Propylene-Based Elastomers Extended with Polyalphaolefins

Propylene-based elastomers (PBE) are co-polymers of propylene and ethylene made with a metallocene catalyst. These polymers possess crystallinity that is derived from isotactic propylene sequences. Polyalphaolefins (PAO) are fully paraffinic liquid plasticizers that are miscible with PBE. In this study we examine PAO plasticized PBE resins, where the PBE ethylene content ranges from 9 wt. % to 16.6 wt. % and the PAO viscosity from 10 cSt (centiStokes at 100°C)  to 1000 cSt. The PAO plasticizer content was varied from 0 to 40 wt. %. Thermal, rheological and mechanical properties of these plasticized PBE resins were measured on samples that were compounded through batch mixing. The morphology of these specimens was determined using Atomic Force Microscopy (AFM). Our study indicates that the lower viscosity PAO is the most effective plasticizer in lowering the glass transition temperature (Tg) of the PBE resin. The Tg depression of PBE by PAO follows the Fox equation. The suppression of Tg in the PBE resin imparts flexibility and lowers flexural modulus. In formulations containing the high viscosity PAO plasticizer, composite droplet morphology is observed, where the PAO-plasticized amorphous PBE domains (or sub-inclusions) are encapsulated by the crystalline phase of the PBE resin. These sub-inclusions soften the PBE crystalline phase and alter the tensile behavior of the PBE by lowering its extensional load, a response described as soft-stretch which is desirable for many elastic applications.