High-performance family of polymeric particles prepared from poly(phenylene oxide)-poly(hexyl isocyanate) liquid crystal block copolymer: synthesis and properties study

Abstract

The poly (phenylene oxide)-block-poly (hexyl isocyanate) copolymers (PPO-b-PHIC)s were synthesized in various ratios of blocks using the organotitanium coordination method at room temperature. The copolymer particles were prepared by precipitation of concentrated solution of the copolymers in non-solvent under stirring. The synthesized copolymers and their particles were characterized by ¹H and ¹³C nuclear magnetic resonance (¹H and ¹³C NMR), Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC), polarized optical microscope (POM), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The effect of block ratio on the anisotropic-isotropic transition and liquid crystal texture of copolymers as a function of temperature and concentration of the solution was investigated. The polymeric particles tend to be aligned along the fibrillar direction by increasing the block ratio of amide in the copolymer.

Introduction

The importance of liquid crystal polymeric (LCP) materials is referred to their applications. Although these materials have not been used in the polymer industry for a long time, today, there are various commercial films and plastics in which the ability of LC behavior has been used to improve the physical and mechanical properties. Solar cells, ¹ flexible displays with high power and display speed, ² LC elastomers, ³ smart materials, ⁴ and membranes ⁵ are the most important applications of LCP materials. Due to the high cost of raw materials for the synthesis of liquid crystalline polymers, ⁶ the idea of making liquid crystalline polymer particles by different methods to achieve the properties of LCP in other matrices along with reducing the amount of used liquid crystalline polymer has been developed in the minds of researchers.^7–15 Different methods for making polymer particles have been reported. ¹⁶ The most important methods used to make LCP particles include emulsion, ¹³ mechanical method, ⁹ lithography, ¹¹ membrane method, ⁷ and synthesis methods.^14,15 In this study, following the research done in this field, the ether-amide copolymer is synthesized, and its anisotropic properties are investigated. In the next step, the particles are prepared using mechanical methods. Recently, poly (n-hexyl isocyanate) (PHIC) and its copolymers have attracted considerable attention because of their potential applications and unique properties in areas such as chiral recognitions, optical switches, liquid crystals, degradable materials, nanocomposites, blend of polymers, electrical devices, biomaterials, nanowires, thermoreversible gels, and activators.^17–31 These copolymers are so important that various behaviors of linear and nonlinear block copolymers based on PHIC have been investigated by Vazaios et al. ³² The known methods used for copolymerization of PHIC are reported in Table 1.

Table 1.

Various copolymerization methods of PHIC reported in literature.

Name of copolymer	Copolymerization method	Temperature (˚C)	Year	Ref
PEG-b-PHIC	Organotitanium coordination	Room	2001	31
P2VP-b-PHIC	Anionic	−78	2004	30
PMMA-b-PHIC	Radical	60	2004	29
PS-b-PI-b-PHIC, PI-b-PS-b-PHIC	Organotitanium coordination and anionic	Various	2005	24
PHIC-b-PEG	Anionic	−98	2008	27
PMMA-b-PHIC	Radical	60	2008	20
P2VP-b-PHIC-b-P2VP	Anionic	−78 to −98	2011	26
PHIC-b-PEG-b-PHIC	Organotitanium coordination	Room	2012	23
PHIC-b-P3HT	Organotitanium coordination	Room	2014	17
PHIC(12K)-PCL(5K)	Ring opening and coordination	Room	2014	22
PHIC(5K,10K)-PCL(10K,17K)	Ring opening and coordination	Room	2015	25
PHIC-b-PB-b-PHIC	Organotitanium coordination	Room	2016	19
PLLA-b-PHIC	Organotitanium coordination	Room	2017	18

