EFFECTS OF HYDROCARBON TACKIFIERS ON THE ADHESIVE PROPERTIES OF CONTACT ADHESIVES BASED ON POLYCHLOROPRENE .3. THE EFFECT OF THE MOLECULAR-WEIGHT OF THE TACKIFIER

Aromatic hydrocarbon resins with different molecular weights (M-w = 13 00-50 400 daltons) were added to a solvent-based polychloroprene adhes ive. The hydrocarbon resins were characterized using infra-red (IR) an d differential scanning calorimetry (DSC) measurements. The properties and compatibility of the polychloroprene/resin blends were studied us ing mechanical tests, DSC measurements, scanning electron microscopy ( SEM), and stress-controlled theology. Tack measurements were also carr ied out and the adhesion strength was obtained from T-peel tests on ro ughened styrene-butadiene rubber/polychloroprene adhesive joints. The addition of low-molecular-weight tackifiers produced a compatible poly chloroprene/tackifier system (only one T-g was found in DSC measuremen ts), while the addition of a high-molecular-weight (and broad molecula r weight distribution) tackifier produced a partially incompatible sys tem (two T-g's were found in DSC measurements). The compatibility of p olychloroprene/tackifier blends was also assessed with stress-controll ed rheology and SEM. An increase in the T-peel strength and tack were produced when the molecular weight of the tackifier increased, althoug h the addition of a hydrocarbon resin with a M-w higher than about 50 000 reduced the tack. A broad molecular weight distribution in the tac kifier favoured incompatibility with the polychloroprene, resulting in a reduction in the tack and rheological properties.