In situ Formation and Compounding of Polyamide 12 by Reactive Extrusion A. Wollny, 1 H. Nitz, 1 H. Faulhammer, 2 N. Hoogen, 2 R. Mu ¨ lhaupt 1 1 Freiburger Materialforschungszentrum und Institut fu ¨ r Makromolekulare Chemie, Stefan-Meier-Strasse 31, D-79104 Freiburg i.Br., Germany 2 Atofina, CERDATO, Route de Rilsan, 27470 Serquigny, France Received 18 October 2001; revised 2 January 2003; accepted 2 January 2003 ABSTRACT: The anionic polymerization of lauryllactam was initiated at 270°C using sodium hydride as an initiator and N,N'-ethylene-bisstearamide (EBS) as an activator (NaH:EBS molar ratio of 2). Polymerization occurred in less than 2 min and was successfully performed in an internal mixer and a twin-screw extruder with corotating intermesh- ing screws (Werner & Pfleiderer ZSK 25). The content of residual monomer, as determined by thermogravimetric analysis, was lower than 0.5 wt %. Molecular weight, as measured by size exclusion chromatography, was governed by the lauryllactam:NaH molar ratio calculated on a M n of 25 kg/mol at a constant NaH:EBS molar ratio of 2. Blends were prepared in situ by polymerization of lauryllactam solutions of various polymers. When poly(ethylene-co-buty- lacrylate) (Lotryl  ; Atofina) was dissolved in lauryllactam, rubber-toughened polyamide 12 blends were obtained. Me- chanical properties of the injection-molded polymers were examined by stress–strain as well as notched Charpy impact tests at different temperatures. Blend morphologies were imaged by scanning electron microscopy (SEM). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 344 –351, 2003 Key words: reactive extrusion; anionic polymerization; polyamide 12; in situ blend formation INTRODUCTION Anionic polymerization of -caprolactam in the pres- ence of strong bases was first described in 1939 by Ritter and Joyce of Du Pont. 1 However, about 20 years later, in 1956, it was the mechanistic studies of Mottus and coworkers on the polymerization mechanism of anionic lactam polymerization that attracted consider- able attention in the literature and stimulated many groups to engage in research in this field. 2 The initia- tors of anionic lactam polymerization are the lacta- mate anions being formed by the reaction of a lactam with a strong base. Schwartz and Paul proposed the use of the alkaline and earth alkaline metals, especially sodium and potassium, and their oxides, hydroxides, hydrides, carbonates, and other reactive compounds of these metals, including organometallic reagents. 3 The disadvantage associated with using alkaline met- als as initiators is the formation of a considerable amount of amine in the reaction mixture. 4 According to the patent literature, the most favored initiator after ethyl magnesium bromide is sodium hydride because the only side product in the reaction with lactam is hydrogen, which can be readily removed from the reaction mixture. A very large number of activators were found in the literature reviewed by Sebenda 5 and Frunze. 6 A rough classification was made by distin- guishing between activators based on lactams carry- ing an electronegative polar substituent on the nitro- gen atom and activators producing such N-substi- tuted lactams in situ during polymerization. Very effective activation in the presence of N-acyl lactams such as N-acetyl and N-benzoyl caprolactam has been very well known for many years. 7,8 Examples of the second class of activating compounds are isocyanates and carbodiimides, which were first described in 1956, by Schnell and Fritz. 9 Because of the toxicity of the isocyanates, isocyanate derivates are often used. For example, the reaction between caprolactam and hexa- methylenediisocyanate affords hexamethylenedicar- bamoylcaprolactam, which is a very effective activator but much less toxic to the isocyanate. 10 –12 Examples of bifunctional activators using adipoyl-biscaprolacta- mat were described by Ueda 13 and employing isoph- talolyl biscaprolactamat by Udipi et al. 14 Activated anionic lactam polymerization proceeds sufficiently fast that it can be used in a reactive extru- sion process. In 1968 Illing wrote the first description of the polymerization of lactams in a corotating twin- screw extruder. He used twin-screw extruder ZSK 53 for manufacturing polyamides 6 and 12 with a molec- ular weight of 70,000 –100,000 g/mol at throughput rates of 27– 43 kg/h. 15 Recent studies of the anionic polymerization of ca- prolactam in a twin-screw extruder have been re- Correspondence to: R. Mu ¨ lhaupt (rolf.muelhaupt@makro. uni-freiburg.de). Journal of Applied Polymer Science, Vol. 90, 344 –351 (2003) © 2003 Wiley Periodicals, Inc.