The Chemistry of Silly Putty

1. The Chemistry of Silly Putty Composition of Silly Putty Bond Types Tetrahedral structural unit of silica (SiO2), The siloxane unit • The polymers in silly putty have covalent bonds within the molecules, but hydrogen bonds between the molecules. • These hydrogen bonds are easily broken, when only small amounts of stress are slowly applied to the putty. Only a few bonds are broken and that’s why the putty can “stretch". • When larger amounts of stress are applied quickly, there are many hydrogen bonds that break, and that is why it can also rip apart 65% - Dimethyl Siloxane 17% - Silica   9% - Thixotrol ST (castor oil derivative)   4% - Polydimethylsiloxane   1% - Decamethyl cyclopentasiloxane   1% - Glycerine   1% - Titanium Dioxide Glycerine Titanium Dioxide Polydimethylsiloxane Cyclopentasiloxane Structure of the major component of caster oil Silicones What is an Inorganic Polymer? This is a single boric acid • Polyorganosiloxanes have empirical formulas of R2SiO, and are called silicones. • Silicones are viscoelastic materials. They behave like liquids at high temperature or when allowed to flow over a long period of time. They behave like elastic solids or elastomers at low temperature. The elastic behavior comes from the very flexible silicon-oxygen bonds. When the molecular weight is high, these flexible chains become loosely entangled which imparts a high level of viscoelasticity. • Polydimethylsiloxane has repeating (CH3)2SiO. Altering the number of repeat units (value of n) in the chain and the degree of cross-linking which ties multiple polymer chains together generates polymers possessing different physical properties. Since silicon-chlorine bonds are very susceptible to cleavage by water, polydimethylsiloxane can be synthesized by hydrolyzing dichlorodimethylsilane. • The initial hydrolysis reaction exothermically generates a silanol Si(CH3)2(OH)2 which condenses through the loss of water to form the siloxane polymer. Since dichlorodimethylsilane is bifunctional (has two chlorines). The Chain will then spread in two directions, and this generates high molecular weight polymers which retain some residual hydroxyl groups. The residual hydroxyl groups react with boric acid B(OH)3 to form Si-O-B linkages between polysiloxane chains. Since boric acid is trifunctional, a single boron has the ability to join three polysiloxane chains together. This joining of chains is called cross-linking. Cross-linking produces a high molecular weight polymer that is a soft and flexible. This is an example of boric acid hydrogen bonding. Thixotrol It is large molecules, usually linear or branched chains with atoms other than carbon in their backbone A Thixotropy is the property of certain gels or fluids that are thick (viscous) under normal conditions, but flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed. Fun Fact How it’s Made You can actually make your own homemade version of silly putty. solution of 55% Elmer's glue solution in water solution of 16% sodium borate (Borax) in water food coloring (optional) Ziploc bags Mix together 4 parts of the glue solution with one part of the borax solution. Add food coloring, if desired. Refrigerate the mixture in the sealed bag when not in use. • Silly Putty is an inorganic polymer • One way to make the polymer is by reacting dimethyldichlorosilane in diethyl ether with water. The ether solution of the silicone oil is washed with an aqueous sodium bicarbonate solution. The ether is evaporated off. Powdered boric oxide is added to the oil and heated to make the putty. • The initial reaction is also known to be violent