Field of the Invention The present invention relates to block copolymer adhesives having enhanced adhesion to polyester substrates, and more particularly to hot melts and polyester laminates containing modified multiblock copolymer adhesives. Background of the Invention Multiblock copolymers having non-el stomeric terminal blocks and an elastomeric non-terminal block are well known from the prior art. Such block copolymers include, for example, polystyrene- polyisoprene-polystyrene and polystyrene-polybutadiene-polystyrene. Because these polymers exhibit both thermoplastic properties owing to the thermoplastic end blocks, as well as elastomeric properties due to the elastomeric internal block, they have found a wide variety of commercial applications. One such commercial application ⁵ employs the multiblock copolymer in a blend with a tackifying resin 6 for pressure sensitive adhesive compositions. The composition is ⁷ typically applied to a film or other substrate to adhere the film or 8 substrate to yet another substrate in a laminated structure. ⁹ One drawback of the prior art multiblock copolymer adhesive ⁰ compositions is that the multiblock copolymers generally have poor ⁱ adhesion to polar substrates such as polyester. Another drawback ² has been that the multiblock copoly er-based hot melt compositions ³ have a relatively high melt viscosity and must generally be used 4 with solvents or at undesirably high temperatures. There remains a 5 need for multiblock copolymers with improved adhesion to polyester 6 films and other substrates made of polyester, and/or with reduced 7 melt viscosity. 8 It is known from U. S. Patent 4,255,536 to Udipi to modify ⁹ copolymers of a conjugated diene and a monovinylarene, such as ⁰ styrene-butadiene-styrene teleblock copolymer, by reaction with a 1 dihydrocarbyl azodicarboxylate such as dimethyl azodicarboxyl te or di-t-butyl azodicarboxylate, to obtain a modified copolymer which can be compounded and cured into a tire tread composition stated to 4 have improved oil resistance and wet skid resistance.

The isopropyl azodicarboxylate modification of polybutadienes is described in Schulz et al, Macromolecules. vol. 13, pp. 1367-1375 (1980); Spiewak et al , Journal of Applied Polvmer Science, vol. 26, pp. 4331-4334 (1981); and Hamed et al , Polvmer Bulletin, vol. 9,

⁵ pp. 525-532 (1983). The modified polybutadienes are stated to have good green strength, cohesive strength and autohesion properties. Other references describing crosslinking and other reactions of polymers with azo compounds include U. S. Patent 4,129,531 to Rauer

9 et al; 2,994,357 to Serniuk et al ; and 4,791,174 to Bronstert et al. 1° Summary of the Invention

11 The present invention provides a laminate containing at least

1 one polyester substrate and an adhesive layer in contact with the

13 polyester substrate. The adhesive layer comprises a dihydrocarbyl

14 azodicarboxylate-modified multiblock copolymer having terminal ⁵ non-elastomeric polyvinyl romatic blocks and a non-terminal l ^β elastomeric block of polymerized polyene. The block copolymer is

I ⁷ modified by reaction of the elastomeric block with, for example, l ^β from 10 to 100 weight percent, especially from 20 to 80 weight

1 ⁹ percent, based on the weight of the unmodified elastomeric block, of

²⁰ a dihydrocarbyl azodicarboxylate. The resulting modified copolymer

21 has pendant bicarbamate groups along the elastomeric block. The

²² laminate may further include another substrate in contact with the

²³ adhesive layer, and the laminate exhibits a cohesive failure mode at

²⁴ the adhesive layer.

²⁵ The present invention also provides a hot melt adhesive

²⁶ composition which can be used for pressure sensitive adhesive

²⁷ applications. The hot melt adhesive composition contains from 10 to

²⁸ 90 parts by weight of a dihydrocarbyl azodicarboxylate-modified

²⁹ multiblock copolymer, from 90 to 10 parts by weight of a tackifier

³⁰ compatible therewith, and zero to 40 parts by weight of a mineral ³ⁱ oil. The multiblock copolymer has terminal non-elastomeric blocks

³² of polyvinylarene and a non-terminal elastomeric block of

³³ polymerized conjugated diene. The multiblock copolymer is modified

³⁴ by reaction with a dihydrocarbyl azodicarboxylate.

