Langmuir 1994,10, 4651-4656
4651
Chain Length Discrimination of Water-Soluble Polymers by a Poly(methacry1ic acid) or Poly(oxyethy1ene) Segment-Carrying Assemblies at the Air-Water Interface Nobuyuki Higashi, Takahiro Matsumoto, and Masazo Niwa* Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Tanabe, Kyoto 610-03, Japan Received June 1, 1994. In Final Form: September 7, 1994@ A poly(methacry1ic acid) (1,) or poly(oxyethy1ene) (2,)-functionalized, double-chain amphiphile, incorporated in organized monolayer assemblies, forms an interpolymer complex with the corresponding guest polymer (poly(ethy1ene glycol) (PEG) or poly(methacry1ic acid) (PMAA)) present in an adjacent aqueous phase. Surface pressure-area isotherm and FTIR spectroscopy have been used for the characterization and investigation of the 1, or 2, host monolayer-guest polymer complexation. In both monolayers (1, and 2,) complexation occurs on acidic subphases. Surfacepressure-area isotherms change sensitively to the chain length (m)of the guest polymers added into the subphase: in the combination of 1, monolayer-PEG the area per molecule decreases with increasing m up to m = n (n is the chain length of polymer segment of l,),and in contrast in the combination of 2, monolayer-PMAA the area increases with increasing m up to m = n. Consequently, these polymer monolayers of 1, and 2, have been found to have an ability to discriminate against the chain length of the guest polymers. The driving force of such a complexation can be assigned to multiple hydrogen bonding between the carboxylic acid and the ether oxygen, which have led to either a shift or the appearance of a new band of C=O stretching in the FTIR spectra.
Introduction The interaction between two different macromolecules plays a key role in a living system since biological phenomena such as enzymatic processes and protein synthesis are indebted principally to specific intermacromolecular interactions and to structural properties of the resultant macromolecular assemblies. Organized monolayers provide peculiar environments for molecular interactions and, consequently, for molecular recognition. Novel molecular interaction systems can be developed by using monolayer assemblies, which may possess characteristics different from those in bulk phases. From this point of view, several investigations have been reported concerning molecular recognition by monolayer systems. Typical host molecules such as crown ether,l cyclodextrin,2 and calixarene3have been modified with long alkyl chains to form surface monolayers. Monolayers of nucleolipids4 have been studied in this regard. Specific interactions different from those in bulk solutions have been observed for a diaminotriazine-functionalizedmonolayer which efficiently binds barbituric acids and nucleic acid bases by complementary hydrogen b ~ n d i n g .Chiral ~ monolayers have recognized the chirality of guest molecules and have induced stereoselective molecular re~ognition.6,~ Most of these monolayer systems are limited to interactions among small molecules. Few reports have been appeared concerning an inter-macromolecular interaction by monolayer @Abstractpublished in Advance ACS Abstracts, November 1, 1994. (1)Matsuhara, H.; Furusawa, K.; Inokuma, S.; Kuwaura, T. Chem. Lett. 1986, 453. (2) Tanaka, M.; Ishizuka, Y.; Matsumoto, M.; Nakamura, T.; Yabe, A.; Nakanishi, H.; Kawabata, Y.; Takahashi, H.; Tamura, S; Tagaki, W.; Nakahara, H.; Fukuda, K. Chem. Lett. 1987, 1307. (3) Ishikawa, Y.: Matsuda, T.; Otsuka, T.; Kunitake, T.; Shinkai, S. J . Chem. SOC.,Chem. Commun. 