Note: Descriptions are shown in the official language in which they were submitted.
349 K-4438 G (CA)
MSB:dl
POLYBUTYLENE
Fîeld of the Invention
-
This invention relates to novel polymers of l-butene.
Background of the Invention
Thermoplastic, predominantly isotactic homo- and copolymers of
l-butene3 referred to herein and in the trade as "polybutylene" or
"poly-l-bu~ene," are well known materials. Isotactic polybutylene is
the subject of U.S. Patent 3,435,017 of Natta et al. The properties and
preparation of isotactic polybutylene are described, for example, in
"Encyclopedia of Chemical Technology," edited by Kirk-Othmer, 2nd Ed.,
Suppl. Vol., pp. 773-787. Methods for producing such polybutylene are
disclosed, i.a., in U.S. Patents 3,362,940 ancl 3,464,962. Thermoplastic,
predominantly isotactic butene-1 homopolymers of the type heretofore
described in the literature, e.g., in U.S. Patents 3,362,940 and 3,435,017,
and produced commercially, are referred to herein as "conventional"
polybutylene.
Conventional polybutylene is produced by contact of l-butene
with coordination catalysts which are generally referred to as Ziegler-
Natta catalysts. Broadly, such catalysts are the products o-f contacting
a compound of a transition metal of Group IV of the Periodic lable of
Elements or of some other transition metals with an organometallic
compound of a metal of Groups I-III.
For convenience of reference herein, the transition metal-
containing components, which are typically solid, are referred to as
"procatalysts", the organometallic compounds as "co-ca~alysts", and any
additional stereoregulating compounds as "selectivi~y control agents",
abbreviated "SCA".
Commercial ~iegler-Natta catalysts are designed to be highly
stereoregulating in order to produce highly isotactic polyolefins~
Several generations of Ziegler-Natta coordination catalysts
have acquired commercial importance in the production of isotactic poly-
olefins Originally, a typical procatalyst was violet TiC13 in the
delta or gamma crystal form, or a violet TiCl3 complex, such as w~
~L~9~34~9
AlCl3. Several types of more active TiC13 procatalysts have since been
developed and put to commercial use. The co-catalysts employed with
TiC13 catalysts are aluminum alkyl compounds, typically halogen-containing
aluminum alkyls such as aluminum diethyl halides.
During the last 10 years, more highly active catalyst systems
have been developed, particularly for production of isotac~ic polypropylene.
These typically comprise a support of magnesium chloride, which may have
been activated such as by ball milling, combined with TiCl~ and an
electron donor--typically an aromatic ester such as ethyl benzoate. The
co-catalyst is again an aluminum alkyl, typically an aluminum trialkyl.
Generally an electron donor is employed as selectivity control agent.
The cocatalyst may be complexed with the selectivity control agent in
whole or in part, prior to being combined with the procatalyst. The
purpose of the selec~ivity control agents is to increase the stereoregulating
activity of the catalysts. Typical selectivity control agents are
aromatic esters such as p-ethyl anisate. Numerous variants of these
systems have been disclosed in the patent literature. These catalyst
systems, referred to herein as supported coordination catalyst systems,
are known to be substantially more active in the production of polypropylene
than the most active TiCl3-based catalyst systems of the prior art.
The goal of commercial Ziegler-Natta catalysis of propylene or
higher alpha-monoolefins generally is the production of highly isotactic
polymers. Isotaoticity refers to the molecular structure of olefin
polymer molecules. The isotactic structure in polyolefins is one in
which all the assyme~ric carbon atoms have the same steric configuration.
The isotactic structure of polybutylene is illustrated and discussed in
U.S. Patent 3~435~017 to Natta et al. High isotac~ici~y of conventional
polymers of butene-l or of prspylene is associated with high crystallinity
of the polymers.
The crystallinity of conventional butene~l-homopolymers,
determined by X-ray diffraction analysis, is typically ln the range from
50 to 55%. Their isotacticity9 determined by ether extraction~ is
typically in the ranye from 97.5% to 99.5%.
-- 2 --
~23~
Another highly stereoregular form of polyolefins is known as
"syndiotactic". In the syndiotactic structure, alternate assymetric
carbon atoms have opposite steric configurations. Syndiotactic poly-
butylene is described by Natta et al in Atti Acad. Naz. Lincei, Cl. Sci.
Fis, Mat. Nat., Rend. [8~ 28, 452 (1960). The polymer is an amorphous
solid. It was prepared by hydrogenation of syndio-tactic polybutadiene.
Syndiotactic polyolefins are difficult to produce and are not at present
of commercial interest.
~ ue to its crystallinity, conventional polyb~tylene exhibits
~o signi~icant stiffness, tensile strength, hardness, and other physical
properties characteristic of such polymers as high density polyethylene
and isotactic polypropylene. It also shares such other properties of
these polyolefins as chemical inertness and dielectric properties.
Outstanding properties o~ conventional isotactic polybutylene
are toughness, resistance to creep and resistance to environmental
stress cracking. The e~ceptional resistance of polybutylene to enYironmental
stress cracking, coupled with the good creep resistance, recommends the
use of conventional poiybutylene for pipe. The exceptional toughness
makes it desirable for the production of film ~or packaging, since films
of conventional polybutylene are significantly stronger than films of
other common polyolefins of the same thickness.
