Chemical Surface Modification of Poly(ethylene terephthalate)

Abstract

Reactions of semicrystalline poly(ethylene terephthalate) (PET) film with ester-selective reagents at the film−solution interface can be controlled to produce modified film samples containing a thin (less than ∼ 40 Å) surface layer of the reagent-induced functionality. Hydrolysis of PET yields a surface mixture of alcohol and carboxylic acid groups. Reduction with lithium aluminum hydride and transesterification with ethylene glycol (glycolysis) both produce surfaces with alcohol functionality (PET−OHR and PET−OHG, respectively). Each of these modification reactions involves chain cleavage and can lead to significant sample degradation (reactive dissolution); for each modification reaction, conditions were optimized to maximize conversion and minimize degradation. The reactivity of surface alcohols (PET−OH) was assessed for samples prepared by both reduction and glycolysis, and a comparative analysis was made: the presence of benzylic alcohols in reduced samples and their absence in glycolyzed samples as well as the difference in surface alcohol concentration between the two surfaces (the surface density of alcohols is higher on PET−OHG than on PET−OHR by a factor of ∼2) affect the reactivity. Reaction with thionyl chloride produces a surface mixture containing alkyl chloride (PET−Cl and sulfite (PET−(O)2SO) functionality. Reactions with acid chlorides yield esters (PET−OC(O)R) and reactions with isocyanates yield urethanes (PET−OC(O)NHR). Reactions with diisocyanates produce surface mixtures containing diurethane and half urethane/half isocyanate functionality (PET−(OC(O)NH)2R/−OC(O)NHRNCO); the composition of these mixtures depends on both the method of PET−OH preparation and the diisocyanate structure. Reactions were monitored and products were characterized by gravimetric analysis, contact angle, XPS, ATR IR, and SEM. Reaction yields were assessed by quantitative XPS analysis and were generally >70%.