Epoxidized poly(decenyloxazoline) in thermoset coatings.

The side chain double bonds of poly(decenyloxazoline) were epoxidized using standard techniques. The epoxidation was facile and a high percentage of the double bonds were converted to oxirane groups. Films of the epoxidized resin were cured at an elevated temperature with either diamine or anhydride crosslinking agents. Both types of crosslinking agents yielded cured films with good solvent resistance, high hardness, and high gloss. The films cured with the anhydride crosslinkers and the higher molecular weight diamine had better properties than the films cured with the low molecular weight diamine. This could be because some of the low molecular weight diamine was lost due to evaporation during the cure cycle, which would result in lower crosslink density.

Keywords: Decenyl oxazoline, epoxidation, thermoset films, anhydride, diamine

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The coatings industry is continually seeking new materials to improve the quality of products offered to the market place. Currently, much effort is being directed toward the development of products that are more environmentally friendly and/or can be derived from renewable resources. (1) One family of polymers that has been investigated for application in many areas is the oxazolines. (2) Oxazoline polymers with a wide variety of attached functional groups have been or can be synthesized because the polymerization conditions employed are mild, leaving such functional groups intact. In addition, the oxazoline polymer backbone is stable enough to allow post-polymerization functionalization of many side chains. An added benefit is that most, if not all, polyoxazolines tested to date are nontoxic to most lifeforms. (3) In this article we discuss the modification of a polyoxazoline and the use of that modified polymer in thermoset coatings applications. The work reported involves the use of solventborne materials and is of a preliminary nature. A future communication will discuss efforts concerning waterborne systems.

EXPERIMENTAL

The decenyl oxazoline monomer and polymer were obtained using the method of Cai and Litt. (4) The monomer and polymer were obtained in high yields (80-86%) and had the structures expected, as confirmed by [.sup.1]H-NMR spectroscopy and elemental analysis. The polymer had [M.sub.N] = 3700 and [M.sub.W] = 5800.

Epoxidation of the Polymer Side Chain

Poly(decenyl oxazoline), 20 g, was dissolved in 200 ml of chloroform in a 500 ml flask equipped with a mechanical stirrer, reflux condenser, and thermometer. 3-Chloro-peroxybenzoic acid (20.8 g of 77%) was added all at once, and 8[degrees]C exotherm was noted. The exotherm subsided after 15 min and the reaction mixture was stirred at ambient temperature for six hr. After filtration, to remove insolubles, the reaction mixture was added to heptane to precipitate the polymer. The [.sup.1]H-NMR spectrum matched that previously reported. (4) The degree of epoxidation was about 90% and the recovered yield of polymer was 86%. The epoxidized polymer had [M.sub.N] = 4500 and [M.sub.W] = 6700.

Coating Formulations

Simple coating formulations were made by dissolving 10 g of the epoxidized polymer and a stoichometric amount of diamine (2.57 g for amine A and 3.52 g for amine B) or anhydride (2.85 g for anhydride A and 3.25 g for anhydride B) in 20 ml of tetrahydrofuran (THF). For the anhydride crosslinkers, 0.1 g of N,N-dimethyl-benzylamine was added as a catalyst. Films were made by drawing portions of the coating formulations over Bonderite 1000 steel panels with a #3 bird bar. The panels were heated in a forced air oven at 140[degrees]C for various lengths of time. After removal from the oven, the panels were cooled to ambient temperature and the films were evaluated for property development. All film tests were made using the appropriate ASTM method.

RESULTS AND DISCUSSION

Poly(decenyloxazoline) was epoxidized using the procedure of Cai and Litt as shown in Figure 1.

Films of the epoxidized polymer were crosslinked using 1,5-diaminopentane (amine A), 1,9-diaminononane (amine B), pyromellitic anhydride (anhydride A), or trimellitic anhydride (anhydride B). All materials were obtained from commercial sources and were used as received. The film properties obtained are summarized in Tables 1 and 2.

