Regardless of hydrophobicity, polymers have been found to imbibe and distribute water within in three states: non-freezable bound water (plasticizing water content), freezable bound water (so called second-layer water, and presumably water at an interface) and freezing free water (phase separated domains). The roles of each of these within these hydrophobic polymers continues to intrigue both industry and academia, as the associated water content can highly influence polymer properties such as transparency and the effective glass transition temperature. Indeed, it is this hydroplasticized glass transition, not only the polarity of the host polymer, that most strongly influences the water update dynamics. Permeability is a function of both solubility and diffusion, and even for more hydrophobic polymers if the system was below the effective glass transition significant phase separated water domains have still been observed. Few have attempted to quantitatively evaluate the dynamics and to correlate the associated water in these different states to the ultimate polymer properties. Here, a pseudo accelerated water-diffusion experiment for hydrophobic waterborne polymers was conducted and rigorously monitored by differential scanning calorimetry (DSC). Systematic variations in composition of hydrophobic polymers derived from emulsion polymerization were analyzed specifically for the dynamic evolution of their distribution of freezable free, freezable bound and non-freezable bound water content. This evaluation has successfully allowed us to not only quantify these distributions, but also to correlate them to specific variations in the host polymer properties. While we have previously reported quantitative analysis of the hydroplasticizing non-freezing bound water content by DSC, we emphasize here that the second-layer freezing free water content can also been quantitatively revealed by DSC. Careful consideration of sample preparation as well as the analytical method development is also highlighted. A second aspect of this work leverages the heat capacity and shape factors for the mixing of water with polymer specific to the glass transition. This has been observed as a result of our dynamic analysis contrasting cycles of the DSC profile as water diffuses into the polymer matrix. This data allows us to predict hydrated polymer DSC profiles for temperature regions that have been historically obscured by other transitions (for example, in the vicinity of 0 °C).

Quantitatively revealing the distribution of water within hydrophobic polymers via differential scanning calorimetry and theoretical prediction of hydrated polymer thermal profiles

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.