Tacticity of Poly n-butyl methacrylate

Quinting and Cai [62] carried out high-resolution C-NMR and pNMR measurements to determine the tacticity of poly(n-butyl methacrylate) (PBMA) with particular focus on the peak assignments for the n-butyl side chain. Both free radical and anionic PBMA were examined, with the former being predominantly syndiotactic and the latter isotactic. The pNMR resonances for the -alkyl chain of these polyacrylics show a combination of effects from configurational sensitivity and homonuclear scalar interactions. A combination of /-resolved pNMR and proton- C-heteronuclear correlated 2-dimensional NMR spectra was used to characterise the long-range chemical shift effects due to tacticity. 

Quinting and Cai [62] determined tacticity through analysis of the carbonyl (Ci), quaternary (C2), side-chain methylene (C2 )j and methylene (C/) resonances. 

Ordinarily, it is possible to distinguish between mm/rr and mr/rm triad stereosequences using standard NMR experiments, however, distinction between the resonances of 

Triple resonance 3D-NMR techniques combined with isotopic labelling have provided powerful tools for biomolecular structure determination [63-65] which have tremendous potential applications in polymer chemistry. 

The H-NMR spectrum of isotactic PBMA at 100 C does not show the quartet for the butyl methyl group (H-T), which instead seems to be the expected triplet. Further scrutiny reveals smaller peaks between the peaks of the triplet. The same long-range tacticity effect exists for isotactic PBMA, but the larger triplet corresponds to the dominant mm triad sequence. The much smaller peaks correspond to the mr sequence. 

Ordinarily, it is possible to distinguish between mm/rr and mr/rm triad stereosequences using standard NMR experiments, but distinction between the resonances of mm and rr triads can be made only if a spectrum from a stereoregular polymer of known relative configuration is available. Triple resonance 3D-NMR techniques combined with isotopic labelling have provided powerful tools for biomolecular structure determination which have tremendous potential applications in polymer chemistry [63-66]. 

5 Identification of Diastereoisomeric Tetramers in the Pyrograms of poiymethyi methacryiate 

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Other homopolytners that are investigated in terms of stereochemical configuration are, for example polystyrene (mainly by means of carbon-13 NMR) and polyfcr-methyl stymie) [125]. More recoidy, the tacticity of poly(n-butyl methacrylate) has beoi studied by high-resolution carbon-13 and proton NMR... 

The tacticity of PMMA blends with poly(vinyl pyrrolidone)(PVP) influenced the blend phase behavior as atatic and syndiotactic PMMA were miscible with PVP, but isotactic PMMA was phase separated [785]. Neo and Goh [786], however, reported that PVP was immiscible with PMMA and PEMA, but miscible with poly(chloromethyl methacrylate) and poly(2-chloroethyl methacrylate. Miscibility with ucst behavior was observed for poly(n-butyl acrylate) PnBA blends with poly(propylene glycol) (linear and three arm star) oligomers [787]. Poly(vinyl butyral)/PMMA blends were found to be phase separated at high PMMA [788]. 

Tacticity measurements can be correlated with reaction mechanisms and physical properties. For example, the incorporation of an electron donor into the polymerization catalyst formulation has been found to increase isotacticity in a propylene-1-butene copolymer [123], and the distribution of propylene and 1-butene contents as a function of molecular weight varied, depending on donor type. External donors, such as dimethox-ysilane, decrease the butene content more than internal electron donors (in this case, di-n-butyl phthalate). Mechanisms of new polymerization reactions, such as the group-transfer copolymerization of methyl methacrylate and lauryl methacrylate, can be elucidated by comparing NMR-derived structural details [124]. The presence of unanticipated peaks in the spectrum of poly(ethylene-co-norbomene) suggest the occurrence of epimerization... 

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