Acrylic polymers

Table of Contents

Acrlic polymers are synthetic resins made from the polymerization of the esters of acrylic acid CH2=CHCOOH (2-propenoic acid), methacrylic acid CH2=C(CH3)COOH (2-methylpropenoic acid) or their esters.

The most common acrylic polymers are polymethylacrylate and polyethylacrylate and are used to make paints, surface coatings, adhesives and in textiles.

Acrylic acid or 2-propenoic acid is obtained from the oxidation of propene to 2-propenal also known as acrolein:

H2C = CH-CH3(g) + O2(g) → H2C = CH-CHO(g) + H2O(g)

In this stage propene and air are mixed and allowed to flow at a temperature of about 380°C over silica coated with catalyst often consisting of a mixture of bismuth oxide (III) Bi2O3 and molybdenum oxide (IV) MoO2.

In the second stage of the reaction the 2-propenal and air are made to flow at the temperature of about 280°C on the silica coated thick catalyst consisting of a mixture of vanadium oxide (V) V2O5 and molybdenum oxide (IV) MoO2 according to the reaction:

2 H2C = CH-CHO(g) + O2(g) → 2 H2C = CH-COOH(g)

which results in the formation of acrylic acid.

Uses

Depending on the R group, which can be any organic radical, the properties of polymers of this type vary and are now used as ingredients in the impregnation of fabrics, for surface finishing, for the production of artificial leather, lacquers and as a plastic intermediate in the so-called “safety” glass. For the latter use, the properties of methacrylic polymers are exploited, which are similar to those of glass (rigidity and transparency), while acrylic polymers are rubbery and plastic.

The most important polymer is methyl polymethacrylate in which the R radical is a methyl; it is prepared by thermal mass polymerization of the pure monomer in the presence of radical initiators such as azo-bis-isobutyronitrile or benzoyl peroxide. To obtain it in powder form, polymerization is carried out with the monomer in aqueous suspension by adding suitable additives to regulate the degree of polymerization. Methyl methacrylate powder is used for the manufacture of manufactured goods by the moulding process.

From the copolymerization of ethyl acrylate and other acrylates in the presence of halogen-containing compounds, elastomers are obtained which have high resistance to oils and fuels and maintain their properties unchanged up to 150°C. They are therefore used by the automotive industry for gaskets, steering systems, automatic transmissions and in general for applications where resistance to petrol and high temperatures are required.

These elastomers also remain unaltered in the presence of ozone and sunlight.

The ethylmethacrylate-methylmethacrylate copolymer known as Paraloid B72 is used in the restoration field as a consolidating agent if it has low concentrations or as an adhesive if it has higher concentrations. It allows excellent waterproofing performance and has the advantage of being reversible and stable over the long term.

Paraloid B72 is used in particular as a wood consolidating agent. In fact, it reduces microporosity, giving greater compactness without altering the natural colors thanks to its transparency.

Acrylic colors are made up of pigments dispersed in an acrylic resin. They have the characteristic of being soluble in water but resistant to water once dried. They dry quickly and are vivid, intense, with high covering power, easy to mix and easy to apply.

Methacrylic polymers (MMA, PMMA), which have properties similar to those of glass (rigidity and transparency even greater than glass), are used for the production of safety glass displays etc., while acrylic polymers (ACM, AEM, PAN) are elastomeric in nature. PMMA, one of the most important polymers of the category (in which the R radical is a methyl) is prepared by thermal mass polymerization of the pure monomer in the presence of radical initiators such as azo-bis-isobutyronitrile or benzoyl peroxide, while to obtain it in powder form, polymerization takes place in an aqueous suspension by adding catalysts which serve to regulate the degree of polymerization.

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