Alkyl-bridged tin-based heat stabilizers for halogenated resins, 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 with a bridging alkyl group between two tin centers are effective stabilizers while effectively doubling the molecular weight of the corresponding non-alkyl-bridged stabilizers. Ongoing testing is expected to confirm that the alkyl-bridged stabilizers are much less volatile, resulting in greater retention of the stabilizer in the final article.

Description

[Technical Field]

[0001] This application claims the benefit of, and is incorporated by reference in its entirety, U.S. Provisional Patent Application No. 62 / 980,834, filed February 24, 2020. This application hereby claims the benefit of, and is incorporated by reference in its entirety, U.S. Provisional Patent Application No. 62 / 980,834, filed February 24, 2020.

[0002] The present invention relates to a stabilizer composition for halogen-containing polymers. More particularly, the present invention relates to a heat stabilizer for halogen-containing polymers, such as polyvinyl chloride or PVC. [Background technology]

[0003] Processors of non-thermoset polymers have historically struggled to balance the ability to process a given polymer-based material, its properties during processing, and the final properties of the finished article. PVC, in particular, is a thermally unstable polymer at traditional processing temperatures, and many stabilizer systems have been developed to address its inherent thermal instability. These approaches include organic-based, mixed metal-based, and tin-based stabilizers. PVC and related polymers are blended and compounded with a variety of other ingredients, including, but not limited to, pigments, fillers, lubricants, processing aids, and impact modifiers. These mixtures are heated during blending and processing, including extrusion and injection molding, which can lead to the release of volatile substances. These substances can result in unpleasant odors and / or potential health effects for exposed workers. During compounding and processing, some of these volatile substances may originate from the stabilization system.

[0004] Examples of techniques to reduce volatility include polymeric plasticizers, post-stripping of stabilizers to remove volatiles, post-addition of alkyltin oxides to react with residual mercaptoesters, and the use of high molecular weight esters.

[0005] Existing technology for tin-based stabilizers for PVC involves the use of "sulfur bridges." In contrast to the alkyl-bridged stabilizers of the present invention, the sulfur bridge moieties are reactive and form part of the stabilizing action of stabilizers containing such groups. As a result, these sulfur bridge groups are essentially temporary and do not effectively increase the molecular weight of such stabilizers and therefore do not reduce the volatility of such materials relative to their non-sulfur-bridged counterparts. The alkyl-bridged stabilizers of the present invention overcome these problems. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention relates to a stabilizer composition for halogen-containing polymers. More particularly, the present invention relates to a heat stabilizer for halogen-containing polymers, such as polyvinyl chloride or PVC. [Means for solving the problem]

[0007] The present invention is a stabilizer composition for halogen-containing polymers. It has recently been discovered that tin-based heat stabilizers with a bridging alkyl group between two tin centers are effective stabilizers and effectively double the molecular weight of the corresponding non-alkyl-bridged stabilizers. These alkyl-bridged stabilizers have significantly lower volatility, which results in greater retention of the stabilizer in the final article. It is expected that other bridging groups, including non-carbon-based bridging groups, will produce similar results.

[0008] The alkyl-bridged materials described herein are based on tin-alkyl bonds that are not active in the stabilization process and are effective in increasing the molecular weight of the stabilized system. This approach is not limited to monomeric species containing two tin moieties with a single bridging group; species with more than two tin moieties based on single or multiple tin-terminated alkyl-based bridges should also behave similarly.

[0009] For a fuller understanding of the nature, objects, and advantages of the present invention, reference should be made to the following detailed description which should be read in conjunction with the following drawings, in which like reference numerals indicate like elements and in which: [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the thermogravimetric analysis in °C. [Figure 2] FIG. 2 shows the TGA of monobutyltin trichloride (MT). [Figure 3] FIG. 3 shows the TGA of octylditin hexachloride (BT). [Figure 4] FIG. 4 shows a preferred embodiment of the stabilizer of the present invention. [Figure 5] FIG. 5 shows other possible crosslinking groups. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention is a stabilizer composition for halogen-containing polymers. It has recently been discovered that tin-based heat stabilizers with a bridging alkyl group between two tin centers are effective stabilizers while effectively doubling the molecular weight of the corresponding non-alkyl-bridged stabilizers. These alkyl-bridged stabilizers have significantly lower volatility, which results in greater retention of the stabilizer in the final article.

