Methyl methacrylate monomer-polymer equilibrium in solid polymer.
OBJECTIVE
Poly(methyl methacrylate) (PMMA) is commonly processed in dentistry by thermally initiating the free-radical polymerization of methyl methacrylate (MMA). Residual MMA, a tissue irritant, is a concern. The concentration of MMA ([MMA]) versus time and temperature was studied to identify optimum processing conditions.


METHODS
One hundred milligram portions of plain and dental PMMA powders were incubated (10-170 degrees C, 1-384 h), with and without 6.0 microL MMA added. After incubation, [MMA] was determined by GC.


RESULTS
For plain PMMA alone, equilibrium was attained in about 100 h. The equilibrium data for log[MMA] versus 1/T was better fitted by a quadratic than a straight line, and formed an upper bound to the values of [MMA] when PMMA was incubated with MMA at temperatures > approximately 120 degrees C. The response surface for [MMA] versus log(time) and reciprocal temperature was fitted. An 'overshoot' in the equilibration process was identified, and postulated to be due to a rapidly formed intermediate of unknown chemistry.


CONCLUSIONS
Minimization of the residual MMA in acrylic denture bases prepared by processing a mixture of PMMA and MMA is important for reasons of mechanical properties and irritancy. The response surface mapped here allows direct identification of the optimum processing conditions.
Lung
C Y K
CY
Dental Materials Science, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Victoria, Hong Kong.
Darvell
B W
BW
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002849:Chromatography, Gas; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008768:Methylmethacrylates / Q000737:chemistry*; D008956:Models, Chemical; D011108:Polymers / Q000737:chemistry; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D011208:Powders; D013696:Temperature; D013997:Time Factors
D003764:Dental Materials; D008768:Methylmethacrylates; D011108:Polymers; D011208:Powders; D019904:Polymethyl Methacrylate