Multi-site phase transfer catalyzed radical polymerization of methyl methacrylate in mixed aqueous–organic medium: a kinetic study

Int J Ind Chem DOI 10.1007/s40090-017-0125-0 RESEARCH Multi-site phase transfer catalyzed radical polymerization of methyl methacrylate in mixed aqueous–organic medium: a kinetic study Vajjiravel Murugesan1 • Elumalai Marimuthu1 • K. S. Yoganand2 • M. J. Umapathy2 Received: 28 December 2015 / Accepted: 12 June 2017 Ó The Author(s) 2017. This article is an open access publication Abstract This work establishes the kinetics of radical polymerization of methyl methacrylate in an aqueous–organic two-phase system using 1,4-bis (triethylmethylammonium) benzene dichloride (TEMABDC) as multi-site phase transfer catalyst and potassium peroxydisulphate (K2S2O8) as water-soluble initiator at 60 ± 1 °C under nitrogen atmosphere. The role of concentrations of monomer, initiator, catalyst, acid and ionic strength, temperature and volume fraction of aqueous phase on the rate of polymerization (Rp) was investigated. The rate of polymerization (Rp); Rp a [MMA]0.64, [TEMABDC]1.24 and [K2S2O8]1.50. The rate of polymerization increases with an increase in the concentration of monomer, initiator, catalyst and temperature. A generalized reaction model was developed to explain the phase transfer catalyzed polymerization reaction. Based on the kinetic results, radical mechanism has been derived. The activation energy and other thermodynamic parameters were calculated. The FTIR spectroscopy validates a band of 1732 cm-1 of ester group of the obtained polymer. The viscosity average molecular weight of the PMMA was found 1.6955 9 104 g/mol. Keywords Kinetics  Multi-site phase transfer catalyst  Radical polymerization  Rate of polymerization  Aqueous–organic media & Vajjiravel Murugesan 1 Department of Chemistry, B S Abdur Rahman Crescent University, Vandalur, Chennai 600 048, India 2 Department of Chemistry, College of Engineering, Anna University, Chennai 600 025, India Introduction Phase transfer catalysis (PTC) is presently a well mature and established technique to accelerate the reactions between mutually insoluble two or more reactants located in different phases. In this technique, the two mutually insoluble reactants, one being an organic liquid or substrate dissolved in an organic solvent and other being an organic or inorganic salt from a solid or aqueous phase, react with the help of a phase transfer catalyst. It has been applied over 600 processes in variety of industries such as intermediates, dyestuffs, agrochemicals, perfumes, flavors, pharmaceuticals and polymers and value exceeds twelve billion (US$) per year [1–4]. In polymer chemistry, they have been employed in synthesis of polymers [5–7], condensation polymerization [8], anionic polymerization [9, 10] and free radical polymerization [11–18]. In order to get the maximum desired product in a short duration of reaction period, the catalyst should be more efficient; with the aim of these requirements, novel ‘‘multisite phase transfer catalysts’’ (multi-site PTC) have been developed which contain more than one catalytic active site per molecule. The concept of multi-sited phase transfer catalyst was introduced by Idoux et al. in which they have synthesized phosphonium and quaternary onium ions containing more than one active site per molecule [19]. The benefits of multi-site PTC are: enhance the rate of reaction with less time consumption and it transfers more number of active species from aqueous phase to organic phase during the reactions in contrast with single site—PTC. The reports on multi-site phase transfer catalyst aided radical polymerization of different alkyl methacrylates were gradually blooming in recent years [20–26]. The acrylic esters especially methyl methacrylate (MMA) are commercially fascinating and significant functional monomer for the 123 Int J Ind Chem synthesis of acrylic resins and various polymers based on poly(methyl methacrylate) (PMMA) with tunable properties. PMMA has good mechanical strength, acceptable chemical resistance and extremely good weather resistance. Further, it has favorable processing properties, good thermoforming and can be modified with pigments, flame retardant and UV absorbent additives [27, 28]. PMMA has vast profound and diverse applications that influence our lives every day. Radical polymerization is one of the best processes for the synthesis of polymers and the few important merits of radical polymerization are: it can be applied to all vinyl monomers under mild reaction condition with a wide range of temperature, it is water tolerant and its cost is relatively low. A curiosity on free radical polymerization has been stimulated to a great extent by the impressive progress made in several methods such as atom transfer radical polymerization (ATRP), nitroxyl radical-mediated polymerization (NMP), and reversible addition fragmentation transfer polymerization (RAFT). These methods and approaches were successfully introduced into polymerization process by different research groups [29–33]. Polymerization of MMA was effectively performed in ATRP [34, 35], NMP [36] and RAFT [37, 38]. The growth of a new kinetic model for the polymerization of methyl methacrylate (MMA) using novel catalyst and different methods at moderate temperature will be one of the major progresses in an industrial perspective. The design, synthesis of novel catalysts and its applications in polymerization and organic reactions are a vital focus in the current research. Inspired by inherent characteristics of PTC technique and considering merits of watersoluble initiator, the present work endeavours to conduct a systematic investigation and explore the kinetics of free radical polymerization of methyl methacrylate (MMA) using potassium peroxydisulphate (PDS) as water-soluble initiator in the presence of synthesized multi-site phase transfer catalyst in cyclohexane/water two-phase system at 60 ± 1 °C. The role of various reaction variables on the rate of polymerization was studied, including the concentration of monomer, initiator, catalyst and temperature, aqueous phase variation. An extraction reaction model was proposed to explain the polymerization pathways and its significance was discussed. Experimental Chemicals and solvents Methyl methacrylate (MMA, Sigma Aldrich, India) was first washed with 5% of aqueous sodium hydroxide to remove the inhibitor and washed with water to remove the 123 alkali and then dried over anhydrous calcium chloride at last distilled under reduced pressure. The middle fraction of the distillate was collected and stored in dark brown bottle at 5 °C in the refrigerator. The initiator, potassium peroxydisulphate (K2S2O8, Merck, India), was purified twice by recrystallization in cold water. The solvents, cylclohexanone, cyclohexane, ethyl acetate, benzene and methanol (Avra, Merck, SRL, India) were used as received. The double distilled water was used to make an aqueous phase. The 1,4-bis (triethylmethylammonium) benzene dichloride (TEMABDC) was synthesized by ado (...truncated)