Giving green polymers the blue light

Article by Neil Clark

BLUE light has been used by researchers to create an interpenetrating polymeric network (IPN) in one step, under ambient conditions.

When linked together, two or more polymer chains with different mechanical properties can form IPNs. This resulting network is not bonded through chemical means, instead polymer chains are entangled and cannot be pulled apart. Subsequently, material performance can be enhanced, with applications including ion exchange resins and medical dressings. However, the process of linkage typically requires a lengthy two-step process or a one-step process requiring high temperatures.

Now, researchers at the University of Delaware, US, have reported in Polymer Chemistry a novel one-step process to produce an IPN. The new network exhibited enhanced toughness, and overcame issues of brittleness without any solvents or additives, making it a greener synthetic approach.

Their method involves using 470 nm blue light to photoinitiate the formation of two networks simultaneously and orthogonally, which occurs at room temperature in air. One reaction was copper-catalysed azide-alkyne cycloaddition (CuAAC) click polymerisation. This reaction is facilitated by copper, and polymerisation occurs in steps. The other was methacrylate polymerisation, which forms a plastic-like material in a manner similar to adding links to a growing chain. 

The researchers created a University of Delaware logo

Co-author Christopher Kloxin said: “This is unique in the way the blue light induces sequential reactions.”

The end result was a material described as a “glassy film”, which was less brittle than pure methacrylate and stronger than pure CuAAC at higher temperature. Other advantages include a saving in time and energy, and increased precision of shaping of polymer networks.

The authors also report that films made from this IPN also exhibit shape memory, and can be returned to their original size and shape with 15 minutes of heating at 80°C.

A provisional patent for the method has been filed by the authors, and Kloxin believes that the chemistries could be attached to other molecules. He has said that the team will test their applications to form hydrogels, dental materials and other polymer networks.

Polymer Chemistry:

Article by Neil Clark

Staff Reporter, The Chemical Engineer

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