~lastomeric polybutylene recovered as a small ~raction of a
product made with poorly stereoregulating catalysts is known from U.S.
Patent 31435~017 to Natta et al. Another elastomeric polybutylene,
having an isotacticity of no more than 50% and produced with a catalyst
having poor stereoregulating activity, is the subject of U.S. ~,298,722
to Collette et al.
References
"Encyclopedia of Chemical Technology~" Kirk-Othmer~ 2nd Ed.,
Suppl. Vol., pp. 773-797 provides a detailed deseription of the state o~
the art of polybutylene production in 1967; the commerc;al aspects have
not significantly changed to date.
-- 3 --
U.S. Patent 3,435,017 to Natta et al describes conventional
isotactic polybutene-l and its preparation and properties.
U.S. Patent 3,175,999 to Natta et al describes polymers of
alpha olefins, primarily of propylene, which are designated "stereoisomer"
block polymers. They are descrihed as polymers in which isotactic
sections alternate with non-isotactic (atactic) sections. Stereoblock
polymers are said to be present in small concentrations in conventionally
prepared Ziegler-Natta polymers; they must be recovered by a series of
solvent extractions, as by treating some of the intermediate fractions
of a sequential solvent extraction of Ziegler-Natta polymers with a
solvent which has a dissolving capacity for the polyolefin intermediate
between that of diethyl ether and n-heptane. In the illustrative examples,
the catalysts are compositions which are now known to have poor or very
poor stereoregulating ability. In Example 4 of the patent, a polymer of
butene-l, produced with a catalyst prepared from vanadium tetrachloride
and triethylaluminum, was extracted with hot ether and the residue of
the ether extraction was then extracted with methylene chloride to
obtain an extract, corresponding to 6% of the residue o~ the first
extraction, which was said to have high reversible elasticity.
U.S. Patent 4,298,722 to Collette et al is directed to production
of an elastomeric polybutene-l whieh is made with a poorly stereoregulating
catalyst and has an ether solubles content of at least 30% and isotacticity
not excee~ing 50%. The reaction products illustrated by example, listed
in Table 3 of the patent, had ether solubles contents of 38-56% (determined
before milling) and isotacticities of 23-46%.
A large number of patents an~ patent applications have now
been published directed to the production of supported coordina'cion
catalyst syst~ms -For the ster~oregular polymerization of alpha olefins;
~he following ~hree patent publications are specifically directed to ~he
polymerization of butene-l.
European Pu~lished Patent Application 2522, published June 27,
1979, of Phillips Petrole~m Company, is directed to the polymerization
oF butene-l to form a polybutylene having the properties oF conventional
-- 4 --
34~
isotactic polybutylene. In order to accomplish this, the patent describes
a modified catalyst preparation and a particular slurry polymerization
process.
Japanese Kokai Patent No. 54/85293, published July 6, 1979,
applied for in Japan on December 21, 1977 by ~itsui Petrochemical
Industries Company, is directed to the production of certain copolymers
of butene-l with another alpha monolefin, having more than 60 but no
more than 98% weight butene-l content and preferably 70-90% butene-l
content and 30-10% propylene. These copolymers are said to have physical
characteristics comparable to polyvinyl chloride.
Japanese Patent Application 51/23607 published September 24,
1980, applied for in Japan by Mitsui Petrochemical Industries Company,
is directed to a modification in the polymerization process for producing
conventional polybutylene over catalysts employing as procatalysts a
composite of titanium, magnesium, halogen and electron donor.
Summary of the Invention
This invention is directed to a product of the polymerization
of butene-l which has high stereochemical order but nevertheless has low
crystallinity and has properties oF a thermoplastic elastomer. The
polymer product of this invention is the total product, or substantially
the total product, of homopolymerization of butene-l over highly stereo
regulating coordination catalysts. The butene-l polymers of this invention
are referred to herein as elastomeric polybutylene.
This product is characterized by an abrupt and discontinuous
change in mechanical properties compared to conventional isotactic poly-
butylene. The properties of the latter are those of conventional thermo-
plastics while the product of this invention is elastomeric. This
reflects a change from a level of crystallinity where the crystalline
portion of the polymer dominates mechanical properties to a level where
the amorphous phase dominates mechanical properties. Moreover, similarly
to thermoplastic elastomer block copolymers, the polymer product of this
invention behaves like a phys~cally crosslinked elastomer, l~eO, it
behaves as if its elastomeric amorphous phase is bound together through
-- 5 --
3~
a network of crystalline domains. Its elastomeric qualities lie between
those of plasticized vinyl polymers and conventional vulcanized rubbers.
Like thermoplastic elastomers such as the well known cor~mercia7
block copolymers based on styrene and diolefins or complex blends of
polypropylene with elas~omeric copolymers of ethylene and propylene, the
butene-l polymers of this invention may be compounded with extenders and
fillers for use as molded or extruded elastomeric products. The butene-
1 polymers of this invention are also useful for those uses where
flexible vinyl polymers, such as highly plasticized poly(vinylchloride)
(PVC), have heretofore been employed. Unlike PVC, they do not require
the use of plasticizers to achieve and retain the desired flexibility.
