Bulk surface photografting process and its applications. II. Principal factors affecting surface photografting

Abstract

The photografting polymerization reactivity of various monomers which can undergo free-radical chain polymerization is examined with benzophenone (BP) as the photoinitiator and LDPE film as the substrate. The results show that acrylate monomers have the highest photopolymerization and photografting reactivities, whereas methacrylate monomers have low reactivity due to the allylic hydrogen atoms in the monomer and no tertiary hydrogens on the polymer formed. Acrylonitrile has a significantly higher photografting efficiency than other acrylic monomers but a low polymerization reactivity. Vinyl acetate and N-vinyl-2-pyrrolidinone have a certain photografting potential, while styrene and 4-vinylpyridine have quite low photopolymerization and photografting reactivities. Using LDPE as the cover film and acrylic acid (AA) and BP as the monomer and photoinitiator, respectively, the photografting reactivity of seven polymer substrates was evaluated. The results show that these polymer substrates can be arranged in a sequence of decreasing photografting reactivity in the order nylon > PET > PP > LDPE > HDPE > OPP > PC. This sequence can be interpreted in terms of differences in surface hydrogens and differences in surface polarity. The self-screening effect plays a significant role in the intertface react ion system and is the main reason for the negative effect of increased photoinitiator concentration on the photografting process. An increase in the thickness of the liquid layer of the monomer and photoinitiator solution between the two substrates has a negative effect on the photografting process, whereas an increase in polymerization temperature in the range of 25-70°C has a positive effect. Added water favors the photografting polymerization of AA on the surface of polyolefins but acetone has a negative effect due to the different solvation of PAA. Adding multifunctional acrylate monomers increases the photografting efficiency to a large extent, whereas adding PVAc or acetyl-cellulose greatly reduces the photografting efficiency.