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.

The mechanical properties of a homologous series of polyolefin block copolymers comprised of glassy poly(cyclohexylethylene) (C), elastomeric poly(ethylene-alt-propylene) (P), and semicrystalline poly-(ethylene) (E) are documented. Monodisperse CPEPC, CPE, and CEPEC with mass fractions w C ∼ 0.39-0.44 and 0 e e 1, where ) w E /(w E + w P ), were synthesized by sequential anionic polymerization of styrene, isoprene, and butadiene followed by catalytic hydrogenation. These materials hierarchically microphase separate into lamellae, within which templated crystallization-induced segregation occurs. As increases, the unoriented, polydomain CPEPC materials exhibit monotonically increasing elastic moduli and yield stresses, comparable ultimate tensile strengths, and decreasing failure strains. Cold drawing the CPEPC polymers yields high-strength materials, the structures of which are examined by small-and wide-angle X-ray scattering. Drawn CPEPC-70 ( ) 0.70) exhibits improved toughness with an ultimate tensile strength σ fail ) 75 ( 10 MPa and elongation at break of fail ) 1.22 ( 0.22, as compared to σ fail ) 92 ( 21 MPa and fail ) 0.86 ( 0.18 for drawn CEC ( ) 1.00). Elasticity measurements on the drawn samples demonstrate that materials with > 0 exhibit low degrees of stress softening, while smaller permanent sets and higher failure strains are observed as decreases.

This study demonstrates that bridging (and possibly knotted looping) pentablock configurations in CEC/CECEC (triblock/pentablock) blends play significant roles in the shear-induced alignment and tensile mechanical properties of lamellae-forming block copolymers. Adding just 15 wt % pentablock to the triblock copolymer results in a perpendicular lamellar orientation at all applied strain amplitudes under reciprocating shear, similar to the behavior of the pure pentablock. In contrast, the triblock copolymer exhibits a transition from the perpendicular to the parallel orientation at high strain amplitudes. Approximately 10 wt % pentablock copolymer leads to a dramatic improvement in the strain at failure in shear aligned specimens when the strain is applied normal to the lamellae, a condition that results in brittle failure at small strains with the CEC triblock material. These findings are consistent with calculations that assume pentablock chains bridge the lamellae, thereby reinforcing the brittle C domains.

A general method for the controlled synthesis of polylactide in solution and from solid supports is presented. The evaluation of stannous(II) trifluoromethane sulfonate [Sn(OTf)2] and scandium(III) trifluoromethane sulfonate [Sc(OTf)3] as catalysts for the ring‐opening polymerization (ROP) of L‐, D‐, and L,D‐lactide is described as a route to polylactide using mild and highly selective conditions. These triflate catalysts must be used in conjunction with a nucleophilic compound such as an alcohol that is the actual initiating species via the active metal alkoxide species. Consistent with this process, 1H NMR analysis revealed that the α‐chain‐end bears the ester from the initiating alcohol, and upon hydrolysis of the active metal alkoxide chain end, a ω‐hydroxyl chain end was clearly detected. Polymers of predictable molecular weights and narrow polydispersities were obtained in high yields in accordance with a controlled polymerization process. The addition of base either as a solvent or additive significantly enhanced the polymerization rate with minimal loss to the polymerization control. The ROP of lactide isomers from an initiator, HO(CH2CH2O)3(CH2)11SH, self‐assembled onto a gold surface using Sn(OTf)2 produced polylactide brushes under living conditions and provides the opportunity to prepare stereoregular or chiral surfaces by polymerization of enantiomerically pure monomers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3529–3538, 2001

We report a study on the mechanical properties of lamellae-forming glassy−semicrystalline block copolymers composed of poly(cyclohexylethylene) (C) and polyethylene (E). Tensile properties of polydomain CEC, ECEC, CECEC, and ECECE block copolymers, and blends of these materials, reveal a critical dependence on the connectivity of the semicrystalline E blocks. A molecular parameter directly related to the fraction of bridging E blocks is identified, which captures the fracture behavior of C/E block copolymers over a range of chain architectures. Tensile testing and small-angle X-ray scattering (SAXS) experiments on aligned block copolymers reveal the role of bridging in the glassy C block and further elucidate the mechanisms that govern the deformation of microphase-separated lamellar domains and macroscopic fracture in glassy−semicrystalline block copolymers.