Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). II. Syndiotactic PMMA as matrix

Publisher Website
Google Scholar
Abstract
Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed syndiotactic PMMA (sMA) with about 90% syndiotactic triads and of different M̄v, viz., sMA‐1, 1.6 × 105; sMA‐2, 3.0 × 105; and sMA‐3, 8.7 × 105. The MMA:sMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. In all cases isotactic PMMA (i‐PMMA) was produced, especially in the initial reaction stages, which associated with the syndiotactic substrate to form acetone‐insoluble 1:2 i/s‐stereocomplexes. The isotacticity decreased with conversion and was highest in the presence of sMA‐3. Characterization of the acetone‐soluble fractions indicated that i,s‐stereoblock polymers were also produced. From these results it is concluded that this reaction can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i‐PMMA and s‐PMMA to associate. With sMA of M̄v below about 1.2 × 105, no i‐PMMA is formed; in other words, no replica polymerization occurs. For polymerizations in the presence of sMA‐2, the critical M̄v of propagating chains, with has to be exceeded before stereoassociation is strong enough to effectuate replica polymerization, has been estimated to be 0.6 × 105.