In all cases the dried film thicknesses were 1.5-2.0 mils. The methyl ethyl ketone (MEK) double rubs reported are the number of rubs required to break through the films to the substrate below. For the films with values of 300+, no visible damage was noted at that number of rubs, so the test was terminated at that point. Control films without either diamine or anhydride crosslinker were tested for property development after heating for 120 min. These films got 3-5 MEK double rubs and had 2B-3B pencil hardnesses. These results indicate that films cured with diamines or anhydrides are crosslinked to a high degree. As an additional estimate of crosslinking level, samples cured with 2,9-diaminononane and trimellitic anhydride were subjected to solvent extraction testing. A weighed sample of each material was allowed to soak in THF in a sealed container at ambient temperature for five days. Insoluble material was removed by filtration and dried to a constant weight. The insoluble, or gel, content for each sample was 92.9% (diamine) and 97.4% (anhydride), again indicating that a high level of crosslinking had been obtained.

[FIGURE 1 OMITTED]

CONCLUSIONS

While epoxidized poly(decenyl oxazoline) is a known material, its use in thermoset coatings had not been previously evaluated in even a cursory manner. The polymer proved capable of yielding films with high levels of crosslinking and very good properties in many respects. This could be important because, as previously stated, oxazolines are nontoxic and the starting material, 10-undecenoic acid, can be made from castor oil, (1) a renewal resource.

References

(1) Earls, J.D., White, J.E., Dettloff, M.L., and Null, M.J., "Development and Evaluation of Terminally Epoxidized Triglycerides for Coatings Applications," JCT Research, 1, No. 3, 243 (2004).

(2) Cai, G. and Litt, M.H., "Synthesis and Characterization of Poly(N-acyl or N-aroyl ethyleneimines) Containing Various Pendant Functional Groups IV," and references contained therein, J. Polym. Sci., Part A, 34(B), 2711 (1996).

(3) Cai, G. and Litt, M.H., "Synthesis and Characterization of Poly(N-acyl or N-aroyl ethyleneimines) Containing Various Pendant Functional Groups I," J. Polym. Sci., Part A, 34(B), 2688 (1996).

(4) Cai, G. and Litt, M.H., "Synthesis and Characterization of Poly(N-acyl or N-aroyl ethylenimes) Containing Various Pendant Functional Groups III," J. Polym. Sci., Part A, 34(B), 2701 (1996).

David L. Trumbo -- S.C. Johnson Polymer*

* 8310 16th Street, Sturtevant, W1 53177.

Table 1 -- Amine Cured Films

             Cure    MEK (a)
             Time    Double   Pencil    Forward     Reverse  60[degrees]
Film  Amine  (min.)  Rubs     Hardness  Impact (b)  Impact   Gloss

1     A       30      20       H        100          80      107
2     A       60      40       H         80          40      108
3     A      120      65      2H         60          40      109
4     B       15     300+     5H        140         100      109
5     B       30     300+     5H        140          80      108
6     B       45     300+     7H        120          40      109
7     B       60     300+     7H         80          10      107
8     B      120     300+     7H         60          10      110

(a) MEK = methyl ethyl ketone.
(b) Forward and reverse impact resistances were measured with a Gardner
Tester; the units are in in.-lb.

Table 2 -- Anhydride Cured Films

                Cure    MEK (a)            Forward
                Time    Double   Pencil    Impact   Reverse  60[degrees]
Film  Anhyride  (min.)  Rubs     Hardness  (b)      Impact   Gloss

 9    A          30     300+     7H         20      <10      114
10    A          60     300+     8H        <10      <10      111
11    A         160     300+     8H        <10      <10      114
12    B          15     300+     6H         20       10      113
13    B          30     300+     7H        <10      <10      114
14    B          45     300+     7H        <10      <10      110
15    B          60     300+     7H        <10      <10      113
16    B         120     300+     8H        <10      <10       11

(a) MEK = methyl ethyl ketone.
(b) Forward and reverse impact resistances were measured with a Gardner
Tester; the units are in in.-lb.