Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-11-15
2001-10-30
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S139000, C521S140000, C521S144000, C521S145000, C521S146000, C521S147000, C521S149000
Reexamination Certificate
active
06310112
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polymer foams from hydrogenated vinyl aromatic polymers.
Polystyrene insulation foam and polyethylene packaging foams are made in commercial quantities using an extrusion process. However, commercial extrusion processes are not easily adapted for use with a wide variety of polymers. Thus, although polystyrene, LDPE (low density polyethylene made in a high pressure process) and some grades of polypropylene are readily processed through an extrusion process, many other common polymers, notably LLDPE (linear low density polyethylene) and HDPE (high density polyethylene), can be extruded into foam with difficulty, if at all. Additionally, these foams have insufficient heat resistance for many applications, such as adiabatic thermal insulation and other applications requiring heat resistance at polymer softening temperatures.
JP-03234741 of Hitachi discloses bead expansion molding (bead stock foam) of a polyvinylcyclohexane resin, having good heat resistance and weatherability. The polymers disclosed include vinylcyclohexane homopolymer and copolymers thereof with fatty acid esters, cyanovinyl compounds, unsaturated dibasic acids, or unsaturated fatty acids.
It remains desirable to obtain other types of foams from hydrogenated aromatic polymers and foams from other copolymers of hydrogenated aromatic polymers.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to a foam of a thermoplastic poly(vinyl cycloaliphatic) polymer having pendant cycloaliphatic groups, alternatively referred to herein as a hydrogenated vinyl aromatic polymer, said foam having a thickness of at least 1 mm and a density of from 3 to 800 kg/m
3
.
It has been discovered that good quality foam can be made easily from such hydrogenated polymers using conventional commercial scale foam equipment, such as extruders and cast rolls. The invention provides foam having good insulating performance, good mechanical properties and heat resistance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The foam of the present invention is prepared from a polymer having pendant cycloaliphatic groups. In this application, such polymers are referred to as hydrogenated vinyl aromatic polymers and can be prepared by hydrogenating polymers prepared by polymerizing at least one vinyl aromatic monomer.
Vinyl aromatic monomers used to prepare the polymers which are subsequently hydrogenated include, but are not limited to those described in U.S. Pat Nos. 4,666,987; 4,572,819 and 4,585,825, which are herein incorporated by reference. Preferably, the monomer is of the formula:
wherein R′ is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene and the like, and mixtures thereof. Homopolymers may have any stereostructure including syndiotactic, isotactic or atactic; however, atactic polymers are preferred.
In addition, a comonomer(s) can be polymerized with the vinyl aromatic monomer to prepare copolymers including random, pseudo random, block, e.g. diblock, triblock, pentablock, multi-block, star block, tapered block, radial block, including symmetrical and asymmetrical versions thereof; and grafted copolymers. For example, hydrogenated copolymers of at least one vinyl aromatic monomer(s) and at least one comonomer selected from: nitriles, acrylates, acids, ethylene, propylene, norbornenes, 1-butene and 1-octene, maleic anhydride, maleimides, vinyl acetate, and vinyl chloride may also be used. Exemplary copolymers include styrene-acrylonitrile, styrene-alpha-methylstyrene and styrene-ethylene. Block copolymers of vinyl aromatic monomers and conjugated dienes such as butadiene, isoprene may also be used. The conjugated diene monomer can be any monomer having 2 conjugated double bonds. Such monomers include for example 1,3-butadiene, 2-methyl-1,3-butadiene, 2-methyl-1,3 pentadiene, isoprene and similar compounds, and mixtures thereof. Further examples of block copolymers may be found in U.S. Pat. Nos. 4,845,173; 4,096,203; 4,200,718; 4,210,729; 4,205,016; 3,652,516; 3,734,973; 3,390,207; 3,231,635 and 3,030,346. Blends of such polymers with other polymers including impact modified, grafted rubber containing aromatic polymers may also be utilized. In addition, the polymerization of the vinyl aromatic monomer may be conducted in the presence of predissolved elastomer to prepare impact modified, or grafted rubber containing products, examples of which are described in U.S. Pat. Nos. 3,123,655; 3,346,520; 3,639,522; and 4,409,369, which are incorporated by reference herein.
In a preferred embodiment, the polymer is a vinyl aromatic-conjugated diene block copolymer, wherein the conjugated diene polymer block is chosen from materials which remain amorphous after the hydrogenation process, or materials which are capable of crystallization after hydrogenation. Hydrogenated polyisoprene blocks remain amorphous, while hydrogenated polybutadiene blocks can be either amorphous or crystallizable depending upon their structure. Polybutadiene can contain either a 1,2 configuration, which hydrogenates to give the equivalent of a 1-butene repeat unit, or a 1,4-configuration, which hydrogenates to give the equivalent of an ethylene repeat unit. Polybutadiene blocks having at least approximately 40 weight percent 1,2-butadiene content, based on the weight of the polybutadiene block, provide substantially amorphous blocks with low glass transition temperatures upon hydrogenation. Polybutadiene blocks having less than approximately 40 weight percent 1,2-butadiene content, based on the weight of the polybutadiene block, provide crystalline blocks upon hydrogenation. Depending on the final application of the polymer it may be desirable to incorporate a crystalline block (to improve solvent resistance) or an amorphous, more compliant block. The conjugated diene polymer block may also be a copolymer of a conjugated diene, wherein the conjugated diene portion of the copolymer is at least 50 weight percent of the copolymer.
The conjugated diene polymer block may also be a copolymer of more than one conjugated diene, such as a copolymer of butadiene and isoprene. Other polymeric blocks may also be included in the hydrogenated block copolymers used in the present invention.
A block is herein defined as a polymeric segment of a copolymer which exhibits microphase separation from a structurally or compositionally different polymeric segment of the copolymer. Microphase separation occurs due to the incompatibility of the polymeric segments within the block copolymer. Microphase separation and block copolymers are widely discussed in “Block Copolymers-Designer Soft Materials”, PHYSICS TODAY, February, 1999, pages 32-38.
Block copolymers can be either rigid or flexible block copolymers, wherein rigid block copolymers are characterized by:
a) a weight ratio of hydrogenated conjugated diene polymer block to hydrogenated vinyl aromatic polymer block of 40:60 or less, typically from 40:60 to 5:95, preferably from 35:65 to 10:90, more preferably from 30:70 to 15:85, based on the total weight of the hydrogenated conjugated diene polymer block and the hydrogenated vinyl aromatic polymer block; and
b) a total number average molecular weight (M
nt
) of from 24,000 to 150,000, wherein each hydrogenated vinyl aromatic polymer block (A) has a M
na
of from 6,000 to 60,000 and each hydrogenated conjugated diene polymer block (B) has a M
nb
of from 3,000 to 30,000;
and flexible block copolymers are characterized by:
a) a weight ratio
Achille Felix
Hahnfeld Jerry L.
Imeokparia Daniel D.
Mackey George A.
Vo Chau Van
Foelak Morton
The Dow Chemical Company
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