Morphology and Tensile Properties of Multigraft Copolymers with Regularly Spaced Tri-, Tetra-, and Hexafunctional Junction Points

Abstract

The effect of chain architecture on the morphological and tensile properties of series of multigraft copolymers, with regularly spaced tri-, tetra-, and hexafunctional junction points, was investigated using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and tensile testing. The materials were synthesized by coupling difunctional polyisoprene (PI) spacers and living polystyrene (PS) branches, made by anionic polymerization, with chlorosilanes of different functionalities. Since the coupling process is a step-growth polymerization, yielding polydisperse products, fractionation was utilized to separate each material into three fractions (high, middle, and low molecular weight), each of low polydispersity. All three fractions have the same chain architecture on a per junction point basis but differ in the number of junction point units per molecule. By applying the constituting block copolymer concept, the physical behavior of these molecules was compared with current theories. It was found that morphological behavior of these graft copolymers can be predicted using theoretical approaches and is independent on the number of junction points. The number of the junction points, however, greatly influences the long-range order of microphase separation. Additionally, two new parameters for adjusting mechanical properties of multigraft copolymers were found in this investigation: (1) functionality of the graft copolymerstri-, tetra-, or hexafunctionalsand (2) number of junction points per molecule. An increase in functionality causes a change in morphology, resulting in a high level of tensile strength for tetrafunctional (cylindrical) and hexafunctional (lamellae) multigraft copolymers, leading to about the twice the strength of the spherical trifunctional multigrafts of similar overall composition. Tetrafunctional multigraft copolymers show a surprisingly high strain at break, far exceeding that of commercial block copolymer thermoplastic elastomers (TPEs). Strain at break and tensile strength increase linearly with the number of junction points per molecule. Hysteresis experiments at about 300-900% deformation demonstrate that multifunctional multigraft copolymers have improved high elasticity as compared to commercial TPEs like Kraton or Styroflex.

Mechanical Properties and Hysteresis Behaviour of Multigraft Copolymers

“…The morphological behaviour of graft copolymers with a complex architecture is predicted by the constituting block copolymer hypothesis [4][5][6][7] and theories for mictoarm stars [8,9] or conformationally asymmetric linear diblocks [10,11] . It has been found that the morphological behavior of regular multigraft copolymers with multiple tri-, tetra-or hexafunctional junction points is generally consistent with the morphologies of their constituting unit [7,12,13] . However, the longrange order that can be achieved is diminished as the number of junction points per molecule increases [12,13] .…”

“…It has been found that the morphological behavior of regular multigraft copolymers with multiple tri-, tetra-or hexafunctional junction points is generally consistent with the morphologies of their constituting unit [7,12,13] . However, the longrange order that can be achieved is diminished as the number of junction points per molecule increases [12,13] . Preliminary studies of the tensile properties of multigraft copolymers with regularly spaced tetrafunctional junction points have proved significantly larger strain at break and similar tensile strength to commercial TPE's [14] .…”

“…In our studies the morphologies formed by the samples studied are in agreement with Milner's model. The TEM and SAXS images of the studied morphologies are shown in our recent study [13] . Tetrafunctional multigraft copolymers show a phase behaviour as known for diblock copolymers [16] .…”

“…The influence of higher PS content on tensile properties will be discussed elsewhere [13] . The stressstrain behaviour of two tetrafunctional multigraft copolymers with about 20 vol.-% PS compared to a Kraton 1 and a Styroflex 1 (BASF) copolymer is shown in elasticity is caused by their specific molecular architecture, because multiple PS branches are grafted to the long rubbery backbone, which results in a physical crosslinking [14] .…”

Sustainable thermoplastic elastomers derived from renewable cellulose, rosin and fatty acids

“…25,[33][34][35][36] For instance, polyisoprene-g-polystyrene (PI-g-PS) has been synthesized via anionic polymerization as gra copolymer-based TPE. 34,35 The Kramer and Bazan groups developed a gra copolymer by graing so n-butyl acrylate from rigid polyethylene copolymer backbone through ATRP. 37 Recently, we used activator-regenerated electron transfer (ARGET) ATRP 38 to prepare a series of cellulose-based gra copolymers, cellulose-g-poly(n-butyl acrylate-co-methyl methacrylate), as new candidate TPE materials.…”