(5j) Chain-transfer agents for emulsion polymerization and polymer products produced therewith.
In the emulsion polymerization of acrylic monomers, an improvement comprises the use of 3-mercaptopropionate esters as chain-transfer agents. Novel polymers are pro- duced by the inventive polymerization process.
This i n v e n t i o n r e l a t e s to emulsion p o l y m e r i z a t i o n p r o c e s s e s . In one a s p e c t , t h i s i n v e n t i o n r e l a t e s to c h a i n - t r a n s f e r agents for use i n
emulsion p o l y m e r i z a t i o n p r o c e s s e s . In ano the r a s p e c t , th i s i n v e n t i o n
r e l a t e s to a c r y l i c polymers produced by emulsion p o l y m e r i z a t i o n . In y e t ano the r a spec t t h i s i n v e n t i o n r e l a t e s to the c o n t r o l of polymer m o l e c u l a r
weight and mo lecu la r weight d i s t r i b u t i o n in the emulsion p o l y m e r i z a t i o n
p r o c e s s e s .
Background
The emulsion p o l y m e r i z a t i o n p rocess enjoys wide usage in t h e
chemical i n d u s t r y . Many monomers can be po lymer i zed using t h i s
t e c h n o l o g y . The method combines the economy and s a f e t y of an aqueous r e a c t i o n medium with a rapid but r e a d i l y c o n t r o l l e d p o l y m e r i z a t i o n t o
p rov ide high mo lecu la r weight polymers in e x c e l l e n t y i e l d . Among t h e
advan tages of emulsion p o l y m e r i z a t i o n are reduced f i r e hazard , h i g h
r e a c t i o n r a t e , p r o d u c t i o n of high mo lecu la r weight polymer r e l a t i v e
s i m p l i c i t y of the t e chno logy and p r o d u c t i o n of low v i s c o s i t y l a t e x e s .
Shor tcomings of emulsion p o l y m e r i z a t i o n s i nc lude the r e l a t i v e d i f f i c u l t y
in s e p a r a t i n g the polymer p roduc t and c o n t a m i n a t i o n of the p o l y m e r
p roduc t with r e s i d u a l e m u l s i f i e r .
C h a i n - t r a n s f e r agents can be and are added to e m u l s i o n
p o l y m e r i z a t i o n systems in order to improve f i n a l polymer p r o p e r t i e s .
C h a i n - t r a n s f e r agents are g e n e r a l l y used in f ree r a d i c a l p o l y m e r i z a t i o n s
and f u n c t i o n as mo lecu la r weight m o d i f i e r s . The c h a i n - t r a n s f e r a g e n t
r e a c t s with a growing polymer chain to form a "dead" polymer with t h e
c o n c u r r e n t fo rma t ion of a new cen te r for polymer growth. The c h a i n
t r a n s f e r mechanism for mercaptan c o n t a i n i n g c h a i n - t r a n s f e r agents can be
d e p i c t e d as f o l l o w s :
Among those polymer p r o p e r t i e s which i t is d e s i r a b l e to c o n t r o l
are polymer mo lecu la r weight d i s t r i b u t i o n , f r e e z e - t h a w s t a b i l i t y of t h e
l a t e x and polymer p a r t i c l e s i ze . A nar row m o l e c u l a r weight d i s t r i b u t i o n
r e f e r s to a more n e a r l y homogeneous polymer sample than a s i m i l a r p o l y m e r blend having a broad mo lecu la r weight d i s t r i b u t i o n . For many a p p l i c a t i o n s , polymers having a narrow m o l e c u l a r weight d i s t r i b u t i o n i s
d e s i r a b l e .
F r e e z e - t h a w s t a b i l i t y r e f e r s to the a b i l i t y of a l a t ex t o
remain as an emulsion even when exposed to h e a t - c o o l t e m p e r a t u r e c y c l e s .
Since emuls ion l a t e x e s produced from a c r y l i c monomers are s u s c e p t i b l e t o
breakdown of the emuls ion when exposed to t e m p e r a t u r e extremes over a
pe r iod of t ime, emuls ion l a t e x e s which are s t a b l e to exposure t o
f r e e z e - t h a w c o n d i t i o n s are d e s i r a b l e in t h a t breakdown of the e m u l s i o n
with r e s u l t a n t s e t t l i n g of the polymer would be a v o i d e d .
For c e r t a i n a p p l i c a t i o n s , such as for example in coa t i ngs and
a d h e s i v e s , a polymer l a t e x having a r e l a t i v e l y uniform p a r t i c l e s i z e
would be d e s i r a b l e . It is g e n e r a l l y obse rved , however, t ha t a c r y l i c
polymers produced by emuls ion p o l y m e r i z a t i o n have a r a t h e r broad p a r t i c l e
s ize d i s t r i b u t i o n , and thus are not well s u i t e d for the p r o d u c t i o n o f
homogeneous coa t ings or the l i k e .
I t is a c o n t i n u i n g goal of those in the emulsion p o l y m e r i z a t i o n
ar t to d i s c o v e r new c h a i n - t r a n s f e r agents which are e f f e c t i v e f o r
mo lecu l a r weight m o d i f i c a t i o n and which p rov ide polymer p roduc t s w i t h
improved p h y s i c a l p r o p e r t i e s .
Objec t s of the I n v e n t i o n
An ob j ec t of t h i s i n v e n t i o n , t h e r e f o r e , is a p rocess for t h e
c o n t r o l of mo lecu la r weight and molecu la r weight d i s t r i b u t i o n of a c r y l i c
polymers produced by emuls ion p o l y m e r i z a t i o n p r o c e s s e s .
