Strategies for Tailoring LC-Functionalized Polymer: Probe

Article pubs.acs.org/Macromolecules

Strategies for Tailoring LC-Functionalized Polymer: Probe Contribution of [Si−O−Si] versus [Si−C] Spacer to Thermal and Polarized Optical Performance “Driven by” Well-Designed Grafting Density and Precision in Flexible/Rigid Matrix Li Han, Hongwei Ma, Yang Li,* Siqi Zhu, Lincan Yang, Rui Tan, Pibo Liu, Heyu Shen, Wei Huang, and Xichen Gong State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116012, China Liaoning Key Laboratory of Polymer Science and Engineering, Dalian, Liaoning 116012, China S Supporting Information *

ABSTRACT: A versatile strategy is highly desired to prepare well-designed side chain liquid crystal polymers (SCLCPs). Two rigid and topological SiH/Vinyl-functionalized polystyrenes (PSs), namely poly(4-vinylphenyldimethylsilane) (PVPDMS) and poly(4-vinylphenyl-1-butene) (PVSt), were synthesized via anionic polymerization (AP) and detailed; subsequently, Vinyl/SiH terminated LCs were treated with PVSt/PVPDMS via hydrosilylation to yield SCLCPs bearing [Si−O−Si]/[Si−C] spacers. Herein, well-designed grafting density, evaluated by 1H NMR, was readily performed by the varying SiH to Vinyl feed mole ratio. The design systematically probes a cooperative effect of architectures on properties and allows for precision in flexible/rigid matrixes. Regardless, PB/PS systems with saturated addition displayed the best performances. Fundamentally, the study compared the dependence of polarized optical and thermal performances on [Si−O−Si] versus [Si−C] spacer, which submitted to be driven by grafting density, providing the first access to tailoring polymer. SCLCPs exhibited essentially constant SmA, but inconsistent dynamic of spacer-induced contribution, in which ΔT was the same in complete addition as if nothing with spacer; surprisingly, followed by decreased grafting density, the decreasing trend in ΔT of [Si−O−Si] as spacer was fast, while that of [Si−C] was slow. This phenomenon was further confirmed by POM. Furthermore, [Si−O−Si] was desired to obtain lower Tg and applicable to the advantageous “decoupling effect”. Endeavor for tailoring SCLCPs and regulating devices, the appropriate spacer and grafting density advanced to an effective role.

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photoinduced anisotropy11 and the earliest discovered cholesterol units were both conventional characteristic LC mesogens; of them, cholesterol mesogen was widespread in nature, offering biological compatibility and unique optical properties such as optical activity, selective reflection, and circular dichroism.12 In theory, macromolecular design of SCLCPs relies on the “decoupling effect”, suggesting flexible spacers were taken into account.13 The spacer, advantageous to avoiding mutual interference, is generated from the introduction of LC mesogens into polymer backbones by diverse grafting means. These grafting reactions occurred mainly by conventional esterification/etherification14 or the highly efficient hydrosilylation15 and click chemistry16 adopted extensively at present.

INTRODUCTION

Innovations in polymer architectures are contributing to the advancement of functionalized material engineering.1 Side chain liquid crystalline polymers (SCLCPs) have been constantly driving rapid development inspired by this field of polymer architectures.2 Major exploration demonstrated that the primary and significant properties of polymers are inherently linked to their architectures.3 The precise control available in polymers was desired for the precise relationship of structure−property.4 Therefore, tailoring polymer architectures is regarded as a superior candidate for targeting a wide array of applications. Generally, tailoring SCLCPs run into three sections including polymeric backbones, LC mesogens, and flexible spacers. Polymeric backbones are divided into many categories according to composition including homopolymer,5 copolymer,6 and complexes/supramolecule.7 Forming polymeric backbones is performed through atom transfer radical,8 living anionic (LAP),9 and ring-opening,10 etc., conventional polymerization methods. In addition, azobenzene units with © XXXX American Chemical Society

Received: July 6, 2016 Revised: July 12, 2016

A

DOI: 10.1021/acs.macromol.6b01429 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules

that they worked as both spacers and introduced units, providing a convenient point of comparison. It has been reported that different spacers influenced LC properties;34−36 however, the typical dependence of LC properties and microstructures on [Si−O−Si] versus [Si−C] spacer “driven by” well-designed grafting density will be first presented. Welldesigned grafting density, evaluated by 1H NMR, was achieved by controlling the reactive SiH/Vinyl molar ratio. In addition, thermal and polarized optical performance could be depicted via DSC and POM combining X-ray, in which POM images were obtained comparably drawing to isotropic temperature.

As we all know, in earlier works, LC properties were determined by many factors such as flexible backbone, the length of spacer, and the major changes of LC moiety.17 In addition, polydispersity that was mostly determined by polymerization and grafting methodology is an indispensable factor in designing SCLCPs and determining their properties.4b,18 Recently, various interactions of side chains and the functionalized density have been also confirmed.19 Furthermore, polymeric architectures can be designed according to topological morphology20 such as linear, star,21 cyclic,22 and network,23 major brushes/combs,24 etc. Because branched SCLCPs with lower viscosity compared with their linear analogues have garnered considerable attention,25 the significant influences of diverse topologies on remarkable physical, chemical, and biological properties have been depicted in some works.4a,26 Major previous study focused on structure−property relationship of SCLCPs based on changes of side mesogens. However, the cooperative effect of various backbone architectures on properties, especially the precision in structural control, are far indistinct, and so further research is highly valuable. Polystyrene (PS) with features of high modulus and high strength was always introduced into diverse copolymers as a stiffening phase. Moreover, PS blocks provide the necessary mechanical stability and confer processability and transparency to the system,27 excellently applicable to polymer materials. The presence of a hard phase improves photoelectric property, and this combined stiffness plays a complementary and dominant role as one of the best candidates for functionalized materials.28 Probably stiff PSs influence LC mobility, so flexible spacers and high grafting density were desired to overcome disadvantageous effect according to “decoupling effect” and the design of “mesogen-jacketed SCLCPs” (MJLCPs).29 Extensive research on PS copolymers LC30 and SCLCPs depicting PS homopolymer backbones containing OH/Cl have seldom been reported but lack of controlled structures.31 Topological PS with well-designed molecular weight and narrow polydispersity could be readily obtained by LAP. However, PS contains no functional groups, submitting to be first functionalized and then postfunctionalized, just in complicated and consuming multisteps. Hence, based on extensive anionic polymerization (AP) study of (4-vinylphenyl)dimethylsilane (VPDMS)32 and 4-(4vinylphenyl)-1-butene (VSt),33 it is necessary to obtain functionalized styrene (St), so that hydrosilylation with facile reaction conditions considered as one of the most highly efficient grafting methods can be employed. Our prior study on PB-SCLCPs focused on flexible backbones;5 therefore, PS-SCLCPs with stiff backbones were obtained in this work, and this convenient strategy first allows for precise difference focused on flexible/stiff backbone of SCLCPs. Tailored PS-SCLCPs contain cooperative architectures, such that systematically probing the structure−property relationship. In addition, the present design exhibited innovations. Topological linear-comb and star-comb architectures of PS-based SCLCPs based on cholesterol as the mesogen and PS as the rigid backbone using AP and hydrosilylation methodology are described. Hence, analogous PS-[Si−C]-Chol and PS-[Si−O−Si]-Chol were synthesized with different molecular weights, conveniently enabling bearing different [Si−C] and [Si−O−Si] spacers. The spacers in italics were not specific units of Si−O−Si or Si−C but regarded as representative due to their presented typical difference in contribution to SCLCPs previously.34 Results demonstrated

