Mechanical Properties and Hysteresis Behaviour of Multigraft Copolymers

Abstract

Summary: PS-PI multigraft copolymers with tri-tetra-and hexafunctional polystyrene branch points have been studied to investigate the influence of molecular architecture on morphological and tensile properties and to find novel material concepts. It was found that the morphological behaviour of these grafted copolymers can be predicted using theoretical approaches. The number of branch points, however, greatly influences the long-range order of microphase separation. Additionally, two new parameters for adjusting mechanical properties of multigraft copolymers are found in our investigations: 1) functionality of the graft copolymer: tri-, tetra-or hexafunctional and 2) number of branch points per molecule. Tetrafunctional multigraft copolymers show surprising high strain at break values up to 1550 %. With increasing number of branch points strain at break and tensile strength increase, where a linear dependence of mechanical properties on the number of branch points is obvious. Excellent elasticity of tetra and hexafunctional multigraft copolymers at high deformation was proved in hysteresis experiments.

Design and Synthesis of Multigraft Copolymer Thermoplastic Elastomers: Superelastomers

“…By further coupling the PS macromonomer with difunctional living polyisoprene anions, centipede‐like multigraft copolymers with two PS at the same branching points was prepared. Using a similar strategy but with different coupling agents such as methyltrichlorosilane or 1,6‐bis(trichlorosilyl)‐hexane (“hexachlorosilane”), comb‐ or barbwire‐like multigraft copolymers with one or four PS chains at each branching points were synthesized …”

“…Since the final coupling reaction employs a step‐growth mechanism, the prepared multigraft copolymers generally have a PDI around 2. Using solvent/nonsolvent fractionation procedures, one can readily isolate multigraft copolymers with different average numbers of branch points and PDI (PDI ≈ 1.2), providing ideal materials with which to study the influence of number of branch points on a wide range of properties such as morphologies, chain dynamics, mechanical properties, and hysteresis behaviors . General nomenclature of these material is MG‐ x ‐ y ‐ z , where MG stands for regular multigraft, x (3, 4, and 6) is the junction point functionality, y refers to the volume percentage of PS, and z represents the average number of junction points per molecules calculated from NMR spectra.…”

“…Multigraft copolymers PI‐ g ‐PS of appropriate architecture and composition are found to have exceptionally high strain at break and low residual strain in hysteresis tests, resulting in superelastic properties, as well as high tensile strength ( Figure ). For tetrafunctional multgraft copolymer with 21 vol% PS and ten branch points (MG‐4‐21‐9.9), an unprecedented elongation at break of 2100% was reported, almost double that of commercial TPEs such as Kraton (1050% at similar composition) (Figure a) .…”

“…These are exceptionally low values of permanent set for TPEs. The superelasticity of multigraft copolymers, in contrast to linear block copolymer TPE, is caused by their distinct molecular architecture ( Figure ), where the rubbery PI backbone is linked to multiple rigid PS domains with two or more PS branches at each junction point . Thus, the elastic PI backbone is “reminded” at multiple points where it should return to once the load is removed.…”

Thermoplastic Elastomers Based on Block, Graft, and Star Copolymers

“…Structure-property relationship of these graft copolymers was elucidated by characterizing morphology [76,77] and mechanical properties [78][79][80] of grafted polymers with different compositions (14-23 vol% of PS) and architectures (trifunctional, tetrafunctional, and hexafunctional junction points). From their research, multigraft polymers with tetrafunctional junction points showed 1550% strain at break which is 500% higher than that for the commercial product Kraton 1102.…”