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Description  |
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This invention relates to the cationic polymerization of monomers under
conditions to exercize control of molecular weight, and to produce low
molecular weight polymers (oligomers) having a relatively low degree of
polymerization (e.g. 5 to 30 mer units) and to produce such polymers in
high yield and at high conversion and having a low polydispersity.
Certain terms used herein are defined as follows.
Monomers, unless the context indicates otherwise, means a simple molecule,
but permissibly a low molecular weight oligomer, which is capable of
cationic polymerization.
Catalyst refers to a substance, typified by a Lewis acid, e.g. BF.sub.3,
which is capable of catalyzing cationic polymerization.
Preinitiator precursor refers to an organic compound which forms, with a
catalyst, an adduct or complex (hereinafter called an adduct), such adduct
being a preinitiator.
Preinitiator refers to an adduct of an organic compound with a catalyst
which results, when brought into contact with a monomer, in the production
of an initiating species which starts (initiates) the formation of a
chain.
Initiator is the species so formed.
The term "living polymer" is often used herein to indicate the positively
charged (cationic) chain resulting from reaction of an initiator with
monomer.
The invention will first be described with reference to the polymerization
of cyclic ethers as monomers and diols as preinitiator precursors. The
invention will then be described in more general terms.
Ordinarily when a cyclic ether such as an epoxide or an oxetane is
polymerized, the polymer has a very high average molecular weight unless
the reaction is quenched at low conversion, and the product is a mixture
having high polydispersity. If the reaction is caused to go to completion,
the product predominates in high molecular weight polymers and/or consists
of a mixture of polymers of low, medium and high molecular weight.
There is a need for lower polymers (oligomers) of cyclic ethers having well
defined molecular weights with low polydispersity and there is a need for
a method of producing such polymers.
Heretofore attempts have been reported in the literature of methods
purporting to achieve this object. Notable among this literature is a
paper by Hammond, Hooper and Robertson in Journal of Polymer Science,
Volume 9, pages 265-279 (1971). Hammond and co-workers used propylene
oxide, tetrahydrofuran (THF) 1,2-butylene oxide, n-propyl glycidyl ether
and mixtures of certain of these cyclic oxides. Such monomers were
homo-polymerized or copolymerized and polymerizations were also carried
out in the presence of a small amount of 1,4-butanediol. Boron trifluoride
etherate was used as the catalyst. Claims are made that the diol was
inserted in the polymer molecules and that it facilitated control of
polymer molecular weight.
I have found that, upon using 1,4-butanediol and boron trifluoride etherate
in ratios suggested by Hammond, either polymerization does not occur or
there is no control over molecular weight in the sense of producing, at
high conversion and in high yield, a narrow range of polymers having
predictable molecular weight and low polydispersity. This is particularly
true where one desires to use such a diol in stoichiometric rather than in
catalytic proportions to produce a low molecular weight polymer (an
oligomer) such as
HO--R--O--R.sub.1 ].sub.n
where R represents the organic radical of the diol, R.sub.1 represents the
organic radical of the cyclic ether and n has a value not greatly
exceeding 10 or 30 rather than, say, 50 to 100 or greater.
It is an object of the present invention to provide a method of conducting
cationic polymerization of monomers under conditions to produce, in high
yield and at high conversion, low molecular weight polymers of low
polydispersity.
It is another object of the invention to provide low molecular weight/low
polydispersity polymers from monomers which are amenable to cationic
polymerization.
The above and other objects will be apparent from the ensuing description
and the appended claims.
These and other objects, as will appear, are accomplished in accordance
with the present invention by conducting cationic polymerization of a
monomer or a mixture of monomers in the presence of a stoichiometric
quantity of a preinitiator precursor. By "stoichiometric quantity" is
meant a quantity considerably greater than would be needed for catalysis.
In this manner a polymeric product of low degree at polymerization, e.g. 5
to 30, is produced which may be represented by the formula
I--M].sub.n.sup.+
where I represents an organic group derived from a preinitiator precursor
(which in the reaction mixture is initially in the form of an adduct with
a catalyst, such adduct being the preinitiator for the reaction); M
represents a group derived from the monomer, and n is an integer from, for
example, 5 to 30. The subscript n is, of course, an average number but
since the product has a low polydispersity, e.g. 1.1 to 1.2, n is close to
the molar ratio of the monomer to the preinitiator precursor.
