Water-borne, functional coatings from maleic anhydride-containing copolymers : chemistry and phase behavior

Abstract

Hydrophobization of polar substrates is an important prerequisite for many applications. Hydrophobic coatings are needed in order to protect materials such as metals, wood, plastics, leather and fabric against the destructive action of water. Chemical modification of polymer surfaces by flame treatment, corona discharge treatment, plasma modification and surface grafting can be applied to control adhesion, wettability and biocompatibility of such substrates. Unfortunately, these techniques do not result in chemically well-defined and lasting surfaces, hampering their design and preparation. The aim of the work described in this thesis was to create water-borne, durable hydrophobic coatings for polar substrates from two different polymer systems, namely poly(styrene-alt-maleic anhydride) (PSMA) and poly(octadecene-alt-maleic anhydride) (POMA). Hydrophobicity can be introduced by partial imidization of the anhydrides in PSMA or POMA with mono-functional, low and high molecular weight amine-terminated polydimethyl siloxanes (PDMS-NH2) and/or n-heptylamine. The carboxylic acids resulting from hydrolyzed anhydrides may be neutralized or ammonolyzed with ammonia, resulting in self-emulsifying polymers in water. After partial chemical modification, the remaining anhydride groups can, in addition to providing adhesion to polar surfaces, be used for cross-linking with e.g. diamines. With such coatings, materials such as wood, cotton etc. can be made hydrophobic. First of all, low molecular weight PDMS-NH2 was grafted onto the main chain of PSMA by partial imidization. The imidization reaction between the model compound 1,2-cyclohexyldicarboxylic anhydride (CDA) and PDMS-NH2 was successfully investigated in detail by using 1H NMR and ATR-FTIR. After imidization of PSMA with PDMS-NH2, self-emulsifying latexes were successfully prepared. The properties of the latex and application of this latex on cotton were analyzed. Furthermore, the effects of composition and the chain length of PDMS on the latex characteristics, the morphology and the surface properties of the films from PDMS-grafted PSMAs and the application of latexes on cotton to design waterborne surfactant-free coatings for polar substrates with low surface energy were studied. X-ray photoelectron spectroscopy (XPS) demonstrated the surface enrichment of the copolymers with the low energy PDMS component and the maximum Si/C ratio was reached already at PDMS loadings as low as 1 mol% imidized PSMA with high molecular weight PDMS without cross-linking. The formation of hard and soft domains in the films was proven by atomic force microscopy (AFM) and, as a consequence, surfaces become rougher with increasing amounts of PDMS in the copolymers and using longer chain length of PDMS. Finally, POMA was used as the polymer backbone since the UV stability of the aliphatic POMA is better than aromatic PSMA, In addition, POMA is a more flexible (low Tg) polymer than PSMA, which is desirable for the applications on wood, cotton etc. Imidization of POMA with different molecular weights of PDMS-NH2 and n-heptylamine, preparation of surfactant-free latexes and application of these latexes onto cotton were analyzed in this part. Water contact angle measurements showed that the hydrophobicity of POMA can be increased by using only n-heptylamine. ATR-FTIR, 1H and 13C NMR, elemental analysis, particle size, ?-potential measurements, XPS, AFM, transmission electron microscopy (TEM), contact angle measurements and washing studies were the main tools for the characterization of all the modified polymers, films, latexes and coatings. To summarize, water-borne, durable, hydrophobic coatings (the water contact angle value is around 142o and 138o on coated cotton with PDMS-modified PSMA and heptylamine-modified POMA, respectively) from modified PSMA and POMA were developed. The PSMA-based coatings showed phase separation behavior, resulting in surface segregation of PDMS. These water-borne resins based on surfactant-free latexes display promising properties, which can be tuned easily by changing the composition of the polymers.