agglomerating char could be produced at 425” C. in a 5-minute treatment using 18- to 100-mesh coal, if oxygen is present. T h e weight loss on treating was about lo%, which is also the B.t.u. loss of the coal, since the heating values of the coal and char are almost identical. I t is desirable and may be necessary to heat the coal internally by the treating gas to prevent the particles from adhering to the wall of the reactor. To obtain data that will permit a more exact evaluation of the process and estimate of the cost of this method of pretreatment, a study of a continuous system is needed. Such a study will allow a realistic determination of the optimum feed gas-coal ratio and minimum average residence time required for pretreatment. In a fluidized bed all the coal is not pretreated for a uniform length of time because of the rapid mixing of the raw coal and treated char. T h e discharged solids contain particles treated to different degrees because the residence time of the individual particles varies. The results of the batch study will be used as a guide for the continuous
studies, but the optimum solids residence timc and conditions of operation may be different from those obtained in the present investigation. literature Cited
(1) Am. SOC. Testing Materials, Philadelphia, Pa., “Standard Specifications for Classification of Coals by Rank,” ASTM D 388-38: ASA M20.1-1938. (2) Chanabasappa, K. G., Linden, H. R., Znd. Eng. Chem. 50 637-44 (1958). (3) Chem. Eng. 69, 17 (Oct. 28, 1962). (4) Foch, Pierre, U. S. Patent 3,011,953 (Dec. 5, 1961). (5) Karl. Alfred. Ger. Patent 1.041.192 (Oct. 16. 1958). (6\ Nathan. M. F . . U. S. Patent 3.032.477 (Mav 1. 1962) (7j Sylvander, N. E., Zbid., 3,070,5’15 (filed M a i 6 , ’1957): (8) JYelinsky, I. H., Zbid., 2,955,077 (Oct. 4, 1960).
RECEIVED for review October 23, 1963 ACCEPTED December 16, 1963 Division of Fuel Chemistry, 145th Meeting, ACS, New York, N. Y., September 1963.
UNSATURATED POLYESTER RESINS FROM EPOXIDES AND ANHYDRIDES H. G . W A D D I L L , J. G.
M I L L I G A N , AND W. J.PEPPEL
Jefferson Chemical Go., Inc., Austin, Tex.
Commercial polyester resin i s prepared using propylene oxide in lithium chloride-catalyzed reaction at 125’ C. with maleic anhydride, phthalic anhydride, and minimum propylene glycol to regulate molecular weight. Subsequent heating of resin to 200’ C. for 2 to 3 hours improves reactivity with styrene b y converting from maleate to fumarate form. Addition of a small amount of phosphoric acid prevents resin darkening. Properties of polyester and resin with styrene after curing compare with products less economically made from propylene glycol b y polyesterification. Latitude in composition of polyester i s indicated.
linear polyester renins are prepared commercially by simply heating dibasic acids or anhydrides with glycols. Since esterification catalysts are not used, a relatively high temperature is necessary to drive the reaction a t a reasonable rate. Recent work has shown that the reaction of epoxides with dibasic acid anhydrides, where applicable, offers a n additional means of obtaining polyesters requiring less severe conditions (3, 5-9, 73). Unfortunately, there has been no reported success in obtaining unsaturated polyesters from maleic anhydride not objectionably dark in color or having other shortcomings. As the investigation described here shows, unsaturated polyesters of good quality, suitable for crosslinking with styrene or other vinylic monomers, can be obtained using the epoxide-anhydride reaction, but the choice of catalyst is important and certain steps in the preparation are necessary to ensure that the resin is light in color and has desired activity in polymerization. Commercially, production savings are possible when the epoxide is used. ARIOUS
Investigation of Epoxide-Anhydride Reaction
Tertiary amines, alkylammonium compounds, and lithium halides effectively catalyze the epoxide-anhydride reaction, which otherwise is slow (6, 7, 73). Homopolymerization of the epoxide is a competing reaction but appears least serious in the case of 1,2-epoxides (6). These catalysts are also efficient for the reaction of epoxides with carboxylic acids (70). Although the mechanism of polymer initiation and termination is not
well understood, hydroxyl-containing substances such as water and alcohols, to the extent present, will regulate polyester molecular weight. 0
II
R”
C
ROH
/\
+ nR’
0
\/ C
I + nCH-CH2
+
\/ 0
/I
0
[i K
RO C-R’-COCHCHsO
] n
H
I n several preliminary experiments maleic anhydride, phthalic anhydride, varying amounts of propylene glycol or ethylene glycol to regulate molecular weight, and 0.2% tetramethylammonium bromide catalyst were heated to 90’ C. in a 2.5-liter stirred pressure vessel. The estimated requirement of propylene oxide was then added as rapidly as jacket cooling would permit. T h e reaction proceeded with a n accompanying drop in pressure. Progress was also followed by removing samples and titrating with standard methanolic potassium hydroxide. Generally, disappearance of acid leveled off after several hours (Table I and Figure 1). T h e acid arises from the initial reaction of the glycol with anVOL 3
NO. 1 M A R C H 1 9 6 4
53
\
\
Table II. Isomerization of Polyester Resin b y Heating to Obtain Active Fumarate Form
Polyester resin.