As will appear, the preinitiator precursor leading to I, the monomer
leading to M and the catalyst which forms an adduct with the preinitiator
precursor may be chosen from large lists of compounds. The requirements
for these reactants and catalysts are as follows:
The monomer is one which is susceptible to cationic polymerization.
The preinitiator precursor is a compound which is capable of forming an
adduct with a catalyst, such adduct being capable of forming with a
molecule of monomer an initiator
I--M--.sup.+
which then adds further monomer units to form a chain
I--M].sub.n.sup.+
the number of such chains being proportional to (and very nearly equal to)
the number of molecules of preinitiator precursor.
The catalyst is effective to catalyse cationic polymerization of the
monomer and of forming a preinitiator with the preinitiator precursor.
The principles of the present invention will now be illustrated by the
polymerization of cyclic ethers under control of a diol and using boron
trifluoride as a catalyst. The particular cyclic ether is the bis(azido
methyl) oxetane 3 of Example 5 below and the particular diol is
1,4-butanediol (BDO). These were reacted in molar proportions of 16 mols
of the oxetane to one mol of BDO. The catalyst was BF.sub.3, which may be
mixed first with BDO to form the preinitiator or it may be used in the
form of its etherate with diethylether, in which event the BDO displaces
the ether to form the preinitiator. In either case a BDO/BF.sub.3 adduct
is formed which is the preinitiator for the overall reaction
##STR1##
where n is close to 16. Provided conditions are proper, e.g. the mol ratio
of BDO to BF.sub.3 is approximately 1 mol of BDO to 2 moles of BF.sub.3
(i.e., about one mole of BF.sub.3 for each hydroxyl of the BDO), a high
conversion of the oxetane to polymer occurs, the molecular weight is close
to the calculated theoretical molecular weight of 2778 and the
polydispersity is low, e.g. about 1.1 to 1.2. Example 6 and Table V below
provide experimental details.
In place of BDO other preinitiator precursors such as those of Table I
below may be used. In place of the bis(azidomethyl) oxetane, other
monomers may be used, such as those described below under the heading
"Monomers Other Than Cyclic Ethers". In place of BF.sub.3 other catalysts
of Table II may be used. General criteria for selection of a preinitiator
precursor, monomer and catalyst are as follows. Each will be selected in
accordance with the definitions stated above. Note will also be taken of
the fact that not all preinitiator precursors of Table I will be operative
with all monomers and not all catalysts of Table II will be operative with
all preinitiator precursors. Thus if diethylether is the preinitiator
precursor of choice and if the reaction is that of its adduct with
BF.sub.3 with tetrahydrofuran (THF), BF.sub.3 may not (and in my
experience it does not) function. This does not mean that the BF.sub.3
/diethylether adduct will not function as a preinitiator for some choice
of monomer. Trial and error, coupled with experience and knowledge of the
state of the art, will suffice, for a given monomer, to make a proper
choice of a preinitiator precursor and a catalyst.
Further guidelines are as follows. If the preinitiator precursor is
polyfunctional, e.g. if it is a diol such as BDO, it may be necessary to
employ approximately one mol of catalyst for each functional group of the
preinitiator precursor to suppress the tendency at free functional groups
to terminate a chain prematurely. Also it may be desirable to avoid a
large excess of catalyst relatively to the preinitiator precursor to avoid
uncontrolled polymerization caused by the free (excess) catalyst.
An illustrative example of choice of a preinitiator precursor is provided
by BF.sub.3 /etherate. As noted, although such an adduct will not, in my
experience, result in controlled polymerization of certain monomers, if
the ether is displaced by another species of preinitiator precursor such
as BDO which binds more strongly to BF.sub.3, an effective preinitiator is
provided. Therefore, if a species from Table I is considered, it can be
determined whether it will displace diethylether from its adduct with
BF.sub.3. If it will do so, then it is more likely to form a preinitiator
with a catalyst from Table III.