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EXPERIMENTAL SECTION

Vinyl/SiH Terminated LC Monomers. Chol-Vinyl (M1) and Chol-SiH (M2) were synthesized according to the previous method.12 1 H NMR (Chol-Vinyl (M1), CDCl3): δ (ppm) = 7.99 (2H, d, Ar−H), 6.92 (2H, d, Ar−H), 6.05 (1H, m, =CH−CH2−), 5.44 (1H, d, one of CH2CH−CH2−O−), 5.40 (1H, t, −CCH− in cholesterol), 5.31 (1H, d, one of CH2CH−CH2−), 4.83 (1H, m, −O−CH− in cholesterol), 4.68 (2H, d, CH2CH−CH2−O−), 2.45 (2H, d, −O− CH−CH2− in cholesterol), 0.86−2.01 (38H, m, H in cholesterol), 0.69 (3H, s, −CH3 in cholesterol). 1H NMR (Chol-SiH (M2), CDCl3): δ (ppm) = 7.99 (2H, d, Ar−H), 6.92 (2H, d, Ar−H), 5.40 (1H, t, −CCH− in cholesterol), 4.83 (1H, m, −O−CH− in cholesterol), 4.69 (1H, s, Si−H), 3.92(2H, d, −CH2−CH2−CH2− O−), 2.45 (2H, d, −O−CH−CH2− in cholesterol), 1.8 (2H, m, Si− CH2−CH2−CH2−O−), 1.02 (2H, Si−CH2−CH2−), besides, 0.86− 2.01 (38H, m, H in cholesterol), 0.69 (3H, s, −CH3 in cholesterol), 0−0.25 (12H, m, Si(CH3)2OSi−(CH3)2). SiH/Vinyl Functionalized Styrene Monomers. VPDMS and VSt were synthesized as previously reported.32,33 The detailed synthetic route is given in the Supporting Information. 1H NMR (VPDMS, CDCl3): δ (ppm) = 7.68 (2H, d, Ar−H), 7.56 (2H, d, Ar− H), 6.88 (1H, m, CH2CH−Ar), 5.42 (1H, d, one of CH2CH− Ar), 5.18 (1H, d, one of CH2CH−Ar), 4.65 (1H, m, Si−H), 0.54 (6H, s, CH3−Si−CH3). 1H NMR (VSt, CDCl3): δ (ppm) = 7.29 (2H, d, Ar−H), 7.11 (2H, d, Ar−H), 6.65 (1H, m, CH2CH−Ar), 5.82 (1H, m, −CH2−CHCH2), 5.66 (1H, d, one of CH2CH−Ar), 5.15 (1H, d, one of CH2CH−Ar), 4.99 (2H, m, −CH2−CH CH2), 2.64 (2H, t, Ar−CH2−CH2−), 2.33 (2H, f, Ar−CH2−CH2− CHCH2). Linear/4-Arm Star Functionalized PS Matrixes. L-/S-PVPDMS (PS-SiH) and L-/S-PVSt (PS-Vinyl) were obtained by the AP of VPDMS and VSt, which was analyzed at different conditions previously. To simplify synthetic procedures and obtain consistent structures for the same series of polymers, benzene as solvent in glovebox at 25 °C was suitable for AP of VPDMS and VSt. The detailed synthetic routes in this work are shown in the Supporting Information. Basic composition and thermal behavior characterizations of PVPDMS and PVSt are given in Table 1. Linear-Comb and Star-Comb PS-Based SCLCPs. L-/SPVPDMS-LCP (L-/S-PS-[Si−C]-Chol) and L-/S-PVSt-LCP (L-/SPS-[Si−O−Si]-Chol) were obtained from the treatment of topological PVPDMS/PVSt, respectively, with Chol-Vinyl (M1)/Chol-SiH (M2) via hydrosilylation. Herein, different grafting density was readily performed by systematically varying SiH to Vinyl feed mole ratio [PVPDMS-LCPs, SiH:Vinyl = 1:0.4, 1:0.7, 1:1; PVSt-LCPs, Vinyl:SiH = 1:0.4, 1:0.7, 1:1]. The detailed synthetic routes are shown in the Supporting Information. The synthetic route is briefly shown in Scheme 1.

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RESULTS AND DISCUSSION Design of Monomer and Polymers. AP is well-known to be an excellent synthetic method for tailoring polymer architectures with well-designed molecular weight and narrow polydispersity.37 Furthermore, hydrosilylation with facile reaction conditions is generally considered as one of the B


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Macromolecules Table 1. Molecular Composition Characterization and Thermal Behavior of Topological PVPDMS and PVSt Matrixes matrix

Mnb

PDIc

Brd

Tge

L-PVP-1.2ka L-PVP-2.5k L-PVP-4.8k L-PVP-8.0k L-PVP-10k S-PVP-4.8k S-PVP-10k L-PVSt-1.2ka L-PVSt-2.5k L-PVSt-4.8k S-PVSt-4.8k S-PVSt-10k

1.25 2.6 4.8 8.7 9.7 4.7 9.0 1.2 2.4 4.8 4.2 7.9

1.12 1.12 1.21 1.21 1.24 1.17 1.21 1.12 1.12 1.21 1.21 1.24

f

21 51 63 68 74 57 68 −12 −4 9 3 18

3.92 3.75

3.75 3.63

Scheme 1. A Brief Synthetic Route of Topological SCLCPs Bearing Different Spacer in Combination Hydrosilylation with AP Methodology

a

Represented SiH/Vinyl-functionalized PS backbones (PVPDMS/ PVSt) with well-designed Mn = 1.2 kg/mol containing topological linear (L) and star (S). bDetermined by GPC; the number-average molecular weight (Mn, kg/mol). cDetermined by GPC; polydispersity index (PDI = Mw/Mn; Mw, precise weight-average molecular weight calculated by GPC). dBr, average branches of star polymers, Br = Mw(S-PS)/Mw(precursor). eGlass transition temperature (°C), determined by DSC, referred to Figure S19. fNone for linear polymers

