Change in Crystal Structure and Polymerization Reactivity for the Solid

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Change in Crystal Structure and Polymerization Reactivity for the Solid-State Polymerization of Muconic Esters Matsumoto,*,†

Akikazu Kunio Oka§

Daisuke

Furukawa,†

Yutaka

Mori,†

Toshihiro

Tanaka,†,‡

and

CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 6 1078-1085

Department of Applied Chemistry, Graduate School of Engineering, Osaka City UniVersity, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, and Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture UniVersity, Gakuencho 1-2, Sakai, Osaka 599-8570, Japan ReceiVed September 25, 2006; ReVised Manuscript ReceiVed March 19, 2007

ABSTRACT: We report the polymerization mechanism and kinetics of muconic esters as the 1,3-diene monomers during solidstate polymerization via a crystal-to-crystal transformation. We have revealed a change in the structure of the muconate crystals accompanying the shrinking and expanding of the lattice lengths, on the basis of the X-ray single-crystal structure analysis of the monomers and polymers as well as a change in the transient structure monitored by powder X-ray diffraction during the continuous X-ray radiation. The polymerization rate is closely related to the molecular stacking distance in the monomer crystals because the polymer chain skeletons have the same conformational structure in the crystals. A lattice length in the direction along which a polymer chain is produced decreases during the transformation from monomer to polymer crystals when monomer molecules are arranged in a columnar assembly with a stacking distance greater than the fiber period of the resulting polymer, and vice versa. A strain in the crystals is formed by a mismatch between the monomer and polymer crystal lattices accumulated and then finally released during the polymerization. Introduction Solid-state organic reactions have recently attracted much attention of organic chemists because of their intrinsic features and significant merits for environmental and green sustainable chemistry.1 The solid-state reactions have many features different from those for reactions performed in solution or in the gaseous state. The topochemical polymerization as well as [2+2] photodimerization of unsaturated compounds have been intensively investigated since the 1960-70s.2 Thirty years later, we are faced with a new era as the renaissance period of crystal engineering3,4 due to the recent development of a single-crystal structure analysis within a very short time with a high accuracy by modern and convenient experimental and analytical methods. A single crystal to single crystal reaction fascinates us because it directly provides a large amount of credible information regarding the solid-state reaction mechanism. In actual cases, however, a crystal change during the reactions has been reported for several reactions under limited conditions.5 When a reaction requires a significant movement of atoms in the crystals, the crystal structure is destroyed. Such a reaction often leads to the formation of amorphous products. In contrast, a topochemical reaction process with the least movement of atoms during the reaction is a promising method to provide highly crystalline materials with a well-controlled stereo- and regiostructure. We have already demonstrated the topochemical polymerization of 1,3-diene monomers to give polymer crystals,6 similar to the polymerization of diacetylenes,7,8 diolefins,9 a triacetylene,10 a triene,11 and quinodimethanes.12 For the polymerization that proceeds via a chain reaction mechanism, the polymerization reactivity is estimated by common topochemical polymerization principles. The monomer stacking distance and stacking angle are the most important factors for determining its polymerization * Corresponding author. Fax: 81-6-6605-2981, E-mail: matsumoto@ a-chem.eng.osaka-cu.ac.jp. † Osaka City University. ‡ Present address: Chemical Resources Laboratory, Tokyo Institute of Technology, R1-5, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan. § Osaka Prefecture University.

reactivity, although other stacking factors, such as the carbonto-carbon distance between bond-forming carbons, are also important. In fact, the topochemical polymerization readily proceeds when monomer molecules are arranged in a columnar structure with a stacking distance of 5 Å for diyne7 and diene6 monomers and 7.4 Å for triyne,10 triene,11 and quinodimethane12 monomers. In the present study, we have investigated the crystals structures of several muconic esters (Scheme 1) and the obtained polymers by topochemical polymerization using X-ray singlecrystal structure analysis as well as powder X-ray diffraction. We propose a reaction mechanism for the polymerization of muconates in the solid state, in which the topochemical polymerization proceeds along with shrinking and expanding of the crystals, and the polymer chain conformation includes any strain depending on the mode of polymerization. The relationship between the polymerization kinetics and monomer stacking structures in the crystals are also revealed. Results and Discussion Shrinking and Expanding Crystals. We determined the single-crystal structures for the monomer and polymer crystals of 4NO2, MDO, and 26F2 (Table 1). The polymer crystals were prepared by the γ-radiation polymerization of the monomer single crystals. The quality of the single crystals decreased during the polymerization and the R1 and wR2 have larger values for the polymer crystals than those for the monomer crystals. The crystal structures of Et, 4Cl, and 4Br, as well as their polymers have already been reported in previous papers.13-16 We carried out an X-ray crystal structure analysis at room temperature in the present study in order to examine the relationship between the crystal structure and polymerization reactivity under the same conditions. The changes in the unit cell lengths and volume before and after the polymerization are summarized in Table 2. The value of lattice length parallel to a fiber axis is equal to the monomer stacking distance (ds) and the fiber period (FP) for the monomer and polymer crystals, respectively.

10.1021/cg0606444 CCC: $37.00 © 2007 American Chemical Society Published on Web 05/02/2007

Solid-State Polymerization of Muconic Esters

Crystal Growth & Design, Vol. 7, No. 6, 2007 1079

Scheme 1

Figure 1. Schematic model for the shrinking and expanding of crystals during domino-type polymerization in the solid state. Monomer molecules translationally stack in a column with a stacking distance (ds) larger or smaller than the fiber period (FP) of the resulting polymer, leading to shrinkage and expansion, respectively, in the column direction.