General Procedure as Applied to Alcohols as Preinitiator Precursors and
Cyclic Ethers as Monomers
The following general description, although directed to alcohols as
preinitiator precursors and to cyclic ethers as monomers, is applicable to
other preinitiator precursors and to other monomers.
(1) The alcohol and the cyclic ether are mixed in the desired molar
proportions of 1 mol of alcohol to n mols of monomer, n being, for example
5 to 30. The purpose is to produce predominantly a living polymer
R--O--R.sub.1 ].sub.n.sup.+
If a mixture of cyclic ethers such as
O R.sub.1 and O R.sub.2
is used the polymer will be an atactic polymer with random distribution of
the bivalent groups
--O--R.sub.1 -- and --O--R.sub.2 --
unless one of the ethers is much more reactive than the other, in which
case one group may predominate in the first segment of the polymer (closer
to R) and the other may predominate in the more remote segment of the
polymer.
It may be preferred to add the catalyst first to the alcohol and allow time
for an alcohol-catalyst adduct (a preinitiator) to form. [See Example
6(c).] A stock of alcohol-catalyst adduct may be prepared and used as
needed. The reaction is usually carried out at relatively low temperature,
e.g. -60.degree. to 50.degree. C. The alcohol and cyclic ether are mixed
in stoichiometric proportions to result in the desired polymer
R--O--R.sub.1 ].sub.n.sup.+
where n is the molar ratio of cyclic ether to alcohol. The time required
for complete or substantially complete conversion will depend upon the
reactants and the catalyst, e.g. three hours is some cases, 24 hours in
others. Certain cyclic ethers, e.g. THF, are less reactive and require
more time while others such as those of Examples 1 to 7 are more reactive
and require less time. Also the reactivity of the alcohol is a factor.
The reaction is carried out in the absence of any substance which would
terminate the polymerization reaction. For example, water should be
excluded.
When conversion is complete or has been carried to the desired extent
(usually complete conversion), the resulting living polymer (a cation) may
be treated in various ways such as the following.
Termination. This may be accomplished by adding water to produce a terminal
hydroxyl group; by adding ammonia or an amine to produce a terminal amino
group, e.g. NH.sub.2 (from ammonia) or --NHCH.sub.3 (from methyl amine);
by adding a carboxylic acid or its salt to produce a terminal ester group,
e.g. an acetate group, CH.sub.3 COO--, by adding acetic acid; by adding a
mineral acid such as HCl, H.sub.2 SO.sub.4 or HF to produce a terminal
chlorine, sulfate or fluorine atom or group. In general any terminating
species known to terminate a living cationic polymer may be used.
Production of Block Polymers
The living polymer
R--O--R.sub.1 ].sub.n.sup.+
is capable of further polymerization with another cyclic ether species
O R.sub.2
Hence alternating blocks of --O--R.sub.1, and --O--R.sub.2 may be produced
by carrying the first polymerization step to completion, then adding a
calculated amount of the second species of ether, etc. to produce an AB
type of block polymer:
R--O--R.sub.1 ].sub.a [O--R.sub.2 ].sub.b [O--R.sub.1 ].sub.c [O--R.sub.2
].sub.d - - -
where the subscripts a, b, c, d--indicate the number of mer units in each
block. For example, with THF and oxetane as the cyclic ethers and
1,4-butanediol (BDO) as the alcohol, a polymer
HO--(CH.sub.2).sub.4 [O--(CH.sub.2).sub.4 ].sub.a [O(CH.sub.2).sub.3
].sub.b - - -
may be produced and may be terminated with water to produce a diol with
alternating blocks derived from THF and oxetane. The subscripts a and b
may, for example, be 5, 10 or 20 and may be the same or different.
An example of a useful hard (glassy) block polymer which can be used in a
thermoplastic elastomer formulation having a T.sub.m (melting point
transition temperature) of about 82.degree. C. can be prepared by
initiating polymerization of 3,3-bis(azidomethyl) oxetane.
