Controlled morphology barrier elastomers made from blends of syndiotactic 1,2-polybutadiene and ethylene-vinyl acetate-vinyl alcohol terpolymers

An elastomer barrier composition comprises a melt blend of syndiotactic 1,2-polybutadiene, a terpolymer of ethylene, vinyl acetate and vinyl alcohol, and a compatibilizing agent. The melt blend is formed under suitable mixing and shear conditions such that the terpolymer exists as a separate domain in generally a flat or plate-like form. The elastomer barrier material can be utilized in rubber compositions such as in the innerliner of the tire.

FIELD OF THE INVENTION 
The present invention relates to a barrier-resistant elastomer having 
controlled morphology in that a terpolymer of ethylene, vinyl acetate, and 
vinyl alcohol exists as a separate, generally flat or plate-like domain 
when blended with syndiotactic 1,2-polybutadiene and a compatibilizing 
agent. 
BACKGROUND 
Heretofore, in the field of tires, it is known to use a halobutyl rubber to 
provide barrier resistance to a gas as in the innerliner portion of a 
tire. 
U.S. Pat. No. 4,281,045 discloses multilayered extrusion molding of 
excellent gas barrier property. The layer is formed of saponified EVA and 
PVA and an adjacent layer of polyolefin. 
U.S. Pat. No. 4,362,844, to Lemstra, discloses biaxially stretched mixtures 
of crystalline polypropylene and ethylene vinyl alcohol copolymer having 
good optical properties and low gas permeability. 
U.S. Pat. No. 4,394,473 to Winter, discloses syndiotactic 1,2-polybutadiene 
bags of films for packaging useful for unvulcanized rubber components 
having good compatibility and dispersibility in rubber compounds. 
U.S Pat. No. 4,905,735 assigned to Tokai Rubber, discloses a rubber hose 
for transportation of cooling medium comprising outer rubber layer, 
fiber-reinforced middle layer, and inner rubber layer comprising inner and 
outer rubber layers and an intermediate resin layer. 
European Patent 193,823 discloses a co-extruded two-layer bag of 
syndiotactic 1,2-polybutadiene for packaging vulcanized or unvulcanized 
rubber or compounding ingredients. 
European Patent 337,279 to Ling discloses improved gas barrier structure 
for pneumatic articles. The gas barrier structure comprises a gas barrier 
film laminated between and bonded to two vulcanizable elastomeric surface 
layers and is a non-elastomeric polymeric layer. 
German Patent 2,341,782 discloses a polyolefin/ethylene vinyl acetate film 
laminate having high resistance to delamination and permeation by gasses. 
Japanese Patent 1152061 to Tokai discloses a hose for transportation of 
cooling medium comprising inner and outer tube layers, with intermediate 
fiber-reinforcing layer. 
Japanese Patent 1301244 assigned to Tokai Rubber, discloses a hose for 
transporting cooling medium comprising an elastic layer of nylon and 
saponified EVA copolymer. 
Japanese Patent 1308452 discloses a gas-impermeable resin composition 
containing nylon and saponified product of EVA copolymer. This material is 
used as coolant feeding hoses, as packaging and containers for food. 
Japanese Patent 1313552 discloses a material comprising 5 to 70 weight 
percent of polyolefinic thermoplastic resin, 30 to 90 weight percent 
olefin/vinyl alcohol resin, 2 to 20 weight percent modified copolymer 
consisting of a vinyl aromatic polymer block and conjugated diene polymer 
block. This patent discloses the use as a layer of a multilayered food 
packaging material. 
Japanese Patent 5057747 discloses a heat-moldable laminated resin sheet 
comprising crystalline polymer sheet, saponified EVA or a polyamide sheet, 
and non-crystalline polymer sheet laminated with adhesive resin. 
Japanese Patent 52141854 discloses a resin molding composition comprising 
solvent-soluble rubbery compound and olefin. 
Japanese Patent 53075278 discloses a transparent, heat-shrinkable 
polyolefin film produced by a blend of high and low melting resins as a 
tube or sheet, and irradiating the product. 
