Influence of Switch Frequency on the Morphology of PP/EPR In-reactor Alloys Prepared by Periodic Switching Polymerization Reza Mehtarani ( ) Supervisor: Professor Zhiqiang Fan Department of Polymer Science & Engineering, Zhejiang University, Hangzhou , China Background and purpose of the work Recently a new polyolefin manufacturing process based on multi-zone circulating reactor (MZCR) was developed by LyondellBasell. In comparison with mechanical blend of PP/EPR and traditional multi-step technologies, the MZCR provides more uniform polymer alloy with smaller dimension of EPR phase (high homogeneity). In this study, a Periodic Switching Polymerization Process (PSPP) was used to simulate PP/EPR synthesis in MZCR. In the PSPP process a continuous feeding policy was adopted. With this method the amorphous phase was dispersed in the matrix of polypropylene very well. Homogenous alloys could be prepared with switching between propylene homopolymerization and ethylene/propylene copolymerization alternatively. In present work, we synthesized a number of polypropylene/poly(ethylene-co-propylene) in- reactor alloys by PSPP method and investigated the influence of different switching frequency on the morphology and state of dispersion of the EPR phase in the alloy samples by scanning electron microscope (SEM). The Method of Polymerization Preparation of Samples for SEM Polymer granules were melt and mixed at 170 ˚C on a Thermo Haake Rheomix and then compression-molded using a 80×10×4 mm mold at 180 ˚C and 17.5 MPa for 15 min. Specimens were slowly cooled down to room temperature. The specimens were fractured in liquid nitrogen. The fractured surfaces were etched by xylene under ultrasonic at 50˚C for 5 min and sputtered with gold and finally subjected to SEM observation. An operating voltage of 5 kV and magnification of 5000 were adopted for the observation. Conclusions The switch frequency is the crucial factor in the synthesis of polymer alloys by PSPP method. The change of the switch frequency influences in several parameters such as EPR%, EPS%, the size of the dispersed phase domains and its distribution. The morphology of the alloys is strongly related to switch frequency and the gas-phase time. With increasing the switch frequency, the size of the dispersed phase domain is reduced and become more uniform in distribution. There is a limitation in switch frequency. With increasing the switch frequency more than this limitation, the monomer could not reach to active center perfectly. So the effect of the switch frequency is decreased. Supports by the Major State Basic Research Programs (Grant No. 2011CB606001) and the National High-tech R&D Program of China (Grant No. 2012AA040305) and are gratefully acknowledged. Comparing P20EP with P10EP5-120, It is obviously clear that the morphology of the alloy is strangely related to the switch frequency. As the switch frequency increased, the size of the dispersed phase domain (mainly EPR) decreased and the domain got more uniform distribution. When the total duration of gas phase polymerization was reduced to 60 min (comparing P20EP10-60 with P5EP2.5-60), as the switching frequency increased, the number of cavities increased and cavity size decreased. Polymerization Condition and Composition of Alloys Sample t gas a (min) SF b Yield (kg polymer/g Ti) EPR c (wt %) EPS d (wt %) EPR + EPS (wt %) P20EP P10EP P20EP P5EP P80EP P20EP P10EP P5EP a t gas = duration of gas phase PSPP polymerization. b SF = switching frequency, number of switching from homopolymerization to copolymerization in the PSPP step. c EPR = random ethylene/propylene copolymer. d EPS = segmented ethylene/propylene copolymer. Phase Morphology of Polymer Alloys But there is a limitation in increasing the switch frequency. when the switching frequency exceeded the certain limit, the alloy’s EPS and EPR content tended to decrease so the number of cavities was not increased further (P10EP5-120 vs P5EP ). This relationship can also be found in samples synthesized with shorter total time of gas-phase polymerization. Effect of Switch Frequency on Morphology of PP/EPR Prepared by Shorter Gas-phase Reaction The phenomena repeated in samples synthesized with 30 min total time of gas-phase polymerization as well. In sample P80EP40-120, due to high content of EPR there were many EPR particles merged with each other. This resulted in irregular shape of the cavities and rather disordered spatial dispersion of the cavities.