Chain copolymerization pressure effect

Solution copolymerization of the MA-styrene pair has been studied in acetone at high pressure (1-4 kbars). At 40°C, the copolymerization reaction rate between MA and the growing polymer chain, having a MA unit preceding the active styrene moiety, increased with pressure for both bulk and solution copolymerizations condition. Thus, Enomoto and coworkers conclude the penultimate effect diminishes or disappears with pressure escalation. Composition and infrared studies show a 1 1 alternating structure for the material, over a wide range of monomer concentration of one component. 

The effectiveness of a modifier depends on its chemical structure, concentration, temperature, and pressure. A concentration-independent measure for its effectiveness is the chain transfer constant, defined as the ratio of kinetic coefficients for the transfer reaction to this substance and radical chain propagation reaction. Usually the effectiveness of chain transfer agents is increased with rising temperature and reduced pressure. The chain transfer constant of modifiers falls from aldehydes, which are more effective than ketones or esters, to hydrocarbons. Unsaturated hydrocarbons typically have higher transfer constants than saturated hydrocarbons and a strong effect on polymer density must be considered because of the ability to copolymerize that give a higher frequency of short-chain branches in the polymer. 

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