Abstract
Removable pressure-sensitive adhesives (PSAs) are used in the production of self-adhesive materials such as protective films, masking tapes or biomedical electrodes. This work presents a new and environmentally friendly method of obtaining this type of adhesive materials, i.e., photochemically induced free radical telomerization. Adhesive binders to removable PSAs, i.e., the photoreactive acrylic telomer syrups (ATS) were prepared from n-butyl acrylate, acrylic acid, and 4-acrylooxybenzophenone. Tetrabromomethane (CBr4) or bromotrichloromethane (CBrCl3) were used as the telogens. ATS was modified with unsaturated polybutadiene resin and a radical photoinitiator. Adhesive compositions were coated onto a carrier and UV cross-linked. The effects of the chemical nature of telomers (i.e., terminal Br or Cl atoms) and their molecular weight (K-value), as well as the cross-linking degree on adhesive properties of PSAs, were studied. It was found that with the increase in telogen content in the system, the dynamic viscosity of ATS and K-value of acrylic telomers decrease, and the conversion of monomers increases. CBr4 turned out to be a more effective chain transfer agent than CBrCl3. Moreover, telomers with terminal Br-atoms (7.5 mmol of CBr4), due to slightly lower molecular weights and viscosity, showed a higher photocrosslinking ability (which was confirmed by high cohesion results at 20 and 70 °C, i.e., >72 h). Generally, higher values of the temperature at which adhesive failure occurred were noted for PSAs based on ATS with lower telogen content (7.5 mmol), both CBr4 and CBrCl3. The excellent result for removable PSA was obtained in the case of telomer syrup Br-7.5 crosslinked with a 5 J/cm2 dose of UV-radiation (adhesion ca.1.3 N/25 mm, and cohesion > 72 h).