Poly(oxazolines)s with Tapered Minidendritic Side Groups. The

Biomacromolecules 2001, 2, 706-728

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Poly(oxazolines)s with Tapered Minidendritic Side Groups. The Simplest Cylindrical Models To Investigate the Formation of Two-Dimensional and Three-Dimensional Order by Direct Visualization V. Percec* and M. N. Holerca Roy&Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6323

S. N. Magonov Digital Instruments, Veeco Metrology Group, Santa Barbara, California 93110

D. J. P. Yeardley and G. Ungar Department of Engineering Materials and Center for Molecular Materials, The University of Sheffield, Sheffield, S1 4DU, U.K.

H. Duan and S. D. Hudson Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106 Received April 21, 2001; Revised Manuscript Received July 6, 2001

The synthesis of 2-[3,4-bis(n-alkan-1-yloxy)phenyl]-2-oxazolines with alkan ) octan, decan, dodecan, and tridecan is presented. Their living cationic ring opening polymerization produces cylindrical macromolecules that self-organize in a hexagonal columnar two-dimensional phase. The structural analysis of these polymers was carried out by a combination of techniques including differential scanning calorimetry, thermal optical polarized microscopy, X-ray diffraction, transmission electron microscopy, electron diffraction, scanning force microscopy, and atomic force microscopy (AFM). The diameter of these cylindrical macromolecules ranges from 33 to 44 Å, and therefore they represent the simplest cylindrical macromolecules that can be directly visualized by AFM on a surface. Preliminary experiments have demonstated the use of these cylindrical macromolecules as models to investigate the creation of two-dimensional and three-dimensional order via direct visualization and thus they represent the simplest nonbiological systems that mimic the role played by the complexes of nucleic acids with proteins in structural analysis by direct visualization. Introduction The origin of order and complexity represents one of the most fundamental problems of natural sciences.1,2 In this publication we will report the synthesis and structural analysis via a combination of differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission optical polarized microscopy (TOPM), transmission electron microscopy (TEM), and electron diffraction (ED) of poly(oxazoline)s containing tapered minidendritic side groups, i.e., poly{2-[3,4-bis(n-alkan-1-yloxy)phenyl] oxazoline} where n-alkan is octan, decan, dodecan, and tridecan. These macromolecules self-assemble intramolecularly into stiff cylindrical macromolecules with diameter ranging from 33 to 44 Å. Subsequently, these stiff cylinders self-organize in two-dimensional (2-D) and three-dimensional (3-D) hexagonal columnar lattices. These cylindrical macromolecules can be visualized by TEM in a lattice and by scanning force microscopy (SFM) and atomic force microscopy (AFM) in disordered and ordered assemblies as well as individual molecules on surfaces. Preliminary experiments have demonstrated that these macromolecules can be used to inves-

tigate via direct visualization the creation of order in one, two, and three dimensions. Therefore these macromolecules provide the simplest class of cylindrical molecules that can be used to visualize the formation of 1-D, 2-D, and 3-D ordered states. The first examples of cylindrical macromolecules generated from polymers coated with tapered minidendritic (i.e., first generation monodendron) side groups that self-assemble intramolecularly in cylindrical macromolecules that subsequently self-organize in hexagonal columnar lattices were discovered in our laboratory and were reported in 1989.3 The hypothesis behind this discovery and the subsequent series of experiments was inspired by our intention to design polymers exhibiting a biaxial nematic phase according to a concept advanced for biaxial nematic low molar mass liquid crystals.4 We have considered that the most suitable architectural motif for the construction of side-chain liquid crystal polymers exhibiting a biaxial nematic phase would have to be a building block containing a combination of half-disk and rodlike segments, i.e. a hemiphasmid that was originally elaborated by Maltheˆte and Levelut.4 The attachment of

10.1021/bm015550j CCC: $20.00 © 2001 American Chemical Society Published on Web 08/17/2001

Poly(oxazolines)s with Tapered Minidendritic Groups

architectural motifs containing an AB3 first generation halfdisk-like monodendron (i.e., minidendron) and a rodlike segment as side groups to a polymer backbones did not produce the desired biaxial nematic side chain liquid crystalline polymer. Instead, the resulting macromolecule had its backbone coated with the tapered side group into a cylindrical shape that subsequently self-organized into a hexagonal columnar 2-D lattice.3 This intramolecular self-assembly resembles that of the self-assembly of the rodlike viruses,5 and therefore, we have initiated a program to develop nonbiological synthetic models that exhibit some of the structural characteristics and functions of rodlike viruses. Indeed, these cylindrical macromolecules undergo a reversible intramolecular first-order transition to an intramolecular 3-D helical structure6 and, therefore, have generated a novel model to investigate hierarchical folding in nonbiological molecules. With the aid of libraries of AB2 and AB3 self-assembling monodendrons of various generations,7 we have expanded the diversity of cylindrical macromolecules that self-assemble in hexagonal lattices to polymers produced from higher generations of monodendrons and to spherical macromolecules that are able to self-organize in cubic lattices.8h Intramolecular selfacceleration7i,8a,c,g and self-inhibition8g of conventional chain and living polymerization reactions, controlled chain stiffness,8b,c internal compartmentalization,3d visualization of individual cylindrical and spherical macromolecules7k,8b-h and of their motion,8c and intramolecular folding6 are some of the conceptual advances generated with the aid of these macromolecules at the interface between various fields of the chemical sciences. These self-assembling dendritic building blocks are finding applications in areas such as the site isolation of electronically active macromolecules.9 At the same time, research in other laboratories is elaborating cylindrical macromolecules derived from dendritic building blocks that do not exhibit the perfection required to self-assemble in lattices.10 Several proceedings of meetings review our earlier research on this topic.11 Dendrimers12a and hyperbranched polymers that fold into other 3-D architectures are also known.12b,c The investigation of cylindrical objects based on larger generations of self-assembling monodendrons is of interest for the elucidation of the design principles required to produce larger nanocylinders and nanospheres, for the design of their 3-D intramolecular structure, and for other biological mimics.6,7,8,13 Nevertheless, we have found that the first generation of monodendrons (i.e., minidendrons) continues to provide the most powerful architectural motifs that can be used as models for higher generations of dendrimers and of polymers based on them.3,6,7,8 The simplest AB2 minidendron used extensively in our laboratory to control the structure of higher generations of dendrimers is 3,4-bis(nalkan-1-yloxy)benzoate.7k,l,n A combination of structurally simple self-assembling tapered units equipped with a polymerizable group that can be manipulated via living polymerizations was and continues to remain part of the original strategy of our research in this field. So far, we have been using living cationic polymerization of vinyl ethers,3k,l living metathesis ring-opening polymerization of norbornenes,3s,t

Biomacromolecules, Vol. 2, No. 3, 2001 707

and living cationic ring-opening polymerization of cyclic iminoethers. While our research on cyclic iminoethers containing minidendritic side groups was in advanced stages,11f,14 a series of reports on the synthesis of poly{2[3,4-bis(n-decan-1-yloxy)phenyl]oxazoline} by cationic ringopening polymerization of the corresponding cyclic iminoether15a and by the N-acylation of poly(ethyleneimine)15b,c was published. The resulting polymer was shown to exhibit a hexagonal columnar (φh) mesophase. These reports have prompted us to delay the publication of our comprehensive series of experiments11f,14 on libraries of cyclic iminoethers until they were completed.3v This paper is the second3v in a series of publications that will demonstrate the capabilities of minidendritic cyclic iminoethers and of their polymers and copolymers as models for higher generations of dendritic building blocks and as biological mimics. This paper will demonstrate that poly{2-[3,4-bis(n-alkan-1-yloxy)phenyl]oxazoline}s containing n-alkan as octan, decan, dodecan, and tridecan provide the simplest cylindrical models to investigate the creation of 2-D and 3-D order via direct visualization. Results and Discussion Synthesis and Polymerization of 2-[3,4-Bis(n-alkan-1yloxy)phenyl]oxazolines. The synthesis of 2-[3,4-bis(nalkan-1-yloxy)phenyl]oxazolines with octan, decan, dodecan, and tridecan as alkan groups follows a method reported in a previous publication from our laboratory (Scheme 1).16 The sequence of reactions illustrated in Scheme 1 was selected since it produces higher than 82% yield at each individual step. This synthesis can be monitored at each step by 1H NMR spectroscopy. A sequence of 1H NMR spectra together with the assignments of proton resonances starting from the first product and ending with the cyclic iminoether monomer is shown in Figure 1. Starting from the minidendritic methyl benzoates 2/n, the potassium benzoates were obtained by reaction with KOH in EtOH (95%) for 12 h at reflux. Further neutralization with HCl afforded the corresponding acids 3/n in 90-94% overall yields. The reaction of the minidendritic benzoic acids 3/n with SOCl2 in CH2Cl2 at 23 °C using DMF as catalyst yielded almost quantitatively (99.9%) the acid chlorides 4/n (n ) 8, 10, 12, 13) within 0.5 h. After the distillation of the solvent and residual SOCl2 under vacuum, the product was used in the subsequent reaction step without additional purification. In the next step, a CH2Cl2 solution of the acid chloride 4/n was added over an ice-cooled solution of ethanolamine in CH2Cl2. After 1 h of stirring at 0 °C, the temperature was increased to 40 °C for 4-5 h. Any variation from the order of addition or sequence of temperature decreases the purity of the products. The formation of the 2-oxazolinium ring 6/n takes place within several minutes when SOCl2 is added to a solution of 3/n in the presence of DMF as catalyst. Nevertheless, 1H NMR indicated traces of secondary products, mostly due to the substitution of OH by Cl, and consequently, the reactions were carried out in the absence of DMF, for only 15 min. Under these conditions, the 1H NMR analysis indicated complete conversion and no secondary products. The resulted

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Scheme 1. Synthesis of Monodendritic 2-Oxazolines

oxazolinium salts 6/n were neutralized to obtain the 2-substituted-2-oxazolines 7/n ((3,4)nG1-Oxz) in good yields (82%-86%). These monomers were stored in a desiccator over CaSO4 and freshly freeze-dried from benzene prior to polymerization. The cationic ring-opening polymerization of the minidendritic 2-substituted-2-oxazolines is presented in Scheme 2. The polymerization of (3,4)nG1-Oxz initiated by MeOTf was conducted either in o-dichlorobenzene (o-DCB) at 100 °C or in bulk at 160 °C. The polymer was end-capped with an OH group by the reaction of its oxazolinium chain end with KOH/THF/H2O,16 or used as resulted from the reaction. The experiments in solution required a longer reaction time and a thorough purification of the polymerization solvent. These disadvantages were alleviated by working in bulk, at 160 °C. Only when the presence of an ionic chain end was affecting the characterization of the polymer, i.e., in the case of TEM, AFM, and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and XRD analysis, the polymer was end capped with the OH end group. On the other hand, it was established that for polymerization experiments that employed [M]0/[I]0 ) 5-1000 there was no difference between the end-capped and non-end-capped polymers in DSC, TOPM, and gel permeation chromatog-

