Poly(trans-4-methacryloyloxyethylenoxyazobenzene) was prepared by homopolymerization of the corresponding monomer, either by radical or anionic initiation, to give the first isotactic photochromic polymer. In the former case the C-13 n.m.r. spectrum exhibits, in the regions of the signals of several carbon atoms, multiplets attributable to pentad, triad or dyad stereosequences. Their intensity distribution closely fits Bernoullian statistics (P(m) = 0.21 ) consistent with an atactic, predominantly syndiotactic, structure of the polymer backbone. On the other hand, in the spectrum of the sample prepared by anionic initiation, all the signals appear as sharp singlets in the region of the isotactic ennads of the radical sample. The intensity distribution of the very small peaks attributable to different stereosequences allows us to assign a 98% isotacticity to this sample and to rule out the occurrence of an enantiomorphic mechanism of polymerization. Molecular dynamics in solution. investigated by C-13 spin-lattice relaxation times and nuclear Overhauser enhancement factor measurements, indicate a comparable mobility for the two samples.
N. m. r. properties of tactic poly(trans-4-methacryloyloxyethylenoxyazobenzene)
ALTOMARE, ANGELINA;SOLARO, ROBERTO
1991-01-01
Abstract
Poly(trans-4-methacryloyloxyethylenoxyazobenzene) was prepared by homopolymerization of the corresponding monomer, either by radical or anionic initiation, to give the first isotactic photochromic polymer. In the former case the C-13 n.m.r. spectrum exhibits, in the regions of the signals of several carbon atoms, multiplets attributable to pentad, triad or dyad stereosequences. Their intensity distribution closely fits Bernoullian statistics (P(m) = 0.21 ) consistent with an atactic, predominantly syndiotactic, structure of the polymer backbone. On the other hand, in the spectrum of the sample prepared by anionic initiation, all the signals appear as sharp singlets in the region of the isotactic ennads of the radical sample. The intensity distribution of the very small peaks attributable to different stereosequences allows us to assign a 98% isotacticity to this sample and to rule out the occurrence of an enantiomorphic mechanism of polymerization. Molecular dynamics in solution. investigated by C-13 spin-lattice relaxation times and nuclear Overhauser enhancement factor measurements, indicate a comparable mobility for the two samples.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