most highly efficient grafting methods.15 Previous research on PB-based SCLCPs has demonstrated that tailored architectures could be carried out by combining AP and hydrosilylation,5 shown to be effective in designing SCLCPs. In this work, this effective strategy was adopted for the preparations of PS-based SCLCPs. Topological SiH/Vinyl-functionalized PSs were based on the AP of bifunctional VPDMS32 and VSt.33 And then by means of hydrosilylation, SiH/Vinyl terminated LCs were incorporated into PVSt/PVPDMS to obtain PS-[Si−O−Si]Chol and PS-[Si−C]-Chol, respectively, such that the set of PSbased SCLCPs bearing different spacers were successfully tailored. Hence, tailored SCLCPs with varieties of architectures were investigated based on rigid PS corresponding to earlier flexible PB backbones. Accordingly, this strategy allows morphological extension of PS-based SCLCPs, in turn targeting precise differences on flexible and rigid matrixes, and first provides a unique opportunity to probe the effect of [Si−O−Si] versus [Si−C] spacer driven by well-designed grafting density on LC properties and microstructures in a cooperative effect of architectures. Because cholesterol mesogons offer biological compatibility and unique optical properties,12 PS naturally confers processability and transparency; thus in this work, both Chol-SiH (M2) and Chol-Vinyl (M1) with cholesterol mesogons were attached into functionalized PS, expected to garner more attention. Accordingly, SCLCPs were obtained conveniently enabling obtaining [Si−O−Si] versus [Si−C] spacer that worked as both spacers and introduced units. The spacers in italics were not specific units of Si−O−Si or Si−C but regarded as representative. The dependence of LC properties on spacers have been reported;34−36 however, the unique difference of [Si−O−Si] versus [Si−C] spacer dependent on a variety of graft densities 90% and 70% to 40% will be investigated for the first time. In fact, in this design (shown in Scheme 1), the representative spacers present two features: first the spacer lengths (the [Si−O−Si] spacer are about five bond lengths more than the [Si−C] spacers) and second the characteristic Si−O−Si units. Study indicated that spacer lengths influenced

the properties,36,34a and extensive study presented typical difference by Si−O−Si and Si−C units in contribution to SCLCPs.34 Hence, the two features above possibly accounted for the difference in properties (in the following discussion). The existence of Si−O−Si was proposed to be the key because of its high flexibility within the range of short chains, especially previously5 that SiH terminated Chol-SiH (M2) was obtained by the preliminary modification of Vinyl terminated Chol-Vinyl (M1) based on hydrosilylation and showed considerable effect on LC properties due to the introduction of Si−O−Si, but the length effect was still not ruled out. According to the “decoupling effect”, it is necessary to choose appropriate spacers, but it also suggests that major LC backbones were flexible, so as not to restrain the chains from moving in the LC state. However, “MJLCPs” without spacers were designed with side groups larger than the repeating unit in backbones, possibly resulting from a high grafting density. Hence, the spacer and grafting density seemed to play an effective role; generally, in cooperative effect, they should exhibit inherently link, value to study. Furthermore, both VPDMS and VSt as bifunctional monomers, readily obtained and purified in a well-developed method, were suitable for LAP and retained in situ functionalized points of polymers, SiH and Viny, respectively. Hence, PVPDMS and PVSt could be grafted C


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Figure 1. Representative FT-IR spectra (a) compared Chol-Vinyl (M1), representative PVPDMS with its corresponding PVPDMS-SCLSPs, (b) compared Chol-SiH (M2), representative PVSt with its corresponding PVSt-SCLSPs.

Figure 2. Representative 1H NMR spectra in the synthetic process of (1) PVPDMS-SCLCPs and (2) PVSt-SCLCPs; (a) compared Chol-SiH (M2)/ Chol-Vinyl (M1) and PVSt/PVPDMS, as well as corresponding PS-based SCLCPs, and (b) SCLCPs with grafting densities of 90%, 70%, and 40%.

separately by Chol-Viny (M2) and Chol-SiH (M1) via the advantageous hydrosilylation. Structural Characterization: FT-IR and 1H NMR. Both Chol-Vinyl (M1) and Chol-SiH (M2) employed in present study were synthesized and characterized, detected by FT-IR and 1H NMR in a previous report,5 shown in Figure S1a for comparison. Bifunctional-St VPDMS and VSt were subjected to rigorous purification procedures under high vacuum to ensure

the absence of impurities. The structural comparison of VPDMS and VSt was attested by 1H NMR, shown in Figure S1b. The 1H NMR spectrum shows peaks and integrations in good agreement with previously reported data.32,33 Representative 1H NMR of PS-[Si−C]-Chol compared with Chol-Vinyl (M2) and PVPDMS is shown in Figure 2(1), and corresponding 1H NMR of SCLCP with different grafting density is simultaneously displayed. 1H NMR of PS-[Si−O−Si]D


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Figure 3. Representative 1H NMR absorption assignment and calculation on PS-SCLCPs with 90% grafting density bearing (a) L-PVP-1.2k and (b) L-PVSt-1.2k backbone (Figures S4b and S7b).

Table 2. Molecular Composition, Grafting Density, and Thermal Characterization Data of Topological Lc-/Sc-PS-[Si−C]-Chol) phase transition (second heating) PVPDMS-SCLCPs

Mnc (kg/mol)

PDIc

EAd (%)

Tge (°C)

a

chol-Vinyl (M1) L-PVP-1.2k-LCPb L-PVP-2.5k-LCP L-PVP-4.8k-LCP L-PVP-8.0k-LCP L-PVP-10k-LCP S-PVP-4.8k-LCPb S-PVP-10k-LCP L-PVP-2.5k-LCP L-PVP-4.8k-LCP L-PVP-8.0k-LCP L-PVP-10k-LCP S-PVP-4.8k-LCP S-PVP-10k-LCP L-PVP-2.5k-LCP L-PVP-4.8k-LCP L-PVP-8.0k-LCP L-PVP-10k-LCP S-PVP-4.8k-LCP S-PVP-10k-LCP

5.4 11.2 20.6 36.9 39.5 20.8 38.9 9.0 17.8 30.1 35.9 17.0 32.0 6.4 11.2 21.0 23.6 12.2 21.8

1.28 1.26 1.19 1.16 1.18 1.22 1.29 1.37 1.25 1.37 1.42 1.31 1.32 1.36 1.37 1.28 1.41 1.35 1.42

117 (Tm) 98 105 106 105 102 99 100 99 100 102 105 97 104 97 93 104 97 95 100

91.7 92.5 92.0 90.8 91.5 92.5 91.8 67.1 76.4 73.1 75.5 74.1 73.7 41.3 42.1 40.2 42.3 44.5 40.7

a

Ti (°C)f [ΔHi (J/g)]g

ΔTi (°C)

Tdj (°C)

a

129 122 135 144 153 158 141 151 112 120 121 122 118 120 103 115 116 118 113 118

−k 350

246 220 240 250 258 260 240 251 211 220 223 227 215 224 200 208 220 215 208 218

[3.0] [2.7] [2.6] [3.5] [3.8] [3.5] [3.0] [2.3] [3.6] [1.4] [2.1] [2.0] [2.3] [0.5] [1.0] [2.2] [0.4] [0.3] [1.0]