They also do not have the disadvantages of potential health and sa-fety
problems associated with vinyl chloride monomer, with burning of PVC and
with PVC plastic;zers.
The elastomeric polybutylenes of this inven~ion possess an
unusual combination of properties, compared to other thermoplastic
elastomeric polymers, in that they combine the resilience and flexibility
typical of elastomers with the surface hardness characteristic of thermo-
plastic polyolefins such as conventional polybutylene.
Brief Description of the Drawing
Figure 1 of the draw;ng shows 13C NMR spectra of conventional
polybutylene and of elastomeric polybutylene of this invention.
Figures IA and lB are expansions of the peak at about 28 ppm,
showing the fine structure in greater detail.
Figure 2 is a graph of damping curves of elastomeric poly-
butylene of this invention, PVC and natural rubber.
Figure 3 is a plot of tensile yield strength v. ether solubles
for elastomeric polybutylene and conventional polybutylene.
Figure 4 is a plot of hardness Yr flexibility as measured by
Young's modulus, for elastomeric polybutylene9 PVC and conventional
elastomers.
Figure 5 is a stress relaxation plot for elastomer-ic poly-
butylene and for PVCs of diFferent plasticizer contents.
~ 6 --
23~9)
Figure 6 is a plot o~ data of a recrystallization procedure
comparing elastomeric polybutylene of this invention with a polybutylene
of relatively low stereoregulativity.
Description of the Invention
Conventional polybu~ylene~ as produced in polymerization with
effective Ziegler-Natta type coordination catalysts, typically has an
isotactic content greater than 92%, as determined by extraction with
boiling diethyl ether. It ~ypically exhibits a crystallinity of the
order of 50-60% by X-ray diffraction analysis and has the tensile strength
~o and stiffness characteristic of highly crystalline thermoplastics.
Like conventional polybutylene, the polybutylene products of
this invention also are highly stereoregular. However, unlike conventional
polybutylene, the polybutylene of this invention nevertheless exhibits
crystallinit~y in the ran~e of only 25-40% by X-ray diffraction analysis.
Even though it has high steric order, the polybutylene of this inYention
exhibits physical properties characteristic of thermoplastic elastomers,
such as the well known commercial block copolymers based on styrene and
diolefins or complex blends of polypropylene with elastomeric copolymers
of ethylene and propylene.
Z0 The elastomeric polybutylene o~ this invention is a total
product of the homopolymeri~ation of butene-l, characterized by ~he
following properties:
Solubility in refluxing diethyl ether, % wt ~ 10
Crystallinity, by X-ray diffraction (Form I3, % 25-40
Mn x 10-3 (a) 20-300
Mw x 10-3 (a) 150-2,200
Mw/Mn 4~~
Melting Point(b), Form I, C ~ lOQ-118
Melting Point(C), Form ~I, C ~ 98~110
Tensile Strength
At yield, psi 40n-1700
At break, psi 3000-45Qo
Elongation at break, % 300-6Q0
3~
~lardness, Shore A, 10 seconds 50-90
In fractional crystallization method A, described below, the resi~ue
of ~he third recrystallization represents no more than about 25% of
the total polymer.
(a) By gel permeation chromatography.
~b) By differential scanning calorimeter (DSC) at heating rate of
20C/minute, using compression molded plaque, crystallized at
7C; after transformation to Form I.
(c) By DSC after crystallizing the melt at 10C/minute cooling rate
and then immediately heating a~ 20C/minute.
In the preferred products of this invention, the total unextracted
reaction product contains no more than 8%, and still more preferably no more
than 5% of ether soluble components. The total polymerization products may
be used without extraction or aFter extraction of all or a portion of
the small ether soluble fraction, which owes its solubility to a combination
of low steric regularity and low molecular weight.
Products of this invention having ether solubles contents close
to the upper permissible llmit may exhibit some degree of surface adhesion
or stickiness. For so~e uses, e.g., as film or sheet, this may make it
desirable to extract some or all of the ether so'luble portion. For other
uses, e.g., for blending with other polymers, the presence of a small
ether-soluble component may not be objectionable. Products having ether
solubles content in the preferred lower ranges do not exhibit significant
surface adhesion or stickiness even though they contain a large proportion
of polymer soluble in boiling n-heptane, whereas polybutylenes produced
with a relatively non-stereoregulating conventional coordination catalyst,
which also exhibit relatively low crystallinity and are also relatiYely
flexible compared to conventional polybutylene, exhibit high surface
adhesion, resulting from a large fraction of low steric regularity.