A model for the solid-state polymerization of 1,3-diene monomers is illustrated in Figure 1. When the polymerization proceeds in a domino-type reaction mechanism, all the monomer molecules include a conrotatory molecular motion for the formation of the polymer chain. Each molecule rotates and changes its conformation to make a new covalent bond between molecules with the least translational movement of the center of the molecular mass. The produced radical species react with neighboring molecules in a columnar assembly. The propagating radicals continue repeated propagation along the column within a very short time. This mechanism is basically similar to the polymerization of diacetylenes in the solid state, which has been extensively investigated.7 Here, the shrinking and expanding of crystals were analyzed and discussed from the viewpoint of the evaluation of the mechanism and reactivity of the solidstate polymerization. When monomer molecules translationally stack in a column with a ds value larger than FP of the corresponding polymer, shrinking is observed along the column direction. In fact, a change in the lattice lengths along the fiber axis is -1.9 to -7.3% for the crystals of Et, 4Cl, 4Br, and 4NO2. The other two axis directions involved expansion (+0.1 to +3.3%), except the shrinking in the perpendicular axis for Et (-4.7%). Reversely, a fiber axis length increases by +6.1 and +12.9% during the polymerization of MDO and 26F2, respectively. Simultaneously, a large shrinking occurs in an orthogonal direction (-6.0 and -10.9%). Overall, the unit-cell volume of these crystals is reduced during the polymerization by 2-5%, except for the volume-expanding polymerization of 26F2 (+3.9%). Volume shrinking is usually observed for the addition polymerization of unsaturated monomers because it is a covalent bond-forming reaction. The volume expansion of the 26F2 crystal during the polymerization is noteworthy. As was already described in the previous paper,17,18 the 26F2 molecule has an S-shaped conformation different from the other muconate monomers. A large structural change is required in the lattices along the a- and b-axes during a change from the monomer to the polymer in the crystals. The ORTEP drawings for the muconates polymer crystals are shown in Figure 2. The thermal ellipsoids of poly(26F2) are clearly larger than those for the other polymers. The weak temperature dependence of the thermal vibration intensity was also confirmed. The packing structure of the poly(26F2) chains formed during the expanding

polymerization may be thermodynamically different from those for the other polymers. It was suspected that the specific structure of poly(26F2) was due to a residual monomer in the polymer crystals. Therefore, we investigated the γ-radiation polymerization reactivity of the muconates using the powder crystals at various radiation doses. The polymer was isolated by removing the unreacted monomer with chloroform after polymerization. The results are shown in Table 3. The polymerization reactivity was in the following order: Et > 4Cl > 4Br > 4NO2 for the shrinking polymerizations and 26F2 > MDO for the expanding polymerization. These results suggest the possibility of contamination by the residual monomer after polymerization under the 200 kGy radiation conditions for the polymer crystals of 4NO2, 26F2, and MDO. To check this point, we determined the single-crystal structure of poly(26F2) after the additional radiation. The structures of poly(26F2) crystals obtained by the polymerization at 200 and 400 kGy dose radiation agreed well with each other, as shown in Table 1. Therefore, we have concluded that there is no contamination due to a residual monomer for the determination of the single-crystal structure of poly(26F2). Single crystals possibly give a polymer in a higher yield rather than powdered polycrystals including grain boundaries under similar radiation conditions. Eventually, the specific thermal vibration of poly(26F2) is not due to the low reactivity of 26F2. Both the unique molecular conformation and the expanding polymerization process of 26F2 may be synergistically attributed to the induction of the metastable molecular packing of polymer chains in the crystals with a low density (Fcalcd ) 1.446 g/cm3). The high density of the 26F2 monomer crystal (Fcalcd ) 1.503 g/cm3) also contributes to an increase in the cell volume during the polymerization. Poly(MDO) and poly(26F2) have a conformational structure different from those for the other polymers, as shown in the ORTEP drawings in Figure 2. The polymers produced during the shrinking polymerization thrust their benzyl ester groups as the side chain into a direction orthogonal to the polymer main chain. On the other hand, the expansion polymerization provides polymers with folded benzyl ester groups. The torsion angles regarding the conformational structures of the polymer main chains are shown in Table 4. The numbering of atoms for them is shown in Figure 3. Some torsion angles are clearly distinguished, depending on the shrinking and expanding polymerization mechanisms; for example, the angles of O(1)-C(1)C(2)-C(3), O(2)-C(1)-C(2)-C(3), and C(1)-O(2)-C(4)C(5) of poly(MDO) and poly(26F2) are different from those for the polymers obtained by shrinking polymerization. However, it has been confirmed that a difference in the parameters

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Table 1. Crystallographic Data of Muconate Monomers and Polymersa

chemical formula fw cryst habit cryst syst space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z Fcalcd (g/cm3) no. of reflns measured no. of unique reflns no. obsd (I > 2σ (I)) R1 (I > 2σ (I)) wR2 (all) GOF T (°C) final diff four map (e Å-3) a

4NO2

poly(4NO2)

MDO

poly(MDO)

26F2

poly(26F2)

C20H16N2O8 412.35 plates monoclinic P21/c 5.79950(10) 5.23930(10) 31.1930(2) 91.1720(10) 947.61(3) 2 1.445 5842 2053 1307 0.0781 0.2017 1.162 23 0.25, -0.25

C20H16N2O8 412.35 plates monoclinic P21/c 5.990(5) 4.855(3) 31.941(14) 92.85(2) 927.8(10) 2 1.476 2120 2120 1073 0.0948 0.3172 1.081 23 0.54, -0.30

C22H18O8 410.36 plates monoclinic P21/a 11.540(2) 4.4318(7) 18.858(4) 102.397(7) 941.9(3) 2 1.447 8628 2156 1241 0.0429 0.0993 0.929 23 0.15, -0.18

