Complex-Radical Terpolymerization of Maleic Anhydride (Styrene), Allyl Propionate and Methyl Methacrylate

The radical terpolymerization reactions of the acceptor-donor-acceptor and donor-acceptor-donor systems, maleic anhydride (MA)-allyl propionate (AP)-methyl methacrylate (MMA) and styrene (St)-MMA-AP, had been studied. The terpolymerizations were carried out in methyl ethyl ketone at 60-75°C in the presence of 2,2’-azoisobutyronitrile (ABIN) used as the initiator. Some kinetic parameters and copolymerization constants for both, system were determined by dilatometric and Kelen-Tudos or Seiner-Lift methods. The obtained results are discussed in terms of the free monomer and complex chain growth models. It is shown that terpolymerization was carried out at a stage close to binary copolymerization of MA...AP complex with free MMA and St...MMA complex with AP in the both studied system, respectively. These systems are also used as model for interpretation of cyclocopolymerization mechanism in allyl methactylate-MA (or St) system. DTA and TGA analyses indicated the relatively high thermal stability of St-MMA-AP terpolymer. It is shown that this terpolymer decomposes through a one-step reaction at 310°C, however MA-AP-MMA terpolymer decomposes through a multi-step reactions at 150, 260 and 310°C. Eurasian ChemTech Journal 2 (2000) 137-147  2000 al-Farabi Kazakh St.Nat. University *corresponding author. E-mail: zakir@curie.chem.metu.edu.tr Introduction Ternary monomer systems in terms of the conjugation type in monomer molecule and the mechanism of chain growth can be classified by following groups: ( a) donor (D1)-donor (D2)-donor (D3), (b) acceptor (A1)-acceptor (A2)-acceptor (A3), (c) donor (D1)-acceptor (A)-donor (D2) and (d) acceptor (A1)donor (D)-acceptor (A 2). Complex-formation not take placed in the (a) and (b) systems monomers of which have similar type of double bound conjugation. Therefore reaction submited to usual equations of random copolymerization and differed by complexity in term of the «controlling» by radical reactions of chain growth. However, ( c) and (d) monomer systems comprised donor-acceptor monomers which can be presented by two D...A 1 and D...A2 complexes for (c) system and A...D1 and A...D2 complexes for (d) system in propagation reactions. Number of elementary chain growth reactions in these ternary systems depended on complex formation and homopolymerization properties of comonomers in given terpolymerization conditions. Ternary monomer systems containing maleic acid derivatives as electron-acceptor monomers and vinyl monomers as electron-donor monomers differ from other multi-component monomer systems in that radical terpolymerization occurs via both free and complexed monomers; the kinetics of these systems can be regarded a copolymerization of two complexomers [1-8]. In several publications some attention has been focused on the study of monomer charge transfer complexes (CTC) effect in radical terpolymerization by using following donor-acceptor ternary systems: maleic anhydride(MA)-styrene(St)-methacrylates [9], MA-St (or trans-stilbene)-N-phenylmaleimide [10,11], MA-St-citraconic anhydride [12], MA-St-vinylacetate [13], MA-trans-stilbene-phenanthrene [11,14], MAallyl-glycigyl ether-methyl methacrylate [15] and other systems containing MA [5,11]. Similar effects were observed in radical copolymerization of bifunctional monomers (allylcinnamate, monoallylmaleate, Nallylmaleimides, allylmethacrylate and etc.) with MA or St which can by also considered as ternary systems containing three donor-acceptor type double bounds [16-20]. The results of these studies were allowed to discover new aspects of the complex-radical copolymerization mechanism and to synthesize the


Introduction
Ternary monomer systems in terms of the conjugation type in monomer molecule and the mechanism of chain growth can be classified by following groups: (a) donor (D 1 )-donor (D 2 )-donor (D 3 ), (b) acceptor (A 1 )-acceptor (A 2 )-acceptor (A 3 ), (c) donor (D 1 )-acceptor (A)-donor (D 2 ) and (d) acceptor (A 1 )donor (D)-acceptor (A 2 ). Complex-formation not take placed in the (a) and (b) systems monomers of which have similar type of double bound conjugation. Therefore reaction submited to usual equations of random copolymerization and differed by complexity in term of the «controlling» by radical reactions of chain growth. However, (c) and (d) monomer systems comprised donor-acceptor monomers which can be presented by two D...A 1 and D...A 2 complexes for (c) system and A...D 1 and A...D 2 complexes for (d) system in propagation reactions. Number of elementary chain growth reactions in these ternary systems depended on complex formation and homopolymerization properties of comonomers in given terpolymerization conditions. Ternary monomer systems containing maleic acid derivatives as electron-acceptor monomers and vinyl monomers as electron-donor monomers differ from other multi-component monomer systems in that radical terpolymerization occurs via both free and complexed monomers; the kinetics of these systems can be regarded a copolymerization of two complexomers [1][2][3][4][5][6][7][8].
The objective of present work is to elucidate some regularities of radical terpolymerization of two new A 1 -D-A 2 and D 1 -A-D 2 systems, MA-allyl propionate (AP)-methyl methacrylate (MMA) and St-MMA-AP, and binary copolymerization of MA with AP as well as to use the results obtained for interpretation of mechanism of radical copolymerization of bifunctional monomer such as allyl methacrylate (AMA)with MA and St.