A prominent feature of our elastomeric polybutylene is its
substantially suppressed level of crystallinity compared to conventional
polybutylenes. A companion ~eature of our elastomeric polybutylene, one
which makes it unique among the large number of polyolefins produced
with s~ereose'lective catalysts, is the fact ~hat this suppression of
-- 8 --
~z~
crystallinity is achieved without the corresponding large increase in
amount of easily extractable polymer (soluble in refluxing ethyl e-ther)
which results when the crystallinity enhancing features o~ a conYentional
Ziegler-Natta polymeri~ation system are removed or reduced. This is
shown by the dramatically di~ferent correlation between extractable
polymer concentration and tensile strength shown by our elastomeric
polybutylene compared to conventional polybutylene as illustrated in
Figure 3. The origin of this unique relationship appears to lie in the
co-enchainment of the isotactic sequences and sequences of frequent,
mostly alternating (syndiotactic), tactic inversions of elastomeric
polybutylene. On the other hand, stereoirregular species in conventional
polybutylene largely coexist as separate fractions which are easily
separable by extraction with ether.
Another distinguishing feature of our elastomeric polybutylene
is its 13C NMR spectrum. The 13C NMR method provides detailed in-formation
about the con-Figuration and conformation of short sections of polymer
chains. A comparison o~ 13C NMR spectra of conventional polybutylenes
with those of the products of this in~ention indicates a significant
di~ference between the products, even though they both have a very high
degree of steric order. The dif-ference shows up as a higher proportion
of polymer comprised of short sequences of Frequent tactic inYersion
alternating with 10nger isotactic seq~ences. This indicates for the products
of this invention a s~ructure o-F short average isotactic sequences, which
contrasts strikingly with the long average isotactic sequences of
conventional polybutylene.
The enchained tactic defect structure which alternates in a
stereoblock structure with isotactic sequences in elastomeric polybutene-l
is responsible ~or 'che fine s~ructure associated ~ith the ~najor 13C NM~
absorptions o~ polybutene-l. As evident in Figure l and lB, this fine
structure is much more prominent in the spectrum oF elastomeric polybutene-l
than it is in conventional polybutylene ~lA~. Integrated intensities o~ the
absorbances in the 26 to ~8 ppm region show 15% tactic defect structure
associated wikh very short tactic inversion sequences (~ 5 Inonomer uni~s)
g
~323~
and 9% alternating (syndiotactic) tactic inversions in sequences ~ S
monomer units. By comparison, typical conventional polybutylene has only
6% defect structure and 2% alternating or sydiotactic sequence stereo-
structure. It is the larger amount of the net defect structure, enchained
in not readily extractable molecules, that accounts for the elastomeric
character of our new form of polybutylene.
13C NMR spectra of the fractionated polybutenes were recorded
on a Bruker WM-360 spectrometer operating at 90.50 MHz under proton
decoupling in FT mode. Instrument conditions were: 90 pulse of 50 ~s,
9 s repetition rate, 14 KHz sweep width and 32 K FID. The numbers of
transients accumulated were 1500 to 3000. Solutions of polymers were
rnade up in 15mm tubes with 0.5 to 1.0 9 per 5 cm3 of 2,2,4-~richlorobenzene
with N2 degassing. Temperature for measurement was 130C. The chemical
shift was presented in ppm down field from TMS as an external standard.
Like all products of olefin polymerizations with coordination
catalysts, the products of this invention are mixtures of molecules
differing from each other to some extent in structure and in molecular
weight. The compositions and structures of such products are to some
extent a function of the specific catalyst composi~ions and reactions
conditions employed in their production.
The elastomeric polybutylene of this invention may be produced
having a wide range of molecular weights. ~umber average molecular weights
(Mn) may be from 20,000 to 300~000 and weigh~ average molecular weights (Mw)
from 150,000 to 2,200,000. A characteristic of the products of this
invention is a narrow molecular weight distribution, as indicated by ~he
ra~io of ~iW/Mn (Q-value) which is typically of the order of 70 to 75%w
or less of the Q~value of conven~ional polybutylene.
Both conventional and elastomeric isotactic polybutylene are
unique compared to other commercial polyolefins in that they are capable
of existing in seYeral crystalline modificatlons which can be isolated
in almost pure forrn. Conventional isotactic polybutylene typically first
solidifies from the mel~ in the crystal form known as Type II. Type II
is unstable with respect to Type I and converts to T~pe I at a rate
- 10 -
~23~
depending on a variety of factors, such as molecular weight~ tacticity,
temperature, pressure, and mechanical shock Properties of the seYeral
crys~al forms oF conventional isotactic polybutylene are well known.
The transformation of Type II to Type I has a marked effect on the
physical properties. Density, rigidity and strength are increased.
Like conventional polybutylene, our elastomeric polybutylene
crystallizes from the melt in the form of crystal Type II, which transforms
to crystal Type I over a period of hours or days, depending on environmental
conditions.
Physical properties of elastomeric polybutylene of this invention,
crystallized in Type I form, are shown in Table 1. Also shown in Table
ls for comparison, are corresponding properties of a butene-l homopolymer
produced on a commercial scale in a solution process.
