Chain extension

Chain extension is a new method to obtain high MW polycondensates. Chain extenders are added during the final processing step (single or twin screw extrusion during spinning or compounding), so that no extra processing step is needed. This has a favourable effect on the system costs. The chain extender couples polycondensate end groups in a statistical way very similar to post-condensation. The difference is that the extender couples two chains within minutes, much faster than observed during post-condensation. In addition, our chain extenders couple two equal end groups, e.g. two amines, two hydroxyls or two carboxyls. Chain extension with ALLINCO® does not change the MW distribution compared with post-condensated polymers.

For more information about the chemistry of the DSM chain extenders, check the following pages:

• Carbonylbiscaprolactam (CBC)
• Phenylenebisoxazoline (PBO)
• Phenylenebisoxazine (PBOX)

In principle, any bifunctional chemical that reacts fast with the end groups of polycondensates may be used. However, in practice most chemicals suffer from severe side reactions, which make them useless for most applications.

The DSM choice of chain extenders is based on the following requirements:

• The system costs of chain extension must be lower than SSP
• The reaction with hydroxy, amino or carboxy groups must be within standard processing time
• No side reactions are allowed
• The chain extenders must be easy to dose and easy to handle
• The viscosity level of the resin must be tunable and stable
• The resin properties must be the same as those obtained via SSP
• No negative SHE-effects of the chain extenders are permitted
• The two chain extenders must have similar reactivities: one with the hydroxy or amino functions, the other with the carboxy functions
• The two chain extenders may not react with each other
• Either the combination of two chain extenders can be used or one of the two.

The DSM system consists of one chain extender (ALLINCO® CBC), or two independent chain extenders (ALLINCO® CBC and ALLINCO® PBO) that meets all requirements. Its composition and concentration can be tailored to the customer's wishes. Experiments show that ALLINCO® CBC is the more effective component. At 0.2-0.8 wt%, ALLINCO® CBC is a very effective chain extender for polyesters and polyamides. At 0.05-0.15 wt%, ALLINCO® CBC is an effective melt stabiliser for polyesters.