One of the main characteristics that sign makers look for when purchasing media is whether the vinyl is polymeric or monomeric, usually associating that description with the quality and performance of the said product.

 

But what is really the difference between a monomeric and a polymeric vinyl?

First, we need to understand that polymeric and monomeric vinyl are different definitions to polymer and monomer plastics. The one used by the print industry is related to the plasticizer used in vinyl production, and not the plastic itself (like PVC).

Polymeric and monomeric, in this context, are related to the molecular weight (g/mole) of those plasticizers. A plasticizer that has a molecular weight of < 500g/mole is defined as monomeric and a plasticizer that has a molecular weight of > 500g/mole is defined as polymeric.

 

And what is a plasticizer?

A plasticizer is used to give plastics increased flexibility and conformability. So, the more molecular weight of plasticizer is present in the plastic, the more flexible and stretchy-er it is, hence why monomeric vinyl is less flexible and polymeric is more flexible.

The reason this happens is that, in the case of plastics, like PVC, its molecules are sharp-edged (see graphic below) which means that, in their original composition, the molecules very easily slot between each other, and become very inflexible (like a puzzle almost, think PVC pipes and guttering). Plasticizers budge in between the plastic molecules, un-slotting them from each other (or creating a gap) and making them more moveable and flexible.

 

 

Also important to note is that, plasticizers are more efficient in lower molecular weight. This means that to achieve a certain initial level of flexibility, you need to use a lot less plasticizer than you would achieve a higher flexibility vinyl. That is the reason why monomeric vinyl is much cheaper to produce than its polymeric counterpart.

 

What about plasticizer migration?

One thing to take into consideration is that monomeric plasticizers, because they are present in less molecular weight (or generally speaking, quantity), have a much harder time binding to the plastic, and because of that, are much more prone to release from said plastic than polymeric plasticizers. What then occurs is what the industry calls plasticizer migration, which, in lay terms, is the phenomenon of the plasticizer separating itself from the plastic that it is bound to. This can, unfortunately, negatively affect adhesives that may be being used with the media, like double-sided tape. When the extruded plasticizer comes in contact with the adhesive, it then makes it more flexible and elastic. This means that you’ll have rubber-based tapes turn into a gooey, unusable mess.

To summarize, better quality and more flexible monomeric vinyl are so, because of the molecule weight of the plasticizer used. And that is why we have 3-year and 1-year monomeric vinyl – we are most likely looking at a vinyl with a 200g/mole worth of plasticizer, that loses quality and flexibility much faster than vinyl with a 450g/mole worth of plasticizer. This also applies to polymeric vinyl of different qualities.