##STR2##
with BDO/BF.sub.3 ; then when the conversion is complete adding THF, etc.
to produce a living polymer containing alternating blocks of mer units
derived from the oxetane and THF. The resulting polymer is
R--A--B--A--B - - - X
where A represents a block derived from the oxetane and B represents a
block derived from THF. R represents the group derived from BDO and X
represents a terminating atom or group. This polymer will have useful
properties due to the fact that the A blocks have a crystalline (glassy)
character while the B blocks are of amorphous (rubbery), character. At
temperatures below T.sub.m estimated at about 82.degree. C., the polymer
will behave as a highly physically crosslinked elastomer but at higher
temperatures it can be molded or extruded to the desired shape, thus
behaving as a linear polymer. By reason of the stepwise, controlled
addition of A and B blocks the degree of crosslinking, i.e. the
crosslinking density, can be controlled. "Crosslinking" as used in this
context refers to the forces which cause the A blocks to cluster together
and it does not refer to covalent crosslinking.
Copolymerization. Where the polymerization is initiated using a diol such
as BDO and the reaction is quenched with water, a diol results such as
HO--R--O R.sub.1 ].sub.n OH
This diol may be employed in any type of polymerization in which diols
participate, e.g. in copolymerization with isocyanates to produce
polyurethanes and in copolymerization with polycarboxylic acids to produce
polyesters.
Specific examples of such copolymers are copolymers of
HO(CH.sub.2).sub.4 --O--(CH.sub.2).sub.4 --.sub.n OH
(n=e.g., 5 to 10) with tolylene diisocyanate, and copolymers of the same
diol with succinic acid to produce, respectively, a polyurethane and a
polyester.
Crosslinking and Control of Crosslinking Density
Under this heading the term "crosslinking" is used to indicate covalent
crosslinking between polymer chains caused by polyfunctional groups. Such
poly (tri- or higher) functional groups may be present in the preinitiator
precursor (e.g. triols and tetrols) or in the monomer (e.g. tri-carboxylic
acids) or both.
The polymers of the invention are particularly advantageous in connection
with control of crosslinking density. Suppose that a polymer is prepared
from, for example, THF or oxetane using the following preinitiator
precursors and the following quenching agents.
______________________________________
Preinitiator Quenching Functionality of
Precursor Agent Resulting Polymer
______________________________________
(1) ROH (a mono- ROH 0
hydric alcohol)
(2) Same as (1) H.sub.2 O 1
(3) HOROH (a diol)
ROH (monohydric
1
alcohol)
(4) Same as (3) H.sub.2 O 2
(5) A triol ROH 2
(6) A triol H.sub.2 O 3
(7) A tetrol ROH [Same as (1)]
3
(8) A tetrol H.sub.2 O 4
______________________________________
The functionalities of the resulting polymers will be as indicated in the
third column. It is apparent that a polymer can be produced having the
desired functionality. If a polymer such as produced according to schemes
(4) or (5) is prepared and is copolymerized with a difunctional monomer
such as a diisocyanate OCN--R'--NCO or a dicarboxylic acid HOOC--R'--COOH,
a linear copolymer will result. If a trifunctional polymer such as is
produced according to schemes (6) or (7) is copolymerized with such a
difunctional species as a diisocyanate or a dicarboxylic acid, there will
be (by reason of the trifunctionality of the polymer) a crosslinking
density which may be regarded as 3, representing the trifunctionality of
the polymer. By mixing a difunctional polymer such as produced by scheme
(4) or (5) with a trifunctional polymer such as produced by scheme (6) or
(7), any degree of crosslinking can be obtained ranging from a little more
than zero to a crosslinking density of 3. This crosslinking density can be
controlled with exactitude.
Other functional groups than OH may, of course, be used such as amino
groups introduced as terminators by quenching with ammonia or an amine and
will give rise, when copolymerized, to crosslinking densities according to
the proportions of difunctional (e.g. one hydroxyl and one amino group per
polymer molecule) and trifunctional (e.g. two hydroxyl and one amino group
per molecule).
Production of Polymers from di-cations
If the alcohol is a diol in which the hydroxyls are remote from one
another, e.g. HO--R--OH where R is a long chain such as --(CH.sub.2).sub.8
--, its adduct with a catalyst such as BF.sub.3 may be a dication .sup.+
R.sup.+, e.g. in the case given above,
.sup.+CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 CH.sub.2
--CH.sub.2 --CH.sub.2.sup..+-.