Japanese Patent 54016582 discloses a laminated film comprising 
polyvinylidene chloride saponified polyamide resin or EVA copolymer, and 
heat-resistant adhesive resin and polyolefin resin. 
Japanese Patent 54046281 discloses polymer laminates produced by extruding 
a blend comprising styrene-based polymer, gas barrier resin and tacky 
resin. 
Japanese Patent 54050084 discloses bonding a laminate of polypropylene 
layer and EVA copolymer using methylmethacrylate-butadiene-styrene 
terpolymer and styrene-butadiene block copolymer adhesive. 
Japanese Patent 54057582 discloses a resin laminate with good gas barrier 
property comprising EVA copolymer, resin layer containing diene block 
copolymer and olefin copolymer, and a polystyrene layer. 
Japanese Patent 54153854 discloses weather-proof polymer compositions 
having good adhesion properties comprising weatherproof polymer and 
polymers containing no unsaturation in the main chain, but containing 
unsaturated side chains and treated with halogen. 
Japanese Patent 55149341 discloses a thermoplastic resin composition used 
in laminate products prepared from unsaturated carboxylic acid-modified 
polyolefin, hydroxy group containing polymer and rubber. 
Japanese Patent 56123862 discloses a heat adhesive resin film for 
manufacturing bags by coating aqueous dispersions of ethylene vinyl 
alcohol and PVA on resin film and drying. 
Japanese Patent 57028157 discloses a flame-retardant composition based on 
non-halogenated polymer containing organopolysiloxane and organo-metallic 
compounds. 
Japanese Patent 57185341 discloses polybutadiene resin composition prepared 
by blending syndiotactic 1,2-polybutadiene resin with dibenzylidene 
alditols or mono(di)(alkyl) phenyl phosphate. 
Japanese Patent 58056822 discloses a primer sheet for lining polyethylene 
sheet or steel pipe comprising thermosetting resin and thermoplastic resin 
with higher melt viscosity. 
Japanese Patent 58084836 discloses an agricultural film composition of high 
fog resistance, transparency, comprising a base polymer of low density 
polyethylene and EVA, PVA or olefin PVA copolymer. 
Japanese Patent 58148761 discloses a gas barrier resin laminated with two 
resin layers with an adhesive resin layer. 
Japanese Patent 59089383 to Motomura discloses a water-swellable packing 
material comprising rubber, water-soluble polymer, and hydrogel. 
Japanese Patent 59157134 discloses a non-flammable composition for coating 
electric cables containing EVA or ethylene-ethyl acrylic copolymer, 
polybutadiene flame retardant, and antimony trioxide, zinc oxide and 
magnesium silicate. 
Japanese Patent 59224343 discloses a laminated structure for wrapping foods 
comprising saponified EVA copolymer layer and olefin polymer layer in 
solid rubber. 
Japanese Patent 6005237 to Toyobo discloses a laminated polyester film for 
molding containers for food, comprising polyethylene terephthalate film, 
said polymer laminated to surface and sparingly gas permeable material. 
Japanese Patent 61108653 discloses a polybutadiene composition prepared by 
mixing crystalline syndiotactic 1,2-polybutadiene with an aqueous 
dispersion and/or organic solution of elastic polymer. 
Japanese Patent 61242841 discloses a laminated oil-resistant vessel for 
foods, having saponified EVA layer and thermoplastic resin layer. 
Japanese Patent 62158042 discloses a readily heat-sealable plastic film 
having charge-controlling coating containing carbon black and an acrylic 
resin layer containing urethane prepolymer. 
Japanese Patent 63037132 discloses a flexible film which can be readily 
incinerated containing thermoplastic polybutadiene, polyolefin, and 
inorganic filler, low density linear polyethylene diaper. 