³⁵ Detailed Description of the Preferred Embodiments

³⁶ The laminate of the present invention contains at least a first

37 substrate of polyester and at least one modified multiblock

1 copolymer adhesive layer in contact therewith. The laminate may

² include a plurality of substrates which are solid, usually and

³ preferably in the form of films, sheets and the like. A second

⁴ substrate in contact with the adhesive layer opposite the first

' polyester substrate may be a polyester substrate, or may be made of another material, such as, for example, wood, metal, glass,

7 thermoset polymer, or thermoplastic polymer. In a preferred 8 embodiment, a second substrate in contact with the modified 9 multiblock copolymer adhesive layer is a thermoplastic so that the 10 laminate is reprocessable. Thermoplastic polymers include both polar and non-polar polymers. As examples of non-polar 1 122 thermoplastics, there may be mentioned polyolefins such as

13 polypropylene, high density polyethylene, low density polyethylene,

14 linear low density polyethylene, other polymers such as polystyrene, 15 and the like. As examples of polar thermoplastics, there may be 16 mentioned polyester, polyamide, polyvinyl chloride, polyvinylidene 17 chloride and the like. In a preferred embodiment, the laminate 18 comprises a polyester sheet or film as a first substrate and a 19 polyester or nonpolyester sheet or film as a second substrate, and 20 the modified multiblock copolymer adhesive composition in a layer 21 between the first and second substrates for bonding the first and 22 second substrates together. 23 The multiblock copolymers which are modified for use in the ²⁴ laminates and hot melts of the present Invention are well known and or

" are commercially available. The copolymer has terminal or end

26 blocks of non-elastomeric polymerized vinylaromatic, preferably 27 monovinylarene, and at least one non-terminal block of elastomeric 28 polymerized polyene, preferably conjugated diolefin. These block 29 copolymers typically come in three-block, five-block and starblock

³⁰ configuration with a molecular weight of from 20,000 to 250,000,

³¹ preferably from 40,000 to 200,000, and a diolefin content of from 40

32 to 90 weight percent, preferably from 57 to 86 weight percent. 33 Commercially, the non-elastomeric blocks are usually polystyrene, 34 poly(α- ethylstyrene), and poly(styrene/α-methylstyrene), but 35 there may also be mentioned terminal blocks containing other 36 suitable polymerized monomers, such as, for example, acenaphthylene, 37 vinylnaphthalene, isopropenylnaphthalene, 4-phenylstyrene,

4-tert-butylstyrene, 4-isopropylstyrene, 4-methoxystyrene,

² 2-vinylpyridine, 2-methyl-5-vinylpyridine, vinylxylene,

³ ethylvinylxylene, methylvinylxylene, and the like. The terminal

⁴ blocks may also include interpolymers and block polymers formed from

⁵ two or more of such monomers, or the tapered blocks comprising one

⁶ of the vinylaromatic monomers and one of the conjugated diolefin

⁷ monomers (minor component).

⁸ The elastomeric block or blocks may be a homopolymer of any

⁹ conjugated diolefin having up to 12 carbon atoms, preferably 4-8

1 ⁰ carbon atoms, or a block copolymer or interpoly er of two or more

11 such diolefins. Polybutadiene and polyisoprene are common, but

1 ² there may also be mentioned other suitable monomers which may be

1 ³ polymerized in the elastomeric block, such as, for example, ⁴ dimethylbutadiene, piperylene, phenylbutadiene, and the like.

1 ⁵ The multiblock copolymer is modified by reaction with a ^lβ dihydrocarbyl azodicarboxylate. The modification may be effected by ⁷ contacting the multiblock copolymer with the dihydrocarbyl

1 ⁸ azodicarboxylate at effective reaction conditions. The dihydrocarbyl

1 ⁹ azodicarboxylates suitable for modification of the multiblock

²⁰ copolymer include the azo esters of the following formula:

² 0 0

²² R ¹ - 0 - C - N . N - £ - 0 - R ²

²³ in which R and R are independently alkyl, cycloalkyl, aryl or

²⁴ combination radicals and can be the same or different. Typically

-**-~ R1 and R2 each contain from 1 to 12 carbon atoms. Preferred are

²⁶ the azodicarboxylates wherein R and are selected from

²⁷ methyl, ethyl, isopropyl, t-butyl, cyclohexyl, phenyl, and the

²⁸ like. Dialkylazodicarboxylates, especially isopropylazodi-

²⁹ carboxylate, are particularly preferred.

