The effect of built-in dicyclopentadiene on selected properties of unsaturated polyester resins

Identical starting compounds, viz., maleic and phthalic anhydrides and ethylene and diethylene glycols, were used to synthesize three unsaturated polyester resins (UPR), I, II and III, of different quantitative compositions. The II and III were modified with dicyclopentadiene (DCPD) used in amounts of 6 and 12 wt.%, respectively. The I (with no DCPD) was mixed with the DCPD-modified III to prepare samples containing 2, 4, 6, 8, and 10 wt.% of DCPD. The primary 6% DCPD resin was compared with the 6% DCPD resin prepared by mixing 1:1 (by wt.) the unmodified I with the DCPD-modified III. The DCPD-modified polyester, cured and uncured, was examined at -10 degrees C and at room temperature to establish miscibility with styrene, curing course (gel time; maximum temperature during copolymerization; time elapsed to attain the max, temperature; ball indentation hardness) and the degree of surface hardening (degree of drying of coatings and Persoz pendulum hardness of coatings). DCPD was found to enhance the solubility of the polyester in styrene, the degree of drying of coatings and the surface hardness. Compositions of the resins with styrene (35-50% by wt.) were prepared and the above-mentioned properties were determined.