The optimal time and temperature of anionic copolymerization of hexyl isocyanate must be determined because at times greater or less than the optimum value, trimer formation or de-polymerization is possible. Due to the sensitivity of anionic polymerization and copolymerization of monoisocyanates to environmental factors and temperature, the coordination method was considered as a method with less sensitivity to these factors. Studies on the coordination of monoisocyanates by organometallic compounds back to 1967. Wher ³³ concluded that the reaction of metallic catalysts with monoisocyanates did not produce a polymer. Metallic catalysts cannot form a stable complex with monoisocyanates and have to react with ether or phenolic compounds to form a ligand. William ³³ proposed the formation of an ether ligand with a metal core to coordinate with monoisocyanates. Controlled coordination polymerization and copolymerization of monoisocyanates in the presence of titanium compounds at ambient temperature was first reported by Patten and Novak.^34,35 In this reaction, the structure of the titanium compounds and the type of ligand attached to Ti are crucial to forming a stable complex. One of the advantages of this method is that it does not form circular trimers and reacts at ambient temperature. Wu et al. ³¹ reported the copolymerization of poly (ethylene glycol methyl ether) with hexyl isocyanate (polyether-block-polyamide) in the presence of titanium tetrachloride (TiCl₄) as a catalyst and dry toluene as solvent at room temperature. We used this method for the synthesis of PPO-b-PHIC. Poly (phenylene ether) or PPO is one of the commonly used engineering polyethers with excellent thermal stability, low flammability, high dimensional stability, low moisture uptake, high electrical resistance, and good mechanical properties.^36–38 Therefore, in this paper, a new family of polyether-block-polyamide LC copolymers was synthesized. This work aimed to study the copolymerization of PPO as a high-performance polyether with PHIC as a LC polyamide, the effect of block ratio on the thermal and optical properties at different temperatures and concentrations, and the geometry of copolymer particles according to the block ratio of copolymers. We hope that the synthesized copolymers will present in broad applications of liquid crystals and reinforcement materials.

Experimental

Materials

Hexyl isocyanate (97%), titanium (IV) chloride solution (1M, ≥99%), 4-Bromo-2,6-dimethylphenol (BDMP, 97%) purified by recrystallization with n-heptane (Merck, 99%), and anhydrous tetrahydrofuran (THF, ≥99.9%) were purchased from Sigma-Aldrich. Pure poly (phenylene oxide) (PPO) was synthesized in our laboratory ( ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 2000–3000 g/mol, MWD = 1.4, T_g = 173°C). Dried toluene (99.9%), methanol, and hydrochloric acid were from Merck. All materials were stored under a vacuum and protected from light.

Characterization

Proton and decoupled carbon nuclear magnetic resonances (¹H NMR and ¹³C NMR) 500 MHz Bruker spectrometer were used to study the microstructure of polymer in CDCl₃ solvent. Fourier transform infrared spectroscopy (FTIR) spectra were recorded in KBr disks using a Perkin-Elmer RXI FTIR spectrometer from 400 cm⁻¹ to 4000 cm⁻¹. The molecular weights of the polymers were measured by gel permeation chromatography GPC-Agilent 1100 in THF (flow rate = 1 mL/min, 23°C). DSC measurements were performed on a Mettler Toledo-DSC1 differential scanning calorimeter. 3 mg samples were weighed and placed into aluminum pans. Heating and cooling scans were carried out at 10˚C/min. Thermogravimetric analysis (TGA) was performed with a Mettler Toledo-TGA thermogravimetric analyzer under an N₂ with a rate of 10˚C/min. X-Ray diffraction (XRD) data were collected on an X’Pert MPD-Philips diffractometer using a cobalt tube (40 kV and 40 mA). The resulting patterns were acquired in the range of diffraction angles from 10 to 70° in a step size of 0.02°/s. The surface morphology, size, and shape of samples were observed using scanning electron microscopy (SEM) with a KYKY-EM3200 (from 20 to 26 kV) microscope. A syringe pump (Allied syrn 200) was used to prepare polymeric particles. The LC phase of samples was identified using polarized optical microscopy (POM) (Leitz Wetzlar 307–148.002514687) equipped with a Zeiss camera.

