“…At present, there are two synthesis methods from butadiene monomer to obtain HTPB: free radical and anionic polymerization . Free radical polymerization has already been industrialized, but its product's low 1,4 unit (<70%) led to poor performance in low‐temperature mechanics.…”
A novel Ni‐based initiator is designed and synthesized for obtaining a hydroxyl‐terminated polybutadiene (HTPB) with higher cis‐1,4 unit content (≥90%). By investigating the effect of the butadiene skeleton structure and counterion on initiating efficiency, it is found that [η3‐Ni(CH2CHCHCH2OOCH3)][BPhF
4] complex is a feasible combination to be used as an initiator. 1H‐NMR data prove that the initiator structure obtained is in accordance with the original design. The result of 1H‐NMR, 13C‐NMR, FT‐IR confirms that HTPB synthesized not only gains a significant amount in cis‐1,4 unit content (≥90%) compared with the HTPBs by free radical and anionic polymerizations, but also its molecular weight and molecular weight distribution can be effectively controlled during synthesis process. Because of the much higher cis‐1,4 unit content, the glass‐transition temperature of HTPB obtained via [η3‐Ni(CH2CHCHCH2OOCH3)][BPhF
4] is markedly reduced; as a result, its low‐temperature mechanical property can also be significantly improved.
“…At present, there are two synthesis methods from butadiene monomer to obtain HTPB: free radical and anionic polymerization . Free radical polymerization has already been industrialized, but its product's low 1,4 unit (<70%) led to poor performance in low‐temperature mechanics.…”
A novel Ni‐based initiator is designed and synthesized for obtaining a hydroxyl‐terminated polybutadiene (HTPB) with higher cis‐1,4 unit content (≥90%). By investigating the effect of the butadiene skeleton structure and counterion on initiating efficiency, it is found that [η3‐Ni(CH2CHCHCH2OOCH3)][BPhF
4] complex is a feasible combination to be used as an initiator. 1H‐NMR data prove that the initiator structure obtained is in accordance with the original design. The result of 1H‐NMR, 13C‐NMR, FT‐IR confirms that HTPB synthesized not only gains a significant amount in cis‐1,4 unit content (≥90%) compared with the HTPBs by free radical and anionic polymerizations, but also its molecular weight and molecular weight distribution can be effectively controlled during synthesis process. Because of the much higher cis‐1,4 unit content, the glass‐transition temperature of HTPB obtained via [η3‐Ni(CH2CHCHCH2OOCH3)][BPhF
4] is markedly reduced; as a result, its low‐temperature mechanical property can also be significantly improved.
“…3 Two synthesis methods using butadiene monomers are currently used to obtain HTPB: free radical polymerization [4][5][6] and anionic polymerization. 7 The details of anionic polymerization to obtain HTPB have been reported so far. 8 However, the content of cis-1,4 in HTPB obtained by anionic polymerization can only reach 30-40%, which is still not satisfactory for standard applications.…”
In this study, novel hydroxyl-terminated polybutadiene (HTPB) with a high cis-1,4 content was developed using a tert-butyl dimethyl siloxy dimethyl propyl lithium (Li)–naphthenate nickel (Ni)–boron trifluoride (B) initiating system (Li–Ni–B).
“…To increase the 1,4 unit content of HTPB, anionic polymerization was often used. To date, the 1,4 unit content in HTPB via anionic polymerization could usually reach 86% [ 1 ]; however, this number is still not satisfactory for many related industries which need HTPBs with much higher 1,4 unit content. Figure 1.…”
A novel alkyl lithium-based initiator with relatively large steric hindrance, tert-butyldimethylsiloxydimethylpropyl lithium (TBDMSODPrLi), was designed and synthesized. By using TBDMSODPrLi, hydroxyl-terminated polybutadiene (HTPB) was prepared via anionic polymerization. The macromolecular structure of HTPB was characterized and verified by FTIR and 1H-NMR. It was found that 1,4 unit content in HTPB initiated by TBDMSODPrLi was significantly higher (over 90%) compared to a HTPB (1,4 unit content of 70%) initiated with another initiator possessing smaller steric hindrance. The possible mechanism, which was based on initiator steric hindrance affecting monomer chain addition behaviour, was deduced. It was that the initiator's larger steric hindrance blocked lithium's intermolecular association during anionic polymerization; as a result, it could effectively increase the 1,4 unit content in HTPB. To further study how to obtain higher and stable 1,4 unit content, the optimal anionic polymerization technique for HTPB was explored including polymerization temperature, time and the amount of initiator used. The study concluded that utilization of an initiator with larger steric hindrance and reducing the polymerization temperature were two important factors to raise the 1,4 unit content in HTPB.
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