C22H18O8 410.36 plates monoclinic P21/a 10.85(3) 4.702(4) 18.73(2) 105.67(2) 920(3) 2 1.481 1984 1984 673 0.0926 0.3188 0.937 23 0.25, -0.28

C20H14O4F4 394.31 needles monoclinic P21/n 4.177(3) 12.580(10) 16.677(10) 96.14(3) 871.3(10) 2 1.503 7949 1976 1167 0.0401 0.0978 0.981 23 0.15,-0.15

C20H14O4F4 394.31 needles monoclinic P21/n 4.716(3) [4.748(3)] 11.213(8) [11.312(6)] 17.130(14) [17.286(8)] 91.32(6) [91.40(4)] 905.5(12) [928.2(8)] 2 1.446 [1.411] 7297 [8048] 2048 [2114] 958 [995] 0.0772 [0.0734] 0.2692 [0.2770] 1.020 [1.049] 23 0.29,-0.17[0.30,-0.14]

Polymer single-crystal structures were determined after γ-radiation at 200 kGy. The values in brackets indicate those after γ-radiation at 400 kGy. Table 2. Change in Lattice Lengths and Cell Volume of the Crystals during Solid-State Polymerization of Muconic Estersa lattice length (Å)

monomer and polymerb

parallel to fiber axisc

perpendicular to fiber axis

perpendicular to fiber axis

cell volume (Å3)

Et poly(Et) 4Cl poly(4Cl) 4Br poly(4Br) 4NO2 poly(4NO2) MDO poly(MDO) 26F2 poly(26F2)

4.931 4.839 (-1.9%) 5.122 4.863 (-5.1%) 5.21 4.856 (-6.8%) 5.239 4.855 (-7.3%) 4.432 4.702 (+6.1%) 4.177 4.716 (+12.9%)

10.232 10.391 (+1.6%) 5.629 5.680 (+0.9%) 5.68 5.837 (+2.8%) 5.800 5.990 (+3.3%) 11.540 10.85 (-6.0%) 12.580 11.213 (-10.9%)

11.497 10.962 (-4.7%) 32.08 32.10 (+0.1%) 32.26 32.742 (+1.5%) 31.193 31.94 (+2.4%) 18.858 18.73 (-0.7%) 16.677 17.130 (+2.7%)

554.3 525.3 (-5.2%) 923.0 886.5 (-4.0%) 953.0 927.8 (-2.6%) 947.6 927.8 (-2.1%) 941.9 920 (-2.3%) 871.3 905.5 (+3.9%)

a Values in parentheses are the changes in the axes and volume during the polymerization. b References 13-16 for the crystal structures of Et, 4Cl, and 4Br. c Corresponding to ds and FP for monomer and polymer crystals, respectively.

regarding the main chain conformation is small. Thus, the polymer chains have a specific conformation in the crystals, depending on the polymerization mode. In Table 2, we noticed the exactly identical FP values for the polymer crystals, regardless of the ds values for the monomers; i.e., FP ) 4.844.86 Å and 4.70-4.72 Å for the polymers obtained by the shrinking and expanding polymerizations, respectively. Previously, a zigzag-type reaction mechanism was proposed for the diacetylene polymerization23 and the stepwise [2+2] photopolymerization of diolefin compounds,24 which have a large stacking angle (i.e., a small tilt angle) in the columnar structure of the monomers. However, we can conclude that the polymerization of the muconates undergoes via a domino-type polymerization mechanism, regardless of the shrinking and expanding polymerizations. Polymerization Rate and Monomer Stacking. Next, we discuss the relationship between the stacking structure and the polymerization reactivity. During the solid-state polymerization, no diffusion of the propagating radical occurs and the radical species at the chain ends of the long polymer chains are eventually trapped in the solid matrix. The propagating radicals located at both chain ends of the formed high-molecular-weight polymers are long-lived and easily detected by electron spin resonance spectroscopy, but they no longer can contribute to any further propagation. As a result, an entire polymerization rate is determined by the rate of the evolving propagating radicals during the initiation step. The polymerization kinetics

in the solid state should be dominated by factors different from those in the homogeneous radical-chain polymerization system in solution.7a,19 In actual cases, however, an apparent first-order reaction is often observed for the solid-state polymerizations via a chain reaction mechanism such as the photopolymerization of 1,3-diene derivatives, especially during the initial stage of the polymerization of muconates.14,20,21 The polymerization was carried out using powdered crystals embedded in a KBr pellet under UV irradiation. The conversion was determined from a change in the absorption intensity of the CdC stretching around 1600 cm-1 in the IR spectrum. The first-order plot of the conversion is shown in Figure 4, as a function of the UV irradiation time. The slight acceleration of polymerization was observed for the shrinking polymerization, whereas the polymerization rate decreased during the expanding polymerization of MDO. This is due to a different mode for quenching the evolved strain though a crystal lattice change or a polymer conformational stress, as will be discussed in the next section. In the present study, we determined the first-order reaction constants (k) from each initial slope in the curves. In Table 5, the k values are summarized together with several molecular stacking parameters for the monomer crystals: ds, dCC, θ1, and θ2. The parameters θ1 and θ2 are the angles between the stacking direction and molecular plane in directions from a view parallel to a vector through the 2- and 5-carbons of the diene moieties and an orthogonally different view. The definition of the parameters was presented in our previous paper.14

Solid-State Polymerization of Muconic Esters

Crystal Growth & Design, Vol. 7, No. 6, 2007 1081

Figure 2. ORTEP drawings for (a) poly(4Cl), (b) poly(4Br), (c) poly(4NO2), (d) poly(MDO), (e) poly(26F2), and (f) poly(26F2) at -70 °C. The structures were determined at room temperature except for (f) from ref 17. Thermal ellipsoids are plotted at the 50% probability level. Table 3. Results of γ-Ray Polymerization of Muconic Esters at Various Radiation Doses polymer yield (%) monomer

