Alkyl bridged tin based heat stabilizers for halogenated resins and their synthesis and use

Abstract

The present invention relates to stabilizer compositions for halogen-containing polymers. It has recently been discovered that tin-based heat stabilizers having bridging alkyl groups between two tin centers are effective stabilizers while effectively doubling the molecular weight of the corresponding non-alkyl bridged stabilizers. Ongoing experiments are expected to confirm that the alkyl bridged stabilizers have lower volatility which results in longer retention of the stabilizer in the finished product.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 980,834, filed February 24, 2020, which is incorporated herein by reference. Priority is hereby claimed to U.S. Provisional Patent Application No. 62 / 980,834, filed February 24, 2020. Technical Field

[0003] This invention relates to stabilizer compositions for halogen-containing polymers. More specifically, this invention relates to heat stabilizers for halogen-containing stabilizers (e.g., polyvinyl chloride or PVC). Background Technology

[0004] Processors of non-thermosetting polymers have consistently strived to balance the ability to handle a given polymer-based material, performance during processing, and final properties in the finished product. PVC, in particular, is a thermally unstable polymer at conventional processing temperatures, and numerous stabilizing agent systems have been developed to address its inherent thermal instability. These diverse approaches include organic, mixed-metal, and tin-based stabilizers. PVC and related polymers are also blended and compounded with a variety of other components, including but not limited to pigments, fillers, lubricants, process aids, and impact modifiers. These mixtures are heated during blending and processing via methods such as extrusion and injection molding, which can lead to the release of volatile materials. These materials can produce unpleasant odors and / or have potential health effects on exposed workers, and some of these volatiles can be traced back to the stabilizing system during blending and processing.

[0005] Examples of techniques for reducing volatile materials include polymer plasticizers, post-stripping stabilizers to remove volatile materials, post-addition of alkyl tin oxide to react with residual mercapto esters, and the use of high molecular weight esters.

[0006] Existing techniques for tin-based stabilizers for PVC include the use of "bridged sulfur." ​​Compared to the alkyl-bridged stabilizers of this invention, the bridged sulfur moiety is reactive and constitutes part of the stabilizing effect of stabilizers containing such groups. Therefore, these sulfur bridging groups are temporary in nature and do not effectively increase the molecular weight of such stabilizers, thus not reducing the volatility of such materials relative to their non-sulfur-bridged counterparts. The alkyl-bridged stabilizers of this invention overcome these problems. Invention Overview

[0008] The present invention is a stabilizer composition for halogen-containing polymers. It has recently been discovered that tin-based heat stabilizers with bridging alkyl groups between two tin centers are effective stabilizers while effectively doubling the molecular weight of the corresponding non-alkyl bridged stabilizers. The alkyl bridged stabilizers have lower volatility which results in longer retention of the stabilizer in the finished product. Other bridging groups, including non-carbon based bridging groups, are expected to produce similar results.

[0009] The alkyl bridged materials described herein are based on tin alkyl bonds which are not active in the stabilization process and are effective in increasing the molecular weight of the stabilization system. This approach is not limited to monomeric species containing 2 tin sites with a single bridging group and species with multiple greater than 2 tin sites based on single or multiple terminal tin alkyl bridges should also perform in a similar manner. BRIEF DESCRIPTION OF DRAWINGS

[0011] For a further understanding of the nature and objects of the present application, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings in which like reference numerals refer to like elements, and wherein:

[0012] Figure 1 is a chart of thermogravimetric analysis in °C;

[0013] Figure 2 is a chart showing thermogravimetric analysis of monobutyltin trichloride (MT);

[0014] Figure 3 is a chart showing thermogravimetric analysis of octyl ditin hexachloride (BT);

[0015] Figure 4 shows preferred embodiments of the present invention stabilizers; and

[0016] Figure 5 shows other possible bridging groups. DETAILED DESCRIPTION

[0018] The present invention is a stabilizer composition for halogen-containing polymers. It has recently been discovered that tin-based heat stabilizers with bridging alkyl groups between two tin centers are effective stabilizers while effectively doubling the molecular weight of the corresponding non-alkyl bridged stabilizers. The alkyl bridged stabilizers have lower volatility which results in longer retention of the stabilizer in the finished product.

[0019] A test to determine the weight loss of stabilizer precursors at elevated temperature demonstrated that non-bridged stabilizers have higher volatility and higher weight loss than the alkyl bridged stabilizers of the present invention. The focus of the test was on halogen-based tin compounds, which are the end products of halogen-containing polymer stabilization (i.e., alkyl chlorotin stabilizers). The test demonstrated that non-bridged stabilizers, represented by monobutyl trichlorotin or MT, have higher volatility and subsequently higher weight loss during the experiment than the bridged analogs, represented by hexachlorooctylditin or BT, see Figure 1 . As Figure 2 and 3 can be further noted, that at about 200°C, the high end of the PVC processing temperature range, MT is completely lost, while the weight loss of BT is less than 20%. BT can be considered as an effective dimer of the MT species, since a conventional non-bridged tin stabilizer, monobutyltin tris-isooctoate (EHMA) was used. Figure 1 The two chlorides in 3-x Cl x Sn-bridge-SnCl x L 3-x The partial substitution species resulting from stabilization of the type L Figure 4 Sn-bridge-SnCl

[0020] PVC compound formulation:

[0021] Test conditions: PVC compounds were mixed following standard additive addition order and temperature. Color stability of each compound was evaluated using a Brabender run at 190°C / 60 rpm, sampling every 2 minutes. Color of each chip was measured relative to a standard white tile and the "L" and "b" values reported in Tables 2 and 3, respectively.