1989, 736. (4) Kitano, H.; Ringsdorf, H. Bull. Chem. SOC.Jpn. 1986,58,2826. ( 5 ) Kurihara, K.; Ohto, K.; Honda, Y.; Kunitake, T. J . Am. Chem. SOC.1991, 113, 5077. (6) Landau, E. M.; Wolf, S. G.; Leiserowitz, L.; Lahav, M.; Sagiv, J. J . Am. Chem. SOC.1989,111, 1436. (7) Harvey, N. G.; Mirajovsky, D.; Rose, P. L.; Verbiar, R.; Amett, E. M. J . A m . Chem. SOC.1989,111, 1115. 0743-7463/94/2410-4651$04.50l0
systems, probably due to the difficulty of preparing monolayer formers carrying a well-characterized polymer segment. We have focused on the design and preparation of polymeric amphiphiles carrying a polyelectrolyte segment such as poly(methacry1ic acid) (PMAA) and poly(Lglutamic acid) and their monolayer properties at the airwater interface. These polymer assemblies have provided characteristics uniquely different from those in homogeneous media For example, it has been found that the stable ,&sheet structure of poly(L-glutamic acid), which has been well-known to be a typical a-helix polypeptide, can be produced by assembling the poly(L-glutamic acid) segment connected with two long alkyl chains at the airwater interface.g Amphiphiles of PMAA connected with a poly(styrene) segmentsJOor with two long alkyl chains'l have been aligned at the air-water interface, and their monolayer state could be controlled by using the conformational change of the PMAA segment. In previous reports,11J2 we showed the preliminary results on a polymer chain length recognizablemonolayer derived from the PMAA amphiphiles: PMAA monolayer assemblies were found to respond sensitively to the chain length of the corresponding guest polymers such as poly(ethy1ene glycol) (PEG)added to the subphase mainly due to a specific multiple hydrogen bonding between polymers. Similar situations were observed for other combinations of host polymer monolayers and guest polymers.13J4 The present paper will describe the results of a more intensive study on chain length recognizable ability of polymer monolayers based upon the spreading behaviors on aqueous guest polymer solutions and FTIR spectroscopy for their multilayer state. We choose two combinations (8) Higashi, N.; Shimoguchi, M.; Niwa, M. Langmuir 1992,8,1509. (9) Niwa, M.; Katsurada, N.; Higashi, N. Macromolecules 1988,21, 1878. (10)Niwa, M.; Hayashi, T.; Higashi, N. Langnuir 1990, 6, 263. (11)Higashi, N.; Shiba, H.; Niwa, M. Macromolecules 1989,22,4650. (12) Higashi, N.; Shiba, T.; Niwa, M. Macromolecules 1990,23,5297. (13)Higashi, N.; Nojima, T.; Niwa, M. Macromolecules 1991,24, 6549. (14)Higashi, N.; Matsumoto, T.; Niwa, M. J . Chem. SOC.,Chem. Commun. 1991, 1517.
0 1994 American Chemical Society
Higashi et al.
4652 Langmuir, Vol. 10,No. 12, 1994 ofhost polymer monolayer-guest polymer; i.e., (i)PMAA amphiphiles, l,-PEG(m) and the reverse pair (ii) poly(oxyethylene) (POE) amphiphiles, 2,-PMAA(m). The guest polymers have been prepared with various chain lengths (m) over a wide range (m = 4-191).
