We describe the synthesis and characterization of a number of polymers with well-defined structures that serve as models for polyethylene with long chain branching. All of them have been made by using anionic polymerization techniques and controlled chlorosilane chemistry to give nearly monodisperse polybutadienes with precise control of the number, length, and placement of long (Mw > 1500 g/mol) branches on each chain. This was followed by hydrogenation to give saturated polymers with the same well-defined long chain branching and the local structure of a typical linear low-density polyethylene. That is, both the backbones and the long branches had 17−25 ethyl branches per 1000 total carbons. Among the structures made were some with no long branches (“linears”), some with a single long branch (“stars”), others with exactly two branch points (the α−ω type, “H's”, “super-H's”, and “pom-poms”), and some with several long branches randomly distributed along the backbone (“combs”). Essentially all types of b...

Well-Defined, Model Long Chain Branched Polyethylene. 1. Synthesis and Characterization

In this report we show by experimental and theoretical investigations that the commonly used GPC universal calibration parameter, the intrinsic viscosity multiplied by the weight average molecular weight ([η] Mw) is incorrect. The error which can arise by using [η] M to calculate the molecular weight across the GPC chromatogram for nonuniformly branched polymers [poly(vinyl acetate) and low density polyethylene] and copolymers with compositional drift, could be very large. We also show conclusively that the number average molecular weight Mn is the correct average to use for the universal calibration parameter. We therefore recommend that our general universal Calibration parameter [η] Mn be used for calculating the molecular weight across the chromatogram for all polymer systems (linear and branched homopolymers, copolymers with or without compositional drift and for polymer blends).

Generalized Universal Molecular Weight Calibration Parameter in GPC

Separation of complex branched polymers by size-exclusion chromatography probed with multiple detection

Long-chain branching in polymers

Mechanistic Investigation of a Starch-Branching Enzyme Using Hydrodynamic Volume SEC Analysis

The effect of long-and short-chain branching in polymer molecules on gel-permeation chromatographic (GPC) separation is discussed. The calculation of calibration curves for branched polymers is developed from the universal calibration technique based on the hydrodynamic volume concept and previously established relationships for the effect of branching on molecular dimensions. Typical calibration curves are shown for different branching models and degrees of branching. As branching increases, the curves are shown to converge. Methods of characterizing branching and molecular weight distributions of franctions and whole polymers from GPC and intrinsic viscosity data are presented.

Determination of polymer branching with gel‐permeation chromatography. I. Theory

The recently developed methods of characterizing branching in polymers from gelpermeation chromatography and intrinsic viscosity data are verified experimentally. An iterative computer program was written to calculate the degree of branching in whole polymers. Long-chain branching in several low-density polyethylene samples was determined by both the fraction and whole polymer methods. The two methods gave consistent ranking of the branching in the samples although absolute branching indices differed. Effects of various experimental errors and the particular model used for branching were investigated. For polyethylene, the data show that the effect of branching on intrinsic viscosity is best described by the relation 〈g3〉W1/2 = [η]br/[η]1 where 〈g3〉w is the weight-average ratio of mean-square molecular radii of gyration of linear and trifunctionally branched polymers of the same weight-average molecular weight.

E. E. Drott

Papers

Determination of polymer branching with gel‐permeation chromatography. I. Theory

Determination of polymer branching with gel‐permeation chromatography. II. Experimental results for polyethylene