Aromatic poly anhydrides

The analysis of NMR spectra of aliphatic and aromatic poly anhydrides has been reported by Ron et al. (1991), and McCann et al. (1999) and Shen et al. (2002), and C NMR has been reported by Heatley et al. (1998). In NMR, the aliphatic protons have chemical shifts between 1 and 2 ppm, unless they are adjacent to electron withdrawing groups. Aliphatic protons appear at about 2.45 ppm when a to an anhydride bond and can be shifted even further when adjacent to ether oxygens. Aromatic protons typically appear with chemical shifts between 6.5 and 8.5 ppm and are also shifted up by association with anhydride bonds. The sequence distribution of copolymers can be assessed, for example in P(CPH-SA), by discerning the difference between protons adjacent to CPH-CPH bonds, CPH-SA bonds, and SA SA bonds (Shen et al., 2002). FTIR and NMR spectra for many of the polymers mentioned in Section II can be found in their respective references. 

Conix, A. (1958) Aromatic poly (anhydrides) a new class of high melting fiber-forming polymers,/ Polym. Sci, 29, 343. 

In the 1930 s, Carothers prepared a series of aliphatic poly(anhydride)s for potential use as fibers in the textile industry (1). However, the hydrolytic stability of these materials was very poor. By the mid-1950 s, Conix was able to synthesize aromatic poly(anhydride)s with improved film and fiber forming properties (2). Despite these properties, the polyanhydrides poor thermal and hydrolytic stability resulted in their limited use, and no conunercial applications were found. By the late 1960 s, however, hydrolytic instability became an important factor for polymers utilized in the manufacture of medical devices such as absorbable sutures and drug delivery systems. 

Therefore, aromatic poly(anhydride)s may prove useful for their potential as irradiatable devices. 

The mechanical properties as well as in-vitro testing of cylindrical dumbbells were also studied (Tables 4-6 and 8-14). As can be seen from the tables, the yield strength and modulus of the aromatic poly(anhydride)s developed by the methods described herein are similar to or greater than poly(p-dioxanone), an absorbable polyester used extensively for medical devices, and poly(anhydride)s described by other researchers. This is another indication that the aromatic poly(anhydride)s have the high molecular weights (I.V. > 1.0 dl/g), and consequently, the high strengths required in wound closure devices. 

As stated earlier, it was believed that aromatic poly(anhydride)s would be cobalt sterilizable since previous work at Ethicon (4a,b) established that incorporation of aromatic subtituents in the polymer backbone yielded irradiation stability. 

Table 3. Fiber Tensile Properties of Aromatic Poly(anhydride)s as a Function of Draw Ratio...

Even though no loss in physical properties was observed for aromatic poly(anhydride)s subjected to gamma irradiation, it is important to establish the polymers physical characteristics as a function of exposure time in-vitro. This is a necessary requirement, since past work has shown that absorbable polymers, and devices formed from them (PDS, Vicryl ), subjected to cobalt may indicate little change in physical properties, but when tested in-vitro rapidly lose strength. However, no difference is observed in in-vitro properties between coupons subjected to cobalt versus unirradiated coupons. In fact, yield strength as a function of weeks in-vitro appears to follow a linear decrease profile for annealed test coupons. However, unnanealed test coupons display an induction period (6 weeks) prior to the linear decrease in physical strength. 

The aromatic poly(anhydride)s also display various physical strength breakdown profiles, from that of low strength/slow breakdown (i.e., 1,6 PA) to that of high strength/fast breakdown (i.e., 1,2 PA), with behavior between the two extremes (i.e., 1,4 PA). 

The present report describes a synthetic process for preparing aromatic poly(anhydride)s, potentially useful as biomedical devices, with high molecular weights as characterized by inherent viscosities in excess of 1.0 dl/g in common organic solvents such as chloroform at ambient (25°C) temperature. 

The aromatic poly(anhydride)s were also extruded into fibers. For example, a sample of poly[l,4-bis(p-carboxyphenoxy)butane] exhibiting a melting point of 190°C was extruded using an Instron capillary rheometer equipped with a 40-mil die with an L/D of 25. 

---