Note: Descriptions are shown in the official language in which they were submitted.
~t~
N()VE1 OXIDE COCATP,LYSTS
IN RI~aG OPENIN~; POL1~ERIZATION OF POI.YCYCLOOLEFINS
Ring opening polymerization with a
5 metathesis catalyst system o cycloolefins is well
known. The cycloolefins for purposes herein are
monomers which contain a norbornene group and
generally include norbornene compounds,
dicyclopentadiene, and similar polycycloolefin
monomers. The metathesis catalyst system includes a
catalyst and a cocatalyst. The catalyst i5 generally
selected from molybdenum and tungsten compounds
whereas the cocatalyst is selected from
organometallics such as alkylaluminums and
al~ylalumlnum halides.
U.S. patent 4,400,340 to Klosiewicz
describes a tungsten-containing catalyst such as
tungsten halide or tungsten oxyhalide. The catalyst
is suspended in a solvent to prevent it from
prepolymerizing a monomer to which is added an
alcoholic or a phenolic compound to facilitate
solubilization of the tungsten catalyst in the
monomer and a Lewis base or a chelant to prevent
premature polymeri~ation of the solution of the
tungsken compound and the monomer. Amount of the
tungsten compound is 0.1 t:o 0.7 mole per liter of
solvent. ~eight ratio of the tungsten compound to
the alcoholic or phenolic compound is 1:1 to 1:3, and
amount of th~ Lewis base or chelant is 1 to 5 moles
thereof per mole of the tungsten compound. Treatment
of the tungsten compound should be carried out in the
absence of moisture and air to prevent deactivation
of the tungsten compound catalyst. The catalyst must
be treated in the manner outlined above in order to
render it soluble in the cycloolefin monomer. The
cocatalyst in this patent is disclosed as being
5~
selected rom tetrabutyltin and alkylaluminum
compounds such as alkylaluminum dihalide or
dialkylaluminum halide where the alkyl group contains
1 to 1~ carbon atoms. The preferred alkyl group is
ethyl with diethylaluminum chloride being the most
preferred cocatalyst. These cocatalysts are
sensitive to air and moisture but are readily soluble
in the cycloolefin monomers.
U.S. patent 4,380,617 to Minchak et al
discloses metathesis catalyst systems for
polymerizing cycloolefins. The catalysts are defined
as organoammonium isopolymolybdates and
organoammonium isopolytungstates and these catalysts
are soluble in cycloolefins and are insensitive to
air and mois~ure. The cocatalysts in this patent are
similar to the cocatalysts disclosed in USP 4,400,340
and are generally selected from organometallics,
particularly alkylaluminum halides although in a less
preferred embodiment, other metals can ~e used in
place o~ aluminum such as lithium, magnesium, boron,
lead, zinc, tin, silicon, and germanium. Also,
metallic hydrides can be used in whole or in part for
the organometallic cocatalysts. Alkylaluminum and
the corresponding organom6~talllc compounds can also
be used as cocatalysts herein.
U.S. patent 4,426,502 discloses the use of
alko~yalkylaluminum halides or arylo~yalkylaluminum
halides as cocatalysts in metathesis catalyst systems
to polymerize cycloolefin monomers. These
cocatalysts are disclosed as especially useful in
conjunction with organoammonium isopolytungstate and
isopolymolybdate catalysts in polymerization of
cycloolefins or norbornene-type monom~rs. By
modifying the alkylaluminum halide cocatalysts to
alko~y or arylo~y alkylaluminum halides, the reducing
~56~
power of the cocatalysts is thus lowered to provide
adequate pot life for mi~ing various ingre~ients at
room temperature, and for work interruptions, before
initiation of polymerization and subsequent rapid
S polymerization.
SUMMARY
Polymerization of cycloolefins containing a
norbornene group is carried out in the presence of a
metathesis catalyst sy~tem composed of a metathesis
catalyst and a metathesis cocatalyst selected from
silo~alane, stanno~alane, germosalane, plumboxalane,
and alumino~ane cocatalysts. These cocatalysts are
generally soluble in inert solvents and in the
cycloolefins but are sensitive to o~ygen and moisture.