Table 1
Conventional PBElastom ric PB
Range Range Typical
Solubility in refluxing diethyl ether,
% ~t. 0.~-2.5 ~ 10 1.5-8
Crystallinity~ % 50-60 25-40 30-35
~n x 10- 25-95 20-300 50-200
Mw x 10-3 ~230-1540 150-2200 500-1500
Mw/Mn 10-12 4-8 6-7
Melting Point~ Form I, C 123~126 ~100-118 ~106-116
Melting Point~ Form II, C 113-117 ~38-110 ~100-107
Tensile Properties
Tensile strength at yield, psi2200-2600 400-1700
Tensile strength at break, psi~500-5500 3000 4500
Elongation at break 200-375 300-600
Hardness, Shore A, 10 sec. 50-90 75-87
The elastomeric character of polybutylene of this invention is
demonstrated in Figure 2 of the drawing, which shows damping curves of
a typ;cal plasticized PVC, of vulcanized natural rubber, and of a typical
elastomeric polybutylene. Damping curves were determined by a free
-- 11 --
3~
vibration torsion pendulum. Since the damping effect varies with the
softness of the product it is accepted practice to recalculate damping
curves for a product of uniform Shore Hardness. The curves in Figure 1
are normalized for product of 75 Shore Hardness, Method A (1 second).
The ordinate is amplitude and the abscissa is time in centiseconds.
The elastomeric polybutylene is shown to be more elastomeric than
plasticized PVC, but less so than natural rubber.
Figure 3 is a plot of tensile yield strength in pounds per
square inch Yersus ether solubles content in percent by weight, it
illustrates the difference between the elastomeric polybutylene of this
invention and conventional polybutylene.
Area A represents a range of values measured on elastomeric
polybutylene of this invention. Line I represents an average curve for
these values. Line II represents average values of conventional poly-
butylenes.
Figure 4 illustrates how polybutylene of this invention differs
uniquely from conventional elastomers in exhibiting a greatly superior
surface hardness at a given flexibility. It is a plot of hardness
versus Young's modulus. Hardness is plotted as Shore Hardness, Method A,
10 seconds. Curve I is an average curve representative o-f commercial
PYC9 containing varying amounts of plasticizer ~o achieve varying degrees
of flexibility. Area A represents a range of values for uncompounded
elastomeric polybutylene of ~his invention. Curve II is an average
curve of ~alues obtained with different compounded elastomers, both
vulcanized SBR and thermoplastic block copolymersg which are identified
on the drawing.
While uncompounded polybutylene of this invention has certain
properties which are close to those of compounded PVC, as shown in
Figure 4~ it also has uniquely advantageous properties compared to PVC.
This is illustrated ;n Fi~ure 5.
Fi~ure 5 relates to stress relaxation. Curve ~ is measured on
a polybutylene according to this invention and curYes II, II' and II" on
samples of commercial PYC con~aining different amounts of plasticizer
- 12 -
3~
and having nominal hardness ~alues of 40, 65 and 95, respectiYely. The
stress relaxation test is conducted by stretching a specimen to 300% of
elongation and observing the decrease ;n stress as a function of time.
In Figure 5, the abscissa is a logarithmic scale of time in seconds and
-the ordinate is the percent of the initial stress at a ~iven time.
It is seen that elastomeric polybutylene of this invention has
a relatively low rate of stress relaxation. This property is particularly
desirable in products to be used for seals, gaskets and the like.
Table 2 provides a comparison of representatiYe properties of
a sample o~ uncompounded elastomeric polybutylene of this invention with
typical commercial PVC and elastomers. The elastomeric polybutylene was
prepared as in Example 6.
Table 2
Uncompounded S-EB-SC) Thermoplastic
Elastomeric ) b)ThermoplasticPolyurethane
Poly~butylene PVCa EPDM Elastomer Elastomer
~ .
Tensile strength,
at break, psi4000 1800 2000 6000 7000
Elongation at
break, % 600 300 600 600 500
Tensile set
at break, % 125 300 200 50 40
Hardness Shore A,
10 sec. 83 65 75 80 80
Young's Modulus,
psi 6500 3000 4500 500Q 600
Stress recovery, %80 25 35 70 50
Hys~eresis loss, %60 60 70 45 55
Tear resistance~
30lbs/linear inch1100 6Q0 450 500 700
Resilience, % 75 35 45 80 70
Processing
temperature, F 350 350 450 500 500
. .
(a) PVC plasticized with about 40% wt dioctyl phthalate
(b~ Mineral filled, vulcanized
(c) Uncompounded
(d~ Pol~yether based
';
- 13 -
39~
The unique composition of elastomeric polybutylene of this
invention, Gontrasted with conventional polybutylene which has been
prepared at conditions leading to lower average isotacticity is demonstrated
by fractional crystallization of the whole polymer from n-heptane. The
method is regarded as representing a fractionation with respect to crystal-
lizabilîty of the polymer, which in turn is believed to be determ-ined by
the distribution of isotactic sequences and tactic inversions in the
polymer molecules. The procedure, referred to herein as fractional
crystallization Method A~ is carried out as follows:
100 grams of the total polymer is dissolved in 1 liter of n-
heptane at 50-60C. The solution is cooled to ambient temperature of
about 25C and allowed to stand ~or at least 24 hours, to permit complete
precipitation of the polymer portion which is crystallizable at those
conditions. The solid fraction is filtered oif, washed with 1 liter
of n-heptane, dried and weighed. The soluble -Fraction is recovered from
~he combined filtrate and wash liquid by evaporation o~ the solvent and
weighed. The procedure is repeated with the total ~irst precipitate
and repeated twice more with the successive precipitates, using the same
amount of n-heptane and the same conditions.