Another o b j e c t of th is i n v e n t i o n is novel a c r y l i c p o l y m e r s
having improved p h y s i c a l p r o p e r t i e s .
These and o ther o b j e c t s of the i nven t ion wi l l become a p p a r e n t from the d i s c l o s u r e and claims p rov ided h e r e i n .
S ta tement of the I n v e n t i o n
In accordance with the p r e s e n t i n v e n t i o n , we have d i s c o v e r e d
tha t at l e a s t one compound s e l e c t e d from the group c o n s i s t i n g o f
3 - m e r c a p t o p r o p i o n a t e e s t e r s , 6 - m e r c a p t o m e t h y l - 2 - m e t h y l - 2 - o c t a n o l , and
2 - p h e n y l - 1 - m e r c a p t o - 2 - e t h a n o l are e f f e c t i v e c h a i n - t r a n s f e r agents i n
emuls ion p o l y m e r i z a t i o n of a c r y l i c monomers. By the p r a c t i c e of t h e
p r e s e n t i n v e n t i o n , a c r y l i c polymers having reduced molecu la r weights a s
well as narrow molecu la r weight d i s t r i b u t i o n s are o b t a i n e d . A d d i t i o n a l
b e n e f i c i a l p h y s i c a l p r o p e r t i e s of the novel polymers produced i n
accordance with the p r e sen t i n v e n t i o n wi l l be d e t a i l e d in the d i s c u s s i o n
which f o l l o w s .
De ta i l D e s c r i p t i o n of the I n v e n t i o n
In accordance with the p r e s e n t i n v e n t i o n , an e m u l s i o n
p o l y m e r i z a t i o n p rocess is p rov ided compris ing p o l y m e r i z i n g at l e a s t one
a c r y l i c monomer in aqueous medium under p o l y m e r i z a t i o n c o n d i t i o n s in t h e
p re sence of a water so lub le f r e e - r a d i c a l i n i t i a t o r , an e m u l s i f i e r and a t
l e a s t one compound s e l e c t e d from the group c o n s i s t i n g o f
3 - m e r c a p t o p r o p i o n a t e e s t e r s , 6 - m e r c a p t o m e t h y l - 2 - m e t h y l - 2 - o c t a n o l , and
2 - p h e n y l - l - m e r c a p t o - 2 - e t h a n o l as c h a i n - t r a n s f e r a g e n t .
In accordance with a n o t h e r embodiment of the p r e s e n t i n v e n t i o n ,
novel compos i t i ons are p rov ided compr i s ing a polymer of at l e a s t one
a c r y l i c monomer, wherein the polymer has a molecu la r weight in the r ange of 500 to 100,000, and a h e t e r o g e n e i t y index not exceeding about 3 . 0 ;
p r e f e r a b l y the h e t e r o g e n e i t y index wi l l not exceed about 2.0; and most
p r e f e r a b l y the h e t e r o g e n e i t y index wi l l not exceed about 1.7. I n
a d d i t i o n , at l e a s t a p o r t i o n of the i n d i v i d u a l molecules of the po lymer
are t e r m i n a t e d by the r a d i c a l :
wherein R is a carbon c o n t a i n i n g r a d i c a l having 1-20 carbon atoms. As
employed h e r e i n , the term "carbon c o n t a i n i n g r a d i c a l s " is in tended t o
inc lude carbon r a d i c a l s c o n t a i n i n g he te roa tom s u b s t i t u t i o n , by such
he te roa toms as N, S, 0, P, Si and B.
A c r y l i c monomers contempla ted to be wi th in the scope of t h e
p r e s e n t i n v e n t i o n are those which conform to the f o r m u l a :
wherein each of R' , R2, R3 and R4 are i n d e p e n d e n t l y s e l e c t e d f r o m
hydrogen and carbon c o n t a i n i n g r a d i c a l s having 1 - 2 0 c a r b o n a t o m s .
Examples of monomers which conform to the above formula i nc lude e t h y l
a c r y l a t e , methyl a c r y l a t e , methyl m e t h a c r y l a t e , butyl a c r y l a t e , 2 - e t h y l
hexyl a c r y l a t e , h y d r o x y e t h y l a c r y l a t e , and the l i k e , and mix tu res of any two or more t h e r e o f .
When a c o p o l y m e r i z a t i o n is c a r r i e d out, i . e . , at l e a s t one
comonomer is employed along with the monomer, the comonomer(s) can be
p r e s e n t in any d e s i r e d amount, i . e . , from t r ace amounts up to a
s u b s t a n t i a l excess with r e s p e c t to the monomer employed. For example, i t
is sometimes d e s i r e d in order to achieve d e s i r a b l e p r o p e r t i e s in t h e
polymer p r o d u c t t h a t a termonomer be employed in the p o l y m e r i z a t i o n
p r o c e s s . Thus, u s e f u l polymer p roduc t s are ob ta ined when m e t h a c r y l i c
acid is used as a termonomer in admixture with e thyl a c r y l a t e and m e t h y l
m e t h a c r y l a t e .
When a termonomer is employed, i t is g e n e r a l l y added i n
r e l a t i v e l y small amounts, e . g . , about 0.01 to 5 wt % based on the t o t a l
weight of monomer ( i n c l u d i n g comonomer and termonomer) c h a r g e d .
P r e f e r a b l y , the termonomer is charged in amounts ranging from about 0 . 1
to 2 wt %, based on the t o t a l weight of monomer c h a r g e d .