Percec et al. Scheme 2. Polymerization of Minidendritic 2-Oxazolines, Poly[(3,4)nG1-Oxz]

raphy (GPC) analysis. Consequently, routine experiments were conducted in bulk without the additional end capping. The 1H NMR chain-end analysis of polymers poly[(3,4)12G1-Oxz] with degree of polymerization (DP) lower than 200 indicated experimental molecular weights identical with the theoretical ones. A molecular weight analysis by GPC was performed on samples withdrawn during the polymerization and on the final polymers, poly[(3,4)nG1-Oxz], obtained after the quantitative conversion of the monomers. The GPC experimental molecular weights of the separated polymers were observed to be lower than the theoretical molecular weights (Tables 1-4). These deviations resulted from the fact that the GPC data was obtained using a calibration against polystyrene standards. The MALDI-TOF analysis (Figure 2) of the end-capped polymers with molecular weights below 10000 confirmed the values determined by NMR and also allowed for the calculation of the Mw/Mn values. The Mw/Mn values determined by GPC agree with those determined by MALDI-TOF. Figure 2a presents the MALDI-TOF spectrum of poly[(3,4)10G1-Oxz]-OH with DP ) 5 and shows that the molecular ion peaks are separated by 459.2 Da. This value corresponds to one repeat unit of the poly[(3,4)10G1-Oxz]-OH. The low abundance peaks at M+ + 23 correspond to the Na+-bound species. In contrast, the spectrum corresponding to poly[(3,4)10G1-Oxz]-OH with DP ) 10 (Figure 2b) shows that the dominating species are the Na+-bound polymers (M+ + 23). This is in agreement with the general observation that the analysis of higher molecular weight polymers by MALDI-TOF may improve by the addition of salts. Both spectra also show peaks that correspond to non-end-capped poly[(3,4)10G1-Oxz]. This is visible at M+ + 155, corresponding to the Na+-bound polymers with oxazolinium triflate chain ends. Since the ionpair oxazolinium triflate would be separated under the analysis condition, it means that the peak at M+ + 155 is due to the covalent form of the oxazolinium triflate salt.



Figure 1. 1H NMR flow chart of the synthesis of oxazolines (3,4)nG1-Oxz with the following assignments: a (Ar, H-C6); b (Ar, H-C5); c (Ar, H-C2); d (CH2OPh); n (CH2N); o (CH2O). Table 1. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of Poly[(3,4)8G1-Oxz]

[M]0/[I]0

time (min)

conv (%)

thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a

Mn,th

Mn,GPC

Mw/Mn

5

10

100

2179

2132

1.27

10

30

100

4194

3635

1.21

20

60

100

8224

4319

1.14

50

90

100

20314

7479

1.11

100

150

100

40464

10960

1.09

200

180

98

80764

14434

1.08

heating b

φhc

cooling id

Tg 36.20 87.48 (0.19) Tg 41.21 φh 87.18 (0.20) i Tg 52.53 φh 95.95 (0.19) i Tg 54.39 φh 95.66 (0.20) i Tg 40.60 φh 100.09 (0.20) i Tg 56.23 φh 100.04 (0.21) i Tg 50.96 φh 105.48 (0.23) i Tg 60.70 φh 105.04 (0.24) i Tg 46.12 φh 108.08 (0.26) i Tg 62.48 φh 107.99 (0.26) i Tg 59.14 φh 110.30 (0.26) i Tg 63.61 φh 110.00 (0.27) i

i 71.08 (0.19) φh 36.08 Tg i 75.46 (0.19) φh 46.86 Tg i 78.17 (0.20) φh 53.17 Tg i 85.03 (0.23) φh 55.05 Tg i 89.63 (0.26) φh 57.17 Tg i 91.19 (0.27) φh 58.10 Tg

a Data from the first heating and cooling scans are on the first line and data from the second heating are on the second line. b T ) glass transition g temperature. c φh ) p6mm hexagonal columnar lattice. d i ) isotropic.

Indeed, we also observed peaks at M+ - 17. They correspond to the polymers with positively charged oxazolinium chain ends without the triflate counterion. These findings are indicating that the end-capping reaction with KOH was not quantitative and a small concentration of polymer species with oxazolinium chain ends is still present. The analysis of the polymerization system suggests that up to DP ) 200 the living character of the polymerization is preserved. However, for DP g 300, the linear increase of the molecular weight with conversion is altered and the polydispersity of the polymers starts to increase (Table 3). We believe that for this range of DPs the control of the living polymerization process is diminished by chain-transfer and/

or termination reactions induced by undetectable quantities of impurity present in the reaction system. Structural Analysis of Polymers by a Combination of DSC and TOPM. The poly(ethyleneimine)s obtained from 3,4-bis(n-alkan-1-yloxy)phenyl)-2-oxazoline monomers [(3,4)nG1-Oxz] form an enantiotropic p6mm columnar hexagonal (φh) phase for values of n ) 8, 10, 12, 13. Nevertheless, the stability and, in few cases, the type of the mesophase can be affected via temperature. Also, the parameters of the hexagonal lattice can be manipulated via the modification of the structural parameters of the dendritic side group, i.e., the length of the aliphatic tails and the degree of polymerization.


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Table 2. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of Poly[(3,4)10G1-Oxz]

[M]0/[I]0

time (min)

thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a

conv (%)

Mn,th

Mn,GPC

Mw/Mn

5

10

100

2459

2411

1.25

10

30

100

4754

5356

1.19

20

60

100

9344

7128

1.12

50

90

100

23114

11529

1.10

100

150

100

46064

15615

1.09

200

180

98

91964

22286

1.08

heating b

φhc

cooling id

Tg 36.55 104.33 (0.20) Tg 40.08 φh 100.95 (0.17) i Tg 40.90 i 81.35 (0.16) φh 110.47 (0.17) i Tg 51.62 i 84.81 (0.19) φh 108.10 (0.17) i Tg 50.50 i 86.00 (0.03) φh 117.56 (0.19) i Tg 54.86 i 85.81 (0.06) φh 116.45 (0.19) i Tg 60.03 φh 122.01 (0.23) i Tg 62.13 φh 122.21 (0.22) i Tg 64.12 φh 125.78 (0.21) i Tg 65.18 φh 125.60 (0.24) i Tg 68.25 φh 128.25 (0.25) i Tg 68.42 φh 128.42 (0.25) i

i 90.75 (0.16) φh 38.29 Tg i 94.40 (0.00) φh 42.00 Tg i 98.20 (0.00) φh 48.80 Tg i 101.99 (0.18) φh 54.00 Tg i 106.76 (0.21) φh 58.10 Tg i 107.08 (0.24) φh 62.03 Tg

a Data from the first heating and cooling scans are on the first line and data from the second heating are on the second line. b T ) glass transition g temperature. c φh ) p6mm hexagonal columnar lattice. d i ) isotropic.

Table 3. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of Poly[(3,4)12G1-Oxz] thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a

time (min)

conv (%)

Mn,GPC

Mw/Mn

heating

cooling

5

10

100

2739

3590

1.22

20

30

100

10474

9102

1.15

50

60

100

25914

13214

1.13

100

90

100

51664

18218

1.11

200

150

100

103164

22356

1.11

300

180

99

151570

22655

1.12

500

180

98

257664

21604

1.15

1000

180

98

515164

20662

1.30

kb -4.89 (2.17) Tgc 49.28 φhd 100.45 (0.14) ie k -7.59 (1.92) Tg 49.09 φh 102.50 (0.16) i k -13.50 (2.43)Tg 63.02 φh 111.75 (0.17) i k -12.66 (2.40) Tg 63.35 φh 111.85 (0.16) i k -3.29 (2.24) Tg 56.79 φh 120.62 (0.25) i k -6.69 (2.21) Tg 64.95 φh 118.34 (0.18) i k -0.79 (1.22) Tg 67.43 φh 121.85 (0.22) i k -6.09 (2.52) Tg 66.20 φh 121.07 (0.19) i k -4.39 (3.59) Tg 67.71 φh 126.71 (0.23) i k -6.09 (3.44) Tg 67.30 φh 126.06 (0.23) i k 0.90 (2.20) Tg 65.38 φh 127.59 (0.30) i k -5.59 (3.62) Tg 67.06 φh 127.82 (0.31) i k 4.10 (-4.02) k 50.43 (0.45) φh 126.18 (0.25) i k -6.29 (2.41) Tg 65.75 φh 126.14 (0.27) i k 28.13 (18.67) φh 121.37 (0.32) i k -6.39 (2.58) Tg 62.30 φh 120.60 (0.33) i

i 57.76 (0.15) φh 34.52 Tg -17.10 (1.29) k i 93.24 (0.09) φh 48.80 Tg -19.13 (1.94)k i 92.23 (0.18) φh 53.60 Tg -16.30 (1.38) k i 94.26 (0.19) φh 58.25 Tg -16.36 (1.60) k i 104.30 (0.22) φh 55.66 Tg -16.56 (2.44) k i 104.70 (0.29) φh 52.95 Tg -17.00 (2.55) k i 107.20 (0.27) φh 53.90 Tg -16.90 (1.62) k i 105.26 (0.33) φh 55.61 Tg -18.36 (1.88) k

[M]0/[I]0

Mn,th

a Data from the first heating and cooling scans are on the first line and data from the second heating are on the second line. b k ) crystalline. c T ) g glass transition temperature. d φh ) p6mm hexagonal columnar lattice. e i ) isotropic.