It has been found that in fractional precipitation of a typical
polybutylene oF this invention by this method, the percent by weight of
the total polymer which remains dissolved in each stage is of the order
of 25% o~ the total polymer. ~y contrast9 when the same procedure was
carried out on a conventional polybutylene which had been prepared with
poorly stereoselective catalysts, and which had an et'ner extractable
content of ~2.2%, the amount of polymer which rema-ined in the first
filtrate was abo~t 27%wt. but decreased to abo~t 16%wt. and ~ 4%~t. in
the second and third filtrates, leaving more than 50%~tO as residue of
the th;rd recrystallization. These results are graphically illus~rated
in Figure 6, which is a plot of cumulative amounts dissolved Yersus
number of recrystallization steps.
Crystallization method ~, carried out on conventional polybutylene,
showed less khan 4% soluble in ~he first recyrskalli~ation and essentially
none in the later recrystallizations.
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~3~3~
There are various theories with respect to the mechanism of
polymeriza-tion over Ziegler-Natta catalysts. A widely held view is
that the selectivity of Ziegler-Natta catalysts in alpha-olefin poly-
merization is simply a ~unction of the relative populations of selective
(isotactic) and non-selective (atactic) sites on the procatalyst.
Accordingly, the isotacticity of a given unextracted polymer i5 considered
to be determined by the relative proportions it contains o~ highly
isotactic product polymerized at selective sites on the procatalyst and highly
heterotactic ~atactic) product polymerized at non-selective sites. The
heterotactic fraction is non-crystallizable or only very slightly
crystallizable and can be separated from the isotactic portion of the
whole polymer by solvent extraction, e.g., in boiling n-heptane, as
typically employed for polypropylene, or in boiling diethyl ether~
typically employed for polybutylene. The amount of extractable polymer
is the most commonly used indication of the select1vity of the ca~alyst
and the isotactic purity of the polymer. Selectivity control agents
which are employed in many commercial Ziegler-Natta systems to control
isotacticity and hence crystallinity are regarded as preferentially
deactivating non-selective catalyst sites.
We now believe that there is an additional dimension of stereo-
selectivity. This additional dimension has to do with the ability of
some cata~lyst sites to exist for shor~ durations in a mode ~hich produces
alternatin~ tac~ic inversions in polymer molecules produced at otherwise
jsotactic selective sites. The inversions or short sequences of mostly
alternating inversions (syndiotactic sequences) interrupt runs of isotactic
sequences~ producing isotactic blocks which are longer or shorter,
depending upon the ~requency or rate of inversion in relation to the
rate of polymeri~ation propagation at the particular active catalyst
site. The isotactic stereoblocks will be long for catalysts where population
of such dual mode sites is small and/or where the ratio kiSotactic!kinyersion
is large, and/or where the time spent by a dual mode si~e in the
inversion or syndiotactic mode is small Such is the predominant
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349
situation in conventional Ziegler-Natta catalysis; the stereoblocks
w-ill be shorter for catalyst where these situations are reYersed.
We have discovered that under certain operating conditions
supported coordination catalyst systems appear to fall in the latter
category in the polymerization of butene-l, as indicated by 13C NMR
analysis of the polymer products. Thus, the steric purity of polybutylene
produced in such polymerizations appears to be not just a function o~
the relative proportions of isotactic and atactic catalyst sites but
also a sensitiYe ~unction of what appears to be highly specific chemistry
leadin~ to tactic inversions at isotactic sites.
Natta et al described certain stereoisomer block copolymers
jn lJ.S. Patent 3,175,999 as polymers in which isotactic sections alternate
with atactic sections. The stereoisomer block copolymers were produced,
as illustrated in the examples, with catalysts which have poor ability
to produce isotactic polymers, and represented only small proportions of
the total polymer product. In contrast to this, our elastomeric polybutylene
can be produced as the total polymerization product by means of catalysts
which are capable o~ being highly stereodirecting for the production of
isotactic polymers. Our polymers may be produced by means of catalyst
systems which, when employed in propylene polymeri~ation, produce highly
crystalline isotactic polypropylene. Our elastomeric polybutylene consists
mainly of isotactic blocks, interrupted by inversions oF only one or a
few molecules largely in alternating (syndiotactic~ stereochemical
configurationsO
The preferred catalyst to be employed for production of elastomeric
polybutylene of this invention is one in which the solid component
comprises a support o~ magnesium chloride in an active ~orm, combined
with an electron donor and titanium halide; typically the componen~s are
MgC12, TiC14 and an aromatlc ester~ e.g., ethyl benzoate or p-ethyl
toluate. This solid component is combined with an alumlnum alkyl,
typically a trialkylaluminum such as triethyl aluminum and a selectiYity
control agent, typically ethyl anisate. Numerous Yariants o~ these
catalysts are described in recent patents7 such as U.S. Pa~ents Nos.
- 16 -
~ ~23~
4,051,313, 4,115,319, 4,235,9~ and 4,250,287. Preferred to da~e arecatalysts prepared as described in U.S. Patent ~,329,253 to Goodall et
al and in European Patent Application 19,330, published November 26,
1 9~0.
