano azobenzene, sulphonyl azobenzene~ and sulphonate
azobenzene, substituted benzylidene aniline compound~, -such as
cyanobenzylidene anillne, nitrobenzylidene aniline, etc.
:i In general, optically non-linear active polyurethanes are obtained
from polymerising a diisocyanate with a diol. The ~donor-~-acceptor
sidegroup may be present in either the diisocyanate or the diol. The
functional groups in the fonmulae 1-5 will the~`stand for -N=C=0 and
-(CH2)n-OH (n=0 or 1), respectively. Since -hydroxy-functionalised
donor-~-acceptorgroups are easy to prepare, their employment in
combination with diisocyanates which do not -contain donor-~-acceptor
groups is preferred.
WO 94/01480 PCI'/EP93/01587
2139671
The invention is also addressed to dihydroxy-functionalised donor-~-
acceptor groups comprising a 3,4-dihydroxy-pyrrolidine group. It was
found that these diols, which have not been disclosed before, are easy
to prepare, while their polymerisation with diisocyanates gives
polyurethanes of outstanding non-linear optically active behaviour.
Such diols satisfy fonmula 6 below:
OH OH
~
- Rl formula 6
(X)n
- 15
R l
y
wherein X is -CR~=DR~-, -N=N-, -CR~=N- or -N=CR~-,
Y is -~N, -N02, CR2=C(CN)2, -CF3, -CCN=C(CN)2 or
-SO2R3 - -
R~ is -halogen, -R2, -OR2, -COR2, COOR2, -CN or
-CF3,
R2 is -H, or an alkyl group having 1-3 carbon atoms,
-R3 is an alkyl or aryl group having 1-8 carbon atoms,
n is an integer from O to 4, and the X groups may be
the same or different if n is greater than 1.
As suitable diisocyanates may be mentioned: isophorone diisocyanate = _
(IPDI), methylene di(p-phenylene isocyanate) (MDI), methylene
di(cyclohexylene-4-isocyanate), toluene diisocyanate (TDI),
hexamethylene diisocyanate (HDI), paraphenylene diisocyanate (PPDI), -
W o 94/01480 213 9 6 71 PCT/EP93/01587
and cyclohexylene diisocyanate. Alternatively, it is possible to
employ diisocyanate mixtures in the polyurethane. It is preferred to
utilise rigid diisocyanates, such as IPDI9 MDI, and TDI, since these
will give maximum Tg.
After being dissolved in an appropriate solvent the polyurethanes may
be applied to a substrate by means of spincoating. Solvents that are
suitable satisfy the following requirements: firstly, of course, the
polyurethane must be soluble in the solvent. further, the solvent
should effect proper wetting of the substrate. The polymer solution
formed must be filterable and, finally, the solvent should have a
boiling point above 80C to ensure that the solvent does not already
evaporate during the spincoating process. Solvents satisfying these
requirements for a silicon substrate or glass substrate include
cyclopentanone and 2-methyl cyclohexanone. After evaporation of the
solvent t~he thus formed film may be poled, for instance using the
so-called DC-induced Pockels effect technique. In this process both an
AC and a DC voltage are applied to the sample. The DC field orients
the molecules and induces the Pockels effect, while the AC field
serves to measure the Pockels coefficient. The strength of the DC
- field ranges from 10 to 30 V/~m.
-: -
The invention also relates to a non-linear optically active waveguide
comprising a non-linear optically active polyurethane according to the
invention.
The invention will be further illustrated with reference to several
unlimitative examples, which are submitted solely for a better
understanding of the invention.
.~ .
_ 30
WO 94/01480 PCI/EP93/0158i
2139671
EXAMPLES
General polymerising method
10 mmoles of diisocyanate (or diisocyanate mixture) were fed to 10
mmoles of diol with donor-~-acceptor group in 20 ml of dry dimethyl
formamide (DMF). The mixture was stirred under nitrogen at room
temperature for 30 minutes. The temperature was then slowly increased
to 90C, and on conclusion of the reaction the reaction mixture was
diluted with 10 ml of DMF and filtered. The clear solution was
precipitated in 300 ml of ethanol. The precipitated polymer was
filtered off, washed twice with 100 ml of methanol being employed each
time, and dried.
example 1: polyurethane of dimethylol dithiafulvene nitrostilbene and
(IPDI) (polyurethane 1)
synthesis of dimethylol dithiafulvene nitrostilbene (diol 1): cf.
diagram 1
Step 1:
To a solution of 7,6 9 (100 mmoles) of CS2, 20,8 9 (100 mmoles) of
~ompQund -~~,~and 50 ml of Et20 were added slowly and dropwise at 0C
-20,2 9- of~ (n-Bu)3P. After cooling to -25C 14,2 g (100 mmoles) of
dimethyl acetylene dicarboxylate (DMAD) were added dropwise. Next, the
whole was stirred at 0C for one hour. After the addition of CH2Cl2
the reaction product was riltered through SiO2, washed with CH2Cl2,
and concentrated. The reaction product was purified by Flash column
--c~r~matography (SiO2: ethyl acetate/n-hexane (1/9)). Compound 2 was
~ obtained in a 57 mole% yield.
