TABLE OF CONTENTS Acrylic polyols represent a special group of amorphous polyols, of molecular weight (MW) of 8000-13000 daltons, obtained by radical copolymerisation of acrylic monomers (ternary or quaternary copolymers), such as acrylic or methacrylic acids and esters. The source of hydroxyl groups in these acrylic polyols is the utilisation in the radical copolymerisation reaction of hydroxyalkyl acrylates or hydroxyalkyl methacrylates [1, 2] as comonomers. The acrylic polyols are used in high performance polyurethane (PU) coatings.
The most important comonomers used as raw materials in acrylic polyols syntheses are shown in Figure 10.1.
The general radical copolymerisation reaction for synthesis of acrylic polyols is shown in reaction 10.1. It is obligatory that one of the comonomers is a hydroxyalkyl acrylate or hydroxyalkyl methacrylate (mainly hydroxyethylacrylate and hydroxyethylmethacrylate) in order to introduce hydroxyl groups (as lateral groups, not as terminal groups) available for the reaction with -NCO groups of diisocyanates (reaction 10.1).
| (10.1) |  |
Generally, the radical copolymerisation reactions of acrylic comonomers are performed in an adequate solvent, by dropwise addition of monomer - initiator (peroxides) mixture.
The resulting performances of acrylic polyol based PU coatings depend profoundly on the chemical nature of the monomers used. Thus, methylmethacrylate (MMA) confers exterior durability, excellent light stability, hardness and water resistance. Styrene confers hardness, water stability but, unfortunately, poor light stability. Butyl and 2-ethylhexyl acrylates and methacrylates confer flexibility and acrylic and methacrylic acids confer adhesion to metals and solvent/grease resistance.
Two representative acrylic polyols,...