[0022] Stabilizer formulation description

[0023] Cl3Sn-C8H 16 -SnCl3(hexachlorooctylditin) synthesis. This material was synthesized according to published procedures, see Organometallics, Vol 21, No. 22, 2002.

[0024] The synthesis of high monooctyltin (RE)3follows Route A below. In this case, the mercapto thioester is 2-mercaptoethyl ester of a C16-C18 unsaturated fatty acid. These are commonly known as the transester PVC stabilizers.

[0025] (RE)3Sn-C8H 16 The synthesis of -Sn(RE)3follows Route B described below. In this case, the mercapto thioester is 2-mercaptoethyl ester of a C16-C18 unsaturated fatty acid. These are commonly known as the transester PVC stabilizers.

[0026] The synthesis of high monooctyltin (EHMA)3follows Route A below. In this case, the mercapto thioester is 2-ethylhexyl mercaptoacetate.

[0027] (EHMA)3Sn-C8H 16 The synthesis of -Sn(EHMA)3follows Route B described below. In this case, the mercapto thioester is 2-ethylhexyl mercaptoacetate.

[0028] Synthesis of Lucie A

[0029] 1.02 equivalents of mercapto sulfur containing ester were reacted with a mixture representing 1.0 equivalent of chloride of monooctyltin chloride (95 wt%) and dioctyltin dichloride (5 wt%) using aqueous sodium hydroxide aqueous solution to convert the chloride to the thiolate. The mixture was allowed to stand for 60 minutes to allow the organic and aqueous phases to separate. The bottom aqueous layer was removed and the remaining organic phase was dried under vacuum and heat. It was then filtered to give a clear liquid.

[0030] Synthesis of Lucie B

[0031] 1.02 equivalents of mercapto sulfur containing ester were reacted with a mixture representing 1.0 equivalent of chloride of octyltin hexachloride using aqueous sodium hydroxide aqueous solution to convert the chloride to the thiolate. The mixture was allowed to stand for 60 minutes to allow the organic and aqueous phases to separate. The bottom aqueous layer was removed and the remaining organic phase was dried under vacuum and heat. It was then filtered to give a clear liquid.

[0032] The stabilizers were evaluated for their effect on PVC processing, specifically their color development as a function of temperature and time, relative to their traditional non-bridged counterparts, high monooctyltin (EHMA)3and high monooctyltin (RE)3. The stabilizers were compounded in PVC formulations as shown in the figures:

[0033] Table 1. Mixed Compositions

[0034]

[0035] Test conditions: The PVC compounds were mixed according to standard additive addition order and temperature. Color stability of each compound was evaluated using a Brabender run at 190°C / 60 rpm, sampling every 2 minutes. Color of each chip was measured relative to a standard white tile and the "L value" and "b value" reported in Tables 2 and 3, respectively.

[0036] Samples 1 and 2 are non-alkyl bridged and alkyl bridged species based on an octyl tin center and EHMA as ligand. According to the color development similarity judgment outlined in Tables 2 and 3, the alkyl bridged species provides an effective equivalent of stabilizing performance to the non-bridged species at equivalent tin.

[0037] Samples 3 and 4 are non-alkyl bridged and alkyl bridged species based on an octyl tin center and RE as ligand. According to the color development similarity judgment outlined in Tables 2 and 3, the alkyl bridged species provides an effective equivalent of stabilizing performance to the non-bridged species at equivalent tin.

[0038] Table 2. Color Values, L Value Data

[0039]

[0040] Table 3. Color Values, b Value Data

[0041]

[0042] The stabilizer composition for halogen-containing polymers according to the present invention preferably comprises at least two tin-based centers with a bridging alkyl group between these tin-based centers. The formula can have multiple tin-based centers and a corresponding multiple bridging alkyl groups. The stabilizer can be one of the following types:

[0043] L3Sn-X-SnL3

[0044] L2Sn-(X)(Y)-SnL2.

[0045] In these types, L is preferably a conventional ligand such as mercaptoacetate, 2-ME ester of C12-C18 fatty acid, carboxylate, maleate, sulfide, 2-ME, thiol, or any mixture thereof. X and Y are preferably alkyl-based bridging groups terminating in tin. X and / or Y can be linear or branched, saturated or unsaturated, with or without heteroatoms, and / or with or without heterocycles. The alkyl bridge is preferably C1 to C80.

