CA1253291A - Process for removal of low molecular weight fractions from vinyl pyridine polymers and copolymers - Google Patents

Abstract

Process for Removal of Low Molecular Weight Fractions From Vinyl Pyridine Polymers and Copolymers Abstract Disclosed is a process for separating high molecular weight polymers of alkenyl pyridine compounds having a pKa of about 2-10 from mixtures thereof with monomers and low molecular weight frac-tions comprising dispersing the mixture in a solution of an acid having a pKa of between about 10 and about 6 at a temperature of between about 50°C and about 70°C, to thereby dissolve the monomers and low molecular weight fractions while maintaining the high molecular weight polymers as a solid, and sub-sequently separating the solid high molecular weight polymer from the solution of monomers and low molecular weight fractions in aqueous acid.

Description

lZS3Z5~L

Descrip'ion Process for Removal of Low Molecular Weigh' ~ractions Prom Vinyl Pyridine Polymer.s and Copolymers Technical Field This inven'ion rela'es to a process for separa~ing high molecular weigh' polymers of alkenyl pyridine compounds from mixtures thereof with monomers and oligomers.

Background of 'he Inven ion For many end-use appIications, it is desirable ~o process high molecular weigh' polymers having low residual monomer concen'ra'ions and low levels of oligomers. The conven'ional me'hods used for rel~oval of unpolymerized monomer from polymer dispersions, la'exes, or suspensions generally depend on s'eam distillation, degasification, or vacuum s'ripping processes. Examples of 'hese conven'ional me'hods are described in liLera~ure references such as:
~a) Ger. Offen. 2, 635, 478; (b) FrO Demande 2, 302, 3~6; (c) B.P. 1468490; and (d) Chem. Eng. Prog., Aug., 1981, pp 55-59. Although 'hese methods are generally effective for removal of vola'ile monomers, they are generally ineffective for removal of ~he nonvolatile low molecular weight componen's from 'he polymer. The presen inven'ion is concerned with a ~ethod for 'he concurren~ removal of residual monomer and low molecular weight componen~s from vinyl pyridine polymers and copolymers.
The increased desirabili'y and use of polymers for pharmaceutical, biomedical, and agriculLural applica-'ions has resulted in the need for efficient and satisfactory methods for removing low molecular weigh' fractions and unpolymerized monomers from 'he polymer 12S3~

mass. Polymers ~hat have been adequately separa.ed from residual monomers and low molecular weight com-ponents are expected to provide greater product uniformity, more consistent physical and chemical properties, and improved s:orage and shelf-life capability. This invention demonstra~es a novel process for the simultaneous removal of residual monomers and low molecular weight components from a vinyl pyridine polymer or copolymer by continuous extraction using dilute aqueous acids.

Disclosure of Invention _ According to the present invention, there is provided a process for separating high molecular weight polymers and copolymers of alkenyl pyridine compounds from mix'ures thereof wi'h monomers and low molecular weight fractions of the compounds comprising dispersing the mixture in a solution of an acid at a tempera~ure of between about 50C. and about 70C., to thereby di~solve the monomers and low molecular weigh' fractions while maintaining 'he high molecular weight polymers as a solid. Subsequently, the solid high molecular weigh' polymer is separated from 'he solu-tion of monomers and low molecular weight fractions in aqueous acid.
The alkenyl pyridine compounds which may be used in accordance with this invention have a p~a of about ~-10 and have the general formula H C=C/ 1 ~ R2 \N~
wherein Rl is hydrogen or alkyl having 1-4 carbon a~oms, and R2 is hydrogen, alkyl having 1-4 carbon atoms, cycloalkyl having up to 8 carbon ~L~S3Z~

atoms, phenyl or alkyl substituted phenyl having up to 12 carbon atoms, or a halogen.

