CRAIN ALLEN L
| US2511942A | 1950-06-20 |
Cyclic carbonate functional polymers have been prepared using several different routes. Bisphenol-A epoxy resins have been transformed into cyclic carbonate functional resins by reaction of the oxirane with C02.
SimilarEy, trimethylolpropane triglycidyl ether has been converted to the corresponding trifunctional cyclic carbonate by reaction with C02. A more usual route has been through the copolymerization of an unsaturated cyclic carbonate functional monomer. A number of investigators have reported on the copolymerization of the methacrylic ester of glycidyl carbonate. This monomer is readily copolymerized with other acrylic monomers.
Limited information exists in the literature, however, on the homo-or copolymerization of vinyl ethylene carbonate, (VEC or 4-ethenyl-1,3- dioxolane-2-one) for the preparation of cyclic carbonate functional polymers.
A few comments regarding polymerization of VEC are given in U. S. Pat. No.
2,511,942 1950. In the only reported study of the copolymerization behavior of VEC, Asahara, Seno, and Imai in Seisan Kenkyu, 1973,25 (7), 297-299 described the copolymerization of VEC with vinyl acetate, styrene, and maleic anhydride and determined reactivity ratios. Their results indicated that VEC would copolymerize well with vinyl acetate, but in copolymerizations with styrene, little VEC could be incorporated into the copolymer. VEC appeared to copolymerize with maleic anhydride, however the compositions of the copolymers was not reported.
Summary of the Invention The present invention provides a process for the preparation of polymers with pendant cyclic carbonate functionality, synthesized via the free radical copolymerization of vinyl ethylene carbonate (4-ethenyl-1,3- dioxolane-2-one, VEC) with other unsaturated monomers. Both solution and emulsion free radical processes may be used.
Detailed Description of the Invention The present invention provides a process for the preparation of polymers with pendant cyclic carbonate functionality, synthesized via the free radical copolymerization of vinyl ethylene carbonate (4- ethenyl-1,3-dioxolane-2-one, VEC) with other unsaturated monomers.
Both solution and emulsion free radical processes may be used. In solution copolymerizations, it was found that VEC copolymerizes completely with vinyl ester monomers over a wide compositional range.
Conversions of monomer to polymer are quantitative with complete incorporation of VEC into the copolymers. Cyclic carbonate functional latex polymers were prepared by the emulsion copolymerization of VEC with vinyl acetate and butyl acrylate. VEC incorporation was quantitative and did not affect the stability of the
latex. When copolymerized with acrylic monomers, however, VEC is not completely incorporated into the copolymer. Sufficient levels can be incorporated to provide adequate cyclic carbonate functionality for subsequent reaction and crosslinking. The unincorporated VEC can be removed using a thin film evaporator. The Tg of VEC copolymers can be modeled over the compositional range studied using either linear or Fox models with extrapolated values of the Tg of VEC homopolymer.
This invention can be further illustrated by the following examples of preferred embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.
EXAMPLES VEC was prepared by the catalyzed addition of C02 to 3,4-epoxy-1- butene using conditions typical of that used industrially, then purified by vacuum distillation. Other raw materials were used as received without any additional purification.
Mixed xylenes, vinyl acetate (VA), butyl acrylate (BA), butyl methacrylate (BMA), methyl methacrylate (MMA), styrene (St), and t-butyl hydroperoxide were obtained from Aldrich Chemical Company. Lupersol 575 (t-amyl peroxy (2-ethylhexanoate)) was supplied by Elf Atochem. Vazo 67 (2,2'-azobis (2-methylbutyronitrile)) was obtained from DuPont Chemical Company. Vinyl pivalate (NE05), vinyl 2-ethylhexanoate (V2EH), Tergitol NP-40 (non-ionic surfactant) and QP-300 (hydroxy ethyl cellulose) were obtained from Union Carbide Corporation. Aerosol OT-75 (surfactant) was obtained from Cytec. Sodium formaldehyde sulfoxylate was obtained from Henkel Corporation. Ethyl 3-ethoxy propionate (EEP), propylene glycol monomethyl ether (PM) and PM acetate (PM Ac) are Eastman Chemical Company products.