WO 94/0148() PCr/EP93/01587
21~9671
Step 2:
The pH of a solution of 25 9 (61,0 mmoles) of compound 2 in 450 ml of
THF and 250 ml of water containing p-TosOH was set at 2, after which
the solution was stirred for 16 hours. After 1 l of water had been
added the whole was extracted using ethyl acetate. The organic layer
was washed with NaHC03 solution and brine, dried on MgS04, filtered,
and concentrated. Recrystallisation fr~m MeOH gave compound 3 in a 75
mole% yield.
Step 3:
To a solution of 6,72 9 (20 mmoles) of compound 3 in 7,24 9 (40
mmoles) of nitrophenyl acetic acid and 60 ml of DMF were added slowly
and dropwise 3,4 9 (40 mmoles) of piperidine. After being stirred for
18 hours the reaction mixture was poured in water. The solid was
fil~ered off, washed, and dried. Recrystallisation from CH3CN gave
compound 4 in a 86 mole% yield.
Step 4:
.
To a mixture of l,OO 9 (2,2 mmoles) of compound 4, 1,22 9 (11,0
mmoles) of CaCl2, 30 ml of THF, and 20 ml of EtOH were slowly added
0,42 9 (11,0 mmoles) of-Na3H4-. ~t ~the end of the reaction H20 was
added, and the whole was ext-racted using ethyl acetate. The organic
layer was washed with water and brine, dried on MgS04, filtered, and
concentrated. Recrystallisation from CH3CN gave diol 1 in a 90 mole%
yield.
_
WO 94/01480 PCT/EP93/01587
213~671
Step 5:
A solution of 5 g (12,5 mmoles) of compound 5, la ml of THF, and 10 ml
of AC20 was stirred at 100C for 2 hours . After cooling ethyl acetate
was added, and the whole was washed with NH4CL solution and brine,
dried on M~S04, filtered, and concentrated. Recrystallisation from
CH3CN gave compound 6 in a 40 mole% yield.
Step 6:
A solution of 15 9 (31,1 mmoles) of compound 6, 300 ml of 10%-NaOH
sol uti on, and 1000 ml THF was kept at refluxing temperature for one
hour. A~ter cooling the layers were separated and the organic layer
was washed with brine, dried on MgS04, filtered, and concentrated.
After agitation with 400 ml of MeOH and filtering off diol 1 was
obtai ned i n a 83 mole% yield.
Polyurethane 1 was prepared with isophorone diisocyanate (IPDI)
according to the general polymerising method disclosed hereinbefore.
For the Tg reference is made to TABLE 1.
example 2: polyurethane of dihydroxypyrrolidine ~~nitrostilbene and
~IPDI) (polyurethane 2)
synthesis of dihydroxypyrrolidine nitr~stilbene (d1ol- 2):-
For the preparation of compound 1 reference is made to J. Am. Chem.
Soc. 76 (1954), 3584.
Step 1: -
11,4 g (63,7 mmoles) of compound 1, 16,3 g t~5S,2 mm~les) of aceticanhydride, 60 ml of THF and 2 ml of triethyl amine were kept at
refluxing temperature for 18 hours. After~concentration by evaporation
WO 94/01480 PCl'/EP93/01587
21396~1
- --
200 ml of ethyl acetate were added, and the mixture was neutralised
with a saturated NaHC03 501 ution. The layers were separated, and the
organic layer was dried on MgS04. After filtration and concentration,
recrystallisation from THF gave compound 2 in a 95 mole% yield.
Step 2:
~ '
8,83 9 (57,7 mmoles) of POCl3 were added dropwise to 20 ml of DMF at a
temperature below 10C. Next, the whole was stirred at room
temperature for one hour. Subsequently, a solution of 13,8 g (52,5
mmoles) of compound 2 and 12 ml of DMF were added dropwise, and the
whole was stirred at 70C for 2 hours. The reaction mixture, after
being cooled down, was poured in ice/water and~ neutralised with 18,5 9
(225 mmoles) of sodium acetate. Next, the whole was extracted with
15~ C~2Cl2~, and the organic layer was washed with H20 and brine, dried on
Mg~S04, filtered, and concentrated. The solid was recrystallised from
MeOH and compound 3 was obtained in an 88 mole% yield.
