Microstructure of Crystallizable α-Olefin Molecular Bottlebrushes: Isotactic and Atactic Poly(1-octadecene)

Abstract

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.

Dynamic Fragility of α‐Olefin Molecular Bottlebrushes

“…The crossover from comb to bottlebrush architecture when the side chain's coil size is equal or greater than the backbone spacer size . Therefore, as recently discussed, poly(α‐olefins) prepared by polymerization of 1‐alkene monomers with alkyl chain length greater than six (i.e., hexene and above) have bottlebrush architecture. Structurally, these are the simplest bottlebrush polymers, with their backbone and side chains consisting of alkanes.…”

Effects of short‐chain branches on strain‐induced polymer crystallization

“…Polyolefins with long‐chain branches perform different shear‐induced crystallization behaviors from linear polymers, but the co‐crystallization behaviors of the branches have not yet been investigated . In an extreme case, the side‐chain crystallization of the bulk poly(1‐alkane) bottlebrushes has raised new interesting . However, so far the effects of the crystallizable short‐chain branches on strain‐induced polymer crystallization, such as their sequence distributions, branch densities, branching chain lengths as well as the blending compositions with linear polymers, have not yet been investigated systematically.…”

Synthesis of Ultrahigh Molecular Weight Polymers Containing Reactive Functionality with Low PDIs by Polymerizations of Long-Chain α-Olefins in the Presence of Their Nonconjugated Dienes by Cp*TiMe2(O-2,6-iPr2C6H3)–Borate Catalyst

“…Transition metal catalyzed olefin polymerization is the core technology in the polyolefin industry, and the recent progress in the catalyst development provides new possibilities for the synthesis of new polymers [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Homopolymers of long-chain (higher) α-olefins are branched macromolecules with a high graft density, and the polymers are thus recognized as the simplest bottlebrush polymers, with their backbone and side chains consisting of alkanes [15,16]. Amorphous poly(α-olefin)s are used in hot-melt applications due to their high melt-flow rate with low density, and the ultrahigh molecular weight (UHMW) polymers possess highly entangled bottlebrush architectures and are used as drag-reducing agents (DRAs) in pipeline transport methods for crude oil and petroleum products for improvement of piping system capacity [17][18][19][20].…”

“…Amorphous poly(α-olefin)s are used in hot-melt applications due to their high melt-flow rate with low density, and the ultrahigh molecular weight (UHMW) polymers possess highly entangled bottlebrush architectures and are used as drag-reducing agents (DRAs) in pipeline transport methods for crude oil and petroleum products for improvement of piping system capacity [17][18][19][20]. Recent reports revealed their melt structure, linear rheology, and interchain friction mechanism, including effect of side-chain length toward their linear viscoelastic response and melt microstructure [15,16].…”

“…However, reports for synthesis of UHMW polymers by polymerization of higher α-olefins (1-decene, 1-dodecene, 1-tetradecene, etc.) still have been limited [15,16,21,22], probably due to their preferred β-hydrogen elimination compared to the repeated insertion of monomer with a steric bulk (of alkane branching), as seen in ordinary metallocene catalysts yielding oligomers [21,23,24]. There are several examples for synthesis of (ultra)high molecular weight poly(1-hexene)s [21,[25][26][27] by using (C5HMe4)2HfCl2 (under ultrahigh pressure) [25], titanium complexes with diamine bis(phenolate) ligands [26].…”