Solution Polymerization.
Solution copolymers were prepared using either a 500 mi or 1000 ml two-piece glass resin kettle equipped with a mechanical stirrer, nitrogen inlet, thermocouple, and condenser. Temperature was maintained using a heating mantle and a Jack-O-Matic (12R) controlled by a Camile TG process control system. In a typical procedure to prepare a vinyl acetateNEC copolymer, 140 g of propylene glycol monomethyl ether (PM) was charged to the reactor and heated with stirring to the polymerization temperature. Then, 10.7 g Lupersol 575,78 g VEC, and 182 g vinyl acetate were mixed in a separate container. When the solvent reached the polymerization temperature, the monomer mixture was fed using a metering pump at a rate of 1.5 g/min. The monomer addition was complete in three hours. One hour after completion of the addition, 0.5 g Lupersol 575 was added, and the reaction was held for an additional one hour and then cooled.
Emulsion Polymerization Emulsion polymerizations were carried out in a one-liter two-piece resin kettle equipped with a mechanical stirrer, heating mantle, nitrogen inlet, thermocouple and condenser. Temperature was controlled as described above and the monomer, initiator and reducer feed rates were also controlled by the Camile TG process control system. To 280 g deionized water was added 24 g of a 5% aqueous solution of QP-300,0.45 g of Aerosol OT-75,19.4 g Tergitol NP-40, and 1.2 g sodium carbonate. With stirring the mixture was heated to 65°C. In a separate container, 400 g of monomers (vinyl acetate, butyl acrylate, and VEC) and 1.7 g of Aerosol OT- 75 were mixed. 40 g of the monomer mixture was added to the reactor.
Feed 2 was prepared consisting of 1.03 g of a 70% aqueous solution of t- butyl hydroperoxide and 38.97 g water. Feed 3 was also prepared consisting of 0.70 g of sodium formaldehyde sulfoxylate and 39.30 g water. After 10 minutes, four solutions consisting of: (1) 0.25 g of a 1 % aqueous solution of FeSO4 7H20 and 2.0 g water; (2) 0.25 g of a 1 % aqueous solution of ETDA and 2.0 g water; (3) 0.51 g of a 70% aqueous solution of t-butyl hydroperoxide and 4.89 g water; and (4) 0.35 g sodium formaldehyde
sulfoxylate and 5.0 g water were added to the reactor. After 10 minutes the monomer mixture was added to the reactor at a rate of 1.71 g/min (total feed time 210 minutes). After 30 minutes Feeds 2 and 3 were started at a rate of 0.190 g/min (total feed time 210 minutes). Thirty minutes after completion of the feeds, solutions consisting of (1) 0.26 g of a 70% aqueous solution of t- butyl hydroperoxide and 1.74 g water and (2) 0.15 g of sodium formaldehyde sulfoxylate and 1.85 g water were added. This addition was repeated after thirty minutes. After an additional 30 minute hold, the reaction mixture was cooled and filtered.
VEC Hydrolysis 0.2 M NaOAc and 0.2 M HOAc solutions were mixed to yield a buffer solution with pH of 4.03.75 mi of this solution was placed in a 100 ml 3- necked flask equipped with a magnetic stirrer, condenser, heating mantle and thermometer. 1.5 ml of VEC was added to the solution. The solution was heated at 80°C for four hours with stirring then cooled to room temperature and analyzed for 3-butene-1,2-diol by gas chromatography.
Solution Polymers (Solution Copolymerization) Since VEC was used to provide cyclic carbonate functionality for subsequent reaction or crosslinking, limited amounts of VEC are used in the copolymerizations. A semi-batch process was used in the copolymerization experiments to approach starved-feed conditions. Starved-feed conditions can result in copolymers with more uniform composition since the conversion is kept high in the reactor. While there are a large number of variables to consider, we elected to focus on monomer composition, polymerization temperature, and initiator level. The initial experiments consisted of screening various monomer combinations to determine if VEC could be successfully copolymerized. Table I lists a number of these initial experiments with typical methacrylate and acrylate monomers as well as styrene.
