Process Optimization of Poly(ε-caprolactone) Synthesis by Ring Opening Polymerization

The reaction conditions employed for the synthesis of biodegradable polymers viacoordinated anionic ring opening polymerization (CAROP) can be very differentand may result in differences between the target and actual product molarmasses. Influence of three parameters, monomer (ε-caprolactone) concentration,initiator/catalyst molar ratio, monomer/initiator molar ratio, on real polymer molar masshas been studied. Our modelling embodied a mathematical equation through which wecalculated the initiator/catalyst (alcohol/stannous 2-ethylhexanoate) ratio for all givenmonomer concentrations and targeted molar masses of the polymers. We haveestablished that in order to synthesize a polymer of certain molar mass, a lower amountof catalyst would be required when higher monomer concentrations are used. Theamount of catalyst required was found to decrease as the target molar mass ofthe polymer increases. This reduction becomes sharper with increasing monomerconcentration. For example, the initiator/catalyst ratios of 33, 24 and 10 are needed tosynthesize polycaprolactones with molar masses of 10,000, 20,000 and 50,000 Daaccordingly at monomer concentration of 1 mol/L. The initiator/catalyst ratio of 40 isless subjected to the influence of monomer concentration and may be used tocalculate the universal amount of catalyst required for the synthesis of polymers with aparticular molar mass by ring opening polymerization. The proposed mathematicalmodel was confirmed by syntheses of polymers with different molar masses andinitiators.