1、Study on Ternary Polymerization of Toluene DiisocyanateQi Zhengjian1 Luo Zhenyang 2 Li Xiangxin 3 *Sun Yueming1 Feng Weidong1 Wanghualin1 Yan Dazhi1(1Department of Chemistry and Chemical Engineering,Southeast University, Nanjing 210096, China) (2 Department of Chemistry and Materials Chemistry,Nanji

2、ng Forestry University, Nanjing 210037, China) (3Shandong Light Industry Engineering School ,Qingdao 266112, China)Abstract: For the production of reactive polyurethane curing agents, it is known to use terpolymeric isocyanates which possess the rigid structures of hexatomic ring and three reactive

3、functional groups. 2,4-Diisocyanate toluene (TDI) terpolymer was synthesized and characterized by FTIR, GPC and chemical analysis method in this paper. The reaction conditions were studied and optimized. A tracking research on the polymerization process of TDI was taken by using GPC. The formation p

4、rocesses of terpolymer,oligomer and higher-polymer were also dealt with . The result showed that TDI terpolymer could be prepared in the presence of Cat-3 catalyst and under the reaction temperatures of 60+2. The reaction time was short, its outcome had narrow molecular weight distributions, namely

5、molecular weight from 530 to 550, Mw/Mn=1.10 and NCO content was 25.0%+0.5%. With the reaction time prolonging, however, TDI would be further higher-polymerized to form higher-polymers. Benzoyl chloride (0.4% concentration),as the stablizing agent, which could effectively inhibit the occurrence of h

6、igher-polymerization. The obtained TDI terpolymer could be stable for more than half a year. Key Words: 2,4-Diisocyanate toluene (TDI); terpolymers; GPC; curing agent;storage stabilityUnder some reaction conditions, 2,4-Diisocyanate toluene(TDI）will undergo ternary polymerization to form TDI terpoly

7、mer, which is also called isocyanurate. The molecules of isocyanurate possess the rigid structures of hexatomic ring, on which there is no active hydrogen atom. This property makes the products made from TDI terpolymer have the outstanding practical performance in hardness, abrasion resistance, ther

8、mal stability, hydrolysis stability, solvent resistance and weatherability. Also, there are three reactive functional groups in the molecular structure of the TDI terpolymer, which makes it much more reactive than other kinds of isocyanates. The TDI terpolymer therefore is a good fast-speed curing a

9、gent. In recent years, it has found wide applications in the fields such as elastomers, coatings, adhesives and foam plastics1-4. The NCO group in the TDI molecule is strongly reactive, therefore, in addition to the ternary polymerization, the higher-polymerization will also take place in the progre

10、ss of TDI polymerization, and this makes the resultant product become a mixture, affecting TDIs practical performance adversely. The previous studies focused on speculating about the polymerization progress based on the changes in the viscosity of reaction system, and this method lacked scientific e

11、vidence, and was hard to control accurately the molecular weight distributions of product. This paper made a tracking research on the polymerization process of TDI by using GPC, and dealt with the formation process of terpolymer and higher-polymers in the course of polymerization and some factors, w

12、hich can affect the said process, based on the molecular weight distributions of polymers. Meanwhile, the resultant products were characterized by using infrared spectra, and the storage stability of TDI terpolymer was also studied. 1Experimental Section1.1 Raw Materials and Reagents2,4-toluene diis

13、ocyanate (Coronate T-100 ) industrial grade, NPU; Cat-3 analytical pure, manufactured by Shanghai Chemical Reagent Company; benzoyl chloride chemically pure, manufactured by Shanghai Chemical Reagent Company; di-n-butyl amine analytical pure, manufactured by Shanghai Chemical Reagent Company; ethyl

14、acetate analytical pure, manufactured by Shanghai Chemical Reagent Company;1.2 Analytical InstrumentsPE series 200 Gel Permeation Chromatograph (GPC) made by PE company; FIR-750 Fourier Infrared Spectrometer made by Nicolet company.1.3 The Synthesis of TDI TerpolymerPlace 100 grams of 2,4-TDI monome

15、r and 100g of ethyl acetate into a dry 250mL four-neck flask, which was equipped with the agitator, thermometer and reflux condenser. Flushed with N2 as protection, the mixture is stirred at room temperature for five minutes, and then the mixture is heated to 55 , and after that, the catalyst is add

