Copolymer composition, degradation

C and is easily processable, whereas the homopolymers do not melt before the onset of thermal degradation, at temperatures as high as 500°C.73,74 Varying copolymer composition permits the adjustment of melting temperature and of other properties (e.g., solubility) to desired values. This method is frequently used for aliphatic and aromatic-aliphatic polyesters as well. 

Deschamps AA, Grijpma DW, and Feijen J. Poly(ethylene oxide)/poly(butylenes terephthalate) segmented block copolymers The effect of copolymer composition on physical properties and degradation behavior. Polymer, 2001, 42, 9335-9345. 

The copolymer compositions were studied by elemental microanalyses and H-NMR, revealing that the content of the copolymer units is in aU cases very similar to that of their corresponding feed. The PU(DiT-HDl) homopolymer exhibited a high crystallinity, but the introduction of the arabinitol-based diols led to a reduction in the crystallinity of the copolymers. In their TGA curves, the copolymers exhibited a mixed trend of the related homopolymers, and all of them were thermally stable, with degradation temperatures above 220°C. The degradation... 

Fig. 75. Comparison of absorbance by copolymers of vinyl chloride and vinyl acetate at three maxima in the UV spectrum for 5% degraded samples with copolymer composition.

The chain statistics method has been applied to the case of a copolyamide with units of adipoyl piperazine (referred to as A) and of truxilloyl piperazine (referred to as B). Photolysis was used for the copolymer degradation. This is a case of totally selective cleavage, since the cyclobutane ring is split quantitatively in two parts by photolysis. Figure 2.27a reports the experimental mass spectrum, whereas Figure 2.2 reports the calculated spectrum. The copolymer composition turned out to be Ca= 0.80, with an agreement factor AF = 6%. 

Since the PHA depolymerases have ndo-hydrolase activity, as mentioned above, the random copolymers with 3HB unit as a major constituent are degradable by PHA depolymerase even though enzymatically inactive monomeric units are introduced. The effects of chemical structure of second monomer units and copolymer compositions on the rate of enzymatic erosion have been examined through the enzymatic degradation of solution-cast films of random copolymers of 3HB with various HA units in the presence of PHA depolymerase. " The enzymatic degradation of solution-cast films of these PHA copolymers was performed in an aqueous solution of purified PHA depolymerase from R. pickettii T1 at 37 °C. The rate of enzymatic erosion of solution-cast PHA films increased markedly with an increase in the fraction of second monomer units up to 10-20 mol.% to reach a maximum value followed by a decrease in the erosion rate (Figure 18). The highest rates of enzymatic erosion were 5-10 times that of the P(3HB) homopolymer film. 

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