Novel Bio-based Poly(vinyl ether)s for Coating Applications
September 2015 www.coatingsworld.com Coatings World | 51
polymer technology is the ability to widely tailor properties
through copolymerization. This was demonstrated using a number of comonomers including cyclohexyl vinyl ether (CHVE),
menthol vinyl ether (MVE), and pentaethylene glycol ethyl vinyl
ether (PEGEVE). Since homopolymers of the plant oil-based
vinyl ethers possess a very low Tg, it was of interest to increase
polymer Tg by copolymerization. As illustrated in Figure 4,
both CHVE and MVE possess the cyclohexyl ring attached
to the vinyl ether oxygen atom with MVE possessing a substituted ring. CHVE is commercially available, while MVE was
synthesized in-house. MVE represents a potentially bio-based
monomer since menthol is a naturally occurring terpene that
can be obtained from the peppermint plant, Mentha x piperita
(Lamiaceae). 16 As expected, copolymerization of 2-VOES with
these cycloaliphatic vinyl ether monomers enabled the formation of crosslinked ;lms with increased Tgs compared to the
control ;lm based on the homopolymer of 2-VOES. Figure 5
shows the variation in Tg as a function of comonomer content
for ;lms cured at room temperature by autoxidation. 17, 18
Copolymerization of 2-VOES with PEGEVE was utilized
as a means to provide dispersability of the polymer in water
without the need for surfactant. The amphiphilic copolymers
produced were shown to be surface active as determined by
measuring critical micelle concentration. 19 Three different copolymers were produced that varied with respect to PEGEVE
repeat unit content. From these copolymers, aqueous dispersions were produced that also contained a water-based drier
package. The solids content of the dispersions was 30 wt.% and
all three copolymers gave stable dispersions. Figure 6a shows
the variation in drying time with copolymer composition, while
Figure 6b provides an image of a coating cast and cured at ambient conditions on a glass panel. As shown in Figure 6a, coatings cured relatively fast with the tack-free time decreasing with
increasing 2-VOES repeat unit content. From Figure 6b, it can
be seen that cured ;lms had excellent optical clarity, which can
be attributed to the lack of surfactant in the ;lms.
Polymers Based on Cardanol
Cardanol is derived from cashew nut liquid, which is a byprod-uct of cashew nut processing. 20 The primary component of cashew nut liquid is anacardic acid, which can be converted to
cardanol by thermal decarboxylation. Cardanol is a mixture
of four different meta-alkyl phenols that differ with respect to
the degree of unsaturation in the alkyl side chain, as shown in
Figure 7. 21 As a result of the success obtained with the plant
oil-based poly(vinyl ether)s described above, it was of interest to
produce and characterize poly(vinyl ether)s containing cardanol
units in the pendent chains of the repeat units. A novel vinyl
ether monomer of cardanol, i.e., cardanol ethyl vinyl ether, was
produced using the Williamson ether synthesis reaction shown
in Figure 7. This monomer was successfully polymerized using
the same polymerization system used for the production of the
plant oil-based vinyl ethers. With this polymerization system, a
soluble, tacky polymer was produced.
A solution of the homopolymer was combined with a drier
package and ;lms were cast on steel panels. Three different curing conditions were investigated. Curing at room temperature
was done over a period of two weeks, while curing at 120 °C
Figure 4. Vinyl ether monomers copolymerized with 2-VOES.
Figure 5. Variation in Tg with comonomer content for 2-VOES-based copolymer ;lms cured at room temperature by autoxidation.
Figure 6. Tack-free time as a function of PEGEVE repeat unit content (a), and
an image of a coated glass panel partially laid over the NDSU logo (b).
