CA2033076A1 - Polymeric compositions - Google Patents

Abstract

ABSTRACT
Polymeric Compositions Polymeric compositions are stabilised against molecular weight degradation by the inclusion in the composition of an inhibitor which is preferably an ethylenically unsaturated compound. The invention is of particular value when the polymer is a polymer of (meth)acrylamide in which the amount of contamination of the polymer with free (meth)acrylamide monomer is extremely low and the inhibitor has LD50 above 400.

Description

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Allied Colloids Limited ~0/2gg6/03 .: Polymeric ~o~po~itions : This inven~ion rel~tes t~ water soluble and water swell~ble polymer~ of e~hylen~c~lly unsa~ur~ted mohomers and ~h~ir stabilis~tion so as ~o r~du~e molecular ~eight degradation during storage ~nd use. It ~lso r~late3 to polyacryl~mide~ in whic~ this p~oblem of deg~d~tion is : particularly significant.
10When mak~ ng a ~atex ~ol~ble or ~well~ble poly~er from ethylenically ~nsa~uxatea mono~er, it is ~orm~l to try ~o acbie~e ~ull polym~risa~iGn o~ the mono~er~ hut in reality ~ome monomer always ~emain uhpolymerisea in the ~; polymeric reaction pr~duct~ This may be relativQly unimportant in the ca~e of som~ mono~ers bu~ it i~ ~nown 5 to ~e undesirable ln ~he c~e of ~thacrylamide or, especially, acrylamide because o~ the tox~city o~ thi~
- ~onomer. It is normal praGtice t~er~fore to ~onduc~
~r': aorylamide polymerisation sv A-~ to reduce the Acrylam~e content to as l~w a value a.~ is conven~en~ly pos~i~le, ~hi~h in practice ge~erally me~ns ~hat the pol~er has a ; r~sidual f~ee acrylami~e content o, typically/ 0.2 ~o : 0.5%, Extensive ~ud es h~v~ been made of the per~orm~nce 2S of polymer~ o~ ethylenically ~nsaturatad ~onomsrs and it is know~ t~a~ they ~re li~ble to undergo degradation durin~ stor~ge or use. ~h~s degradation is p~rtic~larly serious for ~he higher molecula~ we~gh~ polymer~ ~or ~ instance molecular weigh~ a40ve one million. The ~act ` 30 tha~ degra~ation is oc~uring is ~anifested by, ~or in~tance, a reduction in th~ solu~ion ~isc~sity o~ the polymer~ In t~ose circums~ances w~en the p~lymer is being used as a viscosi~ier ~he r~duction in vi~cosity would probably be no~ic~dr b~t ev2n thon thi might be p~t down to other ~actoxs, f~r in~nc~ that ~he polym~r .

