Study of Copolymerization Acrylamide with Methyl Methacrylate

Received Date: Jan 09, 2020 / Accepted Date: Jan 23, 2020 / Published Date: Jan 24, 2020 Abstract Copolymer of acrylamide (AM) with methyl methacrylate (MMA) was synthesized by free radical technique using dimethylsulfoxide (DMSO) as solvent and benzoyl peroxide (BPO) as initiator. The overall conversion was kept low (≤ 15% wt/wt) for all studies copolymer’s samples. The synthesized copolymers were characterized using fourier transform infrared spectroscopy (FT-IR), and their thermal properties were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The copolymers compositions were determined by elemental analysis. The monomer reactivity ratios have been calculated by linearization methods proposed by Kelen-Tudos and Fineman-Ross. The derived reactivity ratios (r1, r2) for (AM-co-MMA) are: (0.03, 0.593). The microstructure of copolymers and sequence distribution of monomers in the copolymers were calculated by statistical method based on the average reactivity ratios and found that these values are in agreement with the derived reactivity ratios. Copolymers of AM with MMA formed alternating copolymers.


Introduction
The properties of polymers can be most effectively modified with the help of the technique of copolymerisation [1][2][3][4]. This technique is designed to manipulate the intraand inter-molecular forces that are exerted amongst similar and dissimilar polymer segments, engendering broad variation in properties like temperature of glass transition, melting point, solubility, permeability, dyeability, adhesion, elasticity and chemical reactivity. The basic explorations of structure property correlations and the variety of commercial and biological applications all attest to the fact that copolymerisation is highly useful [5]. A copolymer composition equation relies greatly on reactivity ratios, which not only indicate the relative reactivity of pairs of monomers, but also outline the elements making up the copolymers. To understand how its utility has developed, it is first necessary to understand the copolymer composition itself. As emphasised above, the reactivity ratios are essential for copolymer composition and the manner in which it is distributed. The empirical data regarding copolymer composition and monomer feed mixtures must be mathematically processed before the monomer reactivity ratios can be determined. The reactivity of various comonomers can be calculated via a range of techniques. Furthermore, different analytical methods have been proposed to find out how much of a comonomer has been included in the copolymer Page: 2 www.raftpubs.com [6]. New scientifically and commercially relevant materials can be obtained when two distinct monomers with various physical and or chemical attributes are incorporated in the same polymer molecule at different ratios. The monomer reactivity ratios of copolymerisation enable the determination of the relative reactivity of a monomer toward a specific polymer radical. A copolymers composition is a critical factor in the assessment of its uses. Controlling the polymer property parameters, for example, molecular weight averages, sequence distribution, and copolymer composition, which is a specific significance in the copolymerization forms [7]. To figure the rate of polymerization or polymer profitability and copolymer synthesis, monomer reactivity proportions must be known [8]. The technique which is utilized frequently recently for evaluating monomer reactivity ratios is to perform low conversion copolymerization at different starting monomer feed compositions. In this way, the copolymer composition is resolved for every reaction. Conventional techniques for evaluating monomer reactivity ratios depend on, first, changing the momentary copolymer composition equation into a frame that is straight in the parameters r1 and r2 and after that assessing the monomer reactivity ratios by graphical plotting or by the direct minimum squares technique. Linearization of the copolymer composition condition will contort the blunder dispersions related with the information [9][10][11]. The aim of this work is to copolymerize AM, a hydrophilic monomer with MMA, a hydrophobic monomer, and to study the best synthetic conditions and characterization of the copolymer. This study also determines the reactivity ratios of AM and MMA. From these parameters, a specific comonomer distribution is estimated.

Materials
The monomers, initiator, and solvents were obtained from Aldrich-oma chemical Co. The monomer AM was purified by recrystallization from methanol and dried in a vacuum. MMA was freed from the inhibitor by shaking with 10% W/V aqueous NaOH. After washing with water, it was vacuum distilled immediately prior to the copolymerization experiment. Initiator (benzoyl peroxide) was purified by twice recrystallizations from chloroform and refrigerated prior to use. Solvents were used as received.

Copolymerization
Copolymerization of (AM) with (MMA) was carried out using (10 ml) dimethylsulfoxide (DMSO) as solvent and (1×10 -3 mol dm -3 ) (BPO) as initiator. In quick fit test glass tubes, the prescribed amount of monomers, initiator and solvent were charged, and then put in water bath at (80 °C). As shown in table 1, the feed ratio was varied in a series of copolymerization of (AM) with (MMA) (AM-co-MMA) whilst the total molar composition of the monomer mixture was maintained at (1 mol dm -3 ). Before starting the reaction, Nitrogen gas was bubbled through the mixture for 10 minutes in order to remove all Oxygen. Low conversion (<15%) of copolymers was obtained by controlling the time of copolymerization. Petroleum ether (b.p. 40-60°C) was used to precipitate the obtained copolymers. All the copolymers were filtered off, dissolved again in dimethylsulfoxide and precipitated in petroleum ether prior to constant weight in vacuum at 40°C. In order to determine the copolymer compositions, samples of the copolymer (0.2 mg) were checked by elemental analysis. Scheme 1 shows the reaction of copolymerization (AM) with (MMA).
Page: 3 www.raftpubs.com Scheme 1: The process formation of AM-co-MMA from AM and MMA as monomers.