16、ed. The reaction mixture is heated to 60+2, and the reaction proceeds under the temperatures. The sampling takes place every a certain amount of time for the purposes of measuring the mass fraction of NCO group in the reaction system and of determining molecular weights and the molecular weight dist

17、ributions through the use of GPC. When the mass fraction of the NCO group drops to a proper value, the antipolymerizer benzoyl chloride is added to the mixture, and the mixture is continually stirred for 30 minutes so that the reaction goes on. Then, the final product is discharged. It is a viscous,

18、 pale yellow transparent product. 1.4 Analysis and TestMolecular weight measurement for the polymer Polymeric molecular weight and its distributions are measured by using GPC. Tetrahydrofuran is used as the solvent to dissolve the test sample, requiring the concentration of the solute (the test samp

19、le, namely the polymer) in the resulting solution is about 2%, so as to facilitate the measurement.IR analysis The test sample is dissolved in the THF (solvent) in the mass fraction of about 2%. The obtained solution is coated on the KBr pellet, and THF is totally evaporated under the irradiation of

20、 IR light, after completing the above steps, measure the resultant test sample. Mass fraction analysis of NCO group This measurement is in compliance with GB12009.4-89. 2Results and Discussion2.1 The Principle of TDI terpolymerizationThe presence of NCO group in the TDI molecule enables TDI to have

21、a tendency to polymerize, and it will undergo terpolymerization reaction to produce isocyanurate having the structures of hexatomic ring if any proper catalyst is present. The TDI terpolymers theoretical molecular weight is 522.6, and NCO% is 24.1%. The reaction formula is as follows: Figure 1 TDI t

22、erpolymerization reactionTDI terpolymerization is a nucleophilic reaction, in which trialkyl phosphine, tertiary amine and alkaline carboxylate can be used as catalysts6 7. The terpolymerization reaction is irreversible. When it reaches a specific conversion rate, the concentration of TDI monomers i

23、s very low, the polymerization reaction will proceed between two or more polymerized oligomers until the spatial weblike arrangement of “l(fā)ong-chain” molecules forms.This arrangement makes the system become a gel. Products with various degree of polymerization can be obtained by controlling over diff

24、erent reaction conditions. Potential higher-polymers have structures as follows: Figure 2 TDI oligomer and higher-polymer 2.2 The Effect of the Reaction Time on Mass Fraction of NCO Group By adopting Cat-3 (its concentration is 0.2% in the reaction system) as the catalyst, and keeping the reaction t

25、emperature at 65, the separate sample should be taken at the reaction time of 15min, 30min, 45min, 60min, 75min, 90min and 105min, and the mass fraction of NCO in the separate sample is measured separately. The mass fraction of NCO changing with time is shown in Figure3.Figure 3Effect of the reactio

26、n time on mass fraction of NCO/%From Figure3, It follows that after the reaction starts, the mass fraction of NCO in the system decreases sharply, and with the reaction time passing, the decreasing tends to smoothness. Theoretically, if all the TDI is polymerized to form terpolymer, the w(NCO) shoul

27、d be 24.1%, namely half the starting value of w(NCO). If the w(NCO) is lower than 24.1%, it is suggested that there are higher-polymers formed in the product. 2.3 The Effect of the Reaction Temperature on TDI Terpolymerization ReactionIt is found that the polymerization reaction proceeded faster wit

28、h the increase in reaction temperature. However, if the reaction temperature is much too high, the reaction system will become cloudy, too viscous and deeper in its color, and this will result in poor product performances. The effects of reaction temperature on reaction speed and product appearance

29、are indicated in Table 1.Table 1 Effect of the reaction temperature on mass fraction of NCO/% and appearanceNo.Reaction Temperature/Time (NCO%=24.5%)/min.Product Appearance140118pale yellow transparent 25095pale yellow transparent36060pale yellow transparent47046brownish yellow transparent58033brown

30、ish yellow , cloudy2.4 IR Spectral Analysis of TDI Terpolymer The IR spectrogram of TDI monomer and TDI terpolymer are shown respectively in Figure 4,5. Figure 4IR of the TDI monomer Figure 5IR of the TDI terpolymer In the IR spectrogram of TDI terpolymer, the dissymmetry stretching vibrational abso