[0046] In other embodiments, the stabilizer composition comprises -[SnL2-X-] nat least three repeat units, where X is a tin-terminated alkyl-based bridging group and L is a traditional ligand. In these embodiments, X can be linear or branched, saturated or unsaturated, with or without heteroatoms and / or with or without heterocycles. Preferably, the alkyl bridge is Ci to C80. Preferably, L is a thiolacetic acid ester, a 2-ME ester of a C12-C18 fatty acid, a carboxylate ester, a maleate ester, a sulfide, 2-ME, a thiol, or any combination of two or more of a thiolacetic acid ester, a 2-ME ester of a C12-C18 fatty acid, a carboxylate ester, a maleate ester, a sulfide, 2-ME, or a thiol.

[0047] The present invention also includes the resulting PVC, CPVC, or PVC and CPVC blends containing the novel stabilizers described above. Preferably, the resulting compositions contain at least 0.5 wt% of the stabilizer.

[0048] Other bridging groups, including non-carbon based bridging groups, are expected to produce similar results. For example, as shown in Figure 5 silicones (siloxanes), silanes (silenes), silazanes, carbosilanes, and silphenylenes can provide easier synthetic routes than carbon-based bridging groups.

[0049] The present invention also includes methods of making the novel alkyl-bridged stabilizers.

[0050] The present invention also includes methods of making PVC, CPVC, or blends thereof containing the novel alkyl-bridged stabilizers. Preferably, these compositions are made according to the synthetic routes A or B described above.

Claims

1. A stabilizer for halogen-containing polymers, said stabilizer comprising an alkyl bridging material based on tin-alkyl bond which is inactive in the stabilization process and effective in increasing the molecular weight of the stabilization system, said stabilizer comprising: at least two tin-based centers; and at least one bridging alkyl between said at least two tin-based centers; wherein said bridging alkyl is tin-bonded, and wherein said stabilizer is of the type L3Sn-X-SnL3, wherein L is a ligand selected from the group consisting of mercaptoacetate, 2-ME ester of C12-C18 fatty acid, maleate, 2-ME, and mixtures thereof, wherein ME represents a mercapto sulfur-containing ester, the ligand L containing a mercapto group; and wherein X is a tin-terminated alkyl bridging group.

2. A stabilizer for halogen-containing polymers, said stabilizer comprising an alkyl bridging material based on tin-alkyl bond which is inactive in the stabilization process and effective in increasing the molecular weight of the stabilization system, said stabilizer comprising: at least two tin-based centers; and at least one bridging alkyl between said at least two tin-based centers; wherein said bridging alkyl is tin-bonded, and wherein said stabilizer is of the type L2Sn-(X)(Y)-SnL2, wherein L is a ligand selected from the group consisting of mercaptoacetate, 2-ME ester of C12-C18 fatty acid, maleate, 2-ME, and mixtures thereof, wherein ME represents a mercapto sulfur-containing ester, the ligand L containing a mercapto group; and wherein X and Y are tin-terminated alkyl-based bridging groups.

3. The stabilizer of claim 2, wherein X and Y can be linear or branched, saturated or unsaturated, with or without heteroatoms, with or without heterocycles, wherein the alkyl bridge is from C1 to C80.

4. A thermal stabilizer for halogen-containing polymers, the stabilizer comprising an alkyl bridged material based on tin-alkyl bonds which are not active in the stabilization process and are effective in increasing the molecular weight of the stabilization system, said thermal stabilizer comprising at least three repeating units of -[SnL2-X- n ​ wherein X is a tin-terminated alkyl-based bridging group; wherein L is a ligand selected from the group consisting of mercaptoacetate, 2-methyl ester of C12-C18 fatty acid, maleate, 2-methyl, and mixtures thereof, the ligand L containing a mercapto group; and wherein said bridging groups are inactive in the stabilization process, thus they are effective in increasing the molecular weight of said stabilizer.

5. A composition of PVC, CPVC or mixtures thereof, comprising a stabilizer, said stabilizer comprising an alkyl bridging material based on tin-alkyl bond which is inactive in the stabilization process and effective in increasing the molecular weight of the stabilization system, said stabilizer comprising: at least two tin-based centers; and at least one bridging alkyl between said at least two tin-based centers, wherein said bridging alkyl is tin-bonded; wherein said stabilizer is of the type L3Sn-X-SnL3, wherein L is a ligand selected from the group consisting of mercaptoacetate, 2-ME ester of C12-C18 fatty acid, carboxylate, maleate, 2-ME, and any combination of two or more of mercaptoacetate, 2-ME ester of C12-C18 fatty acid, maleate, and 2-ME, wherein ME represents a mercapto sulfur-containing ester, the ligand L containing a mercapto group; and wherein X is a tin-terminated alkyl-based bridging group.

6. The composition of claim 5, wherein said stabilizer is of the type L2Sn-(X)(Y)-SnL2, wherein L is selected from the group consisting of thioglycolate, 2-ME ester of C12-C18 fatty acid, carboxylate, maleate, 2-ME, and any combination of two or more of thioglycolate, 2-ME ester of C12-C18 fatty acid, maleate, and 2-ME, and wherein X and Y are tin-terminated alkyl-based bridging groups.

7. The composition of claim 6, wherein X and / or Y are linear or branched, saturated or unsaturated, with or without heteroatoms, with or without heterocycles, wherein the alkyl bridge is from C1 to C80.

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