Carbodiimides are produced from isocyanates using phosphine oxides as catalysts. The disadvantage of using phosphine oxide catalysts is the need to separate the catalyst which is difficult. The patent application publication shown in the diagram describes the production of polycarbodiimide from TMXDI (tetramethylxylylene diisocyanate) that advantageously avoids the use of phosphorous and instead uses a base such as potassium t-butoxide and a phase-transfer catalyst. The base and PTC are easy to remove from the product.
The reaction is performed at a temperature of 175 deg C and is run with an internal process control point of 3.74 isocyanate content that corresponds to a degree of polymerization of 10. The Lewis base is potassium t-butoxide.
When running the reaction without a phase-transfer catalyst, the reaction time required is 26 hours. Following are reaction times with various phase-transfer catalysts:
18-crown-6 & 15-crown-5: 2 hours
PEG550 monomethyl ether: 11 hours
tetrabutylammonium 2-ethylhexanoate: 20 hours
The inventors also screened combinations of phase-transfer catalysts with other bases such as potassium acetate, cesium acetate and sodium ethoxide. Increasing the amount of phase-transfer catalyst could significantly reduce the reaction time.
We speculate that the use of PEG550 monomethyl ether might provide good benefit at reasonable cost and availability.
About Marc Halpern
Dr. Halpern is founder and president of PTC Organics, Inc., the only company dedicated exclusively to developing low-cost high-performance green chemistry processes for the manufacture of organic chemicals using Phase Transfer Catalysis. Dr. Halpern has innovated PTC breakthroughs for pharmaceuticals, agrochemicals, petrochemicals, monomers, polymers, flavors & fragrances, dyes & pigments and solvents. Dr. Halpern has provided PTC services on-site at more than 260 industrial process R&D departments in 37 countries and has helped chemical companies save > $200 million. Dr. Halpern co-authored five books including the best-selling “Phase-Transfer Catalysis: Fundamentals, Applications and Industrial Perspectives” and has presented the 2-day course “Practical Phase-Transfer Catalysis” at 50 locations in the US, Europe and Asia.
Dr. Halpern founded the journal “Industrial Phase-Transfer Catalysis” and “The PTC Tip of the Month” enjoyed by 2,100 qualified subscribers, now beyond 130 issues. In 2014, Dr. Halpern is celebrating his 30th year in the chemical industry, including serving as a process chemist at Dow Chemical, a supervisor of process chemistry at ICI, Director of R&D at Sybron Chemicals and founder and president of PTC Organics Inc. (15 years) and PTC Communications Inc. (20 years). Dr. Halpern also co-founded PTC Interface Inc. in 1989 and PTC Value Recovery Inc. in 1999. His academic breakthroughs include the PTC pKa Guidelines, the q-value for quat accessibility and he has achieved industrial PTC breakthroughs for a dozen strong base reactions as well as esterifications, transesterifications, epoxidations and chloromethylations plus contributed to more than 100 other industrial PTC process development projects.
Dr. Halpern has dedicated his adult life to his family and to phase-transfer catalysis (in that order!).
