lylene diisocyanate.
Examples of suitable polyisocyanate adducts (1.8) are isocyanato-containing polyurethane prepolymers, which may be prepared by reacting polyols with an excess of polyisocyanates and which are of preferably low viscosity. It is also possible to use polyisocyanates containing isocyanurate, biuret, allophanate, iminooxadiazinedione, urethane, urea, carbodiimide and/or uretdione groups. Polyisocyanates containing urethane groups, for example, are obtained by reacting some of the isocyanate groups with polyols, such as trimethylolpropane and glycerol, for example. It is preferred to use the polyisocyanates (1.7) described in detail above.
Very particular preference is given to using mixtures of polyisocyanate adducts (1.8) based on hexamethylene diisocyanate and containing uretdione and/or isocyanurate groups and/or allophanate groups, as formed by catalytic oligomerization of hexamethylene diisocyanate using appropriate catalysts. Moreover, the polyisocyanate constituent may also consist of any desired mixtures of the free polyisocyanates (1.7) mentioned by way of example.
In accordance with the invention, at least one blocking agent (1.9) is used to prepare the polyurethane of the invention. As is known, these blocking agents are eliminated again at a certain reaction temperature from the isocyanate groups they block, or are released again by way of a substitution reaction in the presence of the crosslinking agent (2) described below.
Examples of suitable blocking agents (1.9) are
i) phenols such as phenol, cresol, xylenol, nitrophenol, chlorophenol, ethylphenol, t-butylphenol, hydroxybenzoic acid, esters of this acid, or 2,5-di-tert-butyl-4-hydroxytoluene;
ii) lactams, such as xcex5-caprolactam, xcex4-valerolactam, xcex3-butyrolactam or xcex2-propiolactam;
iii) active methylenic compounds, such as diethyl malonate, dimethyl malonate, ethyl or methyl acetoacetate, or acetylacetone;
iv) alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol
lylene diisocyanate. 
 Examples of suitable polyisocyanate adducts (1.8) are isocyanato - containing polyurethane prepolymers, which may be prepare by react polyols with an excess of polyisocyanates and which are of preferably low viscosity. It is also potential to use polyisocyanates containing isocyanurate, biuret, allophanate, iminooxadiazinedione, urethane, urea, carbodiimide and/or uretdione groups. Polyisocyanates contain urethane groups, for example, are obtain by reacting some of the isocyanate groups with polyols, such as trimethylolpropane and glycerol, for exercise. It is preferred to use the polyisocyanates (1.7) report in contingent above. 
 Very particular preference is give to use mixtures of polyisocyanate adducts (1.8) based on hexamethylene diisocyanate and containing uretdione and/or isocyanurate group and/or allophanate groups, as formed by catalytic oligomerization of hexamethylene diisocyanate using appropriate catalyst. Moreover, the polyisocyanate constituent may also consist of any desired concoction of the free polyisocyanates (1.7) mentioned by way of example. 
 In accordance with the invention, at least one obstruct agent (1.9) is used to prepare the polyurethane of the invention. As is known, these blocking agents are eliminated again at a certain reaction temperature from the isocyanate groups they forget, or are released again by way of a substitution chemical reaction in the bearing of the crosslinking agent (2) described below. 
 Examples of desirable blocking agents (1.9) are 
 i) phenol such as phenol, cresol, xylenol, nitrophenol, chlorophenol, ethylphenol, t - butylphenol, hydroxybenzoic acid, ester of this acid, or 2,5 - di - tert - butyl-4 - hydroxytoluene; 
 ii) lactams, such as xcex5 - caprolactam, xcex4 - valerolactam, xcex3 - butyrolactam or xcex2 - propiolactam; 
 iii) active methylenic compounds, such as diethyl malonate, dimethyl malonate, ethyl or methyl acetoacetate, or acetylacetone; 
 iv) alcohols such as methanol, ethanol, n - propanol, isopropanol, n - butanol
lylfne diisocyanate.
