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Novel Polyether Copolymers Consisting of Linear and Dendritic Blocks.

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[23] M. Ichida, K. Nagai, Y.Sasaki, M . T. Pope, .
Am. Chem. Soc. 1989, ifi,
[24] 2: Monoclinic. space group P2,/c with a =13.193(2), b =16.091(4), c =
23.096(5) A, fl = 92.96(1)"; V = 4896(1) A3, Z = 2 (e,,,, = 1.304 gcm-';
&MoJ = 10.45 cm-I), R = 0.069 for 2067 reflections with 2 R < 50" and
I > 3 ~ ( 1 Rigaku
AFCSS diffractometer, graphite monochromated Mo,,
radiation. The structure was solved using the direct methods routine of the
TEXSAN program package [18 b].
[25] I. D. Brown, K. K. Wu, Acfa Crwfallogr. Sect. B 1976, 32, 1957.
[26] B. Bleany, K. D. Bowers, Proc. R. SOC.London. A 1952,214, 451.
1271 A. P. Ginsberg, E. Koubek, H. J. Williams, Inorg. Chem. 1966,5, 1656; A.
Syamal, Coord. Chem. Rev. 1975,26, 309.
IAm. Chem.
1281 J. W. Johnson, D. C. Johnston, A. J. Jacobson, J. F. Brody, .
SOC.1984, 106. 8123.
[29] G. Villeneuve, K. S . Suh, P. Amoros, N. Casan-Pastor, D. Beltran-Porter,
Chem. Muter. 1992, 4, 108.
[30] Q. Chen, D. P. Goshorn, C. P. Scholes, X.-L. Tan, J. Zubieta, J. Am. Chem.
Soc. 1992, il4,in press.
Novel Polyether Copolymers Consisting of Linear
and Dendritic Blocks**
drimers in a crystalline hydrophilic PEG as well as the properties of the resulting copolymers.
In a first approach PEG copolymers containing dendritic
blocks were prepared by capping the ends of a, w-bifunctiona1 PEGS with dendrimers possessing a reactive functional
group at their core. In order to estimate the influence of the
size of the dendritic molecule on the reaction yields and the
properties of the copolymers that are formed, dendrimers of
the third ([G-3]-Br: 1) and fourth ([G-4]-Br: 2) generations
were used (Scheme 1).
In order to avoid the association of acidic moieties with
PEG@] and the incomplete conversion['] of some
Williamson-type syntheses, the formation of the PEG dianion in situ by reaction with NaH was carried out in the
presence of the dendritic bromide (Scheme 2) as described
previously for the synthesis of PEG rnacromers.I']
H-f O C H 2 C H h O H
n = 24,55,86,243,447
By Ivan Gitsov, Karen L. Wooley, and Jean M . 1 Frichet*
Polyethylene glycols (PEGs), their derivatives and amphiphilic block copolymers have many applications as
phase-transfer reagents,"] as compounds that could potentially encapsulate other materials,[21 and as emulsifying
agents.f31Their properties arise from the existence of both
hydrophilic and hydrophobic parts of the macromolecules.
In spite of the promising results achieved up to now, the
synthesis of novel polymers and copolymers of that type is
still of importance due to the high demand for new materials
with defined architecture and improved properties.
Recently, the synthesis of novel dendritic polyethers was
reported.[4. Because of their dense, but nonentangled
structure these dendrimers are expected to impart unusual
properties to other polymeric materials when incorporated
in the polymer chain. This report explores the incorporation
of these highly branched amorphous and hydrophobic den-
Scheme 2. Synthesis of the copolymers.
Scheme 1. The dendritic macromolecules employed in the reaction with the
polyethylene glycols.
[*] Prof. J. M. J. Frechet, Dr. I. Gitsov, K. L. Wooley
Baker Laboratory, Department of Chemistry
Cornell University
Ithaca, NY 14853-1301(USA)
Financial support of this project was provided by National Science Foundation (DMR-8913278) and The William and Mary Greve Foundation
(fellowship for I.G.).
Verlagsgesellschaff mbH, W-6940 Weinheim, 1992
In all cases investigated, the end-capping reaction proceeded smoothly at room temperature and was complete
within 24 h. The length of the initial PEG block and the size
of the dendritic bromide have no influence on the rate of
formation of the copolymers. In contrast to the previously
reported end-capping reactions of PEGS,[', the low molar
ratio of the dendritic bromides to terminal hydroxyl groups
(1.2:l) does not affect the yields, which remain over 90%.