351 351 350 349 342 340 345 340 334

342

a

Thermal properties of LC monomer from DSC, used as comparison. bLinear-comb and star-comb PVPDMS-LCPs (L-/S-PS-[Si−C]-Chol) with different molecular and grafting density, such as L-PVP-1.2k-LCPs represented linear-comb SCLCPs with designed 1.2 kg/mol PVPDMS backbones. c The number-average molecular weight and polydispersity, determined by GPC. dAddition efficiency (grafting density) calculated by 1H NMR; EA = 90%, 70%, and 40%. eGlass transition temperature on the second cycle heating. fIsotropic transition temperature. gThermal transition absorption enthalpy. hDetermined by DSC. iΔT = Ti − Tg. jThermal decomposition temperature at 5% weight loss. kWithout characterization.

representative FT-IR of PVSt and Chol-SiH (M2) is given in Figure 1b. The results were supported by the apparent appearance of the aromatic characteristic peak of PVPDMS and PVSt, such as the Si−Ar (1632, 1428, 1125 cm−1) of PVPDMS. In addition, the typical characteristic peak including SiH of PVPDMS (2116 cm−1) and Chol-SiH (M2) (2166 cm−1), Vinyl of PVSt (1639, 910 cm−1) and of Chol-Vinyl (M1) (1650 cm−1), double bond (1672 cm−1) in cholesterol groups of Chol-Vinyl (M1) and Chol-SiH (M2), Si(CH3) (1260, 820− 800 cm−1) of PVPDMS and Chol-SiH (M2), and Si−O−Si (broad 1045 cm−1) of Chol-SiH (M2) could clearly be observed in FT-IR. The representative SCLCPs corresponding to PVPDMS and PVSt were also detected by FT-IR. In

Chol compared with that of Chol-SiH (M1) and PVSt is shown in Figure 2(2), likewise displayed corresponding 1H NMR of SCLCP with different grafting density. All other 1H NMR including PVPDMS/PVSt with different molecular weights and corresponding SCLCPs with various grafting density are shown respectively in Figures S2−S3 and S4−S9. The chemical shifts and their intensities in the 1H NMR of prepared SCLCPs corresponding to PVPDMS/PVSt were consistent with their molecular structures. In addition, both PVPDMS and PVSt were consistent with the proposed structures, determined by FT-IR. An example of the FT-IR spectrum of PVPDMS and LC monomer Chol-Vinyl (M1) is given in the same Figure 1a for comparison. Similarly, a E


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Table 3. Molecular Composition, Grafting Density, and Thermal Properties Characterization Data of Topological L-/S-PS-[Si− O−Si]-Chol phase transition (second heating) PVSt-SCLCP

Mnc (kg/mol)

PDIc

EAd (%)

Tge (°C)

Ti (°C)f [ΔHi(J/g)]g

ΔTi (°C)

Tdj (°C)

91.1 93.6 94.4 95.9 92.5 66.8 69.3 68.5 73.9 72.9 40.9 38.1 36.2 40.7 37.1

57 (Tm) 44 45 46 43 45 20 22 30 32 37 26 26 32 29 34

146 [4.5] 174 [6.5] 188 [6.1] 194 [4.1] 188 [5.0] 196 [4.4] 109 [1.7] 114 [1.1] 124 [1.2] 126 [1.0] 146 [1.1] 70 [0.4] 72 [0.6] 83 [0.5] 80 [0.3] 107 [0.7]

89 130 143 148 145 151 89 92 94 94 109 44 46 51 51 73

−k 354

a

chol-SiH (M2) L-PVSt-1.2k-LCPb0 d L-PVSt-2.5k-LCP L-PVSt-4.8k-LCP S-PVSt-4.8k-LCPb0 d S-PVSt-10k-LCP L-PVSt-1.2k-LCPb1 d L-PVSt-2.5k-LCP L-PVSt-4.8k-LCP S-PVSt-4.8k-LCP S-PVSt-10k-LCP L-PVSt-1.2k-LCPb1 d L-PVSt-2.5k-LCP L-PVSt-4.8k-LCP S-PVSt-4.8k-LCP S-PVSt-10k-LCP

6.2 12.4 24.7 21.2 40.0 4.8 9.7 19.5 17.1 33.0 3.4 6.3 12.1 11.1 20.9

1.10 1.12 1.23 1.27 1.29 1.22 1.18 1.22 1.23 1.33 1.28 1.27 1.29 1.33 1.35

a

353 353

326 345

350 344

b

Thermal properties of LC monomer from DSC, used as comparison. Linear-comb and star-comb PVPDMS-LCPs (L-/S-PS-[Si−O−Si]-Chol) with different molecular and grafting density, such as L-PVP-1.2k-LCPs represented linear-comb SCLCPs with designed 1.2 kg/mol PVPDMS matrixes. cThe number-average molecular weight and polydispersity, determined by GPC. dEA, addition efficiency (grafting density) calculated by 1H NMR. b0EA = 90%, b1EA = 70%, b2EA = 40%. eGlass transition temperature on the second cycle heating; fIsotropic temperature. gThermal absorption enthalpy. hDetermined by DSC. iΔT = Ti − Tg. jThermal decomposition temperature at 5% weight loss. kWithout characterization.

combination 1H NMR with FT-IR, all purified PS-SCLCPs gave satisfactory spectroscopic data corresponding to their expected molecular structures. Well-Designed Grafting Calculated from 1H NMR and Proposed Structural Difference. The method of calculating grafting density by 1H NMR has been extensively accepted due to its universality and precision in macromolecule structural analysis. Fundamentally, similar to the precise calculation for PB-based SCLCPs,5 the grafting density of present PS-based SCLCPs measured by addition efficiency (EA) (the percentage of reactive SiH/Vinyl in total SiH/Vinyl of backbones) was calculated by 1H NMR. In general, the key is to choose reasonable peaks as the standard for the calculation and integral, so as to obtain precise data. With respect to PS-based SCLCPs, PVPDMS and PVSt were backbones containing SiH and Vinyl, respectively. Moreover, in the calculation of polymers, SiH is usually not served as an excellent standard because it easily hides. In the synthetic progress of SCLCPs, representative monomer and polymer were detected by 1H NMR (as shown in Figure 2), in which the changes of the characteristic groups were depicted, followed by an increasing grafting densities of 40%, 70%, and 90%, presenting a smaller trend of SiH and Vinyl groups in order of relative intensity to aromatic area. The SiH and Vinyl in respective PVPDMS and PVSt varied from remnants to gradual disappearance, indicating that SiH and Vinyl were gradually consumed by grafting reactions, which was in good agreement with the aforementioned design. Thus, the various grafting densities of 90%, 70%, and 40% could be calculated by 1H NMR. The detailed method and absorption assignment are described in Figure 3 and Figures S4b−S9b. The basic results of SCLCPs are all summarized in Tables 2 and 3. In this work, PVPDMS and PVSt were synthesized, expected to achieve high grafting density, so that LC side chains could play a dominant role breaking through the effect from rigid backbones. Consequently, a complete addition was desired by

