Synthetic Macromolecules with Higher Structural Order - American

Chapter 13

Downloaded by PENNSYLVANIA STATE UNIV on September 2, 2012 | http://pubs.acs.org Publication Date: March 4, 2002 | doi: 10.1021/bk-2002-0812.ch013

Reversed-Type Micelle Formation Property of End-Glycosidated Polystyrene Toyoji Kakuchi and Naoya Sugimoto Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-810, Japan

The controlled radical polymerization of styrene using the TEMPO-based initiators with carbohydrate residues is a novel method for producing end-glycosidated polystyrenes. Xylose, glucose, galactose, cellobiose, maltose, maltotriose, maltotetraose, maltopentaose, and maltohexaose were used as the carbohydrate residues. The well-defined end-glycosidated polystyrene aggregated to form the reversed-type micelle in benzene solution. The aggregation number varied from 2.2 to 62.5 depending on the polystyrene chain length and the number of pyranose units.

Macromolecular design and the synthesis of polymers consisting of hydrophilic and hydrophobic units have drawn attention from the viewpoint of constructing synthetic macromolecules with a higher structural order. Thus, there are many efforts to synthesize various types of well-defined polymers using carbohydrates as hydrophilic units, because carbohydrates, compounds with hydroxy groups, are easily available raw materials. In addition, living polymerization techniques are used for the synthesis of carbohydrate-containing

© 2002 American Chemical Society In Synthetic Macromolecules with Higher Structural Order; Khan, I.; ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

177


178 polymers with well-defined structures. For example, ROMP (7) and living cationic polymerization (2) techniques using appropriate monomers were performed to afford homo- and block copolymers having carbohydrate residues as side chains, and living anionic polymerization methods combined with terminators (3) or initiators (4) possessing carbohydrate residues produced endglycosidated polymers. Recently, we reported the synthetic method for the well-defined endftmctionalized polymers with mono- and disaccharide residues using controlled radical polymerization (5). Sufficient control of the molecular weight and molecular weight distribution as well as the ^nd-functionality was realized in each of the polymer samples synthesised using TEMPO-based initiators having acetylated carbohydrate residues. Thus, of great interest is studying the micelle formation properties of end-glycosidated polystyrenes. In this chapter, we describe the synthesis of well-defined end-functionalized polystyrenes (3) by the polymerization of styrene using the TEMPO-based initiators (1) having acetylated carbohydrate residues, such as xylose (a), glucose (b), galactose (c), cellobiose (d), maltose (e), maltotriose (f), maltotetraose (g), maltopentaose (h), and maltohexaose (i). In addition, the effect of polystyrene chain length and type of end-carbohydrate groups on the aggregation number for the micelle of 3 in benzene solution was investigated. Synthesis of End-glycosidated Polystyrene Georges et al reported that narrow molecular weight polymers can be prepared by the radical polymerization of styrene using a traditional radical initiator, benzoyl peroxide and 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) as the stable free radical (6). For the "living" radical polymerization, the adduct of styrene and TEMPO is isolated as a stable compound, and many TEMPO-based initiators have been used for the synthesis of various macromolecular architectures. Thus the controlled radical polymerization method can be used to obtain carbohydrate residues as end-functional groups. The TEMPO-based initiators having xylose (la), glucose (lb), galactose (lc), cellobiose (Id), maltose (le), maltotriose (If), maltotetraose (lg), maltopentaose (Ih), and maltohexaose (li) were synthesized by the reaction of 4-ethylphenyl derivatives of the corresponding carbohydrates with TEMPO in the presence of di-teri-butyl peroxalate (7). The bulk polymerization of styrene initiated by the TEMPO-based initiators was carried out at 120 °C for 6 h. Table 1 summarizes the typical results using initiators l b and le. The polymer yield was 35 ~ 52 % for 2b and 38 ~ 45 % for 2e. The value of M increased with increasing molar ratio of styrene and initiator ([styrene]/[initiator]) from 10,500 to 31,300 for 2b and from 12,700 to 30,700 n

In Synthetic Macromolecules with Higher Structural Order; Khan, I.; ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

179

Scheme 1


+ η

SAC) : Acetylated sugar residue, R = Ac SQW

: Sugar residue, R = Η

Sugar residues OR

Rcr

ROOR

RO

ROOR

OR

OR

OR

OR

RO'

