| Surface bromination of low density polyethylene (LDPE) films was carried out by brief exposure to gaseous bromine, followed by UV irradiation. The advancing contact angle decreased from 100° to ∼90° after the first cycle of bromination. However, insignificant changes in advancing contact angles were observed after additional bromination cycles. On the other hand, the receding contact angles decreased with increasing number of bromination cycles, especially at 3 bromination cycles where the receding contact angle decreased dramatically. Roughness (Ra value) measured by AFM increased from 2.7 (original PE film), to 3.2, 4.9, and 3.6 nm (1–3 bromination cycles, respectively). Thus, two and three bromination cycles resulted in surface damage. X-ray photoelectron spectroscopy suggests two different types of C-Br groups. The bromine peak at a binding energy of 70.4 eV represents bromine atoms at the top carbon atom in polyethylene chain turns in the lamella structure, while the peak at a binding energy of 68.4 eV results from bromine atoms substituted below the surface. According to the contact angle, XPS, and AFM data, one cycle of bromination provides an optimum bromine concentration on the surface without damage, with the amount of bromine on the surface of 4.7 atomic percent. On the other hand, bromination of quenched PE samples (QPE) took place at the subsurface and changes in the morphology of the surface could be observed.;Substitution reaction of PE-Br with 4-aminothiophenolate anion yielded PE-S-Ph-NH2 films with a reaction yield of 41.5%, and corresponded to the S/C ratio of 4.9%. Furthermore chemical reactions with 4-nitrobenzaldehyde, followed by a hydrolysis reaction, and UV spectral analysis indicated a grafting density of 2.9 bromine atoms per 100 Å2.;Modification of PE-Br film with other aliphatic and aromatic thiolate compounds, including benzene thiolate, 2-hydroxythioethanolate, and cysteine anion showed that aromatic thiolates yielded a higher degree of substitution. The stronger electron donating the substituent on the thiolate anion, the higher is the amount of substitution reaction at the PE-Br surface. The S/C ratio is largest for PE-S-Ph-NH2 due to the enhancing nucleophilicity of thiolate anion by the amino group.;PE-S-Ph-NH2 underwent further modification via amino group chemistry yielding variety PE products, such as fluorinated PE (PE-S-Ph-NH-CO-CF 3), PE-glucose and its derivatives, PE-monomer, PE-dye, PE-initiator, and a model conducting PE (PE-DPPD). |
