Polar silicones: structure-dielectric properties relationship

Figures & data

Table 1. Experimental conditions for synthesis of polar silicones.

Code	Siloxane precursor (amount)	Polar reagent (amount)	Catalyst (amount)	Reaction conditions	RMN/FT-IR	Observations/conversion (modification degree)
P1CN	P1 (1 g, 1.14 mmol SiH)	Allyl cyanide (0.094 g, 1.4 mmol)	Pt, Karstedt (0.02 mL)	70 °C, 8 h, Ar, dried toluene (5 mL)		88%
P1EP	P1 (1 g, 1.14 mmol SiH)	Allyl glycidyl ether (0.15 g, 1.31 mmol)	Pt, Karstedt (0.03 mL)	70 °C, 7 h, Ar, dried toluene (5 mL)	Figure 1(a)	97%
P1Py	P1EP (0.25 g)	4-amino pyridine (0.024 g, 0.25 mmol)		70 °C, 15 h THF/Isopropyl alcohol 2/1 v/v	Figure 1(b)	97%
P1CHO	P1 (0.8 g (0.91 mmol SiH)	Allyl aldehyde (0.16 g, 0.98 mmol)	Pt, Karstedt (0.04 mL)	70 °C, 7 h, Ar, dried toluene (5 mL)	Figure 2(b) and Figure S2	Washing with methanol/86%
P1DR1	P1 (0.24 g (0.27 mmol SiH)	Disperse red 1 (0.087 g, 0.275 mmol)	Pt (Karstedt), 0.02 mL	65 °C, 20 h, Ar, dried toluene (5 mL)	Figure 3(b)	Washing with methanol/84%
P2Cl	P2 (1 g (1.1 mmol vinyl)	Chloropropane-thiol (0.133 g, 1.2 mmol)	DMPA, 0.028 g (0.11 mmol)	RT, Toluene, UV irradiation (366 nm), 1.5 h	Figure 4	Precipitated with methanol/100%
P2COOH	P2 (1 g (1.1 mmol vinyl)	Mercapto-propionic acid (0.144 g, 1.2 mmol)	DMPA, 0.028 g (0.11 mmol)	RT, THF, UV irradiation (366 nm), 30 min	Figure 5	Precipitated with water, filtrated/100%

Figure 1. ¹H NMR spectra of P1EP (a) and P1Py (b) copolymers.

Figure 2. ¹H NMR spectrum of P1CHO (b), compared with the ally-benzaldehyde (a).

Figure 3. ¹H NMR spectrum of P1DR1 copolymer (b), in comparison with the polar reagent (a).

Figure 4. ¹H NMR spectrum of P2Cl.

Figure 5. ¹H NMR spectrum of P2COOH.

Figure 6. Dielectric properties of a series of siloxane copolymers having around 8% different polar groups.

Table 2. Dielectric permittivity, loss, and conductivity (at 10 kHz) of polysiloxanes with different dipoles attached in similar proportion (ca. 8%).

Code	ε′	ε″	σ (S/cm)
P1CN	4.23	4.19 × 10^−03	2.79 × 10^−11
P1CHO	5.0	1.18 × 10^−01	6.56 × 10^−10
P1EP	3.8	1.68 × 10^−03	6.00 × 10^−12
P1Py	7.4	5.90	4.13 × 10^−08
P1DR1	5.4	2.21 × 10^−01	1.55 × 10^−09
P2Cl	3.8	2.08 × 10^−02	1.45 × 10^−10
P2COOH	3.9	1.95 × 10^−02	1.91 × 10^−10

Table 3. Dipole moments, molar polarizability, and molar volume of model molecules containing the polar substituents attached to the silicon atom and a methyl group instead of the polysiloxane chain.

Code	Structure	Dipole moment (D)	Molar polarizability × 10^−24 (cm^3) (calcd. with ACD)	Molar volume (cm^3) (calcd. with ACD)
CN		4.05 ^a	9.96	104.4
CHO		4.24 ^a	21.24	174.6
DR1		10.4^b	34.71	255.1
EP		2.19 ^a	12.35	121.2
Py		5.67 ^a	23.92	188.8
Cl		3.22 ^a	16.92	152.9
COOH		3.29^c	15.62	136.1

^a Calculated with Hyperchem – Density Functional Theory (DFT) Orbital basis set 6–31G*.

^b Calculated with Hyperchem – Density Functional Theory (DFT) Orbital basis set STO-3G.

^c Calculated with Hyperchem – Molecular Mechanics /MM+/Geometry Optimization.

Figure 7. Dielectric permittivity of polar silicones versus a calculated parameter [K1 = (dipol moment) × (molar volume) × (molar polarizability)] of different polar substituents (a) and versus a semi-empirical parameter K2 (b) or K2′ (c), which takes into account the measured moisture sorption capacity, expressed as maximum percents in K2 and as percents for RH = 50% in K2′; K2 = K1 × (% water adsorbed).

Figure 8. Water vapors sorption-desorption isotherms by DVS of the polar silicones.

Scheme 1. Synthesis of the polysiloxane precursors.

Scheme 2. Synthesis of the polar silicones derived from P1.

Scheme 3. Synthesis of the polar silicones derived from P2.