The ends will act with two molecules or monomer to initiate polymerization
and will effect molecular weight control to produce a living, di-cationic
polymer such as
.sup.+ --R.sub.1 O].sub.n (CH.sub.2).sub.8 --OR.sub.1 ].sub.n.sup.+
This living di-cationic polymer may be terminated as in the case of the
monocationic living polymers discussed above. Also this di-cationic living
polymer may be chain extended by adding a highly polar monomer such as the
bisazido monomer of Example 5, then terminating the double chain with
water. The resulting polymer may be represented as
HO--R.sub.1 --R.sub.2 --R.sub.1 --OH
wherein the R.sub.1 's are derived from the bisazido monomer and R.sub.2 is
derived from the dicationic living polymer.
Another type of dication which is amenable to this type of synthesis is
described in Smith and Huben U.S. Pat. No. 3,436,359 and British Pat. No.
1,120,304 and is discussed by P. Dreyfuss in a paper in J. Macromol.
Science--Chem. A-7 (7), pp. 1361-74 (1973) entitled "Survey of Recent
Progress in Polymerization Studies of Selected Heterocycles". This
dication together with its counter ions is described by Dreyfuss as having
the structure
##STR3##
This dication can be employed with a suitable catalyst, e.g. boron
trifluoride, to cause polymerization of a cyclic ether to produce a
di-cationic living polymer
.sup.+ [R.sub.1 --O].sub.n (CH.sub.2).sub.4 O--(CH.sub.2).sub.4
O--CH.sub.2).sub.4 [OR.sub.1 ].sub.n.sup.+
where R.sub.1 is derived from the cyclic ether, e.g. THF. This polymer can
then be end capped with highly polar groups such as the azido monomer of
Example 5 and it can be treated in any of the ways described herein.
Termination by an Anionic Living Polymer. In addition to terminating the
cationic living polymer by small groups or atoms as described above, the
living cationic polymers may be reacted with a living anionic polymer,
e.g. polystyrene living polymer.
In the following Tables I and II suggested preinitiator precursors (Table
I) and catalysts (Table II) are set forth.
Table I Preinitiator Precursors
Monohydric alcohols
Methyl, ethyl and normal and branched chain propyl, butyl, pentyl, hexyl
and C.sub.7 to C.sub.20 alkanols
Cycloaliphatic alcohols such as cyclohexanol and its ring substituted alkyl
derivatives
Aralkyl alcohols such as benzyl alcohol, phenyl ethyl alcohol, di- and
tri-phenyl carbinols
Furfuryl alcohol
Polyhydric alcohols
Ethylene glycol, propylene glycol, 1,3-propanediol, glycerol,
pentaerythritol, 1,4-butanediol; also the diols substituted by functional
groups as in the specific examples
Ethers
Dimethyl, diethyl, di-n and isopropyl ethers; mixed ethers such as methyl
ethyl ether;
Cyclic ethers where not used as monomers, e.g. difficultly polymerizable
substituted tetrahydrofurans such as 2-methyl THF
Carboxylic acids
Formic, acetic, propionic, butyric and other straight and branched chain
acids of formula C.sub.n H.sub.2n+1 COOH; aliphatic dicarboxylic acids
such as succinic acid
Aromatic carboxylic acids such as benzoic; o, n and p toluic acids; o, m
and p chlorobenzoic acids, phthalic acid, salicylic acid, etc.
