Polymer Bulletin, Vol.53, No.5-6, 401-412, 2005
New pathways for modifying the surface of high density polyethylene: Chemically benign adhesion promotion and subsequent reactivity
The surface of high density polyethylene (HDPE) was modified using a two-step chemical process. HDPE panels were initially immersed in a heated, aqueous hypochlorite solution containing a carboxylic acid promoter and quenched with deionized water at room temperature following a heterogeneous chemical reaction process patented by Beholz (U.S. Patents 6,077,913 and 6,100,343). 1-5 mole percent chlorine heteroatoms were identified on the resulting HDPE surface using ESCA techniques. The surface chlorine concentration was optimized as a function of reaction time, reaction stoichiometry and number of repeated chemical treatments. The chlorinated HDPE surface was subsequently exposed to ultra-violet (UV) light and surface alkene moieties were noted using ATR FT-IR methods along with a concomitant reduction in surface chlorine from ESCA measurements. The photochemically induced free radical surface dehydrochlorination mechanism was observed to follow first-order kinetics and potentially produce a focussed pattern for information storage. Facile subsequent reactivity of the isolated surface alkene groups was demonstrated using electrophilic addition of Br-2. Furthermore, poly(4-hydroxy styrene) architectures were covalently tethered to either the chlorinated or unsaturated HDPE surface in an effort to ultimately tailor surface polarity and adhesiveness as well as create laminate poly(alpha-olefin) containing structures. This economical and benign surface chlorination/photochemical two-step treatment process produced relatively small disposal risks as well as no apparent polymer degradation.