PRESERVATION OF SPECIMENS IN PLASTICS 



3' 



polymerization, it is good practice to keep it in a place where the tem- 

 perature is not likely to exceed 20° C. (68° '¥.). 



After the inhibitor has been removed, and especially after the catalyst 

 has been added , it is important to keep all inhibitor-free monomer and 

 partial polymer sirup refrigerated at a temperature of 4° C. (approxi- 

 mately 40° F.) or lower. Whenever chilled monomer or partial polymer 

 sirup is removed from the refrigerator for use during humid weather, 

 it is advisable to allow it to warm up to room temperature before opening 

 the container so as to guard against the entrance of water vapor that 

 tends to condense on the surface as long as it is cold. 



Removal of Inhibitor 



Before methacrylate monomer can be satisfactorily hardened for em- 

 bedment purposes, it must be freed of the hydroquinone inhibitor added 

 to it by the manufacturer in order to prevent premature polymerization. 

 This may be done either by distillation, which is the quicker but more 

 hazardous method, or by alkali extraction which is safer and simpler 

 though more time consuming. 



Removal of inhibitor by distillation. — The removal of hydroquinone, 

 and similar inhibiting substances, can be accomplished by heating the 

 inhibited monomer in such a manner as to volatilize it, and then con- 

 densing the inhibitor-free vapor in a suitable receiving vessel. This 

 should preferably be carried out under vacuum with an arrangement 



THERMOMETER 

 -10° TO 250° 



20° CONDENSER 



GLASS BEAD OR SMALL 

 GLASS TUBE SECTIONS 

 24/20 



STOPPER 



24/40 



PRESSURE 

 MANOMETER 



TO VACUUM 



RETORT HEATER OR 

 HEATING MANTLE 



TO DRAIN-*-C 



3> 



000 ML. FLASK 



Figure 10. — Arrangement of glass apparatus for vacuum distillation of inhibited 

 methacrylate-monomer liquid. This apparatus should be operated under a fume 

 hood. (Courtesy of E. I. du Pont de Nemours & Co. (Inc.), Plastics Dept.) 