The polymer and copolymers of alkenyl pyridine s compounds contain at leas' 50 weight 4 of polymer units derived from a' least one monomer having the structure shown above. The polymer, however, may con-tain up to abou~ 50 weight percent of comonomer derived from o'her copolymerizable monomers such as, for example, styrene, vinyl acetate or methyl me'hacrylate.
Polymers made by emulsion polymeri~ation techniques normally contain small amounts of monomer and low molecular weight polymers. Normally, 'hese monomers and low molecular weight polymers account for less than about 3% of the total weight of polymers and monomers.
-In practicing the process, a mixture of the monomer and polymer (high and low molecular weigh') is first dispersed in an aqueous solution of an acid a' a temperature between about 50C. and 70C., preferably about 55-65~C. The concentra~ion is adjusted such 'hat the solids content ~monomer and polymer) is ; between about 10~ and about 50% by weight. The monomer and low molecular weight polymer dissolves in this acid solution, leaving the higher molecular weight polymers as the only solid. This solid polymer is easily separated from ~he solu'ion by conven'ional techniques well known .o those skilled in the art, such as for example, by filtering.
The acids useful for the purpose of this inven'ion include both organic acids and inorganic acids. Acids suitable are those with pKa values between -10 and 6.
The preferred acids have pKa values between -3 and 3s abou. 5. Suitable acids include the following:

~3~1 Acid pKa a' 25C.
Hydrobromic acid -9 Sulfuric acid -3 Nitric acid -1.64 Pyrophosphoric acid 1.0 Ortho-phosphorous acid 1.8 Ortho-phosphoric acid 2.1 Chloroacetic acid 2.~7 Formic acid 3.75 Ace'ic acid 4.75 Butyric acid 4.8Z
Carbonic acid 6.37 Boric acid 9.14 The pXa is most frequently used to express the ex'ent of dissociation, or the strength of acids, and bases. pKa is defined as pKa = -logl0 Ka where Ka is the thermodynamic equilibrium acidi'y constant. Clearly, the s~ronger the acid, the slnaller the value of pKa; conversely, for bases, the larger .he pKa, .he stronger is the base. Unless otherwise specified, pKa as used herein is determined a' 25C.
- Typically, high molecular weight copolymers of pyridinium vinyl monomers and selecte~ vinyl comonomers are prepared either by batch or continuous emulsion polymerization at 65C. using a water soluble free radical initiator such as potassium persulfate.
The polymer is coagulated by addition of saturated sodium chloride solution, heated to 70C., and collected by filtration. The polymer is redispersed in a fresh portion of water, heated to 70C., and again filtered. This process i5 repeated two addi-tional times. The polymer filter cake is then trans-ferred tQ an extraction vessel and extracted with 1%

i~S3~9~

aqueous acid while maintai~ing the extraction tempera-ture at 50-60C. The polymer mass may be maintained in a fixed-bed and extracted or, more desirably, be dispersed as a fluid-bed alld continuously extracted.
Analysis of the polymer before and after extraction shows a remarkable reduction in the concentration of residual, unpolymerized monomer, and also Lhe low molecular weight fraction of the polymer. Recovery of purified, high molecular weight polymer from the ex'raction equipment at the conclusion of the purifi~
cation step is about g7~.
The following examples are submitted for a better understanding of the invention.

This example demonstrates the effect of ex'rac.ion time on the removal of residual vinyl monomer and low molecular weight fractions from a high molecular weight copolymer of 5-vinyl-2-picoline. The extrac-'ion is performed using a fixed-bed continuous extrac~or charged wi.h 1% aqueous acetic acid. The extraction temperature is maintained at 60-~5C.