SUMMARY OF THE INVENTION 
The present invention relates to a blend of syndiotactic 1,2-polybutadiene, 
a terpolymer, and a compatibilizing agent, which blend serves as an 
effective barrier with regard to a gas such as air. The terpolymer is made 
from monomers of ethylene, vinyl acetate, and vinyl alcohol. The blend is 
prepared by melt mixing the components with controlled morphology wherein 
adequate shear and/or mixing is utilized such that the terpolymer 
generally exists in a flat, platelike, or elongated form. Unexpectedly low 
permeation is obtained due to the morphology configuration of the 
terpolymer within the blend.

DETAILED DESCRIPTION 
Syndiotactic 1,2-polybutadiene (i.e., a polybutadiene containing high 
amounts of syndiotactic 1,2-structure) is commercially available and is 
also known to those skilled in the art as well as to the literature. 
Generally, this compound is formed by solution polymerization utilizing 
organic lithium catalyst or coordination catalysts. These catalysts are 
usually charged under an inert atmosphere of nitrogen or argon before use. 
Solvents that may be used during the polymerization reaction include 
aromatic, aliphatic, and alicyclic hydrocarbons. Three possible structures 
may be formed in the polymerization of butadiene. These structures include 
an isotactic configuration in which all the monomer units add in the same 
configuration; an atactic configuration in which the disposition of the 
units is random; and a syndiotactic structure in which the units are in an 
alternating configuration. Syndiotactic 1,2-polybutadiene (syn 1,2-PBD) is 
distinguished from other polybutadienes in that there is participation of 
only one double bond in the polymerization process. The amount of the 
actual syndiotactic structure of the so-called syndiotactic 
1,2-polybutadiene is generally at least 80 percent, desirably at least 85 
percent, and preferably at least 90 percent by weight based on the total 
weight of the three possible microstructures. The vinyl content of the 
syndiotactic polybutadiene can vary from about 82 to 96 percent, desirably 
from about 82 to 92, and preferably from about 82 to 90. 
Syndiotactic 1,2-polybutadiene tends to be rigid, crystalline, and has poor 
solubility characteristics. The Tg of syn 1,2-PBD will vary depending on 
the vinyl content and specifically at about 83 percent vinyl content the 
Tg is about -15.degree. C. The melting point of syn 1,2-PBD varies with 
the microstructure and the amount of vinyl groups. Typical values range 
from approximately 120.degree. C. at about 80 percent vinyl to 
approximately 210.degree. C. at about 100 percent vinyl content. 
The amount of the syndiotactic 1,2-microstructure containing polybutadiene 
is the weight percent difference of the compatibilizing agent and the 
terpolymer, both of which are discussed herein below. 
The barrier terpolymer is a thermoplastic resin having very low gas 
permeability. The thermoplastic polymer is commercially available and is 
known to those skilled in the art as well as to the literature. It is made 
from monomers of ethylene and [saponified] vinyl acetate, wherein the 
amount of ethylene (that is, repeat units derived therefrom) in the 
terpolymer is generally less than about 50 weight percent and desirably 
from about 30 to about 45 weight percent and [wherein at least half of the 
vinyl acetate is converted to the alcohol.] Such a terpolymer is 
commercially available under the name of EVAL.RTM., specifically the EP 
series, and is manufactured by EVAL Corporation of America. EVAL is 
generally a random copolymer and has the general chemical formula as 
follows: 
##STR1## 
wherein the value of x is such that the weight of the ethylene repeat 
groups are, as noted, generally 50 percent by weight or less of the 
terpolymer and the value of y plus z is such that the weight of the vinyl 
alcohol and the vinyl acetate repeat units is generally at least 50 
percent of the terpolymer, and often from about 55 percent to about 70 
percent by weight. The Tg of the ethylene-vinyl acetate-vinyl alcohol 
terpolymer is generally below about 65.degree. C., desirably less than 
about 60.degree. C., and preferably less than about 57.degree. C., as from 
about 50.degree. C. to about 57.degree. C. 
The following table portrays various polymer properties for several EVAL 
resins. 
TABLE 1 
______________________________________ 
POLYMER PROPERTIES 
EP-F101 
EP-H101 EP-K102 EP-E105 
______________________________________ 
Melt Index, g/10 min. 