Table 4. Theoretical and Experimental Molecular Weights Determined by GPC and Thermal Transitions of Poly[(3,4)13G1-Oxz] thermal transitions (°C) and corresponding enthalpy changes (kcal/mol)a

time (min)

conv (%)

Mn,th

Mn,GPC

Mw/Mn

heating

cooling

5

20

100

2879

3124

1.27

10

30

100

5564

3811

1.21

20

45

100

11024

6544

1.11

50

100

100

27314

13266

1.08

100

180

100

40214

15233

1.07

200

240

100

54464

18110

1.07

kb 41.41 (2.38) Tgc 48.23 φhd 85.75 (0.13) ie k 17.31 (2.82) Tg 43.17 φh 83.32 (0.13) i k -3.53 (3.92) k 61.06 (1.08) φh 104.20 (0.13) i k 5.26 (3.15) Tg 58.13 i 93.80 (-0.04) φh 105.66 (0.08) i k 3.40 (2.01) k 60.53 (1.55) φh 101.93 (0.04) i k 4.53 (3.29) Tg 59.34 i 95.66 (-0.02) φh 108.13 (0.05) i k 7.60 (2.95) Tg 53.53 φh 106.30 (-0.04) i k 4.60 (3.60) Tg 56.78 i 92.30 (-0.01) φh 115.13 (0.05) i k 2.91 (3.28) k 60.40 (1.69) φh 106.66 (0.14) i k 4.60 (3.44) Tg 54.94 i 89.32 (-0.01) φh 115.66 (0.06) i k 8.25 (3.22) k 55.68 (1.42) φh 109.65 (0.06) i k 5.32 (3.50) Tg 55.11 φh 116.84 (0.06) i

i 70.82 (0.10) φh 33.12 Tg 8.39 (2.62)k i 89.12 (0.02) φh 50.86 Tg -0.86 (2.84) k 93.20 (0) φh 52.25 Tg -0.1 (3.12) k i 96.80 (0) φh 50.64 Tg -1.20 (3.28) k i 98.70 (0.02) φh 50.41 Tg -0.73 (3.23) k i 100.23 (0.03) φh 51.33 Tg 1.44 (3.34) k

[M]0/[I]0

a Data from the first heating and cooling scans are on the first line and data from the second heating are on the second line. b k ) crystalline. c T ) g glass transition temperature. d φh ) p6mm hexagonal columnar lattice. e i ) isotropic.

Figure 3 presents the DSC traces of poly[(3,4)8G1-Oxz] with DP ) 5, 10, 20, 50, 100, and 200. The corresponding thermal transitions and their associated enthalpy changes are

reported in Table 1. All polymers exhibit a glass transition (Tg) followed by the formation of a φh phase. This phase was assigned by a combination of TOPM and XRD experi-



Figure 2. MALDI-TOF analysis of poly[(3,4)10G1-Oxz] with (a) [M]0/[I]0 ) 5 and (b) [M]0/[I]0 ) 10.

ments. The φh phase is enantiotropic over the entire range of molecular weights. The Tg along with the isotropization temperature and its associated enthalpy of these transitions increase with increasing the DP and level off at values of DP ) 100-200 (Figures 3 and 4). Similar trends were found for poly[(3,4)10G1-Oxz] (Figure 5 and Table 2), with the difference that in some cases, e.g., DP ) 10 and DP ) 20, an endothermic transition was observed on heating (Figure 5a). This indicates that in these two cases the φh phase forms only on heating above Tg.

Polymer poly[(3,4)12G1-Oxz] presents a slightly different behavior (Figure 6 and Table 3). All poly[(3,4)12G1-Oxz] exhibit a crystalline phase that undergoes melting below the Tg. The formation of this crystalline phase also occurs below the Tg. Most remarkable, the melting and the crystallization temperatures are independent of the DP while the Tg and isotropization temperatures vary with the DP. This means that the melting and crystallization are independent of the motion that is released above the glass transition and, therefore, these polymers exhibit an intramolecular mi-

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Figure 3. DSC traces of poly[(3,4)8G1-Oxz]: (a) second heating scan; (b) first cooling scan.

crophase segregation. This result is in line with previous results reported from our laboratory.8b Above the Tg, all polymers display an enantiotropic φh phase. The lowest molecular weight polymer behaves in a different way. For low values of DP, e.g., DP ) 5, the dendritic side groups are self-assembling in a disk which according to XRD analysis can accommodate maximum 7 units (Table 5). These disks are able to self-assemble into columns, and subsequently they self-organize in a φh phase. With an increase in the temperature, the disks become unstable and adopt conical shapes that self-assemble into spherical supramolecules. Self-organization of the spheres leads to a cubic Pm3hn phase that transformed into an isotropic phase at higher temperatures. For DP g 10, the formation of the seven-unit disks is no longer possible, and therefore the resulting supramolecules display only columnar shape. As observed for shorter tail lengths, an increase in the DP leads to an increase of the phase stability. This stability is expressed by the increase in the isotropization temperature and its associated enthalpy change. Both parameters level off at DP ) 100-200 (Figure 4). This initial increase in the transition temperature with the DP followed by a plateau was theoretically predicted.17 Figure 6 shows that for values of DP g 300, there is a decrease both in the isotropization temperature and in its associated transition enthalpy. This observation is in agreement with the loss of control over the living polymerization process for DP g 300. Accordingly, there is

an increase in polydispersity due to the formation of polymer species with lower molecular weight than the target. Polymer poly[(3,4)13G1-Oxz] presents a crystalline phase below the Tg followed by an enantiotropic φh phase above the Tg (Figure 7 and Table 4). As in the case of poly[(3,4)12G1-Oxz], the melting and crystallization temperatures are not dependent on the molecular weight. However, the Tg and the isotropization temperature first increase and then reach a plateau as the DP increases. These experiments demonstrate that the structure and the dynamic behavior of these four polymers can be divided in two classes. Polymers poly[(3,4)8G1-Oxz] and poly[(3,4)10G1-Oxz] belong to one class, while poly[(3,4)12G1-Oxz] and poly[(3,4)13G1-Oxz] belong to another class. Previous research in our laboratory has demonstrated that cylindrical supramolecules and macromolecules have an intramolecular microphase separated structure;7c,8b i.e., the cylinder is compartmentalized.3u This structure is also detected by DSC in poly[(3,4)12G1-Oxz] and poly[(3,4)13G1-Oxz] but not in poly[(3,4)8G1-Oxz] and poly[(3,4)10G1-Oxz], unless the crystalline transitions occur below -40 °C. This difference must be detectable in their phase behavior. A comparative diagram of the isotropization temperatures and the corresponding enthalpy and entropy changes at isotropization for different lengths of the aliphatic tails are presented in Figure 4. As expected from previous series of experiments,3u,8c at the transition from poly[(3,4)8G1-Oxz] to poly[(3,4)10G1-Oxz] an increase in the isotro-



Figure 4. Phase behavior of poly[(3,4)nG1-Oxz] as a function of [M]0/[I]0: (a) transition temperatures; (b) enthalpy changes at isotropization; (c) entropy changes at isotropization.

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pization temperature was observed (Figure 8a). However, the isotropization temperatures decrease for poly[(3,4)12G1Oxz] and poly[(3,4)13G1-Oxz]. At the same time, on going from poly[(3,4)8G1-Oxz] to poly[(3,4)13G1-Oxz] the enthalpy and entropy changes of isotropization decrease. This change in the classic trend is most probably due to a change from a non- or weakly intramolecular microphase segregated system for poly[(3,4)nG1-Oxz] with n ) 8 and 10 to a microphase segregated system for polymers poly[(3,4)nG1Oxz] with n ) 12 and 13. Retrostructural Analysis of Poly[(3,4)nG1-Oxz] by XRD. On the basis of the XRD results (Table 5), we could determine the variation in the lattice parameter as a function of temperature and DP for poly[(3,4)13G1-Oxz] (Figure 9). A decrease in the diameter of the supramolecular dendrimer with increasing the temperature was observed before for minidendritic alkaline salts of aromatic acids,7j and we present here the first example of such behavior for a macromolecular system. Previously,7j it was suggested that the decrease of the diameter at higher temperature is due to the thinning of the supramolecule as a result of two effects: shrinking of the aliphatic tails and/or shedding off building blocks from the supramolecular structure. The latter explanation cannot be valid here, since the building blocks are covalently bound via a polymer chain. Nevertheless, we believe that a decrease in the diameter of the supramolecule is due to the elongation of the cylindrical structure accompanied by the unwinding of the helical conformation of

the polymer backbone that penetrates through its center. This effect was previously observed when cylinders with helical backbones were dissolved in a good solvent.8c Accordingly, the supramolecular cylinder is thinning by a rearrangement of the building blocks within the cylindrical layers, which leads to a decrease in the occupancy in a cross section of the column (Table 5). The driving force for this rearrangement is the increase in the domain curvature, i.e., a smaller diameter of the supramolecular object, required at higher temperatures for stability reasons. To test the hypothesis of an intramolecular microphase segregation between the aromatic core and the aliphatic periphery, we verified the dependence between the number of carbon atoms (n) in the aliphatic tails and the corresponding lattice parameter (an). It was shown previously,3u,7c that a diagram of the lattice parameter as a function of n can be used to estimate the diameter of the aromatic core (ac) based on an2 ) ac2 +AmH + nAMCH2

(1)

where an is the φh lattice parameter, ac is the diameter of the aromatic core, A is a constant characteristic to the aliphatic tails, and mH and mCH2 are the respective masses of a hydrogen atom and of a CH2 group. The microphase segregation was confirmed by a linear dependence of the an2 as a function of n (Figure 10), and we could also calculate the diameter of the aromatic core, ac ) 18.43 Å, in close agreement with previous experiments.3u,7c



Figure 6. DSC traces of poly[(3,4)12G1-Oxz]: (a) second heating scan; (b) first cooling scan. Table 5. X-ray Scattering Structural Characterization of the P6mm Phase Formed by Supramolecular Dendrimers Self-Assembled from Poly[(3,4)nG1-Oxz] with n ) 8, 10, 12, and 13a

n

DP

T (°C)

d100 (Å)

d110 (Å)

d200 (Å)

8 8 10 12 12 12 13 13 13 13 13 13 13 13 13 13

100 100 100 5 100 500 5 5 5 5 10 10 10 100 100 100

23 95 115 75 90 85 60 70 80 100 60 80 100 60 80 100

30.2 28.8 31.0 32.4 33.3 35.6 39.2 38.4 37.6 36.4 37.4 36.9 35.8 38.4 37.0 35.6

17.2 16.5 17.4 18.7 19.3 20.1

15.0 14.3 15.0 15.5 16.4 17.3 19.2 18.6 18.5 18.0 19.1 18.5 18.0 18.9 18.3 17.5

d210 (Å)

d300 (Å)

15.0

12.9

14.5

12.7

F (g/mL)

a (Å)

µ

R′ (deg)

0.98 0.98 0.98 0.99 0.98 1.01 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99

34.63 33.09 35.07 36.87 38.30 40.42 44.25 43.64 43.07 41.80 43.58 42.66 41.45 43.99 42.49 40.76

7 7 6 6 7 8 9 9 8 8 9 8 8 9 8 7

51.4 51.4 60.0 60.0 51.4 45.0 40.0 40.0 45.0 45.0 40.0 45.0 45.0 40.0 45.0 51.4

a a ) lattice parameter (Å), a ) 2(d 1/2 + 2d 1/2 + d 1/2 1/2 100 + d1103 200 + d2107 30012 )5(3 ). F ) experimetal density at 20 °C. µ ) number of units per disk, µ ) 31/2a2FtNA/2M, where t ) thickness of layer (4.7 Å), NA ) 6.022 × 1023 (mol-1), and M ) molecular weight (g/mol). R′ is the planar angle for the tapered monodendron, R′ ) 360/µ (deg).