C
.,, g u~ '1 ~ 0 r-- ~ ~ rr~
U ~ ~ ~ o ~ _.
Q~ ~ ~ O
E ~ CL
oC l _~
:~ C
_l ~
~ In .,.
U~
~:; Q~ I
C~
~J D r~
. Q ~ o~
. n u~
U~

E
Q

o o . ~ O C~
c r ~ QO ~ 1-- U
O O
C>
O ~ _l ~1 U O
E
o o _ --~ o ~: C
. ~ ' O S:) U .,~
s ~ ' V I
_ 3~
~ . .. ~ ...
'15 ~ E n E E :~
_~ ~ U
E~ ~
c ~ 0~ Q.
C: ."
O
,~
cr L~
v J~
b~
Ia I I
~C C~

~l2S3Z5~1 This example illustrates the important effect of extraction temperature on the efficient removal of residual, unpolymerized monomers, and low molecular weight products from a high molecular weight copolymer of 5-vinyl-2-picoline. The continuous extraction is performed using a fixed-fed ex.ractor for 24 hrs.
using 1% aqueous ace~ic acid a' the selected tempera-tures shown below.

l;~S32~i~

_~
tO O
Ll ~ ~ O r~
E ~ ~ o ~ r~
O l o _~1~
:E: ~
.,_, _~

3 u~
U~
~: a) o 1~ o ~, ~ ~ O o o r~
~ o o o o J U~
Cq ~ V V V

E
Q

..~, O O o ~ a:~
_t .. o 3 o~
O ~: c U~
5: 0 ~1 .u O t) .

_I
~ .~ ~.
t~ L
O a, C:-- JJ O
~ o .~ E o J~ ~
c v I
~ ~ ~1 J ~ ~
X ~ ~ U C,~ V
0 o o " , . o o e u~ u ~
~ _ O O I I --' E~ u~ o o O O
o O ~:
~ ,_ *

3~

_ 9 This example shows the effect of extractan' volume on the removal of residual monomer and low molecular weight components from a h.igh molecular weigh' polymer of 5-vinyl-2-picoline. One-hundred grams of the polymer is placed in a fluid-bed extraction vessel.
The polymer is extracted w:ith 1.25% aqueous acetic acid a' 70-80C. by continuous counter-curren' wash-ing. The following data sllow the rapid removal of residual monomer and low molecular weigh' componen's from the polymer as a function of extraction volume.

- ~S3~

~O Q~
~ C
.d E _~
O O
O ~ ~D ~ O
~: ~ n O c~
I ~ ~ V
_~
fa ~ _I
d C
U) .
a~
D l In CL

~- o . ~ o ~ ~ ~ a~ u~
_I C ~ ~P er ~ _ O O
S

O ~

.,.~
_. ~ o ~ ~ JJ O
o E ~ o .,,_, E
V I
ta E t::

L~ :3 d X O ~ :~
~ ~ ~ .
U~ O C:~ O O --~
~_ O O OO O O
O ~ 1`~

12S329~

The extraction process described in Example 3 is repeated using another polymer sample having different s'arting levels of low mo].ecular weight components and S residual monomer. The following data show the effec.
of extractant volume on removal of residual monomer and low molecular weight fraction from the polymer.

S3'~91 ~n ~
.,., _, o o C O
O ,~ o o .n ~ ~ o ~E ~ ~ ~ ~D 0 U~
a , ~
~3 ~
0 . , X ~
In C~
. ~j O ~D o a~
~ o C o _- o o ,, _, 3 la O L~

_I
O
._, `
~ C:~
~ ~ ~- o O E ~ o .,, _ E
V I
fo E C
..
J -- ~ JJ
XO
li~ ~ 1 ~ .
O Q o o ,_, _ t~ o oo o O
In o U~

:~2S3~9:~

EXAMPLE_ This example demonstrates the u'ility of using dilute aqueous sulfuric acid as an extractant for removal of residual monomer and low molecular weight fraction from a copolymer of 5-vinyl-2-picoline (5~22) and styrene ~ST). One-hundred grams of the copolymer is extrac'ed using the fluid-bed continuous extractor. The ex.ractant is 0.01% sulfuric acid at 70-80C. The extractant Eeed pump ra`e is main.ained a' 21 mL/min.