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as initially made had lower solution ~isco81ty than w~s expe~ted. Also, it may not be practical to m~sur~
solut~on viscosity durins u~e (e.g. when tha polymer is ~eing used downhole). ~n o~her situ~tion~, e.g. as a ~loccul~nt, the solution viscosity of the polyme~ may not normally be measured and the perform~nc~ o~ the polymer may depend upon a whole r~nge of fa~ors o~ whi~h solution viscosity is only one, ~nd ~o ~n theory performance could be pu~ down ~o ~ny o~ th~s~ f~ctors and, ag~in, may ~e attributed ~o in~erlo~ propertie in the polymer as manufactured initially.
Even when i~ is observe~ that solution viscosity has ~een redu~ed ~hi~ reduction could be due to changes in .: the side groups, for ins~an~e, hydrolysis, ox ~ould be due to cle~vage o~ the backbone, i.e reduGtion O~
.-mole~ular weigh~, and it can be relativ~ly ~i~ficult ~o prove clearly Which effect is occurring.
;Pespite these unce~ain~ies as to the ~use of degr~dation, there ~av~ been numerDus proposals to incorporat~ various degradation inhibitors in poly~rylamides~ Exa~ples are given $n the follo~ing : Chemical Abstracts, namely isobutanol, ~ichlorphenolate and amino acids in ~olume 1~8 18~657~, phosphonat~s in volume 106 51187~ methyl-~-pyrrolidone in volu~e 105 22g619t, maleic anhydride acylation deri~ati~es o~ ur~a, thio~rea, phenylurea or ethanolamine in volume 99 1407~9b, va~ious s~lphur compounds ~uch ~s thiocarbon~tes in volume S6 5~294~, thio~rea and polyethylene glycol in volume 91 ~3783g an~ various compound~ such ~s ~apt~o~in~ne in volume 98 1083~2g. M~ny o~ th~
additives are described as being a~ded to pre~ent oxida~ion o~ the polyme~ ~nd in Chemical Abstr~
238~y a~ in~rganic r~ducing agen~ is ~ed~
In FR-A-26044~4 the vi~o~ity of a pol~arylRmide ~or enchanced oil recovery 1~ ~tab~lis4~ hy adding at .
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lea~ S~ a~;:rylamide mc~nomer, based on ~he polymex. In JP-A-60/210657 it i~ proposed ~o stabilis~ poly~c~ylamide homopolymers, and copolymers Of acrylamide Wi~h less th~n 50~ of the monomers, that are ~o be used ~or purpose~
S su~h as ~loccul~tion, paper-maXing, enh~nc~d oil recovery, viscosi~iers and soil imp~ov~rs. This stabilisation i~ b~ t~e ~ddition o~ a~ least 0.5% o~ ~
water solu~le vinyl monomer and in the examples the ; mono~ers used are acr~lamide (in an amount up ~O 7~) s~dium acr~late, me~h~crylamide, acryloni~rile, dimethylaminoethyl acrylate and 2-~crylamido-2-methylpropane sulphonic acid ~A~PS, US q~rade Maxk).
Despit~ all ~h~s extenslve literatl~re the commer~ial re~lity i~ th~ a very limited rahge of aad:ltives are lS . incorporated ~o impxove stability. Urea is include~ for;
various reasons and ~an giv~ some improvernent~ G~eater improv~m~nt is a~hleved wl~h ~hiourea, ~odium nitrit~ or trlme~hoxyphenol but each o~ the~e ~ eri~îs ar~ ~ather inconvenient ts: incorpora~e into ~he p~lyrner, and the ~0 polymer i5 sti~l liab~e to undergo su~st~n~ 1 ViSGoSi~y reducti~n during stora~e and use, e~;pe~ial7y ~t el~v~ted temperature~ .
Sepera~e from ~he s~bilisat~ora o~ conventional polyaorylamide Gontamina~e~ with, for instanc~, O . 2% or ~5 more fre~ acxyl~mide, some polyacrylamides contaminated ~lth less free acrylamide have bee~ produced. For instanc~ polymer that is to be u~ed for th~ pur~fi~at$on of potable ~ater generally has a f~ee acrylamide e~ntent of around O.OS~. The ~isoosity of s~cb ~ polymer ~ not directly significant ~or wat~r-puri~icatlon properti~s ~; ~nd we are una~re of ~ny ~iseosity or other s~ability st~die3 ha~ing being conducted on ~uch polymers, It is also known ~o make ~olyacrylamid~ having eveh lower content~ of f~e~ acrylamid~. ~hl~ ~n ~e a~hie~ed 3S either by care~1 optimi~a~ion o~ the polymoxi~ation `:

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.. 4 çondi~Gns o~ by removal o~ the ~ree acrylami~e ater polymerlsation by washlng~ chem~ cal reaction or biological means, for inStAn~e as de~ribed in European Pa~ent Applic~ion~ 893011~5.~ and ag3011~6.6 ~r U.SO
46~7~7.
Thus the present in~us~rial ~i~u~tion is th~
polyac~ylamides having ~ypic~l levels o~ ~crylamide contamina~iQn ars llable to undergo ~isco~i~y clegrad~tlon on storage or use under ~ome ~ondi~ions, ~he commercially lO used ways of trying to prevent this degrada~ion are not - ~ully satis~ac~ory and incux v~rlous disadvantaqes, methods in t~e li~erature also ~ppear uns~ls~Actory, u FR-A-~604444 and JP-~-60/210657 de~ribe the ` stabili~ation of acrylamide pol~mers by ~he use of ~5 ~crylamide or o~her monomers but ~icity c~side~ations contraindic~te the gener~l ~eachings o the~e patent~
. (for instance the use of large amoun~s o~ acrylamide) and .` relatively pure polyacrylamides (having ~ low content of free ~crylamide) are even more unstabl~.
20 In a first a~pect o~ the inven~ion, we hav~ now found that it is possible to ~tabilise these relatively pure polyacrylamides against molecula~ w~ight d~gradation and that this ~an be achieved easil~ by ~h~ in~orpora~ion of materials that are easy to incorpora~e ~nd t~at dc not reintroduce the toxicity problems that had been avoided by the reduction of the co~tent o~ free ac~ylamide.
; In particular, the ~irs~ a~pect of the invention provides a polymerio composition comprising of blend o a pol~me~ o~ (m~th3 acrylamide, free (met~) ~crylamide 30 ~onome~ and vis~osity-~egradation inhibi~or, a~d in th~
; inventioh the amo~nt of free ~meth) ~crylamide monomer is below 0.1% ~y weight of the polymer and ~he LD S0 ~ the inhibitor is above 400.
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L~ 50 o~ above 400 means ~h~t more th~n 400mg o~ the inhibi~or is xequired per ~i~ogram bodyweight to achi~v~
50~ le~hality when ad~inistxat~d orally to ~ats.
~ hus, rel~tive to conv~ntional c~mmerci~1 S polyacrylamide, the prod~ct of the invention omits most o~ the r~latively toxic (meth~ a~ryl~mide (thereby making th~ produc~ potentially very su~ceptible ~o vi~03i~y degradation) and repl~es ~his monomer by ~ materi~l ~hat is much less toxic and ~hat does st~bill~e the polymer against visco~ity degradation.
The preferred pol~merlc compositions have stability against viscosity degrad~tion at least as good as and pre~erably be~ter ~h~n the s~m~ polymer contain~g 0.~ ~ree ~meth) acrylaimde, Despi~e having ~his equivalent and, ~re~r~1y, grea~ly improved st~bit-ity the overall toxicity tme~sured both ~s ~D 50 and as cumula~ive ~oxicity) of ~he stabili~ed composition can easily b~ no ~rea~er than polyacry~amide contalning 0.~ ~ree (meth~ R~rylamld~ and : ~0 is preferably substan~i~lly less. Thu3, it ifi po~sib~e, by the inve~tion, for the ir~t time, to provid~
polyacrylami~e ~h~t meet~ the hi~h~st en~ixonmen~al standards as regards free ~meth) acrylamide ~nd ~et has exceedingly good viscosity st~bili~y.
Despi~e all the di~cuss.ion in the literature ~out oxidation inhi~itors and sidegroup reac~ions, it appear~
that viscosity degradation is primar~ly due to redu~tion in molecular chain length, ~nd that this in turn ls ~ue ~o ~r~ak~ge of the pol~mer backbones ~y ~nreaeted polymeris~tion initiators~ and degradation product~ of such initiato~s, left ove~ from the polymerisa~ion process, In particul~r ~e pre~ence of ~ree r~dieal ini~iatoxs in the flnal polyme~ seem~ to be a p~rticular cause of molecular w~ight d~gr~da~ion and thu~ vi~osity ~egradatio~.

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203307b .