RO OR

J

n-1

0

R

n = 2:e, n = 3:f η = 4 : g, η = 5 : h η=6: i


180 Table 1. Bulk polymerization of styrène using initiators 1 and 2 '


initiator 3b 3b 3b 3e 3e 3e

[styrene] yield Initiator] (%) 300 35 600 44 900 52 300 38 600 45 900 42

b

MJM >

b>

M

n

n

1.10 1.12 1.14 1.10 1.13 1.15

10,500 20,600 31,300 12,700 23,700 30,700

a) Temp., 120 °C; time, 6 h. b) Determined by GPC using a polystyrene standard.value for 2e, and in all cases the polydispersity (MJM ) was very narrow, i.e., the value of MJM is 1.10 - 1.15. Figure 1 shows the polymer yields for the bulk polymerization of styrene using initiators lb and le ([styrene]/[initiator] = 600). Both systems display similar polymerization rates. The molecular weight of the polymers was found to increase in an approximately linear fashion with conversions, while low M /M s, such as 1.11 ~ 1.13 are maintained throughout the polymerization for both systems. For the polymerization with [styrene]/[initiator] = 600 at 120 °C for 3 h, the polymer yield and the M (MJM ) were 28 % and 14,300 (1.17) for la, 33 % and 12,800 (1.20) for lc, 29 % and 18,000 (1.12) for le, 25 % and 12,500 (1.18) for If, and 24 % and n

n

w

n

n

n

Ο

:M (1b)

M^/M^lb)

•

:M (1e)

Μ„/Μ (1β)

n

n

η

1.5

•

1.4 1.3*

•

• •

Ο

10

20 30 40 50 Conversion (wt %)

1.1 1.0 60 70

Figure 1. Evolution of experimental molecular weight and polydispersity with conversion in the bulk polymerization of styrene initiated by initiators lband le .[styrene]/[initiator] = 600, temp. = 120 °C.



181 20,900 (1.21) for Ii. These results indicated that the TEMPO-based initiator was effective for the controlled radical polymerization leading to well-defined polymers. In the ' H NMR spectra of 2b and 2e, the signals at 5.3 ~ 3.9 ppm for 2b and 5.5 ~ 3.8 ppm for 2e are assigned to the glucose and maltose units, respectively. The degrees of end-fimctionalization, which were determined by the *H NMR peak intensities, were nearly quantitative, i.e., ca. 1.0. It was observed that endfunctionalized poly(styrene)s with glucose and maltose residues were completely separated from the unfunctionalized polystyrene by TLC using an Si0 plate with toluene as the mobile phase. Under the developed conditions, polymers 2b and 2e always gave spots that remained near the spotting points (Rf = ca. 0), whereas unfunctionalized polystyrene was quite mobile to near the top (Rf = 0.9). Since the amount of each spot can be quantitatively detected by a flame ionization detector (FID), the degrees of end-functionalization can be determined by comparing each peak area. Accordingly, the TLC method coupled with FID becomes very effective for the quantitative analysis of the end-functionalized polymers, in which the experimental error is as much as 3 wt %. The degrees of end-functionalization by the analysis of TLC-FID method are also indicated to be nearly quantitative for 2b and 2e. Deacetylation of 2 was performed with sodium methoxide in THF to quantitatively afford the endglycosidated polystyrene, 3. These analytical results suggested that the polymerization of styrene using 2

5

_8 Ε

4

Ο ο IS

3

$

2

3 C C

0 ) i.bß

Ο

2.5 3.5x10* Mw Figure 2. Aggregation number of end-glycosidated polystyrenes in benzene as a function of weight average molarmass.3a( Ο ), 3b( · ), 3c( • ) 1.0

1.5

2.0


182 the TEMPO-based initiators with carbohydrate residues proceeded satisfactorily to afford the well-defined end-glycosidated polystyrenes.


Reversed-type Micelle Formation of End-glycosidated Polystyrenes Recently, block copolymers and end-functionalized polymers have been studied in terms of their phase separation and self-assembly abilities. Eisenberg et al. reported that sodium carboxylates of hydrophilic terminal groups were separated from the hydrophobic polystyrene main chains to form reverse-type micelles in cyclohexane by aggregating several polymer chains (7). In addition, Hirao et al. reported that polystyrene with one and two glucose residues at their chain ends were aggregated to form reverse-type micelles in cyclohexane (5). Thus, for the end-glycosidated polystyrene, of great interest is to study the effect of the number of pyranose units on the reverse-type micelle formation properties. For the *H NMR spectra of end-glycosidated polystyrene, 3, in C D , it was difficult to observe the carbohydrate units in 3, suggesting the aggregation of 3 leading to reverse-type micelle formation. Thus, the micelle formation of endglycosidated polystyrenes was observed by laser light scattering measurements in benzene solution. Figures 2 and 3 show the plots of the aggregation numbers vs. molecular weights of the end-functionalized polystyrenes with glucose and maltose residues (3b and 3e, respectively). The aggregation number decreased with increasing the molecular weight, i.e., from 3.7 to 3.0 with increasing Mw from 12,800 to 28,500 for 3b and from 9.1 to 3.7 with increasing Mw from 6

2.5

3.0

6

H

4.0x10

Mw Figure 3. Aggregation number of end-glycosidated polystyrenes in benzene as a function of weight average molar mas s.3d( Ο ),3e( · )


183 70 60 Φ

JQ

50 -

Ε 3 C


c ο

40

1,30 ν 20

15k

10 Ό 1

α.