Scheme 1 0 II R-0-C R-O-CL
Br I N-C-C-Br
7
1:
MnzW)io
A
m
[ complex)
I1
0
,c=o
Host Polymer Monolayer
7
0
1
3
Br
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1"
0 Br
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OH
0 O II
H
R-0-c R - 0 - C x
A - ~ ~ ~ o ~ c H ~ c H ~ - o2, ~ c H ~ 0
n
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0
OH
Table 1. Chain Length of Host Polymer Amphiphiles and Guest Polymers chain length polymer of polymer guest chain length polymer of polymer ( m ) amphiphile segment (n) PEG 4-191 In 55
120 2n
23
PMAA
6-96
46
Guest Polymer HO+CH~CH~-O+H m
Y
H
z
-
T
~
C=O m I
OH PEG(m)
PMAA(m)
Experimental Section Materials. The amphiphiles, 1, (n= 55 and 120)11and 2, (n = 23 and 46)14were prepared by the method described previously. PMAA(m)s (m = 6-96) and PEG(m)s (m= 4-191) as a guest polymer were prepared according t o the manner described p r e v i o u ~ l y ~and ~ J ~were obtained from a commercial source (nacalai tesque Co., Ltd.), respectively. Spreading Experiment. The monolayers were obtained by spreading benzene-ethanol (8:2 in vol) solutions of polymer amphiphiles (l,,2,) on purified water (MILLI-Q system,Millipore Ltd.) or on aqueous guest polymer (PMAA(m),PEG(m))solutions (5 x unit M). The concentration of the spreading solution was about 1.5 mg/mL. A total of 20 min after spreading, the gaseous monolayer was continuously compressed. The compressional velocity was 1.20cm%. The Wilhelmy plate method and a Teflon-coated trough with a microprocessor-controlled film balance (US1 System Ltd.), with a precision of 0.01mN/m, were used for surface pressure measurements. The measurements of surface pressure (+area (A) curves were repeated several times to check their reproducibility. Deposition of Monolayers onto a Substrate and FTIR Spectroscopy. Langmuir-Blodgett (LB) films of polymer monolayers were transferred in the vertical mode at a prescribed surface pressure and a transfer rate of 10 m d m i n onto CaFz plates. The transmission FTIR spectra of the LB films thus obtained were measured by using a Nicolet System 800 spectrophotometer at a resolution of 2 cm-l.
Results and Discussion
Molecular Design and Preparation of Host and Guest Polymers. Interpolymer complexations of PMAA and PEG have been extensively investigated ever since Bailey's finding.17 Such a complexation can occur even in an aqueous solution mainly through hydrogen bonding between carboxylic acid and ether oxygen due to inherent properties of macromolecules such as a cooperative (15)Niwa, M.; Matsumoto, T.; Izumi, H. J . Mucromol. Sci., Chem. 1987,A24,567. (16) Niwa, M.; Sako,Y.; Shimizu, M. J . Mucromol. Sci., Chem. 1987, A24, 1315. (17)Bailey, F.E.;Lindberg, R. D., Jr.; Callard, R. W. J . Polym. Sci. 1984,A2, 845.
interaction between them. In spite of the character of macromolecules different from that of small molecules, it has seemed to be difficult to elucidate a dynamic, precise interaction mechanism among synthetic polymers in bulk phase. In biological systems, especially in the protein synthesis processes, inter-macromolecular interactions between tRNA and mRNA upon precise nucleic acid base pairing play a key role to govern the sequence of amino acids in the resultant protein. In this regard, we have proposed a monolayer system composed of polymer amphiphiles in which the polymer segments can be aligned a t the two-dimensional interface. The basic structure of the amphiphiles(l,, 2,) prepared in this study consists of a chain-length-controlled polymer segment (PMAA or POE) and two long alkyl chains, which are connected with one terminus of the polymer chain, so as to form a stable monolayer on water. The amphiphiles of 1, were prepared according to Scheme 1. A tribromomethane derivative, 3, was first prepared by reaction of dioctadecyl L-glutamate with tribromoacetyl chloride. Polymerization of methacrylic acid with 3 was carried out with Mnz(CO)lo according to the method established previously. la The resulting amphiphile was confirmed to consist of two long alkyl chains (C1&37-) as the hydrophobic part and a PMAA segment as the hydrophilic part by structural analyses. The chain length of the PMAA segment (n)can be readily controlled by adjusting polymerization conditions such as feed composition of the monomer and the catalyst system and conversion.la The amphiphiles of 2, were successfully prepared by treating dioctadecyl L-glutamate with a large excess of terephthaloyl chloride and then with CH30terminated POE (Japan Catalytic Chemical Industry., Ltd.). Resultant amphiphiles of both 1, and 2, have two different polymer segment lengths (n) as summarized in Table 1. P W s with various chain lengths as one of the guest polymers were prepared by photopolymerization of methacrylic acid with bis(isopropy1xanthogen) disulfide (BX), which can serve as an initiator-chain transfer agentprimary radical terminator. The chain length ( m )could be controlled over a wide range by adjusting feed ratios ([methacrylic acidHBX]) and conversion.15J6 The chain lengths ( m )for PMAks thus obtained are also listed in Table 1,together with those for PEGS used in this study. Effect of Chain Length on Spreading Behaviors. Figure 1shows the n-A isotherms of 155 on pure water and (18)Niwa, M.; Higashi, N.; Okamoto, M. J . Mucromol. Sci., Chem. 1988,A25, 1515.