:l~Z5329~

U~ O !~
~ Q~ D o O lr~ o a~ I cl ~ o r~
5 ~I Q
O l o --l -_ ...~
ro ~
U~
Q~
~: C!~
o~ ~r o o o . ~ ~
:~ Cl ~ V V
U~

E
3 ~
o O ~ ~ o 4 o O
_ ~
O C:
~: O _~
...

i a _i ._ O
s~ ~
.,~ ~, ~1 _ o~ o C ~ J O
O E t~ o .,, _ E~ ~
V I
E ~:
L~ ~ .r~
x o ~ 3 J
D~ O o O o _~
_ o O ~ o O
~ O u ~~:
o ~ ~ ~ I_ l~S3%~ ~

This example compares the effect of extraction of the vinyl pyridine copolymer using 0.01~ sulfuric acid and also with an equal voLume of distilled water. The polymer is extracted using the same equipment and procedure described in Example Nos. 3 and 5. The following results show that extraction of the polymer with distilled wa.er is useful for reducing the residual monomer level, but is not effective for removing the 19w mol. wt. frac.ions from the polymer.

~S3~

.

_l O
o o ~ o~
ta ,, ~. ~ ~ C~
C ~ o æ c ~ i U~
~ C
~n a~ o o ~ D~
~ ~- V V
~ ."
.

E
3 C~, .~ C) o o _~ ~ o o 0 O ~ r~
:E: O
~1 3 ~
O U
a~

~, a) J O
al E
O ~n ~ ~ O
C ~ .,~ o O E h --~ O
~rl ~ ~ ~ dP
J- ~ ~
C) Q~ ~ U~ C~ V I
~1 E
o _~ ~ ~
O C ~ ~ 3 :~ .,1 E E
o o _~
~5 0 0 0 ~S32~1 Unless otherwise specified, all parts, percentages, ratios, e'c., are by weigh', and molecular weight is on a weight average basis~
The invention has been described in detail with particular reference to preferred embodiments .hereof, bu' it will be understood t:hat variations and modifi-cations can be effected within the spirit and scope of the invention.

Claims (5)

We Claim:

1. Process for separating relatively high molecular weight polymers of alkenyl pyridine compounds having a pKa of about 2-10 and of the formula wherein R1 is hydrogen or alkyl having 1-4 carbon atoms, and R2 is hydrogen, alkyl having 1-4 carbon atoms, cycloalkyl having up to 8 carbon atoms, phenyl or alkyl substituted phenyl having up to 12 carbon atoms, or halogen, from mixtures thereof with monomers and relatively low molecular weight fractions of said compounds comprising dispersing said mixture in a solution of an acid having a pKa of between about -10 and about 6 at a concentration of between about 10% and about 50%
solids and at a temperature of between about 50°C.
and about 80°C., to thereby dissolve said monomers and polymers having a molecular weight of less than about 2000 g/mole while maintaining said high molecular weight polymers as a solid, and subsequently separating said solid high molecular weight polymer from the solution.

2. Process according to Claim 1 wherein said compounds are dispersed in said solution of an acid at a temperature of about 55-65°C.

3. Process according to Claim 1 wherein said acids have a pKa of about -3 and 5.

4. Process according to Claim 1 wherein said alkenyl pyridine compound is a polymer or copolymer of vinyl pyridine.

5. Process for separating relatively high molecular weight polymers or copolymers of vinyl pyridine from mixtures thereof with monomers and relatively low molecular weight fractions thereof comprising dispersing said mixture in a solution of an acid having a pKa of between about -3 and about 5 at a concentration of between about 10% and about 50%
solids and at a temperature of between about 55°C.
and about 65°C., to thereby dissolve said monomers and polymers having a molecular weight of less than about 2000 g/mole while maintaining said high molecular weight polymers as a solid, and subsequently separating said solid relatively high molecular weight polymer from the solution.