1.3 1.6 2.9 5.5 
Density, g/cc 
1.19 1.17 1.17 1.14 
Melting Point, .degree.C. 
181 175 175 164 
Crystallization 
161 151 151 142 
Temperature, .degree.C. 
Glass Transition 
69 62 62 55 
Point, .degree.C. 
Vicat Softening 
173 165 159 155 
Point, .degree.C. 
Heat Distortion 
100 90 90 80 
Temperature, .degree.C. 
Ethylene Content, 
32 38 38 44 
Mol % 
______________________________________ 
The preferred EVAL resin is EP-E105. The amount of terpolymer is generally 
from about 10 to about 40 weight percent, desirably from about 15 to about 
30 weight percent, and preferably from about 18 to about 25 weight percent 
based upon the total weight of the blend, that is, the terpolymer, the 
syndiotactic 1,2-polybutadiene, and the compatibilizing agent. The 
thermoplastic terpolymer generally has a higher melting point than the 
elastomer, and a higher viscosity. The melting point is generally from 
about 160.degree. C. to about 185.degree. C. The terpolymer has unique 
properties not found in copolymers of ethylene-vinyl acetate. Some 
important physical properties include good barrier resistance, and high 
crystallinity. 
In comparison, ethylene vinyl acetate (EVA) polymers are not satisfactory 
barriers to air and hence would not provide the necessary properties for 
the present invention. EVA generally melts in the range of about 
103.degree. C. to about 108.degree. C. and, thus, does not have a higher 
melting point than the matrix elastomer. As stated above, it is important 
to the present invention that the barrier terpolymer have a higher melting 
point than the matrix polymer. The formation of a laminar structure 
depends on establishing a melted heterogeneous blend of incompatible 
polymers so that when the melt is stretched, orientated, one polymer is in 
the form of a discontinuous phase. To achieve the structure necessary for 
forming platlets, it is necessary for the barrier polymer to be the lesser 
component and to generally have a higher melting point and melt viscosity 
than the matrix polymer. 
The blend composition desirably contains an ingredient that functions as a 
compatibilizing agent in order to achieve improved permeability 
resistance. These compatibilizing agents typically contain from 3 to 12 
carbon atoms and are usually unsaturated carboxylic acids, anhydrides, or 
esters thereof; or polymers containing these groups. Specific examples 
include maleic acid, methacrylic acid, acrylic acid, ethacrylic acid, 
fumaric acid, phthalic acid, maleic anhydride, phthalic anhydride,glycidol 
methacrylate, diethyl maleate, itaconic acid, and the like. The amount of 
compatibilizing agent varies, but generally is from about 0.2 percent by 
weight to about 3 percent by weight, and preferably an amount of from 
about 1 to about 2 percent by weight based upon 100 parts by weight of the 
elastomer barrier composition blend, that is, the terpolymer, the 
syndiotactic containing polybutadiene, and the compatibilizing agent. 
A desirable aspect of forming the morphology-controlled barrier elastomer 
of the present invention involves the mixing of the melt blend. The mixing 
procedure desirably is such that a laminar morphology of a thermoplastic 
component is formed so that even lower permeability values are obtained. 
The unexpected low permeability values obtained by this invention can 
generally be attributed to these laminar morphologies. In order to achieve 
the improved barrier properties, the two polymers must be immiscible, 
i.e., the syndiotactic polybutadiene and the terpolymer should have two 
different Tg's and form a melted, heterogeneous blend. A desired laminar 
morphology is achieved when the terpolymer exists in an elongated or 
flat-like configuration as a separate phase within the melt blend and 
desirably in substantially parallel (i.e., plus or minus 30.degree. or 
plus or minus 15.degree.) orientations or configurations. The length to 
height ratio of the plate-like terpolymer structures, as an average of the 
total platelike structures, is generally at least 5, desirably at least 
10, more desirably at least 20, and preferably at least 50 with an upper 
limit being about 200 and even about 500. The elongation or stretching can 
be accomplished by several means such as compression molding, blow 
molding, extrusion, calendering, or the like. Such elongations have been 
found to yield the above length to height ratio of the platelike 
structures. 
