The AlCl 3 -catalyzed low-temperature polymerization of a-pinene in the presence of various activating additives was studied.Polyterpene resins (PTRs) are prepared by acidcatalyzed polymerization in the course of deep processing of turpentine. These resins are widely used in industry, especially beyond Russia. Depending on the composition of the raw materials and preparation procedure, PTRs have different consistency: from viscous liquids to high-melting solids. The wide spectrum of physicochemical properties determines the applications of PTRs. Of most interest are solid high-melting PTRs with the ring-and-ball softening point T s above 90oC (PTR 90 ). Specifically these products, produced mainly in the United States from turpentine enriched in b-pinene, are successfully used for more than 30 years as thermoplastic adhesive additives in production of hot-melt and pressure-sensitive adhesives, and also of paint-and-varnish, sealing, and insulating materials [13 4]. In oleoresin and sulfate turpentine produced in Russia, the content of b-pinene does not exceed 5%, and the major component is a-pinene, from which it is difficult to prepare PTR 90 in a high yield [5310]. This is primarily due to the specific features of the molecular structure of a-pinene, in which the double bond, in contrast to b-pinene, is sterically shielded, which hinders the polymeric chain propagation. Therefore, the development and choice of the best catalytic systems and conditions for a-pinene polymerization, providing high yield of PTR 90 , is of considerable theoretical and applied interest.The polymerization of a-pinene was studied in the temperature range from 328 to +10oC in the presence of a mixture of Friedel3Crafts catalysts (AlCl 3 and SbCl 3 ), and also of heteropoly acids (HPAs) H 3 PW 12 . O 40 (PW 12 ) and H 4 SiMo 12 O 40 (SiMo 12 ). As a result, we obtained PTR 90 samples in yields reaching 84%. These samples were solid glassy substances with the color from light yellow to light brown and T s = 923 115oC (Table 1). The molecular weight (MW) of PTR 90 is 580 3800, and the intrinsic viscosity h at 20oC, 0.0124 3 0.0289 dl g 31 . The PTR 90 is a mixture of oligomers of monoterpene hydrocarbons with the chain length from 3 to 6 C 10 H 16 units (so-called polyterpenes, PTs) and of a small amount of dimers of a-pinene and/or other monoterpene hydrocarbons (diterpenes, DTs).The DT fraction isolated from PTR 90 is a transparent light yellow oily liquid with a kinematic viscosity at 20oC of 130 3200 mm 2 s 31 and a density of 936 3 942 g dm 33 . The boiling point of DT is 150 3200oC at 0.5 kPa, refractive index n D 20 1.5126 31.5157, and MW 270 3290.The polymerization of a-pinene is accompanied by its isomerization; along with PTR 90 , the products contain camphene, dipentene, terpinolene, and p-cymene. As shown in [537], the same monoterpenoids are formed by polymerization of a-pinene at temperatures exceeding 100oC in the presence of acid catalysts of other types: aluminosilicates, natural zeolites, or titanium catalyst.The influenc...