Styrene-MMA copolymers

Bamford and Mullik [62] have succeeded in photografting a vinyl monomer onto a styrene-MMA copolymer using the Mn2(CO)io/C2F4 photoinitiating system in acetic acid. The following scheme was reported for this process ... 

The reactions were carried out in dilute homogeneous solution in dipolar aprotic solvents ([ester]g=0.2-0.4 mole.l- ) using stereoregular (pure I or S) or predominantly syndiotactic radical (R) PMMA, polymethylacrylate (PMA) and radical azeotropic styrene-MMA copolymer (PSMMA, MMA mole.fraction = 0.47) as well as model monomeric (methylpivalate) and dimeric (dimethylglutarate) compounds. The overall reaction is outlined in the simplified scheme ... 

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 ... 

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). 

Of special interest to the present study is the calculation of the compositions and sequence distributions of styrene-MMA copolymers derived from styrene-methacrylic anhydride copolymers. 

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). 

These equations are similar to those assumed for the reactivity ratio determination. In contrast to what has been observed for conventional styrene-MMA copolymers, however, these equations indicate that a substantial proportion of the (SMM+MMS)-type resonance appears to occur in the C-area. The proportion of methoxy resonance observed in the C-area, in fact, exceeds P(SMS) by a substantial amount for many of the copolymers. This can be due to the assumption of an inadequate model for the copolymerization reaction, to the use of incorrect reactivity ratios and cyclization constants for the calculations or to an inadequate understanding of the methoxy proton resonance patterns of S/MMA copolymers. It is possible that intramolecular reactions between propagating radicals and uncyclized methacrylic anhydride units present on propagating chains result in the formation of macrocycles. Failure to account for the formation of macrocycles would result in overestimation of rc and rc and in underestimation of the proportions of MMA units in SMS triads in the derived S./MMA copolymers. This might account for the results obtained. An alternate possibility is that a high proportion (>50%) of the M-M placements in the copolymers studied in this work can be expected to have meso placements (], J2), whereas only a small proportion of such placements ( 20%) are meso in conventional S/MMA copolymers. Studies with molecular models (20) have indicated that the methoxy protons on MMA units centered in structures such as the following can experience appreciable shielding by next nearest styrene units. 

The GPC curves of the products were, with the exception of the polysiloxane-polyMMA block copolymer, all multimodal, and their Mn values, measured by GPC, were approximately 4x those calculated by NMR analysis, assuming one polysiloxane segment per molecule. This indicates that the copolymers containing statistical styrene-MMA copolymer segments had multiblock structures similar to those of copolymers with polystyrene segments. 

Bovey [77] suggested that the methoxy resonance patterns of styrene-MMA copolymers could be explained if all MIvIM type resonance occurred in the A area, if (SmM + MMS) type resonance occurred essentially equally in the A and B areas and if SMS type resonance occurred in all three areas, according to the ratio 30 50 20 for the A, B and C areas, respectively. Assuming that the resonance observed in a given area is due to contributions from methoxy protons... 

Although much evidence has been presented in support of the Ito-Yamashita interpretation, several things cause us to be cautious about accepting it. First of all, the a value (0.5) obtained for S — M placements in styrene-MMA copolymers is much larger than the corresponding values estimated for M —M (0.2) and S — S (0.3) placements in polyMMA and polystyrene. Secondly, our work indicates that y" values for some copolymer systems are definitely not zero, especially when the spectra are obtained from copolymers in aromatic solvents. In addition, I-Y plots of methoxy resonance patterns recorded at 100 MHz are not super-imposable. An example of this is shown in Fig. 7. Finally, the chemical shifts between the A, B and C areas are very large (0.5 ppm) to be attributed to stereoregularity effects. 

It seemed that an improved understanding of the NMR spectra of styrene-MMA copolymers could be obtained if copolymers having a variety of sequential arrangements for a given composition could be prepared and studied. The approaches that can be taken to obtain such materials are the following ... 

In the polymer analogous reaction approach, styrene-MMA copolymers are derived by transesterification, methylation or methanolysis-methylation reactions from copolymers of styrene with aryl methacrylates, methacrylic acid, or meth-acrylic anhydride, according to the following reactions ... 

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-... 

Studies on the methoxy resonance patterns of the derived styrene-MMA copolymers suggest that interpretations of methoxy resonance patterns rendered thus far are not entirely adequate [29 — 27]. Considerable evidence indicates that about 10 percent of (MMS -h SMM) type resonance occurs in the C area this should not be the case if the Ito-Yamashita interpretation is correct. Thus, H-R plots of C type methoxy resonance often have a positive slope (y 0), as can be seen in Fig. 8, which shows results obtained for styrene-MMA copolymers derived... 