The mixing device utilized to form the elongated plate-like separate 
terpolymer phase can be a low shear extruder, a mill, or the like. The two 
polymers must be mixed together to form a heterogeneous blend of the 
barrier material being distributed in the continuous matrix of the 
elastomer. This is best accomplished by using a low shear process such as 
an extruder with a low compression screw generally used for metering with 
low shear rates generally in the range of about 10 to 80 reciprocal 
seconds, and preferably about 20 to 50 reciprocal seconds. High shear 
extruders or a Banbury mixer will intensively mix the blend, homogenize 
the blend and will not result in platlets or elongated zones of the 
barrier polymer and the composition will not have suitable permeability 
for an effective inner liner. The mixing temperature is generally such 
that the syndiotactic 1,2-polybutadiene melts along with the terpolymer to 
form a heterogenous blend. Such a melting temperature is generally from 
about 120.degree. to about 210.degree. C. and preferably from about 
165.degree. to about 195.degree. C. During the course of mixing, care must 
be taken that adequate shear is utilized so as to produce a blend having 
the above-noted plate-like structures, and overmixing is avoided so that a 
dispersion or lack of plate-like structures is produced. 
The controlled morphology barrier elastomer blends of the present invention 
can be utilized in various elastomers wherein improved impermeability to 
air and other gases is desired, such as in rubber components and goods. A 
particular end use is within the innerliners of tires, and also in hoses, 
bladders, containers, and the like. Due to the high amounts of 
syndiotactic polybutadiene utilized, the barrier compositions have good 
flexibility. 
Tire innerliners are generally comprised of any conventional elastomer 
including those known to the art and to the literature, such as for 
example butyl rubber which is a copolymer of isoprene and a small amount, 
for example less than 10 percent by weight, of isobutylene. Halobutyl 
rubber made from chlorobutyl or bromobutyl rubbers are particularly 
desirable. Moreover, various butyl rubbers can be blended with natural 
rubber to form a suitable tire innerliner material. The polyisobutylene 
portion of the butyl molecular provides a low degree of permeability to 
gases, hence leads to the use of butyl rubber in tire innerliners. 
The invention will be better understood by reference to the following 
examples. 
EXAMPLE I (Control) 
Syn 1,2-PBD, amount of vinyl approximately 83 percent, was provided as a 
light yellow powder, and passed through an 80-mesh screen prior to use. 
Ethylenevinyl alcohol-vinyl acetate copolymer EP E-105 purchased from EVAL 
Company of America with a melting point of 164.degree. C. was added. The 
polymers were hand-mixed and vacuum-dried. Melt blending was done using a 
Haake Model 40 Banbury mixer at 185.degree. C. with a rotor speed of 50 
rpm for a 5-minute mixing cycle. The shear rate was maintained at about 
100 sec-1. These blends were intensively mixed. Various compositions were 
prepared as summarized in Tables I and II varying in range from 90 percent 
syn 1,2-PBD/EVAL to 10 percent syn 1,2-PBD/EVAL. 
The following tables summarize the physical properties. 
TABLE I 
______________________________________ 
CONTROL BLEND PROPERTIES 
NO COMPATIBILIZING AGENT 
TENSILE ELONG. TEAR PERMEABILITY 
SAMPLE (psi) (%) (ppi) (units*) 
______________________________________ 
100 SYN 3150 420 714 471 
90 S/10 E 
3500 391 588 572 
80 S/20 E 
2776 338 516 662 
70 S/30 E 
1807 185 404 647 
50 S/50 E 
395 2 235 402 
30 S/70 E 
783 2 490 32 
10 S/90 E 
1095 2 618 1 
100 EVAL 
8437 5 1814 0.7 
______________________________________ 
TABLE II 
______________________________________ 
DSC THERMAL TRANSITIONS 
NO COMPATIBILIZING AGENT 
SAMPLE Tm (.degree.C.) 