Direct Visualization of Supramolecular Objects Formed by Poly[(3,4)nG1-Oxz] by Transmission Electron Microscopy and Atomic Force Microscopy. Direct visualization of the 3-D structure of the polymers by TEM and AFM experiments, together with ED experiments are complementary to the XRD experiments.7f,8c TEM and AFM imaging of single molecules on flat substrates is a routine procedure in topological analysis of

DNA18 when its diameter is increased by complexation with proteins. Also, complexes of nucleic acids with proteins, i.e., virus self-assemblies, were visualized on surfaces.19 Direct visualization attracted attention of polymer scientists after visualization of individual chains was demonstrated in studies of PS-b-PMMA block-copolymers.20 HoweVer, direct structural analysis of single polymer chains became accessible when supramolecular structures formed by the intramolecu-

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lar self-assembly of monodendron-jacketed polymers were obserVed in the TEM, SFM, and AFM images.7f,k,8b-f,21,22 Figure 11 presents the TEM micrographs of the cylindrical supramolecules formed by poly[(3,4)12G1-Oxz] with DP ) 200. The corresponding φh phase was oriented by surface anchoring in thin films. A homeotropic alignment of the supramolecular columns was achieved upon annealing on untreated carbon films. A planar alignment was achieved on polar substrates, i.e., water or glycerin. No staining agents were required for the visualization of these samples by TEM. The aromatic cores of the columns is shown dark in both figures, indicating regions of high-electron density, while the low electron density of the aliphatic periphery is displayed in lighter tones. These images confirm the cylindrical shape of the supramolecules as indicated by XRD and demonstrate the capability of these macromolecules to align on surfaces as well as their ability to self-assemble and self-organize into lattices. We have applied AFM for studies of poly[(3,4)nG1-Oxz] with the intention to visualize their conformation and their self-organization on a graphite surface. For AFM studies, samples of polymers were prepared by spin coating from methylene chloride solutions of the polymer on highly ordered pyrolitic graphite. Depending on the sample, either a minimal force or a force increase was required for visualization of single macromolecules. This is illustrated in the images in Figure 12 for poly[(3,4)10G1-Oxz] with DP ) 100. These images correspond to samples spin cast

from relatively concentrated solutions. As a general observation, the visualization of the macromolecular self-assemblies on substrates by AFM is facilitated by an optimal sample preparation. The choice of the substrate, concentration of the applied solution, and thermal annealing are the most important components of the sample preparation. The use of graphite ensures the registry between alkyl groups and surface lattice, yet these interactions could be dominant only for the layer lying immediately on the substrate. Therefore, an appropriately diluted solution is necessary for the highresolution observation of the individual macromolecules and their packing. When, the solution concentration is too high, then the AFM can observe only traces of the ordered structures (Figure 12b). Only a few bright features are seen in this image, most likely related to the self-assemblies. Thermal annealing leads to better packing of the macromolecules on graphite. However, the ordered domains might be hidden underneath poor ordered top layers. A demonstration of such case is presented in panels c and d of Figure 12, which were recorded at alternate low and elevated tip forces, respectively. A penetration of the AFM probe while imaging with a highly elevated tip force was needed to observe ordered domains corresponding to the first layer of supramolecules with features oriented along the graphite lattice directions. Fully developed images obtained at elevated tip forces are presented in panels e and f of Figure 12 for the visualization of a nonordered top layer in a thick sample. These images are indicative on preferential ordering in the



Figure 9. Dependence of the diameter of the supramolecular dendrimer formed by poly[(3,4)13G1-Oxz] on temperature in the p6mm columnar hexagonal phase.

Figure 8. Phase behavior of polymers poly[(3,4)nG1-Oxz] with DP ) 100 as a function of n: (a) isotropization temperatures; (b) enthalpy change at isotropization; (c) entropy change at isotropization

first layer lying on the graphite substrate, followed by a gradual loss in the degree of ordering in subsequent layers. The optimal solution concentration was achieved for the samples of poly[(3,4)10G1-Oxz] with DP ) 100 shown in panels a and b of Figure 13. These images show domains consisting of bright rods 40-50 Å in diameter, which are oriented in registry with the substrate. These domains are scattered over the whole substrate and some are neighboring nonordered layers. This sample was subjected only to roomtemperature “annealing” that did not provide complete ordering. In the sequence of these images one can also see

that short rods change their position with the respect to the neighboring longer rods. This might be explained by a poor adhesion to the substrate and to the neighbors. Therefore, the short rods might be slightly pushed by the AFM probe and this leads to the change in their position. When the sample is heated to 120 °C, the AFM image did no show any adsorbate layer, which indicates that a displacement of the adsorbed macromolecules from the surface during the analysis occurred due to the poor adhesion induced by the high mobility at elevated temperatures. After the temperature was reduced to 75 °C, a buildup of the crystal-like domains was observed. The images in panels c and d of Figure 13 were obtained during this process. Further cooling to room temperature led to a perfect order within this domain (Figure 13e-f). The size of the macromolecule correlates with numerous bright particles seen on the top surface of the domains, and they can be assigned to individual molecules, which were not built into the domain. Similar images are presented in Figure 14 for poly[(3,4)12G1-Oxz] with DP ) 500. Large-scale images show numerous extended domains, which are scattered on graphite terraces and which are oriented along three main directions with approximately 60° and 120° between them. Such order is common for an epitaxial arrangement of alkyl chains on graphite, and we suggest that the slightly elevated borders (bright edges) might represent mobile chain ends. The highresolution image of one of the domains (Figure 14d) shows that it is formed of stiff supramolecules, and we attribute the irregularities of the domains to variations in the length of the component supramolecules. The pitch of 47 Å along the domains gives an interchain distance at 23 °C, which is in close agreement to the hexagonal columnar lattice parameter a ) 40.42 Å at 85 °C found in bulk by XRD (Table 5). At higher polymer concentration, the poly[(3,4)12G1-Oxz] macromolecules covered completely the graphite surface. Extremely large domains of uniform alignment were obtained after annealing at 120 °C in their φh phase, as shown in Figure 14e-f. The domains with differently oriented supramolecules also exhibit different interchain separations. The domain in the central part is characterized by a pitch of 47 Å in agreement to the interchain distance found in the domains. A larger interchain distance (61 Å) is observed in

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Figure 10. Estimation of the aromatic core diameter in the cylindrical supramolecular dendrimers formed by poly[(3,4)nG1-Oxz] at 90 °C for DP ) 100.

Figure 11. Phase-contrast TEM micrographs of (a) homeotropically and (b) planar aligned φh assemblies generated by supramolecular cylinders generated from poly[(3,4)12G1-Oxz] with DP ) 200. Insets represent the electron diffraction patterns.

the domain located in the top left corner of Figure 14e. Also the chain orientations in these domains are not consistent

with 60° or 120°, which is common for the epitaxial arrangement governed by the graphite lattice. Therefore, it is reasonable to suggest that the extended chain order found in the top left domain has been induced by the graphite plane edge rather than by the graphite lattice. This might also explain the increase of the interchain distance. An increase in the concentration of solutions showed that the entire surface could be covered in one-, two- and three-layered films and that beyond the third layer the degree of epitaxial order is more and more altered. Figure 14e,f demonstrates that the molecules are interacting not only laterally but also longitudinally. This suggests that the lateral hydrophobic recognition is in this case accompanied by longitudinal selforganization due the head-to-head interactions of the hydrophilic cores. The fact that these supramolecules are very short and amphiphilic is probably increasing the relevance of such interactions for the overall self-organization of these particular polymers, as opposed to the previously studied systems, where the longitudinal self-organization was not observed. Small scale images of poly[(3,4)12G1-Oxz] with DP ) 100 prepared from very dilute solutions are shown in panels a and b of Figure 15. A first observation is that the domains are more regular in width, which is in agreement with the GPC measurements (Table 3) that indicate a narower polydispersity of poly[(3,4)12G1-Oxz] with DP ) 100 compared to poly[(3,4)12G1-Oxz] with DP ) 500. Enlargements of the AFM images show individual domains and afforded direct measurement of the contour length of each component of the domains, and thus we determined the experimental contour length distribution (Figure 15c). Accordingly, the number-averaged contour length determined by AFM is Ln,AFM ) 236 Å while the contour length distribution is Lw/Ln ) 1.07. An estimated contour length of these supramolecules is Ln,XRD ) 122 Å. The estimation of the length was based on the XRD data that indicated the number of monomer units in a stratum of the cylinder,7c and then the number of strata was calculated from the degree of polymerization. The final length was calculated under the assumption that the thickness of one stratum is 4.7 Å.7c This value of Ln,AFM is in direct contradiction with the estimated



Figure 12. AFM height images of poly[(3,4)10G1-Oxz] with DP ) 100 (samples spin cast from 0.01 mg/mL solutions in CH2Cl2): (a, b) images obtained at low tip-force level, at room temperature, and after 14 h at room temperature; (c, d) images obtained at elevated tip-force level, at room temperature, and after 14 h at room temperature; (e, f) images obtained at elevated tip-force level after annealing for 2 h at 120 °C and then cooling to room temperature.

value and demonstrates that one cylindrical substructure of the domains is in fact formed from two or more supramolecules that are head-to-head interacting. This also explains

the reduced Lw/Ln obtained by AFM, since such interaction would statistically reduce the actual value of contour length distribution.

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Figure 13. AFM height images of polymers poly[(3,4)10G1-Oxz] with DP ) 100: (a, b) images obtained at room temperature after 14 h at room temperature (sample spin cast from 0.003 mg/mL solutions in CH2Cl2); (c) image obtained at 75 °C, after heating to 150 °C, cooling to 75 °C, and annealing at 75 °C for 1.5 h (sample spin cast from 0.005 mg/mL solutions in CH2Cl2); (d) image obtained at 75 °C, after heating to 150 °C, cooling to 75 °C, and annealing at 75 °C for 1 h and 53 min (sample spin cast from 0.005 mg/mL solutions in CH2Cl2); (e) image obtained after heating to 120 °C, cooling to 75 °C, annealing for 5 h at 75 °C, and finally cooling to room temperature (sample spin caste from 0.005 mg/mL solutions in CH2Cl2); (f) detail of image e.