1- θ -Of^

3

5x10

4

Mw

Figure 4. Aggregation number of end-grycosidated polystyrenes in benzene as afonctionof weight average molar mass. 3b ( Ο ), 3e( · ), 3f ( • ) 3g( • ),3h( Δ ),3i( • ) 20,200 to 35,000 for 3e. For the end-iuctionalized polymer with a monosaccharide, the micelle formation property of the polymers with xylose and galactose residues, 3a and 3c, slightly differed from that of 3b, because the aggregation numbers for 3a and 3c deviated from the straight line for 3b, as shown in Figure 4. A similar tendency for the end-fuctionalized polymers with the disaccharides, 3d and 3e, was also observed in Figure 3, These results indicated that micelle formation property of the end-glycosidated polystyrene may be affected by the type of carbohydrate residues. Figure 4 shows the plots of the aggregation numbers vs. molecular weights of the end-functionalized polystyrenes with mono-, di-, and oligosaccharides, i.e., glucose (3b), maltose (3e), maltotriose (3f), maltotetraose (3g), maltopentaose (3h), and maltohexaose (3i). For all the end-glycosidated polystyrene, the aggregation number decreased with increasing molecular weight, e.g., from 62.5 to 26.0 with increasing Mw from 20,900 to 45,800. In addition, the aggregation number increased with the increasing number of pyranose units, i.e., the aggregation number increased in the order of glucose (3b) > maltose (3e) > maltotriose (3f) > maltotetraose (3g) > maltopentaose (3h) > maltohexaose (3i). These results indicated that changing the polystyrene chain length and the number of pyranose units should control the micelle size of the end-glycosidated polystyrenes.


184 Experimental Part Materials and measurements. The molecular weights of the resulting polymers were measured in chloroform using a Jasco GPC-900 gel permeation Chromatograph equipped with two polystyrene gel columns (TSKgel GMHHRM , TOSOH Corporation). The number-average molecular weight (M ) and molecular weight distribution (M /M ) of the polymers were calculated on the basis of polystyrene calibration. The TLC-FID measurements were carried out using an IATRON MK-5 (Iatron Laboratories, Inc.). Laser light scattering measurements were performed with a Super-Dynamic Light Scattering Spectrophotometer DLS-7000AL (Ohtsuka Electronics Co., Ltd.) in benzene. All the polymer solutions were clarified using a 0.1 μιη millipore filter. Polymerization. A mixture of lb (29.2 mg, 0.048 mmol) and styrene (3.0 g, 28.8 mmol) was heated at 120 °C for 15 h under a N atmosphere. After cooling, the reaction mixture was diluted with CHC1 , and then poured into methanol (300 mL) after which the precipitate was filtered off. The obtained precipitate was purified by reprecipitation in chloroform-methanol and dried in vacuo to yield the polymer (1.82 g, 59 %). The M and MJM were 25,200 and 1.13, respectively. Deacetylation. After a mixture of 0.5 g of 2b (M„ = 20,600) and 2[M] sodium methoxide (5 mL) in 15 mL of dry THF was stirred at room temperature for 12 h, the whole solution was poured into 200mL of methanol/water (v/v, 9:1). The precipitate wasfilteredoff, washed with water and then methanol, and purified by two reprecipitations from chloroform/methanol. After freeze-drying of a benzene solution of the product (3b), a white powder was quantitatively obtained. n


w

n

2

3

n

n

References 1. Nomura,K.;Schrock, R. R. Macromolecules, 1996, 29, 540. 2. Yamada,K.;Yamaoka,K.;Minoda,M.;Miyamoto, T. J. Polym. Sci.: Part A: Polym. Chem., 1997, 35, 255. 3. Hayashi,M.;Loykulnant,S.;Hirao,Α.;Nakahama, S. Macromolecules, 1998, 31, 2057. 4. Aoi, K.; Suzuki,H.;Okada, M . Macromolecules, 1992, 25, 7073. 5. Sugimoto,N.;Kakuchi, T. Polymer Preprints, 1999, 40, 111. 6. Georges, M . K.; Veregin R. P. N . Macromolecules, 1993, 26, 2987. 7. Yamada, B. Macromolecules, 1998, 31, 4659. 8. Desjardins, Α.; Theo, G.M.;Eisenberg, A. Macromolecules, 1992, 25, 2412.


Synthetic Macromolecules with Higher Structural Order - American

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