PROPYLENE-ETHYLENE COPOLYMERS - ETHYLENE CONTENT INFLUENCE ON MOLECULAR AND THERMOMECHANICAL PROPERTIES

Propylene-ethylene copolymers with ethylene content of 1.6 - 5.4 % w/w were obtained by bulk polymerization in laboratory reactors through h igh activity MgCl2/TiCl4 based catalysts. The influence of ethylene co ntent on the molecular and thermomechanical properties was studied. Th e techniques applied for the characterization were: Fourier-Transform Infrared Spectroscopy (FTIR), Viscosimetry, Rotational Rheometry, Diff erential Scanning Calorimetry (DSC), Dynamic-Mechanical Analysis (DMA) and Pendulum Impact Test. It was observed that up to a certain ethyle ne content (similar to 3 % w/w in the system studied), the copolymer i s characterized by isolated ethylene comonomeric units in the macromol ecular chain. The addition of ethene causes a perturbation in the prop ylene crystalline structure, which is reflected in a decrease of melti ng and crystallization temperatures. Solubility tests allow the ethyle ne-propylene rubber (EPR) to be separated from the crystallizable frac tion. Samples with higher ethylene content are characterized by a rise in the EPR content and a decrease in the glass transition temperature . The melting of the copolymers investigated by DSC techniques and ana lyzed through kinetic theories is characterized by only one apparent m elting activation energy which describes the melting of the copolymer crystals and is related to the introduction of the ethylene comonomeri c units into the macromolecular chains.