Linear viscoelastic response and melt microstructure of ultra-high molecular weight poly(α-olefins) (UHMW PO) with bottlebrush architectures, from poly(1-hexene) to poly(1-octadecene) synthesized by metal coordinative insertion polymerization, were measured as a function of side-chain length, N sc . All these bottlebrush POs are highly entangled, with an average number of entanglements per chain, Z, greater than 50, which allows accurate determination of their rubbery plateau moduli, G N 0 , and their entanglement molecular weights, M e . Their plateau moduli scale with their side-chain lengths as G N 0 ∼ N sc −1.47 , in agreement with the scaling theory for the dense bottlebrush limit that predicts. Melt structures of these bottlebrush poly(1-olefin)s and their melt structural changes with temperature were determined by wide-angle X-ray scattering. Concomitant with thermal expansion of these bottlebrush PO melts is a nonmonotonic change in backbone-to-backbone distance (d 1 ) and a monotonic increase in side-chain spacing (d 2 ). Both the melt-flow interchain friction coefficient and the viscosity of these UHMW PO bottlebrushes show a very strong dependence on d 2 , characterized by two exponential decay regimes, with decay constants having an exponential dependence on N sc .

Isotactic and atactic poly(1-octadecene) (iPOD and aPOD) have been synthesized by organometallic coordinative insertion polymerization of 1-octadecene. Analyzing X-ray and neutron scattering data of POD melts identifies their bottlebrush structures as flexible rods where the rod length is the extended backbone length and rod radius is the side chain coil dimension. Upon cooling, both iPOD and aPOD melts crystallize by fully extending their coiled side chains to form orthorhombic alkane crystals in iPOD and nematically ordered rotator alkane crystals in aPOD, as determined by X-ray scattering and Raman spectroscopy. Molecular dynamics simulations of isotactic and atactic 48-mers of 1-octadecene were applied to define and verify melt and crystalline structures and scattering peak assignments, respectively. Modeling suggests that side chains of both crystallized isotactic and atactic PODs align at 70°and 160°to the 4/1 spiral backbone of equal probability, at an average of 115°, and POD chains pack in an antiparallel pattern. Large wheat-sheaf structural assembly of fibril bundles can be observed in aPOD, which render high opacity to these samples. Each of those fibrils is made of several bottlebrush molecules packed into a hexagonal lattice. Faster crystallization observed in iPODs hinders the formation of large crystallites, which results in translucent samples.

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The crystallization of α-olefin molecular bottlebrushes occurs via side-chain crystallization exclusively, which is fundamentally different from the common chain folding process occurring in linear polyolefin crystallization. However, the exact mechanisms of side-chain crystallization have not been explored to date. Herein, we report the melting and crystallization behaviors of a series of poly(α-olefin) homopolymers with a syndiotactic backbone (sPαO) and side-chain lengths (N sc ) ranging from 4 to 16 carbons. Only sPαOs with N sc ≥ 10 are able to crystallize into a hierarchical morphology, as revealed by a combination of SAXS, SALS and optical microscopy measurements. A monotonic increasing dependence on N sc of the thermal properties (melting temperature, enthalpy, and entropy of fusion) and of the crystallinity is observed on the sPαOs, which reveal that the odd−even effect on those properties (as observed on n-alkanes) does not operate in α-olefin bottlebrushes. The side chains in the crystallizable sPαOs arrange into a nematic rotator phase, similar to atactic poly(1-octadecene) recently reported [Macromolecules 2018, 51 (3), 872−883]. The bottlebrush molecules pack into fibril bundles made of several molecules packed into a hexagonal lattice. On a larger scale, density fluctuations give rise to a bicontinuous microstructure with characteristic size on the order of 1 μm.

High melt strength (HMS), shear thinning, and extensional strain hardening (SH) are highly desirable properties in commercial polypropylene, which are typically achieved by the incorporation of long-chain branching (LCB). The current state-of-the-art approach to produce LCB involves post-reactor modification steps, which are not only costly but also generate undesirable side products as a result of polymer chain scission. We report a novel one-pot synthetic route to produce HMS isotactic polypropylene (iPP) ionomers bearing aluminum carboxylate groups. The synthesis of iPP ionomers is achieved by the direct copolymerization of an alkenyl aluminum comonomer and is facilitated by a novel C 1 -symmetric metallocene catalyst, producing highly isospecific iPP ionomers (T m > 157 °C) with high activity (>200 000 g-polymer mmol-Zr −1 h −1 ). X-ray scattering experiments conducted in the solid and melt states confirm the presence of ion clusters as independent entities from the crystalline lamellae. The ion content in the iPP ionomers is very low (<0.1 mol %), which results in insignificant effects on the crystallinity, melting point, and mechanical properties when compared to the iPP homopolymer. Remarkably, such a low level of ion content is sufficient to drastically improve the processability of the ionomers, as indicated by the increase in melt strength, shear thinning, and extensional SH.