The molecular weights of the starting materials and the
resulting block copolymers are listed in Table 1. The molecular weights at the peak apex M , in the size-exclusion chromatography (SEC) traces are used as characteristic values
for each product since they are less affected by low- and
high-molecular weight impurities. The molecular weight distribution is calculated as the average of three measurements.
It should be noted that most copolymers obtained have narrower molecular weight distributions than the inital PEGs,
and all of them have apparent molecular weights lower than
the values predicted for triblock copolymers of the type [Gm]-PEG-[G-m] (Table I , Fig. I). This difference between calculated and apparent molecular weights increases with the
length of the initial PEG block.
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Angew. Chem. Inf. Ed. Engl. 1992, 31, No. 9
Table 1. Molecular weights of PEGs H-(OCH,CH,).-OH and their dendritic copolymers as determined by SEC versus PEG standards with narrow molecular distributions
(THE 30°C flow rate 1 mL min-".
M, of the dendritic copolymers
[G-31 copolymers
[G-4] copolymers
initial PEGs
24 1050 1.03
23 1700 1.05
55 2400 1.03
56 2500 1.08
86 3800 1.08
243 10700 1.04
447 19700 1.11
3600 1.02
3360 [a] 3000 1.03
5000 1.01
4160 [b] 4000 1.03
6400 1.05
12600 1.03
20300 1.10
4980 [a] 3900
5780 [b] 4850
[a] Reaction product of monofunctional lauryl PEG C,,H,,(OCH,CH,),,-OH
359 and dendritic bromide. [b] Reaction product of monofunctional methyl PEG
CH,(OCH,CH,),,-OH and dendritic bromide.
, , , , , , ,
Fig. 1. SEC calibration curves for polystyrene (PS) standards, PEGs with narrow molecular weight distributions, and dendritic triblock copolymers [GIPEG-[GI. THF. 30°C. flow rate 1 mL min-' ;columns: PLGel500 ?+, 1000 .&,
In order to check the efficiency of the end-capping reaction, experiments with monofunctional PEGS were also performed (Table 1, Fig. 2). It is seen that the end-capping reactions of both mono- and bifunctional PEGS of similar
molecular weight with a dendritic bromide proceed to completion. In the SEC traces of the monofunctional PEGS the
shoulders at high molecular weights originate most probably
from bifunctional impurities in the starting materials. Thus,
it may be assumed that the lower values of the apparent
molecular weights are caused not by incomplete functional-
1 '
10 0
30 0
Fig. 2. SEC traces of the initial PEGs. A: H-(OCH,CH,),,-OH, B: reaction
and 1, C : reaction mixture of Hmixture of H-(OCH,CH,),,OC,,H,,
(OCH,CH,),,-OH and 1. THF, 30 "C, flow rate 1 mL min- ' ;columns: PLGel
500 .&, 1000 A, mixed-C.
Angrn. Chem. I n l . Ed. Engl. 1992, 31, No. 9
ization (end-capping), but most probably by the smaller size
of the resulting dendritic copolymers. A similar behavior was
reported for dendritic versus linear macromolecules.['. 91
Another factor contributing to the differences in the calculated and apparent molecular weights discussed above might
be the formation of monomolecular micelles. The calibration
curve for PEGS has a more negative slope compared to that
for polystyrenes (PS) (Fig. l), which confirms the wellknown fact that the solubility of PEGS in THF decreases as
their molecular weight increases. Thus, in copolymers with
dendritic and linear blocks, the central PEG block should
shrink in THF as its length increases, while the dendritic end
blocks would undergo an intramolecular association. Since
there are no other reports on copolymers consisting of linear
and dendritic blocks, our results are best compared to those
obtained for polyethylene oxide-polystyrene block copolymers. Indeed, a similar phenomenon was reported for
polystryrene-b-polyethylene oxide-b-polystyrene."O' Some
authors have predicted a narrowing in the molecular weight
distribution of block copolymers undergoing an association
of their end groups.["] However, with the copolymers in this
study it would be very difficult to estimate quantitatively the
contribution of both factors-collapse of the linear central
block in solvents in which the PEGS are not well soluble
(THF), and intramolecular association of the dense, hyperbranched endgroups-to the overall decrease in the molecular dimensions of the synthesized copolymers.
