Powder XRD Analyses

4.3.4.1. Side-Chain Polymers AmBn. The molecular arrangements of side-chain polymers AmBn in different mesophases were investigated by XRD measurements at various temperatures upon cooling (see Figures 4.10-4.11). As shown in Figure 4.10a (also see Figures S4.3a of the supporting information), the 2D XRD pattern of polymer A16B1 at 150 °C during the cooling process revealed a diffuse peak at wide angles corresponding to a d-spacing value of 4.6 Å, which

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demonstrated that similar liquid-like in-plane orders with average intermolecular distances were prevalent inside the layers of bent-core units. Two single sharp peaks were observed at corresponding d-spacing values of d₁ = 35.4 Å and d₂ = 17.7 Å in small angle regions, where the longest d-spacing value d1 was indexed as (001). The d-spacing value (d₁) is shorter than the theoretical coplanar molecular length (L) (about 47 Å) of self H-bonded benzoic acidic dimmer to indicate the tilted smectic arrangement. In addition, temperature dependent XRD results of polymer A16B1 were also provided in Figure 4.10b. Two sharp peaks appeared during the cooling process from the isotropic to mesophasic states. An additional peak with a corresponding d-spacing value (~ 46 Å) similar to its theoretical molecular length was obtained as the temperature was equivalent to or lower than 130 °C, and the orthogonal arrangement of the crystalline phase or highly ordered smectic phase was generated. Polymers A1B0 and A10B1 illustrated similar XRD results as shown in the supporting information (see Figures S4.2a and S4.4a) to indicate the analogous smectic mesophase.

Polymer A4B1 did not obtain any sharp diffraction peak at small angle regions in the mesophasic temperature (120 °C) to reveal one dimension order of nematic phase as shown in Figure S4.5 of the supporting information, but two broad peaks were observed at the corresponding d-spacing values of 17.1 Å and 4.6 Å. Until the temperature reaching the crystalline state (100 °C), a d-spacing value of 66.5 Å was produced to indicate the orthogonal arrangement of the crystalline phase or highly ordered smectic phase. The powder XRD results of polymer A4B1 in various temperatures was also provided in Figure S4.5a of the supporting information to reveal its phase transition in the cooling process from the isotropic to crystalline states.

supporting information), several sharp peaks were detected at corresponding values of d1 = 37.5 Å, d2 = 25.4 Å, and d3 = 19.1 Å in small angle regions (along with some other undefined sharp peaks). The ratio of d₁ to d₃ was 2 : 3 : 4 to index (002), (003) and (004), and a d-spacing value ca. 76 Å was correspondent to the essential peak indexed as (001), which might be lost duo to the limitation of the XRD instrument. A broad peak was gained at the wide angle regions to account for the natural mesogenic stacking width. This similar result was reported in the literature^[17] to mean the long range ordered smectic structure of SmC2. The XRD investigations of polymer A1B13 at various temperatures from the isotropic to crystalline states were performed in Figure S4.7a of the supporting information, and polymers A1B2, A1B5, and A0B1 exhibited similar XRD results with those of A1B13 in the supporting information (see Figures S4.6a, S4.8a, and S4.9).

In comparison the variation of d-spacing values in all side-chain polymers AmBn as shown in Table 4.4 (also see Figures S4.10a of the supporting information), the d-spacing values of copolymers were larger than those of homopolymers to indicate that more tilted smectic arrangements were produced in both homopolymers A1B0 and A0B1, which meant that less tilted smectic arrangement existed in copolymers with both H-bonded acidic dimers and covalent-bonded bent-cores.

Hence, the variations of molecular arrangements, including two kinds of tilted smectic orders (i.e., SmC1 and SmC2), in side-chain polymers were further identified by the XRD experiments.

0 5 10 15 20 25 30

170 ^oC 160 ^oC 150 ^oC 130 ^oC 120 ^oC 110 ^oC 100 ^oC

Intensity (a.u.)