Sulfonic acids
Any of the above acids wherein SO.sub.3 H replaces COOH
Esters
Methyl, ethyl, straight and branched chain C.sub.3 to C.sub.20 alkyl esters
of any of the carboxylic and sulfonic acids mentioned above
Carbonic esters such as diethyl and dimethyl carbonates
Ureas
Urea, methylol urea, dimethylol urea, other N-substituted ureas
##STR4##
where R, R.sub.1, R.sub.2 and R.sub.3 are selected from H, C.sub.1 to
C.sub.12 alkyl, phenyl, benzyl, cyclohexyl, etc., at least one R being an
essentially hydrocarbon group
Amides
Amides of any of the carboxylic acids mentioned above including N-mono- and
di-substituted amides
##STR5##
wherein R represents an organic group such as described above and in
connection with carboxylic acids, R.sub.1 and R.sub.2 are selected from H,
C.sub.1 to C.sub.20 alkyl, phenyl, benzyl, cyclohexyl, etc.; any of the
amides listed in Morrison and Boyd, "Organic Chemistry", 3d ed., page 660,
published by Allyn and Bacon, Inc. of Boston
Isocyanates
RNCO where R=C.sub.1 to C.sub.10 straight and branched chain alkyl, aryl
such as phenyl and the tolyl isocyanates
Amines
C.sub.1 to C.sub.10 straight and branched chain alkylamines; aromatic
amines, e.g. aniline; aliphatic cyclic amines, e.g. piperidine; and
R--NR.sub.1 R.sub.2 wherein R is an organic group and R.sub.1 and R.sub.2
are selected from H, straight and branched chain C.sub.1 to C.sub.10
alkyl, aryl (phenyl, o, m and p tolyl) and aralkyl, e.g. benzyl;
cycloaliphatic amines, etc.; any of the amines listed in Morrison and
Boyd, op. cit., page 729
Acid anhydrides
Anhydrides of any of the carboxylic and sulfonic acids mentioned above; any
of those listed in Morrison and Boyd, op. cit., page 660
Ketones
RCOR.sub.1 where R and R.sub.1 are C.sub.1 to C.sub.10 alkyl, phenyl,
benzyl, cyclohexyl; any listed in Morrison and Boyd, op. cit., page 620
Aldehydes
RCHO where R is as defined under "Ketones" above; also any listed in
Morrison and Boyd, op. cit., page 620
Analogues of the above
Sulfur, selenium and tellurium analogues of the above may be used, such as:
Thiols, e.g. C.sub.n H.sub.2n+1 SH where n=1 to 10
Thioethers, e.g. RS--R.sub.1, R and R.sub.1 defined as under the heading
"Ketones"
Thioacids
##STR6##
where one or both of X and Y are sulfur, the other, if not sulfur, being
oxygen, R being an organic group as under the heading "Carboxylic Acids"
Thioureas--As under the heading "Ureas", doubly bonded O being substituted
by S
Thioamides--As under the heading "Amides", doubly bonded O being
substituted by S
Thioesters--As in "Thioacids" esterified as under "Esters"
Table II Catalysts
Acids generally which are known to be effective for cationic polymerization
of tetrahydrofuran and other cyclic ethers, e.g. strong acids and super
acids such as
FSO.sub.3 H
ClSO.sub.3 H
HClO
HIO
CF.sub.3 SO.sub.3 H
Lewis acids such as
AlCl.sub.3
BF.sub.3
TiCl.sub.4
ZnI.sub.2
SiF.sub.4
SbF.sub.5
PF.sub.5
AsF.sub.5
SbU.sub.5
In general any substance known to catalyze cationic polymerization of
monomers may be used. Many are described in scientific journals, in texts
and in patent literature, e.g. British Pat. No. 1,120,304 to Minnesota
Mining and Manufacturing Company and literature referred to in such
patent.
Solvents
Any solvent known to be compatible with cationic polymerization as to
solubility of reactants, stability of the cation formed on initiation,
etc. may be used. Usually it will be a polar aprotic solvent. Examples
are:
Methylene chloride
Methyl chloride
Ethylene chloride, ClCH.sub.2 --CH.sub.2 Cl
Nitromethane
Chlorinated and fluorinated aromatic hydrocarbons such as chlorobenzene and
fluorobenzene
Monomers Other Than Cyclic Oxides
The cationic polymerization of cyclic ethers, which is described in detail
herein, is the best known type of cationic polymerization. The cyclic
ethers which are susceptible to this type of polymerization are those
having three, four and five membered rings, which are characterized by
ring strain. Some of these monomers are difficult or impossible to
homopolymerize, e.g. 2-methyl THF. Other classes of monomers susceptible
to cationic polymerization include certain vinyl compounds, e.g.
isobutylene. Despite the paucity of non-cyclic ether monomers which are
susceptible to cationic polymerization, there are such monomers. The
method of molecular weight control herein described is applicable to such
non-cyclic ether monomers. Reference may be had to texts and journal
articles on the subject. One such source is Vol. 37 of Advances in Polymer
Science, entitled "Cationic Ring--Opening Polymerization of Heterocyclic
Monomers", edited by S. Penczek, P. Kubisa and K. Matyjaszewski, published
in 1980 by Springer-Verlag. Cyclic oxides, such as 1,3-dioxalanes having
two oxygen atoms in the ring are discussed in this work and may be used as
monomers for purposes of the present invention.