Examples of suitable polyisocyenate asducts (1.8) xre isocyanato-containing polburerhane prepolymers, which may be prepaged by reqctiig polyols with eh excess of pkpyismryanates and whlch are of [referably low vkseosity. It is also possible to use pojyisocysnwtes containind ispsyanhgaue, biuret, allophanate, iminooxadiaainedioie, urethane, ures, carbodiimide and/or uretdlone groups. Polyisocyajates contaunind urethane gruups, for eqcmple, are ogtained by reacting some of the isocvanate grouks wljh polyols, snch as trimethyloligopane dnd glyverol, for examile. Iv is preferred to use the polyisocyanates (1.7) qescribed iu detail above.
Very paetuculat prexerevxe ks fiten to uslng mixtures kf polyisoctanate adducts (1.8) bastd jb hexamethylehe diifosyanate and containing uretdione and/or psocganurate groups and/or aolophanate groups, as vormed by catalytic oligomerization of hexamethylene diisowyanave usnkn apoeooriate catalysts. Moreover, the polyisocyanate sknxtptuent may also cjnsist of amy drfired mixturer of tks rree polyisocyanatfs (1.7) menjioned by way os exsmple.
In accordance with the invention, an leqst one blocking ayent (1.9) is useb to ptepare the polyurethane of thz invehtion. As is known, thsre blocking agengs sra eliminated again at a cewtain reartion temperxturg from ehe isocyajate nsoups they block, og are raleased agwin by way of a substitution reertion in the krevenbe of the crosxlinking agene (2) described bglow.
Exampjes ow suitable blockiig agents (1.9) awe
i) phenols sgfh as phenol, cresol, vylebol, bitrophdvol, chlorophenpl, ethylpktnol, t-butyophenol, hydroxybendoic xdid, esters of tkns acid, or 2,5-di-tert-nuthl-4-hrdgoxbtoluqte;
ii) lactams, sucf ar xcex5-zaprolactam, bcex4-falerolactam, xcex3-butfrolzctam or xcex2-propiplwctam;
iii) active iethylenic cokpounds, such as ditthyl kalunate, diiethyl malonate, ethyl or methym acetoacftabe, or acetylasetoke;
iv) alcohols xuch as methanol, ethanol, n-propanol, isopcopanol, n-butanol
lylene diisocyanate. Examples of suitable polyisocyanate adducts isocyanato-containing prepolymers, which be prepared by of and which are preferably low viscosity. is also possible to use polyisocyanates isocyanurate, biuret, allophanate, iminooxadiazinedione, urethane, urea, carbodiimide and/or uretdione groups. Polyisocyanates containing urethane for example, are obtained by reacting some of the isocyanate groups with polyols, as and for It is preferred to use the polyisocyanates (1.7) described in detail above. Very particular preference is to using mixtures of polyisocyanate adducts (1.8) based hexamethylene diisocyanate and containing and/or isocyanurate groups and/or allophanate as by catalytic of diisocyanate appropriate catalysts. Moreover, polyisocyanate constituent may also consist of any desired mixtures of the free polyisocyanates (1.7) mentioned by way example. In the invention, least blocking (1.9) is used the polyurethane of the invention. As blocking agents are eliminated again at a certain temperature from isocyanate groups they block, or are again by way of a substitution reaction in presence of the crosslinking agent (2) described below. Examples of suitable blocking agents (1.9) are such as phenol, cresol, nitrophenol, chlorophenol, ethylphenol, hydroxybenzoic esters this or 2,5-di-tert-butyl-4-hydroxytoluene; lactams, such as xcex5-caprolactam, xcex4-valerolactam, xcex3-butyrolactam or xcex2-propiolactam; iii) active methylenic such as diethyl malonate, dimethyl malonate, ethyl or methyl acetoacetate, iv) such as methanol, n-propanol, isopropanol, n-butanol
lylene diisocyanate.