Tc (.degree.C.) 
______________________________________ 
100 SYN 136 98 
90 SYN/10 EVAL 133, 166 109, 139 
80 SYN/20 EVAL Broad, 165 109, 140 
70 SYN/30 EVAL Broad, 166 110, 141 
50 SYN/50 EVAL None, 168 107, 140 
30 SYN/70 EVAL None, 166 107, 140 
10 SYN/90 EVAL None, 166 None, 141 
100 EVAL None, 168 None, 141 
______________________________________ 
EXAMPLE 2 
Additional blends were prepared by adding 1.5 percent maleic anhydride to 
the composition of Example 1. The maleic anhydride was mixed in situ with 
the syn 1,2-PBD/EVAL. After mixing, the blends were compression molded 
into 6.times.6.times.0.15 inch films. These blends were intensively mixed 
as in Example 1. The shear rate was maintained at about 100 sec-1, using a 
Banbury mixer. 
The following tables summarize the results. 
TABLE III 
______________________________________ 
BLEND PROPERTIES 
1.5% MALEIC ANHYDRIDE 
TENSILE ELONG. TEAR PERMEABILITY 
SAMPLE (psi) (%) (ppi) (units*) 
______________________________________ 
100 Syn 3150 420 714 471 
80 S/20 E 
3180 216 621 356 
70 S/30 E 
2814 12 495 280 
50 S/50 E 
3803 6 626 83 
30 S/70 E 
5328 4 712 49 
20 S/80 E 
4930 2 684 33 
10 S/90 E 
7378 3 1102 20 
______________________________________ 
*Permeability units are cc/mil 100 sq. in./24 hrs. at 30.degree. C. 
NEED TO DISCUSS THE IMPROVED RESULTS. 
TABLE IV 
______________________________________ 
DSC THERMAL TRANSITIONS 
1.5% MALEIC ANHYDRIDE 
SAMPLE Tm (C.) Tc (C.) 
______________________________________ 
80 SYN/20 EVAL 137 106 
70 SYN/30 EVAL 152 106 
50 SYN/50 EVAL 158 106, 122 
30 SYN/70 EVAL 154 107, 123 
20 SYN/80 EVAL 163 106, 129 
10 SYN/90 EVAL 163 None, 131 
______________________________________ 
As apparent from Table III, even though intensively mixed, reductions with 
regard to permeability improvement are achieved utilizing small amounts of 
a compatibilizing agent in comparison with Table I. Moreover, improved 
tear strengths and higher tensile strengths were obtained utilizing the 
compatibilizing agent. 
EXAMPLE 3 
An intensively mixed 80/20 EVAL blend was prepared as in Example 2 
including the compatibilizing agent. The laminar EVAL blends were formed 
by extruding the mixture at a melt temperature of approximately 
185.degree. C., through a Haake low compression (laminar) screw with L/D 
of 25:1. The shear rate was maintained at about 30 reciprocal seconds. The 
blends were then extruded through a 4-inch film die producing a film of 
approximately 60 to 80 mils thick and 3 to 31/2 inches wide. The film was 
then elongated to double its original size by pressing at approximately 
165.degree. C. between two platlets. The physical properties of the 
comparative blends along with the permeability are shown in Table V. 
TABLE V 
______________________________________ 
PROPERTIES OF EVAL BLENDS 
50% 
SAMPLE TENSILE ELONG. MOD TEAR PERM 
RATIO (psi) % (psi) (ppi) (cc/mil) 
______________________________________ 
Laminar 3347 271 2271 733 232 
85/15 
Laminar 2425 151 2101 690 85 
80/20 
Intensive 
3180 216 2206 621 356 
80/20 
______________________________________ 
As apparent from Table V, a dramatic reduction in the permeability level 
was achieved by obtaining a laminar morphology, that is, a plate-like 
structure of the terpolymer in accordance with the present invention. 
While in accordance with the Patent Statutes, the best mode and preferred 
embodiment has been set forth, the scope of the invention is not limited 
thereto, but rather by the scope of the attached claims.