No abstract

No abstract

A detailed analysis is made of the 13C NMR spectra of ethylene-propylene rubbers at high field. The complex spectral features are interpreted as resulting from ethylene-propylene sequence placements, inverted propylene structures, and propylene tacticity. The new set of assignments permits more accurate determinations of copolymer composition, sequence distribution, and tacticity. Moreover, the detailed assignments enable several types of tacticity effects to be found; the relative meso/racemic contents provide information on the polymerization mechanism.

Crystal growth rates of spherulites or axialites of low molecular mass (MW = 15 OOO) and high molecular mass (MW = 300 000) isotactic polypropylene (i-PP) fractions crystallized from the melt have been investigated in an extensive supercooling range (20-70 K). On the basis of the regime theory, a transition between regimes I and I1 is found at AT Y 37 K for the low molecular mass fraction and a transition between regimes I1 and I11 is at AT = 48 K for both low and high molecular mass fractions of i-PP.Accordingly, the morphological changes observed by a polarized optical microscope at the supercooling range in the vicinity of regime transitions have been examined. The morphological change in this supercooling range does not correlate to the regime transitions.

No abstract

No abstract

CompleteNMR spectral analysis is carried out for ethylene-vinyl chloride, ethylene-vinyl alcohol, and ethylene-vinyl acetate copolymers. Three approaches (two-dimensional NMR, empirical shift rules, and computerized "analytical" method) have been used in concert to provide detailed 1H spectral assignments and quantitative analysis. It is shown that the use of these three approaches permits detailed compositional and comonomer sequence information to be obtained from high-field NMR spectra.

The present work describes the isolation of cellulose nanoparticles (CNs) with different morphologies and their influence on rheological properties of CN and CN-poly (vinyl alcohol) (PVA) suspensions. Cottonseed hulls were used for the first time to extract three types of CNs, including fibrous cellulose nanofibers, rod-like cellulose nanocrystals and spherical cellulose nanoparticles through mechanical and chemical methods. Rheology results showed that the rheological behavior of the CN suspensions was strongly dependent on CN concentration and particle morphology. For PVA/CN systems, concentration of PVA/CN suspension, morphology of CNs, and weight ratio of CN to PVA were three main factors that influenced their rheology behaviors. This research reveals the importance of CN morphology and composition concentration on the rheological properties of PVA/CN, providing new insight in preparing high performance hydrogels, fibers and films base on PVA/CN suspension systems.