Those of s k i l l in the ar t r ecogn ize tha t a d d i t i o n a l comonomers
can be employed, so t ha t copolymers compris ing mixtures of t h r e e , four o r
more monomers s a t i s f y i n g the above d e f i n i t i o n are w i th in t h e
c o n t e m p l a t i o n of the p r e s e n t i n v e n t i o n .
S u i t a b l e f ree r a d i c a l i n i t i a t o r s are well known in the a r t and
can be r e a d i l y chosen by the a r t i s a n . Exemplary m a t e r i a l s i n c l u d e w a t e r
so lub le i n i t i a t o r s , such as, for example, peroxygen compounds, e s p e c i a l l y
i n o r g a n i c p e r s u l f a t e compounds such as for example ammonium p e r s u l f a t e ,
po ta s s ium p e r s u l f a t e and sodium p e r s u l f a t e ; pe rox ides such as for example
hydrogen p e r o x i d e ; o rgan ic h y d r o p e r o x i d e s , such as for example cumene
h y d r o p e r o x i d e , t - b u t y l h y d r o p e r o x i d e , a c e t y l p e r o x i d e , l a u r o y l p e r o x i d e ;
p e r a c e t i c acid and p e r b e n z o i c acid; redox i n i t i a t o r s where in a w a t e r
so lub le reducing agent such as a f e r rous compound promotes t h e
decompos i t ion of p e r o x i d e s , p e r s u l f a t e s and the l i k e ; as well as o t h e r
free r a d i c a l p roduc ing m a t e r i a l s such as 2 , 2 ' - a z o b i s i s o b u t y r o n i t r i l e ,
4 , 4 ' - a z o b i s ( 4 - c y a n o v a l e r i c a c i d ) , and the l i k e .
A wide v a r i e t y of e m u l s i f i e r s are u s e f u l in the p r a c t i c e of t h e
p r e s e n t i n v e n t i o n , as can r e a d i l y be de te rmined by one of s k i l l in t h e
a r t . S u i t a b l e e m u l s i f y i n g agents inc lude c a t i o n i c , a n i o n i c or n o n i o n i c
e m u l s i f i e r s or d e t e r g e n t s c u s t o m a r i l y used in emulsion p o l y m e r i z a t i o n s .
R e p r e s e n t a t i v e types of e m u l s i f i e r s are the a lky l a ry l s u l f o n a t e s , a l k a l i
metal a lkyl s u l f a t e s , s u l f o n a t e d a lky l e s t e r s , s a l t s of high m o l e c u l a r
f a t t y ac ids , amine soaps, a l k a l i n e metal s a l t s of r o s i n a c i d s , e t h y l e n e
oxide condensa tes of long chain f a t t y a c i d s , a l c o h o l s or m e r c a p t a n s .
The c h a i n - t r a n s f e r agents employed in the p r a c t i c e of t h e
p r e s e n t i n v e n t i o n are s e l e c t e d from the group c o n s i s t i n g o f
3 - m e r c a p t o p r o p i o n a t e e s t e r s which conform to the f o r m u l a :
wherein R is a carbon c o n t a i n i n g r a d i c a l having 1-20 carbon a t o m s ,
6 - m e r c a p t o m e t h y l - 2 - m e t h y l - 2 - o c t a n o l and 2 - p h e n y l - l - m e r c a p t o - 2 - e t h a n o l .
Examples of m e r c a p t o p r o p i o n a t e s which conform to the above f o r m u l a
i n c l u d e
m e t h y l - 3 - m e r c a p t o p r o p i o n a t e ,
b u t y l - 3 - m e r c a p t o p r o p i o n a t e ,
i - o c t y l - 3 - m e r c a p t o p r o p i o n a t e ,
i - d e c l y - 3 - m e r c a p t o p r o p i o n a t e ,
d o d e c y l - 3 - m e r c a p t o p r o p i o n a t e ,
o c t a d e c y l - 3 - m e r c a p t o p r o p i o n a t e ,
2 - e t h y l h e x y l - 3 - m e r c a p t o p r o p i o n a t e ,
and the l i k e , as well as mix tures of any two or more t h e r e o f .
One s k i l l e d in the a r t can r e a d i l y de t e rmine an e f f e c t i v e
amount of c h a i n - t r a n s f e r agent to employ in order to ach ieve the d e s i r e d
degree of molecu la r weight c o n t r o l . It is of course r e c o g n i z e d tha t t h e
amount of c h a i n - t r a n s f e r agent employed wi l l vary based on the p a r t i c u l a r
c h a i n - t r a n s f e r agent , the p a r t i c u l a r monomer or mix ture of monomers
employed, the i n i t i a t o r employed, the p o l y m e r i z a t i o n r e a c t i o n c o n d i t i o n s ,
etc. Gene ra l l y , 0.01 to 20 moles of c h a i n - t r a n s f e r agent per 100 moles
monomer wil l be employed. P r e f e r a b l y , about 0.1 to 10 moles o f
c h a i n - t r a n s f e r agent per 100 moles of monomer w i l l be employed .
The p a r t i c u l a r c h a i n - t r a n s f e r agent employed in the p r a c t i c e o f
the p r e s e n t i n v e n t i o n can be s e l e c t e d as a f u n c t i o n of the degree o f
molecular weight c o n t r o l de s i r ed and the s o l u b i l i t y of the c h a i n - t r a n s f e r
agent with r e s p e c t to the a c r y l i c monomer or monomers u n d e r g o i n g
p o l y m e r i z a t i o n .