[0012] Tests to determine the weight loss of stabilizer precursors at elevated temperatures confirmed that uncrosslinked stabilizers have higher volatility and greater weight loss than the alkyl-crosslinked stabilizers of the present invention. The focus of this testing was on halogenated tin compounds, i.e., alkyltin chlorides, which are the end products of stabilizing halogen-containing polymers. This testing confirms that uncrosslinked stabilizers, represented by monobutyltin trichloride (MT), have higher volatility and therefore greater weight loss over the test period relative to their crosslinked analogs, represented by octylditin hexachloride (BT) (see Figure 1). It may be further noted that, as shown in Figures 2 and 3, at approximately 200°C (which is at the high end of the PVC processing temperature range), MT is completely lost, while BT suffers less than 20% weight loss. BT can be viewed as an effective dimer of the MT species, which can occur with the use of conventional uncrosslinked tin stabilizers such as monobutyltin tris(EHMA). Both chlorides in Figure 1 are produced as final stabilizer compositions by replacement of reactive ligands in their respective starting thermal stabilizers. In addition to lower mass loss during processing, the crosslinked species are also expected to be less susceptible to extraction during their useful life. These species are L 3-x Cl x Sn-crosslinked-SnCl x L 3-x The expected lower volatility of partially substituted species with stabilization of the type (where x=1 or 2 for crosslinked stabilizers and L can be, among other things, a mercaptide ligand, as shown in Figure 4) is predicted to result in improved odor properties. [Example]

[0013] PVC Compound Formulation: Test conditions:The PVC compounds were compounded according to the usual additive addition order and addition temperatures. The color stability of each compound was evaluated using a Brabender operating at 190°C / 60 rpm with samples taken at 2 minute intervals. The color of each chip was measured relative to a standard white tile, and the "L value" and "b value" are reported below in Tables 2 and 3, respectively.

[0014] Description of stabilizer preparation Cl3Sn-C8H 16 Synthesis of -SnCl3 (octylditin hexachloride). This substance was synthesized according to a published method. See Organometallics, Vol. 21, No. 22, 2002.

[0015] The synthesis of high monooctyltin (RE)3 follows Route A, described below. In this case, the mercapto sulfur ester is C 16 -C 18 These are 2-mercaptoethyl esters of unsaturated fatty acids. These are commonly referred to as reverse ester PVC stabilizers.

[0016] (RE)3Sn-C8H 16 The synthesis of -Sn(RE)3 follows Route B described below. In this case, the mercaptosulfur ester is C 16 -C 18 These are 2-mercaptoethyl esters of unsaturated fatty acids. These are commonly referred to as reverse ester PVC stabilizers.

[0017] The synthesis of high monooctyltin (EHMA)3 follows Route A, described below. In this case, the mercaptosulfur ester is 2-ethylhexylmercaptoacetate.

[0018] Synthetic Route A 1.02 equivalents of the mercaptosulfur-containing ester were reacted with a mixture of monooctyltin trichloride (95% by weight) and dioctyltin dichloride (5% by weight) to yield 1.0 equivalent of chloride using aqueous sodium hydroxide to convert the chloride to the mercaptide. The mixture was allowed to stand for 60 minutes to allow the organic and aqueous phases to separate. The lower aqueous layer was removed, and the remaining organic phase was dried under reduced pressure and heat. This was then filtered to yield a clear liquid.

[0019] Synthetic Route B 1.02 equivalents of the mercaptosulfur-containing ester were reacted with a mixture of octyltin hexachlorides (1.0 equivalent of chloride) using aqueous sodium hydroxide to convert the chloride to the mercaptide. The mixture was allowed to stand for 60 minutes to allow the organic and aqueous phases to separate. The lower aqueous layer was removed, and the remaining organic phase was dried under reduced pressure and heat. It was then filtered to yield a clear liquid.

[0020] These stabilizers were evaluated for their effect on PVC processing, particularly their effect on color development as a function of heat and time, in comparison with their conventional, non-crosslinked counterparts, high monooctyl Sn(EHMA)3 and high monooctyl Sn(RE)3. The stabilizers were compounded into the indicated PVC formulations.

[0021] [Table 1]

[0022] Test conditions: The PVC compounds were blended according to the standard additive addition order and addition temperature. The color stability of each compound was evaluated using a Brabender operating at 190°C / 60 rpm with samples taken at 2 minute intervals. The color of each chip was measured relative to a standard white tile, and the "L value" and "b value" are reported below in Tables 2 and 3, respectively.

