An alkylene is another name for an alkene, or an alkanediyl functional group, especially one having the free valencies of adjacent carbon atoms.

Carl Campbell has written:

'The crystallinity of uniform triblock oxyethylene/alkylene/oxyethylene - EmCnEm - oligomers'

'Earth Science'

This is the solvent in the ink (dye). Toluol and Xylol were common synthetics used as solvents but have now been replaced by safer chemicals such as cyclic alkylene carbonates. (this is the sweet smelling gas you detect) The solvent is the substance into which the dye is diluted. Water can also act as a solvent in ink. When released from the marker, the solvent evaporates and leaves the solid ink on the surface