The present state-of-the-art in high voltage polymeric capacitors is dominated by metallized biaxially oriented polypropylene (BOPP). BOPP, however, has a low dielectric constant (~2.2) and provides a low energy density of (3-5) J/cm3 at breakdown. Yuan et al. (Macrom.(2010), 43:4011-4015) recently reported the synthesis of hydroxyl-functionalized polypropylene (PPOH) that exhibited energy density 2-3 times that of BOPP.In this study, we investigate the effect of incorporation of OH groups (0-4 mol%) on the structure and thermal and rheological properties of polypropylene. Presence of H-bonding between the OH groups is confirmed using Fourier transform infrared spectroscopy (FTIR). The H-bonding densify the amorphous domains and increases the glass-transition temperature with an increasing degree of functionalization.Differential scanning calorimetry (DSC) analysis shows that the incorporation of comonomer in PP reduces the crystallinity by as much as 15%. It also disrupts the growth behavior of PP crystals resulting in a reduction in the lamellar thickness measured using small angle X-ray scattering (SAXS), and therefore the melting point. However, the a-monoclinic crystal structure of PP remains unaffected. Small-amplitude oscillatory shear (SOAS) measurements from 165-250oC show that the storage (G') and loss (G?) modulus are higher for PPOH copolymers due to H-bonding. For PPOH containing 3.9 mol% -OH groups, G'>G? over the entire frequency range. It appears that the H-bonding in this polymer is sufficient to provide a weak gel network.

Probing the structure-property relationship in hydroxyl-functionalized polypropylenes

246th National Meeting (2013)

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