Reactive mesogens for ultraviolet-transparent liquid crystal polymer networks

Figures & data

Table 1. Summary of phase behaviour, enthalpy of LC phase transition and maximum absorption wavelength (λ_max) of the synthesised reactive mesogens. Monotropic LC phases are indicated in the brackets

Compound	Acrylic functionality	Phase behaviour	ΔH, kJ/mol	λmax, nm
11	1	Cr 62.0 I	-	276
12	1	Cr 43.3 (N 14.6) I	0.63	276
13	1	Cr 31.9 (N 18.5) I	0.80	276
14	1	Cr 38.0 (N 32.8 SmA 27.7) I	0.74/3.49	276
15	1	Cr 49.5 I	-	277
16	1	Cr 71.6 I	-	263
17	1	Cr 49.3 I	-	276
18	1	Cr 56.4 (N 23.5) I	0.22	277
19	2	Cr 47.9 I		276
20	2	Cr 15.4 (SmC −8.5) I	5.10	277
21	2	Cr 90.6 SmA 106.8 I	6.14	256
22	2	Cr 47.8 SmX 51.5 N 65.4 I	0.79/1.02	257
23	2	Cr 50.8 I	-	277

Table 2. Chemical compositions (in wt.%) of the test network (TN) and reference networks (RN1 and RN2) and their total transparencies in different UV spectral regions

	TN	RN1	RN2
Composition, wt%	12 (8%) 13 (24%) 14 (48%) 22 (20%)	C6BPhCN (80%) RM-257 (20%)	C6BP (20%) C6BP6 (60%) RM-257 (20%)
Transparency in UV-A (315–400 nm), %	96.7	62.8	92.6
Transparency in UV-B (280–315 nm), %	48.9	0	18.6
Transparency in broad UV range (280–400 nm), %	72.8	31.4	55.6
Resilience to UV^a	+	+	-

^a1 hour of exposure to UV light (312 nm, 5.8 mWcm⁻²).

Figure 1. Synthesis of compounds 1, 2, 3, 12, 13 and 14. i: K₂CO₃, KI, 6-bromohexanol, EtOH, reflux 48 h; ii: NEt₃, acryloyl chloride, THF, 0°C 1 h, r.t. 16 h

Figure 2. Synthesis of compound 15. i: K₂CO₃, KI, bromohexane, EtOH, reflux 48 h; ii: 6-bromohexanoyl chloride, NEt₃, THF, 0°C 1 h, r.t. 16 h; iii: potassium acrylate, KI, DMSO, 52°C 72 h

Figure 3. Synthesis of compound 16. i: NaBH₄, MeOH, r.t. 90 min. ii: 6-bromohexanoyl chloride, NEt₃, THF, 0°C 1 h, r.t. 16 h; iii: potassium acrylate, KI, DMSO, 52°C 72 h

Figure 4. Synthesis of compound 17. i: K₂CO₃, KI, 1,6-dibromohexane, EtOH, reflux 48 h; ii: potassium acrylate, KI, DMSO, 52°C 72 h; iii: hexanoyl chloride, NEt₃, THF, 0°C 1 h, r.t. 16 h

Figure 5. Synthesis of 18. i: NEt₃, acryloyl chloride, THF, 0°C 1 h, r.t. 16 h

Figure 6. Synthesis of 19. i: K₂CO₃, KI, 1,6-dibromohexane, EtOH, reflux 48 h; ii: 6-bromohexanoyl chloride, NEt₃, THF, 0°C 1 h, r.t. 16 h; iii: potassium acrylate, KI, DMSO, 52°C 72 h

Figure 7. Synthesis of 20. i: NaH, 1,6-dibromohexane, THF reflux 78 h; ii: potassium acrylate, KI, DMSO, 52°C 72 h

Figure 8. Synthesis of 21, 22 and 23. i: DCC, DMAP, 4-((6-(acryloyloxy)hexyl)oxy)benzoic acid, CH₂Cl₂, 30°C 24 h. ii: 4-((6-(acryloyloxy)hexyl)oxy)-2-methylbenzoic acid, triethylamine, 2,4,6-trichlorobenzoyl chloride, DMAP THF 18 h r.t.; iii: NEt₃, acryloyl chloride, THF, 0°C 1 h, r.t. 16 h

Figure 9. Polarised optical microscopy images of LC textures of compound 14 demonstrating the transition from smectic A to nematic (a) upon cooling, and fan-like texture of smectic A obtained at 22°C (b). Planar boundary conditions. Scale bars correspond to 100 and 50 µm, respectively. Polariser and analyser are shown as white arrows

Figure 10. Normalised absorbance spectra of mono- (a) and diacrylates (b). Spectra are measured in CH₂Cl₂ at room temperature

Figure 11. (a) Chemical structures of commercially available reactive mesogens used for the production of reference networks RN1 and RN2. (b) Transmittance spectra of the studied LCPNs before and after exposure to UV light (312 nm, 5.8 mWcm⁻²) for 1 h