Polymeric coatings, miscible

Kiran, E., Malki, K., POhIcr, H. (1996) High-pressure miscibility and extraction of polymeric coatings and hot melt adhesives with carbon dioxide + pentane mixtures. Towards supercritical recycling of paper-plastic waste. Proc, ACS. Div. Pofym. Mater. Set A Eng., 74,231-232. 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

Poly thiophene, PTP, and polypyrrole, PPR, blends with PS and PC were prepared by Wang et al. [1990] by thiophene or pyrrole electrochemical polymerization using electrodes coated with PS or PC hlms. The thiophene or pyrrole diffuses into the fihn and polymerizes in-situ in the film. Threshold conductivity occurs at 18 wt% for both conducting polymers in PS. Lower levels exist for PTP (12 wt%) and PPR (7 wt%) in PC. Miscibility of PPR/PC is attributed to the lower threshold limit as phase separated blends would be expected to have higher values. Previous studies with polyacetylene/PS blends reported threshold conductivity at 16 wt% polyacetylene [Aldissi and Bishop, 1985]. 

Unlike the porous membrane, colloidal particles (such as PS or silica particle) are another type of template for the preparation of CPCs (Figure 11.10c). In previous work, core/shell PS/PANI composite particles were prepared by chemical oxidative seeded dispersion polymerization. A conventional coating protocol was employed as follows. The aniline monomer was dissolved in a strongly acidic solution in the presence of the PS seed latex (an alternative method involves using a miscible aniline hydrochloride monomer without external acid). Then polymerization was initiated by the addition of oxidant aqueous solution. The suspended PS particles were coated with PANI by in situ deposition of the formed conducting polymer or oligomer from the aqueous phase. 

Yan et al. [52] explored the use of IPN techniques to produce a composite vinyl-acrylic latex. The first-formed polymer was produced using VAc and divinyl benzene (DVB), while the second formed polymer constituted a BA/DVB copolymer. In both cases the DVB was added at 0.4 wt%. They compared this product with another product, a bidirectional interpenetrating netwodc (BIPN) in which VAc was again polymerized over the first IPN. They noted that the compatibility between the phases was more pronounced in the BIPN than in the IPN as determined using dynamic mechanical measurements and C nuclear magnetic resonance spectroscopy. The concept of polymer miscibility has also been used to produce composite latex particles and thus modify the pafamance properties of VAc latexes. Bott et al. [53] describe a process whereby they bloid VAc/ethylene (VAc/E) copolymers with copolymers of acrylic acid or maleic anhydride and determine windows of miscibility. Apparently an ethyl acrylate or BA copolymer with 10-25 wt% AA is compatible with a VAc/E copolymer of 5-30 wt% ethylene. The information obtained from this woik was then used to form blends of latex polymers by polymerizing suitable mixtures of monomers into preformed VAc/E copolymers. The products are said to be useful for coating adhesives and caulks. 

Interpenetrating Polymer Networks (IPN). Polymerization of vinyl and diene monomers over an already formed molecule held in a pol5uner particle represents a special case of copoljnnerization. The interpenetrating polymer networks (qv) thus formed overcome many of the miscibility and other problems associated with physical blends of individual copolymers and leads to new compositions that are useful for coatings, adhesives, and caulks (14). Polychloroprene IPNs have been made by co-curing copolymers of l-chloro-l,3-butadiene [627-22-5], The 1-chloro-l,3-butadiene comonomer polymerizes in a fashion to increase the allylic chloride concentration in the copolymer backbone. The butadiene copolymer with l-chloro-l,3-butadiene (29) and octyl acrylate copolymer (30) improved the low temperature brittleness, oil resistance, and heat resistance of polychloroprene. 

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