2 theta / degree

(b)

Figure 4.10. Powder X-ray data of polymer A16B1: (a) 2D pattern in the tilted smectic phase (150 °C); (b) Powder X-ray diffraction intensity against angle profiles at various temperatures upon cooling from the isotropic to crystalline phases.

(a)

Table. 4.4. Powder XRD data of side-chain polymers

4.3.4.2. Bent-Core Side-Chain Polymer Complexes AmBn-N. The molecular arrangements of bent-core side-chain polymer complexes AmBn-N were also surveyed by XRD measurements and their related results are illustrated in Table 4.5.

Compared with side-chain copolymers AmBn, the corresponding polymer complexes AmBn-N generally exhibited larger d-spacing values (except polymer complex A1B2-N), which might be due to the coexistence of bent-core covalent- and H-bonded units in side-chain polymer complexes, and thus to have less ordered smectogenic packings and to induce lower phase transition temperatures. Similar to side-chain copolymers AmBn, most polymer complexes AmBn-N in Table 4.5 (also see Figures S4.10b of the supporting information) generally demonstrated larger d-spacing values than homopolymer complex A1B0-N (with bent-core H-bonded units only), which might have better and homogeneous packing of bent-core H-bonded units in the tilted smectic arrangement of the homopolymer complex.

Similarly, smaller d-spacing values were observed in A1B13 (d1 = 37.5 Å), A1B13-N (d₁ = 38.0 Å), and A0B1 (d₁ = 36.4 Å), which might be attributed to the major component of bent-core covalent-bonded structure B, and the influence of co-stacking effect contributed from bent-core H-bonded structure A-N was much less.

Polymer complex A16B1-N displayed two sharp peaks at the associated d-spacing values of d₁ = 43.2 Å and d₂ = 21.6 Å in small angle regions and a broad peak at the related d-spacing value d = 4.5 Å at 130 °C (upon cooling) as shown in Figure 4.11a (also see Figures S4.3b of the supporting information). The largest d-spacing value (d1 = 43.2 Å) is less than the theoretical length of bent-core H-bonded structure A-N (about 58 Å) to indicate the tilted smectic arrangement of polymer complex A16B1-N. The XRD results of A16B1-N at various temperatures upon cooling from the isotropic to crystalline phases were demonstrated in Figure 4.11b.

reached 140 °C during the cooling process. Afterwards, an additional peak developed when the temperature was lower than 80 °C, where the new d-spacing value of 35.1 Å was correspondent to the crystalline state. Polymer complexes A10B1-N, A4B1-N and A1B2-N revealed similar X-ray diffraction patterns (see Figures S4.4b, S4.5b, and S4.6b of the supporting information) to indicate the analogous type of the tilted smectic mesophase. Polymer complex A1B13-N manifested the long range ordered smectic organization in mesophasic and crystalline temperatures duo to the exhibition of several sharp diffraction peaks (see Figure S4.7b of the supporting information). In addition, polymer complex A1B5-N revealed X-ray diffraction patterns (see Figure S4.8b of the supporting information) similar to that of A1B13-N, which suggested the analogous type of the tilted smectic phase in both polymer complexes.

Table 4.5. Powder XRD Data of bent-core side-chain polymer complexes polymer complex cooling temp. (°C) 2 theta (degree) d-spacing (Å)

A1B0-N 140 2.19

5 10 15 20 25 30

160 ^oC 150 ^oC 140 ^oC 130 ^oC 120 ^oC 110 ^oC 100 ^oC 90 ^oC 80 ^oC 70 ^oC

Intensity (a.u.)

2 theta / degree

(b)

Figure 4.11. Powder X-ray data of polymer complex A16B1-N: (a) 2D pattern in the tilted smectic phase (130 °C); (b) Powder X-ray diffraction intensity against angle profiles at various temperatures upon cooling from the isotropic to crystalline phases.

(a)

4.3.5. Switching Current Behaviors and Spontaneous Polarization (Ps) of