Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl methacrylate)

Abstract

Abstract Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed isotactic PMMA (iMA) with about 90% isotactic triads and different M̄ v 's, viz., iMA‐1: 7.2 × 10 5 ; iMA‐2, 5.0 × 10 5 ; iMA‐3, 3.5 × 10 5 ; iMA‐4, 1.25 × 10 5 ; and iMA‐5, 1.15 × 10 5 . The MMA:iMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. It is found that the M̄ v of the polymer formed ran parallel to the M̄ v of iMA. In all cases syndiotactic PMMA (s‐PMMA) was produced which associated with the isotactic substrate to form acetone‐insoluble stereocomplexes. The syndiotactic polymers probably consist of long syndiotactic and heterotactic sequences. The syndiotacticity decreased with conversion and was generally highest in the presence of iMA‐1. With iMA‐1 even the formation of some additional i‐PMMA (in the acetone‐insolubles) was indicated, especially in the later stages of the polymerization. Characterization of the acetone‐soluble fractions indicated that i,s‐stereoblock polymers were also produced, of which the persistence ratios ρ increased with the M̄ v of iMA. From these results it is concluded that this reaction differs from the conventional radical polymerization and can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i‐ and s‐PMMA to associate. The formation of i,s‐stereoblock polymers and additional i‐PMMA indicates that s‐PMMA in its turn can also act as a polymer matrix.