Butyl rubber, i.e., polyisobutylene (PIB) with a few percent isoprene units, is unsurpassed as a cost-effective barrier elastomer against penetrants of many types including biological and chemical warfare agents (CWA). Thus it can be used as a thin barrier lamina over woven or non-woven textile fibers to create protective clothing for soldiers. However, it is uncomfortable when used as such because it also acts as a barrier to perspiration moisture. Being a simple hydrocarbon elastomer, it also has no capacity for chemical deactivation of CWA. The work presented herein describes the synthesis, characterization, and properties of PIB-based block copolymers (BCP), specifically, poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) (PAA-PS-PIB-PSPAA), that spontaneously phase separate into a three-dimensionally continuous, elastomeric PIB barrier phase and a semi-continuous, hydrophilic, water-transmitting phase (typically hexagonally arranged cylinders). These materials are soluble, thermoplastic elastomers, which can be formed into adhesive layers or films either through solvent or melt processing. The center PIB block forms a continuous dynamic phase that provides membrane flexibility. The PS blocks form discontinuous hard domains providing membrane dimensional stability. Finally, the PAA blocks form hydrophilic domains that provide pathways for moisture transmission. The block copolymers were synthesized from the center of the molecule outward in two directions using a difunctional carbocationic initiator. First isobutylene (IB) was reacted with the initiator in the presence of a Lewis acid catalyst to form the center PIB block via quasiliving carbocationic chain polymerization. Upon full conversion of the IB, styrene was added directly to the actively growing chains to form the PS blocks. At an intermediate conversion of the styrene monomer (typically 50 - 70 %), the Lewis acid was destroyed and PS-PIB-PS triblock copolymer was isolated. This intermediate polymer carries sec-benzyl chloride end groups as a natural consequence of the cationic polymerization mechanism. These end groups were then used to initiate atom transfer radical polymerization (ATRP) of tert-butyl acrylate to form outer blocks of poly(tert-butyl acrylate), which in a final step were cleaved by simple heating (thermolysis) to remove the tert-butyl groups (as isobutylene) and render the final PAA blocks as pictured.


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    Titel :

    Chemically resistant barrier films with enhanced water permeability


    Weitere Titelangaben:

    Chemisch beständige Barrierefilme mit verstärkter Wasserdurchlässigkeit


    Beteiligte:


    Erscheinungsdatum :

    2009


    Format / Umfang :

    33 Seiten, 5 Bilder, 1 Tabelle


    Anmerkungen:

    (davon S.968-995 Folienvortrag)



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch