Latent Curing Activity of Dimethylaminoethoxy Hetero-oxy Borane for Epoxy Resin†

doi:10.7503/cjcu20130826

Abstract

Abstract:

2-(2-Dimethylaminoethoxy)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane(PDB), 2-(2-dimethylaminoethoxy)-5,5-dimethyl-1,3,2-dioxaborinan(NDB) and 2-(2-dimethylaminoethoxy)-1,3,2-benzodioxaborole(CDB) with five-membered ring or six-membered ring contained intramolecular nitrogen boron coordinate bond(N→B), which hydrolytic stability was determined by exposure observation method. Differential scanning calorimetry, oven curing experiments, gelation time experiment and infrared spectroscopy(FTIR) were used to investigate their effect on the curing activity and latent property of E51 epoxy resins. The apparent activation energy associated with curing reaction(E_a) was calculated by Ozawa-Avrami method. The electron density of boron atom and the degree of N→B complexation in dimethylaminoethoxy hetero-oxy borane were influenced by the conjugative effect of phenyl ring, the donor effect of alkoxy and the steric hindrance effect. The conjugative effect of phenyl ring decreased the electron density of boron atom and strengthened the complexation degree of N→B of CDB, which induced a lower hydrolytic stability and curing activity on E51 than NDB and PDB with the donor effect of alkoxy substitution. A higher shielding effect of six-membered ring on boron atom caused a higher hydrolytic stability and curing activity than five-membered ring while a lower curing activity exhibited good latent performance for E51. The degree of conversion of one-pot E51-PDB epoxy resin[a_E₍_t₎] after depositing 3 months at room temperature was 0.22.

Key words: Hetero-oxy borane, Hydrolytic stability, Epoxy resin, Latent performance curing activity

CLC Number:

O632.6

TrendMD:

GAO Yubin, LIU Shumei, ZHAO Jianqing, JIANG Zhijie, YUAN Yanchao. Latent Curing Activity of Dimethylaminoethoxy Hetero-oxy Borane for Epoxy Resin^†[J]. Chem. J. Chinese Universities, 2014, 35(2): 396.

Figures/Tables 9

Scheme 1 Molecular structures of PDB, NDB and CDB

Scheme 2 Curing mechanism of boron-amine complex/epoxy resin system

Scheme 3 Electronic effect of PDB, NDB and CDB

Fig.1 DSC thermograms curves of three one-pot epoxy resins(A) a. E51-CB, b. E51-PB, c. E51-NB; (B) a. E51-PDB, b. E51-NDB, c. E51-CDB.

Scheme 4 Spatial structure of PDB and NDB

Fig.2 DSC thermograms curves of E51-PDBScan rate/(℃·min-1): a. 5; b. 10; c. 20; d. 30.

Fig.3 Plots of lnk' vs. T-1 for E51-PDB a. Entire process; b. later stage; c. early stage.

Table 1 Cure kinetics data obtained by Ozawa-Avrami method

System	$T tr NA$ /℃	$E a oA$ /(kJ·mol^-1)	$E a eA$ /(kJ·mol^-1)	$E a lA$ /(kJ·mol^-1)	$E a eA$ / $E a lA$
E51-PDB	210	214.1	292.6	165.8	1.8
E51-NDB	180^[12]	200.5	276.3	161.2	1.7

Table 1 Cure kinetics data obtained by Ozawa-Avrami method

System	$T tr NA$ /℃	$E a oA$ /(kJ·mol^-1)	$E a eA$ /(kJ·mol^-1)	$E a lA$ /(kJ·mol^-1)	$E a eA$ / $E a lA$
E51-PDB	210	214.1	292.6	165.8	1.8
E51-NDB	180^[12]	200.5	276.3	161.2	1.7

Fig.4 FTIR spectra of E51-PDB as a function of storage time

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