5 kGy dose

10 kGy dose

Et 4Cl 4Br 4NO2

85 31 19

∼100 88 51 0

26F2 MDO

trace 8

20 kGy dose

50 kGy dose

100 kGy dose

200 kGy dose

500 kGy dose

∼100 80 5

∼100 83

∼100

expanding polymerization 68 83 25 57

96 74

∼100 92

shrinking polymerization 94 67 0

4 11

15 22

96 76 trace

Table 4. Torsion Angles for the Conformational Structure of

C(1)-C(2)-C(3)-C(3′) C(1)-O(2)-C(4)-C(5) C(2′)-C(2)-C(3)-C(3′) C(4)-O(2)-C(1)-C(2) O(1)-C(1)-C(2)-C(3) O(2)-C(1)-C(2)-C(3) a

1000 kGy dose

∼100

Polymersa

poly(4Cl)

poly(4Br)

poly(4NO2)

poly(MDO)

poly(26F2)

123.35 168.7(4) 118.13 178.1(3) 33.5(6) 147.8(3)

123.50 170.7(5) 116.74 176.4(4) 35.0(9) 147.6(6)

121.4(7) 170.8(4) 119.8(7) 174.9(4) 30.2(9) 148.4(5)

139.0(7) 77.6(6) 103.4(8) 166.5(4) 49.6(7) 134.9(5)

123.6(5) 167.4(4) 113.9(5) 176.2(3) 125.1(5) 53.4(4)

Unit in degrees. For the crystal structures of poly(4Cl) and poly(4Br), see refs 14 and 15, respectively.

For the photopolymerizable ester monomers, all the compounds have similar stacking parameters, independent of the structure of the ester groups: ds ) 4.43-5.24 Å, dCC ) 3.563.89 Å, θ1 ) 72-79°, and θ2 ) 43-52°. It has been pointed out that ds and θ2 are the most important for determining the reactivity during the solid-state polymerization of the 1,3-diene compounds.6c,14,22 The ds and θ2 values compensate each other. Namely, the θ2 value decreases as the ds value increases (see also Figure 1) because of the close packing of the monomer molecules with a constant molecular thickness for the π-bond. All the dCC values are smaller than 4 Å, with no clear relationship between the k and dCC values. This indicates that the closer contact of the double bond and the reacting carbons are necessary for the polymerization, but it does not determine the polymerization rate. In contrast, the polymerization rate

significantly depends on the absolute value of the change in the lattice length. The k values become greater as the change in the lattice is smaller, as is clearly shown in a plot of Figure 5. Interestingly, this unique relationship is true for both the shrinking and expanding polymerizations. If monomers are stacked with an ideal monomer stacking structure with a ds value exactly equal to its FP in the solid state, the isolation and the structure determination of the monomer crystals could be difficult under ambient conditions because the crystallization of the monomers is immediately followed by the spontaneous polymerization. For the unimolecular reactions and dimerization, the reactivity in the solid state has been explained by the mobility of the atom and groups as well as the free volume surrounding a reacting center.25 The intermolecular space can act as a buffer to reduce

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Figure 3. Numbering of atoms for the determination of torsion angles in Table 4.

Figure 5. Relationship between relative polymerization rate and degree of shrinkage (open circles) or expansion (closed circle) during topochemical polymerization of muconates.

Figure 4. Semilogarithmic plots of monomer fraction versus the UV irradiation time for the topochemical polymerization of muconates. Table 5. Polymerization Rate and Monomer Stacking Parameters for Solid-State Polymerization of Muconatesa monomer

k × 103 (s-1)

Et 4Cl MDO 4Br 4NO2 26F2

5.16 ( 0.84 1.15 ( 0.12 0.75 ( 0.04 0.25 ( 0.02 0.10 ( 0.02 ∼0b

lattice θ1 θ2 change (%) ds (Å) dCC (Å) (degree) (degree) 1.9 5.1 6.1 6.8 7.3 12.9

4.93 5.12 4.43 5.21 5.24 4.18

3.79 3.56 3.68 3.89 3.61 4.15

79 78 72 72 76 73

49 43 52 49 43 63

a d is the monomer stacking distance. d s CC is the distance between the reacting carbons. θ1 and θ2 are the stacking angles (ref 14). The polymerization rate was determined by IR spectroscopy. k is the first-order reaction constant for the polymerization. b [2+2] photodimerization is preferred rather than polymerization under UV irradiation, although γ-radiation provided a polymer (ref 17).

the strain evolved during these reactions. Differing from them, successive covalent bonds are present along the produced polymer chain and the predetermined and ideal conformation of a polymer chain is required for polymerization to occur and yield a high-molecular-weight polymer. As a result, the stacking distance in the monomer crystals exactly determines the topochemical polymerization rate. Change in Crystal Lattice during Polymerization. Finally, we discuss a continuous change in the crystal structure and the strain accumulated in the crystals during the shrinking and expanding polymerizations. Figure 6a shows the change in the powder X-ray diffraction profiles of 4Cl by continuous X-ray radiation. The change in the cell lengths was estimated from some characteristic lines. For example, the a- and c-axis lengths for the crystal of 4Cl were calculated using the d100 and d002 values, respectively. Figure 7 shows the single-crystal structure of the 4Cl monomer and a change in the lattice lengths during the X-ray radiation polymerization. A change in b-axis could not be monitored because of a difficulty in the separation of the characteristic diffraction lines. A temporary increase was observed up to the ca. 2% increment in the lattice length along the a- and c-axes during an initial stage of the polymerization. Half-line width values for the d100 and d002 decreased after the shift of the lines (Table 6). Because a structural change of the

Figure 6. Powder X-ray diffraction profiles of 4Cl during the continuous X-ray radiation. (a) Whole diffraction profiles for 1-15 scans in the range of 2-40° and (b) a change in the diffraction lines of d002 and d100 for 1-25 scans in the range of 5.0-6.0 and 15.0-16.0°, respectively.