,
S~ep 3:
- 20
To 2,12 3 (52,8 mmo~es) of NaH (60% in oil) a solution of 13,0 9 (44,7 ~
~-~ mmoles~ of compound 3, 12,0 9 (44,0 mmoles) of compound 4, and 150 ml
of DMF~was added slowly and dropwise, with stirring. The mixture was
stirred for 18 hours and the poured in 1,5 1 of water. After bein~ -
sttrred for one hour the mixture was filtered and washed with H20. The
solid was dissolved in ethyl acetate, washed with a saturated NaHCO~ -
solution and brine, dried on MgS04, filtered, and concentrated. After
purification by column chromatography (SiO2/CH2Cl2) compound 5 was: ~ ~
obtained in an 80 mole% yield. -- -
_ _ _
'
,
WO 94~01480 PCa/~P93/~1~87
2139671
Step 4:
A solution of 14,0 9 (36,3 mmoles) of compound 5 in 200 ml of THF was
added dropwise to a suspension of 4,32 9 (80 mmoles) of NaOMe and 50
ml of MeOH. After one hour of stirring 100 ml of MeOH were added and
the reaction mixture was poured in H20 The solid was dissolved in
ethyl acetateS washed with saturated NaHC03 solution and brine, dried
on MgSOq, filtered, and concentrated. After purification by Flash
chromatography (SiO2: CH2Cl2tn-hexane (95/5)) diol 2 was obtained in a
90 mole% yield.
Polyurethane 2 was prepared according to the above-described general
polymerising method using isophorone di-isocyanate (IPDI). The Tg was
measured by DSC and was 200C.
comparison example: polyurethane of
4-di-(2-hydroxyethyl)amino-4'-nitrostilbene and (IPDI)
.
For the preparation of 4-di-(2-hydroxyethyl)amino-4'-nitrostilbene
reference is made to EP-A1-0 350 112. Po1yurethane 3* was prepared by
means of the above-described conventional polymerising method using
this diol and isophorone diisocyanate.
Test samples were made of the prepared optically non-linear active
polymers for use in Fabry-Perot experiments (r13) and crossed
polariser experiments (r33-r13) in transmission. To this end a
polyurethane layer provided between two planeparallel, semi-
transparent metal electrodes was applied to a glass substrate. Prior
to being metallised in a Balzers evaporation chamber, the substrate
was cleaned in situ with a glow discharge. The polyurethane was
dissolved in cyclopentanone and filtered through a millipore0 filter
having a pore size of 0,45 ~m. The films were prepared by spincoating.
After the spincoating process the samples were placed on a hot stage
and heated slightly above Tg for 0.5-3 hours.
WO 94tO1480 PCrtEP93/01587
~139~71
The polyurethane film 1 and 2 were poled using the DC-induced Pockels
effect technique as described hereinbefore at a temperature above the
polyurethane's Tg (180C and 200C, respectively) for 15 minutes~ The
freezing in efficiency ~ (i.e., the ratio of the Pockels coefficient
(r13) for a switched off DC-field after freezing in at room
temperature to the Pockels coefficient for the switched on DC-field,
r13 field off/r13 field on) is shown in TABLE 1, which also lists the
Tg (measured by DSC~ and the Pockels coefficients (r33), it being
assumed that r33 =~ 3 x r13. It proved possible to pole the film of
polyurethane 3* at 140C in one minute.
The relaxation measurements were carried out at various temperatures.
The temperatures employed for polyurethane 1 and 2 were in the range
of 100to 175C, for polyurethane 3* they were in the range of 100 to
135C. These values were plotted in an Arrhenius plot and from them
the values of the half-life, i.e., the ttme which signifies the loss
of 50% of the Pockels coefficient, could be calculated. The half-life
(t~) is indicative of the film's stability. The results are compiled
2a in TABLE 1.
TABLE I
~, _ . . ---
25-polyurethan~ Tg r33 ~ t~
(oo) (pm7V) (%) (ho~r) at:
140C 155C 160C
. _
1 175 1,3 40 S,88 1,21 0,73
2 200 1,2 45 20,6 4,5 2,78
3~ ~--3* 140 2,2 60 0,0108 0,00027 0,00008C
_
The data shows that films prepared from the optically non-linear
active polyurethanes according to the invention have a higher Tg than
WO 94/01480 PCl'/EP93/0158i
2139671
the already known optically non-linear active polyurethanes, and can
be poled. In addition, the thermal stability of poled films containing
polyurethanes according to the invention was found to be much higher
at elevated temperatures such as 140-160C than that of poled films
of already known optically non-linear active polyurethanes. This means
that the optically non~linear active polyurethanes according to the
invention are highly resistant to momentary heating such as occurs in
soldering.
`- _
WO 94/01480 PCI'/EP93~01587
2139671
14
Dia~am_ 1
CHO
COOMe
¦1 + CS2+ ~)step 1
COOMe
C~(OEt) 2
Ct:)OMe
COOMe COOMe S ~ COOMe
~J ~COOMe ~COOMe
[~ step 2 ~ [~ stel~ 3
CH(OEt)2 CXO
2 ~ ~ 4
N02
CH20H -CH20Ac-- CH20H
~ CH20Ac ~ CH20
~; _step 5 ~ ~ step 6 ~
N2 5 N2 6 ~2 5
SVBSTJTUTE SHEET
WO 94/01480 2 1 3 9 6 7 1 PCI`/EP93/01587
Diaqram 2
HO ~SOH AcO ~OAc AcO ~OAc
steP 1 ~ N steP 2 ~ N
2 CHO 3
AcO ~OAc HO OH
step 3 ~ ~3 step 4
~,PO(OEt)
NO 2
4 NO2 ~ 6
:
SUBSTITUTE SHEEl-
