Synthesis of energetic thermoplastic elastomers containing both polyoxirane and polyoxetane blocks

Abstract

This thermoplastic elastomer is present in a substantially solid state suitable for use as a binder for a propellant, explosive, and/or gas generant of a supplemental restraint system. The thermoplastic elastomer is formed from a composition including A blocks which are crystalline at temperatures below about 75° C. and B blocks which are amorphous at temperatures above about −20° C. The A blocks are derived from oxetane derivatives and the B blocks are derived from oxiranes and derivatives thereof. The A blocks and B-blocks are end-capped with a diisocyanate having a first isocyanate moiety that is substantially more reactive with the terminal groups of the blocks than the second isocyanate moiety, whereby the more reactive first isocyanate moiety is capable of reacting with the terminal groups of the blocks, leaving the less reactive second isocyanate moiety free and unreacted. The end-capped A blocks and the end-capped B blocks are linked together with a linking compound having two isocyanate-reactive groups which are sufficiently unhindered to react with the free and unreacted isocyanate moieties of the end-capped polymers.

1 . A binder comprising: 
 from about 50 wt % to about 95 wt % of at least one solid selected from the group consisting of fuel material particulates and oxidizer particulates; and    at least one energetic thermoplastic elastomer having A blocks and B blocks, comprising: 
 A blocks terminated with isocyanate-reactive groups, wherein the A blocks are derived from monomers comprising at least one oxetane derivative and are crystalline at a temperature below about 75° C.;  
 B blocks terminated with isocyanate-reactive groups, wherein the B blocks are derived from monomers comprising at least one member selected from the group consisting of oxirane and derivatives thereof and are amorphous at a temperature above about −20° C.; and  
 linking groups derived from at least one diisocyanate and at least one linking compound.  
   
     
     
         2 . The binder of  claim 1 , wherein the at least one diisocyanate comprises a first isocyanate moiety which is substantially more reactive with terminal groups of the A blocks and the B blocks than a second isocyanate moiety of the at least one diisocyanate, wherein the first isocyanate moiety is capable of reacting with, and end capping, the terminal groups of the A blocks and the B blocks, leaving the second isocyanate moiety free and unreacted, and wherein the at least one linking compound has two isocyanate-reactive groups which are sufficiently sterically unhindered to be reactive with the second isocyanate moiety.  
     
     
         3 . The binder of  claim 1 , wherein the A blocks are crystalline at a temperature below about 60° C.  
     
     
         4 . The binder of  claim 1 , wherein the A blocks comprise homopolymers, copolymers, or terpolymers derived from at least one symmetrically substituted oxetane monomer comprising at least one member selected from the group consisting of 3,3-bis(methylnitraminomethyl)oxetane and 3,3-bis(azidomethyl)oxetane.  
     
     
         5 . The binder of  claim 1 , wherein the B blocks comprise a difunctional glycidyl azide polymer.  
     
     
         6 . The binder of  claim 1 , wherein the B blocks comprise poly(glycidyl nitrate).  
     
     
         7 . The binder of  claim 1 , wherein the isocyanate-reactive terminal groups of the B blocks are secondary hydroxyl groups.  
     
     
         8 . The binder of  claim 1 , wherein the at least one solid comprises at least one member selected from the group consisting of aluminum, ammonium perchlorate, and ammonium nitrate.  
     
     
         9 . The binder of  claim 1 , further comprising at least one member selected from the group consisting of cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0 5,9 0 3,11 ]-dodecane (CL-20), and 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo[5.5.0.0 5,9 0 3,11 ]-dodecane (TEX).  
     
     
         10 . The binder of  claim 1 , further comprising at least one high energy plasticizer selected from the group consisting of nitroglycerine, butanetriol trinitrate (BTTN), alkyl nitratomethyl nitramines, trimethylolethane trinitrate (TMETN), diethylene glycol dinitrate, triethylene glycol dinitrate, glycidyl azide polymer (GAP), and bis(dinitropropylacetal/-bis(dinitropropyl)formal (BDNPA/F).  
     
     
         11 . The binder of  claim 1 , wherein the isocyanate-reactive terminal groups of the A blocks and the B blocks are hydroxyl groups.  
     
     
         12 . The binder of  claim 1 , wherein the at least one energetic thermoplastic elastomer is present in a substantially solid state to immobilize the fuel material particulates and the oxidizer particulates.  
     
     
         13 . A rocket motor propellant comprising the binder of  claim 1 .  
     
     
         14 . A gun propellant comprising the binder of  claim 1 .  
     
     
         15 . An explosive comprising the binder of  claim 1 .  
     
     
         16 . A gasifier comprising the binder of  claim 1 .  
     
     
         17 . A method of preparing an energetic thermoplastic elastomer having A blocks and B blocks, comprising: 
 providing A blocks and B blocks, wherein the A blocks are terminated with isocyanate-reactive functional groups, are derived from monomers comprising oxetane derivatives, and are crystalline at temperatures below about 75° C. and wherein the B blocks are terminated with isocyanate-reactive functional groups, are derived from monomers comprising at least one member selected from the group consisting of oxiranes and derivatives thereof, and are amorphous at temperatures above about −20° C.;    end-capping the A blocks and the B blocks by reacting the A blocks and the B blocks with at least one diisocyanate in which at least a first isocyanate moiety thereof is substantially more reactive with the terminal groups of the A blocks and the B blocks than a second isocyanate moiety thereof, wherein the first isocyanate moiety is capable of reacting with the terminal groups of the A blocks and the B blocks, leaving the second isocyanate moiety free and unreacted; and    reacting the end-capped A blocks and the end-capped B blocks with a linking compound having two isocyanate-reactive groups which are sufficiently unhindered to react with the second isocyanate moiety.    
     
     
         18 . The method of  claim 17 , wherein reacting the A blocks and the B blocks with at least one diisocyanate comprises reacting the A blocks and the B blocks with toluene diisocyanate.  
     
     
         19 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing A blocks that are crystalline at a temperature below about 60° C.  
     
     
         20 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing A blocks that are homopolymers, copolymers, or terpolymers derived from at least one symmetrically substituted oxetane monomer comprising at least one member selected from the group consisting of 3,3-bis(methylnitraminomethyl)oxetane and 3,3-bis(azidomethyl)oxetane.  
     
     
         21 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing B blocks that comprise a difunctional glycidyl azide polymer.  
     
     
         22 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing B blocks that comprises poly(glycidyl nitrate).  
     
     
         23 . The method of  claim 17 , wherein the energetic thermoplastic elastomer has a weight average molecular weight of at least 40,000 and a number average molecular weight of at least 10,000.  
     
     
         24 . The method of  claim 17 , wherein the energetic themmoplastic elastomer has a weight average molecular weight of at least 60,000 and a number average molecular weight of at least 12,000.  
     
     
         25 . The method of  claim 17 , wherein the energetic thermoplastic elastomer has a weight average molecular weight of at least 80,000 and a number average molecular weight of at least 15,000.  
     
     
         26 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing the A blocks and the B blocks at a weight ratio that ranges between about 15:85 to about 40:60.  
     
     
         27 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing A blocks and B blocks having hydroxyl groups as the isocyanate-reactive functional groups.  
     
     
         28 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing B blocks having secondary hydroxyl groups as the isocyanate-reactive functional groups.  
     
     
         29 . The method of  claim 17 , wherein providing A blocks and B blocks comprises providing the A blocks and the B blocks at approximately the stoichiometric ratios that are intended to be present in the energetic thermoplastic elastomer.