~ETAI~E~ ~ES~RI~TION O~ TH~ INVENTION
This invention resides in the use of
modified cocatalysts in the ring opening
polymerization of cycloolefins containing a
norbornene group. These cocatalysts ars soluble in
hydrocarbon solvents and in the cycloolefin monomers
which contain a norbornenel group. Metathesis
catalyst~, particularly th~ose selected from
mol~bdenum and tungsten compounds, together with
other ingredients, can be used in conjunction with
the modified cocatalysts described herein to
polymerize cyclooleEins containing a nor~ornene group
by solution or bulk polymerization.
Suitable cocatalysts herein are define~ by the
following formula:
(Rnk!O) aRb~lXc
where: ~ is silicon (Si), t;n (Sn), germanium SGe),
lead ~Pb), or aluminum ~Al);
3~
R and Rl are individually selected from
alkyl, alkylene, alkynyl, aryl, aralkyl, aral~ylene,
and aralkynyl groups containing l-lB carbon atoms,
preferably, R and Rl are individually selected from
i alkyl groups of 1 to 3 carbon atoms and phenyl
groups, however, when M is aluminum, one o~ th~ R
groups can be a halide;
X is selected from chlorine, fluorine,
bromine, or iodinA, but preferably chlorine;
a = 1/2 to 2 1/2, preferably 1 to 3/4
b = 1/4 to 2, preferably 1/2 to 1
c = 0 to 2, preferably 3/4 to 1 1/4
a t b ~ c = 3
n = 3 e~cept n is 2 when M is aluminum
Alcohols and phenols are described as
cocatalyst modifiers by the Minchak USP 4,426,502 in
polymerization of cycloolefins containing norbornene
group. These cocatalysts are defined as
~RO)aRlAlXC, where the various parameters are
de~ined above. Replacing the (OR) group with a
silo~y group (OSiR3) also generates an active
cocatalyst system in combination with a metathesis
catalyst component. The ~silo~alane~, dascribed
herein a~ suitable cocatalysts, can be prepared by
reacting an appropriate silyl alcohol with an alkyl
aluminum. A general reaction shown below for triethyl
aluminum and trimethysilyl alcohol demonstrates
preparation of a silosalane cocatalyst:
2 5 3 ~ 3)3SioH ~ (C2H5)2Al-~-Si(CH )
The resulting cocatalyst is diethylaluminum tri-
methylsilosalane. Alternatively, a triethylaluminum
can be reacted with octamethylcyclotetrasilane to
produce disthylaluminum dimethylethyl silo~alane.
;~0~
Other pref~rred cocatalysts include
trimethyl diethylsiloxalalle, dimethylethyl
diethylsilo~alane, methylethyl diethylsilo~alane, and
methyl isobutylsiloxalane.
A preparation of the silo~alanes is
described in USP 3,969,332, which is incorporated
herein by reference.
Similarly, stanno~alane cocatalysts can be
synthesized by reacting an alkyltin hydro~ide, such
as trimethyl or triphenyltin hydro~ide, with an
alkylaluminum, such as triethylaluminum, to produce a
stannosalane cocatalyst, in the following manner:
3 ( 2H5)3A~ (C2H5)2Al-o-snR3
The cocatalysts containing germanium or lead
are prepared in the same way as the si:Lo~alanes and
stanno~alanes. The cocatalysts containing another
alurninum atom, the alumino~anes, are prepared
differently by reacting an alkyl aluminum or an alkyl
aluminum halide, as follows:
C2H5 ~ C2H5
HOH ~ (C2H5)3Al ~ Al-O-Al
C2~5 C2H~
Ths new cocatalysts are particularly
efficient and allow for th~ us~ of halogen-free
cocatalysts in combination with metathesis catalysts.
The catalysts suitable herein are metathesis
catalysts which include halides, osyhalides, and
o~ides of molybdenum, tungsten, and tantalum
compounds, and organoammonium molybdates and
tungstates. The latter catalysts are insensitive to
oxygen and moisture in the environment.
