# Isothermal heat flow calorimetry for one-step determination of polymerization heat and rate of poly(acrylic acid) at varying pH

## TL;DR

This study uses heat flow measurements to determine how pH affects the energy and speed of acrylic acid polymerization in a single experiment.

## Contribution

The study introduces a one-step method using isothermal calorimetry to measure both polymerization heat and rate of acrylic acid at varying pH.

## Key findings

- The polymerization heat of acrylic acid increases from 72.5 kJ/mol at acidic pH to 75.3 kJ/mol at 75% neutralization.
- Time-corrected calorimetry enables accurate determination of polymerization rates comparable to prior studies.
- Size-exclusion chromatography confirmed molar mass and polydispersity data after polymerization.

## Abstract

The radical polymerization of olefinic monomers in solution is an exothermic process. Despite the widespread use of acrylic acid, the pH dependence of its polymerization heat has not been reported. In this study, we employ time-corrected isothermal heat-flow calorimetry to simultaneously determine the heat and the rate of polymerization of acrylic acid at different degrees of neutralization ranging from 0% to 125%. We find a heat of (72.5 ± 0.6) kJ mol−1 under acidic conditions and a maximum value of (75.3 ± 2.3) kJ mol−1 at a neutralization degree of 75%. Additionally, we demonstrate that the time correction of the experimental calorimetry data enables the determination of the polymerization rate of acrylic acid at different degrees of neutralization, yielding values comparable to those reported in previous studies. Therefore, the calorimetric experiment reported here allows the determination of the heat of polymerization and the rate of polymerization of acrylic acid in a single experiment.

Isothermal calorimetry, incorporating a time-correction method, was employed to measure the pH-dependent polymerization heat and polymerization rate of acrylic acid. Subsequent size-exclusion chromatography provided molar mass and polydispersity data.