31、rption peak of NCO group appears at the site of 2270cm-1 , there are three absorption peaks of terpolymer at the sites of 1710 cm-1，1410 cm-1 and 760 cm-1, which show the appearance of terpolymer in the product. There is an absorption peak of bipolymer at the site of 1600cm-1 , showing the presence

32、of bipolymer in the product. There is no absorption peak at the site of 2130 cm-1, indicating no carbodiimide exists. 2.5 GPC Analysis for TDI Terpolymerization Reaction ProcessDuring the course of self-polymerization reaction, the separate sample is taken at the reaction time of 20min, 40min, 60min

33、, 80min, 100min and 120min, and the separate samples molecular weight distributions are determined by using GPC. The separate GPC spectrogram is shown in Figure 6. Figure6GPC of the TDI terpolymerIn the above Figures, the peak of retention time of 10.43 to 10.41min is the solvent peak; The peak of 9

34、.80 to 9.70min corresponds to the molecular weights: 530 to 550; The peak of 9.45 to 9.30min corresponds to the molecular weight 950; The peak of 9.15 to 9.08min corresponds to the molecular weight 1050; The peak of 8.65 to 8.61min corresponds to the molecular weight 3400. It follows from the GPC sp

35、ectrogram that, a single peak corresponding to the molecular weight 530 or so appears at the reaction time of 20min, showing the formation of TDI terpolymer. The peak corresponding to the molecular weight 530-550 become larger in size and a peak corresponding to the molecular weight 950 or so is pre

36、sent at the reaction time of 40min, showing the formation of TDI higher-polymers. At the reaction time of 40min, the TDI monomer peak becomes smaller, and the peak corresponding to the molecular weight 550 continues to enlarge in size, also the peak corresponding to the molecular weight 950 becomes

37、markedly larger, meanwhile, a peak corresponding to the molecular weight 1050 or so appears. Based on the molecular weights, it is calculated that the formed products should be double TDI terpolymer structural units and the bipolymer structural units consisting of double TDI terpolymer structures. A

38、t the reaction time of 80min, the peak corresponding to the molecular weight 550 becomes smaller, but the both peaks corresponding to the molecular weight 950 and 1055 continue to enlarge. At the reaction time of 100min, the monomer peak almost disappears, and a peak corresponding to the molecular w

39、eight 3400 appears, showing formation of the higher crosslinking degree of TDI higher-polymer structures. At the reaction time of 120min, the peak corresponding to the molecular weight 3400 continues to become larger, but the acceleration of enlarging is not big. This indicates that the reaction spe

40、ed tends to become lower, when the mass fraction of NCO group drops to a very low level. The above-said results are consistent with the described results in figure 3. 2.6Study on Storage Stability of TDI TerpolymerThe hexatomic ring of isocyanurate molecule in the TDI terpolymer possesses the strong

41、 electron-attracting effect, which causes the increase in electric potential difference of CN bond within the NCO group, so raises the reactivity. Therefore, in the course of TDI terpolymerization reaction, when the reaction reaches the desirable degree, the antipolymerizer must be added to deactiva

42、te the catalyst, if not added, the reaction will continually go deeper. In addition, when TDI terpolymer is stored, the three NCO groups in its molecular structure can react or be polymerized further with the moisture in the air, causing reduction in the NCO group content. So the system becomes more

43、 viscous until entirely solidifying. Therefore, it is necessary to use the stabilizing agent to stop the reduction in the NCO group content. The available stabilizing agents are: benzoyl chloride, Methyl p-toluenesulfonate, phenyl phosphate and phosphoric acid, etc. This experiment uses benzoyl chlo

44、ride as the stabilizing agent, and its amount added is 0.4%. After TDI terpolymer is treated in this way and kept in a sealed container for six months, there is little change in the product performances. Even if you often open the containers cover to take the sample for use, the mass fraction of NCO

45、 group in the sample only decreases by 28%, representing a better stable performance.Figure 7 Stability of TDI terpolymer3Conclusion(1)The TDI terpolymer products with better quality can be obtained by using Cat-3 as the catalyst, keeping the appropriate reaction temperature and reaction time. (2)When TDI self-polymerization reaction takes place, TDI terpolymer is produced first, then with the reaction proceeding, the TDI higher-polymers will be further produced. And with the reaction time prolon