-- 6
Preferred catalysts are organoammonium
isopolymolybdates and tungstates that are selected
from those defined as follows:
4 ~(2y-6~ y or ~R3NH~(2 6 ~
whsre O represents o~ygen; M repre~ents either
molybdenum or tungsten; ~ and y represent the number
of M and O atoms in the molecule based on the valence
of ~6 for molybd~num, ~6 or tungsten, and -2 for
o~ygen; and the R and Rl radicals can be same or
different and are selected from hydrogen, alkyl, and
alkylene groups each containing from 1 to 20 carbon
atoms, and cycloaliphatic groups each containing from
5 to 16 carbon atoms. All of t~e R and Rl radicals
cannot be hydrogens nor be small in the number of
carbon atom~ since such a condition will render the
mo].ecule essentially insoluble in hydrocarbons and
mo~t organic solvents. In a preferred embodiment,
the ~ radicals are selected from alkyl groups each
containing 1 to 18 carbon atoms wherein the sum of
carbon atoms on all the R radicals is from 20 to 72,
more preferably rom 25 to 48. In a preferred
embodiment, the Rl radica:L~ are selected from alkyl
groups each containing from 1 to 18 carbon atoms
wherein tha sum of carbon atoms on all of the Rl
radicals i~ ~rom lS to 54, more preferably from 21 to
42.
The norbornene-type monomers or cycloolefins
3Q that can be polymerized in accordance with the
process described herein are characterized by the
presence of the norbornene group, defined
structurally by the following formula I:
~ (I)
3~
Pursuant to this definition, suitable norbornene-type
monomers include substituted and unsubstituted
norbornenes, dicyclopentadienes,
dihydrodicyclopentadienes, trimers of
s cyclopentadiene, and tetracyclododecenes.
Contemplated herein are also lower alkyl norbornenes
and lower allcyl tetracyclododecenes wherein the lower
alkyl group contains 1 to about 6 carbon atoms.
Preferred monomers of the norhornene-type are those
defined by the following formulas II and III:
~ Rl ~ ~ ~ R3
(II)1 (III)
where R and R are independently selected from
hydrogen, alkyl groups of 1 to 20 carbon atoms, and
saturated and unsaturated hydrocarbon cyclic groups
formed by R and Rl to~ether with the two ring
carbon atoms connected thereto containing 4 to 7
carbon atoms. In a preferred embodiment, R and
are independently selected from hydrogen, alkyl
groups of 1 to 3 carbon atoms, and monounsaturated
hydrocarbon cyclic groups containing 5 carbon atoms,
the cyclic group being ormed by R and Rl as well
as by the two carbon atom~ connected to R and ~1
In reference to formula III, R2 and R3 are
independen~ly selected from hydrogen and alkyl groups
containing 1 to 20 carbon atoms, preferably 1 to 3
carbon atoms. E~amples of pref2rred monomers
referred to herein include dicyclopentadiene,
trimers and tetramers of cyclopentadiene:
methyltetracyclododecene; 2-norbornene and other
norbornene monomers such as 5-methyl-2-norbornene,
~0~
5,6-dimethyl-2-norbornene, 5-ethyl-2-norbornene,
5-butyl-2-norbornene, 5-hesyl-2-norbornene,
5-octyl-2-norbornene, and 5-dodecyl-2-norbornene;
vinyl norbornene, and ethylidene norbornene.
The monomer or mixture of norbornene-type
monomers can contain up to about 20% by weight
thereof of at least one other polymerizable monomer.
Such other polymerizable monomers are preferably
selected from monocycloolefins containing 4 to 12
carbon atoms, preferably 4 to 8 carbon a~oms,
e~amples of which include cyclobutene, cyclopentene,
cyclopentadiena, cycloheptene, cyclooctane,
1,5-cyclooctadiene, cyclodecene, cyclododecene,
cyclododecadiene, and cyclododecatriene~ As should
be apparent, cycloolefins that cannot be polymerized
hy ring opening, i.e., cyclohe~ene and derivatives
thereof, are not employed in the polymerization
process o this invention e~cept as solvents.
In solution pol~nerization, a hydrocarbon
reaction solvent is mised with a cycloolefin monom~r
or a misture thereof, with or without other
polymeri2able monomers, and the mi~ture of the
monomer and solvent is charged into a reactor. A
molecular weight modi~ier selected from nonconjugated
acyclic olefins is then charged into ~he reactor
ollowed by ths cocatalyst of the pres~nt invention
and at least one molybdate or tungstate compound
catalyst that is soluble in the cocatalyst and the
monomer~ The reaction can be conducted at 0 to
100C, preferably ~0 to 80C, or at ambient
temperature an~ carried out to completion in less
than two hour~ and shortstopped by addition of an
alcohol. The resulting product is a smooth, viscous
polymer cement. Upon removal of the solvent, the
polymer is ~ thermoplastic, solid material.
~0~
Suitable solvents for solution
poly~erization include aliphatic and cycloaliphatic
hydrocarbon solvents containing 4 to lO carbon atoms
such as pentane, hesane, heptane, octane,
cyclohe~ane, cyclohe~ene, cyclooctane and the like;
aromatic hydrocarbon solvents containing 6 to 14
carbon atoms which are liquid or easily liquified
such as benzene, toluene, naphthalene and the like;
and substituted hydrocarbons wherein the substituents
are inert, such as dichloromethane, chloro~orm,
chlorobenzene, dichlorobenzene, and the like.
Cyclohesane was found to be an escellent solvent.
The polymer need not be soluble in the solvent. The
solvent may be added at any point in the charging
procedure, but a portion, preferably 0.1 to 10% of
the total solvent, is used to dissolve the catalyst
and the remainder added before the catalyst
solution. Generally, 1/2 to 2 liters of solvent is
used per lO0 grams of monomer.
A solution polymerization activator may be
used but is not generally needed. Examples of
activator~ include water, methanol, ethanol,
isopropyl alcohol, benzyl alcohol, phenol, ~thyl
mercaptan, 2-chloroethanol, 1,3-dichloropropanol,
p-bromophenol, epichlorohydrin, ethylene 03ide,
cyclopentene-2-hydropero~ide, cumyl hydropero~ide,
tertiary butyl pero~ide, benzoyl pero~ide, and air or
ogygen. The activator may be employed in a ranye
from about 0 moles to ahout 3 moles per mole o~ the
cocatalyst, more preferably from about 0 to about l
mole per mole. The activator may be added at any
point in the charge procedure but it is more
preferably added last, or with the catalyst.
At least one nonconjugated acyclic olefin
can be used as a molecular weight modifier ha~ing at
-- 10 --
least one hydrogen on each double-bonded carbon atom
and containing 2 to 12 carbon atoms, more preerably
3 to 8 carbon atoms. E~amplas of suitable acyclic
olefins include l-olefins, 2 olefins, 3-olefins, and
nonconjugated triolefins. More preferably, the
nonconjugated acyclic olefin is selected from the
group consisting of l-olefins and 2-olefins
containing 3 to 8 carbon atom~ such as l-butene,
3-methyl-1-butene, 2-pentene, 4-methyl-2-pentene, and
the like. Compounds not having hydrogen atoms
substituted on double-bonded carbons are unreactive
in this invention.
The nonconjugated acyclic olefin can be used
in a molar ratio to total monomer charge of from
~5 about O.Q001 to about 1 mole per mole of the monomer
charge. The nonconjugated acyclic olefin can be
charged directly or in solution at any point in the
charge procedure, but it is more preferably charged
along with the monomers. When charged last, the
nonconjugated acyclic olefin is pre~erably charged
before reaction begins.
The monomer can be added at any point in the
charging procedure. Normally, however, the monomer,
solvent and nonconjugated acyclic olefin are added
first to the reactor vessel. These ingredients can
be added separat~ly or as a mi~ture o ingredients.
~e~t, th~ cocatalyst and the catalyst are added
separately, usually in the hydrocarbon solvent
deseribed above. The metathesis catalyst component
is added following addition of the cocatalyst
component although the order can be reversed.
Completion of the polymerization reaction is
indicated by the disappearance of the monomer in the
charge, as monitored by gas chromatography.
~3~
Bulk polymerization is carried out in
absence of a solvent by polymerizing cycloolefin
monomer or a mixture thereof by means of a metathesis
catalyst system wherein the catalyst component is a
molybdate or tu~gstata compound and the cocatalyst
component is a cocatalyst of this invention. The
monomer can be formed into a hard object in a single
step by means of reaction injection molding (RIM)
process wherein polymerization takes place in a
mold. E~amples of such objects include business
machine housings, furniture, window frames,
automobils and recreation vehicle parts, and the like.
Since the metathesis catalysts described
herein are soluble in a norbornene-type monomer or a
mi~ture thereo, the polymerization can be carried
out in absence of a solvent and other additives used
in solution polymerization. Since the cocatalysts
ar~ also soluble in such monomers, this, of course,
facilitates polymerization in bulk and makes it
possible to polymerize the norbornene-type monomer(s)
by reaction injection moltling process.
Ths catalysts, or mistures thereof, are
employed at a level of 0.01 to 50 millimoles of the
metal~s) per mole of totaL monomer(s), preferably 0.1
to 10 millimoles. The molar ratio of the cocatalyst
to the catalyst is not critical and can range from
about 200:1 or more to 1:10 , preferahly 10:1 to 2:1
of the matal(s) in the cocatalyst to the combined
amount of molybdenum or tungsten in the catalyst.
If the cocatalyst does not contain any
halide or if more halogen is desired, then a halogen
source is used. Suitable halogen source is selected
from halosilanes which are used in amount of 0.05 to
10 millimoles per mole of the norbornen~-type
monomer, prefera~ly 0.1 to 2 millimoles per mole of
5~
the monomer. 5pecific e~amples of preferred halogen
source are chlorosilanes such as
dimethylmonochlorosilane, dimethyldichlorosilane,
diphenyldichlorosilane, tetrachlorosilane, and the
S like. In bulk polymeriYation such as reaction
injection molding pro~sss, conversion of in e~cess of
95~, preferably in e~cess of 98~ can be attained,
measured by the thermal gravimetric procedure.
In order to further illustrate the invention
described herein, the following e~amples are
presented that demonstrate certain aspects of the
invention herein in greater dstail. It is to be
understood, however, that the e~amples are presented
for illustrative purposes and not in any sense are to
limit the scope of the invention herein, the scope of
which is defined by thc appended claims.
EXA~PLE 1
This e~ample demonstrates preparation of the
~ silo~alana cocatalyst which is ~elieved to have the
following formula:
(~2H5)0.5 [(C2~5)3si]l 5 AlCl
~5 The monomer mixtulre used her~in was 92.5
weight parts dicyclopentadliene ~DCPD) and 7.5 weight
parts ethylidene norbornene (E~
The preparation procedure involvPd
dissolving liquid triethyl silanol
[(C2H5)3SiOHl in a liquid DCPD/ENB monomer
mi~ture in a bottle under nitrogen to give a 1 molar
solution or solution(A~. Diethylaluminumchloride in
solid form was dissolved in the DCPD/ENB mcnomer
mi~ture to give a 0.5 molar solution or solutiontB).
Then, 0.9 ml of solution(A) was added with mixing to
~3~
- 13 -
25.4 ml of DCPD/ENB to make solution(c). Then, 1.2
ml of solution(s) was added with mixing to
solution(C) which resulted in a colorless solution of
the cocatalyst in the monomer mixture. The resul~ing
cocatalyst ~olution became warm on mi~ing and tha
reaction was accompanied by evolution of ethane gas.
EXAMPLE 2
This e~ample demonstrates preparation of the
stanno~alane cocatalyst which is believed to have the
following formula:
( 2H5)0.8 ~(C6H5)3sn]l 2 AlCl
The monomer mi~ture used herein was that of
dicyclopentadiene (DCPD~ and ethylidene norbornene
(E~B) in 92.5/7.5 weight ratio.
This cocatalyst was prepared in a similar
manner to that of the siloxalane cocatalyst of
E~a~ple 1 by dissolving solid triphenyltin hydroxide
in the DCPD/ENB mi~ture u,nder nitrogen to give a 1
molar solution or solution~A). Then, solid
di~thylaluminum chloride ~was also dissolved in the
~CPD/E~B monomer mi~ture to give a 0.5 molar solution
or solution(B). Then, 0.9 ml of solution(A) was
added to 25.4 mls of the DCPD/ENB monomer mi~ture to
yield ~olutiontC). Finally, 1.2 mls o~ solution(B)
was added with agitation to solution~C) and a
colorless cocatalyst solution in the monomer mi~ture
was obtained. The solution became warm on mi~ing and
the reaction was accompanied by evolution of ethane
gas.
- 14 -
XAMP~E 3
This e~ample demonstrates polymerization of
a monomer misture of dicyclopentadiene ~DCPD) and
ethylidene norbornene ~ENB) in weight ratio of
92.5~7.5 with a ilosalane cocatalyst of this
invention.
