SynopsisA series of polycarbodiimides was prepared from isocyanates using l-phenyl-3-methyl-2-phospholene-1 oxide as catalyst. The molecular weight of the series was varied by employing controlled amounts of phenyl isocyanate as a terminating agent. The resultant polymers showed improved processing over very high molecular weight unterminated polymer, while still maintaining good thermal stability and equivalent mechanical properties. A study of the viscoelastic properties of these polymers using modulustemperature plots showed that the materials underwent a crosslinking reaction at elevated temperatures (2OO-25O0C). These reactions could be explained on the basis of a model, diphenylcarbodiimide, and most likely include the formation of carbodiimide dimers and trimers.
Mold filling is an important aspect of the RIM process. Component tempera tures and viscosities, mold temperatures, gel times and material flowrate are all significant variables in the equation for optimal mold filling. In this work, an automated data collection system is used to monitor flow in a mold for two RIM processed systems; the use of a specially designed tool allowed the calculation of the viscosities of the reacting materials at different locations in the tool.
SynopsisTheoretical equations were developed to relate the extent of reaction at the gel point for a system where three functional groups trimerize to a ring structure during the polymerization reaction. Specific relationships were developed for a difunctional monomer where the two functional groups are of unequal reactivity and for a mixture of difunctional and monofunctional monomer where all three functional groups are of unequal reactivity. These two cases were tested experimentally by determining the extent of reaction at the gel point for the system isocyanate reacting to form isocyanurate. In the case of 4,4'-diisocyanatophenylmethane (MDI), the extent of reaction a t gelation was determined experimentally to be 60%. When this data was analyzed according to the theory developed, a reactivity ratio of 2.38 was calculated for the rate of the first isocyanate group to react as compared to the second. Experiments were also performed with 2,4-toluene diisocyante, which gave a 72% conversion a t the gel point. The extents of reaction at the gel point for mixtures of MDI and phenyl isocyanate were also determined experimentally. An analysis according to the theory developed further supported the idea that all three isocyanate groups in this system have different reactivities. Theoretical relationships also were developed for a trifunctional isocyanate reacting to form isocyanurate. Experimentally, a crude MDI was used, and approximate relationships were used to analyze the results.
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