Abstract
Two-component polyurethane coatings were prepared by blending benzoic acid poIycaprolactone modified polyester polyol (BZAOs), synthesized with components of adipic acid/1,4-butanediol/polycaprolactone/bensoic acid, and polyisocyanate (TDI- adduct). Kinematic viscosity of BZAO was gradully decreased with increasing benzoic acid content in BZAO. The kinematic viscosity of modified polyesters are decreased as the benzoic acid content increases. After the film was coated with the prepared polyurethane coatings, the various physical properties were measured. They showed drying time of 4~6 hour and pot-life time of 15~27 hour, so they were proved to be coatings with long pot-life time. They showed good physical properties such as flexibility, impact resistance, cross hatch adhesion, and rust resistance. These advantages are the results of introducing polycaprolactone polyol.ram and conventional Avraml plot. At PPG contents greater than 10%, the overall crystallization rate decreased because of the uncrystallizable PPG unit. The induction time for crystallization increased, and the ratio of primary crystallization to overall crystallization increased at the same degree of undercooling. On the other hand, crystal growth rate increased with PPG content. The presence of PPG unit in the block copolymer has two opposing effects on crystallization. First, as the amount of PPG unit increases it interferes with nucleation. As a result the induction time for crystallization increases and the crystallization rate decreases. Secondly, it increases the mobility of the block copolymers because of the ether linkage and allows faster diffion of the copolymer chain to the crystal surface. Consequently the crystal growth rate after nucleation increases. Between the two effects the first one seems to be dominating and the overall crystallization rate decreases with increasing PPG content in block copolymers. Furthermore there are some different crystallization behaviors between the block copolymers and PCL homo polymer. Nucleation of block copolymers of PPG content up to 10% occurs faster than in the case of homo PCL because small amounts of PPG unit may act as heterogeneous nuclei. Also the chain mobility increased with the introduction of PPG unit, therefore the overall crystallization rate was faster than homo PCL. But if the PPG content exceeds 10% the overall crystallization rate of the block copolymers becomes slower than homo PCL.