Two-Step Emulsion Polymerization—Polycondensation Method for Synthesizing Polycaproamide at Low Temperature

Abstract

678.675:66 09The synthesis of fiber-forming polycaproamide by a two-step emulsion hydrolytic polymerizationpolycondensation method using as the solvent an organosilicon liquid at a temperature below the polymer melting point was investigated. The principal parameters of low-temperature caprolactam polymerization and emulsion polycondensation of the pre-polymer that provided high-molecular-weight polyamide-6 were determined.Polymer syntheses that are carried out in dispersions (emulsion polymerization and polycondensation) and enable the properties of the synthesized polymers to be intentionally regulated are widely employed on an industrial scale. Their principles were reviewed in several monographs [1][2][3][4]. It should be emphasized that the studied and implemented versions of heterophase synthesis are based on polymer production from unsaturated monomers (emulsion polymerization) or from monomers containing highly reactive functional groups (interphase polycondensation) in systems where the particle size of the dispersed phase varies from 10-500 nm up to 1-100 μm depending on the reaction conditions.The polycaproamide quality indicators and, as a result, the physicomechanical properties of the threads can be improved by low-temperature liquid-phase synthesis [5]. However, low-temperature synthesis involves production of polyamide-6 in plug-flow apparatuses in which the polymer molecular-weight distribution can vary because of stagnant zones and uneven temperatures in the melt bulk. Heat-and mass-exchange processes can be made as even as possible during polymerization of caprolactam (CL) in an emulsion [6,7]. Information on the use of synthesis principles in emulsions for producing polymers via polymerization of cyclic monomers has been reported in the literature [6,7].Emulsion polymerization by a single-step method at 210°C using H 2 O and AG salt as activators could produce in 24-42 h polycaproamide with polymerization degree (P) 160-170 and content of low-molecular-weight compounds (LMC) 11-13%, i.e., with characteristics far from the equilibrium values [7]. Also, a polymer with parameters allowing subsequent polycondensation in an emulsion, i.e., with P = 90 and LMC content 12%, could be produced in 12 h with an initial activator (H 2 O) content of 12%. However, it is noteworthy that the synthesis was carried out [7] under conditions where the volume of the gas phase could be neglected and practically all added H 2 O remained in the reaction mixture.In contrast with these conditions, the first step of liquid-phase synthesis in the present work (synthesis time 12 h, 210°C, at which the equilibrium product should be produced in approximately this time [8]) was carried out without a dispersant (organosilicon liquid PES-5). Part of the H 2 O transitioned from the reaction mixture into the gas phase, which occupied a significant part of the reactor volume. The resulting decrease of the melt water content necessitated a determination of the optimum activator amount.According to the results (Table 1), adding wat...

Influence of redox initiator component ratios on the emulsion copolymerisation of vinyl acetate and neodecanoic acid vinyl ester

“…25,26 Reducing the initiation temperature without altering the product contributes positively to process intensication and process safety. [27][28][29] For example, reducing the temperature can thereby result in a reduction of the production costs, since less heating of the reactor is required (which saves energy). Slowing down the conversion rate through process optimisation also reduces the risk of leakage when approaching the boiling point of the chemicals used, therefore increasing the safety of employees or workforce.…”