These AFM images revealed that these supramolecules exhibit on graphite surface fully extended conformations; i.e.,

these short supramolecules are stiff. We have not been able so far to observe individual supramolecules unless they were



Figure 14. AFM images of poly[(3,4)12G1-Oxz] with DP ) 500: (a) height image at room temperature after 24 h (sample spin cast from 0.002 mg/mL solutions in CH2Cl2); (c, d) details of image a at progressively smaller scale; (e) phase image at room temperature after 2 h of annealing at 120 °C (sample spin cast from 0.005 mg/mL solutions in CH2Cl2); (f) detail of image e.

on top of a domain, and we believe that this is due to a series of factors that will be discussed below. The interaction

between the short single supramolecule and the graphite surface is not strong enough to resist tip force that would

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ecules into clusters could be determined laterally, due to hydrophobic recognition, and also longitudinally, by hydrophilic recognition. Such a combination of fast dynamics, strong self-interaction, and weak surface interaction led to the observation of domains instead of individual supramolecules even in samples obtained from very dilute solutions. Conclusions Model monodendrons for the self-assembling process were designed and synthesized as the minidendritic 2-oxazolines (3,4)nG1-Oxz (n ) 8, 10, 12 and 13). These compounds were polymerized via a living cationic ring-opening isomerization mechanism, and thorough analytical investigation shows that the resulting macromolecules are able to selfassemble into supramolecules with cylindrical shapes. Further self-organization of these supramolecular dendrimers leads to the formation of a columnar hexagonal P6mm lattice. Manipulation of the molecular parameters such as the length and width of the minidendron and the molecular weight of the macromolecule led to controlled variations in the stability, shape, and size of the resulting supramolecular dendrimer. The TEM and AFM analysis of the macromolecular dendrimers formed by these dendritic poly(ethyleneimines) shows for the first time that short rigid-rod molecules cannot exist individually on the surface due to their high tendency to self-organize in clusters. The role of these minidendrons should be considered analogous to that of minidendritic salts that were used in the understanding of the self-assembly and self-organization processes. The main advantages of using such models are the minimal chemistry effort and the simple conceptual approach. The capability of these models to allow controlled modifications of the supramolecular properties via manipulation of their molecular parameters demonstrated their suitability to be used as references in the elaboration of higher generations of self-assembling monodendrons. The macromolecular systems employed here also represent a step further in the modeling of biological rodlike viruses that are composed of a helical RNA strand surrounded by protein subunits. We employed a polymer backbone as analogue of the RNA and minidendritic units as analogues of the proteins, and we believe that the events involved in their selfassembling and self-organization are also common to complex biological supramolecular systems. Figure 15. (a) Height image of poly[(3,4)12G1-Oxz] with DP ) 100 obtained at room temperature after 24 h (sample spin cast from 0.002 mg/mL solutions in CH2Cl2). (b) Detail of image a. (c) Contour length distribution obtained from direct measurement of the contour length of 93 cylindrical polymers of the lamellae. The estimated value Ln,XRD ) 122 Å was determined based on XRD data.

drag-and-cluster the aggregates. Also, the dynamics of these short molecules is very fast and, by analogy with low molar mass liquid crystals,23 their self-assembly and self-organization processes are rapid. Moreover, these supramolecules have an amphiphilic character given by the hydrophobic coating and the hydrophilic poly(ethyleneimine) core. Consequently, self-organization of these amphiphilic supramol-

Experimental Section Materials. THF and Et2O (Fisher, A.C.S. reagent) were refluxed over sodium ketyl and freshly distilled before use. CH2Cl2 (Fisher, A.C.S. reagent) was refluxed over CaH2 and freshly distilled before use. o-DCB and benzene (both Fisher, A.C.S. reagents) were shaken with concentrated H2SO4, washed twice with water, dried over MgSO4, and finally distilled over CaH2 or sodium ketyl, respectively. Methanol (MeOH), ethanol (EtOH), H2SO4, pyridine, dimethylformamide (DMF), KOH, K2CO3, and NaHCO3 (all Fisher, A.C.S. reagents) were used as received. SOCl2 (97%), 3,4-dihy-



Figure 16. Phase images of 8a/13 with DP ) 100 after annealing 2 h at 80 °C (sample spin cast from 0.005 mg/mL solutions in THF). Images b and d represent details of images a and c, respectively.

droxybenzoic acid (98%), ethanolamine (EtOH) (99+%), 1-bromooctane (99%), 1-bromodecane (98%), and 1-bromotridecane (98%) (all from Aldrich) were used as received. Methyl trifluoromethanesulfonate (MeOTf) (Fluka, g97%) was vacuum distilled. 1-Bromononane (99%), 1-bromoundecane (98%), and 1-bromododecane (98+%) (all from Lancaster) were used as received. General Methods. 1H NMR (200 MHz) and 13C NMR (50 MHz) spectra were recorded on a Varian Gemini 200 spectrometer. CDCl3 was used as solvent and TMS as internal standard unless otherwise noted. Chemical shifts are reported as δ, ppm. The purity of products was determined by a combination of techniques including thin-layer chromatography (TLC) on silica gel plates (Kodak) with fluorescent indicator and high-pressure liquid chromatography (HPLC) using a Perkin-Elmer Series 10 high-pressure liquid chromatograph equipped with an LC-100 column oven, Nelson

Analytical 900 series integrator data station, and two PerkinElmer PL gel columns of 5 × 102 and 1 × 104 Å. THF was used as solvent at the oven temperature of 40 °C. Detection was by UV absorbance at 254 nm. Relative weight average (Mw) and number average (Mn) molecular weights were determined with the same instrument from a calibration plot constructed from polystyrene standards. Thermal transitions of samples that were freeze-dried from benzene were measured on a Perkin-Elmer DSC-7 differential scanning calorimeter (DSC). In all cases, the heating and cooling rates were 10 °C min-1. First-order transition temperatures were reported as the maxima and minima of their endothermic and exothermic peaks. Glass transition temperatures (Tg) were read at the middle of the change in heat capacity. Indium and zinc were used as calibration standards. An Olympus BX-40 optical polarized microscope (100× magnification) equipped with a Mettler FP 82 hot

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stage and a Mettler FP 80 central processor was used to verify thermal transitions and characterize anisotropic textures. X-ray diffraction experiments on liquid crystal phases were performed using an image plate area detector (MAR Research) with a graphite-monochromatized pinhole-collimated beam and a helium tent. The samples, in glass capillaries, were held in a temperature-controlled cell. Densities, F, were determined by flotation in glycerol/H2O or glycerol/MeOH. MALDI-TOF analysis of monomers and polymers was performed on a PE Biosystems Voyager-DE workstation operating in linear mode, with a nitrogen laser wavelength of 337 nm. TEM experiments were conducted on a JEOL JEM-100CX electron microscope operated at 100 kV. A thin film was cast from a 1% solution in toluene onto carbon-coated mica. To prevent dewetting of the sample during heat treatment, another layer of carbon (much less than 100 nm in thickness) was evaporated on top of the material. The sample was then floated on water and retrieved onto copper grids. Samples were heat treated by first heating to 130 °C (i.e., isotropic). They were then cooled to 70 °C at a rate of 1 °C/min and annealed at this temperature for approximately 2 h. Finally, the samples were quenched in liquid nitrogen and examined without staining by TEM. AFM studies were performed with a scanning probe microscope MultiMode Nanoscope IIIa (Digital Instruments, Santa Barbara, CA). The microscope was equipped with a heating accessory, which includes a modified vertical Jscanner, and an optical control system. All AFM images were obtained in tapping mode. Height and phase images were collected simultaneously. The samples were prepared by spin-coating (the spinning rate 2000 rpm) on graphite (HOPG, highly ordered pyrolitic graphite) from dilute solutions of the polymer. AFM measurements were performed on spin cast samples and also after annealing just below isotropization temperature. Synthesis. The synthesis of 2-[3,4-bis(n-dodecan-1-yloxy)phenyl]-2-oxazoline was reported previously.16 General Procedure for the Synthesis of Methyl-[3,4Bis(n-alkan-1-yloxy)]benzoates with n ) 8, 10, and 13. Methyl-[3,4-bis(n-octan-1-yloxy)]benzoate (2/8). Compound 1 (11.76 g, 0.07 mmol) was dissolved in 300 mL of DMF under Ar, and K2CO3 (38.64 g, 0.28 mol) was added. The mixture was purged with Ar for 0.5 h at reflux, then the n-bromooctane (27.02 g, 0.14 mol) was added. The heterogeneous mixture was stirred at reflux under Ar for another 8 h, then the suspension was poured into ice-cooled water and acidified to pH ) 1 with HCl (10%). The precipitate was filtered, washed thoroughly with water on filter, and then recrystallized two times in acetone to yield 23.87 g (87.0%) of a white powder. mp 108-110 °C. 1H NMR (CDCl3, δ, TMS): 0.89 (t, 6H, J ) 6 Hz, CH3), 1.11.9 (m, 24H, CH3(CH2)6), 3.9 (s, 3H, COOCH3), 4.02 (t, 4H, J ) 6 Hz, CH2OAr), 4.8 (s, 1H, OH), 6.85 (d, 1H, J ) 8 Hz, meta to COO), 7.5 (s, 1H, ortho to COO), 7.6 (d, 1H, J ) 8 Hz, ortho to COO). 13C NMR (CDCl3, δ, ppm): 14.0 (CH3), 22.7 (CH3CH2), 26.0 (CH2CH2CH2O), 29.2, 29.3, 31.7

Percec et al.