The conditions under which the polymerization is conducted,
including the method of combining the catalyst components, can also
affect the type of polymer produced. In a preferred method, all three
catalyst components are pre-mixed before being introduced into the
polymerization zone, and the procatalyst and cocatalyst are combined
before the electron danor is combined with the catalyst mixture.
The polymerization is preferably conducted as a solution poly-
merization process, using butene-l as the reaction medium. However, it
may be conducted in liquid butene-l at conditions under which the polymer
is produced as a solid in a so-called slurry polymerization. The poly-
merization may be carried out in batch or continuous modes.
Suitable ratios of the several catalyst components are as
follows-
Ti content o^f procatalyst, ~wt. 1 - 5
Al:Ti atomic ratio ~ 50-150; preferably about 65-100
SCA:Ti molar ratio > 4.5-20, preferably about ~.5-15
Al:SCA molar ratio 5:1-15:1
H2:Ti molar ratio 0-2500
The interaction of procatalyst, cocatalyst~ selectivity control
agent and hydrogen in the production of iso~actic polymers is basically
the same in the production of elastomeric polybutylene as it is in the
production of other isotactic polyolefins. However, i~ has been observed
that the molar ratio of cocatalyst to ~itaniumS when using appropriate
amounts of SCA, is preferably not above 100 and should not exceed ahout
150. At ratîos approaching and exceeding 150, the polymer product
gradually becomes less elastomeric and more nearly like conventional
polybutylene.
The catalysts employed in the production of elastomeric poly-
butylene may be of sufficiently hi~h activity that no product deashing
- 17 -
349
step is required. If catalyst residues are to be deactivated and removed,
this may be accomplished by conventional means employed in cleanup of
olefin polymers produced over such catalysts, e.g., by contact with an
alcohol, followed by extraction with water.
The elastomeric polybutylene of this invention, which combines
the chemical properties of polybutylene with physical characteristics
resembling those oF plasticized PVC and of thermoplastic elastomers, is
expected to find many uses.
Unblended products of this invention are relatively homogeneous
materials of excellent chemical resistance as well as physical toughness.
Polybutylene of this invention has been converted into films, including
heavy gauge film use~ul for bagging of industrial powdered goods. It is
also useful for conversion into stretchable plastic -Fibers and filaments.
For applications in which thermoplastic elastomers have hereto-
before been employed, the products of this invention can be compounded
and processed similarly to conventional hydrocarbon elastomers, e.g.,
by blending with other polymers such as polypropylene7 with extenders such
as mineral oils and waxes, and with fillers such as calcium carbona~e,
for use as molded or extruded products in various applications for which
2~ hydrocarbon elastomers are conventionally employed.
The butene-l polymers of this invention are also useful for
those uses where flexible vinyl polymers, such as highly plasticized
poly(vinylchloride) (P~C), have heretofore been employed, including
conversion into sheets and tubing for a variety of uses. UnlikP P~C,
they do not require the use of plasticizers to achieve and retain the
des;red ~lexibility. They do not have the disadvantages of potential
health and safety problems associated with vinyl chloride monomer, with
burning of P~C and with PVC plasticizers.
The butene-l polymers of this invention share th~ chemical
properties of conven-tional isotactic polybutylene. Additi~es relying
on chemical action, such as stabilizers again~t deterioration due to heat
or light, can be expected to have the same effectiveness in the polybutylene
1~
~ ~23~
of this ;nvention as in conventional polybutylene. The elastomeric poly-
butylene may also be mod;fied by addition of fillers or pigments.
Mechanical properties reported in Table 2 and in the following
examples were determined on compression molded specimens.
For the data in Table 2 and in Figures 2-5, the specimens were
about 25 mil thick, prepared by compression molding at 177C and aged 7
days at room temperature for conversion to crystal form I.
For the data in the following examples, specimens were prepared
by compression molding at 177-204C and subjected to accelerated aging
at room temperature for 10 minutes under 207 MPa (megaPascals) hydro-
static pressure ~or conversion to crystal form I.
For determination of ether extractables, a 2.5 gram film
specimen or a similar amount of polymer crumb or extruded pellets is
extracted in a Soxhlet extraction apparatus with 100 ml refluxing
diethyl ether for 3 hours.
Melt index is determined according to ASTM method D-1238,
Procedure A.
Tensile properties reported in the Examples are dekermined
according to ASTM nnethod D-638 on specimen about 0.10 inch thick and
0.24 inch wide. Tensile properties reported in Table 2 and in Figure 3
are determined according ~o ASTM method D-412.
Other properties are determined by the following standard
methods or variations thereof:
ASTM No.
Hardness, Shore A, 10 seconds D-678
Tear resistance D 624
Resilience D-94
a) using free Yibration torsion pendulunl.
The plot of stresS ~. strain of elastomers7 including our
elastomeric polybutylene, does not show the decrea$e of stress which
defines the yield point for true thermoplastic resins. Rather, the
curve shows a rise at an ~nltial slope, a continued rise at a lesser
Z3~S~
slope, and a final rise to the break point, which may again be at an
increased slope. The slope of the initial rise, expressed as psi, is
Young's modulus. The slope of the next7 more gradually rising part oF
the curve, is referred to as modulus of chain extension. The point at
which these two slope lines intersect is taken as defining the yield
stress.
