Polyanhydrides aliphatic

In contrast, aliphatic polyanhydrides such as poly(SA) and poly-(PDP) decreased in molecular weight over time. The decrease in molecular weight shows first-order kinetics, with activation energies... 

Fatty acids have also been converted to difunctional monomers for polyanhydride synthesis by dimerizing the unsaturated erucic or oleic acid to form branched monomers. These monomers are collectively referred to as fatty acid dimers and the polymers are referred to as poly(fatty acid dimer) (PFAD). PFAD (erucic acid dimer) was synthesized by Domb and Maniar (1993) via melt polycondensation and was a liquid at room temperature. Desiring to increase the hydrophobicity of aliphatic polyanhydrides such as PSA without adding aromaticity to the monomers (and thereby increasing the melting point), Teomim and Domb (1999) and Krasko et al. (2002) have synthesized fatty acid terminated PSA. Octanoic, lauric, myristic, stearic, ricinoleic, oleic, linoleic, and lithocholic acid acetate anhydrides were added to the melt polycondensation reactions to obtain the desired terminations. As desired, a dramatic reduction in the erosion rate was obtained (Krasko et al., 2002 Teomim and Domb, 1999). 

Polyanhydrides Polyanhydrides have a hydrophobic backbone with a hydrolytically labile anhydride linkage. These polymers widely vary in chemical composition and include aliphatic, aromatic, and fatty acid-based polyanhydrides. The rate of degradation depends on the chemical composition of the polymer. In general, aliphatic polyanhydrides degrade more rapidly than the aromatic polymer. Hence, copolymer blends with varying ratios of aliphatic-to-aromatic polyanhydrides can be synthesized to suit specific applications. 

Poly(anhydrides) are polymers containing the group -C(0)-0-C(0)- in their backbone. Several polyanhydrides such as poly(oxyisophthaloyl), poly(oxycarbonyl-1,4-phenylene methylene-1,4-phenylene carbonyl), poly(oxycarbonyl-1,4-phenylene isopropylidene-1,4-phenylene carbonyl), and poly(oxycarbonyl-1,4-phenylene isobutylidene-1,4-phenylene carbonyl) were synthesized with the expectation of good biodegradability. They do have good hydrolytic stability as opposed to aliphatic polyanhydrides [1]. The structures of these polymers are shown below. 

The first aliphatic polyanhydride was synthesized from the monomer adipic acid (AA), which is thermally unstable and forms cyclic dimers and polymeric rings... 

Aliphatic polyanhydrides H2 X = A, Adipic anhydride (AA) X = S, Sebacic anhydride (SA)... 

Over the last decade, SIMS and XPS have been shown to be powerful complementary techniques for determining the interfacial chemistries of polymers [68]. The surface chemical structure of aliphatic polyanhydride films has been examined using time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) [65, 66]. The Cls and Ols core level spectra are displayed for the homologous series of aliphatic polyanhydrides in Fig. 12. The main peak at 285 eV corresponds to the C-H. The peak at 289.5 eV arises from 0-C=0. The XPS data confirmed the purity of the surface, and the experimental surface elemental ratios were in good general agreement with the known stoichiometry of polyanhydrides. 

The melting point, as determined by differential scanning calorimeter, of these aromatic polyanhydrides is mnch higher than aliphatic polyanhydrides. The melting point of aliphatic-aromatic copolyanhydrides is proportional to aromatic content. For this type of copolymers, there is characteristically a minimnm between 5 and 20mol% of lower-melting component. The introdnction of fatty acids in the copolymer chain lowers the melting point as compared to that of bulk polymer [14]. 

The majority of polyanhydrides dissolve in solvents such as dichloromethane and chloroform. However, the aromatic polyanhydrides exhibit much lower solubility than aliphatic polyanhydrides. But the copolymers of two different aromatic monomers showed increased solubility with a decrease in T [15]. 

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