Rapid method for the determination of molecular weight distribution in high polymers: A thermal gradient‐turbidity technique

Abstract

SynopsisA rapid method for determining the molecular weight distribution of polymers has been the aim of polymer chemists for a long time. The method presented here requires less tban two hours, including dissolution of the polymer. It is an exteneion of a photoelectric turbidimetric technique presented by Taylor and Tung in 1961. The equipment has been completely redesigned and presently consists of a copper block containing a turbidity cell, optical system and attendant electronic circuitry for measuring relative changes in turbidity of polymer solutions aa a function of temperature. An X-Y recorder is used t o plot turbidity versus temperature. A parameter determined from the plot is correlated with a meaaure of molecular weight distribution determined on known samples for each type polymer by another means. Baaed on this correlation unknown samples may be analyzed. The instrument is eaay t o operate and has shown excellent stability over a two year period. Polymers studied by this technique include ethylene-propylene copolymer (EPR), polypropylene, polyethylene, and butyl, however, the only results to be reported here are those on ethylene-propylene copolymer.

Use of solution crystallization analysis by laser light scattering for studying the solution crystallization of various Ziegler–Natta‐catalysed polypropylenes

“…SCALLS is considered to be one of the newest fractionation techniques for semi‐crystalline polymers and involves analysis of the turbidity of a polymer solution. Long ago, turbidity measurements were focused on fractionating polyolefins based on molecular weight using either a solvent/non‐solvent approach or a thermal gradient technique . In 1966 Imhof studied the compositional distribution of ethylene copolymers and blends of ethylene homopolymers and copolymers using a turbidimetric thermal gradient technique .…”

“…Long ago, turbidity measurements were focused on fractionating polyolefins based on molecular weight using either a solvent/non-solvent approach or a thermal gradient technique. 31 In 1966 Imhof studied the compositional distribution of ethylene copolymers and blends of ethylene homopolymers and copolymers using a turbidimetric thermal gradient technique. 26 More recently, Shan et al described how the short chain branching distribution of polyethylene can be determined using a turbidimetric method.…”