(CH3CH2(CH2)3), 29.2 (CH2CH2O), 51.91 (COOCH3), 68.15 (CH2OPh), 111.8 (meta to COO, ortho to O), 113.2 (ortho to COO, ortho to O), 122.8 (ortho to COO, meta to O), 126.7 (ipso to COO), 146.3, 156.4 (ipso to O), 165.2 (COO). Methyl-[3,4-bis(n-decan-1-yloxy)]benzoate (2/10). Starting with 1 (11.76 g, 0.07 mol), K2CO3 (38.64 g, 0.28 mol), and n-bromodecane (30.94 g, 0.14 mol) in 300 mL of DMF at reflux for 8 h, 28.85 g (92.0%) of a white powder was obtained after two recrystallizations from acetone. mp 7374 °C (lit.24 mp 73-74 °C). 1H NMR (CDCl3, δ, TMS): 0.89 (t, 6H, J ) 6 Hz, CH3), 1.2-1.9 (m, 32H, CH3(CH2)8), 3.9 (s, 3H, COOCH3), 4.0 (t, 4H, J ) 6 Hz, CH2OAr), 4.7 (s, 1H, OH), 6.8 (d, 1H, J ) 8 Hz, meta to COO), 7.5 (s, 1H, ortho to COO), 7.6 (d, 1H, J ) 8 Hz, ortho to COO). 13C NMR (CDCl , δ, ppm): 14.1 (CH ), 22.6 (CH CH ), 3 3 3 2 26.0 (CH2CH2CH2O), 29.1, 29.3, 29.5, 29.6, 31.7 (CH3CH2(CH2)5), 29.4 (CH2CH2O), 51.9 (COOCH3), 68.1 (CH2OPh), 111.8 (meta to COO, ortho to O), 113.2 (ortho to COO, ortho to O), 122.8 (ortho to COO, meta to O), 126.7 (ipso to COO), 146.3, 156.4 (ipso to O), 165.2 (COO). Methyl-[3,4-bis(n-tridecan-1-yloxy)]benzoate (2/13). Starting with 1 (11.76 g, 0.07 mol), K2CO3 (47.3 g, 0.348 mol), and n-bromotridecane (37.08 g, 0.14 mol) in 300 mL of DMF at reflux for 8 h, 32.36 g (86.9%) of a white powder was obtained after two recrystallizations from acetone. mp 5658 °C. 1H NMR (CDCl3, δ, TMS): 0.89 (t, 6H, J ) 6 Hz, CH3), 1.1-1.8 (m, 44H, CH3(CH2)11), 3.9 (s, 3H, COOCH3), 4.1 (t, 4H, J ) 6 Hz, CH2OAr), 4.8 (s, 1H, OH), 6.8 (d, 1H, J ) 8 Hz, meta to COO), 7.5 (s, 1H, ortho to COO), 7.6 (d, 1H, J ) 8 Hz, ortho to COO). 13C NMR (CDCl3, δ, ppm): 14.0 (CH3), 22.7 (CH3CH2), 26.0 (CH2CH2CH2O), 29.2, 29.3, 29.5, 31.8 (CH3CH2(CH2)8), 29.1 (CH2CH2O), 51.91 (COOCH3), 68.15 (CH2OPh), 111.8 (meta to COO, ortho to O), 113.2 (ortho to COO, ortho to O), 122.8 (ortho to COO, meta to O), 126.7 (ipso to COO), 146.3, 156.4 (ipso to O), 165.2 (COO). General Procedure for the Synthesis of 3,4-Bis(n-alkan1-yloxy)benzoic Acids with n ) 8, 10, and 13. 3,4-Bis(noctan-1-yloxy)benzoic Acid (3/8). Compound 2/8 (11.76 g, 30 mmol) was dissolved in 100 mL of EtOH (95%), and KOH (12.42 g, 90 mmol) was added. The mixture was stirred at reflux for 12 h, then cooled to 30 °C. The resulted suspension was poured into ice-cooled water and acidified to pH ) 1 with HCl (10%). The precipitate was filtered, washed with water on filter, then recrystallized three times in EtOH (95%) to yield 10.1 g (89.1%) of a white powder. mp 132-133 °C. 1H NMR (CDCl3, δ, ppm, TMS): 0.88 (overlapped t, 6H, CH3), 1.23-1.62 (m, 20H, CH3(CH2)5), 1.70 (m, 4H, CH2CH2OAr), 4.06 (overlapped t, 4H, CH2OAr), 6.90 (d, 1H, J ) 9 Hz, meta to COOH), 7.59 (d, 1H, J ) 2 Hz, ortho to COOH), 7.72 (dd, 1H, J ) 9 Hz J ) 2 Hz, ortho to COOH). 13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.6 (CH3CH2), 26.1 (CH2CH2CH2O), 29.2, 29.3, 31.5 (CH3CH2(CH2)3), 29.1 (CH2CH2O), 68.2 (CH2OPh), 113.4 (meta to COOH, ortho to O), 113.9 (ortho to COOH, ortho to O), 118.1 (ortho to COOH, meta to O), 131.5 (ipso to COOH), 147.9, 153.7 (ipso to O), 165.2 (COOH). 3,4-Bis(n-decan-1-yloxy)benzoic Acid (3/10). Starting with 2/10 (13.44 g, 30 mmol) and KOH (12.42 g, 90 mmol)


in 100 mL of EtOH (95%) at reflux for 12 h, 11.79 g (90.6%) of a white powder was obtained. mp 126-127 °C (lit.24 mp 113-114 °C). 1H NMR (CDCl3, δ, ppm, TMS): 0.89 (overlapped t, 6H, CH3), 1.23-1.68 (m, 28H, CH3(CH2)7), 1.77 (m, 4H, CH2CH2OAr), 4.02 (overlapped t, 4H, CH2OAr), 6.88 (d, 1H, J ) 9 Hz, meta to COOH), 7.53 (d, 1H, J ) 2 Hz, ortho to COOH), 7.70 (dd, 1H, J ) 9 Hz J ) 2 Hz, ortho to COOH). 13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.6 (CH3CH2), 26.1 (CH2CH2CH2O), 29.2, 29.3, 29.5, 31.6 (CH3CH2(CH2)5), 29.1 (CH2CH2O), 68.2 (CH2OPh), 113.4 (meta to COOH, ortho to O), 113.9 (ortho to COOH, ortho to O), 118.1 (ortho to COOH, meta to O), 131.5 (ipso to COOH), 147.9, 153.6 (ipso to O), 165.1 (COOH). 3,4-Bis(n-tridecan-1-yloxy)benzoic acid (3/13). Starting with 2/13 (15.12 g, 30 mmol) and KOH (12.42 g, 90 mmol) in 100 mL of EtOH (95%) at reflux for 12 h, 13.42 g (91.3%) of a white powder was obtained. mp 96-97 °C. 1H NMR (CDCl3, δ, ppm, TMS): 0.89 (overlapped t, 6H, CH3), 1.261.70 (m, 40H, CH3(CH2)10), 1.77 (m, 4H, CH2CH2OAr), 4.05 (overlapped t, 4H, CH2OAr), 6.91 (d, 1H, J ) 9 Hz, meta to COOH), 7.54 (d, 1H, J ) 2 Hz, ortho to COOH), 7.73 (dd, 1H, J ) 9 Hz J ) 2 Hz, ortho to COOH). 13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.6 (CH3CH2), 26.1 (CH2CH2CH2O), 29.2, 29.3, 29.5, 31.6 (CH3CH2(CH2)8), 29.1 (CH2CH2O), 68.2 (CH2OPh), 113.4 (meta to COOH, ortho to O), 113.9 (ortho to COOH, ortho to O), 118.1 (ortho to COOH, meta to O), 131.5 (ipso to COOH), 147.9, 153.7 (ipso to O), 165.1 (COOH). General Procedure for the Synthesis of 3,4-Bis(n-alkan1-yloxy)benzoyl Chlorides with n ) 8, 10, and 13. 3,4Bis(n-octan-1-yloxy)benzoyl Chloride (4/8). Compound 3/8 (22.6 g, 60 mmol) was suspended in 300 mL of CH2Cl2, and a catalytic amount of DMF was added. SOCl2 (13 mL, excess) was added dropwise, and the mixture was heated to reflux for 0.5 h. After cooling to room temperature, the solvent and the excess of SOCl2 were distilled to yield 23.7 g (99.9%) of a white powder which was used without further purification. 1H NMR (CDCl3, δ, ppm, TMS): 0.88 (overlapped t, 6H, CH3), 1.26-1.65 (m, 20H, CH3(CH2)5), 1.78 (m, 4H, CH2CH2OAr), 4.04 (overlapped t, 4H, CH2OAr), 6.90 (d, 1H, J ) 9.2 Hz, meta to COCl), 7.55 (d, 1H, J ) 1.8 Hz, ortho to COCl), 7.72 (dd, 1H, J ) 9.2 Hz, J ) 1.8 Hz, ortho to COCl). 3,4-Bis(n-decan-1-yloxy)benzoyl Chloride (4/10). Starting with 3/10 (21.7 g, 50 mmol), SOCl2 (10 mL, excess), and a catalytic amount of DMF in 300 mL of CH2Cl2 at reflux for 0.5 h, 22.6 g (99.9%) of a white powder was obtained, which was used without further purification. 1H NMR (CDCl3, δ, ppm, TMS): 0.89 (overlapped t, 6H, CH3), 1.23-1.68 (m, 28H, CH3(CH2)7), 1.77 (m, 4H, CH2CH2OAr), 4.02 (overlapped t, 4H, CH2OAr), 6.88 (d, 1H, J ) 9.2 Hz, meta to COCl), 7.53 (d, 1H, J ) 1.8 Hz, ortho to COCl), 7.70 (dd, 1H, J ) 9.2 Hz, J ) 1.8 Hz, ortho to COCl). 3,4-Bis(n-tridecan-1-yloxy)benzoyl Chloride (4/13). Starting with 3/13 (15 g, 29 mmol), SOCl2 (20 mL, excess), and a catalytic amount of DMF in 200 mL of CH2Cl2 at reflux for 0.5 h, 15.5 g (99.9%) of a white powder was obtained, which was used without further purification. 1H NMR


