Advantages of polycarboxylic over dicarboxylic anhydrides in the melt modification of PPC

We present an alternative polymer modification of poly (propylene carbonate) (PPC). A conventional practice for PPC melt processing is the melt – modification with maleic anhydride (MAH) – a di-carboxylic anhydride –. In our work, PPC is melt-modified with pyromellitic di-anhydride (PDAH) – a tetra-carboxylic dianhydride –. Using MAH modified PPC as reference, the polymer degradation and the thermal and viscoelastic properties of the materials are studied. Both anhydrides after their melt compounding have similar efficiency in the conservation of the molecular weight. Strikingly, the use of PDAH is advantageous over MAH considering the improvement of the thermal stability, the decrease of the complex melt viscosity and higher storage modulus (stiffness) of the modified PPC. It is speculated that the changes in the material performance arise from the occurrence of long chain branching and non-covalent interactions from the PDAH modifier.