The p o l y m e r i z a t i o n process of the p r e s e n t i n v e n t i o n can be
ca r r i ed out b a t c h w i s e , s tepwise or c o n t i n u o u s l y with ba tch a n d / o r
cont inuous a d d i t i o n of monomers and/or r eagen t s in a c o n v e n t i o n a l manner
as r e a d i l y de te rmined by those of s k i l l in the a r t . P r e f e r a b l y , t h e
p o l y m e r i z a t i o n r e a c t i o n is c a r r i e d out by c o n c u r r e n t a d d i t i o n of monomer
along with a d d i t i o n a l r e a c t i o n components and an aqueous feed into an
aqueous phase which has been p rehea t ed to between about 40°C and 100°C
and main ta ined under a g i t a t i o n . Addi t ion r a t e s may vary and can r a n g e
from about 0.1 hour to 10 hours , with about 0.3 to 1 hour being m o s t
p r e f e r r e d . The system is allowed to r eac t in t o t a l for about 0.1 to 10
hours before coo l ing for p roduc t r e c o v e r y . In order to s u c c e s s f u l l y carry out f r ee r a d i c a l i n i t i a t e d
p o l y m e r i z a t i o n r e a c t i o n , i t is h igh ly d e s i r a b l e t h a t the r e a c t i o n be
c a r r i e d out in the s u b s t a n t i a l absence of oxygen. P r e f e r a b l y , t h e
p o l y m e r i z a t i o n r e a c t i o n wi l l be c a r r i e d out under an i n e r t a t m o s p h e r e .
The novel polymers of the p r e s e n t i n v e n t i o n can be
c h a r a c t e r i z e d as polymers having at l e a s t one monomer of the f o r m u l a
wherein each of R', R2, R3 and R4 are i n d e p e n d e n t l y s e l e c t e d f rom
hydrogen and carbon c o n t a i n i n g r a d i c a l s having 1-20 carbon atoms. The
novel polymers of the i n v e n t i o n have a mo lecu la r weight in the range o f
about 500 to 100,000 as de te rmined by high r e s o l u t i o n gel p e r m e a t i o n
chromatography, and a h e t e r o g e n e i t y index not exceed ing about 3 . 0 .
P r e f e r a b l y the h e t e r o g e n e i t y index wil l not exceed about 2.0; and m o s t
p r e f e r a b l y the h e t e r o g e n e i t y index w i l l not exceed about 1.7. The
" h e t e r o g e n e i t y index" as employed h e r e i n is c a l c u l a t e d as Mw/Mn, i . e . , by
d i v i d i n g polymer weight average m o l e c u l a r weight (Mw) by polymer number
average molecu la r weight (Mn) wherein Mw and Mn are de termined by h i g h
r e s o l u t i o n gel pe rmea t ion ch romatography . At l e a s t a p o r t i o n of t h e
i n d i v i d u a l molecules of the novel polymers of the p r e s e n t i n v e n t i o n a r e
t e r m i n a t e d by the r a d i c a l having the f o r m u l a
wherein R is a c a r b o n c o n t a i n i n g r a d i c a l hav ing_1-20 carbon a t o m s .
The novel polymers of the p r e s e n t i n v e n t i o n are u se fu l in a
v a r i e t y of a p p l i c a t i o n s , such as for example, in c o a t i n g s , a d h e s i v e s ,
t e x t i l e s , paper , p o l i s h e s , l e a t h e r t r e a t m e n t , s e a l a n t s , and the l i k e .
The novel polymers of the p r e s e n t i n v e n t i o n have s e v e r a l u n i q u e
and u s e f u l p r o p e r t i e s . For example, a polymer l a t e x p repa red from a
mixture of e thyl a c r y l a t e , methyl m e t h a c r y l a t e and m e t h a c r y l i c a c id , and
then b a s i f i e d to a pH in the range of 7-10 with ammonium h y d r o x i d e ,
produces an e x c e p t i o n a l l y f r e e z e - t h a w s t a b l e l a t e x .
A f u r t h e r advantageous p r o p e r t y of the novel polymer p r o d u c t s
produced by the p rocess of the p r e s e n t i n v e n t i o n is the r e l a t i v e l y na r row
p a r t i c l e size d i s t r i b u t i o n of the polymer p r o d u c t . For example, when a
mixture of e thyl a c r y l a t e , methyl m e t h a c r y l a t e and m e t h a c r y l i c a c i d
( 2 : 1 : 0 . 0 3 weight r a t i o ) was s u b j e c t e d to emuls ion p o l y m e r i z a t i o n
c o n d i t i o n s in the absence of a c h a i n - t r a n s f e r agen t , p roduc t p o l y m e r
p a r t i c l e s ize ranged g e n e r a l l y from about 0.5 to 5 pm. When t e r p o l y m e r
of the same molar p r o p o r t i o n s was p r e p a r e d in accordance with the p r e s e n t
i n v e n t i o n employing buty l 3 - m e r c a p t o p r o p i o n a t e as the chain t r a n s f e r
a g e n t , the p a r t i c l e s ize var ied w i t h i n the much nar rower range of a b o u t
0.25 to 1 pm. A f u r t h e r u n d e r s t a n d i n g of the p r e s e n t i n v e n t i o n and i t s
advantages wi l l be provided by r e f e r e n c e to the f o l l owing n o n l i m i t i n g
e x a m p l e s .