(CDCl3, δ, ppm, TMS): 0.89 (overlapped t, 6H, CH3), 1.261.70 (m, 40H, CH3(CH2)10), 1.77 (m, 4H, CH2CH2OAr), 4.05 (overlapped t, 4H, CH2OAr), 6.91 (d, 1H, J ) 9.2 Hz, meta to COCl), 7.54 (d, 1H, J ) 1.8 Hz, ortho to COCl), 7.73 (dd, 1H, J ) 9.2 Hz, J ) 1.8 Hz, ortho to COCl). General Procedure for the Synthesis of N-[3,4-Bis-(nalkan-1-yloxy)benzoyl]-2-aminoethanols with n ) 8, 10, and 13. N -[3,4-Bis(n-octan-1-yloxy)benzoyl]-2-aminoethanol (5/8). Compound 4/8 (23.7 g, 59 mmol) was dissolved in 125 mL of CH2Cl2 and slowly added to ice-cooled ethanolamine (25 mL, excess) under vigorous stirring. The mixture was stirred at 0 °C for 1 h, and then the temperature was raised to 40 °C for another 4 h. The solution was poured into a separatory funnel and washed three times with H2O, dried over MgSO4, and filtered. The solvent was removed by rotary evaporation, and the crude product was recrystallized twice from acetone at 0 °C to yield 21.6 g (85.7%) of a white powder. Purity (HPLC), 99+% TLC (1:1 hexanes: EtOAc): Rf ) 0.20. 1H NMR (CDCl3, δ, ppm, TMS): 0.87 (t, 6H, CH3, J ) 6.3 Hz), 1.22-1.68 (overlapped peaks, 20 H, CH3(CH2)5), 1.85 (m, 4H, CH2CH2OAr), 2.74 (bs, 1H, OH), 3.63 (q, 2H, CH2OH, J ) 5.0 Hz), 3.85 (t, 2H, NHCH2, J ) 5.1 Hz), 4.05 (overlapped t, 4H, CH2OAr), 6.53 (bs, 1H, NH), 6.87 (d, 1H, meta to CONH, J ) 8.2 Hz), 7.28 (dd, 1H, ortho to CONH, J ) 8.2 Hz, J ) 2.4 Hz), 7.40 (d, 1H, ortho to CONH, J ) 2.4 Hz). 13C NMR (CDCl3, δ, ppm): 14.2 (CH3), 22.5 (CH3CH2), 26.0 (CH2CH2CH2O), 29.2, 29.5 (CH3CH2CH2(CH2)2), 30.3 (CH2CH2O), 31.6 (CH3CH2CH2), 42.8 (NHCH2), 62.3 (CH2OH), 69.1, 69.2 (CH2OAr), 112.1, 112.4 (meta to CONH, ortho to CONH and O), 119.6 (ortho to CONH), 126.3 (ipso to CONH), 148.8, 152.2 (meta to CONH, ipso to O and para to CONH), 168.5 (CONH). N -[3,4-Bis(n-decan-1-yloxy)benzoyl]-2-aminoethanol (5/10). Starting with 4/10 (22.6 g, 49 mmol) and ethanolamine (25 mL, excess) in 125 mL of CH2Cl2 at 0-40 °C for 5 h, 19.7 g (83.6%) of a white powder was obtained after two recrystallizations from acetone. Purity (HPLC), 99+% TLC (1:1 hexanes/EtOAc): Rf ) 0.22. 1H NMR (CDCl3, δδ, ppm, TMS): 0.87 (t, 6H, CH3, J ) 6.3 Hz), 1.25-1.65 (overlapped peaks, 28H, CH3(CH2)7), 1.86 (m, 4H, CH2CH2OAr), 2.77 (bs, 1H, OH) 3.66 (q, 2H, CH2OH, J ) 5.0 Hz), 3.84 (t, 2H, NHCH2, J ) 5.1 Hz), 4.03 (overlapped t, 4H, CH2OAr), 6.52 (bs, 1H, NH), 6.88 (d, 1H, meta to CONH, J ) 8.2 Hz), 7.28 (dd, 1H, ortho to CONH, J ) 8.2 Hz, J ) 2.4 Hz), 7.40 (d, 1H, ortho to CONH, J ) 2.4 Hz). 13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.5 (CH3CH2), 26.2 (CH2CH2CH2O), 29.1, 29.4, 29.6 (CH3CH2CH2(CH2)4), 30.2 (CH2CH2O), 31.8 (CH3CH2CH2), 42.9 (NHCH2), 62.3 (CH2OH), 69.1, 69.3 (CH2OAr), 112.2, 112.6 (meta to CONH, ortho to CONH and O), 119.5 (ortho to CONH), 126.3 (ipso to CONH), 148.9, 152.2 (meta to CONH, ipso to O and para to CONH), 168.5 (CONH). N-[3,4-Bis(n-tridecan-1-yloxy)benzoyl]-2-aminoethanol (5/13). Starting with 4/13 (23.5 g, 50 mmol) and ethanolamine (25 mL, excess) in 125 mL of CH2Cl2 at 0-40 °C for 5 h, 21.3 g (86.2%) of a white powder was obtained after two recrystallizations from acetone. Purity (HPLC), 99+% TLC (1:1 hexanes/EtOAc): Rf ) 0.32. 1H NMR

726


(CDCl3, δ, ppm, TMS): 0.87 (t, 6H, CH3, J ) 6.2 Hz), 1.24-1.66 (overlapped peaks, 40H, CH3(CH2)10), 1.85 (m, 4H, CH2CH2OAr), 2.75 (bs, 1H, OH) 3.60 (q, 2H, CH2OH, J ) 5.2 Hz), 3.82 (t, 2H, NHCH2, J ) 5.2 Hz), 4.01 (overlapped t, 4H, CH2OAr), 6.62 (bs, 1H, NH), 6.85 (d, 1H, meta to CONH, J ) 8.4 Hz), 7.24 (dd, 1H, ortho to CONH, J ) 8.4 Hz, J ) 2.4 Hz), 7.38 (d, 1H, ortho to CONH, J ) 2.4 Hz). 13C NMR (CDCl3, δ, ppm): 14.3 (CH3), 22.8 (CH3CH2), 26.2 (CH2CH2CH2O), 29.2, 29.3, 29.4, 29.5, 29.7 (CH3CH2CH2(CH2)7), 30.2 (CH2CH2O), 31.7 (CH3CH2CH2), 42.7 (NHCH2), 62.4 (CH2OH), 69.0, 69.3 (CH2OAr), 112.2, 112.7 (meta to CONH, ortho to CONH and O), 119.7 (ortho to CONH), 126.3 (ipso to CONH), 148.8, 152.0 (meta to CONH, ipso to O and para to CONH), 168.2 (CONH). General Procedure for the Synthesis of 2-[3,4-Bis(nalkan-1-yloxy)phenyl]-2-oxazolines with n ) 8-13. 2-[3,4Bis(n-octan-1-yloxy)phenyl]-2-oxazoline (7/8). Compound 5/8 (21.05 g, 50 mmol) was dissolved in 550 mL of CH2Cl2 and SOCl2 (13.14 mL, 0.18 mol) was added dropwise at 23 °C. The mixture was stirred for 15 min, after which the 1H NMR indicated complete conversion. The reaction was neutralized by addition of 550 mL of saturated NaHCO3 and vigorous stirring for 1 h. The aqueous layer was discarded, and the organic layer was washed three times with 300 mL water, dried over MgSO4, and filtered. The solvent was distilled and the product was recrystallized twice from hexanes, purified on column chromatography (SiO2, hexane/ EtOAc 5:1), and recrystallized again in acetone to yield 16.52 g (82.0%) of a white solid. mp 39-41 °C. Purity (HPLC), 99+%; TLC (CHCl3), Rf ) 0.59. 1H NMR (CDCl3, δ, ppm, TMS): 0.88 (t, 6H, CH3, J ) 6.3 Hz), 1.25-1.70 (m, 20H, CH3(CH2)5), 1.79 (m, 4H, CH2CH2OAr), 4.01 (overlapped t, 6H, CH2OAr, OCH2CH2N), 4.43 (t, 2H, OCH2CH2N, J ) 9.0 Hz), 6.87 (d, 1H, meta to CON, J ) 9.2 Hz), 7.46 (d, 1H, ortho to CON, J ) 2.6 Hz) 7.51 (dd, 1H, ortho to CON, J ) 9.2 Hz, J ) 2.6 Hz). 13C NMR (CDCl3, δ, ppm): 14.3 (CH3), 22.7 (CH3CH2), 26.0 (CH2CH2CH2O), 29.3, 29.6 (CH3CH2CH2(CH2)2), 30.2 (CH2CH2O), 31.9 (CH3CH2CH2), 54.5 (NCH2), 67.6 (OCNCH2), 69.3, 69.5 (CH2OAr), 112.5, 113.1 (meta to OCN, ortho to OCN), 119.8 (ipso to CON) 121.6 (ortho to OCN), 148.5 (meta and para to CON), 164.8 (OCdN). 2-[3,4-Bis(n-decan-1-yloxy)phenyl]-2-oxazoline (7/10). Starting with 5/10 (18.8 g, 40 mmol) and SOCl2 (8.62 mL, 0.12 mol) in 600 mL of CH2Cl2 at 23 °C for 15 min and neutralized by 500 mL of saturated NaHCO3, 15.78 g (86.0%) of a white solid was obtained after recrystallization in hexanes followed by purification by flash column chromatography (SiO2; hexanes/EtOAc (5:1)) and a final recrystallization from acetone. mp 45-46 °C. Purity (HPLC), 99+%; TLC (CHCl3), Rf ) 0.50. 1H NMR (CDCl3, δ, ppm, TMS): 0.89 (t, 6H, CH3, J ) 6.4 Hz), 1.22-1.72 (m, 28H, CH3(CH2)7), 1.77 (m, 4H, CH2CH2OAr), 4.00 (overlapped t, 6H, CH2OAr, OCH2CH2N), 4.43 (t, 2H, OCH2CH2N, J ) 9.0 Hz), 6.85 (d, 1H, meta to CON, J ) 9.2 Hz), 7.47 (d, 1H, ortho to CON, J ) 2.6 Hz) 7.49 (dd, 1H, ortho to CON, J ) 9.2 Hz, J ) 2.6 Hz). 13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.7 (CH3CH2), 26.0 (CH2CH2CH2O), 29.2, 29.4, 29.7

Percec et al.

