Catalytic Selectivity and Process Optimizing of the Trimerization of Toluene Diisocyanate

Catalytic selectivity and process optimizing of the trimerization of toluene diisocyanate

Jin Hu, Xinya Zhang*

––––––––– *corresponding author: School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China Tel. & fax: +862087112047; E-mail: [email protected] (X. Zhang).

Preparation of Mannich base catalysts.

Mannich base catalysts used in this study were prepared via a Mannich reaction of phenols with aldehydes, preferably formaldehyde, and secondary amines, preferably dimethylamine. Traditional Mannich base catalyst used in the catalysis of cyclotrimerization of isocyanates is DMP-30, from the reaction of phenol with formaldehyde and dimethyl amine. DMP-30 was a commercially supplied yellow viscous liquid and solved in butyl acetate as 10 wt% solution before use. Besides phenol, we used bisphenol A and linear phenolic resin as starting materials. Tetra(dimethylaminomethyl)bisphenol A (TDBA) is the Mannich base of bisphenol A based on dimethylamine and formaldehyde. TDBA is used as an improved catalyst with lighter colour and better colour stability, instead of traditional DMP-30[28]. The reaction is showed in Scheme S1. Scheme S1

45g of a 40% aqueous dimethylamine solution was mixed with 22.8g of bisphenol A in a stirring flask in a 80℃ water bath, followed by the addition of 32.4g of a 37% formaldehyde solution. After 2 hours at 80℃, the mixture separated into two layers. The organic phase was separated and then purified by vacuum distillation. The final product is a white powder. Elemental analysis gave: N, 12.15% (12.26%); C, 71.32% (70.94%); H, 10.37% (9.63%) (calculated value in the brackets). OMB is the Mannich base of the linear phenolic resin. The linear phenolic resin used in this study is bisphenol A novolac resin, which has an improved colour stability than phenol novolac resin. The preparation of OMB, showed in Scheme S2, is similar

1 to preparation of TDBA, which involved the synthetic reaction of bisphenol A phenolic resin and the addition reaction of dimethylaminomethyl groups. Scheme S2

8.1g of a 37% formaldehyde solution, 22.8g bishpenol A and 20g n-propanol in a stirring flask in a 80℃ water bath, followed by the addition of 0.2g oxalic acid as catalyst. The reaction was kept at 80℃ for 3h. Then 22.5g of a 40% dimethylamine solution was added to the mixture, followed by the addition of 16.2g formaldehyde solution over a period of 30min. The reaction mixture was kept for another 2h. Then the product was purified by distillation at 90℃/1.33Pa. The final product is dissolved in DMF while it is still hot, and the concentration is 10 wt%.

Characterization of Mannich base catalysts

Both structures of TDBA and OMB were determined by 13C NMR as shown in Fig. S1 and Fig. S2. The peak assignments of the spectrum of TDBA were shown in Fig. S1, and it could be a reference for the attribution of the spectrum of OMB and the confirmation of its characteristic groups. The peaks at the region of 154.7 ppm are assigned to the carbon on the benzene ring attached to the phenolic hydroxyl group, and the peaks at the region of 141.7 ppm are assigned to the para- carbon on the benzene ring relative to the phenolic hydroxyl group. The peaks at the region of 121- 129 ppm are attributed to the ortho- and meta- carbon relative to the phenolic hydroxyl group. The multiple peaks at the region of 121-129 ppm on the spectrum of OMB, different from the double peaks on the spectrum of TDBA, are the results of incomplete addition of dimethylaminomethyl groups on all the meta- position of the bisphenol A novolac resin. The peak at 63.6 ppm on the spectrum of OMB, which deviated from the peak at 60.7 ppm, has the same reason. This means OMB does not have a perfect structure as we predicted. To the contrary, it is a mixture of complete addition product and incomplete addition product. Fig. S1

Fig. S2

The GPC chromatograms of TDBA and OMB are showed in Fig. S3 and the ESI- MS spectrum of OMB is showed in Fig. S4. The comparison of GPC chromatograms of TDBA and OMB confirms the existence of various oligomers in OMB, and the

2 ESI-MS spectrum can assist in this confirmation. The GPC chromatogram of OMB suggests that the degree of polymerization is n=1-10. The highest component is still TDBA and the content of oligomer decreases as the n goes up. The numerous impurity peaks appeared in the MS spectrum suggest that the structure of Mannich base is not thermal stable, and tends to decompose as the temperature goes up. And this property is confirmed in the temperature study of OMB showed later in this paper. Fig. S3 Fig. S4

Characterization of TDI-based polyisocyanates

The FTIR spectra of TDI monomer and TDI-based polyisocyanates are showed in Fig. S5. The strongest band at 2273 cm-1 appears in both of them is attributed to the stretching vibration of N=C=O groups. The existence of isocyanurate ring is verified by the bands at 1714, 1412 and 756 cm-1, which are the three characteristic bands of isocyanurate six-membered ring. Fig. S5 The 13C-NMR spectrum of TDI-based polyisocyanurate is shown in Fig. S6. The singlet at 206.2 ppm and the heptet at 29.8 ppm belong to the deuterated solvent acetone-d6 and the six peaks at 171.0 ppm, 64.4 ppm, 31.4 ppm, 20.8 ppm, 19.7 ppm, 13.9 ppm are attributed to the residual solvent butyl acetate after vacuum drying of TDI-based polyisocyanate product. The peaks at about 149.8 ppm is attributed to the three carbons in the isocyanurate rings and the peak at 124.0 ppm is attributed to the carbon in isocyanate groups. As for the peaks between 126-136 ppm are assigned to the carbons in benzene rings. The peak at 18.0 ppm is attributed to the carbon in methyl groups of 2,4-TDI, and the peak at 13.4 ppm is attributed to the carbon in methyl groups of 2,6-TDI. The relative height of these two peaks is consistent with the contents of the two isomers in TDI-80. Fig. S6 The MALDI-TOF-MS spectrum of TDI-based polyisocyanates in Fig. S7 identifies the different components of the reaction mixture according to their molar mass. The sample was blocked by methanol, so the exact m/z was the sum of molar mass of correspondent oligomer, methanol and Na+ or K+. The gap between two

3 adjacent peaks is 380, the exact molar mass of the sum of two TDI and one methanol, which is the exact difference of two neighboring oligomers. The highest degree of polymerization confirmed in the MALDI-TOF-MS is 19, which is consistent with peak separation results of GPC chromatogram in Fig. S8. The sample showed in Fig. S8 was chosen at the NCO conversion of 65%, in order to illustrating the peaks of higher-molecular-weight oligomers more clearly. The peak fitting and separation were obtained by using PeakFit software.

Fig. S7

Fig. S8

Supplementary Figure Captions

Scheme S1 Preparation of TDBA

Scheme S2 Preparation of OMB

Fig. S1 13C NMR spectrum of TDBA

Fig. S2 13C NMR spectrum of OMB

Fig. S3 GPC chromatograms of TDAE and OMB

Fig. S4 ESI-MS spectrum of OMB

Fig. S5 FTIR spectra of TDI and TDI-based polyisocyanates

Fig. S6 13C-NMR spectrum of TDI-based polyisocyanates

4 Fig. S7 MALDI-TOF-MS spectrum of TDI-based polyisocyanates

Fig. S8 Peak separation of GPC chromatogram of TDI-based polyisocyanates