Table 1. Copolymerization of VEC with (Meth) acrylate Monomers.
Sample Monomers Ratio Wt. % Temp. Unreacted Percent Initiator (°C) VEC, GC Conv.
A VEC/BMA/St 25/50/25 2 80 25.2 64.9 B VEC/BMA/St 25/50/25 2 100 24.0 73.7 C VEC/St/BA 25/50/25 2 100 23.8 67.8 D VEC/MMA/BA 25/50/25 2 100 16.8 83.8 E VEC/MMA/BA 25/50/25 2 120 15.0 83.1 F VEC/BA/MMA 25/50/25 2 100 13.8 85.8 G VEC/BA/MMA 25/50/25 4 100 11.5 88.3 H VEC/BA 25/75 4 100 8.0 93.0 Reaction conditions: Solvent: mixed xylenes; Monomer addition time: 3 hours; Initiator: 2,2'-Azobis (2-methylbutyronitrile) (Vazo 67); Theoretical solids: 60%.
Copolymerizations carried out in the presence of styrene resulted in low conversions with essentially none of the VEC charged being incorporated into the polymer (A, B, C). There was a slight increase in conversion noted with a polymerization temperature increase from 80° to 100°C; thus 100°C was used for the rest of the experiments.
When styrene is eliminated from the monomer mix, there is an increase in conversion from 67 percent to 84 percent (D vs. C) with a corresponding decrease in the amount of unreacted VEC. Increasing the temperature from 100° to 120°C did not have a significant effect. Increasing the amount of butyl acrylate monomer relative to MMA improved the conversion (F), as did increasing the level of initiator (G). One of the better results we have been able to attain thus far is the copolymer with butyl acrylate (H), however, there is still some unreacted VEC present in the copolymer.
The copolymerizations in Table I were all conducted using 2,2'- azobis (2-methylbutyronitrile) as the initiator. All of the polymer solutions, while clear, had a bright yellow color. When the copolymerizations were conducted using t-amyl peroxy (2-ethylhexanoate), the polymer solutions
were clear and colorless. Thus, we continued using the t-amyl peroxy (2- ethylhexanoate) for the rest of the solution copolymerizations.
In order to more systematically understand the effects of VEC copolymerization with butyl acrylate, a series of copolymers was prepared.
Table Il lists the compositions and characteristics of these copolymers.
Table II. VECButyl Acrylate Copolymers Sample % % % % Tg % GPC GPC VEC BA Solids Conv. (°C) Unreacted Mn Mw VEC A 0 100 65.64 100.98-51.6 0.00 3780 7840 B 5 95 64.23 98.81-46.4 1.95 3970 7390 C 10 90 62.90 96.77-42.1 3.71 3240 7370 D 15 85 60.70 94.40-39.1 5.97 3040 6570 E 20 80 59.58 91.66-29.5 7.72 2620 5890 F 25 75 57.71 88.78-26.3 10.60 2790 5920 G 30 70 56.10 86.31-22.0 13.85 2690 5580 H 35 65 54.01 83.09-16.6 16.88 2530 5060 1 40 60 51.98 79.97-13.9 18.51 2490 4790 J 45 55 49.60 76.31-11.2 21.89 2380 4520 K 55 45 45.14 69.45-3.3 30.31 2150 3850 Conditions: Solvent: mixed xylenes; Theoretical solids: 65%; Temperature: 100°C; Monomer addition time: 3 hours; Initiator: t-amyl peroxy (2- ethylhexanoate) Complete incorporation of VEC into the copolymers was not achieved under these conditions. The unreacted monomers consisted predominately of VEC; only a trace of unreacted butyl acrylate was detected. The amount of VEC actually incorporated into the copolymer can be determined by subtraction either using the unreacted monomer data or the conversion data.
If the amount of VEC incorporated into the copolymer is compared to what was charged to the reaction, level of incorporation is relatively constant at 60-65%.
