Synthesis of energetic thermoplastic elastomers containing oligomeric urethane linkages

Abstract

A 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/or tetrahydrofuran derivatives. The B blocks are derived from oxetanes, tetrahydrofuran, oxiranes, and derivatives thereof. The A and B blocks are end-capped with at least one diisocyanate and linked with at least one difunctional oligomer having two functional groups which are reactive with free and unreacted isocyanate moieties of the diisocyanate.

1 . A binder comprising: 
 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 thermoplastic elastomer having A blocks and B blocks and being present in a substantially solid state to immobilize the fuel material particulates and the oxidizer particulates, the at least one thermoplastic elastomer formed from a composition comprising, as constituents: 
 A blocks terminated with isocyanate-reactive groups derived from monomers comprising at least one member selected from the group consisting of oxetane derivatives and tetrahydrofuran derivatives, the A blocks being crystalline at temperatures below about 75° C.;  
 hydroxyl-terminated B blocks terminated with isocyanate-reactive groups derived from monomers comprising at least one member selected from the group consisting of oxetane and derivatives thereof, tetrahydrofuran and derivatives thereof, and oxirane and derivatives thereof, the B blocks being amorphous at temperatures above about −20° C.; and  
 linking groups derived from at least one diisocyanate for end-capping the A blocks and the B blocks and at least one difunctional oligomer comprising two functional groups which are reactive with isocyanate moieties of the at least one diisocyanate.  
   
     
     
         2 . The binder according to  claim 1 , wherein: 
 the at least one diisocyanate contains a first isocyanate moiety which is at least five times more reactive with terminal groups of the A blocks and the B blocks than a second isocyanate moiety thereof, wherein the more reactive first isocyanate moiety is capable of reacting with and end-capping the terminal groups of the A blocks and the B blocks, leaving the less reactive second isocyanate moiety free and unreacted; and    the at least one difunctional oligomer has two isocyanate-reactive hydroxyl groups which are sufficiently sterically unhindered to be reactive with the free and unreacted second isocyanate moieties of the end-capped terminal groups of the A and B blocks.    
     
     
         3 . The binder as defined in  claim 1 , wherein the A blocks are crystalline at temperatures below about 60° C.  
     
     
         4 . The binder as defined in  claim 1 , wherein the at least one difunctional oligomer comprises a reaction product of at least one diol and at least one diisocyanate, the at least one diol being selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, and 1,4-cyclohexanedimethanol, and any combination thereof.  
     
     
         5 . The binder as defined in  claim 1 , wherein the at least one difunctional oligomer comprises a reaction product of at least one diol and at least one diisocyanate, the at least one diisocyanate being selected from the group consisting of hexane diisocyanate, methylene-bis(4-phenyl isocyanate), phenylene diisocyanate, toluene diisocyanate, and xylylene diisocyanate, and any combination thereof.  
     
     
         6 . The binder as defined in  claim 1 , wherein the at least one solid is at least one member selected from the group consisting of aluminum particulates, ammonium perchlorate, and ammonium nitrate.  
     
     
         7 . The binder as defined in  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).  
     
     
         8 . The binder as defined in  claim 1 , further comprising at least one energetic plasticizer selected from the group consisting of glycidyl azide polymer (GAP), nitroglycerine, butanetriol trinitrate (BTTN), alkyl nitratomethyl nitramines, trimethylolethane trinitrate (TMETN), diethylene glycol dinitrate, triethylene glycol dinitrate, and bis(dinitropropylacetal/-bis(dinitropropyl)formal (BDNPA/F).  
     
     
         9 . The binder as defined in  claim 1 , wherein the isocyanate-reactive terminal groups of the A and B blocks are hydroxyl groups.  
     
     
         10 . A rocket motor propellant comprising the binder of  claim 1 .  
     
     
         11 . A gun propellant comprising the binder of  claim 1 .  
     
     
         12 . An explosive comprising the binder of  claim 1 .  
     
     
         13 . A gasifier comprising the binder of  claim 1 .  
     
     
         14 . A method of preparing a thermoplastic elastomer having A blocks which are crystalline at temperatures below about 75° C. and the B blocks which are amorphous at temperatures above about −20° C., the method comprising: 
 providing A blocks and B blocks at approximately the stoichiometric ratios that are intended to be present in the thermoplastic elastomer, the A blocks being terminated with isocyanate-reactive functional groups, crystalline at temperatures below about 75° C., and derived from monomers comprising at least one member selected from the group consisting of oxetane derivatives and tetrahydrofuran derivatives, the B blocks being terminated with isocyanate-reactive functional groups, amorphous at temperatures above about −20° C., and derived from monomers comprising at least one member selected from the group consisting of oxetane and derivatives thereof, tetrahydrofuran and derivatives thereof, and oxirane and derivatives thereof;    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 a first isocyanate moiety thereof is at least about five times more reactive with the terminal groups of the A blocks and the B blocks than a second isocyanate moiety thereof, wherein the more reactive first isocyanate moiety is capable of reacting with the terminal groups of the A blocks and the B blocks, leaving the less reactive second isocyanate moiety free and unreacted; and    linking the end-capped A blocks and the end-capped B blocks together with a difunctional oligomer comprising two isocyanate-reactive groups which are sufficiently sterically unhindered to react with the free and unreacted second isocyanate moieties of the end-capped A blocks and B blocks.    
     
     
         15 . The method as defined in  claim 14 , wherein the at least one diisocyanate comprises toluene diisocyanate.  
     
     
         16 . The method as defined in  claim 14 , wherein the A blocks are crystalline at temperatures below about 60° C.  
     
     
         17 . The method as defined in  claim 14 , further comprising preparing the difunctional oligomer by reacting at least one diol and the at least one diisocyanate, the at least one diol being selected from the group consisting of ethylene glycol, propylene glycol, butylene glycol, and 1,4-cyclohexanedimethanol, and any combination thereof.  
     
     
         18 . The method as defined in  claim 14 , further comprising preparing the difunctional oligomer by reacting at least one diol and the at least one diisocyanate, the at least one diisocyanate being selected from the group consisting of hexane diisocyanate, methylene-bis(4-phenyl isocyanate), phenylene diisocyanate, toluene diisocyanate, and xylylene diisocyanate, and any combination thereof.  
     
     
         19 . The method as defined in  claim 14 , wherein the isocyanate-reactive terminal groups of the A blocks and the B blocks are hydroxyl groups.