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The pros and cons of polymer solubility

23 February 2012 No Comment

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Wheras a low solubility is an advantage for most applications of polymers,  it can be a problem when you want to analyze them.

Used for products ranging from cling film, drinking straws, carrier bags and food packaging, to crates, boxes, and bottles, we routinely benefit from the properties of  organically derived thermoplastics such as polyethylene and polypropylene that mean that they are not soluble in most solvents at ambient conditions. However, trying to analyze polymers that are difficult to dissolve and keep in solution  can be tricky, requiring the operator to work with dangerously hot, and often unpleasant and somtimes expensive solvents.

Dissolution of polyolefins

The process required to dissolve a polymer depends not only on their chemistry, but also on their physical structure. While the general principle that ‘like dissolves like’ remains appropriate, parameters such as: polarity, molecular weight, branching, crosslinking degree, and crystallinity, all contribute  to polymer solubility.

A polymer produced from a simple olefin, referred to in the petrochemical industry as a ’polyolefin’, is extremely chemically inert. Manufactured  from by-products of the oil and natural gas industries, by a process of polymerisation, polyolefins account for more than 47% (11.2 million tonnes) of Western Europe’s total consumption of 24.1 million tonnes of plastics each year, according to the Plastics Portal.

Polyethylene and polypropylene are two of the most commercially important polyolefins. Sparingly soluble, they can only be dissolved, and kept in solution, through the application and maintenance of temperatures  as high as 160 degrees and the use of solvents that typically present significant toxicological and/or environmental issues. Analysis can therefore be a major challenge.

Viscotek HT-GPC makes polyolefin analysis safer

High Temperature Gel Permeation Chromatography (HT-GPC) is a technique for measuring the average molecular weight, molecular weight distribution, composition and structure of polymers requiring higher analysis temperatures.

Bringing advanced multi-detector technology to these demanding applications, the Viscotek HT-GPC consists of an integrated autosampling device, called the Vortex, and heated multivial stirrer so the sample is prepared with temperature control up to 170°C, then automatically injected according to the method schedule. The Vortex eliminates the need to transfer hot sample from a preparation vial to an autosampler vial and the HT-GPC filters the sample automatically on injection.

By removing the operator from the sample preparation process,  the entire procedure is more efficient, more precise, and most importantly, safer.