Chain Length Discrimination of Polymers
Langmuir, Vol. 10, No. 12, 1994 4653
60
-
A
E
\
z
5
40-
a
fa
a a
1 . 2 ,e ,
2
4
6
8
,
1
0
P
8 'r
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Area (nm*/molecule)
Figure 1. Surface pressure (n)-area (A) isotherms of 155 on water (a) and on aqueous PEG(191)(b) at pH 4.0,20 "C. The inset shows pH dependence of the molecular area on water (a) and on aqueous PEG(191)(b) at a constant surface pressure of 20 mN/m on the basis of n-A curves measured at different pH values.
on aqueous PEG(191) at pH 4 , 2 0 "C. With addition of PEG to the subphase, the JG-Acurve was considerably compressed compared with that on pure water. The inset in Figure 1 shows the pH dependence of the molecular area at a constant surface pressure of 20 mN/m on the basis of JG-Acurves measured at different pH values. The molecular area on water (without PEG) increased drastically at around pH 6 with increasing the pH in the subphase. A PMAA in a bulk aqueous solution has been known to show conformationaltransition in the pH region 5-6,19 and thus this pH-induced expansion of the monolayer is ascribable to such conformational change of the PMAA segment in 155 from a compact globular coil in acidic subphase to an expanded form at higher pH due to cooperative, electrostatic repulsive forces among the deprotonated carboxylic acid groups. On the other hand, the pH dependence on aqueous PEG was different from 6) the that on water: at the lower pH region (pH monolayer was remarkably compressed compared with that on water as described above though the limiting molecular area (at pH 41, estimated by extrapolating the solid-like regions to zero pressure, 0.47 nm2, is close to the cross section of the vertically oriented hydrocarbon chains (0.40 nm2). The observed monolayer compression should be produced by formation of an interpolymer complex between the PMAA segment of 155and PEG in the subphase. The driving force of such complexation is supposed to be the multiple hydrogen bonding of COOH-OCHZCH~,though hydrophobic interaction such as a-methyl group in PMAA and methylene unit in PEG may not be excluded. In fact, in our previous studied0on comparison in the thermal behavior between a poly(acry1ic acid) segment-carryingamphiphile (4,) without a-methyl group and 155 with a-methyl group, it was found that in the 4,-PEG complexed monolayer the hydrogen bonding of carboxylic acid and ether oxygen would be a main factor for complexation but in the 155-PEG monolayer the hydrophobic interaction of a-methyl groups and methylene (19) Olea, A. F.; Thomas, J.K. Macromolecules 1989,22,1165, and references cited therein.
\
PH In the Subphm
1.O
1.5
2.0
2.5
Figure 2. Surface pressure (n)-area (A) isotherms of 223 on water (a) and on aqueous PMAA(24)(b) at pH 4.0,20 "C.The inset shows pH dependence of the molecular area on water (a) and on aqueous PMAA(24)(b) at a constant surface pressure of 30 mN/m on the basis of n-A curves measured at different pH values.