Examples
The gene ra l procedure employed for a l l p o l y m e r i z a t i o n r e a c t i o n s
was as f o l l o w s :
The r e a c t i o n mixture was p r e p a r e d by adding 28.5g Tr i ton X-200 ,
240g water , 242g monomer (u sua l ly only e t hy l a c r y l a t e (EA) or 121g EA and
121g methyl m e t h a c r y l a t e (MMA)), 0 .480g ammonium p e r s u l f a t e and 0-8 mphm
(moles per hundred monomer) c h a i n - t r a n s f e r agent (CTA) into screw capped
glass b o t t l e . (Sometimes 10-30mg of EDTA were added p r i o r to CTA
a d d i t i o n . ) The mixture was then shaken. S ix ty mL of the above m i x t u r e
was added to a r e a c t i o n f lask which was a I L r e s i n k e t t l e f i t t e d with a
r e f l u x condenser , a mechanical s t i r r e r , a the rmocouple probe and an a r g o n bubb le r . Then 60 mL of H20 was added to the r e a c t i o n f l a s k . The
remaining emulsion mixture was put in to an a d d i t i o n funnel for l a t e r u s e .
The -120 mL of m a t e r i a l in the r e a c t o r is termed the "seed" . The
t empera tu re was i n c r e a s e d over a p e r i o d of about 0.5 hour to r e f l u x
(82-86°C) with a s t i r r i n g rate of 540 rpm. The c o n t r o l l e r set po in t was
90°C. When seed m a t e r i a l in the r e a c t o r had reached r e f l u x t e m p e r a t u r e ,
i n t r o d u c t i o n of the remaining emuls ion mix tu re from the a d d i t i o n f u n n e l
was commenced. The a d d i t i o n ra te was a d j u s t e d so tha t a d d i t i o n was
complete a f t e r e x a c t l y 1.5 hours. When a d d i t i o n was comple te , 0.08 o f
ammonium p e r s u l f a t e in -3g H20 was q u i c k l y added and the se t po in t was
a d j u s t e d to 93°C. F i f t e e n minutes l a t e r , the set po in t was i n c r e a s e d t o
98°C. One hour a f t e r the comple t ion of a d d i t i o n , the set po in t was
i n c r e a s e d to 100°C. Exac t ly 2 hours a f t e r the comple t ion of a d d i t i o n ,
the hea t i ng was t e r m i n a t e d and the r e a c t i o n mix tu re was al lowed to c o o l
with s t i r r i n g to 25-35°C. The r e a c t i o n mix tu re was then s t r a i n e d t h r o u g h
c h e e s e c l o t h .
A weighed sample of the r e a c t i o n mix tu re was dr ied in a vacuum
oven. When the bulk of the water was removed, the sample was hea ted t o
-105°C at 22 inches Hg vacuum f o r 3 hours . The r e s u l t i n g dr ied s amp le
was weighed. Pe rcen t s o l i d s can then be c a l c u l a t e d .
Mw and Mn v a l u e s , and h e t e r o g e n e i t y index c a l c u l a t e d t h e r e f r o m ,
were de termined employing high r e s o l u t i o n gel p e r m e a t i o n c h r o m a t o g r a p h y
of the l a t ex samples, which r e s u l t s were then matched to c a l i b r a t i o n
curves based on p o l y b u t a d i e n e s t a n d a r d s . The c a l i b r a t i o n curve f o r
weight average mo lecu la r weights were p r e p a r e d by s u b j e c t i n g known
molecu la r weight s t a n d a r d s to l i g h t s c a t t e r i n g measurements while t h e
c a l i b r a t i o n curve for number average m o l e c u l a r weights were p repared by
s u b j e c t i n g known molecu la r weight s t a n d a r d s to membrane osmometry. Vapor
p r e s s u r e osmometry was used to de t e rmine the number average m o l e c u l a r
weights for the low molecu la r weight s t a n d a r d s .
Example I
A s e r i e s of p o l y m e r i z a t i o n r e a c t i o n s was c a r r i e d out i n
accordance with the genera l p rocedure se t f o r t h above employing 2.4 moles
of a 50/50 weight r a t i o mixture of e t h y l a c r y l a t e and m e t h y l
m e t h a c r y l a t e . The t o t a l r eagen t charge c o n s i s t e d of the f o l l o w i n g
approximate r a t i o s :
The s p e c i f c amounts of e m u l s i f i e r , i n i t i a t o r and c h a i n - t r a n s f e r a g e n t
employed in each run are summarized in Table I .
Runs 1-12 of Table I are c o n t r o l and comparison runs, w h i l e
runs 13-20 are i n v e n t i o n runs. Run 1 d e m o n s t r a t e s that very h i g h
m o l e c u l a r weight polymer (Mw=571,000) is produced in the absence o f
c h a i n - t r a n s f e r agent . The % c o n v e r s i o n for s e v e r a l of the c o m p a r i s o n
runs , e .g . runs 2, 3 a n d 6 are qu i t e low, i n d i c a t i n g t h a t
P - m e r c a p t o e t h a n o l , 3 - m e r c a p t o p r o p a n o l and 4 - m e r c a p t o - 3 - m e t h y l - l - b u t a n o l
are not s a t i s f a c t o r y chain t r a n s f e r agents for the e m u l s i o n
p o l y m e r i z a t i o n of EA/MMA comonomers. While the g y l c o l a t e e s t e r s ( r u n s
8-12) do p rov ide r e l a t i v e l y good mo lecu l a r weight c o n t r o l , none of t h e
e s t e r s t e s t e d gave a polymer p r o d u c t with a h e t e r o g e n e i t y index (HI) o f
l ess than 1.71. Only the i n v e n t i o n runs employing 3 - m e r c a p t o p r o p i o n a t e
e s t e r s as chain t r a n s f e r agen ts produced polymer p r o d u c t s with a HI o f
1.70 or below. Such r e s u l t s r e p r e s e n t o u t s t a n d i n g c o n t r o l of p o l y m e r
m o l e c u l a r weight d i s t r i b u t i o n . Note t ha t even where the water s o l u b i l i t y
of the chain t r a n s f e r agent becomes more l i m i t e d , e . g .
