Post-Polymerization Heat Effect in the Production of Polyamide 6 by Bulk Quasiliving Anionic Ring-Opening Polymerization of ε-Caprolactam with Industrial Components: A Green Processing Technique

Zsófia Osváth,Anita Szőke,Szabolcs Pásztor,Györgyi Szarka,Béla Iván,László Balázs Závoczki

doi:10.3390/pr8070856

Abstract

Bulk, solventless anionic ring-opening polymerization (AROP) of ε-caprolactam (CPL) with high yields, without side products and with short reaction times, initiated by caprolactamate-carbamoylcaprolactam initiating systems belong to green polymerization processes, leading to poly(ε-caprolactam) (Polyamide 6, PA6, Nylon 6). However, the effect of post-polymerization heat (i.e., slow, technically feasible cooling) on the fundamental characteristics of the resulting polymers such as yield and molecular weight distributions (MWDs) have not been revealed thus far. Significant post-polymerization effect was found by us in terms of both monomer conversions and MWDs by carrying out CPL polymerization with industrial components under conditions mimicking thermoplastic reaction transfer molding (T-RTM). Remarkably, higher monomer conversions and molecular weights (MWs) were obtained for Polyamide 6 samples prepared without quenching than that for the quenched polymers at the same reaction times. Independent of quenching or non-quenching, Mn of the resulting polymers as a function of conversion fell in the theoretical line of quasiliving AROP of CPL. At high monomer conversions, significant increase of the MW and broadening of the MWDs occurred, indicating pronounced chain–chain coupling. These findings have fundamental importance for designing processing conditions for in situ polymerization processes of ε-caprolactam by various techniques such as T-RTM, reaction injection molding (RIM), and other processing methods of Polyamide 6.

Highlights

According to the major requirements of green chemical processes [1], the most efficient green techniques do not use solvents and reach quantitative conversions without by-products, aside from minimal energy consumption
It is widely accepted that the anionic ring-opening polymerization (AROP) of ε-caprolactam (CPL) initiated by the industrially used sodium caprolactamate initiator in conjunction with carbamoylcaprolactam (CCPL) activators proceeds via rapid ring-opening and insertion of the caprolactamate in the CCPL, as shown in Scheme 1
In the absence of chain breaking side reactions until the monomer is present, repeating this process yields Polyamide 6 with well-defined average molecular weights determined by the ratio2018, of monomer toREVIEW

Summary

Introduction

According to the major requirements of green chemical processes [1], the most efficient green techniques do not use solvents and reach quantitative conversions without by-products, aside from minimal energy consumption. Processes 2020, 8, 856 ε-caprolactam (CPL) to prepare poly(ε-caprolactam) (PCPL, Polyamide 6, PA6, Nylon 6) can be a green industrial process This can be carried out without any side products and with nearly quantitative yields [7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Is the process is “green”, but the monomer, CPL, can be obtained from renewable resources [21,22,23,24] and the product (Polyamide 6) can be recycled either by physical processes or chemically (via depolymerization) to regenerate the ε-caprolactam starting material [25,26,27]. Since the discovery of synthetic polyamides nine decades ago [28], these aspects make Polyamide 6 an attractive material among this class of polymers both for academia and industry, generating continuous interest and intensive research and developments

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Results

Conclusion