Viscoelastic, Mechanical, and Glasstomeric Properties of Precision Polyolefins Containing a Phenyl Branch at Every Five Carbons

Mechanical and viscoelastic properties of precision polyolefins, poly­(4-phenylcyclopentene) (P4PCP) and its hydrogenated analog (H₂-P4PCP) containing atactic phenyl branches at exactly every five carbons along the backbone are explored. Both materials are amorphous with a glass transition temperature of ∼17 ± 3 °C. Rheological investigations determined that P4PCP has an entanglement molar mass (<i>M</i>_e = 10.0 kg mol^–1) much higher and closer to polystyrene than H₂-P4PCP (<i>M</i>_e = 3.6 kg mol^–1). Both materials have elastomeric and shape memory properties at ambient temperatures, which were further explored through strain hysteresis measurements. H₂-P4PCP has an elastic recovery of ∼95% at max strain values up to 500% as determined by uniaxial tensile testing. Time–temperature superposition analysis, Williams–Landel–Ferry constants, and further mechanical analysis are discussed and compared to previously reported ethylene–styrene copolymers of similar phenyl-branch content within the microstructure

Comparison of Polypentenamer and Polynorbornene Bottlebrushes in Dilute Solution

Bottlebrush (BB) polymers were synthesized via grafting-from-atom transfer radical polymerization (ATRP) of styrene on polypentenamer and polynorbornene macroinitiators with matched grafting density (ng = 4) and backbone degrees of polymerization (122 ≥ Nbb ≥ 61) to produce a comparative study on their respective dilute solution properties as a function of increasing side chain degree of polymerization (116 ≥ Nsc ≥ 5). The grafting-from technique produced near quantitative grafting efficiency and narrow dispersity Nsc as evidenced by spectroscopic analysis and ring closing metathesis depolymerization of the polypentenamer BBs. The versatility of this synthetic approach permitted a comprehensive survey of power law expressions that arise from monitoring intrinsic viscosity, hydrodynamic radius, and radius of gyration as a function of increasing the molar mass of the BBs by increasing Nsc. These values were compared to a series of linear (nongrafted, Nsc = 0) macroinitiators in addition to linear grafts. This unique study allowed elucidation of the onset of bottlebrush behavior for two different types of bottlebrush backbones with identical grafting density but inherently different flexibility. In addition, grafting-from ATRP of methyl acrylate on a polypentenamer macroinitiator allowed the observation of the effects of graft chemistry in comparison to polystyrene. Differences in the observed scaling relationships in dilute solution as a function of each of these synthetic variants are discussed