o c t a d e c y l - 3 - m e r c a p t o p r o p i o n a t e , the degree of m o l e c u l a r weight c o n t r o l i s
s u p e r i o r than t h a t o b t a i n e d with an analogous long chain e s t e r , o c t a d e c y l
t h i o g l y c o l a t e (compare runs 12 and 2 0 ) .
Example I I
A d d i t i o n a l p o l y m e r i z a t i o n r e a c t i o n s were c a r r i e d out i n
a c c o r d a n c e with the g e n e r a l p r o c e d u r e se t f o r t h above. The monomer
charge r a t i o and t o t a l r e a g e n t charge employed was the same as employed
in Example I, except no EDTA was employed. S p e c i f i c r eagen t q u a n t i t i e s
employed and p o l y m e r i z a t i o n r e s u l t s are summarized in Table I I .
The r e s u l t s summarized in Table II sugges t tha t the e m u l s i o n
p o l y m e r i z a t i o n of EA/MMA is r e l a t i v e l y i n s e n s i t i v e to the p resence o f
EDTA. Comparison runs 5, 21 and 22 d e m o n s t r a t e t h a t polymer y i e l d s a r e
c o n s i s t e n t l y reduced and HI c o n s i s t e n t l y i n c r e a s e d in the absence of EDTA
(which f u n c t i o n s to p r e v e n t premature p o l y m e r i z a t i o n of monomer i f
r e d u c i b l e i ron i m p u r i t i e s are p r e s e n t in the r e a c t i o n m i x t u r e ) .
I n v e n t i o n runs 15 and 23 as well as 16 and 24 d e m o n s t r a t e t ha t c o m p a r a b l e
r e s u l t s are o b t a i n e d in the p resence or absence of EDTA.
Example I I I
Seve ra l emuls ion p o l y m e r i z a t i o n r e a c t i o n s were c a r r i e d out i n
a c c o r d a n c e with the g e n e r a l p rocedure se t f o r t h above, employing v a r y i n g
amounts of c h a i n - t r a n s f e r agent , in o rder to d e t e r m i n e the e f f e c t of s u c h
v a r i a t i o n on the degree of molecu la r weight c o n t r o l . S p e c i f i c r e a g e n t
q u a n t i t i e s employed and p o l y m e r i z a t i o n r e s u l t s are summarized in T a b l e
I I I .
Comparison runs 25-27 demons t ra te t ha t the HI f o r
t - d o d e c y l m e r c a p t a n is r e l a t i v e l y i n s e n s i t i v e to c o n c e n t r a t i o n o f
c h a i n - t r a n s f e r agent . Thus, over an 8 - fo ld v a r i a t i o n in c h a i n - t r a n s f e r
agent c o n c e n t r a t i o n , the HI is c o n s i s t e n t l y about 2. The s eve ra l s e r i e s
of i n v e n t i o n runs, i . e . 28-31; 32-34; and 34-37, demons t r a t e a
s u b s t a n t i a l degree of mo lecu la r weight c o n t r o l . Not only are t h e
a b s o l u t e m o l e c u l a r weights (Mw and Mn) reduced, as expec ted , upon
i n c o r p o r a t i o n of g r e a t e r amounts of c h a i n - t r a n s f e r agen t , the m o l e c u l a r
weight d i s t r i b u t i o n , as measured by HI, is also s i g n i f i c a n t l y r e d u c e d
when h ighe r l e v e l s of c h a i n - t r a n s f e r agent are employed. Thus, run 31
gave a polymer with an HI of only 1.51, while run 37 gave a polymer w i t h
an HI of only 1.48. These r e s u l t s demons t ra te e x c e l l e n t mo lecu la r w e i g h t
c o n t r o l is p o s s i b l e with 3 - m e r c a p t o p r o p i o n a t e e s t e r s as c h a i n - t r a n s f e r
a g e n t s .
Example IV
Severa l p o l y m e r i z a t i o n r e a c t i o n s were c a r r i e d out to d e t e r m i n e
the e f f e c t of using d i f f e r e n t e m u l s i f i e r s and i n i t i a t o r s w i t h
3 - m e r c a p t o p r o p i o n a t e e s t e r s in accordance with the p r e s e n t i n v e n t i o n .
Reagents employed and p o l y m e r i z a t i o n r e s u l t s are summarized in Table IV.
In a d d i t i o n , s e v e r a l p o l y m e r i z a t i o n r e a c t i o n s which have a l r e a d y b e e n
r e p o r t e d were r epea t ed to de te rmine the r e p r o d u c i b i l i t y of t h e
e x p e r i m e n t a l and a n a l y t i c a l t e chn iques employed. Resu l t s of t h e s e
compar isons are p r e s e n t e d in Table V. All r e a c t i o n s were c a r r i e d out i n
accordance with the gene ra l p rocedure set fo r th a b o v e .
The r e s u l t s p r e sen t ed in Table IV demons t ra t e tha t e x c e l l e n t
molecu la r weight con t ro l is achieved with b u t y l - 3 - m e r c a p t o p r o p i o n a t e a s
c h a i n - t r a n s f e r agent, r e g a r d l e s s of the e m u l s i f i e r or i n i t i a t o r employed .