units should also play an important role for complexation on water as well as the hydrogen bonding. 0
y
Br
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The same spreading experiment was carried out for 1120 having longer PMAA segment. Similar pH dependence of isotherms was observed though the molecular area of the 1120monolayer was always larger than that of the 155 monolayer. Subsequently the same experiment was undertaken for the reverse pairing of the host monolayer (2,) and the guest polymer (PMhWm)). Figure 2 shows the JG-A isotherms of 2 2 3 on pure water and on aqueous PMAA(24) at pH 4 , 2 0 "C. With addition of PMAA to the subphase, the monolayer was found to expand compared with that on pure water (without PMAA), which is a result reverse to what was observed for the combination of 1, and PEWm). The pH dependence of the molecular area at a surface pressure of 30 mN/m (A30) is shown in Figure 2 (inset). Without PMAA in the subphase, the A30 value was not affected at all by varying pH in the range pH 2.5-9.5, as was expected. When PMAA(24)was added to the subphase, theAsovalues were always larger than those on pure water over the whole pH region, suggesting formation of a surface interpolymer complex between the POE segment of the monolayer former and the guest PMAA upon binding of PMAA via hydrogen bonding from the bulk aqueous phase. It is also clear from the figure that the A30 value depends markedly upon pH in the subphase: with decreasing pH, the A30 value increases gradually, and below pH ca. 5, in particular, a steep increase in A30 is observed. At higher pH, the POE segment-PMAA interaction may be weak since the carboxylic acid groups of PMAA are ionized. The As0 value is relatively close to that on pure water. Upon a decrease of the pH, the POE segment can interact with PMAA
Higashi et al.
4654 Langmuir, Vol. 10, No. 12, 1994
I
40 I
Chain Length of PEG (m) 80 120 160 200 I
I
I
I
A
0.7k
.O
1.8
1.6 1.4
20 40 60 80 100 Chain Length of PMAA (m)
Figure 3. Area changes of 1, (A) and 2, (B) monolayers on aqueous PEG and PMAA, respectively, at a constant surface of the pressure of 30 mN/m responding to the chain length (m) corresponding guest polymers at 20 "C. Broken lines indicate the chain length (n)of the polymer segment of host monolayer formers (l,,2,J. through hydrogen bonding since the carboxylate groups are protonated, which caused expansion of the monolayer. Similar observations were made for the 146 monolayer. The effects of the chain length (m)of guest polymers (PEG, PMAA)on the host monolayers were then examined. Figure 3 displays the molecular area changes of 1, and 2, monolayers a t a surface pressure of 30 mN/m, pH 3.0, responding to the chain length (m) of PEG and PMAA, respectively, in the subphase. In the case of 1, monolayers, the molecular area decreases systematically with increasing m up to around m = 55 (for 155 monolayer) and m = 120 (for 1120 monolayer), beyond which the area is independent of m for each monolayer. In contrast, the molecular area for 2, monolayers increases with increasing m up to around m = 25 (for 223 monolayer) and m = 50 (for 246 monolayer). Observed difference in the molecular area change occurred by adding guest polymers into the subphase is supposed to be ascribable to the difference in the size of each polymer segment of the host monolayer former at the air-water interface adopted before and after complexation with guest polymers. Before complexation, the PMAA segment in 1,-assembled monolayers may occupy a relatively large volume due to dimer structure formation of carboxylic acid groups of the PMAA segment (as described later) and/or solvation with water. By addition of PEG into the water phase, the complexation occurs and simultaneously dehydration of the PMAA segment must take place, and thus hydrophobicity of the complexed PMAA segment with PEG should increase compared with that of the bare PMAA segment. Consequently the occupied volume of the complexed PMAA segment at the interface might become smaller than that before complexation, providing such decrease in the