In order to gain qualitative information on the possible
formation of micelles, we recorded 'H NMR spectra in solvents selective for solubilizing the PEG and dendritic blocks.
An interesting phenomenon is observed in [DJTHF. At
room temperature the initial PEG block with molecular
weight of 19700 is obviously not soluble. Therefore, only
signals for the protons of the groups -CH,O- (6 = 3.283.58) and -CH,CH,- (6 = 1.57-1.73) of THF molecules are
observed in the spectrum. The integrals of the two signals
should be equal, but that of the CH,CH, protons is greater
= 1.35) due to the different isotopic distributions at the two positions. When the sample in the NMR
tube is heated to 50 "C for 15 min, PEG visibly dissolves and
the ratio of the integrals is strongly shifted towards the
= 0.17). The 'HNMR spectra
CH,O protons (ICH2CH2:ICH10
of dendritic copolymers having the same PEG as above for
the central block are not temperature dependent. Theoretically, the ratio of the methylene PEG protons to the protons
in the dendritic side-blocks for [G-4]-PEG19700-[G-4]
should be equal to 4.84. In CDCI, the ratio of their integrals
is about 4.9, but in [DJTHF, the values obtained at room
temperature and 50 "C are 2.49 and 2.30, respectively, after
the integral intensity of solvent protons is subtracted. Thus,
it may be assumed that attachment of dendritic blocks to
PEG increases its solubility in T H F to a certain extent; however, the screening of the PEG core by the dendritic outer
shell in the micelles that are formed prevents further solubilization at higher temperatures.
Figure 3 presents the 'H NMR spectra of [G-31(OCH,CH,),,,-O-[G-3] in CDCI, (A, both blocks are soluble) and CD,OD (B, the PEG block is selectively soluble).
It is noteworthy that while the signal for the methylene PEG
protons remains sharp and is only slightly shifted downfield
in CD,OD (from 6 = 3.32-3.72 to 3.29-3.70), the signals of
the aromatic protons in the dendritic end blocks become very
broad (6 =7.06 (Av = 120 Hz), 6.38 (204 Hz), 4.72 (571 Hz)
(Fig. 3, B.). It is quite surprising that the signals of the [G-31
block are observed, since the corresponding dendritic bromide and its derivatives are not soluble in methanol and
consequently not evident in the NMR spectra recorded in
Verlagsgrsellschajt mbH. W-6940 Wemheim. 1992
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that solvent. The PEG block seems to carry its dendritic
counterpart into solution as was observed for G blocks in
[DJTHF. However, the broadness of the signals is evidence
of the limited flexibility of the dendritic blocks of the copolymers. When hyperbranched blocks of the next generation are
attached to the same bifunctional PEG, the methanol solution of the resulting copolymer is milky and opalescent, and
the aromatic signals are not seen in the NMR spectra (Fig. 3,
C.). A similai Jehavior and the same values for Av are also
or in which one block is selectively soluble. Further investigations on their properties are in progress.
Experimental Procedure
A typical end-capping reaction was performed as follows: PEG of molecular
mol) and 1 (0.029 g,
weight 3800 [H(OCH,CH,),,OH] (0.031 g, 8.3 x
1.72 x lo-' mol), synthesized according to ref. [XI, were mixed and dissolved in
mol), and
dry THF (2 mL). To the solution was added NaH (0.001 g, 4 x
the reaction mixture was stirred at room temperature under nitrogen for a set
time. The conversion was followed by SEC. After the PEG peak in the chromatogram had disappeared, the reaction mixture was filtered and purified by
precipitation into acetone/methanol (1 :3) and reprecipitation from THF into
heptane. Yield: 0.056 g (93%). 'H N M R (300 MHz CDCI,, 22 "C): 6 =7.2X7.33 (m, SOH; H in outer aromatic rings of [G-3]),6.51-6.62 (m. 42H; H in
inner aromatic rings of [G-3]), 4.89, 4.94 (d, 60H; benzylic CH, in [G-3]),
3.55-3.73 (m, 344H; CH,CH,O in PEG). All other experiments were performed by the same procedure with similar yields.
Received: March 25, 1992 [Z 5260 IE]
German version: Angew. Chem. 1992, 104, 1282
CAS Registry number:
[GI-PEG[G] (block copolymer), 143104-76-1.
