This lab involves the synthesis of an acrylic polymer. The reagents of hydroxyethyl acrylate, styrene, and butyl acrylate were reacted in a semi-batch process The product was then stored for one week before being crosslinked with a melamine-formaldehyde resin and a catalyst. The resulting coating was applied to an Al panel, cured, and tested according to ASTM D5402 for solvent resistance. This process was repeated and the formulation adjusted until a formulation exceeded 200 MEK double-rubs. The formulation was then created in a larger batch and applied to Al, steel, and free-film substrates by drawdown bars. These samples were then cured and characterized using various ASTM methods based on mechanical and chemical properties.
Melamine-Formaldehyde, Acrylic Resins, Crosslinking, Characterization, Semi-Batch
Acrylic resins were first used in the 1950s in the automotive industry.2 They have since increased their durability and practicality. Acrylic resins are formed by radical chain polymerization. This process has three stages: initiation, propagation, and termination. The formation of a radical is what begins this polymerization. That radical species is then able to react with monomer to produce a carbon radical on the monomer. This new radical can then react with other monomer creating a longer and longer chain of monomer. This polymer continues to grow being driven forward by the reactivity of the radical until it is terminated by either another radical or by other means.2
The objective of this lab is to successfully synthesize an acrylic resin with favorable PDI, then crosslink the polymer with melamine-formaldehyde. This reaction looks to create a coating that will be able to be tested using numerous characterization techniques following ASTMs.
The first step in this experiment was the synthesis of the acrylic resin. A semi-batch process was used in this synthesis. Xylene (100.0g) was added to the resin kettle and began heating to 90?°C. A nitrogen flow was then started to blanket the entire apparatus. Special care was taken to not have an excessive flow to preserve the solvent. While the solvent is heating, hydroxyethyl acrylate (15.0g), styrene (82.6g), butyl acrylate (52.5g), and Vazo 67 (3.75g) was mixed in an Erlenmeyer flask until the initiator, Vazo 67, was fully dissolved. This solution was then added to an addition funnel that ran into the kettle of xylene. The monomer solution began being deposited into the heated solvent dropwise. The temperature was monitored constantly. The temperature goal of the addition period was 90-95?°C. To control the temperature, the mantle was turned off and lowered to cool and raised and turned on to heat. This back-and-forth heating and cooling cycle created a predictable and steady heating throughout the addition. The entire addition lasted 56 minutes. Once the entire monomer solution was added, the batch was held at the 90-95?°C for an additional 30 minutes. A chaser of xylene (2.5g) and Vazo 67 (0.5g) was added directly into the kettle after this waiting period. The temperature was then maintained for an additional hour.
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