Copolymer molar mass determination, light

Molar mass determination requires the knowledge of the specific RI increment dn/dc, which in the case of complex polymers depends on chemical composition. Copolymer RI increments (dn/dc)copo can be accurately calculated for chemically monodisperse fractions if comonomer weight fraaions /, and homopolymer values are known, which is rarely the case. Light-scattering investigations of copolymers are even further complicated by the fact that SEC does not separate into chemically monodisperse fractions. Accordingly, due to compositional heterogeneity, the RI increment of a particular... 

The mass-average molar mass of the block copolymer solute, M , and the second virial coefficient, A2, can be obtained from SLS. These quantities can be determined from the concentration dependence of the scattered light intensity using the relationship (cf. Section 1.4.10)... 

Recently, Siu et al. [139] studied the effect of comonomer composition on the formation of the mesoglobular phase of amphiphilic copolymer chains in dilute solutions. The copolymer used was made of monomers, N,N-diethylacrylamide (DEA) and N,N-dimethylacrylamide (DMA). like PNI-PAM, PDEA is also a thermally sensitive polymer with a similar LCST, but PDMA remains water-soluble in the temperature range (< 60 °C) studied. At room temperature, copolymers made of DMA and DEA are hydrophilic, but become amphiphilic at temperatures higher than 32 °C. Before the association study, each P(DEA-co-DMA) copolymer was characterized by laser light scattering to determine its weight average molar mass (Mw) and its chain size ( Rg) and (R )). The copolymer solutions (6.0 x 10 A g/mL) were clarified with a 0.45 xm Millipore Millex-LCR filter to remove dust before the LLS measurement. 

Fig. 6.1. Determination of the exponent a from the slope and the constant K[ from the intersection with the y-axis when plotting log [q] as a function of log M. Values for the intrinsic viscosity [q] of the polycation poly(acrylamide-co-(A/,A/,A/-trimethyl-A/-[2-methacryloethyl]-ammoniumchloride) (PTMAC) in 0.1 mol/l NaN03 solution are taken from Fig. 4.2. The copolymer consists of 8 mol% TMAC and 92 mol% AAm. Molar mass values were determined with multi-angle laser light scattering (MALLS), data from [102]...

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