Polymer characterization by refractometry

Abstract

In the use of refractometry for polymer characterization, it is shown that interpretation of data through use of a molar refractivity as defined by the Lorenz‐Lorentz equation is more accurate than by use of the parachor. The disagreement between experimental and calculated values of the unit molar refractivity may be attributed to the arbitrary definition of the residue unit and the method of summation of group refractivities. In general, refractive index should depend on molecular weight and the conditions of polymerization, but this may depend on the dielectric properties and volume fraction of the domains comprising chain ends, initiator fragments, and free volume. The effect of polymer conformation on the molar refractivity of polyisoprene is found to be slight. For copolymer systems, there is a linear dependence of refractive index on weight fractional composition only where there is little order. The refractive index of a copolymer is not independent of the nature of the distribution of the residues along the chain.

Polymer-nanoinclusion interactions in carbon nanotube based polyacrylonitrile extruded and electrospun fibers

“…It is usually found that solvents and plasticizers have a large depressive effect on T g of PAN [35]. Variation in crystallinity, molecular weight [36], sample form (film or fibers), initiators, comonomers [37] of acrylonitrile polymer may bring further changes in the glass transition temperature.…”

Dispersion Polymerization in Supercritical CO2 with Siloxane-Based Macromonomer. 2. The Particle Formation Regime

“…The refractive index of PMMA is assumed to be constant at 1.4874, as it has been shown to be invariant for molecular weights larger than 2700 …”

“…The refractive index of PMMA is assumed to be constant at 1.4874, 37 as it has been shown to be invariant for molecular weights larger than 2700. 38 However, the effect of composition on the refractive index of the particle phase is significant due to the high solubility of both CO 2 39 and MMA. To obtain a volume fraction of CO 2 in PMMA, the molar volume of dissolved CO 2 was estimated to be 44 cm 3 /mol.…”

Polyphosphazenes with High Refractive Indices: Optical Dispersion and Molar Refractivity

“…The refractive index of a polymer is a measure of an average property of the material in its aggregated state, and the molecular weight and density of the polymer influence the overall value of the refractive index , The measurement of this quality provides a good means for correlating the molecular structure of a system with the optical properties. − According to Denbigh and Stein, the molar refractivity ( R ) can be assumed to be an additive function arising from the sum of the individual refractions ( R i ) from all the bonds that make up the polymer ( R = ∑ R i ). , For the case of a homopolymer, the molar refractivity is given by R = (DP) R m , where DP is the degree of polymerization and R m is the monomer repeat unit molar refractivity . The value DP can be obtained quite easily if the molecular weights of both the polymer (M) and the repeat unit (M m ) are known, because DP = M / M m .…”