There appears to be a slight decrease in the molecular weight as a function of VEC level. It is important to recognize that this molecular weight decrease could be an artifact of the GPC method: either due to changes in the hydrodynamic volume or refractive index of the copolymers as a function
of composition. However, if this is a real decrease in molecular weight as a function of VEC content, a number of possibilities can be speculated. One possible cause for this effect is that VEC may more readily undergo termination by disproportionation than can butyl acrylate due to its allylic proton. Also, the allylic proton on VEC could be abstracted, reducing the molecular weight via chain transfer.
The glass transition temperature also increases systematically as the level of VEC increases. The Tg data will be discussed below.
To form crosslinked coatings, the polymer must be free of unreacted functional monomer that would act as a chain terminator in the crosslinking reaction. The unreacted VEC could be easily removed from the acrylic copolymer by passing the resin solution through a wiped film still under vacuum, then redissolving the polymer in solvent. GC analysis indicated that the unreacted VEC had been totally removed.
Table III lists the initial solution copolymerization experiments conducted using vinyl ester monomers.
Table III. Copolymerization of VEC with Vinyl Ester Monomers.
Sample Monomers Ratio Percent Solvent Temp. % Initiator (°C) Conv.
A VEC/V2EH/NEOS 20/40/40 4 Xylene 100 88. 9 B VEC/V2EH/NE05 20/40/40 4 EEP 100 101.7 C VEC/V2EH/NEO5 20/40/40 4 PM Ac 100 99.5 D VEC/V2EH/NEO5 20/40/40 4 PM 100 99.7 E VEC/VA/NEO5 10/45/45 4 PM 80 100.6 F VEC/VA/NEO5 30/35/35 4 PM 80 101.2 G VEC/VA/NEO5 17.5/20/62.5 2 PM 80 101.0 Conditions: Theoretical solids: 65%; Addition time: 5 hours; Initiator: t-amyl peroxy (2-ethylhexanoate)
In order to produce polymers for durable coatings, these experiments were conducted using more hindered vinyl monomers which are reported to have better durability than vinyl acetate.
The first set of experiments indicates the importance of using the appropriate solvent for the copolymerizations. Sample A (Table hi) was conducted using similar conditions used for the acrylic copolymerizations.
While there were no signs of insolubility of the polymer in the solvent, only low conversion was achieved. Using a more polar solvent such as ethyl 3- ethoxy propionate (EEP) (B), propylene glycol monomethyl ether (PM) (D) and its acetate (PM Acetate) (C) resulted in essentially complete conversion of monomer to polymer. (Copolymerizations using PM and EEP solvents generally indicate higher conversion than theoretical, indicating that these solvents are becoming incorporated into the polymer via a chain transfer process.) The remainder of the copolymerizations listed in the table demonstrate some of the compositional variations useful in the invention.
A series of copolymers of VEC with vinyl acetate was prepared to study the copolymerization with vinyl esters more systematically. Table IV contains the results from those copolymerizations. As in the initial experiments, complete conversion of the monomers was achieved, with complete incorporation of VEC into the copolymers. Unreacted monomer levels were less than 0.1 percent and not listed in the table. Also, as before, many of the conversions are greater than theoretical possibly indicating incorporation of solvent due to chain transfer. The copolymer solution with 40% VEC was hazy due to insolubility in the PM solvent and was not analyzed. This solution could be cleared by adding dimethyl formamide or N- methyl pyrrolidinone.
Table IV. VEC/Vinyl Acetate Copolymers Sample % % % % Tg GPC GPC VEC VA Solids Conv. (°C) Mn Mw A 0 100 64.52 99.68 20.6 5150 7400 B 5 95 65.19 100.29 26.5 3900 6300 C 10 90 66.43 102.20 29.2 3250 5700 D 15 85 65.13 100.20 32.7 2950 5100 E 20 80 65.30 100.46 34.0 2800 4900 F 25 75 65.73 101.10 41.6 2750 4900 G 30 70 66.08 101.66 41.5 2650 4700 H 35 65 66.02 101.60 46.0 2700 4900 1 40 60-Hazy-57. 0 Conditions: Theoretical solids: 65%; Solvent: PM; Initiator: t-amyl peroxy 2- ethyl hexanoate; Temperature: 80°C The Tgs of the copolymers increase systematically as the level of VEC increases. As in the case of copolymers with butyl acrylate the molecular weights also decreases with increasing levels of VEC. However, unlike with the butyl acrylate copolymers, the molecular weight appears to be reaching a limiting value as the VEC content increases.
