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Compositions comprising sulfur-containing prepolymers such as polythioether prepolymers, polyepoxides, and a blocked 1,8-diazabicyclo5.4.0undec-7-ene bicarbonate catalyst useful as aerospace sealants are disclosed. The compositions exhibit extended working time and the curing rate can be tailored fo

Compositions comprising sulfur-containing prepolymers such as polythioether prepolymers, polyepoxides, and a blocked 1,8-diazabicyclo5.4.0undec-7-ene bicarbonate catalyst useful as aerospace sealants are disclosed. The compositions exhibit extended working time and the curing rate can be tailored for specific applications.

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1. A composition comprising: (a) a thiol-terminated sulfur-containing prepolymer;(b) a polyepoxide curing agent; and(c) a blocked 1,8-diazabicyclo[5.4.0]undec-7-ene bicarbonate catalyst. 2. The composition of claim 1, wherein the catalyst is in the form of a powder. 3. A composition comprising: (a)

1. A composition comprising: (a) a thiol-terminated sulfur-containing prepolymer;(b) a polyepoxide curing agent; and(c) a blocked 1,8-diazabicyclo[5.4.0]undec-7-ene bicarbonate catalyst. 2. The composition of claim 1, wherein the catalyst is in the form of a powder. 3. A composition comprising: (a) a thiol-terminated sulfur-containing prepolymer;(b) a polyepoxide curing agent; and(c) a blocked 1,8-diazabicyclo[5.4.0]undec-7-ene bicarbonate catalyst, wherein, the catalyst is in the form of a powder; andthe powder is characterized by an average particle diameter from 25 μm to 200 μm. 4. A composition comprising: (a) a thiol-terminated sulfur-containing prepolymer;(b) a polyepoxide curing agent; and(c) a blocked 1,8-diazabicyclo[5.4.0]undec-7-ene bicarbonate catalyst, wherein, the catalyst is in the form of a powder; andthe powder is characterized by an average particle diameter less than 100 μm. 5. The composition of claim 1, wherein the polyepoxide curing agent comprises an epoxy novolac resin, a bisphenol A/epichlorohydrin epoxy resin, or a combination thereof. 6. The composition of claim 1, wherein the composition comprises: from 35 wt % to 65 wt % of the thiol-terminated sulfur-containing prepolymer;from 4 wt % to 11 wt % of the polyepoxide curing agent; andfrom 0.2 wt % to 0.36 wt % of the blocked 1,8-diazabicyclo[5.4.0]undec-7-ene bicarbonate catalyst. 7. The composition of claim 1, wherein the thiol-terminated sulfur-containing prepolymer comprises a thiol-terminated polythioether prepolymer. 8. The composition of claim 7, wherein the thiol-terminated polythioether prepolymer comprises a thiol-terminated polythioether prepolymer of Formula (2), a thiol-terminated polythioether prepolymer of Formula (2a), or a combination thereof: HS—R1—[—S—(CH2)p—O—(R2—O)m—(CH2)2—S—R1—]n—SH  (2){HS—R1—[—S—(CH2)p—O—(R2—O)m—(CH2)2—S—R1—]n—S—V′—}zB  (2a)wherein: each R1 independently is selected from C2-10 alkanediyl, C6-8 cycloalkanediyl, C6-14 alkanecycloalkanediyl, C5-8 heterocycloalkanediyl, and —[(—CHR3—)p—X—]q—(—CHR3—)r—, wherein: p is an integer from 2 to 6;q is an integer from 1 to 5;r is an integer from 2 to 10;each R3 is independently selected from hydrogen and methyl; andeach X is independently selected from —O—, —S—, —NH—, and —N(—CH3)—;each R2 is independently selected from C1-10 alkanediyl, C6-8 cycloalkanediyl, C6-14 alkanecycloalkanediyl, and —[(—CHR3—)p—X—]q—(—CHR3—)r—, wherein p, q, r, R3, and X are as defined as for R1;m is an integer from 0 to 50;n is an integer from 1 to 60;p is an integer from 2 to 6;B represents a core of a z-valent, vinyl-terminated polyfunctionalizing agent B(—V)z wherein: z is an integer from 3 to 6; andeach V is a group comprising a terminal vinyl group; andeach —V′— is derived from the reaction of —V with a thiol. 9. The composition of claim 7, wherein the thiol-terminated polythioether prepolymer comprises the reaction product of reactants comprising: (a) a dithiol of Formula (3): HS—R1—SH  (3)wherein, R1 is selected from C2-6 alkanediyl, C6-8 cycloalkanediyl, C6-10 alkanecycloalkanediyl, C5-8 heterocycloalkanediyl, and —[—(CHR3)p—X—]q—(CHR3)r—;wherein: each R3 is independently selected from hydrogen and methyl;each X is independently selected from —O—, —S—, —NH—, and —N(—CH3)—;p is an integer from 2 to 6;q is an integer from 1 to 5; andr is an integer from 2 to 10; and(b) a divinyl ether of Formula (4): CH2═CH—O—[—R2—O—]m—CH═CH2  (4)wherein, each R2 is independently selected from C1-10 alkanediyl, C6-8 cycloalkanediyl, C6-14 alkanecycloalkanediyl, and —[(—CHR3—)sp—X—]q—(—CHR3—)r, wherein p, q, r, R3, and X are as defined for R1;m is an integer from 0 to 50;n is an integer from 1 to 60; andp is an integer from 2 to 6. 10. The composition of claim 9, wherein the reactants further comprise (c) a polyfunctional compound B(—V), wherein: z is an integer from 3 to 6; andeach —V is a moiety comprising a terminal group that is reactive with a thiol group. 11. The composition of claim 1, further comprising an unblocked amine catalyst. 12. The composition of claim 1, formulated as a sealant. 13. A cured sealant prepared from the composition of claim 12. 14. A part comprising the cured sealant of claim 13 on at least a portion of the part. 15. A method of sealing a part, comprising: applying the composition to at least a portion of a part; andcuring the applied composition to provide a sealed part. 16. The method of claim 15, comprising heating the composition before applying the composition to the part, after applying the composition to the part, or both before and after applying the composition to the part. 17. The composition of claim 1, wherein the thiol-terminated polythioether prepolymer comprises a backbone comprising a structure of Formula (1): —R1—[—S—(CH2)p—O—(R2—O)m—(CH2)2—S—R1—]n—  (1)wherein: each R1 independently is selected from C2-10 alkanediyl, C6-8 cycloalkanediyl, C6-14 alkanecycloalkanediyl, C5-8 heterocycloalkanediyl, and —[(—CHR3—)p—X—]q—(—CHR3—)r—, wherein: p is an integer from 2 to 6;q is an integer from 1 to 5;r is an integer from 2 to 10;each R3 is independently selected from hydrogen and methyl; andeach X is independently selected from —O—, —S—, —NH—, and —N(—CH3)—;each R2 is independently selected from C1-10 alkanediyl, C6-8 cycloalkanediyl, C6-14 alkanecycloalkanediyl, and —[(—CHR3—)p—X—]q—(—CHR3—)r—, wherein p, q, r, R3, and X are as defined as for R1;m is an integer from 0 to 50;n is an integer from 1 to 60; andp is an integer from 2 to 6. 18. The method of claim 15, wherein the part comprises a surface of an aerospace vehicle. 19. An aerospace vehicle comprising the composition of claim 1. 20. An aerospace vehicle comprising the cured sealant of claim 13.