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Abstract
Telechelic dihydroxy terminated poly[(R)-3-hydroxybutyrate] (PHB-diol) with number average molecular weight ~ 4800 has been synthesized from PHB by catalytic transesterification with ],4-butanediol. Two series of poly(ester-urethane) block copoiymers were synthesized from, PHB-diol, acting as ”hard segments” and po)y(E-caprolactone)-diol, PCL-diol, ”as soft segments” (with number average molecular weight either 1260 or 2200), using 1,6-hexamethylene diisocyanate, HDI, as non-toxic connecting unit. The prepared copoiymers were characterized by ’H-NMR spectra, FTIR spectroscopy, gel permeation chromatography (GPC), viscosity and thermal properties by thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). DSC results of copoiymers based on PCL with number average molecular weight 1260, showed an increase in Tgs with increasing PHB content, while in the case of copoiymers based on PCL with number average molecular weight 2200 Tgs were nearly the same. The thermogravimetric results of the prepared copoiymers showed three distinct weight loss steps assigned to the thermal degradation of PHB, PCL blocks and urethane linkage with increasing temperature, respectively. For all the prepared copoiymers, regardless of the PCL molecular weight, the intrinsic viscosity decreased with increasing the PHB content. The prepared copoiymers as well as PHB homopolymer were subjected to UV-irradiation for different time intervals, it was found that the rate of photodegradation of the investigated copoiymers increases with increasing the content of PCL and the time of irradiation. Also the biodegradability in soil has been studied, for the samples either subjected to UV-irradiation or unsubjected. It has been observed that the jate of biodegradation increases with increasing PHB content and with photo radiated samples, and as the time of UV irradiation increases the rate of biodegradation increase.