POLYMERIZATION PROCESS

Abstract

Provided is a method of forming a polymer, comprising (a) providing a reaction mixture comprising (i) one or more vinyl monomers, (ii) one or more pH-sensitive inhibition systems, (iii) one or more initiators, and (iv) water; (b) establishing conditions in said reaction mixture such that a free radical polymerization of said vinyl monomer occurs at a location, and (c) after steps (a) and (b) and prior to completion of said free radical polymerization, changing the pH of said reaction mixture to increase the rate of generation of said free radical polymerization at the location of said free radical polymerization.

Claims

1. A method of forming a polymer, comprising (a) providing a reaction mixture comprising (i) one or more vinyl monomers (ii) one or more pH-sensitive inhibition systems (iii) one or more initiators (iv) water (b) establishing conditions in said reaction mixture such that a free radical polymerization of said vinyl monomer occurs at a location, and (c) after steps (a) and (b) and prior to completion of said free radical polymerization, changing the pH of said reaction mixture to increase the rate of generation of said free radical polymerization at the location of said free radical polymerization.

2. The method of claim 1, wherein said free radical polymerization is a suspension polymerization.

3. The method of claim 1, wherein said pH-sensitive inhibition system comprises one or more inhibitor selected from the group consisting of phenol, derivatives of phenol, and derivatives of a nitrite salt.

4. The method of claim 1, wherein said pH sensitive inhibition system comprises a nitrite salt.

5. A method of forming a polymer, comprising (a) providing a reaction mixture comprising (i) one or more vinyl monomers, located at a monomer location, (ii) one or more pH-sensitive inhibition systems, (iii) one or more initiators (iv) water wherein the amount of any buffer in said reaction mixture is 0 to 0.1% by weight based on the weight of said reaction mixture, wherein said reaction mixture has pH value at which said pH-sensitive inhibition system is in low-generation-rate mode; (b) after step (a), establishing conditions in said reaction mixture such that a free radical polymerization of said vinyl monomer occurs.

Description

EXAMPLE 1: NAOH ADDITION AT EXTENT OF REACTION OF 53%

Preparation of Example 1

[0102] Aqueous suspension polymerization was conducted on the reaction mixture as follows. The reaction mixture was heated to 80° C., and the extent of reaction was monitored. At certain points, a portion of a solution of NaOH was added to the reaction mixture. The amount of NaOH added is characterized by the ppm by weight of NaOH based on the weight of water. The preparation proceeded as follows

TABLE-US-00003 Extent Event 53% Add 210 ppm NaOH 88% add 100 ppm NaOH, and increase temperature to 92° C.
At the start of the polymerization, pH was 6.5. At completion of the polymerization, pH was 10.8. The product was polymeric beads of harmonic mean size of 210 μm.

[0103] The results for Example 1 were as follows:

TABLE-US-00004 extent rate (%) (%/hr) 2 14 7 13 12 17 20 22 26 23 34 27 41 29 53 note.sup.(4) 55 31 60 51 64 51 68 51 73 46 80 38 85 35 88 note.sup.(4) 90 32 note.sup.(4): addition of NaOH solution

[0104] All measurements taken after extent of 90% showed rate of 20%/hr or lower. Prior to NaOH addition at extent of 53%, the rate was leveling off at ˜30%/hr; following NaOH addition, the rate quickly increased to 51%/hr and stayed above 30%/hr until extent of 90%. This demonstrates that addition of NaOH accelerated the rate, which would not have occurred without NaOH addition

Comparative Example CA: No NaOH Addition at Extent of 53%

[0105] Comparative Example CA used the same materials and methods as Example 1, except that no addition of NaOH was made at extent of 53%. The results through extent of 75% are shown:

TABLE-US-00005 Comparative Example CA extent rate (%) (%/hr) 2 15 4 16 6 13 8 11 12 17 18 19 25 22 30 25 40 27 50 28 52 28 54 28 56 28 60 27 62 26 65 25 72 19 75 17

[0106] The results of rate vs. extent for Comparative Example CA are very similar to those of Example 1, up to the extent of 53%. After extent of 53%, the rate of Comparative Example CA gradually declined. This further demonstrates that the increase in rate of Example 1 after extent of 53% was caused by the addition of NaOH to Example 1 at 53%.

