Interrelationship between feeding profiles and chains composition-morphology-mechanical properties for forced composition copolymers synthesized by redox initiation

A semicontinuous emulsion copolymerization via redox initiation (tetramethylenediamine with potassium persulfate) is used to show how, by variations in the comonomers feeding profile, substantial modifications can be obtained in the composition of the copolymer chains that are formed along the reaction, which in turn modifies in a significant manner the morphology and mechanical properties of the materials. That is, changing the comonomers feeding profile and building a histogram for the composition distribution of the synthesized copolymer chains, changes in mechanical properties can be explained along with changes in morphology. Styrene and n-butyl acrylate 50/50 w/w were used to prepare the copolymers. To study the effect of the aforementioned changes caused by the feeding profiles, three pairs of feeding profiles were considered; the “A profiles” were selected to promote different composition histograms, whereas the “B profiles” represent modified “A profiles”. Global conversion was determined by gravimetry and the global copolymer composition along conversion by 1 H NMR. Stress–strain tests and dynamic-mechanical analysis were performed to evaluate their mechanical properties. An equivalent statistical copolymer was the reference material. Using redox initiation, the results show for a semicontinuous process, that a fast reaction at low temperature is very convenient. In addition, the interrelation analysis for feeding profiles-histogram-morphology-mechanical properties performance, allows for the first time, the understanding of copolymers mechanical performance as a whole, which can be used as a basis to ease their tailored design.