Synthesis of poly (phenylene oxide)-block-poly (hexyl isocyanate)

The poly (phenylene oxide)-block-poly (hexyl isocyanate) (PPO-b-PHIC) was synthesized using organotitanium coordination polymerization reported by Novak et al.^34,35 Scheme 1 shows different steps of PPO-b-PHIC synthesis. In a 15 mL test tube, PPO ( ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 3000 g/mol, MWD = 1.4) (0.6 g, 0.2 mmol) was easily dissolved in 7 mL dry toluene. TiCl₄/toluene solution (0.2 mL, 0.2 mmol) was added to the polymeric solution under N₂ pure gas and cooled to 0°C using an ice-salt bath. There was the formation of HCl from the reaction of PPO with TiCl₄ that was removed with the flow of N₂. After 1 h, the reaction solution was transferred to room temperature and purged with a rapid flow of N₂ under vigorous stirring to remove the HCl gas and toluene solvent (step 1). The remaining yellow solid was redissolved in 7 mL dry toluene, and hexyl isocyanate (10 mmol) was added dropwise to the solution and stirred under N₂ (step 2). After 1 h, the reaction was stopped in acidified methanol and reprecipitated from THF to remove the unreacted polyether at 25°C (the synthesized copolymer was dissolved in THF at 45°C) (step 3). Purification of the copolymer was repeated 3 times by dissolving in toluene and precipitation in methanol. The white powder (PPO-b-PHIC) was separated by filtration and dried under vacuum at room temperature for 4 days. The yield of the reaction was determined gravimetrically (Equation (1)). The reaction was also carried out for 2 and 3 h. The reaction was repeated for PPO with ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 2217 g/mol and BDMP with ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 201.06 g/mol to investigate the effect of the ether/amide block ratio on the formation of the LC phase. The products obtained from the reaction of hexyl isocyanate with PPO with a molecular weight of 3000 g/mol and 2217 g/mol and BDMP (molecular weight = 201.06 g/mol) are named P₁, P₂, and P₃, respectively.

$$\mathbf{Yield}\left(\mathbf{\%}\right)=\left(\left({\mathbf{W}}_{\mathbf{Copolymer}}\right)/\left({\mathbf{W}}_{\mathbf{PPO}}\mathrm{+}{\mathbf{W}}_{\mathbf{HICmonomer}}\right)\right)\mathrm{\times }\mathbf{100}$$

(1)

Scheme 1.

Different steps of PPO-b-PHIC synthesis.

Preparation of polymeric particles

The polymeric particles were prepared from 1 mL concentrated solution of the synthesized copolymer in pure toluene (60% wt) at room temperature. The solution was injected in methanol as a non-solvent (20 mL, rotating at 500 r/min) using a syringe pump with a rate of 1 mL/h. The polymeric particles simultaneously appeared in methanol with the injection process. After 1 h, settled particles were separated from methanol and dried at room temperature under a vacuum.

Result and discussion

FTIR, ¹H NMR, and ¹³C NMR analysis of copolymer

FTIR spectrum of PPO ( ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 3000 g/mol, n = 25), HIC monomer, and copolymer synthesized from PPO ( ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 3000) and HIC (sample P₁) was shown in Figure 1. The FTIR spectrum of the HIC monomer indicated the absorbance at 2270 cm⁻¹ for O = C = N stretching vibrations. The broad peak at 3422 cm⁻¹ was assigned to hydroxyl end groups of the PPO. For the copolymer (PPO-b-PHIC, yield = 72.12%), the absence of hydroxyls of PPO and isocyanate peak (2270 cm⁻¹) of the HIC monomer indicates that the hydroxyls reacted with isocyanate groups in the copolymer. The absorbance at 720 to 800 cm⁻¹ was assigned to the PHIC block. ³⁹ The weak peak at 1072 cm⁻¹ was assigned to the copolymer’s ether-amide connection (O-C = O).^40–42 The peaks at the 1207 cm⁻¹ region represent the carbonyl group of PHIC (C = O)^19,23 which overlaps with ether groups (C-O-C) of PPO. The stretching vibrations due to –C-N bonds appeared at 1706 cm⁻¹.^23,28,30,39 The stretching vibrations due to alkyl groups of PHIC ³⁹ and methyl groups bonded to the aromatic ring of PPO appeared at 2800 to 3000 cm⁻¹.

Figure 1.

FTIR spectra of HIC monomer, PPO ( ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 3000 g/mol) and PPO-b-PHIC copolymer (sample P₁).

