BMI-1700 Amorphous, Low Molecular Weight Bismaleimide Oligomer

How does BMI 1700 adheres to various substrates?

An evaluation of adhesion was performed using BMI-1700 (part number R1191) and various quantities of epoxy

• Aluminum studs cured onto various substrates, cured for 1 hour at 175ºC
• >230 indicates machine maximum reached, no breakage

TDS states that BMI 1700 has the same Molecular weight with BMI 1400 but their Viscosity is different. Is this correct?

Good question. The TDS documents are a little (a lot?) misleading. The molecular weight (MW) referenced on the TDSs is for the idealized structure where n (the number of repeating units) =1. Since BMI-1400 and BMI-1700 are siblings - made from the same raw materials and using the same process - they share the same basic molecular structure as shown on the top of each TDS. 

In actuality, BMI-1400 and BMI-1700 are oligomers which means they are made up a number of different MW species (e.g. n = 1 to 10). We change the ratio of starting materials in order to grow the backbone larger in the BMI-1700 (higher "n" value) and smaller in the BMI-1400 (lower "n" value) which corresponds to higher average MW and lower average MW respectively. The average MW directly influences the viscosity so that is why there are differences in viscosity between the two products.

BMI 1400 GPC Chromatograph

This MW difference can be seen in the Gel Permeation Chomatography traces for the two products:

• The traces show the products separated into groups (peaks) by MW with the highest values on the left and the lowest values on the right.
• The large peak around 24.8 minutes is the BMI-689 component which keeps these products liquid.
• The next peak to the left (~22.2 minute retention time) is the n=1 or idealized structure component. 
• Moving to the left you can see that BMI-1700 has a higher number of peaks and a larger area under the curve indicative of a larger percentage of the product is of a higher MW when compared to the BMI-1400.

BMI 1700 GPC Chromatograph

When we actually measure the MW of the two products we do see a difference: the weight average molecular weight (Mw) is 5,000 - 7,000 Daltons for the BMI-1700 and less than 4,000 Daltons for the BMI-1400 which ties to the viscosity differences.