Pg may be less than that expected based on the Ito-Yamashita interpretation. Finally, the spectra (Fig. 9) of approximately 50/50 styrene-MMA copolymers... 

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. 

As can be seen in Fig. 4, the a-methyl resonance of styrene-MMA copolymers in deuteriobenzene consists of two general areas which change in relative intensity as the styrene content of the polymers changes. It seems that the higher field area is due to a-methyl protons in (SMM -h MMS) and SMS environments, as can be seen from the correlation shown in Table 2. 

In our own laboratories, Dr. Masao Murano [52] has used Mochel s methods to study the aromatic proton resonance patterns obtained with styrene-MMA copolymers. Spectra recorded with a 100 MHz spectrometer revealed separate resonances for the o- and (m + p)-aromatic protons of isolated styrene units. Six curves were therefore used to reproduce each observed aromatic proton resonance pattern gaussian curves were used to represent the resonance of o-aromatic protons lorentzian curves were used to represent the resonance of (m + p)-aromatic protons. The o- and (m + p)-resonance areas corresponding to protons in each type of styrene centered triad were maintained in a 2 3 ratio. It proved possible to obtain an excellent fit of observed aromatic resonance patterns to calculated triad distributions for copolymers of all compositions. Fig. 14 shows how the aromatic proton resonance pattern for one copolymer could be matched by summing o- and (m + p)-curves representing the various possible... 

Qualitative study of the resonance of methine protons in styrene-MMA copolymers indicates that it is shifted upheld by neighboring styrene units and is therefore sensitive to sequence distribution. Unfortunately, the resonance of methoxy protons interferes with methine resonance at low fields and methylene proton resonance interferes with methine resonance at high fields. The methine resonance of styrene-MMA copolymers is hardly observable. The situation is somewhat better when copolymers of styrene with methacrylic acid [75, 78] or methacrylonitrile [27] are studied, since the low field methine signals of such copolymers can be observed unobstructed. In addition, the electronegativity of the acid and nitrile units shifts the resonance of MSM and MSS type methine protons to low fields, so that interference by methylene proton resonance is small. However, the highest field methine resonance can be observed directly only if all methylene groups are substituted with deuterium atoms. 

Polystyrene is immiscible with PC however, tetramethyl Bisphenol A polycarbonate (TMPC) is miscible and exhibits lest behavior [439]. The CPMAS NMR analysis gave indication of homogeneity of the TMPC/PS blend at the level of a few nanometers [440], consistent with SANS data of 2 nm [441]. Styrene-MMA copolymers are immiscible with PC, but miscible with TMPC [442]. Miscibility maps for SMMA copolymer blends with hexafluorobisphenol A-tetramethyl bisphenol A copolymers show areas of single phase behavior. TMPC miscibility windows with a series of styrene copolymers (SAN, SMA, styrene-allyl alcohol (SAAl)) have been reported [443 ]. Miscibility of the copolymers with TMPC was maintained for SAN (0-13 wt% AN), SMA (0-8 wt% MA) and SAAl (0-19 wt% aUyl alcohol). Dimethyl bisphenol A-tetramethyl bisphenol A PC copolymer blends with SMMA yielded miscibility with SMMA (< 37 wt%) and PC copolymer with > 60 wt% tetramethyl bisphenol A content [444]. Tetramethyl Bisphenol S polycarbonate is not miscible with polystyrene, but is miscible with styrene-acrylonitrile copolymers (range estimated to be 14 to 42 wt% AN) [445]. Miscibility was also observed with an a-methyl styrene-acrylonitrile copolymer (31 wt% AN). 

Wang and Smith [60] applied Py-GC to determine the composition and microstructure of styrene-MMA copolymers. The composition of these copolymers was quantified by monomer peak intensities obtained from pyrolysis. Becanse of the poor stability of MMA oligomers, neither MMA dimers nor trimers were detected nnder normal pyrolysis conditions. The number average sequence length for styrene was determined from pure and hybrid styrene trimer peak intensities. The number average sequence... 

In many other polymer cases, because of the stability of the trimer components, they do not always contain all the trimer peaks in the pyrogram. An example is the styrene-MMA copolymer system [33]. The dimers and trimers of methyl methacrylate do not normally exist in the pyrogram under any pyrolysis conditions. However, the structure information can still be obtained by utilising the monomer peak intensity to generate the composition along with the information obtained from other trimers. 

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