Figure 2(a) and (b) shows the ¹H NMR spectra obtained for P₁. All signals were assigned to the corresponding protons. It is clear that block copolymer has successfully been synthesized. The signals are seen at about 6.456, and 2.046–2.109 ppm corresponds to the aromatic protons (a) and methyl protons (b) of PPO, respectively. ⁴³ The peak of the methyl group of PHIC (c) appears at 0.859–0.886 ppm. Hydrogen atoms of the methylene groups of PHIC were as follow: (d, e, f, 1.263–1.326 ppm), (g, 1.445–1.521ppm), (h, 3.615–3.682 ppm).^{19,20,23,24,30} The end of the chain (i) gives a weak peak at 7.074 ppm.^30,35,44 Number-average molecular weight $\left({\overline{\mathrm{M}}}_{\mathrm{n}}\right)$ and the number of units in each block of the copolymer were calculated from the ¹H NMR spectrum by the following equation ⁴⁵ :

$$\begin{array}{c}{\overline{\mathbf{M}}}_{\mathbf{n,NMR}}{\mathbf{=MW}\hspace{0.17em}\mathbf{of}\hspace{0.17em}\mathbf{end}\hspace{0.17em}\mathbf{group}}_{\hspace{0.17em}\mathbf{B}\mathbf{r}}\mathrm{+}\mathbf{MW}\hspace{0.17em}\mathbf{of}\hspace{0.17em}\mathbf{end}\hspace{0.17em}\mathbf{grou}{\mathbf{p}}_{\mathbf{H}}\mathrm{+}\left(\mathbf{MW}\hspace{0.17em}\mathbf{of}\hspace{0.17em}\mathbf{ether}\hspace{0.17em}\mathbf{unite\times n}\right)\mathrm{+}\left(\mathbf{MW}\hspace{0.17em}\mathbf{of}\hspace{0.17em}\mathbf{amide}\hspace{0.17em}\mathbf{unite\times m}\right)\\ \frac{{\mathit{I}}_{\mathit{\alpha }}/\mathbf{2}}{{\mathit{I}}_{\mathit{i}}}=\mathit{n,}\frac{{\mathit{I}}_{\mathbf{c}}/\mathbf{3}}{{\mathit{I}}_{\mathit{i}}}=\mathbf{m}\end{array}$$

(2)

Where I_a, I_c, and I_i are the integrals of a, c, and i signals in Figure 2. The molecular weight calculated from the ¹H NMR spectrum is equal to 7893.64 g/mol. ¹³C NMR spectrum was used to characterize PPO-b-PHIC copolymer (sample P₁) in CDCl₃ (Figure 2 (c)). The results were in good agreement with that obtained from ¹H NMR. The peaks of various carbons are presented in the attached chemical structure of the copolymer. ¹³C NMR (CDCl₃, ppm): δ = 14.454–16.299 (C_D, C_F), 22.460–48.598 (C_G, C_H, C_L, C_I, CK), 114.095–154.407 (C_A, C_E, C_C, C_B), 156.765 (C_L).^31,46–49

Figure 2.

¹H NMR (a,b) and ¹³C NMR (c) spectrum of PPO-b-PHIC copolymer (sample P₁).

The effect of the ether-amide block ratio on the physical properties of liquid crystals was considered. Therefore, the copolymer was also synthesized from PPO with ${\overline{\mathrm{M}}}_{\mathrm{n}}$ = 2217 g/mol (sample P₂) and BDMP (sample P₃). ¹H NMR of two samples is shown in Figure 3. The peaks are similar to that of P₁ in Figure 2. The molecular weight calculated from the ¹H NMR spectrum equals 6831.24 g/mol (yield = 72.39%) and 5535.16 g/mol (yield = 77%) for P₂ and P₃, respectively (Equation (2)). The results obtained from the ¹H NMR of copolymers are summarized in Table 2.

Figure 3.

¹H NMR spectrum of PPO-b-PHIC copolymer (P₂ sample) (up) and BDMP-b-PHIC (P₃ sample) (down).

Table 2.

Results from ¹H NMR of samples.

Sample	n:m ratio	${\overline{\mathrm{M}}}_{\mathrm{n}}$ , HNMR (g/mol)	Yield (%)
P1	25.50 : 37.13	7893.64	72.12
P2	17.02 : 36.78	6831.24	72.39
P3	1.11 : 41.57	5535.16	77.38

DSC analysis of P₁, P₂, and P₃ samples:

The DSC results of samples are shown in Figure 4. The glass transitions of blocks (T_gPPO and T_gPHIC) for different ratios of n: m are listed in Table 3. T_gPHIC was in good agreement with that reported by other researchers.^23,24,31,50 The heating and cooling curves exhibit a broad endothermal peak from 20 to 90°C and a broad exothermal peak at 80 to 3°C, respectively due to conformation change of the PHIC chain (T_conf,tr).^17,18,51

Figure 4.