complete or excess input of LC moieties based on backbones (Vinyl:SiH = 1:1, input molar ratio). Experimental results showed that for both PVSt and PVPDMS SCLCPs, EA values were more than 90% (approach to 100%, i.e., complete addition), demonstrating that the aromatic introduction overcame steric hindrance compared with PB, and that the pensile functionalized points indeed have a higher kinetic constant. As is known,5 the EA values of high 1,4-PB and high 1,2-PB SCLCPs are approximately 40% and 70%, respectively, in sitespecific “saturated addition”, meaning that no more LC moieties could be attached to PBs, in which LC moieties by site-specific arrangement will be incorporated into backbones; in other words, it was incomplete but saturated. In fact, the “saturated addition” showed an excellent functional degree, in which presenting relative site-specific structures. Sometimes, it is also necessary to perform “unsaturated addition with welldesigned density” for special applications. When it was in “saturated addition” simultaneous for PB-SCLCPs and PSSCLCPs, the EA values were different. Thus, diverse grafting densities were designed, including 40% and 70%, in order to compare with PB-SCLCPs in the same grafting density, and study the dependence of properties on spacers followed by different grafting densities. Accordingly, different input mole ratios were performed to control grafting density. Experimental results showed that 40% and 70% with “unsaturated but welldesigned addition” for synthesized PS-SCLCPs were realized, but site-uncontrolled due to small steric hindrance and interactions. Concerning these results, it was deduced that Star structures were probably more precise due to inherent steric hindrance in comparison to their linear counterpart. GPC Characterization. A detailed discussion on the LAP of VPDMS and VSt is given in the Supporting Information. GPC traces with a narrow and symmetric monomodal distribution of PVPDMS and PVSt with different molecular weight are shown in Figure S12. The phenomenon of typical bimodal distribution F


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Figure 4. GPC curves of PS-SCLCPs (EA = 90%) (1) PVPDMS-SCLCPs and (2) PVSt-SCLCPs with different molecular weight as well as topological (a) linear-comb and (b) star-comb structures.

Figure 5. Representative POM-50 μm images near Ti comparison of (1) PS-[Si−C]-Chol and (2) PS-[Si−O−Si]-Chol with different grafting density: (a−d) fan-shaped and focal conic textures in EA = 90%, (e, f) indistinct textures in EA = 70%, and (g, h) indistinct textures in EA = 40%.

was observed in GPC traces of the crude S-PVPDMS/S-PVSt, as shown by the representative GPC curves in Figure S11. S-

PVDMS/PVSt was purified from fractionation, taking on a narrow monomodal distribution in GPC curves (shown in G


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Figure 6. Typical WAXD patterns of (a) PVPDMS-LCPs upon cooling to 130 °C and (b) PVSt-LCPs upon to cooling 60 °C, SCLCPs with different molecular weights in EA = 90%. The relative intensity (I) corresponding to the first-order Bragg diffraction within 2θ < 5°, such as 2θ = 2.48 and I = 562, is displayed in black. And the second-order Bragg diffraction angle is displayed in green.

backbones, as the stiff and black patterns were always observed in POM. Even when applying pressure on the film or drawing near to an isotropic state, the typical textures were not observed for PS-[Si−C]-Chol (EA = 40%). Meanwhile, images gradually turned into bright colors depending on increased for grafting densities of 40% and 70% to 90% for PS-[Si−C]-Chol. However, typical textures were not still observed, but black patterns disappeared in EA = 70%, until typical focal conic textures were obviously observed by POM in EA = 90%. In addition, based on spacer [Si−C] versus [Si−O−Si], compared with PS-[Si−C]-Chol, similarly, PS-[Si−O−Si]-Chol (EA = 40%) exhibited indistinct textures. However, the stiff and black patterns were not displayed, and brighter textures in its POM were different from those of PS-[Si−C]-Chol (EA = 40%), and images gradually turned into brighter colors due to increased grafting densities of 40% and 70% to 90%. PS-[Si−O−Si]-Chol (EA = 70%) displayed an approximately focal conic in spite of incomplete textures, until well-formed fan-shaped textures were distinct in its POM (EA = 90%), the same as PS-[Si−C]-Chol (EA = 90%). Therefore, when EA = 90%, the polarized optical performances of PS-based SCLCP were almost the same and best, while the contribution of [Si−O−Si] versus [Si−C] to optical performance exhibited differences, and the difference was closely associated with different grafting density. These results revealed that PS-[Si−O−Si]-Chol has displayed a better effect on polarized optical performance than PS-[Si−C]-Chol, especially for lower grafting density, so [Si−O−Si] as spacer was better at overcoming the influence of stiff backbones and played a more significant role in the advantageous “decoupling effect” than [Si−C]. With regard to PS-based SCLCPs dependent on different molecular weight with analogous architectures, similar textures are displayed in Figures S16 and S17. And SCLCPs in analogies were not obviously controlled by various topologies. In

Figure S12). The precise molecular weights of star and one-arm precursor polymers were determined by GPC, and the branches could be calculated by precise molecular weights. All obtained PVPDMS and PVSt were grafted with LC moieties to obtain PS-based SCLCPs. Excess of Chol-Vinyl (M1) and Chol-SiH (M2) were removed from the crude products to obtain pure SCLCPs with different grafting density; the narrow and symmetric monomodal distribution of PSSCLCPs (EA = 90%) is described in Figure 4 (others with different grafting density are shown in Figures S13 and S14.) The retention time of the peaks moved slightly followed by different molecular weight in analogous systems in line with structural design, and the shape of the peaks was similar, but the symmetry were worse with decreased grafting density due to site-uncontrolled 70% and 40% “unsaturated addition with well-designed density”. The basic compositions of SCLCPs are summarized in Tables 2 and 3. Polarized Optical Performance Based on LC. CholVinyl (M1) and Chol-SiH (M2) were excellent LCs. In particular, Chol-Vinyl (M1) has been reported in many studies,12 and Chol-SiH (M2) was derived from the hydrosilylation of Chol-Vinyl (M1). The typical textures verified5 by POM are shown in Figure S15. Accordingly, Chol-Vinyl (M1) presented a cholesteric phase while smectic A (SmA) was substituted in Chol-SiH (M2) due to the introduction of flexible −Si−O−Si− groups, exhibiting typical fan-shaped textures. All colors observed in POM were not due to selective reflection. With regard to PS-based SCLCPs, all exhibited LC phases, as can be seen in Figure 5. However, it was demonstrated that there were distinct differences for the polarized optical performance due to different grafting density in analogies. Based on PS-based SCLCPs with 40% grafting density (Figure 5g,h), both PS-[Si−O−Si]-Chol (EA = 40%) and PS-[Si−C]Chol (EA = 40%) exhibited indistinct textures, especially for PS[Si−C]-Chol (Figure 5g), obviously influenced by stiff H


