The synthesis of a near infrared-sensitive tackifier

A general method to prepare near infrared absorbing abietic acid derivatives is described in which the carboxylic acid of abietic acid is sterically hindered, making the seemingly simple esterification of the acid with a functional near infrared dye the most troublesome stage of the synthesis. Optimum results were obtained by constructing the chromophore from components previously attached to abietic acid. The spectral properties of the desired compound both in solution and within polymer films are discussed. The tackifiers increase the near infrared absorption, offering the potential for near infrared-activated hot-melt adhesives.