³⁰ A method for the reaction between the dihydrocarbyl

³ 1 azodicarboxylate and the multiblock copolymer is described, for

³² example, in aforementioned U. S. Patent 4,255,536, which is hereby

³³ incorporated herein by reference. Briefly, the multiblock copolymer

³⁴ may be reacted in a suitable solvent with the dihydrocarbyl

azodicarboxylate in suitable amounts at moderately elevated temperatures below about 150°C, for a period of time from about 0.1 hours to several days or more under an inert atmosphere at atmospheric or superatmospheric pressure. Preferred amounts of the dihydrocarbyl azodicarboxylate are in the range of from 10 to 100 percent by weight of the diene content of the block copolymer, and especially from 20 to 80 weight percent. The modified multiblock copolymer contains pendant bicarbamate moieties along the length of the polydiene chain, while the polyvinylarene blocks are essentially unmodified. The modified copolymer may be recovered by evaporation of the solvent or by precipitation with an antisolvent and filtration, although it is contemplated that the solution resulting from the reaction mixture may be used to cast the adhesive layer directly onto a substrate. The dihydrocarbyl azodicarboxylate-modified block copolymer may e used as an adhesive layer in the polyester laminate by conventional laminating techniques, such as, for example, coextrusion, extrusion coating, solution coating, and the like. In a preferred embodiment, the block copolymer is applied to the substrate as a hot melt adhesive containing the modified block copolymer and a compatible tackifier. The tackifiers typically have a softening point of from 70° to 130°C, preferably from 80 ^β to 110 ^β C; a number-average molecular weight of from 500 to 1300, preferably from 700 to 1300; a weight-average molecular weight of from 1000 to 3000, preferably from 1200 to 2500; an acid number of from 0 to 50; a bromine number of from 5 to 30; and a specific gravity of from 0.80 to 1.30. As suitable tackifiers there may be mentioned rosin esters, terpene-phenolic resins and mixed aliphatic- aromatic resins, well known in the art. Exemplary rosin esters include those available under the trade designations Foral, Pentalyn, Permalyn, Bevilite, Bevitack, Zonester, Dertolyne, Granolite, Tergum, Resiester, Unitac, Oulutac, etc. Exemplary terpene-phenolic resins include those available under the trade designations Dertophen, Uravar, Nirez V, etc. Exemplary mixed aliphatic-aromatic resins include those available under the trade designations Escorez, Regalite, Hercures AR, Imprez, Norsolene M, Marukarez, Arkon M, Quintone, etc. Other tackifiers may also be

employed, provided they are compatible with the nonterminal block of the modified block copolymers,

The weight ratio of tackifier to modified block copolymer may be from about 10:90 to 90:10, preferably from 20:80 to 80:20, and especially from 30:70 to 70:30. Mineral oil is desirably used in the hot melt adhesive composition when ambient temperature tack is desired, for example, in pressure sensitive hot melt adhesives. Depending on the nature and amount of the tackifiers used, the oil may comprise from zero to 40 weight percent of the adhesive composition, preferably from 5 to 20 weight percent of the adhesive composition. The hot melt composition may also include conventional additives such as pigments, fillers, antioxidants, stabilizers, and the like, in conventional amounts, but the hot melt is preferably essentially free of solvents. Antioxidants such as Irganox 1010, when used, are typically present at 0.5 weight percent of the hot melt adhesive composition. The hot melt adhesive is prepared by conventionally melt blending the components together at elevated temperatures (from about 150 ^β C to about 200°C) under an inert gas blanket until a homogeneous mix is obtained. Any mixing method producing homogeneous blend without degrading the hot melt components is satisfactory. One well known method to the art of blending materials of this type is to carry out the hot melt blending in a heated vessel equipped with a stirrer.

The hot melt adhesive, in addition to having enhanced adhesion to polyester and other polar polymeric substrates, has the further advantage that the hot melt composition has a reduced viscosity relative to hot melt adhesives prepared from similar but unmodified multiblock copolymers. As a result, the present hot melt adhesive leads itself to improved processability, permitting lower temperatures to be used, and avoiding the necessity for solvents or other viscosity-reducing additives.

The invention is illustrated by way of the following examples.

Example 1

A polyester laminate was prepared and evaluated using a styrene-isoprene-styrene block copolymer (SIS) which was modified

with isopropyl azodicarboxylate (IAD). The SIS was obtained commercially under the designation Kraton 1107 and contained 86

³ weight percent isoprene and had a number average molecular weight

⁴ (M ) of 110,000 and a ratio of weight average molecular weight

⁵ (Mw to M„n of 1.61. The SIS was modified with IAD by dissolving

⁶ 20 weight percent SIS in hot benzene or toluene solution in a

⁷ nitrogen purged reaction vessel. The SIS solution was cooled to

⁸ ambient temperature, and a 10 weight percent solution of IAD in

⁹ benzene or toluene was added in a quantity corresponding to 30

10 percent by weight of the SIS isoprene content. The solution was

11 then stirred, heated and maintained at reflux conditions at about

12 80 ^β C for benzene and about 110 ^β C for toluene under a nitrogen purge

1 ³ for 24 hours. Reaction was evidenced by a reduction in the yellow

1 ⁴ color of the reaction solution with the passage of time. The

1 ⁵ IAD-modified SIS was recovered by precipitation with methanol , l ^β filtration and drying in a vacuum oven at 50 ^β C overnight. The I ⁷ IAD-modified SIS had viscoelastic loss peaks as determined on a

IS Rheometrics System IV spectrometer at -44 ^β C and 112*C, as compared ⁹ to the same peaks at -59 ^β C and 121 ^β C for the unmodified SIS. The 0 IAD-modified SIS had an M _n of 141,000 and an M _w /M _n ratio of