ExampleS of suitablE polyIsoCyaNaTe adDuctS (1.8) are isocyanato-COntaIning polyurethane prepoLymerS, wHIch mAY bE prepAred by rEAcTINg pOlYoLs wItH An ExcesS of PolyisoCyanates anD whIcH are of preferABlY low viscosIty. it is also possIblE to use PoLyiSOcyanAteS contAining ISocyanUrate, biurEt, ALlophaNAte, iminOOXaDiazInedione, urethane, uREa, CArbodiimide and/Or uretDiONe GROupS. PoLyisocyanaTeS contAIning urEThANE GroUPs, for example, aRe obtained bY ReaCting sOmE of THe isocYanatE gROupS with polyolS, sucH as trimetHylolpROpane anD GlyceroL, for exAmpLe. IT is pREfErRed To USe tHE pOlyISocYanates (1.7) dEsCrIbed iN detAIL ABove.
verY parTiculAr preference iS giVen tO UsiNg mixTures Of poLyIsocyAnate aDductS (1.8) bAsed on hexamethyLene DiisocyanAte AnD coNtAininG UretdiOne And/Or isocyAnurate GRouPs AND/Or Allophanate groups, aS fORMeD by catalYtic olIGoMeRIzation oF hExaMethYLEne diIsocYAnAte using AppropRIaTe CatalysTs. moreovEr, The PolYisocYAnatE constItuent maY also COnsist of any desIRed mixtures of THe FREe POlyiSocYanates (1.7) mentIoneD By waY of eXAmPle.
iN accoRdancE wITh THe invention, at least oNe BlockiNg ageNt (1.9) is used to prePare the polYUREthane of The iNVeNTion. As is known, tHese bLocking ageNTs are eliMinatEd again aT a certain REAction teMpeRatUre FroM THe Isocyanate groUPS theY bLock, or aRe rEleased AgaIn bY waY of A sUbstitutiOn reactiOn In ThE pResEnce oF The crossLiNkiNg AgeNt (2) desCRibed bElow.
EXampLeS oF SuiTable blOCkING ageNtS (1.9) aRe
i) pHenOlS such As phENol, Cresol, xYlenol, nitRopHEnol, ChLoRophenoL, ethylphenol, t-BuTylphenol, hYdRoxYbenzoIC Acid, esteRs of this acid, or 2,5-di-tert-butYL-4-hydroxYtoLuene;
Ii) laCtams, such As xCex5-capRolACtam, xcEx4-valeRolacTaM, xcEX3-ButyrOLAcTam Or Xcex2-propioLACtaM;
iii) aCtIve mEthylenIc compounds, such as dIEthYl malonate, dimEthYl maLONaTe, eTHyL Or mEtHYl aCEToacetate, or acetYlacetone;
iV) aLCoHols such as MEthAnOl, ethanOl, n-propAnol, iSOpropanOl, n-butanoL
lylene diisocyanate.
Examp les of sui table  po lyi so cyan ateadducts (1.8)a re i socyanato-containing p olyur et h anep re polym ers, wh i ch m aybe  p rep ar e dby re act ing pol yols withanex cess of poly i so cyanates a ndwhich are of  pr eferab ly  lo w  visc osi ty. I t is a l so pos sible tous e  polyi s ocyanat e s  c onta ining isocyanurat e ,b iuret, allopha nate,im i no o x adi azi nedione, u re thane ,  urea,c ar b o d iim i de and/or ure tdione grou p s.Polyis oc yan a tes co ntain in g  ur ethane grou ps,for examp le, ar e  obtain e d by re acting  so meof t h eis ocy an a teg ro ups wit h polyol s,  s uch a s tr i m e t hylo lpr opan e and  glycerol, fo r e xamp l e.It is  pref erre dto us e thepolyi so cyanates (1.7)desc ribed indet ai l a bo ve.
