Microstructure and Mechanical Properties of Semicrystalline−Rubbery−Semicrystalline Triblock Copolymers

Abstract

Microstructure of and mechanical properties of a series of symmetric EPE (E = poly(ethylene-co-1-butene) and P = poly(ethylene-alt-propylene)) triblock copolymers with M n = 27−372 kg/mol have been investigated in the solid state. Microphase separation of EPE triblock copolymers originates from either (i) chemical incompatibility-induced microphase separation in the melt before crystallization at high overall molecular weights or (ii) crystallization-induced microphase separation from a homogeneous melt at low overall molecular weights. Small-angle X-ray scattering demonstrates that these EPEs (f E ≈ f P ≈ 0.5) adopt a lamellar morphology over the range of molecular weights studied. The observed interlamellar domain spacing (d) scales with the molecular weight as d ∼ N 0 β, where N 0 is the degree of polymerization and β = 0.22 for crystallization-induced segregation and β = 0.63 for microphase-separated melts. The mode of microphase separation strongly affects the chain folding microstructure of the polyethylene crystallites within the lamellar structure. The consequences of these observations on the ultimate tensile strengths of these materials are discussed.

Amphiphilic PLGA‐PEG‐PLGA triblock copolymer nanogels varying in gelation temperature and modulus for the extended and controlled release of hyaluronic acid

“…Monodisperse triblock copolymers form softer, yet denser hydrogels, with more uniform micelles, allowing for intermicellar slip under shear stress. This hypothesis is supported by the literature …”

Synthesis and characterization of soft-hard stereoblock polybutadiene with Fe(2-EHA)3 /Al(i -Bu)3 /DEP catalyst system

“…As shown in Figure , the polymer gave two different phase domains, that is, the hard segments (s‐1,2‐PBD) aggregated and acted as nodal points distributed in the polymer matrix homogeneously, whereas the phase corresponding to the soft segments (e‐PBD) surrounded the hard segment phase. The microdomain formation in semicrystalline block copolymer could result either from the incompatibility of two blocks or the crystallization of one or both blocks . Two major mechanisms might govern the assembly morphology of the stereoblock PBD.…”

Crystal Orientation within Lamellae-Forming Block Copolymers of Semicrystalline Poly(4-vinylpyridine)-b-poly(ε-caprolactone)

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The number of available possible conformations reduces because the restricted geometries imposed on crystallizing polymer materials are on a nanometer scale, which is approximately the length of a polymer chain in coil form. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] Therefore, the nanoscaled confinement size plays an important role in crystallization kinetics.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The number of available possible conformations reduces because the restricted geometries imposed on crystallizing polymer materials are on a nanometer scale, which is approximately the length of a polymer chain in coil form. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] Therefore, the nanoscaled confinement size plays an important role in crystallization kinetics. 9e, 16,17 Our previous work indicated that a distinct transformation of isothermal crystallization kinetics, from heterogeneous to homogeneous nucleation, occurred between two neighboring glassy lamellar layers when the confined size became less than 8 nm (equivalent to the size of forming a stable nucleus via heterogeneous nucleation), leading to an abrupt shift in crystallization to a lowtemperature region.…”