Aspects of polymer surface science: Part A. Hydrosilation-cured polydimethylsiloxane networks. Part B. Synthesis and characterization of dual-function oxetane macromonomers

A method for measuring the intrinsic advancing (&thetas;_adv) and receding (&thetas;_rec) water contact angles was developed for hydrosilation-cured polydimethylsiloxane (PDMS) network coatings. Static and dynamic contact angle (DCA) measurements were used to evaluate coatings prepared from commercially available divinyl-terminated polydimethylsiloxane (C-PDMS) and from synthesized narrow polydispersity divinyl-terminated polydimethylsiloxane (N-PDMS). According to DCA measurements, all PDMS network coatings rapidly contaminated the water surface during analysis. Intrinsic contact angles on the PDMS coatings were measured using either a large surface area reservoir or by repeatedly changing the water reservoir between DCA cycles when measured in small surface area reservoirs. The intrinsic advancing contact angle (&thetas; _adv), for hydrosilane network coatings was determined to be 118° ± 2°. Values for the receding contact angles (&thetas;_rec ) were from 81–97° with the most commonly observed values in the 83–86° range. For a given set of samples, both &thetas; _adv and &thetas;_rec measurements typically had standard deviations of <2°. The factors contributing to the wide range of &thetas; _rec values are not well understood, but appear to stem from differences in composition. After water surface contamination, &thetas;_adv decreased to 110° ± 2° while &thetas;_rec increased by 7° irrespective of the initial “uncontaminated” &thetas; _rec value.; Homo- and co-macromonomers prepared from cationic ring-opening polymerization of 3-trifluoroethoxymethyl-3-methyl oxetane (3-FOx) and 3-bromomethyl-3-methyl oxetane (BrOx) were synthesized and characterized. A procedure reported by Malik1,2 was modified to prepare the BF₃-etherate and 1,4-butanediol co-initiator for the macromonomer preparation. Co-initiators prepared using this modified method provided more control over molecular weight than did co-initiators prepared by Malik's procedure.1,2 Additionally, purification procedures have been developed which remove the low molar-mass impurities (that are reactive with isocyanates) otherwise present in these macromonomers.; Proton nuclear magnetic resonance (1H NMR) spectroscopy and elemental analysis provided information on co-macromonomer stoichiometry. Samples were prepared in 3:1, 1:1, and 1:3 ratios of 3-FOX to BrOx. Integration of 1H NMR provided evidence of final macromonomers prepared having 3-FOx to BrOx ratios close to those predicted by monomer stoichiometry. 1H NMR data also provided proof that the co-macromonomers were not mixtures of homo-macromonomers. Glass transition temperatures (Tg) in the range of −28 to −47°C were measured using differential scanning calorimetry (DSC). (Abstract shortened by UMI.)...