EXAMPLE 2: NAOH ADDITION AT EXTENT OF 32.5% TO 51%, WITH PH MEASUREMENTS

[0107] Three further polymerizations (Examples 2-1, 2-2, and 2-3) were conducted using the same materials and methods as in Example 1. In Example 2, the extent at which NaOH was added varied, and the overall batch size in Example 2 was smaller than in Example 1. In Example 2, the pH was measured immediately after addition of NaOH. The results were as follows:

EXAMPLE 2

[0108]

TABLE-US-00006 2-1 2-2 2-3 initial pH 6.4 6.5 6.5 Extent at first NaOH addition   42%   51% 32.5% ppm of first NaOH addition 210 210 210 pH immediately after first NaOH addition 11.26 11.27 11.58 Extent at second NaOH additon 87.5% 86.0% 87.5% pH immediately before second NaOH 7.31 7.75 7.24 addition ppm of second NaOH addition 100 100 100 pH immediately after second NaOH addition 11.0 10.78 10.89 final pH 10.5 10.1 10.5

[0109] These data show that the reaction mixture undergoes a sudden rise in pH due to the addition of NaOH. Because of the similarities between the polymerizations in Example 2 and the polymerization in Example 1, it is concluded that Example 1 showed the same increase in pH immediately after addition of NaOH, even though it was not directly measured in Example 1.

[0110] The data for rate (%/hr) versus extent(%) for Example 2 are shown below:

TABLE-US-00007 Example 2-1 Example 2-2 Example 2-3 extent rate extent rate extent rate 21 15 26 17 15 13 42 Add 51 Add 31 21 NaOH NaOH 47 45 56 26 32.5 Add NaOH 57 43 66 72 37 34 71 60 77 54 52 45 80 48 64 56 77 69

[0111] The polymerizations in Example 2 all show desirably high rates after the addition of NaOH.

EXAMPLE 3: NAOH ADDITION AT EXTENT OF 0%

[0112] Methods used for preparing the reaction mixture were the same as in Example 1. The materials and their proportions were as follows:

Droplet Ingredients

[0113]

TABLE-US-00008 Ingredient amount.sup.(1) Styrene balance.sup.(2) DVB 10.2% BPO  0.3% Note .sup.(1)% by weight based on the total weight of droplet ingredients. Note .sup.(2)to make up 100% by weight

[0114] The ingredients intended for the aqueous liquid medium were as follows:

TABLE-US-00009 Aqueous-Phase Ingredients ingredient amount.sup.(3) DI water  100% CMMC 0.15% PVOH 0.06% NaNO.sub.2 0.025%  Note .sup.(3)% by weight based on the total weight of aqueous phase ingredients

[0115] The weight ratio of droplet ingredients to aqueous phase ingredients was 0.61:1.

[0116] Two polymerizations were performed, Example 3 and Comparative Example CB. The reaction mixtures were prepared identically. Then, prior to the beginning of polymerization, NaOH was added to Example 3 to establish pH of 10.8. Both reactions were heated to 72° C. and maintained there. No further additions of NaOH were made to either reaction. At the end of the procedure, pH was 5.5 for both reactions. Both reactions produced polymeric beads of harmonic mean size approximately 460 μm.

[0117] The extent of reaction versus time at 72° C. for each reaction was as follows:

TABLE-US-00010 Extent (%) versus Time (hours) Time Comparative Example CB Example 3 0 <5 <5 1 <5 <5 2 <5 5 3 <5 10 4 <5 17 5 <5 22 6 <5 32 7 <5 45 8 <5 58 14 82 20 68

[0118] Example 3 shows much higher extent of reaction after the first hour than does Comparative Example CB. This result demonstrates the effect that the addition of NaOH increases the polymerization rate.

EXAMPLE 4: POLYMERS WITHOUT DVB

[0119] Methods used for preparing the reaction mixture were the same as in Example 1. The materials and their proportions were as follows:

[0120] Droplet ingredients:

TABLE-US-00011 Ingredient amount.sup.(1) Styrene balance.sup.(2) DVB   0% BPO 0.5% Note .sup.(1)% by weight based on the total weight of droplet ingredients. Note .sup.(2)to make up 100% by weight

[0121] The ingredients intended for the aqueous liquid medium were as follows:

TABLE-US-00012 Aqueous-Phase Ingredients ingredient amount.sup.(3) DI water  100% CMMC 0.23% PVOH 0.06% NaNO.sub.2 0.11% Note .sup.(3)% by weight based on the total weight of aqueous phase ingredients

[0122] The weight ratio of droplet ingredients to aqueous phase ingredients was 0.30:1.