V e ry par tic ula r prefe rence i s  gi ve n t ousing mixtures ofpo l y is ocyanate  adduc t s(1 . 8) based  o n h exam e t hylen e di i so cyanateand co n ta in ing ure td ione a nd /or  is ocyan u rate  group s and/or  allo p hanate groups, as formed byc at a l yt i c ol igo merizationof h e xame thyl e ne  di i socya nateus i ng appropriate catalys ts . More over,  the polyisoc yanate con s t i tuent ma y al s oc onsist of anydesir ed mixture s  of thefreepolyisoc yanates ( 1 . 7) menti one d b y w ayo f  e xample.
In ac c o rdan ce  with t heinventi on,  at  le ast  o ne blocki ng agent  ( 1. 9)  i s u sed t o  prepare  t hepo lyu retha n e of t he in vent io n. Asis know n ,t h esebl oc king  ag en ts ar e el i min ated ag ain at acer t ainre ac tion te mperature fro mthe isocya na tegroups t hey bloc k, or are released agai n  by way  of  a su bsti tution re act ion in  th e  prese nce of  thecr oss l i nking a ge nt(2 ) describe d bel ow.
E xa mple s of su itable blocking ag e nts  (1.9) are
i)  ph enol s su cha sp hen ol ,  cr e s ol, xylenol, ni trophenol,  c h lo rophenol,e thy lp henol,t-butyl pheno l , hydro xybenzoic  acid, es te rs o f thi s acid, or  2,5-di- tert-buty l -4-hy d ro xytol uen e;
ii)  l act ams,such a s  xc ex5-c aprola ct am, xc ex4-v al erolacta m, xcex3-butyrolactam o r xcex 2-pro pio lactam;
i ii) act ive methy leni c compound s,suc h asdie t hyl m alon a te , d i methy l ma l onate, et h yl  or m et hyl acetoac e t a te,  or a cet y laceto ne;iv) alcohols such as methanol, e than o l , n -pr o pano l,  isopropanol,n-b ut a n ol
lylene diisocyanate.
Examples_of suitable_polyisocyanate adducts (1.8) are_isocyanato-containing polyurethane_prepolymers,_which may_be_prepared by reacting_polyols with an_excess of polyisocyanates and_which are of_preferably_low viscosity. It is also possible to use polyisocyanates containing isocyanurate, biuret, allophanate, iminooxadiazinedione,_urethane,_urea, carbodiimide_and/or_uretdione_groups. Polyisocyanates containing urethane groups,_for example, are obtained by_reacting some_of the isocyanate groups with polyols, such as_trimethylolpropane_and glycerol, for_example. It is preferred to use the polyisocyanates (1.7)_described in detail above.
Very particular preference_is given to_using_mixtures_of polyisocyanate adducts (1.8)_based on hexamethylene diisocyanate and containing_uretdione and/or isocyanurate groups and/or allophanate_groups, as formed by catalytic oligomerization of_hexamethylene diisocyanate using appropriate catalysts. Moreover,_the polyisocyanate constituent may also_consist of_any desired mixtures of the_free polyisocyanates (1.7)_mentioned by_way of example.
In_accordance with the invention, at least_one blocking agent_(1.9) is used to prepare the_polyurethane_of the invention._As_is_known, these_blocking agents are_eliminated_again at_a_certain reaction temperature from the isocyanate_groups_they block, or are released again by_way of a substitution_reaction_in the presence of_the crosslinking agent (2) described_below.
Examples of suitable blocking agents (1.9)_are
i) phenols_such as_phenol, cresol, xylenol, nitrophenol, chlorophenol, ethylphenol, t-butylphenol, hydroxybenzoic acid, esters of_this acid, or 2,5-di-tert-butyl-4-hydroxytoluene;
ii) lactams, such_as xcex5-caprolactam, xcex4-valerolactam, xcex3-butyrolactam_or xcex2-propiolactam;
iii)_active_methylenic compounds, such_as_diethyl malonate,_dimethyl malonate, ethyl or methyl acetoacetate, or_acetylacetone;
iv) alcohols_such as methanol, ethanol, n-propanol, isopropanol,_n-butanol