Styrene-methacrylic anhydride copolymers

Styrene-Methyl Methacrylate Copolymers Derived from Styrene-Methacrylic Anhydride Copolymers... 

Mathematical procedures for calculating structural features of cyclocopolymers and of copolymers derived from them are proposed and are used in studies on the 1H-NMR spectra of styrene-methyl methacrylate copolymers derived from styrene-(methacrylic anhydride) copolymers. Reactivity ratios and cycliza-tion constants for styrene-methacrylic anhydride copolymerization were determined from structural features of the derived styrene-methyl methacrylate copolymers. The amount of uncyclized methacrylic anhydride units present in styrene-methacrylic anhydride copolymers having high styrene contents is considerably less than that predicted by these copolymerization parameters. The methoxy proton resonances of the derived copolymers are more intense in the highest field methoxy proton resonance area than would be expected if such resonance were due only to cosyndiotactic SMS triads. Possible explanations for these discrepancies are proposed. 

Studies on the properties of the derived copolymers can thus be helpful in understanding structure-property relationships of copolymers. Furthermore, since nuclear magnetic resonance can be used to characterize the structures of S-MMA copolymers ( 7,8), structural studies on the derived copolymers can provide information about cyclocopolymerization processes. For these reasons, we have developed a procedure for converting styrene-methacrylic anhydride copolymers into styrene-methyl methacrylate copolymers, have developed methods for calculating structural aspects of the derived S-MMA copolymers and, have investigated the 1H-NMR spectra of S/MMA copolymers derived from styrene-methacrylic anhydride copolymers. 

In the present study, this information was obtained primarily from structural studies on S/MMA copolymers derived from styrene-methacrylic anhydride copolymers. A computer oriented procedure was used to analyze the data and this made it unnecessary to employ simplifying assumptions. 

Hydrolysis of styrene-methacrylic anhydride copolymers. One gram samples of the copolymers were suspended in distilled water (150 ml.) and the mixtures were refluxed, with stirring, until solutions were obtained that were stable at room temperature. Copolymers with high styrene contents hydrolyzed slowly and required 108 hr. reaction times. These polymers formed soap-like solutions when completely hydrolyzed. The hydrolyzed polymers were isolated by freeze-drying and were examined by infrared spectroscopy to establish the completeness of hydrolysis. 

Figure 1. Olefinic proton resonances of styrene-methacrylic anhydride copolymers containing both uncycttzed methacrylic anhydride units and absorbed monomer (top), and uncyclized methacrylic anhydride units but little absorbed monomer (bottom). This sample was prepared by reacting a styrene-methacrylic acid copolymer with methacrylic anhydride.

H-NMR studies. Varian A-60 and HR-100 NMR spectrometers were used to measure the 1H-NMR spectra of styrene-methacrylic anhydride copolymers in DMSO-dg solution at 90° and of the derived styrene-methyl methacrylate copolymers in CCli, and C6D6 solution at 75-80°C. Solvent resonances interfered with composition determinations in the case of styrene-methacrylic anhydride copolymers, but the ratio of uncyclized methacrylic anhydride to styrene units (X) could be measured from the relative intensities of resonances observed at 6=5.72 and 6.15 ppm (olefinic protons) and at 6.5-7.5 ppm (aromatic protons). The compositions of the derived styrene/-MMA copolymers were calculated from the proportion of aromatic proton resonance observed in the spectra of copolymers dissolved in CClm as was described previously (6). Letting Y represent the ratio of styrene to MMA units in the derived copolymers, the compositions of the parent styrene-methacrylic anhydride copolymers were calculated as follows ... 

Table I lists compositions determined this way for styrene-methacrylic anhydride copolymers prepared at 40°.

Compositions of Styrene-Methacrylic Anhydride Copolymers Prepared at 40°... 

B - 6 2.7-3.2 ppm and C - 6 = 2.2-2.7 ppm). Figure 2 compares the aliphatic proton resonance patterns of styrene-MMA copolymers prepared by direct polymerization and by modification of styrene-methacrylic anhydride copolymers. The methoxy and a-methyl proton resonance patterns of the copolymers differ considerably even though they have similar compositions. The proportions of MeO resonance occurring in the A- and B- areas (FAi Fg) were calculated by dividing the A- and B- resonance areas by the total MeO resonance area expected, based on the compositons of the copolymers (i.e., MeO resonance area expected = 3/8 x % MMA/100). The proportion of MeO resonance occurring in the C- area was calculated by subtracting these quantities from one (Fq = 1 - Fa - Fg). 

Figure 2. Aliphatic proton resonance (100 MHz) of styrene-methyl methacrylate copolymers in CeD9 solution at 80°C containing 49 mol % of styrene derived from a styrene-methacrylic anhydride copolymer (top), and containing 56 mol % styrene prepared directly from styrene and methyl...

Following methods reviewed previously (16), these transition probabilities can be used to calculate the compositions of styrene-methacrylic anhydride copolymers. Thus, the method of Price (17) yields the following results, where P(S), P(A) and P(B) represent the relative concentrations of the following groups. 

Knowing these relative concentrations and transition probabilities, probabilities for various sequences of S, A and B entities present in styrene-methacrylic anhydride copolymers can be calculated in the usual way, viz.,... 