molecular area of 1,. In contrast, the POE segment in 2, assemblies adopts a relatively small size on pure water. By incorporation of the guest PMAA molecules into the POE segments, the occupied volume of the complexed POE monolayer at the interface must become larger than that before complexation, consequently giving increase in the molecular area of 2,. These considerations can consistently explain the observed results. Interestingly, the chain length (m)of guest polymers at each inflection point as observed in Figure 3 is in good agreement with the chain length (n) of the corresponding polymer segment of 1, or 2,. These results suggest that a cooperative interaction between the polymer segment of 1, or 2, monolayer and the guest polymer chain is enhanced with increasingm up tom = n. The interesting match between n of the amphiphile and m of the guest polymers in the subphase is due to formation of the most expanded (for the combination of 1, and PEG) or the most compactly condensed (for the combination of 2, and PMAA) conformation. Conceivably, the complexation event occurring a t the air-water interface is most efficiently transmitted to the monolayer state under the condition of m L n. These results clearly demonstrate that the monolayers of 1, and 2, have a discriminating ability against the chain length of the corresponding guest polymer, PEG(m) and PMAA(m), respectively, at the air-water interface. FTIR Spectroscopy for the Complexed Monolayers. To elucidate the interaction mode between host monolayers and guest polymers, transmission FTIR spectra were measured for the complexed monolayers. All monolayers were transferred in the vertical mode at a constant surface pressure of 30 mN/m, where monolayers are in a condensed phase, and a transfer rate of 10 mm/ min onto CaF2plates. pH in the subphase was adjusted to 3.0 so that all monolayers should form complexes with the corresponding guest polymers at the air-water interface. Figure 4 shows typical FTIR spectra of the LB films (10 layers deposition) from pure 155 monolayer (denoted A) and 155-PEG(191) complex monolayer (denoted B). We focused on absorptions in the carbonyl stretching region (1600-1800 cm-'). A salient feature of the spectrum of the LB film from pure 155 monolayer is the presence of an infrared band at 1700 cm-' which is ascribed to the carboxylic acid dimer.20 Thus, the large majority of the carboxylic acid groups of 155 exist as intermolecular dimers (shown schematically in Figure 4). Though the molecule of 1 5 5 has two ester groups in its hydrophobic portion, the content of them is much smaller compared with that of the carboxylic acid group and thus the absorption band based upon ester carbonyl (at around 1750 cm-') may be too weak to appear in the spectrum. In the spectrum of complexed 155-PEG(191) LB film, a new band appeared at 1728 cm-l. This band is assigned to free C=O groups20that occur when a n intermolecular interaction (hydrogen bond) is formed between the carboxylic acid group of PMAA segment and the ether oxygen atom of PEG as depicted in Figure 4. The same spectral feature was observed for the combination of 2,-PMAA(m). These results clearly demonstrate that a main driving force for complexation between host monolayers and guest polymers is due to a multiple hydrogen bonding between the carboxylic acid and the ether oxygen atom. It is important to reveal chain length (m) effects of the guest polymers on such an inter-macromolecular hydrogen bonding. The peak area at 1728 cm-l(A1728) in infrared spectra was estimated by means of a curve resolution technique. A scale-expanded spectrum in the carbonyl (20) Lee, J. Y.; Painter, P. C.; Coleman, M. M. Macromolecules 1988, 21,346.