DSC curves of P₁, P₂ and P₃ samples.

Table 3.

Data obtained from DSC thermograph.

Sample	n:m	TgPHIC	TgPPO	Tconf,tr heating	Tconf,tr cooling
P1	25.50 : 37.13	−72	142.61		3.02–43.69
P2	17.02 : 36.78	−65.67	130.59	20–90	26.35–48.35
P3	1.11 : 41.57	−55.34	-		48.35–80.36

Peak intensity decreases with a decreasing number of ether units, indicating decreasing conformational energy of copolymers from rod to coil and vice versa. The steric hindrance due to the ether block restricts the chain conformation of copolymers. Size and optimal geometry of polymeric chains of samples synthesized in various ratios of n: m were estimated by material studio software (Figure 5). As can be seen, the molecular dimensions increased with the length of the ether block, which confirms the increase of rod to coil conformational energy. Rod to coil conformations and dynamics of the nematic LCPs was investigated by Warner et al. ⁵² using mathematical relations. The conformational behavior of poly-alkyl isocyanates (such as poly-hexyl isocyanate) was also investigated as a function of the relaxation time of chains using dipole relaxation analysis (DR). ⁵³

Figure 5.

Material studio simulation for samples (a) P₁, (b) P₂ and (c) P₃.

POM analysis of samples

Figures 6 and 7 show microphotographs of the LC texture of the samples taken under a polarized optical microscope (POM) equipped with a heater (POM photos taken during heating), and the results are summarized in Table 4. Results show that the solution’s tendency to form anisotropic phases has increased with decreasing the ether-amide block ratio. This is because the PHIC is a LC block in the chemical structure of the copolymer. The higher percentage of LC block in the structure, the higher tendency of the copolymer to form an anisotropic phase.^{22,25–30,32,39,50,54} The phase transition of the solution is a function of two parameters of temperature and concentration. The orientation change of LC molecules as a function of free energy and temperature was discussed by Guo et al. ⁵⁵ The effect of solution concentration (0.2, 0.4, and 0.6 mg/mL in toluene) and temperature (25–100°C) on the LC texture of samples was investigated. As can be seen, for 0.2 and 0.4 mg/mL of P₁ in toluene, only the isotropic phase (I in Table 4) was observed (black under the polarized microscope). When the copolymer concentration in toluene reached 0.6 mg/mL (Figure 6(a) and (b)), the copolymer formed an anisotropic phase (AI in Table 4). The images show a mixture of colors without any shear or mechanical strain, indicating that the copolymer solution is birefringent at room temperature. The results obtained from POM micrographs are similar to those reported for other copolymers of PHIC.^17,31 In Figure 6 (c),(d),(e),(f), with the decrease in the ratio of ether block in copolymer P₂, the LC phase was observed for 0.4 mg/mL solution concentration at 25°C (Table 4). As the ether block ratio of the copolymer was increased, the rainbow circular nematic disclinations were observed under a polarized microscope. The emergence of the circular texture of the nematic phase is related to the strength-number of LC^56,57 (In this case, the strength-number is equal to +1) (see supplementary data, Figure S1). The colors are due to the variation in the molecular orientation of LC copolymers in toluene. As the copolymer concentration in the solution is 0.4 mg/mL, the banded and circular textures coexist.

Figure 6.

Polarized optical micrographs of (a,b) 0.6 mg/mL solution of copolymer P₁ in toluene at 25°C and 45°C and 0.4 and 0.6 mg/mL solution of copolymer P₂ in toluene at 25°C and 45°C (c,d,e,f).

Figure 7.

Polarized optical micrographs of 0.2, 0.4 and 0.6 mg/mL solution of BDMP-b-PHIC (P₃) in toluene at 25°C, 45°C and 60°C.

Table 4.

Liquid crystal phase transition of copolymers (PPO_n-b-PHIC_m) as a function of concentration and temperature (I: Isotropic, AI: Anisotropic).