The amount o4 degrada~ion inhihit~r tha~ h~ to be added, to achi~ve any particula~ ~ability, i~ therefor~
reduced if the amount o~ initia~or de~ri~ i~ the polym~r is reduced. Pref~ably therefore the poly~ne~isa~ion is co~du~ted using tech~ique~ that result ln the lowest possibl~ ini~lato~ residues in the final produc~. For - in~tance, the rate o~ addition of initi~tor is prefer~bly : ~ont~olled so a~ to mlnimis~ initi~tor re~idue in th~
final polymerisation product. If the polyme~ is substantially free o~ such residues then ~he amount of visco~ity-degradation inhibitor that has to be added can ~e rela~ively low. It is t~en possibl~ to u~e any o~ the d~grad~ti~n inhibit~rs ~hat ~e known from the lit~r~ure and whioh both ~unc~ion a~ ~ fre~ ~adical 3ink and whic~
.: 15 have ~D 50 ~bove 40Q.
Preferably, howevex, t~e inhi~i~or i~ ~n ethylenically uns~t~rated mater~al ~hat h~s ~ 50 ~bove ~00 -- Ac~ylamide itself (LD 50 ~ 124) i8 0~ COU~
excluded f~om ~oncider~tion as are other monomexs th~t have ~imilar or worse tox~ci~y values, such ~s ac~ylo-nitrile (W 50 = 78) ~nd acryllc a~ld ~LD 50 ~250)~
Mono~ers that can be used inGluds low toxiclty ethylenically unsaturated carboxylic ~cid~, or instanc~
m~leic acid (L~ 50 = 708) and fumaric acid ~L~ S0 ~
: 10700) and ethylenically uns~ura~e~ ca~loni~ ~onomers, especially dialkyl aminoalkyl ~meth) ~cxylatas such a~
dimethyl ~minoethyl ~me~h) a~ryla~e ~L~ 50 = 17513 and dialkyl aminoalkyl (me~h~ ac~ylamides e~pec~ally those 30 where the central alkylene gxoup contains at least two .. chain carbon atoms, ~or instance methyl ~hloride quatenary salt o~ dim~thyl aminop~opyl (meth~ acr~rlamide (Maptac LD SO a 71~) . D~ ally~ dialk~ monomBrs can be .: used especially diall~l dimethyl ammoniu~ chlo~i~e (Dadmac, ~D 50 - 1700)~
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~`~ 7 A wide variety oS other ethylenic~lly u~s~turated mono~ers are o~ course w~ll know~ anfl po~enti~lly use~ble~ for instanoe~ monoallvl triallyl qua~ernary compounds ~ch as allyl trimethyl ~mmonium chloriae (atmac), other allyl materlals such ~s allyl ~ulphonate, other anionic materials such ~s vinyl sulphona~e and sytrene phosponate, m~leic ~nhydrid~, fuma~ic anhydride, ~imethyl amino ethyl ~cryl~te and dim~th~l a~ino propyl acryl~mide.
~he use of monomer~ containing one or m~re ~llyl groups is part:icularly p~ferred, e~peci~lly Dadm~c.
The ethylenically uns~ur~ted m~t~rial do¢~ no~ have to be ~ monomer ~nd i~ can ins~e~d be ~ rial that co~t~ins ~ polymeric backhone with e~ylenic unsa~uration ei~er in ~he ba~bone, in ~exminal groups or in pendant ~roups. The use of a polyme~ in thi~ manner is p~rti~larly desirabl~ cince it can co~tri~ute tn the VisGOSity or othçr properties of the polymer th~t is being stabilised or, ~t least, minim.ise ~h~ dilu~io~
~eot on ~he polymer ~h~t might be pxovided othe~ise by the monome~. Pre~err~d Folymer~ are polymer~ ~orm~d from allylic ~ono~er (either ~one or ~ th up to 90~, preferably ~n~ moxe than 50%, o~her ethylenically unsa~urated monomer. Preferred ~llylic mono~ers are diallyl dialkyl ammoniu~ compounds. ~he polyme~s of diallyl di~ethy~ ammor.ium chloride (especially the h~mo polymer) are pa~ti~ularly prefer~ed in this respec~.
Such polym~rs are believ~d .~o be termin~ted by free allyl oups~ , Other suitable poly~e~s are ~crylic terminated polyethylene glycols ~nd o~h~r un~aturatsd pol~me~s including, e~pe~ially, ~he prepolylners desc~ibed in our Europear, ~pplication 8g301075 (EP~A-32~321)~
It can be a~ceptable for ths ethyleni~ally 35 unsatur~ted ma~exial to undergo polym~ri~tion durlng thc .