² 1 1.62. A polyester laminate was prepared by compression of a 4 mil

² thickness of the IAD-modified SIS between 4 mil Mylar polyester films at 180 ^β C using 40 psi for 5 minutes. The laminate was cut

24 into 1-inch wide strips and subjected to T-peel strength testing at

25 2 inches/minute. The laminate made with the IAD-modified SIS had a

26 peel strength of 5.7 lb/in. and exhibited a cohesive failure mode,

27 while the identically prepared laminate made with the unmodified SIS

28 had a peel strength of 4.2 lb/in. and exhibited an adhesive failure

29 mode. Viscosity results are as follows:

³⁰ Vi i P i

31

32

33

34

35

³⁶ Laminates were prepared as in Example 1 using Kraton 1102

styrene-butadiene-styrene block copolymer (SBS) containing 72 weight percent butadiene. The unmodified SBS had an _n of 67,000 and an Mw ,/Mn ratio of 1.45. Fol lowing modi fication with 30 weight percent IAD based on the butadiene weight, as described in Example

⁵ 1,

^• the IAD-modified SBS had an M„n of 74,000 and the

⁶ ratio was unchanged. The IAD-modified SBS had viscoelastic loss peaks at -60 ^β C and 81 ^β C, compared to -82°C and 87 ^β C for the unmodified SBS. Mylar polyester laminates prepared as described in

⁹ Example 1 with the IAD-modified SBS had a peel strength of 9.0 1° lb/in. and exhibited a cohesive failure mode, compared to a peel

1 strength of 2.0 lb/in. and an adhesive failure mode for the

12 identically prepared laminates using the unmodified SBS.

1 ³ Viscosities at 120 ^β C are 3.7 x 10 ⁵ poises and 1.5 x 10 ⁵ poises

1 ⁴ for the unmodified and modified polymers, respectively.

1 ⁵ Examples 3 and 4 l ^β The procedures of Examples 1 and 2 were followed to prepare

1 ⁷ laminates of 4 mil aluminum foil. Both the IAD modified copolymers

18 and the unmodified copolymers exhibited an adhesive failure mode.

19 The unmodified SIS laminate had a better peel strength of 8.4

² 0 lb/in., compared to 6.9 lb/in. for the IAD-modified SIS. The

² IAD-modified SBS, however, had a peel strength of 9.8 lb/in.

²² compared to 8.6 lb/in. for the unmodified SBS.

²³ Example 5

²⁴ A polyester laminate was prepared and evaluated using a tapered

25 styrene-butadiene-styrene block copolymer (SBS) which was modified

²⁶ with isopropyl azodicarboxylate (IDA). The SBS was obtained

²⁷ commercially under the designation Stereon 840A and contained 57

²⁸ weight percent butadiene and had a number average molecular weight

²⁹ (M _n ) of 60,000 and an M _w /M _n ratio of 2.0. Identical reaction

³⁰ conditions as in Example 1 were used to modify the polymer except

³ 1 that the amount of IAD added was in a quantity corresponding to 20

³² percent by weight of the SBS butadiene content. The hot melt

33 adhesive was then prepared by melt blending 60 weight percent of 34 Foral 105, 30 weight percent of the modified Stereon polymer, and 10

³⁵ weight percent of mineral oil (Kaydol® from Witco Chemical

³⁶ Corporation) at 180 ^β C under a nitrogen blanket. A 0.5 weight

percent of an Irganox 1010 stabilizer based on the total hot melt blend was added to the formulation. A polyester laminate was prepared by compression of a 6 mil thickness of the formulated adhesive based on this IDA- odified Stereon polymer between 4 mil Mylar polyester film at 150 ^β C using 40 psi for 10 seconds. The laminate was cut into 1-inch wide strips and subjected to T-peel strength testing at 2 inches/minute. The laminate had a peel strength of 7.8 lb/in. and exhibited a cohesive failure mode. The adhesive material itself showed pressure sensitive tack. The laminate containing the identical formulation based on the unmodified block copolymer had a peel strength of 4.7 lb/in. and exhibited a cohesive failure mode. Example 6

The procedures of Example 5 were followed to prepare laminate of 4 mil polyester film except that Foral 105 was replaced by Bevilite 62-85 in the hot melt blend composition. The laminate had a peel strength of 6.6 lb/in. and exhibited a cohesive failure mode. The adhesive material itself showed pressure sensitive tack. The laminate containing the identical formulation based on the unmodified block copolymer had a peel strength of 4.4 lb/in. and exhibited a cohesive failure mode.

The foregoing is illustrative and explanatory of the invention, and many variations in the specific details thereof will become apparent to those skilled in the art in view thereof. It is intended that all such variations within the scope or spirit of the appended claims be embraced thereby.