SynopsisAn integral equation taking account of the limited resolution of the chromatographic columns is given to relate the gel permeation chromatogram and the true molecular weight distribution function. Three approaches to solve the integral equation are described. The first approach provides a special solution for the log-normal molecular weight distribution function; the other two approaches give two numerical solutions for general distribution functions. The use of these solutions in the treatment of gel permeation chromatography data is discussed.

synopsisThe use of a single detector in gel permeation chromatography (GPC) for samples of varying composition leads to erroneous conclusions. With certain simplifying assumptions, a gel permeation chromatograph equipped with properly selected dual detectors yields composition and molecular weight distribution information that is meaningful. Examples discussed are a mixture of homopolymers and a sample supposed to have been a styrene-butadiene block copolymer. The ultraviolet absorption is used in conjunction with the refractive index trace to give qualitative information that is much more informative than could be obtained with one detector. Calibration of the relative responses of the detectors to each of the components of the mixture is described, and these calibrations are used to calculate point-by-point composition, molecular weights, and molecular weight averages.

Soluble difunctional organolithium initiators were prepared by the addition of oligomeric poly(styryllithium) to stoichiometric amounts of double 1,1-diphenylethylene (DDPE) compounds: bis[4-(l-phenylethenyl)phenyl]ether;l,4-bis(l-phenylethenyl)benzene,and4,4,-bis(l-phenylethenyl)-l,r-biphenyl.The resulting products of this addition reaction were soluble in benzene and were capable of initiating diene polymerization. A reversal was detected at the end of the addition reaction to one of the three DDPE compounds, bis[4-(l-phenylethenyl)phenyl] ether. The diphenyl ether group in bis[4-(l-phenylethenyl)phenyl] ether, which might have reacted with poly(styryllithium) to cause a shift of equilibrium, was suspected to be the cause of the anomaly. The styrene-butadiene-styrene triblock copolymer prepared from these difunctional initiators gave narrow and symmetrical chromatograms by GPC. The tensile strength of the block copolymers, however, was low. A potential route of preparing soluble organolithium initiators with functionality higher than 2 was demonstrated.

Melt viscosities of polyethylene fractions were measured at low rates of shear in a cone‐and‐plate rotational viscometer and extrapolated to zero shear viscosity. More accurate molecular weight determinations could be made on these fractions since they were free from extra large molecules. Such molecules are known to be present in unfractionated polyethylenes, and they interfere with light‐scattering molecular weight determinations. The zero shear viscosity of both high‐density and low‐density polyethylene was found to obey the equation where M̄w is the light‐scattering molecular weight. At 165°C. the zero shear viscosities of both types of polyethylene could be correlated by one single equation, but at higher temperatures and more branched low‐density polyethylene has a lower melt viscosity. The activation energy of flow was found to be 7.5 kcal./mole and 14.6 kcal./mole for high‐density and low‐density polyethylene, respectively. This difference activation energy is attributed to long‐chain branches in low‐density polyethylene rather than short‐chain branches. A discrepancy was observed between molecular weights of many high‐density polyethylene fractions determined by light‐scattering methods and the molecular weight of the same fractions calculated from inherent viscosity using a known intrinsic viscosity–molecular weight relationship. Examination of the data showed that the existence of a small amount of long‐chain branches in these high‐density polyethylene fractions was the probable explanation for this discrepancy.

SynopsisThe calculation scheme for correcting the broadening effect due to imperfect resolution on gel permeation chromatograms was compared with actual performances of a gel permeation chromatography (GPC) column. The experiment consisted of fractionating a high-density polyethylene on a GPC unit and then determining the chromatograms of the cuts collected. The chromatograms of the cuts were also computed from the starting chromatogram using experimentally determined resolution factors. The degree of agreement between the calculated and experimental chromatograms of the cuts shows convincingly that the previously proposed calculation scheme is satisfactory for the treatment of GPC data.