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to discussed above, the first-order diffraction peak was observed in low angles at corresponding d-spacing values of d = 40.1− 52.7 Å, which was 2 times as long as the molecular length (L), namely d ≈ 2L, which suggested a double molecular layer-like arrangement and confirmed the SmA combined with POM. Furthermore, these SCLCPs showed a diffraction peak at 2θ ≈ 4.2°, which was weakly visible as well, corresponding to a Bragg spacing of 21 Å (with a second-order peak at half the first-order Bragg spacing). The second-order peaks were also used, especially for the SCLCPs (EA = 40%) in Figure S18(2); the first-order diffractions were not observed obviously due to the limitation of the WAXD, but the corresponding second-order peaks were observed, so as to calculate the d-spacing. The data from WAXD are summarized in Table S1. Accordingly, the aforementioned clear fan-shaped texture observed was assigned to the SmA phase. With respect to PS-[Si−C]-Chol, Figure 6a and Figure S18a display the sharpest first-order Bragg reflection at 2θ = 2.4°− 2.7° and a broad peak at 2θ = 16.1°; then d-spacing values of 32.6−36.7 and 5.5 Å were derived, respectively, while the second-order diffractions were not clearly observable and only a few were somewhat visible. The existence of long-range positional order in the polymers again ruled out the possibility of nematic/cholesteric phase classification, suggesting a smectic packing. Likewise, we simulated a molecular model of the single polymerization unit (PS-[Si−C]-Chol) via ChemBio3D in Figure S22d, and the theoretical coplanar molecular length (L) after energy minimization was 20.2 Å (more than Chol-Vinyl (M1), in Figure S21a). Meanwhile the sharp reflection at low angles corresponded to experimentally obtained layer thickness of 32.6−36.7 Å, which was in considerable excess of the molecular length (L = 20.2 Å). This confirmed the SmA nature of the mesophase and suggested that the mesogens were either packed in a monolayer structure or probably involved a bilayer arrangement, in which side chains were interdigitated in an antiparallel fashion in the mesophases temperature. A particular phenomenon was verified by POM and WAXD. Chol-Vinyl (M1) presented a typical cholesteric phase, but when grafted onto PVPVDMS, these SCLCPs turned into SmA phase. Concerning this result, the broad peak (somewhat intense but broad, stronger than that of PB-based SCLCPs) observed at wide angles could probably be ascribed to the ordered nature of rigid backbones; the broad diffraction peaks (2θ ≈ 16°) corresponded to d-spacing values of d ≈ 5.53 Å, due to the order of adjacent PS backbones. This suggested that the stiff contributed to inducing LCs tend to crystallize but did not change the nature of the order. The microstructures from WAXD are summarized in Table S2. Probably microstructures of PS-SCLCPs in EA = 40% were not controlled due to the siteunspecific addition aforementioned. In summary, by comparing WAXD of PS-[Si−C]-Chol and PS-[Si−O−Si]-Chol in analogues, the d-spacing values of PS[Si−O−Si]-Chol were all dramatically in excess of that of PS[Si−C]-Chol. Clearly, the spacers [Si−C] and [Si−O−Si] affected LC layer packing, so that PS-[Si−O−Si]-Chol presented a bilayer arrangement, while PS-[Si−C]-Chol exhibited a monolayer structure, or probably involved a side chain interdigitated bilayer arrangement. Regardless of any changes, the nature of the SmA remained constant. However, macroscopically oriented samples may be not very accurate in small-angle regions due to the limitation of the WAXD instrument. To confirm our view, SAXS was performed for more precise structures. The typical SAXS patterns are

particular, PVPDMS attached by Chol-Vinyl (M1) to obtain PS[Si−C]-Chol, and Chol-Vinyl (M1) exhibited the typical cholesteric phase, while PS-[Si−C]-Chol exhibited SmA, demonstrating that rigid backbones restrained the helix structure of the cholesteric phase tend to form crystal or Sm phase. Therefore, it was deduced that the stiff backbones may stabilize the LC phase to prolong the temperature range of mesophasic formation and also restrain the formation of LC phase to some extent. Confirmation of LC Phase and Deduction of Layerlike Order Arrangement Based on X-ray. It is difficult to distinguish cholesteric and SmA phase because the focal conic textures displayed in two phases are indistinguishable by means of POM. To precisely identify the type of mesomorphic phase, X-ray was essential to analyze mesophases. Especially for polymers, the texture analysis from POM was far from being sufficient. WAXD was used to indicate a layerlike correlation according to the detected correlation period that approximately corresponded to the Bragg domain spacing (d-spacing). Hence, powder WAXD patterns containing sufficient quantity of samples treated by annealing were tested upon cooling at the temperature within the range of mesophasic formation. The Bragg intensity at broad angles is well-known to reveal molecular order of adjacent side chains or adjacent backbones. For a highly ordered layerlike structure, the Bragg intensity at broad angles is relatively weak and the distribution was very broad, while the Bragg intensity at small angles is only relevant to the molecular layer order employed to speculate the LC phase. A comparison of Chol-SiH (M2) and Chol-Vinyl (M1) powder WAXD patterns was shown in a previous work,5 and Chol-SiH (M2) was proven to be SmA with a double-molecular layer-like arrangement, while Chol-Vinyl (M2) exhibited a cholesteric phase, combined with POM. Hence, Si−O−Si groups introduced were confirmed by WAXD to indeed disrupt molecular layer order to generate a new arrangement order. In this work, Chol-SiH (M2) and Chol-Vinyl (M1) were not discussed, but there was a relevant discussion concerning PSbased SCLCPs, so that the types of LC phase were speculated combined with POM. The microstructures from WAXD are summarized in Tables S1 and S2. The microstructures based on rigid backbones were associated with the molecular weight, grafting density, and topology, which are also briefly described in the Supporting Information. And then the difference of [Si−O−Si] versus [Si−C] spacer was deeply described in this work. PS-based SCLCPs (EA = 90%) exhibited typical WAXD patterns in Figure 6. For PS[Si−O−Si]-Chol (EA = 90%), as shown in Figure 6b, a sharp first-order peak and a weak second-order peak in order of decreasing intensity were observed in low angles, and the two diffraction peaks are the sharpest and best defined for the developed long-range order, while a very broad distribution but relatively strong intensity peak was obviously observed in wide angles, which can probably be ascribed to relatively short-range order, thus suggesting a typical pattern observed for the lamellar order of the SmA and SmC types. The sharp first-order diffraction at the low-angles (2θ = 1.7°−2.2°) corresponding to Bragg d-spacing, indicated a layer thickness of approximately d = 40.1−52.7 Å for these SCLCPs. In addition, we simulated a molecular model of the single polymerization unit (PS-[Si−O− Si]-Chol) via ChemBio3D (in Figure S22c). The theoretical coplanar molecular length (L) after energy minimization was 23.3 Å (more than Chol-SiH (M2) in Figure S21b). According I


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Figure 7. Several representative SAXS traces of (1) PS-[Si−C]-Cho (at 130 °C) and (2) PS-[Si−O−Si]-Chol (EA = 90% at 60 °C, EA = 70% at 50 °C, EA = 40% at 40 °C) with different grafting density.

