Preparation and characterization of bismaleimide monomers with various structures

Figures & data

Scheme 1 Synthesis of bismaleimides BMI(1–2).

Scheme 2 Synthesis of 2,2′-bis[4-(4-aminophenoxy)-3,5-dibromophenyl] propane.

Scheme 3 Synthesis of bismaleimides BMI(3–4).

Figure 1 FTIR spectra of monomer BMI-2.

Figure 2 ¹H−NMR spectra of monomer BMI-3.

Figure 3 ¹H−NMR spectra of monomer BMI-4.

Table 1. Solubility of monomers BMI(1–4)^a.

Monomer	Solvent
	DMF	NMP	DMSO	DCE	CHCl3	Toluene	Acetone
BMI-1	+	+	+	++	+	±	++
BMI-2	+	+	+	±	+	±	±
BMI-3	+	+	+	+	+	±	+
BMI-4	+	+	±	−	+	−	+
Note: ^aSolubility: (++) soluble at room temperature; (+) soluble on heating; (±) partially soluble on heating; (−) insoluble.

Figure 4 DSC curves of BMI(1–4).

Table 2. Thermal properties of bismaleimides BMI(1–4).

Monomer	mp (°C)	T end ^a (°C)	T p ^b (°C)	T exo ^c (°C)	∆H^d (kJ/mo)l	IDT^e (°C)	PDTmax ^f (°C)	Y c ^g (%)
BMI-1	117^d	123	198	235	–	375	448, 680	58
BMI-2	137^d	148	170	199	–	422	350, 475	45
BMI-3	212–216	230	243	286	83	449 (426)^h	460 (450, 560)	46 (29)
BMI-4	230–233	242	–	299	107	408 (355)	442, 522 (430, 580)	48 (44)
^aEndothermic peak temperature by DSC.^bStarting polymerization temperature^by DSC.cExothermic peak temperature by DSC.dHeat of polymerization by DSC.eOnset degradation temperature by TGA.fMaximum polymer degradation temperature by TGA.gChar yield at 700°C by TGA. hValues in parentheses were determined in air.hValues in parentheses were determined in air.

Table 3. Some PLM data for bismaleimides BMI-3 and BMI-4.

Monomer	Solid–solid transition temperatures (^oC)				T m ^c (^oC)	T i ^d (^oC)	T exo ^e (^oC)
BMI-3	–				230 (63.64)	^–f	291 (100.7)
BMI-4	146^a	164^b	186^a	192^b	^–	250	299 (133.1)
^aEndothermal peak.^bExothermal peak.^cMelting transition temperature.^dTransition temperature from liquid crystalline phase to isotropic phase.^eMaximum temperature of thermal polymerization exotherm.^fThe transition temperature could not be determined. The enthalpy of each transition [J/g] is given into brackets.

Figure 5 Space fill models of bismaleimides BMI-3 and BMI-4 after modeling using molecular dynamic. The rigid core part of the two mesogenic branches was evidenced.

Figure 6 Optical polarized light microscopy images of: (a) BMI-3, 233 ^oC, magnification 400× and (b) BMI-4, 239 ^oC, magnification 400×.

Figure 7 TGA curves of bismaleimides BMI(2–4).