Cyclic polymers possess properties that are significantly different from their linear analogs, such as higher densities, smaller hydrodynamic volumes, and higher glass transition temperatures. Poly(4-methyl-1-pentene) (PMP), a linear polyolefin, is a commercial transparent thermoplastic and has applications in packaging materials and release membranes. Polymerizing 4-methyl-1-pentyne with a tungsten alkylidyne catalyst and subsequent hydrogenation (>99%) provided cyclic poly(4-methyl-1-pentene) (c-PMP). Evidence of a cyclic topology comes from rheology/viscosity studies, light scattering measurements, and size-exclusion chromatography. Importantly, atactic c-PMP exhibits a T-g (39 degrees C) 10 degrees C higher than the linear analog. A 15 g-scale cyclic polymerization was also achieved with 1-pentyne. Subsequent hydrogenation yielded 10 g of cyclic poly(1-pentene). Measurements of initial rates during the polymerization of 1-pentyne reveal a catalyst activity of 180,000,000 g/mol(cat)/h.