Sample	Concentration of copolymers in toluene (mg/ml)	Temperature (˚C)
		25	45	60	80	100
P1	0.2	I	I	I	I	I
	0.4	I	I	I	I	I
	0.6	AI	AI	I	I	I
P2	0.2	I	I	I	I	I
	0.4	AI	I	I	I	I
	0.6	AI	AI	I	I	I
P3	0.2	AI	AI	I	I	I
	0.4	AI	AI	AI	I	I
	0.6	AI	AI	AI	I	I

Investigations by POM for BDMP-b-PHIC (P₃) showed that all samples (0.2, 0.4, and 0.6 mg/mL) exhibit a LC phase at 25°C and 45°C. LC mesophase was also seen for samples with the solution concentrations of 0.4 and 0.6 mg/mL at 60°C (Figure 7 and Table 4). The thread texture of the nematic phase can be seen for 0.2 and 0.4 mg/mL concentrations. The disclinations with a strength-number of +1 were observed for a solution concentration of 0.6 mg/mL at 25–60°C (see Figure S2). Complex tensors of orientations are calculated to find the relationship between the texture and strength-number of liquid crystals.^58–60

SEM analysis

Figure 8 shows SEM images of the particles of copolymers in different ratios of ether-amide blocks (n:m). As can be seen, the prepared particles change to a fiber-like shape by increasing the amide’s block length (P3 sample). The helical structure of PHIC^19,23 tends to form fibers. Electrospinning of PHIC with a high molecular weight of 76,000 g/mol was also reported by Lin et al. ⁶¹ The particle size range in SEM images is 322.6 nm-2.847 μm (Figure 8 (b)), 445.1 nm-2.889 μm (Figure 8 (c)), and 279.1 nm–46.3 nm (Figure 8 (f)).

Figure 8.

SEM images of prepared particles as a function of ether-amide ratio (n:m) (a,b) P₁, (c,d) P₂, (e,f) P₃.

XRD analysis

X-Ray diffraction of particles of PPO-b-PHIC copolymers (P₁ and P₂) and BDMP-b-PHIC (P₃) shows three broad peaks from 13° to 22° (Figure 9). The appearance peaks were attributed to the physical structure of PHIC.^17,22,62 The intensity of peaks increased with increasing the amide-ether block ratio which is in good agreement with particle shape in SEM images.

Figure 9.

X-ray diffraction pattern (solid state) of copolymers at room temperature a) P₁, b) P₂, c) P₃.

TGA analysis

The thermal stability of the prepared particles and pure PPO was examined by TGA (Figure 10). It can be seen that P₃ started to have a weight loss at about 158°C. In the TGA curve of P₁, the weight loss occurs at 180°C. The weight loss of P₂ appears in the temperature range similar to that observed with P₁. The thermal stability of the three products is clearly lower than that of the PPO homopolymer. This is because of the low thermal stability of the PHIC block (160–200°C)^{18,22,31,51,63,64} in copolymer so that residual of P₃ approaches zero at the end of the TGA thermogram (at 700°C).

Figure 10.

TGA thermograms of PPO and PPO-b-PHIC copolymers (P₁ and P₂) and BDMP-b-PHIC (P₃).

Conclusion

Three different block ratios of the PPO_n-b-PHIC_m and BDMP-b-PHIC were synthesized using coordination polymerization. DSC results clearly showed that the conformational energy of copolymers decreases with increasing the amide block ratio. The various nematic textures were observed for the solution of synthesized samples in toluene. The sample tendency to form the anisotropic orientation increases by increasing the amide block ratio. The formation of the anisotropic phase and the type of nematic texture are both temperature and concentration-dependent. A fibrous-like shape was observed under SEM for the particles obtained from the sample with an amide block ratio of 41.57. The particles of copolymers with ratios of 25.50:37.13 and 17.02:36.78 were irregular. The XRD was in good agreement with that obtained from SEM images. TGA showed that the thermal stability of copolymers increases with increasing the ether block ratio in molecular structure.

Supplemental Material

Supplemental Material - High-performance family of polymeric particles prepared from poly(phenylene oxide)-poly(hexyl isocyanate) liquid crystal block copolymer: synthesis and properties study

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