The following specific examples will serve further to illustrate the
practice and advantages of the invention.
Examples 1 to 3
3-(2,2-dinitropropoxymethyl)-3-methyl oxetane (1) and
2-(2,2-dinitropropyl)-butane-1,4-diol (2) were used as the monomers and
boron trifluoride etherate (BF.sub.3.Et.sub.2 O) was used as catalyst.
Formulas of 1 and 2 are:
##STR7##
Homopolymerization of 1 using the same catalyst and under varying reaction
times and conditions consistently formed polymers of molecular weight
6600. These polymers had a high polydispersity.
By adding stoichiometric amounts of 2 molecular weights could be controlled
and predicted and the major fraction of the reaction product in each
instance had a low polydispersity. This resulted where stoichiometric
ratios of 1 to 2 were 4:1, 6:1 and 8:1. Calculated molecular weights were
1157, 1625 and 2093, respectively, while observed molecular weights were
1200, 1600 and 2000, respectively. The experimental procedure was as
follows:
To a flame dried resin flask was added a known weight of cyclic ether as a
20% w/w solution in dried methylene chloride. A calculated weight of the
diol was then introduced and the solution stirred at room temperature for
10 minutes. A calculated weight of freshly distilled BF.sub.3.Et.sub.2 O
was then added and the reaction run for 6 hours. The polymerization was
quenched with a volume of saturated aqueous sodium chloride solution equal
to the volume of catalyst added. The organic layer was removed, washed
with 10% sodium bicarbonate solution and dried over magnesium sulfate.
Example 4 Determination of Mechanism
The diol, represented as (A), may serve as a dication with oxetane
molecules (represented as O) adding to both ends, thus
- - - O--O--A--O--O - - - (1)
Alternatively the initiating cation may be a mono-cation resulting in the
structure
A--O--O - - - (2)
The oxetane 1 and the diol 2 were mixed in molar proportions of 6 to 1.
Reaction was carried out as in Example 1 using the same proportion of
catalyst to diol except that the reaction was quenched with an excess
(i.e. 2 molar proportions) of the diol. If polymer (1) should result the
major product would be
A--O--O--O--A--O--O--O--A (1a)
but if polymer (2) should result, the major product would be
A--O--O--O--O--O--O--A (2a)
The major product was determined by gpc, confirmed by nmr analysis for
methylene groups, to be 2(a).
If steps are taken to start with a di-cation as described above, the
polymer (1a ) will result. However with initiating species such as the
lower alcohols 2 and 1,4-butanediol, a mono-cation is formed and the
polymer (2a) results.
Example 5 Polymerization of Diol 2 with 3,3-Bis(azidomethyl)-oxetane (3)
The formula of 3 is
##STR8##
It was mixed with 2 and with the same catalyst as in Examples 1 to 4 in
molar proportions of one mol of the diol 2 and ten moles of oxetane 3 and
with the same catalyst to diol ratio as in Examples 1 to 4. Solvent,
reaction time and temperature were as in Examples 1 to 4. The mixture was
quenched with water. Calculated molecular weight of the polymer, assumed
to be
A--O--O--O--O--O--O--O--O--O--O--OH
(A representing the diol residue, O except for terminal OH representing the
group resulting from the oxetane) is 1901. Upon workup as in Examples 1 to
4, 80% of a polymer having a molecular weight of 2200 was recovered. Its
polydispersity was 1.1 to 1.2.
Examples 6(a) to 6(f)
The reactants were 1,4-butane diol (4) and the oxetane 3. The procedure was
as in Examples 1 to 4 except that in Example 6(c) the diol was added first
to the catalyst which was dissolved in a small quantity of methylene
dichloride and time (about 2 hours at 20.degree. C.) was allowed for an
adduct of catalyst (BF.sub.3) and diol to form.
