THE CHAIN STRUCTURE AND LIGHT-SCATTERING-STUDIES FOR ACRYLAMIDE-SODIUM ACRYLIC-ACID (AM-AA) COPOLYMERS

A set of AM-AA copolymer samples with the same comonomer content and different average molecular weight have been characterized by C-13 NMB and light scattering methods in this paper. The chemical composition (comonomer AA, mole content 16.9 +/- 1.1%) of these samples is uniform. the sequence of AA in the macromolecular chain is of alone and random distribution and the light scattering theory from polyelectrolyte in added-salt solutions is suitable for the AM-AA copolymers-0.12 mol/L NaCl water systems. The actual values of M(w), the second Virial coefficient A(2) and the mean square radius of gyration (R(2)), for the studied samples have been obtained. The relationships between the molecular parameters are as follows: A(2)=0.0619 ($) over bar M(w)(-0.24), < R(2) >(1/2)(t)= 0.0210 ($) over bar M(w)(0.54).

A DYNAMIC LASER LIGHT-SCATTERING STUDY OF CHITOSAN IN AQUEOUS-SOLUTION

The solution behavior of four chitosans (91% deacetylated chitin) with different molecular weights in 0.2M CH3COOH/0.1M CH3COONa aqueous solution was investigated at 25 degrees C by dynamic laser light scattering (LLS). The Laplace inversion of the precisely measured intensity-intensity time correlation function leads us to an estimate of the line-width distribution G(Gamma), which could be further reduced to a translational diffusion coefficient distribution G(D). By using a combination of static and dynamic LLS results, i.e. Mw and G(D), we were able to establish a calibration of D = k(D)M(-alpha D) with k(D) = (3.14 +/- 0.20) X 10(-4) and alpha(D) = 0.655 +/- 0.015. By using this calibration, we successfully converted G(D) into a molecular weight distribution f(w)(M). The larger alpha(D) value confirms that the chitosan chain is slightly extended in aqueous solution even in the presence of salts. This is mainly due to its backbone and polyelectrolytes nature. As a very sensitive technique, our dynamic LLS results also revealed that even in dilute solution chitosan still forms a small amount of larger sized aggregates that have ben overlooked in previous studies. The calibration obtained in this study will provide another way to characterize the molecular weight distribution of chitosan in aqueous solution at room temperature. (C) 1995 John Wiley & Sons, Inc.

ON HALL AND KIERS TOPOLOGICAL STATE AND TOTAL TOPOLOGICAL INDEX

The topological state and the total topological index, tau, have been tested systematically. Counterexamples are provided proving that the topological state method cannot determine classes of symmetrically equivalent atoms in a molecule fully correct. The

SMALL-ANGLE X-RAY-SCATTERING STUDY ON THE INTERFACE IN BLOCK-COPOLYMERS WITH FRACTAL PROPERTIES

The interface thickness in two triblock copolymers were determined using small-angle x-ray scattering in the context of the theory proposed by Ruland. The thickness was found to be nonexistent for the samples at three different temperatures. By viewing th

STRUCTURE OF MESOMORPHIC FORM OF ISOTACTIC POLYPROPYLENE

The structure of quenched isotactic polypropylene (iPP) films, including samples etched with fuming nitric acid (FNA), has been studied by infrared (IR) spectra, wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), and differential scanning calorimetry (DSC) measurements. The changes of IR, SAXS, DSC, and WAXD results induced by annealing for etched samples have been compared with those for unetched ones. The IR absorbance spectrum of the quenched iPP etched by FNA did not change. In addition, the SAXS intensity did not increase when these samples were annealed, indicating that the total (IR) crystallinity (i.e., the content of chain segments in the helical conformations) of the etched samples does not increase. However, WAXD patterns of the samples changed in a manner similar to those of the unetched one, from the original two blurred diffraction peaks to the sharp crystal patterns of alpha-form iPP, suggesting that the mesomorphic (or liquid crystal-like) phase has reorganized to alpha-form crystals. It is concluded that the change of WAXD of quenched iPP films during annealing results mainly from transformation of order in the mesomorphic phase, rather than only from an increase of crystal size. In other words, mesomorphic-form iPP is not constituted by any known crystals (such as alpha or beta crystals) in small sizes; its WAXD pattern reflects truly the degree of order in the mesomorphic phase.