Time-resolved micro-indentation hardness measurement to probe the Form II/Form I crystal polymorphism in random copolymers of butene-1 with either ethylene or propylene

Time-resolved micro-indentation hardness measurements have been performed on random copolymers of butene-1 with minor amount of ethylene or propylene during the room-temperature transition of the Form II mesophase into Form I crystals. The microhardness depends on the present crystal polymorph and increases during the Form II–Form I phase transformation, which is completed faster in the random copolymers than in the butene-1 homopolymer. It is furthermore observed that the microhardness decreases with increasing concentration of ethylene and propylene co-units in the random copolymers. This experimental result is comprehensively discussed in view of the observed decreases of the crystallinity and crystal perfection in copolymers containing ethylene or propylene, respectively. Analysis of a copolymer with about 11 mol% propylene revealed that the microhardness of copolymers containing Form I’ crystals, formed directly from the melt, is higher than the initial microhardness of samples of lower co-unit content containing only Form II mesophase.