The diol and catalyst were used in different molar ratios and the oxetane
and diol were used in the molar ratio of 16:1, calculated to produce a
polymer of molecular weight 2778. The reaction was allowed to run for
three hours at room temperature and was then quenched with water. The
results are set forth in Table III below. Figures in the first three
headed columns are mol fractions.
TABLE III
______________________________________
Catalyst Observed
Diol (BF.sub.3 Etherate)
Oxetane Mol. Wt.
Yield, %
______________________________________
6(a) 2 1 16 -- 0
6(b) 1 1 16 -- 0
6(c) 1 1.5 16 2900 63
6(d) 1 2 16 2800 68
6(e) 1 3 16 3700 77
6(f) 1 4 16 5000 83
______________________________________
Commenting upon Table III, no polymerization occurred in 6(a) and 6(b). The
oxetane 3 is known to be very reactive, more so than the cyclic ethers of
Hammond; hence it was concluded that the lack of reactivity at molar
ratios of diol to catalyst in 6(a) and 6(b) is indicative of the need, in
the case of a less reactive diol such as 1,4-butanediol, to control its
mol ratio to the catalyst. A 2:1 and a 1:1 mol ratio of diol to catalyst
were ineffective. A large excess of catalyst as in 6(e) and 6(f) resulted
in loss of molecular weight control presumed to be due to the large excess
catalyst acting to cause uncontrolled polymerization. A moderate
excess.sup.1 of catalyst to diol is indicated. Such close control over
alcohol/catalyst mol ratio need not be exercised with more reactive
alcohols such as those of Examples 1 to 5. However a large excess of
catalyst is preferably avoided.
1. Excess refers to catalyst in excess of one mol per hydroxyl group; that
is, in excess of two mols of BF.sub.3 per mol of diol.
Yields in Table I were measured on purified product. Polydispersities of
product in Examples 6(c) and 6(d) were about 1.1. In Examples 6(e) and
6(f) polydispersities were much higher.
Example 7
The diol 2 and the oxetane 5 [3-(2-fluoro-2,2-dinitroethoxymethyl)-3-methyl
oxetane]
##STR9##
were reacted in varying molar ratios, using boron trifluoride etherate as
catalyst under conditions as in Examples 1-4 above and the reaction
mixtures were quenched with water. The catalyst was used in the amount of
6.6% by weight based on total monomer. Results are set forth in Table VI.
TABLE VI
______________________________________
Mols of Mols of Observed Calculated
Oxetane 5 Diol 2 Mol. Wt. Mol. Wt.
______________________________________
4 1 1200 1157
6 1 1600 1625
8 1 2000 2093
______________________________________
Conversions were 100% and yields were 80-90%. The products had low
polydispersity, about 1.1-1.2.
In the course of work done in connection with this invention, certain novel
monomers were synthesized. Two such novel monomers, Monomers I and II
##STR10##
namely 3-azidomethyl THF (I) and 3,4-bisazidomethyl THF (II) were prepared
as follows.
Monomer I. Furan-3-methanol was reacted with dihydropyran to produce the
tetrahydropyranyl ether. This is a conventional step carried out to
protect the hydroxyl group. Other vinyl ethers may be used in place of
dihydropyran. The ether was reduced by hydrogen at 1100 psi at 120.degree.
C. using a commercially available 56% nickel catalyst. The resulting
product was subjected to hydrolysis in acid solution to produce the
alcohol III
##STR11##
which is believed to be a new compound. The corresponding tosylate was
prepared by treatment of III with tosyl chloride and the tosylate was
reacted with sodium azide in DMF at 95.degree. C. for 24 hours.
##STR12##
Monomer I was a colorless liquid which, on distillation formed a 1:1 molar
complex with DMF which boils at 78.degree. C./15 mm.
Monomer II. Furan-3,4-dimethanol was reduced to 3,4-dimethylol THF which in
turn was converted to the ditosylate, such steps being carried out as in
U.S. Pat. No. 3,855,237. This ditosylate was treated with sodium azide in
DMF at 95.degree. C. for 24 hours.
##STR13##
Monomer II was a colorless liquid boiling at 68.degree. C./0.01 mm.
The structures of I and II were confirmed by infra red, nmr and chemical
analysis.
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