Aliphatic polymers, degradation

TGA analysis shows that polymer degradation starts at about 235°C which corresponds to the temperature of decomposition of the cellobiose monomer (m.p. 239°C with decom.). Torsion Braid analysis and differential scanning calorimetry measurements show that this polymer is very rigid and does not exhibit any transition in the range of -100 to +250 C, e.g. the polymer decomposition occurs below any transition temperature. This result is expected since both of the monomers, cellobiose and MDI, have rigid molecules and because cellobiose units of the polymer form intermolecular hydrogen bondings. Cellobiose polyurethanes based on aliphatic diisocyanates, e.g. HMDI, are expected to be more flexible. 

Yu T, Zhou Y, Liu K, Zhao Y, Chen E, Wang E, Wang D (2009) Improving thermal stability of biodegradable aliphatic polycarbonate by metal ion coordination. Polym Degrad Stab 94 253-258... 

Kaspersma, J. Doumen, C. Munro, S. Prins, A. M. Fire retardant mechanism of aliphatic bromine compounds in polystyrene and polypropylene, Polymer Degradation and Stability, 2002, 77(2), 325-331. 

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. 

Polymers do not normally biodegrade until they are broken down into fairly low molecular weight chemical species that can be assimilated by microorganisms. Aliphatic polyesters degrade in the presence of water by sequential hydrolytic cleavage of the backbone ester bonds leading to production of monomeric hydroxyl carboxylic acids which in turn can be metabolized by bacteria (5). 

M. Predel and W. Kaminsky Pyrolysis of Mixed Polyolefins in a Fluidised-Bed Reactor and on a Pyro-GC/MS to Yield Aliphatic Waxes. Polym. Degrad. Stabil, 70, 373 (2000). 

M. Predel and W. Kaminsky, Pyrolysis of mixed polyolefins in a finidized-bed reactor and on a pyro-GC/MS to yield aliphatic waxes. Polymer Degradation and Stability, 70, 373-385 (2000). 

Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy have also been used to authenticate polyanhydride structures. Aliphatic polymers absorb at 1740 and 1810 cm while aromatic polymers absorb at 1720 and 1780 cm All the polyanhydrides show methylene bands because of deformation, stretching, rocking, and twisting. Aside from being used to ascertain polyanhydride structures, these techniques can be used to determine degradation progress, by monitoring the area of carboxylic acid peak (1770-1675 cm ) with respect to the characteristic anhydride peaks over time. 

It is interesting to note that both polyurethanes derived from aliphatic diisocyanate and aromatic diisocyanate were degraded. With a few exceptions, the more rigid aromatic polymers degraded at slower rates than the aliphatic polymers. 

For a simplified case in which the entire polymerization reaction is assumed to occur at a constant temperature under conditions that eliminate the reverse reaction (see Reaction 32), the time needed to polymerize nylon 66 to 99% conversion is given by Equation 41. This equation yields a reaction time of 17 min for polymerization at 280 °C of nylon 66 to 99% conversion (DP = 100). This calculation emphasizes the need for condensation reactions with a fast reaction rate in view of the high reaction yield needed. Reactions with rate constants significantly smaller than the constants for aliphatic amidation will require long reaction times and, therefore, will be impractical for polymer formation, particularly if monomer side reactions or polymer degradation can occur under conditions of the polymerization. 

FUJ 98] Fujimaki T., Processability and properties of aliphatic polyesters, BIONOLLE , synthesized by polycondensation reaction . Polymer Degradation and Stability, vol. 59, nos. 1-3, pp. 209-214,1998. 

RUT 01] Rutot D., Duquesne E., Ydens I., etal, Aliphatic polyester-based biodegradable materials new amphiphthc graft copolymers . Polymer Degradation and Stability, vol. 73, no. 3,pp. 561-566,2001. 

K. Gorna, S. Gogolewski, In vitro degradation of novel medical biodegradable aliphatic polyurethanes based on -caprolactone and Pluronics with various hydrophilicities, Polym. Degrad. Stab. 75 (1) (2002) 113-122. 

Buchanan, C.M., Boggs, C.N., Dorschel, D., Gardner, R.M., Komarek, R.J., Watterson, T.L., and White, A.W., 1995, Composting of miscible cellulose acetate propionate-aliphatic polyester blends, y. Environ. Polym. Degrad, 1-11. 

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