Hard-Soft Conversion in Network Polymers: Effect of Molecular Weight of Crystallizable Prepolymer

A series of hard-soft convertible network polymers were obtained using Diels-Aider reaction between semicrystalline prepolymers, furyl-telechelic poly(epsilon-caprolactone) with number-averaged molecular weights ranging front 2450 to 8800 (PCLnF2; n(degree of polymerization) = 18, 22, 26, 33, and 74), and a tris-maleimide linker (M-3). The reaction between PCLnF2 and M-3 was conducted in the semicrystalline state or in the molten state, resulting in two different cross-linked polymers exhibiting harder and softer mechanical properties, respectively (PCLnF2M3-CRY1st and PCLnF2M3-CL1st). The difference in the properties can be attributed to the difference in size and order of crystalline domains for n >= 22 and that in degree of crystallinity for n = 18. The network polymers exhibit the hard-soft conversion behavior via melt/recrystallization process without de-cross-linking. The molecular weight of PCLnF2 strongly affects this hard-soft conversion.