The results of such calculations need to be "translated to obtain the relative concentrations of styrene units, Fs, cyclized metha-crylic anhydride units, Fc, and uncyclized methacrylic anhydride units, Fu, present In styrene-methacrylic anhydride copolymers. 

Since A- and B- entities can both become MMA-units in the derived copolymers, the calculation of sequence probabilities is more difficult than for the case of styrene-methacrylic anhydride copolymers there are often many combinations of A-, B- and S- entities that can yield a given sequence of styrene and MMA units. For example, an MMM triad can result from the following sequences ... 

In many samples, no resonances due to uncyclized anhydride units were detected. This was particularly true of copolymers with high styrene contents. Table I lists the compositions determined for styrene-methacrylic anhydride copolymers prepared at 40°. The styrene contents of the copolymers are in good agreement with those reported by Smets, et al., for copolymers prepared from comparable monomer ratios, but where the anhydride concentration was 2M. However, Smets, et al. report that 30-50 percent of the anhydride units were uncyclized in their copolymers and it appears that the extent of cyclization is better than 90 percent, generally about... 

Smets, et al. (12) noted that the compositions of styrene-methacrylic anhydride copolymers prepared from given styrene-methacrylic anhydride mixtures were independent of the amount of solvent present in the system and concluded that ri and r3 in the kinetic scheme outlined above must be equal. This conclusion, which was also accepted by Baines and Bevington (13), enabled reactivity ratios for this copolymerization system to be calculated by use of the standard copolymer equation. Unfortunately, this is not a valid conclusion the results in Table II show that for conditions similar to those employed in the previous work, the styrene contents of the copolymers are imperceptibly affected by dilution of the system, even when r3 is five times greater or less than ri. 

Due to the difficulty of working with styrene-methacrylic anhydride copolymers, we have elected to determine reactivity ratios and cyclization constants from the compositions and structures of styrene-MMA copolymers derived from these copolymers. As is discussed in the experimental section it is possible to measure the styrene contents and the proportions of methoxy proton resonance occurring in three different areas (designated A, B and C) from the 1H-NMR spectra of S/MMA copolymers. The proportions of methoxy proton resonance observed in the A (F ), B (Fjj) and C (Fc) areas obey the following relationships in conventional styrene-MMA copolymers (6 7). 

Figure 3. Mole fraction of styrene units in styrene-methyl methacrylate copolymers %S (S/MMA) derived from styrene-methacrylic anhydride copolymers, as a function of the molar percentage of styrene (% S,) in the monomer mixture used to prepare the styrene-methacrylic anhydride copolymers. The solid line was calculated using rt = r, = 0.19, r, = 0.11, rc = 37 and rc = 7.7. Key O, 60°C polymerization and , 40°C polymerization.

Figure 4. HR-Plots of methoxy proton resonance data for styrene-methyl methacrylate copolymers derived from styrene-methacrylic anhydride copolymers prepared at 60°C. Key O, (FA-P(MMM))/P(SMS) vs. P(SMM + MMS)/P(SMS) V, Fb/P(CMS) vs. P(SMM + MMS)fP(SMS) , F /P(SMS) vs. P(SMM +...

Should the resonance of such protons occur in the C-area, the apparent observation of (SMM+MMS) resonance in this area in the present study, might be explained. Thus, the concentration of such structures can be expected to be higher in S/MMA copolymers derived from styrene-methacrylic anhydride copolymers than in conventional S/MMA copolymers. 

The reactivity ratios for styrene-aryl methacrylate copolymerizations [79 — 27] differ significantly from those for the styrene-MMA system, so that copolymers derived from the aryl methacrylate copolymers should have different structures (sequence distributions) than conventional styrene-MMA copolymers of equivalent composition. In the system used to prepare styrene-methacrylic acid copolymers [75], the monomer reactivity ratios are comparable to those of the styrene-MMA system, but the stereochemical structure of the conventional copolymers and of those derived from the methacrylic acid copolymers might be expected to differ. In addition, change of the copolymerization solvent can alter the reactivity ratios for the styrene-methacrylic acid system. Finally, styrene-MMA copolymers derived from styrene-methacrylic anhydride copolymers [22] were expected to have especially interesting structures. The tendency of the anhydride units to become incorporated into the copolymers as cyclic units is very high and there is a great tendency for styrene and cyclic anhydride units in the co-... 

Fig. 9. 60 MHz NMR spectra of styrene-methyl methacrylate copolymers derived from styrene methacrylic anhydride copolymers [22]. The parent copolymers were obtained from monomer mixtures containing 86 (A), 78 (B), 73 (C), 64 (D) and 60 (E) mole percent styrene...

The methoxy resonance patterns observed for derived styrene-MMA copolymers in aromatic solvents correlate reasonably well with calculated pentad distributions according to the assignments given in Table 1, provided the content of SSMSS and (SSMSM + MSMSS) pentads is low. However, the spectra of 50/50 styrene-MMA copolymers derived from styrene-methacrylic anhydride copolymers show appreciable resonance in the C area, and this not consistent with the pentad assignments given. 

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