FT-IR spectra of typical VEC-butyl acrylate and VEC-vinyl acetate copolymers shows the cyclic carbonate carbonyl absorbance clearly at 1800 cari'. This peak is useful for determining cyclic carbonate content of the copolymer. Since this absorbance is well-resolved, it can also be used to follow reactions of the cyclic carbonate group. Resin percent solids was determined by weighing approximately 1 gram of resin solution into an aluminum weighing pan, covering with additional solvent, then determining weight retention after heating in an oven for 1 hour at 150°C. Percent conversion is calculated as the ratio of the measured solids to theoretical solids. Unreacted monomer content was determined by gas chromatography and data (e. g., Table I) reported as a percent of theoretical polymer solids.
FTIR spectroscopy was conducted using a Midac Prospect-IR. A solution of the polymer was cast on a sodium chloride crystal and the solvent (and any
unreacted monomers) removed by force drying in an oven at 150-160°C. For differential scanning calorimetry (DSC), 1-3 grams of resin solution was placed in an aluminum pan and placed in an oven at 160°C for 1-2 hours.
Analysis was run using a TA Instruments Model 2200 DSC at a rate of 20°C/min. Reported Tg values are the midpoint of the inflection. Gel Permeation Chromatography was done using a PL-Gel Mixed B and 100 A columns (Polymer Laboratories) in N-methyl pyrrolidinone solvent at 1 ml/min. Average molecular weights are reported relative to polystyrene standards.
Latex Potymers (Emulsion Copolymerizations Percent solids was determined using a CEM Labwave 9000 microwave solids analyzer. Viscosity was determined using a Brookfield Digital Viscometer Model DV II using a #3 LV spindle at 30 rpm. Minimum film-formation temperature was determined using a Rhopoint MFFT Bar 90 from Paul N. Gardner, Inc. Particle size was determined using a Brookhaven Instruments Corporation BI-90 Particle Sizer. Samples for DSC were prepared by drawing down a sample of latex onto release paper and allowing to air dry for one week. Unreacted monomers were determined using Gas Chromatography.
Due to the good copolymerizability of VEC with vinyl ester monomers, it seemed likely that VEC could be incorporated into a vinyl acetate/butyl acrylate latex. First, it was important to determine if VEC is prone to hydrolysis in the acidic medium used for vinyl acetate emulsion polymerization. As a check, a single experiment was carried out using an acetic acid-sodium acetate buffer at pH=4 and heating for 4 hours at 80°C.
In this experiment, 6.1% of the VEC was hydrolyzed to the 3-butene-1,2-diol.
Since VEC is only soluble in water up to 3.3 %, it is expected that most of the VEC will be in the oil phase during the emulsion polymerization and that only a small amount will be hydrolyzed.
A series of latex copolymers were prepared using a typical emulsion polymerization recipe and procedure; only the monomer composition was varied. The control composition (80/20 vinyl acetate/butyl acrylate) is similar
to that used for interior latex paint. Table V lists the compositions and properties of the latexes.
Percent solids, pH, and particle size are similar for all the latexes.
Viscosity varies somewhat, but is within limits for this type of latex. The only unreacted monomer detected was the vinyl acetate. Thus, the incorporation of VEC into the emulsion polymerization via the monomer mixture did not affect the latex synthesis. The Tg and minimum film formation temperature (MFFT) of the latexes increase with increasing VEC content, which is expected based on the previous results.
Table V. Properties of VEC-containing Latex Resins.