The r e s u l t s p r e sen t ed in Table V demons t r a t e tha t degree o f
molecu la r weight con t ro l is very r e p r o d u c i b l e , there being less than 2%
v a r i a t i o n in the HI r e s u l t s for repea t runs 15 and 40; with s i m i l a r
r e p r o d u c i b i l i t y ( i . e . , wi th in 2%) even where widely va r i ed i n i t i a t o r
l eve l s are employed (see runs 34 and 4 1 ) .
Example V
Several t e r p o l y m e r i z a t i o n r e a c t i o n s were c a r r i e d out employ ing
e thyl a c r y l a t e , methyl m e t h a c r y l a t e and m e t h a c r y l i c acid in v a r y i n g
r a t i o s , as summarized in Tables VI and VII. Reac t ions were c a r r i e d o u t in accordance with the genera l p rocedure set f o r t h a b o v e .
The r e s u l t s in Table VI demons t r a t e t h a t some c h a i n - t r a n s f e r
agent is r e q u i r e d to con t ro l polymer mo lecu la r we igh t , o t h e r w i s e
i n s o l u b l e , high m o l e c u l a r weight polymer is o b t a i n e d . In a l l c a se s , good
molecu la r weight c o n t r o l is ach ieved when c h a i n - t r a n s f e r agent i s
employed, e s p e c i a l l y in i n v e n t i o n runs 46 and 48. Al though c o m p a r i s o n
runs 44 and 45 give good HI v a l u e s , note t ha t the a b s o l u t e weight a v e r a g e molecu la r we igh t s are c o n s i s t e n t l y h igher than Mw va lue s o b t a i n e d i n
i n v e n t i o n runs 43, 46 and 48, which is f u r t h e r i n d i c a t i o n of the d e g r e e
of m o l e c u l a r weight c o n t r o l p o s s i b l e with 3 - m e r c a p t o p r o p i o n a t e e s t e r s a s
c h a i n - t r a n s f e r a g e n t s . The r e s u l t s p r e s e n t e d in Table VII d e m o n s t r a t e t h a t e x c e l l e n t
molecu la r weight c o n t r o l is ach ieved over a wide range of t e rmonomer
r a t i o s .
Each of the termonomer s o l u t i o n s produced in runs 42-52 were
a d j u s t e d to pH of about 8 . 5 -9 .5 with ammonium h y d r o x i d e and s u b j e c t e d t o
s eve ra l f r e e z e - t h a w cyc le s . The emuls ions were than v i s u a l l y i n s p e c t e d
to see i f s u b s t a n t i a l s e t t l i n g had occur red or i f the polymer l a t e x
remained s u s p e n d e d .
Con t ro l runs 44 and 45 produced l a t e x p r o d u c t which u n d e r w e n t
s u b s t a n t i a l s e t t l i n g during the f r e e z e - t h a w t r e a t m e n t . Of the i n v e n t i o n
runs (43 and 46-52) a l l but run 49 gave e x c e p t i o n a l l y f r e e z e - t h a w s t a b l e
emuls ions . Thus, where EA/MMA monomer r a t i o s are at l e a s t 1:1, and
3 - m e r c a p t o p r o p i o n a t e e s t e r s are employed as chain t r a n s f e r a g e n t s , v e r y s t a b l e emuls ions are p r o d u c e d .
The emuls ions produced in runs 42 and 43 were f u r t h e r
c h a r a c t e r i z e d by obse rv ing the range of polymer p a r t i c l e s i ze under t h e
mic roscope . Con t ro l emulsion 42 d i s p l a y e d a wide v a r i a t i o n in p o l y m e r
p a r t i c l e s i z e , r anging from about 0.5 to about 5 µm. In c o n t r a s t ,
i n v e n t i o n emuls ion 43 d i sp l ayed a much na r rower range of polymer p a r t i c l e
s i ze , v a r y i n g only between about 0 .25-1 µm. The examples have been p rov ided merely to i l l u s t r a t e t h e
p r a c t i c e of our i n v e n t i o n and should not be read so as to l i m i t the s cope
of our i n v e n t i o n or the appended claims in any way. R e a s o n a b l e
v a r i a t i o n s and m o d i f i c a t i o n s , not d e p a r t i n g from the e s sence and s p i r i t
of our i n v e n t i o n , are con templa ted to be w i t h i n the scope of p a t e n t
p r o t e c t i o n d e s i r e d and s o u g h t .
1. An e m u l s i o n p o l y m e r i z a t i o n p r o c e s s c h a r a c t e r i -
z e d b y p o l y m e r i z i n g in a q u e o u s med ium a t l e a s t o n e
a c r y l i c m o n o m e r h a v i n g t h e f o r m u l a I
w h e r e i n R , R2, R3, and R a r e e a c h i n d e p e n d e n t l y s e l e c t e d f r o m h y d r o g e n and c a r b o n c o n t a i n i n g r a d i c a l s h a v i n g 1 - 2 0 c a r b o n a t o m s , in t h e p r e s e n c e o f :
(a) a w a t e r s o l u b l e f r e e - r a d i c a l i n i t i a t o r ,
(b) an e m u l s i f i e r , a n d
(c) a t l e a s t one c h a i n - t r a n s f e r a g e n t s e l e c t e d f r o m
c o m p o u n d s h a v i n g t h e f o r m u l a HS-CH2CH2CO2R w h e r e i n R i s a c a r b o n c o n t a i n i n g r a d i c a l h a v i n g
1 -20 c a r b o n a t o m s , 6 - m e r c a p t o m e t h y l - 2 - m e t h y l - 2 -
o c t a n o l , and 2 - p h e n y l - 1 - m e r c a p t o - 2 - e t h a n o l .