4Cl crystals occurred soon after the beginning of polymerization, we more precisely determined the shift of the characteristic lines in the limited scan range. The diffraction profiles monitored by rapid scans in the narrow region of 5.0-6.0 and 15.0-16.0° clearly show the shift of the line toward a low-angle region, i.e., an increase in the lattice length, at the beginning of the polymerization (Figure 6b). The temporary increase in the axis lengths observed in the present study is due to a disturbed structure in the crystals containing a small number of polymer chains surrounded by the unreacted monomer molecules in the crystals and suggests the random formation of the polymer chain and the distribution of strain throughout the crystals. The lattice lengths then gradually decrease and approach the values for the single crystals of poly(4Cl); that is, a +0.9 and 0.1% increase relative to the monomer lattice lengths for the a- and c-axes, respectively. The conversion of 4Cl into the polymer was estimated to be ca. 30% by IR spectroscopy after the 37 X-ray diffraction measurement cycles. In the diffraction profile of MDO (Figure 8), the shift of each line was more clearly observed. The diffraction data summarized in Table 6 indicate an increase in the value of half-line width induced by the structural change. The line width has a maximum

Solid-State Polymerization of Muconic Esters

Crystal Growth & Design, Vol. 7, No. 6, 2007 1083 Table 6. Change in Selected Diffraction Lines of 4Cl and MDO during Solid-State Polymerization by X-ray Irradiation monomer

hkl

scan number

2θ (deg)

4Cl

002

0 1 3 5 7 10 15 30 0 1 3 5 7 10 15 30 1 5 10 20 40 60 1 5 10 20 40 60 1 5 10 20 40 60

5.493 5.463 5.417 5.436 5.439 5.462 5.460 5.478 15.762 15.459 15.540 15.597 15.599 15.599 15.599 15.598 15.381 15.381 15.441 15.580 15.740 15.840 19.238 19.240 19.298 19.379 19.439 19.442 24.719 24.679 24.501 24.220 24.040 23.961

100

MDO

20-1

004

013

Figure 7. (a) Single-crystal structure of 4Cl and (b) a change in the lattice lengths during the continuous X-ray radiation. Polymer chains are formed along the b-axis. The conversion into the polymer was approximately 30% after 37 measurement cycles; a-axis (red), c-axis (green). The single-crystal structure is from ref 14.

Figure 8. Powder X-ray diffraction profiles of MDO during the continuous X-ray radiation (1-70 scans at five-scan interval).

value at the intermediate stage of the reaction. In the case of MDO, we successfully determined the changes in the three axis lengths using changes in the d20-1, d004, and d013 values (Figure 9). Differing from the results of 4Cl, all the axes monotonically change their length without exhibiting a temporary peak; an increase in the b-axis length as the fiber axis, and a decrease in the other orthogonal axes. An induction period was detected in the structural change; no change was observed in the lattice lengths during the initial several scans for the X-ray diffraction measurement. It was confirmed by IR spectroscopy that the polymerization actually occurred from the initial radiation cycle under the same radiation conditions. Thus, we have revealed the features of a reaction mechanism observed during the shrinking and expanding polymerizations in the solid state. In conclusion, we have reported the polymerization mechanism and kinetics of muconic esters as the 1,3-diene monomers during solid-state polymerization via a crystal-to-crystal transformation. We have revealed a change in the structure of the

intensity 737 605 346 280 208 198 214 901 945 1478 1939 2160 1909 1822 1170 1110 879 576 438 482 1073 1083 941 768 741 691 1193 1127 823 777 773 821

half-line width 0.152 0.173 0.146 0.162 0.165 0.147 0.138 0.123 0.134 0.249 0.248 0.157 0.130 0.127 0.128 0.131 0.148 0.165 0.195 0.267 0.300 0.257 0.140 0.137 0.157 0.170 0.171 0.165 0.196 0.193 0.291 0.309 0.290 0.228

muconate crystals accompanying the shrinking and expanding of the lattice lengths, on the basis of the X-ray single-crystal structure analysis of the monomers and polymers as well as a change in the transient structure monitored by powder X-ray diffraction during the continuous X-ray radiation. The polymerization rate is closely related to the molecular stacking distance in the monomer crystals because the polymer chain skeletons have the same conformational structure in the crystals. The polymer chain conformation depends on the mode of polymerization, i.e., shrinking or expanding. During the shrinking polymerization of 4Cl and the other monomers, an initially evolved strain induces the temporary expansion of the crystal, i.e., an increase in the crystal lattice lengths in two directions. A strain is accumulated in both the formed polymer chain and the remaining monomer crystal during the initial stage of the reaction and would be finally released after the polymerization. On the other hand, a stressed polymer conformation is observed during the expanding polymerization of MDO and 26F2. A crystal phase transition from the monomer crystals to the polymer crystals is often observed for the solid-state polymerization of diacetylenes and dienes. We are now continuing the investigation of the phase transition and detailed lattice changes for the polymerization of muconates in the crystalline state. Experimental Section General Methods. The NMR spectra were recorded by a JEOL JMN A-400 spectrometer at room temperature. The IR spectra were taken by a JASCO FT/IR-430 spectrometer. The UV spectra were recorded using a Shimadzu UV-160 spectrometer. Single-crystal X-ray data were collected by a Rigaku RAXIS RAPID imaging plate diffractometer using Mo KR radiation (λ ) 0.71073 Å) monochromated by graphite at room temperature. The crystal structures were solved by direct methods using SIR92 and refined by the full-matrix least-squares