Composition A B C D E %VEC 0 2 5 10 15 % Vinyl Acetate 80 78 75 70 65 % Butyl Acrylate 20 20 20 20 20 Properties %Solids 50. 2 50. 4 50. 0 50. 2 50. 0 PH 5.3 5.2 5.3 5.3 5.2 Visc, cps 1304 792 1048 1244 1776 Mean dia, mn 377 318 401 410 368 PD 0.15 0.10 0.20 0.22 0.19 Tg, °C 19.9 21.1 25.8 30.7 34.0 MFFT, visual 8.8 11.5 11.7 15.7 17.5 MFFT, resistance 17.3 22.0 19.3 ~24 >25 Unreacted Monomers (ppm) <BR> <BR> VEC -- ND ND ND ND<BR> Vinyl acetate 960 831 671 573 1237 Butyl Acrylate ND ND ND ND ND ND = none detected Stability testing was conducted at 50°C for 10 and 30 days. The pH of the latexes was adjusted to 7.0 using triethylamine, then, the pH and viscosity measured after oven aging. The data is listed in Table VI.
Table VI. Stability Testing of Latexes at 50°C.
A B C D E pH-10 days Initial 7.24 7.19 7.40 7.26 7.19 Final 5.64 5.70 5.75 5.82 5.66 % Retained 77.9 79.3 77.7 80.2 78.7 pH-30 days Initial 7.05 7.10 7.11 7.22 7.15 Final 5.30 5.42 5.38 5.50 5.35 % Retained 75.2 76.3 75.7 76.2 74.8 Viscosity (cps)-10 days Initial 1208 600 940 1144 1328 Final 948 256 700 1036 992 % Retained 78.5 42.7 74.5 90.6 75.0 Viscosity (cps)-30 days Initial 1160 664 848 1100 1216 Final 772 236 580 996 652 % Retained 66.6 35.5 68.4 90.5 53.6 The pH data indicates no difference among the samples. There are some differences in the change of viscosity, however, these results do not indicate a problem of latex stability as a result of VEC incorporation.
Analysis of Copolymer Tg Data.
The Tg data of the copolymers can be fit to appropriate models to determine the values of the homopolymer glass transition temperatures of the individual monomers. Since the Tg of butyl acrylate and vinyl acetate are well known, we hoped to use this analysis to determine the Tg of a VEC homopolymer. We chose a linear model (also known as the Gibbs-DeMarzio theory): Tg = WATgA + WsTgs
where WA and WB are the weight fractions of monomers A and B and TgA and TgB are the respective Tgs of the individual homopolymers. We also fit the data to the Fox Equation: where WA, WB, TgA, and TgB are defined as above. The composition of the butyl acrylate copolymers was corrected using the GC analysis of unreacted VEC.
In all cases the data fit the models equally well. The data is summarized in Table VII. In the case of the solution copolymers, the extrapolated Tg values for butyl acrylate and vinyl acetate agree reasonably well with typical literature values of-54°C and 32°C. However, there is a wide variation in the values determined for VEC.
Table VII. Analysis of VEC Copolymer Tg Data.
Comonomer Model r Tgl (°C) TgvEC (°C) Butyl Acrylate Linear 0.983-50.2 86.6 Butyl Acrylate Fox 0.971-49.3 185.7 Vinyl Acetate Linear 0.952 20.7 99.9 Vinyl Acetate Fox 0.961 21.1 114.6 Vinyl Acetate-Latex Linear 0.981 93.3 191.5 Vinyl Acetate--Latex Fox 0. 978 47. 0 218.4 In the latex systems, the Tg of poly (butyl acrylate) was fixed at 54°C and the butyl acrylate content fixed at 20 percent. The fit of the data is good for both models, however, the calculated Tg for poly (vinyl acetate) using the Fox model is closer to literature values. The calculated Tg for poly (VEC) is much higher than that calculated for the solution polymers.
The variation in the extrapolated values for the Tg of poly (VEC) is primarily due to the fact that experiments were conducted only in the lower compositional range of VEC (<50 %).
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
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