Molecular weight distribution microstructural analysis

More recently, the same author [41] has described polymer analysis (polymer microstructure, copolymer composition, molecular weight distribution, functional groups, fractionation) together with polymer/additive analysis (separation of polymer and additives, identification of additives, volatiles and catalyst residues) the monograph provides a single source of information on polymer/additive analysis techniques up to 1980. Crompton described practical analytical methods for the determination of classes of additives (by functionality antioxidants, stabilisers, antiozonants, plasticisers, pigments, flame retardants, accelerators, etc.). Mitchell... 

The same initiator was also used to produce a three-arm PBd star.26 Complete monomer consumption was observed, but SEC analysis showed a bimodal distribution. This behavior was attributed to the strong association effects of the trifunctional initiator in a nonpolar solvent. The problem was overcome when s-BuOLi was added in the reaction mixture in a ratio [s-BuLi] [s-BuOLi] = 2. s-BuOLi was shown to be capable of disrupting the initiator association without affecting appreciably the microstructure of the PBd chains. Therefore, a well-defined star polymer with low molecular weight distribution was obtained. 

The initial use of analytical TREF was to characterize polyethylene fractions [120]. Mirabella and Ford used TREF to fractionate LDPE and LLDPE for further characterization using SEC, X-ray C-NMR, DSC and viscosity measurements [121]. These investigators determined that the melting behavior of LLDPE correlated well with a multimodal SCB distribution and the distribution became narrower with increasing molecular weight. Mingozzi and collaborators [122] have applied both analytical and preparative TREF to the analysis of tacticity distribution in polypropylene. The results showed that both methods could be used successfully analytical TREF gave faster qualitative results on the polymer microstructure, while preparative TREF, with subsequent analysis of the fractions, could yield detailed quantitative tacticity information. Hazlitt has described an automatic TREF instrument to measure SCB distributions for ethylene/ a-olefin copolymers [123]. 

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