Prepolymer purification

The biodegradable polymer available in the market today in largest amounts is PEA. PEA is a melt-processible thermoplastic polymer based completely on renewable resources. The manufacture of PEA includes one fermentation step followed by several chemical transformations. The typical annually renewable raw material source is com starch, which is broken down to unrefined dextrose. This sugar is then subjected to a fermentative transformation to lactic acid (LA). Direct polycondensation of LA is possible, but usually LA is first chemically converted to lactide, a cyclic dimer of LA, via a PLA prepolymer. Finally, after purification, lactide is subjected to a ring-opening polymerization to yield PLA [13-17]. 

A reactor was charged with poly[(R)-3-hydroxybutyrate], diethylene glycol, dibutyltin dilaurate, and diglyme and then heated overnight and the telechelic hydroxylated prepolymer isolated and used without further purification. 

All chemicals used in this study were reagent grade. Butyl isocyanate (BuNCO, 99% from the Upjohn Chemical Co.), hexamethy-lene diisocyanate (HDI, 99% from the Mobay Chemical Co.), phenyl isocyanate (PhNCO, 99%, from the Upjohn Chemical Co.), p-tolyl isocyanate (MePhNCO, 99% from the Aldrich Chmical Co.), p-chloro-phenyl isocyanate (CIPhNCO, 99%, from the Aldrich Chemical Co.) and cyclohexyl isocyanate (CHI, 98%, from the Aldrich Chemical Co.) were purified by vacuum distillation. Methylene diphenyl diisocyanate (MDI, 99%+, from the Mobay Chemical Co.) was used without further purification. N,N-Dimethylformamide (DMF, reagent grade, from the Mallinckrodt) was dried by molecular sieves 4a. The NCO-terminated prepolymers were prepared from poly(oxy-tetramethylenediol) (POTMD, mol. wt. 650, 1000, 2000, Quaker Oats Chem. Co.) and MDI. 

Naphthalene evolves at heat treatment of prepolymer in the first case. Anthracene evolves in the second case. Purification polymer from residual impurities occurs when the temperature of heat treatment rise. According to spectral researches, the absorption caused by presence of sp-hybrid carbon is not observed in films. Absorption in the field of 1,480 cm" caused by presence of C=C bonds in Spectra KP of considered polymers, is shifted compared to the absorption observed in polyacetylene, received by other methods (1,460 cm ). 

Tetramethylene diamine and diethyl oxalate were prepol5onerized in a 50/50 phenol/trichlorobenzene mixture at 140°C. The prepolymer, after purification, was subjected to solid-phase polymerization under nitrogen at 250 300°C to form poly(tetramethylene oxalamide) or nylon-4,2 [78], The polymer exhibited rjuih as high as 2.7 dl/g as measured from a 0.5% solution of polymer in 96% sulfuric acid. Interestingly, the polymer was soluble in trifluoroacetic acid, dichloroacetic acid, and 96% sulfuric acid, but not in 90% formic acid. It had a melt temperature of 388-392°C and heat of fusion of 148-154 J/g (35-37 cal/g). 

Several synthetic strategies have been developed to prepare phosphonated aromatic polymers, where the acid groups are attached either directly " or via spacers to an aromatic backbone. " These polymers can be prepared either by post-phosphonation of prepolymers via, e.g. transition metal catalyzed Michaelis-Arbuzov reactions and lithiation chemistiy, or by direct polymerization of phosphonated monomers via polycondensation. Both synthetic strategies then require hydrolysis of the esters to obtain the free acid. The former strategy requires the formation of C-P bonds in the polymer structure, and the latter necessitates the synthesis and purification of suitable monomers. 

The lactide monomer for PLA is obtained from catalytic depolymeiization of short PLA chains under reduced pressure [4]. This prepolymer is produced by dehydration and polycondensation of lactic acid under vacuum at high temperature. After purification, lactide is used for the production of PLA and lactide copolymers by ROP, which is conducted in bulk at temperatures above the melting point of the lactides and below temperatures that cause degradation of the formed PLA [4]. 

GPC analysis of the prepolymer formation and purification (starting molar ratio P0TM-T8/MDI=1 10, Fig. 10a), and of the chain extension reaction (extender Diol-2, Fig. 10b) the log M scale on the upper abscissa is based on polystyrene (—) Rl-detector (...) UV-detector. 

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