,
Chain Length Discrimination of Polymers
1.51
Langmuir, Vol.10,No.12,1994 4655 Chain Length of PEG (m)
l?O
3?0
2pO
4?0
S?O
A
n=55
m
E
sdao
lis0
1500
1250
1000
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1.4
Wavenumber cm” 0 0
C
b
1
I
1
I
20
40
60
80
I
100
I
120
Chain Length of PMAA (m)
Figure 4. FTIR spectra of the LB films (10 layers deposition) prepared from pure 155 monolayer (A) and from 155-PEG(191) complex monolayer (B) in the 750-2000 cm-l region. Part C
shows a scale-expanded spectrum in the carbonyl stretching region of the latter LB film. stretching region is shown in Figure 4. Figure 5 displays a relationship between the relative content of intermacromolecular hydrogen bonding (A172dA2992)in the LB films and the chain length (m) of guest polymers for 155PEG(m) (denoted A) and 246-PMAA(m) (denoted B). The Y-axis (A172$A2992) is normalized with the absorption intensity of CH2 stretching (A2992) based upon the alkyl chains of 1, and 2,, which must be inert against hydrogen bonding. The ratio ofA172$A2gg~for both 155-PEUm) and 246-PMAA(m) increases systematically with increasing the chain length (m)of guest polymers up to when m is almost equal to the segment length ( n )of host monolayer formers, beyond which the ratio shows a tendency to decrease. A similar chain length dependency was observed for other combinations of 1120-PEGtm) and 223-PMAA(m). These spectroscopic data mean that a most effectiveintermacromolecular hydrogen bonding occurs when the segment length of monolayers (n) is matched with that of the corresponding guest polymers (m)and are also comparable to the results obtained from the spreading experiments. There is, however, only a significant discrepancy in the chain length effects of guest polymers between the monolayer behavior and the infrared spectroscopy: in the former case the chain length (m)dependence of the molecular area disappeared a t m n, but in the latter case the ratio of A172$&992 (the content of an intermacromolecular hydrogen bond in the LB films) showed an obvious chain length dependence even at m > n as can be seen from Figures 3 and 4, respectively. The spectroscopic analyses were made on LB films deposited on CaF2 plates. Since LB films were prepared through the deposition process of surface monolayers at the air-water interface, a structural change in surface complexed
Figure 5. Relative content of inter-macromolecularhydrogen bonding (A172dA2992)in the LB films from &-PEG(m) (A) and 2&-PMAA(m) (B)complexmonolayers as a function of the chain length ( m )of guest polymers.
monolayers might occur during that process. For instance, a guest polymer having much longer chain length compared with the segment length of monolayer prefers existing in bulk aqueous phase to complexing with the monolayer probably due to a hydrophilicity of the long, uncomplexed segment, and consequently might destroy such interpolymer complexes and could not be deposited onto the substrates together with monolayer formers. Therefore, the above spectroscopic data (Figure 5)can be assigned to a stability of the complexed monolayers at the air-water interface. The monolayer composed of combination of n = m would provide a most stable complex through multiple hydrogen bonding between carboxylic acid and ether oxygen atom.
Conclusions Interactions working between PMAA and PEG at the air-water interface were examined by means of a spreading experiment and an FTIR spectroscopy. One terminus of those polymer chains was modified with two long alkyl chains (l,,2n),so as to function as amphiphiles. They formed stable monolayers on water. With addition of the corresponding guest polymers (PEGfor 1, and PMAA for 2,) into the subphase, x-A isotherms were drastically changed, which are sensitive to the chain length ofthe guest polymers, due to rearrangement of a multiplehydrogen bonding mode and subsequent formation of the interpolymer complex. These polymer assemblies of 1, and 2, were found to have the ability to discriminate against the guest polymers. Host-guest combinations are summarized in Table 2, in which the other combinations of a poly(acry1ic acid) (4,)- and a poly(methacry1-
4656 Langmuir,Vol. 10,No.12, 1994
Higashi et al.
Table 2. Combinations of the Host Polymer Monolayers and the Guest Polymers in the Subphasea chain length host monolayer former recognition guest polymer remarks this work and ref 12
-
HO~2CH2-O)-H
m
/
this work
c=o I
ref 13
OH
amide) (&)-bearing- amphiphile are also included These phenomena were achieved owing to linked properties of the two-dimensionally assembling of polymer segments in a surface monolayer state and the structural feature of the component molecules that possess a well-defined polymer segment having the abilities of hydrogen bonding, ion-dipole interaction, and so on. We believe that these findings provide a first example of the macromolecular
assembly system that can recognize the different macromolecules and that this system is of particular significance not only in view of its applicability for a sensor but also in view of the model of a biofunctional polymer.
Acknowledgment. Financial support from the Aid of Doshisha University's Research Promotion Fund (1993) (to M.N.) is gratefully acknowledged.
