Ziegler-Natta Oligomers

Surface Effects

Movement of these molecules to the surface of a part is a common cause of blooming and mold fouling. As the part cools, the ziegler-natta oligomers are squeezed out of the crystallizing regions and migrate to the air-plastic interface. This creates a waxy film that can interfere with the printing of labels or the effectiveness of heat seals.

In injection moulding, the buildup of these materials on the mold surface requires frequent cleaning to maintain the part’s appearance and dimensions.

Regulatory Extraction

Limits on the amount of material that can be extracted from a polymer are largely defined by these short-chain fractions. Tests using solvents like n-hexane or xylene are designed to dissolve the ziegler-natta oligomers and measure their mass. If the level of extractables is too high, the resin will fail to meet standards like 21 cfr 177 1520.

Resin manufacturers often use a post-polymerization step to strip away these volatiles and produce a cleaner, more compliant product.

Processing Impact

Influence of these small molecules on the rheology of the melt can be significant. They act as a plasticizer, reducing the viscosity and making the resin easier to process at lower temperatures. However, this benefit is often outweighed by the risks of contamination and surface defects.

Choosing a resin with a narrower molecular weight distribution is the standard way to reduce the impact of these oligomers on the final product quality.