Abstract
The radical polymerisation of acrylic acid is largely concentration dependent and affected by the type of the surrounding solvent. This work investigates reaction rate constants, the activation energy, heat flux and the molecular weight in the industrially relevant synthesis of low molecular mass acrylic acid polymers in 2-propanol. The polymerisations were carried out isothermally in an RC1e calorimeter with inline Raman spectroscopy for monomer concentration monitoring. For a non-neutralised acrylic acid in isopropanol (150 g/L), a monomer reaction order of 1.73 ± 0.15, an activation energy of 58.6 ± 0.8 kJ/mol (0.5 mol% AIBN) and 88.5 ± 1.5 kJ/mol (1.0 mol% AIBN), and a reaction enthalpy of 66.4 ± 4.8 kJ/mol could be shown. This data is in accordance with the literature values for acrylic acid polymerisation in water. In addition, linear correlations between the respective reaction parameters and the molecular weight for customised polymer synthesis in the range from 1.2 to 1.7 × 104 g/mol could be established. In comparison with aqueous acrylic acid polymerisation, it was found that the reaction rate constants in isopropanol were slower by a factor of approximately 10 under similar reaction conditions.
Highlights
IntroductionPolymers of acrylic acid are versatile and have a wide range of applications
When using thermal initiators such as AIBN, cooled initiator solutions are usually used in order not to generate radicals before the solution is joined with the reaction mixture
The synthesis of especially low molecular acrylic acid polymers is an interesting topic for industrial applications, mainly as dispersing agents for inorganic pigments or salt scaling inhibitors [6,7,8]
Summary
Polymers of acrylic acid are versatile and have a wide range of applications. Their partial biodegradability [1] in particular makes their applications in cosmetic products attractive. Poly(acrylic acid) is a weak polyelectrolyte which can be used, if cross-linked, as a powerful, super absorbent material. It is used as a thickener, emulsifier and deflocculating agent in industry [2,3,4,5]. Low-molecular polyacrylic acid from polymerisation in isopropanol or mixtures of isopropanol and water is used as a dispersant for inorganic pigments [6] in, e.g., the oil industry or water treatment due to its salt scale inhibiting effect [7,8]
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