Soluble-shell polymers (SSPs) are emulsion particles with a core-shell morphology where the core is a high-molecular weight acrylic polymer with low to no acid and the shell is a lower-molecular weight (typically 3,000-50,000 Da), high-acid oligomer. The soluble “shell” is often referred to in the literature as an alkali-soluble resin (ASR) due to its solubility in water at high pH and can be used in partial or full replacement of surfactant to stabilize the subsequent core. We have synthesized a series of acrylic soluble-shell polymers with an end-chain alkoxysilane crosslinkable moiety. The crosslinking was achieved by using mercaptopropyltrimethoxysilane (MPTMS) as a chain transfer agent in the first stage of the acrylic synthesis. Introducing crosslinking functionality via a functional chain transfer agent allowed for end-functionality rather than a random distribution of reactive groups. MPTMS was effective at mitigating the molecular weight of the acrylic shell. The resulting dried films showed improved mechanical properties and thermo-mechanical stability, as shown in the figure below. Polymers without reactive crosslinking groups flowed at elevated temperature, as did a polymer with a randomly distributed alkoxysilane crosslinker (methacryloxypropyl trimethoxysilane, MATS). However, polymers synthesized with end-functional alkoxysilane crosslinkable groups did not exhibit this necking behavior.

Soluble-shell polymers (SSP) with end-functional crosslinking technology

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ACS Fall 2022

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