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BRANCHING IN ETHYLENE VINYL ACETATE (EVA) COPOLYMERS

November 16th, 2012 | by | chemistry, properties

Nov
16

The free-radical polymerization of ethylene leads to formation of both short and long branches off the main polymer chain via side reactions of the growing polymeric radical.  These side reactions occur during homopolymerization of ethylene to form low density polyethylene (LDPE) and they also occur during free-radical copolymerization of ethylene with comonomers such as vinyl acetate (VA).  Here I will generally describe two major side reactions involved and how they affect the polymer architecture and some of its resultant properties. Read full story

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    MELTING BEHAVIOR OF ETHYLENE VINYL ACETATE (EVA) COPOLYMERS

    November 9th, 2012 | by | pharma applications, processing, properties

    Nov
    09

    A previous post discussed the degree of crystallinity of ethylene vinyl acetate (EVA) copolymers and its dependence on the vinyl acetate (VA) content of the polymer.  Differing degrees of crystallinity in turn result in different melting temperature ranges as a function of VA content.  The melting point temperature is reduced with increasing VA content due to the resulting reduction of the thickness of the crystalline lamella, which are comprised only of series of ethylene units not interrupted by incorporation of a VA unit.  As more VA is randomly incorporated into the polymer backbone, the average block length of sequential ethylene units becomes shorter, resulting in fewer, thinner crystals which have lower melting temperatures.  Read full story

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      WHAT IS MELT INDEX?

      September 24th, 2012 | by | processing, properties

      Sep
      24

      A common measurement used to characterize thermoplastic polymers is called melt index.  It is essentially an indirect, and inversely proportional, measure of the viscosity of the polymer when molten.  One measures the mass of polymer melt which will flow through an orifice in a given amount of time under defined conditions of temperature, pressure, and geometry.  The larger the melt index value, the lower is its viscosity, and therefore, the average molecular weight of the polymer is lower.  Read full story

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        HIGHLIGHTS FROM THE CONTROLLED RELEASE SOCIETY ANNUAL MEETING

        August 13th, 2012 | by | industry news-commentary, pharma applications

        Aug
        13

        Four colleagues and I attended the Controlled Release Society’s (CRS) annual meeting in Quebec City July 15-18.   Quebec City was a delightful venue with the Old City filled each day and night with tourists for the annual music festival, outdoor Cirque du Soleil presentations, and summer Images presentations, coupled with celebration of the 400th anniversary of the founding of Quebec.

        CRS was a good meeting and I saw a number of posters and several presentations related to melt extrusion of polymers for drug delivery formulations.  I attended the following three technology workshops: Read full story

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