Figure 8. Comparison of representative (a) SAXS traces of PS-[Si−C]-Chol and PS-[Si−O−Si]-Chol and (b) corresponding SAXS patterns in EA = 90%.

shown in Figures S19 and S20; the halo was observed on the meridian, and representative traces are shown in Figure 7. These profiles showed the formation of SmA phase, as observed for PS-[Si−O−Si]-Chol (EA = 40%) (Figure 7(2) and Figure S18b); the obvious halo on the meridian and sharp peaks at small angles are in agreement with the aforementioned data for the proposed first-order diffraction peak at low angles, illustrating indistinct first-order diffraction of PS-[Si−O−Si]Chol (EA = 40%) due to the limitation of WAXD. The

microstructures from SAXS are summarized in Tables S1 and S2. In particular, compared with the typical SAXS, the q values of PS-[Si−O−Si]-Chol were less than that of PS-[Si−C]-Chol (Figure 8a), and the sharp halo of PS-[Si−O−Si]-Chol was nearer to the equator (Figure 8b). These profiles more clearly showed the difference in the d-spacings of PS-[Si−O−Si]-Chol and PS-[Si−C]-Chol in analogies constructed from different spacers, which likewise confirmed the deduction from WAXD. In addition, similar to WAXD, SAXS revealed the same J


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Figure 9. DSC curves (10 °C/min) of PS-[Si−C]-Chol with different grafting density of (1) EA = 90%, (2) EA = 70%, (3) EA = 40%, and containing topological (a) linear-comb SCLCPs, the second heating (the first-cycle cooling shown in Figure S25), and (b) star-comb SCLCPs, the first-cycle cooling and the second-cycle heating.

Analysis of Thermal Properties Based on Thermotropic LC. A series of SCLCPs with [Si−O−Si] and [Si−C] spacers were investigated for their thermotropic properties. The results from DSC and TGA are all summarized in Tables 2 and 3 with respect to DSC curves of Figures 9 and 10. Evidently their qualitative characteristics are similar to those of the respective LC monomers including Chol-Vinyl (M1) and Chol-SiH (M2) except that Tm transformed to Tg. Compared with Chol-Vinyl (M1) (Figure S24b), Chol-SiH (M2) (Figure S24a) had a lower Tm and a shorter ΔT due to the introduced highly flexible Si−O−Si.5 Thus, SCLCPs containing siloxane linkages were expected to show a lower Tg, as confirmed by major study.5,34 In this study, PS-[Si−O−Si]-Chol had a lower Tg than that of PS-[Si−C]-Chol. In addition, in spite of a

transformation discipline along with the grafting density, molecule weight, and topology in analogies. Generally, it indicated that LC structure is a single-layer SmA type,38 while the bilayer packing arrangement was observed in PS/PB-based SCLCPs. In this work, the observed fan-shaped or focal conic textures were assigned to SmA phase. Although there was an indistinct texture observed for SCLCPs (EA = 40%), WAXD and SAXS confirmed the existence of the SmA phase. Accordingly, it is necessary to contain dense graft or appropriate spacer pursued for good optical performance and more access to the advantageous “decoupling effect”. In combination of POM and XRD, SCLCPs in analogies exhibited essentially constant SmA. K


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Figure 10. DSC curves (10 °C/min, the first-cycle cooling and second-cycle heating) of PS-[Si−O−Si]-Chol with different grafting density of (1) EA = 90%, (2) EA = 70%, and (3) EA = 40% and containing topological (a) linear-comb SCLCPs and (b) star-comb SCLCPs.

shorter ΔT due to the introduction of flexible Si−O−Si for Chol-SiH (M2), both PS-[Si−O−Si]-Chol and PS-[Si−C]-Chol had an approximately equivalent and highly desired wide ΔT in the case of a complete addition (EA = 90%), which can be ascribed in part to the stiff PS backbones that stabilized the LC phase, which probably can be partly associated with the large interaction of side chains resulting from dense grafting. By comparison Table 2 and Table 3 (with the same color in analogies), the lower Tg of PS-[Si−O−Si]-Chol was exhibited, and the equivalent ΔT with different spacers was observed in the complete addition (i.e., 90%).The equivalent ΔT with different spacers as if had nothing to do with spacers. However, as observed in DSC of PS-SCLCPs along with different grafting density, a surprising phenomenon was found that the ΔT values of PS-[Si−O−Si]-Chol and PS-[Si−C]-Chol decreased with

decreased grafting density from 90% to 40%. However, for PS[Si−C]-Chol, the descending trend was slow [representative, 144−120−115 °C] (in green, shown in Table 2); especially for the variation from EA = 70% to EA = 40%, ΔT values were basically constant. In comparison with PS-[Si−O−Si]-Chol, its descending trend was fast [representative, 148−94−51 °C] (in green, shown in Table 3), especially for the dramatically decreasing Ti values. In light of the above discussion, a higher grafting density was able to generate a wider ΔT. And the spacers driven by diverse grafting density can be proposed for tailoring polymer architectures. For PS-[Si−C]-Chol, stiff PS backbones were better at stabilizing LC phase, but the weak “regulation effect” limited macromolecular design. Meanwhile, for PS-[Si−O−Si]Chol, when EA values were more than 90%, the flexible [Si−O− L


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Figure 11. Difference in ΔT values of PB/PVSt-SCLCPs based on different factors (with the same EA and MW, in yellow; with the same MW and N, in green; with the same EA and N, in pink) corresponding to Table S3 (PB-SCLCPs as object compared with PVSt-SCLCPs in analogies).