J. M. Harris, M. G. Case, J. Org. Chem. 1983, 48, 5390 and references
T. K. Khan, R. H. Mobbs, C. Price, J. R. Quintana, R. B. Stubbersfield,
Eur. Polym. J . 1987, 23, 191.
H.-Ba Gia, B. Jereme, P. Teyssie, J Pulym. Sci., Polym. Phys Ed. 1980, 18,
C. J. Hawker, J. M. J. Frechet, J. Chem. Sue., Chem. Commun. 1990,1010.
K. L. Wooley, C. J. Hawker, J. M. 1 Frechet, J. A m . Chem. Soc. 1991, 113,
J. M. Harris, J. Macromol. Sci., Rev. Macromol. Chem. Phys. C 1985, 2s.
D. Chao, S . Itsuno, K. Ito, Pulym. J. 1991, 23, 1045.
C. J. Hawker, J. M. J. Frechet, J A m . Chem. Soc. 1990, 112, 7638.
A. Morikawa, M. Kakimoto, Y. Imai, Macromolecules 1991, 24, 3469.
I. Berlinova, N. Vladimirov, I. Panayotov, Mukromol. Chem. Rapid Commun. 1989, 10, 163.
K. Solc, H. G. Elias, J. Polym. Sci. Polym. Phys. Ed. 1973, i f , 137.
K. Nakamura, R. Endo, M. Takeda, J. Polym. Sci. Polym. Phys. Ed. 1976,
14, 135.
J. Spevacek, Makcromol. Chem. Rapid Commun. 1982.3, 697.
Fig. 3. 'H NMR spectra of [G-3]-(OCH,CH2),,,-O-[G-3] in CDCI, (A), "3-31in
(OCH2CH,),,,-O-[G-3] in CD,OD (B), and [G-4]-(OCH2CH,),,,-O-[G-4]
CD,OD (C). 300 MHz, 22 "C, polymer concentration I wt %.
observed for dendritic copolymers of monofunctional PEGS.
Thus, it could be assumed that in methanol both di- and
triblock copolymers undergo the same type of transformation. Similar phenomena were reported for polystyrene-bpolyethylene oxide" and other micelle-forming copolym e r ~ [ ' ~and
] were also interpreted as micelle formation.
Although additional investigations are necessary to evaluate
the number of molecules in the micelles formed, the results of
SEC and 'H NMR experiments strongly suggest that in selective and poor solvents the copolymers might undergo different size and shape transitions (Scheme 3).
Indigoid para-Quinodirnethanes""
By Rudolf Gompper,* Robert Kellner, and Kurt Polborn
Dedicated to Professor Wolfgang Beck
on the occasion of his 60th birthday
Scheme 3. Left: Collapse of the central PEG block as the length increases. The
dendritic G blocks are partially associated. Middle: Both blocks are soluble in
the solvent. Right: Collapse and association of G blocks of higher generations.
The PEG block expands.
The results show that the relatively bulky dendritic
wedges, up to fourth generation, do not affect the reactivity
and accessibility of the functional group at the core of the
dendritic macromolecules. Thus, novel amphiphilic block
copolymers of PEGShaving different extents of hydrophobic
and hydrophilic character can be formed in a single reaction
under mild conditions. The preliminary characterization
studies of these products show that they are able to form
micelles in solvents in which both blocks are poorly soluble
0 VCH Verlagsgesellschuft mbH,
W-6940 Weinheim, 1992
Indigo and indigoid compounds are important technical
dyes because of their applications in coloration, especially in
textile dying. The nature of the indigo chromophore was
studied intensively and is now well understood.[lb31' However, the search for new indigoid compounds continues. The
UVjVIS absorption of these systems at very long wavelengths makes them attractive materials for optical data storage,13,41since such materials must absorb in the near-IR
(>750 nm). This can be accomplished, for example, by com~lexation.[~]
Alternatively, the indigo chromophore and
structurally related chromophores can be fused to 7[: electron
systems to produce compounds with the desired
bathochromic shift and the stability of the indigoid system.
We have succeeded in synthesizingpara-quinodimethane homologues of this type, 1-3; their absorption is at a consider[*] Prof. R. Gompper, Dip].-Chem. R. Kellner, Dr. K. Polborn
Institut fur Organische Chemie der Universitit
Karlstrasse 23, D-W-8000 Miinchen 2 (FRG)
This research was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
0570-0833/92/0909-12023 3.50+.25/0
Angew. Chem. I n t . Ed. Engl. 1992, 31, No. 9
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