1084 Crystal Growth & Design, Vol. 7, No. 6, 2007

Matsumoto et al. CHCO2R), 130.96 (p-Ph), 123.73 (CHdCHCO2R), 111.76 (ipso-Ph), 111.42 (m-Ph), 54.00 (OCH2); IR(KBr) 1597 (νCdC), 1700 (νCdO) cm-1; UV(acetonitrile) λmax 262 nm ( ) 29 700). Bis(3,4-methylenedioxybenzyl) (E,E)-muconate (MDO): plates, mp 145.5-146.3 °C (CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.32 (m, CHd CHCO2R, 2H), 6.78-6.88 (m, Ar, 6H), 6.21 (m, CHdCHCO2R, 2H), 5.97 (s, OCH2O, 4H), 5.11 (s, CH2, 4H); 13C NMR (100 MHz, CDCl3) δ 165.65 (CdO), 147.83 (Ar), 141.15 (CHd), 129.28, 128.24, 122.47, 120.48, 109.14, and 108.29 (Ar and CHd), 101.21 (OCH2O), 66.71 (CH2); IR (KBr) 1612 (νCdC), 1712 (νCdO) cm-1; UV (acetonitrile) λmax 266 nm ( ) 36 700). Polymerization Procedures. For fabrication of the polymer single crystals, the monomer single crystals were cut into an appropriate size and charged in a Pyrex tube, degassed, and then sealed. γ-Radiation was carried out with 60Co at room temperature. The irradiation dose was 200 kGy. The radiation polymerization of the powdered crystals was also carried out similarly. After irradiation, the polymer formation was checked by IR or NMR spectroscopy. The poly(4NO2) and poly(26F2) were insoluble in the organic solvents. The polymers were isolated after removing the unreacted monomer with chloroform, and the polymer yield was determined gravimetrically. Poly(MDO): mp g250 °C (decomp); 1H NMR (400 MHz, CDCl3) δ 6.68-6.72 (m, Ar, 6H), 5.86 (s, OCH2O, 4H), 5.55 (br, CHdCH, 2H), 4.78 (q, OCH2, 4H), 3.30 (br, CH, 2H); 13C NMR (100 MHz, CDCl3) δ 170.28 (CdO), 147.66 (Ar), 129.62 (CHd), 129.01, 122.45, 109.17, and 108.13 (Ar), 101.12 (OCH2O), 66.82 (OCH2), 51.74 (CH); IR (KBr) 982 (νCdC), 1732 (νCdO) cm-1. Kinetic Analysis of Polymerization by IR Spectroscopy. Photoirradiation was carried out in the crystalline state under atmospheric conditions (at 25 ( 0.5 °C) using a high-pressure Hg lamp (Toshiba SHL-100-2, 100W) at a distance of 20 cm through a Pyrex filter.14 The crushed monomer (ca. 3 wt %) and KBr powder were mixed, pressed, and provided for the IR measurement. The rate constant k was determined from the intensity of the absorbance due to the CdC bond observed at 1585-1592 cm-1 and 1612 cm-1 for the ZZ and EE monomers, respectively.

Figure 9. (a) Single-crystal structure of MDO and (b) a change in the lattice lengths during the continuous X-ray radiation. Polymer chains are formed along the b-axis. The conversion into the polymer was approximately 50% after 70 measurement cycles; a-axis (red), b-axis (blue), c-axis (green). method on F2 with anisotropic displacement parameters for nonhydrogen atoms using SHELXL-97.26 The powder X-ray diffraction profile was recorded by a Rigaku RINT-2100 with monochromated Cu KR radiation (λ ) 1.54184 Å, 40 kV, 40 mA, scan speed 1.0°/min, scan range 2-40°) equipped with a high-resolution parallel-beam optics system consisting of a parallel slip analyzer and a graded multiplayer. Using eq 1 for a monoclinic system, we estimated each lattice length from the 2θ values of the indexed peaks with the assumption that thr β angle is constant as 90 and 102° for 4Cl and MDO, respectively.

1 dhkl

2

)

(

)

1 h2 k2 sinβ l2 2hl cos β + + 2ac sin2 β a2 b2 c

(1)

Materials. (Z,Z)-Muconic acid, supplied from Mitsubishi Chemical Co., Ltd., Tokyo, or purchased from Acros Organics (Belgium), was used without any further purification. (E,E)-Muconic acid was purchased from Aldrich Co., Ltd. All of the esters were prepared by the reaction of the muconic acids with the corresponding benzyl bromides or chlorides.27 Di(4-nitrobenzyl) (Z,Z)-muconate (NO2): plates, mp 174.1175.2 °C (CHCl3); 1H NMR (400 MHz, CDCl3) δ 8.21-8.26 (m, Ar, 4H), 7.96 (m, CHdCHCO2R, 2H), 7.52-7.56 (m, Ar, 4H), 6.09 (m, CHdCHCO2R, 2H), 5.29 (s, OCH2, 4H); 13C NMR (100 MHz, CDCl3) δ 164.88 (CdO), 147.72, 142.84, 138.94, 128.42, 123.86, and 123.63 (Ar and CHd), 64.80 (OCH2); IR (KBr) 1588 (νCdC), 1712 (νCdO) cm-1; UV (acetonitrile) λmax 271 nm ( ) 43 100). Bis(2,6-difluorobenzyl) (Z,Z)-muconate (26F2): needles, mp 109.5110.4 °C (CHCl3); 1H NMR (400 MHz, CDCl3) δ 7.90-7.92 (m, CHd CHCO2R, 2H), 7.29-7.35 (m, p-Ph, 2H), 6.90-6.94 (m, m-Ph, 4H) 5.97-5.99 (m, CHdCHCO2R, 2H), 5.28 (s, OCH2, 4H); 13C NMR (100 MHz, CDCl3) δ 165.06 (CdO), 161.88 (o-Ph), 138.24 (CHd