Three polymerizations were conducted with
triethylsilanol, designated below as (SiOH), silicon
tetrachloride (SiC14), tris(tridecyl)ammonium
molybdate designated as AM below which has the
formula t~t~ l3H27)H]3 M826;
diethylaluminum chloride (DEAC~. Order of addition
of th~ materials and amounts in milliliters (mls~ is
given below:
Order of Addition
and Material ~ B C
DCPD/E~B 12.7 25.4 25.4
SiOH, 1.0M 0.333 0.84 0.84
DEAC, 0.5~ 0.6 1.2 1.2
SiCl~, 0.25M 0.6 1.2 1.2
AM, 0.1N 0.75 1.5 1.5
Wt. Ratio SiOH/DEAC 1.1/1 1.4/1 1.4/1
Ths materials given above in solution form,
w~re prepared in the monomer mi~ture of DCPD~ENB, in
which they are soluble.
It should ba apparent that the first three
steps noted abo~e involve preparation of the
cocatalyst of this in~ention.
The material~ were added in the given order
to 7 oz. bottles provided wit}l injection caps~ The
bottles were vigorously agitated after each addition
and each addition was made in quick succession.
3S Bottl~ A was allowed to remain at room temperature
~5~
while bottle B was allowed to stand at room
temperature or about 10 minutes and then was placed
in an oven maintained at 140C.
The contents of bottle A polymerized
immediately into a dark brown ma~s. Contents of
bottle B polymerized within a few minutes after being
placed in the 140C oven.
~ottle C was allowed to stand at amhient
t~mperature for 3 hours after which time no reaction
had occurred. The bottle was then placed in an oven
at 140C after which polymerization to a solid mass
occurred within a few minutes. This e~ampla serves
to illustrate the e~cellent pot-life properties of
the catalyst mi~tures of the current invention.
EX~MP~E_4
This example demonstrates polymerization of
the monomer mi~ture of dicyclopentadiene (DCPD) and
ethylidene norbornene (EN~) in weight ratio of
92.5/7.5 using tha stannosalane cocatalyst of this
invention.
Procadure involve~d the addition of 25.4 mls
of the DCPD/ENB monomer mi~ture to a bottle followed
by 0.72 ml of a 1 molar solution of triphenyltin
hydro~ide ~(C~H5)3SnOH], and 1.2 mls of a 0.5
molar solution of diethylaluminum chloride (DEAC).
This procedure is the same as that for pr2paration of
the novel cocatalyst of this invention.
Preparation of the cocatalyst was followed
by addition of 102 mls of 0.25M solution of silicon
tetrachloride and 1.5 mls of a O.lN solution of
tri(tridecyl)ammonium molybdate catalyst. Weight
ratio of the triphenyltin hydro~ide to DEAC wa~ 1.2/l.
Upon addition of the amine molybdate
catalyst, solution polymerized immediately into a
solid mass of a dark brown color.
3 aJ fi ~ ~3
-- 16 --
EXAPIPLE 5
This e~ampls demonstrates preparation of the
alumino2ane catalyst and polymerization therewith of
a monomer mi~ture of dicyclopentadiene (DCPD) and
ethylidene norbornene ~EN~) in weight ratio of
92.5~7.5. Preparation of the cocatalyst was under
nitrogen.
To 28.59 of the monomer mi~ture of DCPD and
ENB in a reaction bottle was added 6.0mg (0.33m mol)
o~ distilled water. The resulting solution was
shal~en to ensure good mi~ing and it was then added to
a 0.5 molar solution of diethylaluminum chloride
(DEAC) in the monomer misture. The resulting
aluminosane cocatalyst is believed to have the
~5 following structural formula:
Cl Cl
\ Al-O-Al
C2H5 ~ C~H5
(diethyldichlorodialuminumo~ane)
To the above solution in the reaction bottle
was added 1.25 ml (0.31m mol) of a 0.25 molar
solution of silicon tetrachloride in the monomer
mi~tur~. On addition o 1.6 ml. o the 0.1 molar
amine molybdate catalyst solution in the monomer
mi~ture with shaking, polymerization in the reaction
bottle ensued almost immediately. Polymerization was
evident from the color change to dark brown of the
polymerization mi~ture, a high esotherm, and
thickening of the contents of the reaction bottle.
The oontents of the bottle was rapidly converted to a
solid mass.
6fi~
When the above polymerization was run with
unmodified DEAC, what was obtained was encapsulation
of the catalyst and incompleke conversion of the
monomers ~
