ISSN:
0360-6376
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
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.
Zusätzliches Material:
6 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1973.170110507
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