Caprolactam magnesium bromide

The terms in Equation 1.3 (Malkin s autocatalytic model) are described in Nomenclature. In Malkin s autocatalytic model, the concentration of the activator, [A], is defined as the concentration of the initiator times the functionality of the initiator. For a difimctional initiator [e.g., isophthaloyl-bis-caprolactam, the concentration of the activator (acyllactam) is twice the concentration of the initiator]. The term [C] is defined as the concentration of the metal ion that catalyzes the anionic polymerization of caprolactam. In a magnesium-bromide catalyzed system, the concentration of the metal ion is the same as the concentration of the caprolactam-magnesium-bromide (catalyst) because the latter is monofunctional. 

In our studies, the catalyst and initiator system was comprised of caprolactam-magnesium-bromide and isophthaloyl-bis-caprolactam, respectively. We determined the optimum values of the kinetic parameters in Malkin s autocatalytic model (Eq. 1.3), which consist of k, U, and b, by regression analysis. 

In the only other reported study on the kinetics of anionic ring opening homopolymerization of caprolactam using caprolactam-magnesium-bromide, Greenley et al. [57]... 

Figure 1.11 Adiabatic conversion of nylon 6 Experimental data for initial polymerization temperatures of 117°C (bottom line), 136°C (middle line), and 157°C (top line) with acyllactam and caprolactam-magnesium-bromide concentrations of 70 and 108mmol/L, respectively...

We calculated the values of U, k, and b for caprolactam-magnesium-bromide/ isophthaloyl-bis-caprolactam system to be 30.2kJ/mol, 1.49 x 104L/mol, and... 

Figure 1.13 Isothermal complex viscosity rise during anionic polymerization of caprolactam using caprolactam-magnesium-bromide/isophthaloyl-bis-caprolactam as the catalyst/initiator system. Run numbers and polymerization temperatures are shown in the legend...

The single feed composition investigated consisted of 133mmols/L of caprolactam-magnesium-bromide and 45 mmols/L of the difunctional isophthaloyl-bis-caprolactam. Note that 45 mmols/L of the difunctional isophthaloyl-bis-caprolactam contain 90 mmols/L of the active acyllactam group, which react with the monolunctional caprolactam-magnesium-bromide to initiate the polymerization reaction. 

For sodium/hexamethylene-l,6-bis-carbamidocaprolactam system, Sibal et al. [64] found the value of the constant k in Equation 1.4 to be 17.5. Note that the values of the constant k in Equation 1.4 that defines the relative complex viscosity rise during anionic ring opening polymerization of caprolactam are comparable for both caprolactam-magnesium-bromide/isophthaloyl-bis-caprolactam and sodium/hexamethylene-l,6-bis-carbamidocapro-lactam as the catalyst/initiator systems even though the kinetic constants for anionic polymerization for these systems are extremely different (see Table 1.2). 

The kinetics of anionic ring opening polymerization of caprolactam initiated by iso-phthaloyl-bis-caprolactam and catalyzed by caprolactam-magnesium-bromide satisfactorily fit Malkin s autocatalytic model below 50 percent conversion. The calculated value of the overall apparent activation energy for this system is 30.2kJ/mol versus about 70kJ/mol for Na/hexamethylene-l,6,-bis-carbamidocaprolactam as the initiator/catalyst system. 

The most commonly-used catalysts for caprolactam polymerization are sodium caprolactam and caprolactam magnesium bromide. The latter catalyst can be made by reacting a Grignard reagent with caprolactam. 

The alkaline catalyst systems used for caprolactam polymerization are suitable for both the prepolymer and copolymerization reactions. The preferred catalyst Is caprolactam magnesium bromide, prepared by reaction of Grignard reagent with caprolactam. With NYRIM copolymers, a two-package system Is used—reactive prepolymer and catalyst concentrate. These are dissolved in caprolactam to make up the two reactive streams. 

The success of this technology is primarily based on the apphcation of e-caprolactam magnesium bromide (CLMgBr) 29 as initiator. This salt enables the pseudoadiabatic polymerization to proceed at a high rate, and the product to crystallize below the melting point of PA 6. Hence, molding can be completed within several minutes, which is main requirement for RIM processes. 

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