Characterization
Perken Elmer-1650 spectrometer was used to record FTIR spectra of the copolymers on KBr Pellets in the range 200-4000 cm -1 . Intrinsic viscosity [ŋ] was determined according to the Solomon Gotessman relationship [12] by using an Ostwald Viscometer with negligible kinetic energy correction. By following the variation of estimated nitrogen content arising from (AM) comonomers units, copolymer compositions were determined by elemental analysis. DSC-Mettler calorimetric system was employed to determine the glass transition temperature (Tg) whilst Perkin Elmer in a nitrogen atmosphere at a heating rate of 10 °C /min from 0 to 800 °C was used to study the thermal degradability of the copolymers.

Results and Discussion
The absorption bands which appear in the FTIR spectra of the copolymer Figure 1

Copolymer Composition
It is very useful to study the monomer reactivity in the copolymer system because the composition of the copolymer depends mainly on the monomer feed composition. In AM/MMA copolymers, composition of the monomer in the copolymer was assessed by assurance N % in the copolymers and this proportion indirectly gave the mole fraction of AM in the copolymer.  Figure 2 shows the plots of mole fraction of AM in the copolymer (F1) vs. that of mole fraction of MMA in the feed (f1).
In AM/MMA system, AM forms alternate copolymer with MMA ( Figure 2). Here, the presence of carbonyl and amide groups for each AM and MMA monomers units gave rise to a significant attraction of free electron in the double bond and generate a positive charge in the growing polymer chain and stabilization of the corresponding macroradical. Since both monomers are electron rich, it forms the bond easily with electron deficient species, thus they easily involved in polymerization. f1 is the mole fraction of monomer-1 (AM) in the initial feed; f2 = 1-f1 (b) F1 is the mole fraction of monomer-1 (AM) in the copolymer; F2 = 1-F1

Reactivity Ratio
The sort of copolymer framed can be best comprehended from the information of reactivity ratios of the copolymers. The most widely recognized scientific model of copolymerization depends on finding the connection between the composition of the monomer feed and the composition of copolymers in which the monomer reactivity ratios are the parameters to be resolved [13]. In our work two procedures have been used for the best fitting of (r1& r2) pair from a set of [M1],  [14,15] of these methods should be consulted for more details about the mathematical processes. The values are showed in figure 3 and figure 4, and represented in table 2.    Page: 6 www.raftpubs.com  Table 3 shows the values of reactivity ratios by different methods, the values (r1, r2) from the different methods are very close. It is easy to observe that (AM/MMA) copolymer has the r1r2 values less than unity demonstrating the alternation behavior of the monomers. The alternative behavior for the two monomers (AM and MMA) could be explained in terms of increasing the stabilization of their radicals by the carbonyl groups resonance. On the other hand, the value of r2 is slightly greater than r1 which lead to a greater incorporation of MMA units compared to AM units. In this case, the double bond of MMA appears to have slightly more positive charge due to the presence of carbonyl ester bond. The charge density generated on carbonyl carbon atom would favor a significant electron attraction in MA radicals, which creates a slightly more positive charge on the double bond. A similar behavior was observed in our earlier case [16] wherein acrylamide was copolymerized with 3-(Trimethoxysilyl) Propyl Methacrylate, which contained similar carbonyl ester bond attached to the double bond.

Study of Copolymerization
When the reactivity ratios of the two monomers are less than unity, the synthesized copolymer shows an alternating behavior. Each monomer prefers to react with other monomer more than itself [17]. The possibility of an azeotropic composition increases in case of r1, r2 are both > 1 and < 1. For (AM/MMA) copolymer system, this condition is fulfilled since r1 and r2 < 1. Figure 2 (copolymer composition curve) proves this fact, in which a value of 0.25 for f1 (az.) could be clearly observed. The azeotropic feed composition f1 (az.) can be expressed by the following equation: The results of reactivity ratios were then utilized for microstructural figuring.
The following equations were then used to calculate the probabilities of finding the sequence and the average length sequences of AM and MMA units [21,22]; the data are listed in Table 4.

Thermal properties
For (AM and MMA) homopolymers, Tg value observed around 155 °C and 90 °C respectively whereas AM/MMA-1 copolymer showed the Tg around 110 °C. It is found that by increasing the amount of AM content in the copolymers result in increased Tg, this may be due to the presence of rigid amide group in the backbone in AM side chain. TGA results are presented in Figure 5. The AM/MMA copolymer is more stable than the homopolymer of MMA with 10 % weight loss at about 350 °C of AM/MMA-1 which is higher than 100 °C of Poly (MMA). This result could be attributed to the presence of methyl group in the backbone in MMA side chain which significantly lowers the Tg value and the thermal stability of AM/MMA copolymer. Values of Tg and data of TGA are given in table 5.