Acknowledgment. This work was supported by Grants-inAid for Scientific Research on Priority Areas (Area 432, 16072215) and for Scientific Research (16350067) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. Supporting Information Available: X-ray crystallographic information files (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) (a) Desiraju, G. R. Crystal Engineering: The Design of Organic Solids; Elsevier: Amsterdam, 1989. (b) Ramamurthy, V., Ed. Photochemistry in Organized & Constrained Media; VCH: New York, 1991. (c) Ohashi, Y., Ed. ReactiVity in Molecular Crystals; Kodansha-VCH: Tokyo, 1993. (d) Weber, E., Ed. Topics in Current Chemistry Vol. 198, Design of Organic Solids; Springer: Berlin, 1998. (e) Tanaka, K.; Toda, F. Chem. ReV. 2000, 100, 1025. (f) Toda, F., Ed. Organic Solid-State Reactions; Kluwer: London, 2002. (g) Toda, F., Ed. Topics in Current Chemistry Vol. 254, Organic Solid State Reactions; Springer: Berlin, 2005. (h) Braga, D.; Grepioni, F. Eds. Making Crystals by Design: Methods, Techniques and Applications; Wiley-VCH: Weinheim, Germany, 2007. (2) (a) Schmidt, G. M. J. Pure Appl. Chem. 1971, 27, 647. (b) Wegner, G. Pure Appl. Chem. 1977, 49, 443. (3) (a) MacNicol, D. D., Toda, F., Bishop, R., Eds. Comprehensive Supramolecular Chemistry, Vol. 6, Solid State Supramolecular Chemistry: Crystal Engineering; Pergamon: Oxford, UK, 1996. (b) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry; Wiley: New York, 2000; pp 389-462. (c) Desiraju, G. R. Nature 2001, 412, 397. (d) MacGillivray, L. R. CrystEngComm. 2002, 4, 37. (e) Braga, D. Chem. Commun. 2003, 2751. (4) Matsumoto, A. Top. Curr. Chem. 2005, 254, 263. (5) (a) Cheng, K.; Foxman, B. M. J. Am. Chem. Soc. 1977, 99, 8102. (b) Ramamurthy, V.; Venkatesan, K. Chem. ReV. 1987, 87, 433. (c) Osano, Y. T.; Uchida, A.; Ohashi, Y. Nature 1991, 352, 510. (d) Enkelmann, V.; Wegner, G.; Novak, K.; Wagener, K. B. J. Am.

Solid-State Polymerization of Muconic Esters

(6)

(7)

(8)

(9) (10) (11) (12)

Chem. Soc. 1993, 115, 10390. (e) Koshima, H.; Ding, K. L.; Chisaka. Y.; Matsuura, T. J. Am. Chem. Soc. 1996, 118, 12059. (f) Leibovitch, M.; Olovsson, G.; Scheffer, J. R.; Trotter, J. J. Am. Chem. Soc. 1997, 119, 1462. (g) Tokitoh, N.; Arai, Y.; Sasamori, T.; Okazaki, R.; Nagase, S.; Uekusa, H.; Ohashi, Y. J. Am. Chem. Soc. 1998, 120, 433. (h) Tanaka, K.; Toda, F.; Mochizuki, E.; Yasui, N.; Kai, Y.; Miyahara, I.; Hirotsu, K. Angew. Chem., Int. Ed. 1999, 38, 3523. (i) Honda, K.; Nakanishi, F.; Feeder, N. J. Am. Chem. Soc. 1999, 121, 8246. (j) Irie, M.; Kobatake, S.; Orichi, M. Science 2001, 291, 1769. (k) Ohba, S.; Hosomi, H.; Ito, Y. J. Am. Chem. Soc. 2001, 123, 6349. (l) Kim, J. H.; Hubig, S. M.; Lindeman, S. V.; Kochi, J. K. J. Am. Chem. Soc. 2001, 123, 87. (m) Kaupp, G. Curr. Opin. Solid State Mater. Sci. 2002, 6, 131. (n) Takahashi, S.; Miura, H.; Kasai, H.; Okada, S.; Oikawa, H.; Nakanishi, H. J. Am. Chem. Soc. 2002, 124, 10944. (o) Gao, X.; Frisˇcˇic´, T.; MacGillivray, L. R. Angew. Chem., Int. Ed. 2004, 43, 232. (p) Kobatake, S.; Irie, M. Bull. Chem. Soc. Jpn. 2004, 77, 195. (q) Kaupp, G. Top. Curr. Chem. 2005, 254, 95. (r) Braga, D.; Grepioni, F. Chem. Commun. 2005, 3635. (a) Matsumoto, A.; Matsumura, T.; Aoki, S. J. Chem Soc., Chem. Commun. 1994, 1389. (b) Matsumoto, A.; Odani, T. Macromol. Rapid Commun. 2001, 22, 1195. (c) Matsumoto, A. Polym. J. 2003, 35, 93. (a) Enkelmann, V. AdV. Polym. Sci. 1984, 63, 91. (b) Tieke, B. AdV. Polym. Sci. 1985, 71, 79. (c) Nakanishi, H.; Matsuda, H.; Okada, S.; Kato, M. In Frontier of Macromolecular Science; Saegusa, T., Higashimura, T., Abe, A., Eds.; Blackwell Scientific Publications: Oxford, UK, 1989; pp 469-474. Recent papers: (a) Lee, S. B.; Koepsel, R.; Stolz, D. B.; Warriner, H. E.; Russell, A. J. J. Am. Chem. Soc. 2004, 126, 13400. (b) Morigaki, K.; Kiyosue, K.; Taguchi, T. Langmuir 2004, 20, 7729. (c) Curtis, S. M.; Le, N.; Fowler, F. W.; Lauher, J. W. Cryst. Growth Des. 2005, 5, 2313. (d) Peng, H.; Tang, J.; Pang, J.; Chen, D.; Yang, L.; Ashbaugh, H. S.; Brinker, C. J.; Yang, Z.; Lu, Y. J. Am. Chem. Soc. 2005, 127, 12782. (e) Mori, T.; Shimoyama, K.; Fukawa, Y.; Minagawa, K.; Tanaka, M. Chem. Lett. 2005, 34, 116. (f) Itoh, T.; Shichi, T.; Yui, T.; Takagi, K. Langmuir 2005, 21, 3217. (g) Sun, A. W.; Lauher, J. W.; Goroff, N. S. Science 2006, 312, 1030. (h) Arai, M.; Okada, S. Chem. Lett. 2006, 35, 1012. (i) Xu, R.; Gramlich, V.; Fraenrath, H. J. Am. Chem. Soc. 2006, 128, 5541. Hasegawa, M. AdV. Phys. Org. Chem. 1995, 30, 117. Xiao, J.; Yang, M.; Lauher, J. W.; Fowler, F. W. Angew. Chem., Int. Ed. 2000, 39, 2132. Hoang, T.; Lauher, J. W.; Fowler, F. W. J. Am. Chem. Soc. 2002, 124, 10656. Nomura, S.; Itoh, T.; Nakasho, H.; Uno, T.; Kubo, M.; Sada, K.; Inoue, K.; Miyata, M. J. Am. Chem. Soc. 2004, 126, 2035.