(CH3CH2CH2(CH2)4), 30.2 (CH2CH2O), 31.9 (CH3CH2CH2), 54.7 (NCH2), 67.5 (OCNCH2), 69.1, 69.3 (CH2OAr), 112.5, 113.1 (meta to OCN, ortho to OCN), 119.8 (ipso to CON) 121.6 (ortho to OCN), 148.7 (meta and para to CON), 164.7 (OCdN). 2-[3,4-Bis(n-tridecan-1-yloxy)phenyl]-2-oxazoline (7/13). Starting with 5/13 (5 g, 8.91 mmol) and SOCl2 (1.82 mL, 0.025 mol) in 400 mL of CH2Cl2 at 23 °C for 15 min and neutralized by 400 mL of saturated NaHCO3, 5.97 g (81.0%) of a white solid was obtained after recrystallization in hexanes followed by purification by flash column chromatography (SiO2; hexanes/EtOAc (5:1)) and a final recrystallization from acetone. mp 55-57 °C. Purity (HPLC), 99+%; TLC (CHCl3), Rf ) 0.38. 1H NMR (CDCl3, δ, ppm, TMS): 0.88 (t, 6H, CH3, J ) 6.5 Hz), 1.25-1.69 (m, 40H, CH3(CH2)10), 1.76 (m, 4H, CH2CH2OAr), 4.02 (overlapped t, 6H, CH2OAr, OCH2CH2N), 4.42 (t, 2H, OCH2CH2N, J ) 9.0 Hz), 6.88 (d, 1H, meta to CON, J ) 9.2 Hz), 7.45 (d, 1H, ortho to CON, J ) 2.4 Hz) 7.45 (dd, 1H, ortho to CON, J ) 9.2 Hz, J ) 2.4 Hz). 13C NMR (CDCl3, δ, ppm): 14.2 (CH3), 22.4 (CH3CH2), 26.3 (CH2CH2CH2O), 29.2, 29.3, 29.6 (CH3CH2CH2(CH2)7), 30.2 (CH2CH2O), 31.9 (CH3CH2CH2), 54.7 (NCH2), 67.6 (OCNCH2), 69.2, 69.5 (CH2OAr), 112.5, 113.3 (meta to OCN, ortho to OCN), 119.5 (ipso to CON) 121.7 (ortho to OCN), 148.8 (meta and para to CON), 164.9 (OCdN). General Procedure for the Synthesis of Poly{N-[3,4bis(n-alkan-1-yloxy)benzoyl]ethyleneimine} {poly[(3,4)nG1Oxz]} in Solution. Polymerization of (3,4)12G1-Oxz. A Schlenk tube equipped with a magnetic magnetic stirrer was dried at 200 °C overnight and charged with (3,4)12G1-Oxz (typically 0.3 mmol). The monomer was dissolved in a minimum amount of dry benzene and freeze-dried in the septum-sealed Schlenk tube. The Schlenk tube was filled with Ar, and o-DCB (0.5 mL) was added under a stream of Ar. MeOTf initiator was added via syringe according to the desired theoretical DP. The Schlenk tube was resealed, immersed in an oil bath that was preheated to 100 °C, and stirred vigorously. The polymerization was checked periodically by GPC and 1H NMR analysis until a conversion of 100% was achieved or the reaction did not advance further. The tube was cooled to room temperature and end capped by the addition of 25% aqueous KOH (1 mL, excess) followed by stirring for 2 h at 23 °C. The viscous solution was precipitated in acetone, and the solid product was filtered. The polymer was dissolved in benzene and freezedried. 1H NMR (CDCl3, δ, ppm, TMS): 0.88 (m, CH3), 1.26-1.95 (m, CH3(CH2)n), 2.60-3.8 (br, NCH2CH2N, NCH2), 3.8-4.0 (br, CH2OAr, 6.75 (br, Ar). General Procedure for the Synthesis of Poly{N-[3,4bis(n-alkan-1-yloxy)benzoyl]ethyleneimine} {poly[(3,4)nG1Oxz]} in Bulk. Polymerization of (3,4)12G1-Oxz. A Schlenk tube equipped with a magnetic stirrer was dried at 200 °C overnight and charged with (3,4)12G1-Oxz. The monomer (typically 0.4 mmol) was dissolved in a minimum amount of dry benzene and freeze-dried in the septum-sealed Schlenk tube. After freeze-drying, the Schlenk tube was flushed with Ar. The initiator MeOTf was added via syringe according to the desired theoretical DP, and the tube was



placed in a preheated oil bath at 160 °C. The melt was stirred until 1H NMR indicated the complete conversion of the monomer. For selected experiments poly[(3,4)12G1-Oxz was dissolved in THF (2 mL) and end capped by the addition of 25% aqueous KOH (2 mL) and stirring for 1 h. Acknowledgment. Financial support by the National Science Foundation (DMR-9996288) ONR and ARO-MURI is gratefully acknowledged. References and Notes (1) Kauffman, S. A. The Origins of Order. Self-Organization and Selection in EVolution; Oxford University Press: New York, 1993. (2) Kauffman, S. A. At Home in the UniVerse. The Search for the Laws of Self-Organization and Complexity; Oxford University Press: New York, 1995. (3) (a) Percec, V.; Heck, J. Am. Chem. Soc., DiV. Polym. Chem. Polym. Prepr. 1989, 30 (2), 450. (b) Percec, V.; Heck, J. Polym. Bull. 1990, 24, 255. (c) Percec, V.; Heck, J. Am. Chem. Soc., DiV. Polym. Chem. Polym. Prepr. 1991, 32 (1), 263. (d) Percec, V.; Heck, J. Polym. Bull. 1991, 25, 55. (e) Percec, V.; Heck, J. Am. Chem. Soc., DiV. Polym. Chem. Polym. Prepr. 1991, 32 (3), 698. (f) Percec, V.; Heck, J. Polym. Bull. 1991, 25, 431. (g) Percec, V.; Heck, J.; Ungar, G. Am. Chem. Soc., DiV. Polym. Chem. Polym. Prepr. 1992, 33 (1), 152. (h) Percec, V.; Heck, J. Am. Chem. Soc., DiV. Polym. Chem. Polym. Prepr. 1992, 33 (1), 217. (i) Percec, V.; Heck, J. J. Polym. Sci., Part A: Polym. Chem. 1991, 29, 591. (j) Percec, V.; Heck, J.; Ungar. G. Macromolecules 1991, 24, 4957. (k) Percec, V.; Lee, M.; Heck, J.; Blackwell, H. E.; Ungar, G.; Alvarez-Castillo, A. J. Mater. Chem. 1992, 2, 931. (l) Percec, V.; Lee, M.; Heck, J. A.; Blackwell, H.; Ungar, G.; Alvarez-Castillo, A. J. Mater. Chem. 1992, 2, 1033. (m) Percec, V.; Heck, J. A.; Tomazos, D.; Ungar, G. J. Chem. Soc., Perkin Trans. 2 1993, 2381. (n) Percec, V.; Heck, J.; Tomazos, D.; Falkenberg, F.; Blackwell, H.; Ungar, G. J. Chem. Soc., Perkin Trans. 1 1993, 2799. (o) Percec, V.; Tomazos, D.; Heck, J.; Blackwell, H.; Ungar, G. J. Chem. Soc., Perkin Trans. 2 1994, 31. (p) Percec, V.; Schlueter, D.; Kwon, Y. K.; Blackwell, J.; Mo¨ller, M.; Slangen, P. J. Macromolecules 1995, 28, 8807. (r) Johansson, G.; Percec, V.; Ungar, G.; Zhou, J.-P. Macromolecules 1996, 29, 646. (s) Percec, V.; Schlueter, D.; Ronda, J. C.; Johansson, G.; Ungar, G.; Zhou, J.-P. Macromolecules 1996, 29, 1464. (t) Percec, V.; Schlueter, D. Macromolecules 1997, 30, 5783. (u) Percec, V.; Schlueter, D.; Ungar, G.; Cheng, S. Z. D.; Zhang, A. Macromolecules 1998, 31, 1745. (v) Yeardley, D. J. P.; Ungar, G.; Percec, V.; Holerca, M. N.; Johansson, G. J. Am. Chem. Soc. 2000, 122, 1684. (4) (a) Maltheˆte, J.; Liebert, L.; Levelut, A.-M.; Galerne, Y. C. R. Acad. Sci. Paris 1986, 303 (II), 1073. (b) Maltheˆte, J.; Tinh, N. H.; Levelut, A. M. J. Chem. Soc., Chem. Commun. 1986, 1548. (5) (a) Klug, A. (Nobel Lecture) Angew. Chem., Int. Ed. Engl. 1983, 22, 565. (b) Bawden, F. C.; Pirie, N. W.; Bernal, J. D.; Fankuchen, I. Nature 1936, 138, 1051. (c) Bernal, J. D.; Fankuchen, I. Nature 1937, 139, 923. (6) (a) Kwon, Y. K.; Chvalun, S.; Schneider, A. I.; Blackwell, J.; Percec, V.; Heck, J. Macromolecules 1994, 27, 6129. (b) Kwon, Y. K.; Danko, C.; Chvalun, S.; Blackwell, J.; Heck, J.; Percec, V. Macromol. Symp. 1994, 87, 103. (c) Kwon, Y. K.; Chvalun, S.; Blackwell, J.; Percec, V.; Heck, J. Macromolecules 1995, 28, 1552. (d) Chvalun, S.; Kwon, Y. K.; Blackwell, J.; Percec, V. Polym. Sci., Ser. A 1996, 38, 1298. (e) Chvalun, S.; Blackwell, J.; Kwon, Y. K.; Percec, V. Macromol. Symp. 1997, 118, 663. (f) Chvalun, S.; Blackwell, J.; Cho, J. D.; Kwon, Y. K.; Percec, V.; Heck, J. Polymer 1998, 38, 4515. (g) Chvalun, S.; Blackwell, J.; Cho, J. D.; Bykova, I. V.; Percec, V. Acta Polym. 1999, 50, 51. (h) Chvalun, S.; Shcherbina, M. A.; Bykova, I. V.; Blackwell, J.; Percec, V.; Kwon, Y. K.; Cho, J. D. Polym. Sci., Ser. A 2001, 43, 33. (7) (a) Percec, V.; Johansson, G.; Heck, J.; Ungar, G.; Batty, S. V. J. Chem. Soc., Perkin Trans. 1 1993, 1411. (b) Johansson, G.; Percec, V.; Ungar, G.; Abramic, D. J. Chem. Soc., Perkin Trans. 1 1994, 447. (c) Ungar, G.; Abramic, D.; Percec, V.; Heck, J. A. Liq. Cryst. 1996, 21, 73. (d) Percec, V.; Johansson, G.; Ungar G.; Zhou, J. J. Am. Chem. Soc. 1996, 118, 9855. (e) Balagurusamy, V. S. K.; Ungar, G.; Percec, V.; Johansson G. J. Am. Chem. Soc. 1997, 119, 1539. (f) Hudson, S. D.; Jung, H.-T.; Percec, V.; Cho, W.-D.; Johansson, G.; Ungar, G.; Balagurusamy, V. S. K. Science 1997, 278, 449. (g) Hudson, S. D.; Jung, H.-T.; Kewsuwan, P.; Percec, V.; Cho, W.-D. Liq. Cryst. 1999, 26, 1493. (h) Percec, V.; Cho, W.-D.; Mosier, P.

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BM015550J

Poly(oxazolines)s with Tapered Minidendritic Side Groups. The

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