Si] spacers were confined by dense side chains and high interaction of side chains, seriously hindered its flexible movement, so that LC phase was stabilized, similar to the design of “MJLCPs”. However, when the EA values were decreased, the flexible [Si−O−Si] spacers could take a dominant role, in that its relaxation produced advantageous “decoupling effect”, thus realizing the independence of stiff backbones and LC side chains. Likewise, together with POM, it was also illustrated that the typical SmA textures were indistinct, but the black blocks disappeared for PS-[Si−O−Si]-Chol (EA = 40%), and the unique difference between PS-[Si−O−Si]-Chol and PS-[Si−C]-Chol was observed by POM. Accordingly, the appropriate spacers could produce an advantageous “decoupling effect”, realizing the control of structure and property. Hence, it was necessary to increase grafting density and choose appropriate spacers to design SCLCPs with stiff backbones, especially for stronger rigidity than that of PS, as sometimes PS was regarded as semirigid backbones.39 In addition, molecular weight and topology were discussed in this work, as observed in Tables 2 and 3. The Tg value basically held constant, but the Ti and ΔT values increased dependent on the increased molecular weight. However, the topology did not dramatically affect thermal property, which is not in accordance with the research that topological systems lead to a shorter ΔT compared with their analogous counterparts. In fact, the microstructures with different the Bragg intensity obtained by WAXD (Tables S1 and S2) resulted from the interaction forces, which will lead to diverse phase transitions. Hence, thermal behaviors of the thermotropic SCLCPs could be illustrated by more direct microstructure information. The Bragg intensity at small angles was relevant to the molecular order in a previous report.5 Hence, the structures were closely

related to properties. The relationship between the microstructures and thermal properties was briefly described that generally the dependence of increased Ti and ΔT values on the Bragg intensity increased in analogies. The intensity was decreased along with the decreased grafting density, mainly due to small interactions of side chains and the relaxed backbones. The thermal stabilities of SCLCPs were analyzed by TGA under a nitrogen atmosphere, and the results are summarized in Tables 2 and 3. TGA thermograms are displayed in Figures S26 and S27. The polymers showed a high thermal stability with decomposition temperatures (Td) at 5% weight loss occurred higher than 300 °C without being controlled by various architectures. Precision in Flexible/Rigid Matrix Based on PB/PSBased SCLCPs. In our previous work, PB-SCLCPs bearing flexible matrix were investigated, and in this work, PS-SCLCPs bearing rigid matrix were investigated, so as to make a brief comparison for precise difference on flexible and rigid matrixes to property and structure. PB-SCLCPs had shown that it was impossible to obtain complete addition due to native steric hindrance but that welldesigned grafting densities of 70% (high 1,2-PB SCLCPs) and 40% (high 1,4-PB SCLCPs) were achieved by excess of relative LC to PBs. In these PS-SCLCPs, a complete addition (i.e., more than 90%) could be obtained, and a well-designed grafting density could be realized by controlling input mole ratio. This exactly satisfied our desire to obtain well-designed grafting density. The microstructures of PS-SCLCPs in Tables S1 and S2 showed that d-spacing values were increased followed by decreased grafting density; it demonstrated that the low grafting density generated small steric hindrance. Then as seen in Table S3, d-spacing of PB-SCLCPs was almost less than M


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Figure 12. POM of PB/PS-SCLCPs with different grafting density in analogies (rigid systems grafting density: a-90%, b-70%, c-40%; flexible systems: high 1,2-PB b-70% and high 1,4-PB c-40%).

available in regulating polymer architectures. Compared with [Si−C], [Si−O−Si] as spacer was better to generate polarized optical performance and desired to obtain a lower Tg; [Si−C] as spacer was able to stabilize LC phase but lost “regulation effect” for polymers. It was emphasized that the typical difference in properties and microstructures was probably resulted from different bond type of flexible Si−O−Si and Si− C or inevitably the length of linkages. In addition, based on PB/ PVSt-SCLCPs, it permitted focusing on the difference in the flexibility/rigidity of matrixes. As evidenced that the best polarized optical performance and widest ΔT were obtained in “saturated” addition with analogies, and both exhibited essentially constant SmA. PB-SCLCPs exhibited better optical performance, but the higher grafting density for PVSt-LCPs was found to overcome the effect of stiff backbones. On the basis of analysis from 1H NMR, a well-designed grafting density of PSSCLCPs was evaluated at densities of 40%, 70%, and 90%, which was realized by controlling the input mole ratio of reactive SiH/Vinyl, while it was impossible to obtain a complete addition of PB-SCLCPs only in 70% (high 1,2-PB) and 40% (high 1,4-PB) “saturated” addition. PS as semirigid backbones, the appropriate spacer and grafting density played an effective role for regulating architectures. These approaches are expected to provide new concepts and possibilities for new LC polymer devices.

that of PS-SCLCPs in analogies. Hence, it deduced that large steric hindrance accounted for incomplete addition for PBSCLCPs. Several typical POM images were displayed for comparison in Figure 12. When both PVSt-SCLCPs and PB-SCLCPs were in “saturated addition”, the typical LC textures were verified by POM (PVSt, a-90%; high 1,2-PB, b-70%;5 high 1,4-PB, c40%5). They exhibited constant SmA. Whereas with the same grafting density (b-70% and c-40%), it showed that PBSCLCPs had a better polarized optical performance, mainly due to the flexibility of their backbones, and possibly because of functional degree, the “saturated addition” of PB-SCLCPs was able to generate more interactions resulting from side chains, which showed good LC performance. In addition, several results from DSC are displayed in Table S3. Obviously, high 1,4-PB-LCPs had the lowest Tg, while high 1,2-PB-LCPs was close to PVSt-LCPs. Based on ΔT values (in colors), molecular weight (MW) of matrix, grafting density (EA) and the number of grafted LC units (N) were proposed as undefined factors in analogies. In Figure 11, obviously only in higher EA, the ΔT of PVSt-LCPs was more than that of PBLCPs; in combination with the results from POM, PVSt-LCPs were desirable for generating typical textures in complete addition, and it was accordingly that higher EA was found to overcome the effect of stiff backbones.

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CONCLUSIONS We have shown a versatile strategy to prepare SCLCPs with controlled architectures, in which SiH/Vinyl terminated LC with cholesterol mesogens were incorporated into PVSt/ PVPDMS templates in combination AP with hydrosilylation methodology, conveniently enabling obtaining varying spacers [Si−O−Si]/[Si−C] and well-designed grafting density. The resulting macromolecules were tested for thermal and polarized optical performances. The study highlighted that the different contribution of [Si−O−Si] versus [Si−C] spacer to properties was inherently linked to grafting density, and the difference was inconsistently driven by grafting density. The inconsistent dynamic was verified by thermal behavior, in which the ΔT values were the same in complete addition (i.e., more than 90%) as if nothing with spacers; surprisingly, followed by decreasing grafting density, the decreasing trend in ΔT of [Si− O−Si] as spacer was dramatically fast, while that of [Si−C] was slow. This phenomenon was further confirmed by POM, evidence showed that focal conic textures were both observed in complete addition, while the difference was evident followed by decreasing grafting density, in which [Si−O−Si] as spacer was applicable to the advantageous “decoupling effect”. According to discussed above, the inconsistent dynamic was

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b01429. Related characterization results that were inexistent in the text but were referred to including 1H NMR, WAXD, 2D SAXS, POM, and TGA; in addition, some data summarized in Table; related calculation from 1H NMR and absorption peak assignment (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (Y.L.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by National Basic Research Program of China, Grant No. 2015CB654700 (2015CB654701), and National Natural Science Foundation of China (No. 21304013, No. U1508204 and No. U1462126). N


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