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Soluble block copolymers based on natural rubber and polyurethane oligomers derived from 1,3 butane diol and toluene diisocyanate were synthesized for the first time. The dilute solution properties of these block copolymers dissolved in tetrahydrofuran (THF) were studied by viscometry and gel permeation chromatography (GPC). The Mark-Houwink constants K and a of the block copolymer system were determined by the molecular weight data from GPC combined with the viscosity data. Both the values were found to be in the range usually given by flexible elastomers. The intrinsic viscosity values were found to decrease successively with a decrease in the NCO/OH ratio from 1.12 to 1.05. The unperturbed chain parameters, K h and B were determined from the viscosity data. The K h calculated was used to get the unperturbed end-to-end distance and radius of gyration of the block copolymer systems in THF. The viscosity data were also used to study the chain conformation in dilute solutions. It was found that the molecules adopt a compressed core and shell conformation in which the higher molecular weight component, NR, forms the shell, which compresses the PU core. All the block copolymers assume a compressed segregated core and shell model which changes to a partially segregated core and shell conformation, or partially Gaussian conformation, at the transition temperature located at 70 8C.

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Segmented block copolymers from different grades of hydroxyl terminated liquid natural rubber (HTNR) (Mn 3000, 8800, 10,000, and 17,000) and polypropylene oxide (PPO) (Mn 1000, 2000, 3000, and 4000) have been synthesized and characterized by spectral analysis, thermal analysis, scanning electron microscopy (SEM), and mechanical testing. The glass transition temperature of NR block was found to be at about −64°C, which is independent of the PPO whose transition is around 15°C. The thermogravimetric analysis (TGA) shows that the thermal degradation of the samples proceeded in two steps characteristic of the immiscible components. The inability of PPO segments to provide physical crosslinking and the subsequent formation of hard domains is reflected in the low tensile properties and tear properties. The amorphous nature of the PPO phase and its immiscibility with NR phase are evidenced by the SEM studies. The effect of molecular weight of PPO as well as HTNR on the properties of the block copolymers has also been discussed. © 2006 Wiley Periodicals, Inc. JAppl Polym Sci 103: 909–916, 2007