[0123] Two polymerizations were conducted: Example 4 and Comparative Example CC. Method of polymerization was the same as in Example 1, with the differences in the extent at which NaOH was added shown along with the results below. Results are extent of reaction (%) and pH versus time at 80° C. (minutes):

TABLE-US-00013 Extent versus time (minutes) Comparative Example 4 Example CC Time Extent pH Extent pH 0  0% 6.67 0% 6.67 165 21% 23% 225 28% 285 34% 34% 345 42%.sup.(4)  7.6 before 43% 7.36 11.38 after 375 49% 45% 420 51% 435 58% 480 57% 495 67% 540 61% 555 86%.sup.(5)  8.42 before 11.24 after 1500 11.27 final 73% 7.90 Note .sup.(4)215 ppm of NaOH added. The pH values shown are before and after addition of NaOH. Note .sup.(5)108 ppm of NaOH added. The pH values shown are before and after addition of NaOH.

[0124] In comparing Example 4 to Comparative Example CC, it can be seen that after the addition of NaOH at 345 minutes, Example 4 had consistently higher extent of reaction. This result demonstrates that the addition of NaOH caused an increase in the polymerization reaction rate of Example 4. Additionally, Comparative Example CC never progressed beyond an extent of the polymerization reaction of 73%, even after 1500 minutes, while Example 4 reached extent of 86% at 555 minutes.

EXAMPLE 5: EVOLVED GAS ANALYSIS OF COMPARATIVE EXAMPLE CD

[0125] In Comparative Example CD, droplet composition was the same as in Example 1. The ratio of droplet composition to aqueous phase was similar to Example 1. In Comparative Example CD, there was no PVOH and no CMMC. Gelatin was present in the aqueous phase. Sodium nitrite was present in the reaction mixture. Boric acid was present in the reaction mixture Immediately prior to the beginning of polymerization, pH was approximately 10. The reaction mixture was formed at ambient conditions and then the temperature was raised to approximately 80° C. and held there until the reaction reached extent of over 85%. Once the temperature was raised and the polymerization reaction began, no adjustment was made to the pH. When the reaction was stopped, the pH was approximately 9.

[0126] The particles produced in Comparative Example CD were analyzed by the Evolved Gas method described above. No peak was found in the gas chromatography result. It is concluded that no nitrogen monoxide gas was evolved by Comparative Example CD.

EXAMPLE 6: EVOLVED GAS ANALYSIS OF COMPARATIVE EXAMPLE CE

[0127] Comparative Example CE was the same as Comparative Example CD except for the following differences: The amount of DVB in the droplet was 4.8% instead of 5%. No sodium nitrite was used. A dichromate salt was used as an additive to inhibit the progress of emulsion polymerization. As in Comparative example CD, no nitrogen monoxide was released from the dried polymer beads of Comparative Example CE.

EXAMPLE 7

[0128] Evolved gas analysis of the polymeric particles of Examples 2-1, 2-2, and 2-3. were analyzed as described in Example 5 and the results were as follows. The substance having retention time of 103 seconds in the gas chromatography was analyzed by mass spectrometry and verified as containing nitrogen monoxide by the same method as used for PVP, described above. This result demonstrates that the released substance either was nitrogen monoxide or else was a substance or mixture of substances that formed nitrogen monoxide after release from the polymeric particles.

[0129] Comparison of Example 7 to Comparative Examples CD and CE shows that the comparative examples had no releasable nitrogen monoxide, while the inventive example did have releasable nitrogen monoxide.

EXAMPLE 8: MASS SPECTROMETRY OF EXAMPLE 4

[0130] The polymerization process of Example 4 was conducted, and sample polymer was obtained at extent=20%. That sample polymer was separated using size exclusion chromatography to obtain a small sample having degree of polymerization of about 45. The small sample was tested by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Examination of the results from 4422 atomic mass units to 4440 atomic mass units showed a pattern of peaks that was consistent with a mixture of 0.4 mole of structure S1 for every one mole of structure S2, as follows:

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[0131] The results from the MALDI mass spectrometry are consistent with the presence of some polymer molecules that have covalently bound NO groups.