Polymethylmethacrylate - Lucy Dennell 1/9/2003

Biochemistry

 

Acrylics and acrylic resins are common names for polymers of acrylic and methacrylic acid derivatives.

1920’s PMMA was one of the first plastics used industrially in its strong transparent form as ‘plexiglas’.

1,2 propenoic acid =acrylic acid, 2 methyl 1,2 propenoic acid = methacrylic acid

 

acid + alcohol = ester, methacrylic acid + alcohol =methylmethacrylic acid, its polymer is PMMA

 

The reaction is exothermic promoted by free radicals. Free radicals are generated from peroxide

 

 

Powder             PMMA spheres10-40um 90%            

Peroxide initiator dibenzoyl peroxide 10-2%   

Ba SO4 or Zirconium dioxide 4-8%

Heat stable antibiotic powder Gentamicin,Tobramycin, erythromycin, Vancomycin or Cephalosporin

Methylene blue or chorophyll to give colour

 

Liquid                MMA 85%        

comonomers 10-15%

NNdimethyl-p-toluidine 1-2% (accelerator sets off the release of free radicals at room temperature)                        

hydroxyquinone stabiliser 50-100 ppm

 

Dough time 2-3 mins+ working time 5-8 mins = setting time7-11 mins

 

Factors which affect cement during mixing

 

Manual vs mechanical improves the uniformity of the cement mass

Vacuuming decreases voids

Centrifugation   evidence not strong either way

Speed of mixing/length of mixing time – too fast or too long can promote the loss of monomer

Temperature increases shorten dough and setting times by 5% per centigrade



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