Anionic polymerization and transport of diethyl methylidene malonate on polyolefin copolymer surfaces

Abstract

Polymer coatings are increasingly applied to polymeric substrates to improve interfacial properties in high wear environments. Thus, there is a need for chemically grafted coatings synthesized under practical conditions. Here, we explored methylidene malonates chemically grafted to commodity polymeric substrates with small amounts of nucleophilic initiator in the backbone. The polymerization and grafting conditions were evaluated by polymerizing diethyl methylidene malonate monomer (DEMM) from poly(ethylene-co-acrylic acid) (pEAA), both the acid form and the sodium salt, with varying concentrations of acrylic acid. For the first time, grafting of pDEMM was demonstrated on the substrates containing carboxylic acid and carboxylate salts using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). By studying the increase in monomer droplet area against a non-reactive control, we determined that the transport phenomena were reaction mediated and resulted in heterogenous amounts of grafted polymer. The area change over time was linear or stagnant at the beginning of the reaction (<30 min), and the slope increased with increasing initiator for the base treated samples (between 0.01–0.03 cm² min⁻¹). A heat map was constructed from ATR-FTIR spectra, which suggests heterogenous grafting on pEAA with 10% acrylic acid and the sodium salt of pEAA with 10% acrylic acid, and homogenous grafting on the sodium salt of pEAA with 3% acrylic acid. By understanding the transport and homogeneity of grafted pDEMM, we can optimize the covalent attachment of methylidene malonate polymers, which holds potential to increase the adhesion and durability of coatings.