Copolymerization
Reactions were carried out in degassed glass tubes or dilatometers at 60-75°C in methylethylketone (MEK) under nitrogen atmosphere in the presence of ABN as a initiator. After the reaction for a given time, the reaction mixtures prepared were poured into a large amount of n-hexane to precipitate the copolymer and the powder-like product obtained was purified by multiple washing in n-hexane and in diethyl ether, and was dried under vacuum at 40°C to constant weight. Terpolymers were characterized by nonaqueous potentiometric titration of the free anhydride group in side chain (for MA-AP-MMA terpolymer), by elemental analysis and by FTIR spectroscopy. Composition of terpolymers was also determined by chromatographic analysis of reaction mixture before and after copolymerization for a given time.

Measurements
Fourier transformation IR spectra were recorded with FTIR Nicolet 510 spectrometer in the 4000-400 cm -1 range where 30 scans are taken at 4 cm -1 resolution. 1 H-NMR. specrta were taken with a AC-80 Broker spectrometer with tetramethylsilan as internal standart and deutered acetone as solvent at 35 ± 0.1°C. For the determination of charge transfer complex (CTC) formation constant (K c ), the 1 H-NMR method [21] was used.
Copolymerization constants ( r 1 , r 2 , r 1c , r 1c1 and r 1c2 ) are determined by Kelen-Tüdöº [22] and Seiner-Litt [23] methods. Contents of AP and MMA monomers were found by chromatographic analysis (CHROM-5) of monomer mixture before and after reaction at low convention of ≤ 15 %; conditions of analysis: column temperature 200°C, evaporator temperature 300°C, absorbent -10 % Apiezon on Celite-545, internal standard -chlorobenzene, carrier gashighly purified helium. The yield and composition of the copolymer were found from the quantities of unreacted AP and MMA.
Differential thermal (DTA) and thermogravimetric (TGA) analyses were carried out with a Paulik-Erday derivatograph in air at a heating rate of 5°C /min.

Charge Transfer Complex Formation
From the donor-acceptor properties of monomers for ternary systems studied, one can predict that the formation of equimolecular (1 : 1) CTC's as follows: Equilibrium constants of 1:1 mixtures (K c ) between MA as acceptor monomers and AP as donor monomer were determined using "H-NMR spectral data and the well known Hanna-Ashbaugh equation [21]: where ∆ exp is the difference between the chemical shifts (free and complexed) of MA protons, ∆ c is the chemical shift of MA protons in the MA/AP mixtures, K c is the equilibrium constant of a 1:1 complex, [D] is the concentration of AP monomer. The concentration of the acceptor monomer (MA) was kept constant at 0.1 mol/L while that of the donor was varied. The change chemical shift for anhydride protons (δ f == 6.95 ppm) with excess of donor monomers (∆ exp = δ fδ c ) allows determination of K c from the relationship of 1/∆ exp → [D] (Fig. 1). The K c obtained for MA...AP complex is 0.14 ± 0.01 L/mol. For identification of St…MMA complex known K c value for St…AMA (allyl methacrylate) [25] complex was used (K c = 0.22 ± 0.02 L/mol).