[0023] Samples 1 and 2 are non-alkyl-bridged and alkyl-bridged species based on an octyltin center with EHMA as the ligand. As outlined in Tables 2 and 3, at equivalent tin weights, the alkyl-bridged species provides virtually equivalent stabilization performance to its non-bridged counterpart, as judged by the similarity in color development.

[0024] Samples 3 and 4 are non-alkyl-bridged and alkyl-bridged species based on an octyltin center with RE as the ligand. As outlined in Tables 2 and 3, at equivalent tin weights, the alkyl-bridged species provides virtually equivalent stabilization performance to its non-bridged counterpart, as judged by the similarity in color development.

[0025] [Table 2]

[0026] [Table 3]

[0027] The stabilizer compositions of the present invention for halogen-containing polymers preferably contain at least two tin-based centers with a bridging alkyl group between them. This formula can have multiple tin-based centers and corresponding multiple bridging alkyl groups. The stabilizer can be one of the following types: L3Sn-X-SnL3 L2Sn-(X)(Y)-SnL2 In these types, L is preferably a conventional ligand, such as an ester of thioglycolic acid, a 2-ME ester of a C12-C18 fatty acid, a carboxylate, a malate, a sulfide, 2-ME, a mercaptan, or a mixture (blend) thereof. X and Y are preferably tin-terminated alkyl-based bridging groups. X and / or Y may be linear or branched, saturated or unsaturated, with or without heteroatoms, and / or with or without heterocyclic rings. The alkyl bridge is preferably C1 to C80.

[0028] In another embodiment, the stabilizer composition is -[SnL2-X-] n wherein X is a tin-terminated alkyl-based bridging group and L is a conventional 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 C1-C80. Preferably, L is an ester of thioglycolic acid, a 2-ME ester of a C12-C18 fatty acid, a carboxylate, a malate, a sulfide, 2-ME, a mercaptan, or any combination of two or more of an ester of thioglycolic acid, a 2-ME ester of a C12-C18 fatty acid, a carboxylate, a malate, a sulfide, 2-ME, or a mercaptan.

[0029] The present invention is also directed to the resulting PVC, CPVC, or blends of PVC and CPVC containing the novel stabilizers described above. Preferably, the resulting compositions contain at least 0.5% by weight of the stabilizer.

[0030] Other crosslinking groups, including non-carbon-based crosslinking groups, are expected to yield similar results. For example, silicones (siloxanes), silanes (silylenes), silazanes, carbosilanes, and silphenylenes, as shown in Figure 5, may offer easier synthetic routes than carbon-based crosslinking groups.

[0031] The present invention also includes a method for preparing the novel alkyl-bridged stabilizers.

[0032] The present invention also includes a method for preparing PVC, CPVC, or blends thereof containing the novel alkyl-bridged stabilizers. Preferably, these compositions are prepared according to Synthetic Route A or B described above.

Claims

1. (i) A compound of the following formula: L 3 Sn-X-SnL 3 wherein L is a ligand selected from the group consisting of esters of C12-C18 fatty acids with 2-mercaptoethanol (2-ME); X is a C1-C80 alkylene bridging group attached at its end to the Sn atom. A compound represented by the formula: (ii) (EHMA) 3 Sn-C 8 H 16 -Sn(EHMA) 3 (wherein EHMA represents a 2-ethylhexyl-O-C(=O)-CH 2 -S- group). wherein (i) X and (ii) C 8 H 16 are not active with respect to stabilizing halogen-containing polymers; or (iii) A combination of (i) and (ii) 1. A stabilizer composition for halogen-containing polymers comprising:

2. 1. A composition of PVC, CPVC, or blends thereof, comprising a stabilizer, the stabilizer comprising: (i) a compound of the following formula: L 3 Sn-X-SnL 3 wherein L is a ligand selected from the group consisting of esters of C12-C18 fatty acids with 2-mercaptoethanol (2-ME); X is a C1-C80 alkylene bridging group attached at its end to the Sn atom. A compound represented by the formula: (ii) (EHMA) 3 Sn-C 8 H 16 -Sn(EHMA) 3 (wherein EHMA represents a 2-ethylhexyl-O-C(=O)-CH 2 -S- group). wherein (i) X and (ii) C 8 H 16 are not active with respect to stabilizing halogen-containing polymers; or (iii) A combination of (i) and (ii) A composition comprising:

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