Crystal Growth & Design, Vol. 7, No. 6, 2007 1085 (13) Tashiro, K.; Zadorin, A. N.; Saragai, S.; Kamae, T.; Matsumoto, A.; Yokoi, K.; Aoki, S. Macromolecules 1999, 32, 7946. (14) Matsumoto, A.; Tanaka, T.; Tsubouchi, T.; Tashiro, K.; Saragai, S.; Nakamoto, S. J. Am. Chem. Soc. 2002, 124, 8891. (15) Matsumoto, A.; Nakazawa, H. Macromolecules 2004, 37, 8538. (16) Matsumoto, A.; Katayama, K.; Odani, T.; Oka, K.; Tashiro, K.; Saragai, S.; Nakamoto, S. Macromolecules 2000, 33, 7786. (17) Mori, Y.; Matsumoto, A. Cryst. Growth Des. 2007, 7, 377. (18) The single crystal structures of the monomer and polymer of 26F2, abbreviated as (Z,Z)-2 and poly[(Z,Z)-2], at -70°C were reported in ref. 17. (19) (a) Baughman, R. H.; Yee, K. C. J. Polym. Sci. Macromol. ReV. 1978, 13, 219. (b) Bloor, D. In DeVelopments in Crystalline Polymers II; Bassett, D. C., Ed.; Applied Science Publishers: London, 1982; pp 151-193. (c) Hasegawa, M.; Shiba, S. J. Phys. Chem. 1982, 86, 1490. (d) Ba¨ssler, H. AdV. Polym. Sci. 1984, 63, 1. (20) Tashiro, K.; Kamae, T.; Kobayashi, M.; Matsumoto, A.; Yokoi, K.; Aoki. S. Macromolecules 1999, 32, 2449. (21) Matsumoto, A.; Nagahama, S.; Odani, T. J. Am. Chem. Soc. 2000, 122, 9109. (22) Matsumoto, A.; Sada, K.; Tashiro, K.; Miyata, M.; Tsubouchi, T.; Tanaka, T.; Odani, T.; Nagahama, S.; Tanaka, T.; Inoue, K.; Saragai, S.; Nakamoto, S. Angew. Chem., Int. Ed. 2002, 41, 2502. (23) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Dougherty, D. A.; Grubbs, R. H. Angew. Chem., Int. Ed. 1997, 36, 248. (24) Hasegawa, M.; Saigo, K.; Mori, T.; Uno, H.; Nohara, M.; Nakanishi, H. J. Am. Chem. Soc. 1985, 107, 2788. (25) (a) Cohen, M. D. Angew. Chem., Int. Ed. 1975, 14, 386. (b) Gavezzotti, A. J. Am. Chem. Soc. 1983, 105, 5220. (c) Ohashi, Y.; Yanagi, K.; Kurihara, T.; Sasada, Y.; Ohgo, Y. J. Am. Chem. Soc. 1981, 103, 5805. (d) Zimmerman, H. E.; Alabugin, I. V.; Chen, W.; Zhu, Z. J. Am. Chem. Soc. 1999, 121, 11930. (e) Brett, T. J.; Alexander, J. M.; Clark, J. L.; Ross, C. R. II; Harbison, G. S.; Stezowski, J. J. Chem. Commun. 1999, 1275. (f) Turowska-Tyrk, I.; Ba¸kowicz, J.; Scheffer, J. R.; Xia, W. CrystEngComm 2006, 8, 616. (g) Davaasambuu, J.; Busse, G.; Techert, S. J. Phys. Chem. A 2006, 110, 3261. (i) Kaupp, G. CrystEngComm. 2003, 5, 117. (26) Sheldrick, G. M.; SHELXL-97: Program for the Refinement of Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997. (27) (a) Matsumoto, A.; Tanaka, T. Mol. Cryst. Liq. Cryst. 2005, 440, 215. (b) Matsumoto, A.; Tanaka, T.; Oka, K. Synthesis 2005, 1479.

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