Terpolymerization Free monomer propagation mechanism
In generaly, there are nine types of possible growth reactions that determine the composition of a ternary copolymer product [25]. Consumption rates of monomers are expressed by the following equations: The relative terpolymer composition can be derived from the ratio of Eq. (7) to Eq. (8): For the stationary state, we have: The experimental data on the terpolymerization of both systems are presented in Table 1. It follows from these results that a change made in the content of monomers within a wide range in the initial monomer mixture, low affects the m 1 /m 2 ratio in both terpolymers.
From the data of Table 1    for the condition of k 1c = k 1c1 + k 1c2 , K c is CTC formation constant.
The reactivity ratios of monomers and complexomers of both systems studied were calculated by using of data of Table 2 and 3 and by means of the known equations (33) and (34). In Table 4 are summarized the values of the apparent reactivity ratios for the monomer systems studied. From the values of copolymerization constants it follows that alternating copolymerization reactions occur mainly in the MA-AP, MA-AMA [20] and St-AMA [22] systems.
For the St-MMA -AP system   Table 3 Experimental data used for determination of copolymerization constants for MA(M 1 )-AP(M 2 ) and MMA(M 1 )-AP(M 2 ) monomer pairs. Reaction conditions as in Table 1.
* Calculated for alternating copolymer with 1 : 1 composition: AN 495.9 mg KOH/g. ** Compositions of MMA-AP copolymer are calculated by using of chromatographical analysis data of monomer mixtures before and after reaction.  The reactivity ratios of MA and AP pair also were calculated by means of the Seiner-Litt equation (34). From the plot of (y-1) vs. χ (Fig 3) were determined following values of the apparent reactivity ratios: r 1c =0.025, r 1c1 =0.49 and r 1c2 =0.51. These values obtained by taking into consideration the K c on the relative activity of the monomers, confirm the fact that chain growth proceeds primary by addition of MA...AP complex to growing macroradicals.
In the MA-AP-MMA and St-MMA-AP ternary systems studied, binary copolymerization reactions realize in result of which terpolymers formed primary contain m 1 and m 2 units with ratios near to 1 : 1. This fact observed also is confirmed the effect of complexformation in ternary copolymerization reactions. In Table 4 are summarized the values of copolymerization constants for MA...AP-MMA and St…MMA-AP pairs. It follows from these values in the St-MMA-AP system as compared with MA-AP-MMA system that near to an alternating terpolymerization reaction occurs.
bifunctional monomer AMA with MA (R p = 0.18.1 -5 mol/L×s) and with St (R p = 0.11.10 -5 mol/L×s), is more than copolymerization rate of ternary systems studied (Fig. 5b). This fact observed allows one to conclude that the allyl and methacryl double bounds show high reactivity when they are belonged to the same monomer (AMA) as compared with ternary systems in which these double bounds belonges to different monomers (AP and MMA).
Using the kinetic data of terpolymerization of both ternary systems studied (Fig.6a) with constant concentrations of monomers and initiator at different temperatures (60-75°C) as well as data of Arrhenius plots for copolymerizations of AMA with MA and St (Fig.6b) -FTIR spectra of AP monomer, MA-AP-MMA and St-MMA-AP terpolymers synthesized are illustrated in Fig. 4. A comparative analysis of monomer and terpolymers spectra revealed that the characteristic bands for C=C (1680-1630 cm -1 ) and allyl group (3100-3030, 990 cm -1 ) of AP are disappeared by the transfer from monomer form to terpolymer molecule. The changes observed as well as the presence of characteristic bands for anhydride, phenyl and ester groups allow qualitatively to identify of terpolymer compositions.
As evidence from the kinetic data (Fig. 5a) the copolymerization rate of MA-AP-MMA at 0.8-2.45 mol/L total monomer concentration is more than the rate of St-MMA-AP system: R p are 0.43-1.07.10 -6 mol/L×s and 0.2-0.71.10 -6 mol/L×s for two ternary systems, respectively. On the other hand, the copolymerization rate of model systems, reaction of MMA-AP ternary systems, respectively; 68.7 and 62.4 kJ/mol for AMA-MA and AMA-St monomer pairs, respectively. The comparative low values of E a for binary systems can be explained by changes of mechanism of chain growth and initiation reactions with participation of CTC's in the cyclic and linear chain growth reactions leading to energetically advantageous position. These values also indicate that allyl degradative chain transfer does not take part in binary and ternary systems studied because of complex formation.

Thermal Stability of Terpolymers
Thermostability of terpolymers synthesized is studied by thermogravimetric (TGA) and differential ther-  mal (DTA) analysis methods. These analyses were carried out in air from ambient temperature up to 500°C. The results obtained are illustrated in Fig. 7. These data show that St-MMA-AP terpolymer with composition of m 1 : m 2 : m 3 = 35.8 : 38.3 : 25.9 preparing at initial monomer ratio of 1 : 2 : 1 have higher thermal stability (curve 1) than the MA-AP-MMA terpolymer preparing in the analogous conditions. The weight loss till 200°C is 5.2 %, but at 300°C it is equal to 10.5 %. The degradation point (beginning of degradation) of St-MMA-AP terpolymer is 295°C, and it loses almost 50 % of its weight at 350°C. From character of TGA curve of St-MMA-AP terpolymer it is evident that terpolymer decomposes through a one-step reaction at 310°C.
MA-AP-MMA terpolymer with composition of 45.5 : 47.8 : 6.7 shows relatively low thermal stability. The weight loss begin from 140°C and at 250°C it is equal to more 50 %. Unlike St-containing terpolymer this terpolymer decomposes through a multi-step reactions at 150, 260 and 310°C, respectively (curve 2) which can be explained by degradation processes of macromolecules associated with decarboxylation, breaking of methacrylic fragments and side-chain groups as well as chain cleavage.