The following examples illustrate the invention, but are not
to be considered as limiting it.
EXAMPLES
Pol~merization Method
Unless other~ise statedg polymerizations were carried out as
follows:
2000 ml of carefully dried butene-l (99.5% wt pure~ ~as charged
to a dry l-gallon autoclave reactor, equipped with a turbine type agitator.
A predetermined amount of hydrogen was charged to the reactor from a
calibrated pressure vessel. The reactor was heated to about 60C. With
the agitator operating at 1000 rpm, a freshly prepared slurry of all
three catalyst components was injected; the temperature of the agitated
reaction mixture was held at about 66C by heating or cooling, as
required. Reactions were typically run for 1 hour, resulting in a
solution of about 20% of polymer in butene-l. At the end of the run,
the reactor contents were transferred to a 15 liter vessel containing
water. This killed-the polymerization reaction, flashed off unreacted
monomer, precipita~ed the polymer as solid crumbs9 and transferred
catalyst residue into the water phase. The solid polymer was recovered,
chopped, inhibited with 0.1% wt of 2,6-di-tert butyl-4-methyl phenol and
dried in a vacuum oven.
EXAMPL.ES 1-5; COMPARATIVE EXAMPLES 1-3
Table 3 lists the results of a number of polymerizations
conducted as described above. The procatalysts (solid catqlyst com-
ponents) employed are designated as Follows:
Procata~st
_
A TiC14-McJCI2-Ethyl ben~oate (EB) composite
- 20 -
3~
B TiC13.1/3 AlC13 = commercial product
Stauffer catalyst AA
~ n the examples of the invention shown in Table 3, the pro-
catalyst was combined with the other components as a suspension in n-
heptane, containing 0.0~ mmol Ti/per ml. The cocatalyst was triethyl
aluminum ~TEA) employed as a 25%wt solution in n-heptane. The electron
donor was p-ethyl anisate (PEA3, employed as the neat liquid.
The amo~nts of the seYeral catalyst components employed in
each example are shown in Table 3.
10In the examples of the lnvention shown in Table 3, the catalyst
components were combined in a serum vial in a dry box, and injected into
the reactor. Unless otherwise stated, the -time elapsed while the
components were combined and injected into the reactor was no more than
three minutes.
The catalyst components were comblned as follows:
In Example 1, PEA was added to TEA at room temperature and
allowed to react for 10 minutes. This mixture and the procatalyst were
separately injected into the reactor.
In Examples 2-5 and comparative Example 1, all three catalyst
components were combined in a serum vial and the total catalyst mixture
injected into the reactor.
The order of combina~ion o~ the catalyst components was as
~ollows:
Example 2: TEA added to procatalysti
PEA added to the mixture.
Example 3: TEA added to procatalysti
mixture held for 30 minutes at room temperature;
PEA added to the mixture.
Example 4: Procatalyst added to TEA,
30mixture added to PEA.
Example 5: TEA added to procatal~st;
pEA added to mixture.
- 21 -
323~
The method of Example ~ is preferred for production of SSPB.
The method of Examples 2 and 5 is also satisfactory.
In Comparative Example 1, the order of addition was: TEA
added to PEA; mixture added to procatalyst. This resulted in a total
polymer having an excessively high content of ether soluble polymer.
Cor~parative Example 2 in Table 3 shows physical properties of
a commercial butene-l polymer, produced with a commercial TiC13 type
Ziegler/Natta catalyst.
Comparative Example 3 in Table 3 was carried out in laboratory
equipment of the same mode as that in Examples 1-5, but using a commercial
TiC13 procatalyst.
EXAMPLES 6-9
Additional illustrative examples were carried out in a 15
liter autoclave.
The catalys~ components were used as described above, that is~
the procatalyst was used as 0.03 mmol Ti per liter suspension in n-
heptane5 T~A as 25%wt solution in n-heptane~ and PEA added next. The
procedure was essentially as described above, except that larger amounts
were employed. The autoclave contained about 22.7 kg o-F carefully dried
20 butene-l~ 211 mmoles oF hydrogen was added. The catalyst mixture was
prepared by adding the procatalyst to the TEA and adding the resulting
suspension to the PEA in 5 ml n-heptane. The total catalyst mixture was
injected into the butene-l in the autoclave, which was at 60QC and hPld
at that temperature, with agitation, for one hour.
Product recovery was as described above.
Reagent proportions and product properties are shown in Table ~.
- 22 -
3~
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- 2~ -
23~
EXAMPLE 10
Elastomeric polybutylene prepared as in Example 6 was converted
by compression molding into a film of approximately 0.535 mm thickness.
The film had the following properties:
Melt index 1-0
Tensile strength at break, psi 3970
Elongation~ % 550
Young's modulus 6200
Shore hardness A, 10 sec. 83
Trouser tear, lbs/linear inch 1140
Hysteresis loss, % 59
- 25 -
