High Temperature SEC

In the early days of SEC, it was appreciated that this was a technique that could be used at high temperature and be applied to polymer types for which there was no room temperature solvents, particularly polyethylene and polypropylene, and appropriate commercial instrumentation was soon introduced. Despite this early appreciation of the value of high temperature SEC, it remains a difficult application.

High temperature SEC is carried out either to be able to dissolve the polymers of interest, as with polyolefins, or to reduce the viscosity of the solvents. In practice, SEC of polyolefins requries a minimum temperature of 140°C and is usually carried out with chlorinated aromatic solvents; the SEC of polyesters (such as PET) or polyamides is carried out using phenolic solvents at temperatures of at least 110°C, while SEC with polar solvents, such as dimethylfor-mamide is carried out at temperatures around 80°C. In addition, some SEC is carried out at raised temper ature to enhance the efficiency (particularly aqueous SEC).

Polyolefins tend to come out of solution if there is a cool spot in the total instrumentation, which is the main complication with these polymer types but there is potential for other temperature incompatibilities (e.g. temperature cycling on an RI detector). In addition, solvents at high temperature are likely to swell polymer components in the SEC instrumentation (e.g. pump seals) and it is desirable to dedicate the instrumentation to specific applications. With the high temperature SEC using phenolic or polar solvents, the main complications are not necessarily directly related to the high temperature.

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Solar Panel Basics

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