POLYESTER A
Hours at 200' C. 1 2 3 4 a,b,c S P I
0
I
2
3
4
5
Peak Exotherm,a Gel Time,b Cure Time,c ' C. -+fin.-See. Min.-Sec. 112.8 7-45 18-50 145.8 5-1 6 10-12 162.8 4-54 9-33 168.1 4-0 9 7-55
Hardness, Barcol 24 27 28 30
standard tests ( 7 7).
Table 111.
Figure 1. Rate of reaction as function of amount and type of glycol initiator used Polyesters identified in Table I
hydride, as expected. Molecular weight of the polyester finally was determined by vapor pressure osmometry. The molecular weight values observed reflect incomplete reaction and possibly some homopolymerization of epoxide. Polyesters C and D (Table I), while having properties suggesting adequacy for blending with styrene and polymerization with the usual peroxide-type catalysts. darkened appreciably on heating to above 150' C., a temperature that is usually reached or exceeded during curing. Moreover, copolymerization with styrene was sluggish and the resulting cured resin was brittle. An explanation for this behavior was found in the observation by others that esterification of maleic anhydride a t relatively low temperatures (100' C.) takes place with little isomerization to the fumarate form, which is the more reactive (2, 4, 72). Further heating a t a higher temperature is reported as bringing about improvement (7). Commercially, polyesterification is carried out a t temperatures reaching 200' C. Samples of polyesters prepared from epoxide \vere heated a t 200' C. for several hours and changes noted by measuring the peak exotherm, gel time. and cure time on polymerization with styrene. Table I1 shows that the peak exotherm increased and the gel and cure times were shortened as the heating time was extended. The shift from maleate to fumarate form ]vas confirmed by infrared spectroscopy. using essentially the method of Park e t al. (72). The cured resin improved in hardness but a n undesirable result was the increase in final color resulting from heating the polyester.
Polyester Molecular Weight Related to Amount of Glycol Initiator Used
Polyester Reactants, Moles a A B c D Maleic anhydride 1.33 1.33 1.33 1.33 Phthalic anhydride 2.67 2.67 2.67 2.67 Propylene glycol 1 .o 0.5 0.25 ... Ethylene glycol ... ... ... 0.25 Propylene oxide 3.2 3.7 3.95 3.95 Acid number, final6 98.7 59.0 53.3 37.8 Molecular weight, found 724 1243 1363 1798 Molecular weight, theoryc 788 1558 3097 2862 a Tetramethylammonium bromide, 0.2%, added. M g . KOH/g. sample. C Calculated assuming complete reaction of gbcol.
54
Color, Gardner 2-3 3-4 3-4 3-4
6
HOURS HEATING AT 90'C.
Table 1.
1 .33 moles maleic anhydride 2.67 moles phthalic anhydride 0 . 5 mole propylene glycol 3 . 7 moles propylene oxide Tetramethylammonium bromide catalyst
I&EC P R O D U C T RESEARCH A N D DEVELOPMENT
Properties of Epoxide-Based Polyester Compared with Glycol-Based Polyester
PolyesterQ from Epoxide
Acid number, mg. KOH/g. sample Viscosity, Gardnerd Color, Pt-Cod Gel time, min.-sec.d Cure time, min.-sec.d Peak exotherm, ' C.d
36.4 M-N 50-75 4:39 8:02 181.2
Polyesterbgc from Glycol 25-39 P-s