2. The p r o c e s s of c l a i m 1 c h a r a c t e r i z e d in t h a t s a i d p o l y - m e r i z a t i o n i s c a r r i e d o u t a t a t e m p e r a t u r e in t h e r a n g e of 40 to 100°C f o r a t i m e p e r i o d in t h e r a n g e of 0.1 t o
3. The p r o c e s s of c l a i m 1 or 2 c h a r a c t e r i z e d in t h a t s a i d
a t l e a s t one monomer i s e t h y l a c r y l a t e .
4. The p r o c e s s of c l a i m 1 o r 2 c h a r a c t e r i z e d in t h a t s a i d
a t l e a s t one m o n o m e r c o m p r i s e s a m i x t u r e o f e t h y l a c r y - l a t e and m e t h y l m e t h a c r y l a t e .
5. The p r o c e s s of c l a i m 4 c h a r a c t e r i z e d in t h a t t h e m o l a r
r a t i o of e t h y l a c r y l a t e to m e t h y l m e t h a c r y l a t e r a n g e s f r o m 1 : 1 0 to 1 0 : 1 .
6. The p r o c e s s of c l a i m 1 o r 2 c h a r a c t e r i z e d in t h a t s a i d
a t l e a s t one m o n o m e r c o m p r i s e s a m i x t u r e o f e t h y l a c r y - l a t e , m e t h y l m e t h a c r y l a t e and m e t h a c r y l i c a c i d .
7. The p r o c e s s o f c l a i m 6 c h a r a c t e r i z e d in t h a t t h e w e i g h t
p e r c e n t a g e o f m e t h a c r y l i c a c i d r a n g e s f r o m 0 .01 t o 5 w t %
b a s e d on t h e t o t a l w e i g h t of m o n o m e r c h a r g e d .
8. The p r o c e s s of any of t h e p r e c e d i n g c l a i m s c h a r a c t e r i z e d
in t h a t t h e c h a i n - t r a n s f e r a g e n t i s s e l e c t e d f r o m m e t h y l
3 - m e r c a p t o p r o p i o n a t e , b u t y l 3 - m e r c a p t o p r o p i o n a t e , i - o c t y l
3 - m e r c a p t o p r o p i o n a t e , d e c y l 3 - m e r c a p t o p r o p i o n a t e , d o d e -
c y l 3 - m e r c a p t o p r o p i o n a t e , 2 - e t h y l h e x y l 3 - m e r c a p t o p r o -
p i o n a t e , o c t a d e c y l 3 - m e r c a p t o p r o p i o n a t e , a n d m i x t u r e s
of any two o r more t h e r e o f .
9. The p r o c e s s of any of t h e p r e c e d i n g c l a i m s c h a r a c t e r i z e d
in t h a t s a i d c h a i n t r a n s f e r a g e n t i s p r e s e n t in t h e
r a n g e of 0 . 01 to 20 m o l e s p e r h u n d r e d m o l e s o f m o n o m e r .
10. The p r o c e s s of any o f t h e p r e c e d i n g c l a i m s c h a r a c t e r i z e d
in t h a t s a i d w a t e r s o l u b l e f r e e - r a d i c a l i n i t i a t o r i s a n
i n o r g a n i c p e r s u l f a t e c o m p o u n d .
11. A c o m p o s i t i o n of m a t t e r c o m p r i s i n g a p o l y m e r of a t l e a s t
one m o n o m e r h a v i n g t h e f o r m u l a I as d e f i n e d in c l a i m 1 ,
w h e r e i n s a i d p o l y m e r has a m o l e c u l a r w e i g h t in t h e r a n g e
of 500 to 100 000 as d e t e r m i n e d by h i g h r e s o l u t i o n g e l
p e r m e a t i o n c h r o m a t o g r a p h y ; w h e r e i n s a i d p o l y m e r has a
h e t e r o g e n e i t y i n d e x Mw/Mn no t e x c e e d i n g a b o u t 3 . 0 ; a n d
w h e r e i n a t l e a s t a p o r t i o n of the i n d i v i d u a l m o l e c u l e s
of s a i d p o l y m e r is t e r m i n a t e d by a r a d i c a l h a v i n g t h e
f o r m u l a I I
w h e r e i n R i s a c a r b o n c o n t a i n i n g r a d i c a l h a v i n g 1 - 2 0
c a r b o n a t o m s .
12. The c o m p o s i t i o n of c l a i m 11 f u r t h e r c h a r a c t e r i z e d b y
t h e c o n d i t i o n s of any one or more of c l a i m s 3 to 7 .
13. The c o m p o s i t i o n of c l a i m 11 or 12 c h a r a c t e r i z e d in t h a t
f rom 0 .001 to 0.1 of t he i n d i v i d u a l p o l y m e r m o l e c u l e s
a r e t e r m i n a t e d by t he r a d i c a l h a v i n g t he f o r m u l a I I .
14. The c o m p o s i t i o n of claim 11 o r 13where inR i s s e l e c t e d f r o m
- m e t h y l , - b u t y l , i - o c t y l , - d e c y l , - d o d e c y l , 2 - e t h y l
h e x y l , o c t a d e c y l , and m i x t u r e s of any two or more t h e r e -