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storage or use conditions ~hat would othexwi~e h~ve ca~sed viscosity degradation, bu~ it ~s qe~er~lly prefe~red ~ha~ the ma~erial merely ~c~ as a free radi~l sink 2nd does not under~o any su~stan~i~l ch~mical ch~nge S as a result of ~hi~. One disadY~ntage o th~ monom~r being t~o re~ctive is th~ it may tend to ~e~c~ onto the polymer its~lf ~nd this may al~r ~he per~ormance cha~ac~eris~ics of t~e polymer. In som~ inst~nces ~his is undesira~le. For inst~nce if ~h~ poly~er is soluble, it may tend to ~e insolubli~ed by reaction o~ a monomer ~h~t is too re~ctlve. ~mps is a example of ~ monomer that tends to have too high a re~ctivity ~ is to be used in an environment where ~om~ deg~ee o~
in ol~bili~ation i9 un~c~ep~abl~.
15 ` The.material may be non-ionic or i~ may be co~ioni~ i or counter-ionic with th~ polymer. If i~ is counter-ionic th~ amount must not be 3uch th~t ~he monomer ~orms an insoluble complex with the poly~er. The initia~or should normally ~e ~er soluble ~o tha~ i~ can be introduoed ~e introdueed as an aqu~ou~ solution.
- ~he polymer th~ is ~o be s~abilised in ~hi3 ~irs~
aspect of the ~ nvention is foxmed fro~ (math) ~cryl~mide ~alone or ~it~ other ethylenically unsa~urated monomer~
When there is ~ blend o4 ~onomers, the blend (and usu~lly each of the monomer~ in ~he blendl p~e~erably is ~a~er soluble.
``The polymer th~t ls ~o be s~bilised is preferably soluble in aqueous liqui~, b~ th~ lnvent~on can also be `!applied to polymers that ar~ insol~ble~ ~or in~anc~ as a ;30 r~sult o~ bei~g cross-linked by polyethylenlcally unsaturated monomer or o~her sui~ble crosslinking ~gent.
If i~ ig insoluble~ it may be cros~linked ~o ~uch an extent that it is ~u~stantial~y nor-swelling but g~nerally it is relA*ively lightly cros~linked such tha~
35 i~ iB swellable ~nd has high ~bsorption cap~ci~y, ~or :

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in~tance at least 30 gramm~s di~ioni~ed w~er per gr~mme polymer.
The pvlymer may ~e a sub~tan~ial homopolymer o~
(meth)acrylamide, ~en~rally pol~a~rylamide homopolymer in which event i~ should be non-ionic. ~o~/eve~ ~ay be anioni~ as a resul~ o~ a small degr~ hydr~lysis of a~r~lamide ~ro~ps o~ as a result of copolymerisation o~
the (meth)~crylamide with ekhylenically ~n~aturated carboxylic or æulphonic M~nomer. Sultable monomers are lo an~ o~ t~e conventional wa~er solu~le anionic monomers such as (~e~h) acrylic acid (gen~r~lly as ~ water ~oluble salt) or AMPS.
The polymer ~ay ~e cationlc, ln which event it is co-pol~marised with ethylenically unsatur~ed ca~ionic mono~er. S~itabl~ oationic monomer~ include dialkylaminoalkyl(m~th)-acrylate~, -meth~crylates, -acrylamide~, and -me~h~crylamides {especially wh~n the central alkylene group cont~ins ~t lea~ 2 oh~ln atoms) and d~allyl dialkyl monomers. Pre~erred ex~pl~s are any of the ~ationi~ monomers ~entionad ~bove, in par~cula~
dime~hyl ~dr die~hylJ aminoe~hyl tmethJ ~cxyl~te~ and dimethyl ~or diethyl~ aminop~opyl (meth) acrylami~es, and DadTnac. The Irne~h) ac~ylates and ~meth~ rylamid~s will noxrnally be pr~3sen~ as acid . ~ddi~i~n or qua~ernary salt~ .
.. ~ 25 The amount o~ (me~h) acrylami d~ in ~h~3 monomers ~om which ~h~ polymer i~ ~ormed may range ~ m 5 ~o 100% by weight, often ~0. to 1O0%D
l~he pol~m~r ~enera~ly has ~nolec~llar w~ight above 1 million, often ~b~ve S mill~on. I~ g~hexal~y has 30 intrinsic~ viscosity (measured in 1 molar sodium chlorid~
at 2~ C by suspended level Vi~c~met~r) 3trovo 4 dl/g .
when th~ polynler is an~oni~ the IV is typ~cally in the range 10 to 30. When the polymer :Is ca~ioni~ ~he ~V i~
typical1y ln the r~ng~ 6 to 1 B .

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~ he polym2r ~ay be mad~ by p~lymerisation in conv~ntion~l mannex condu~ted wi~h c~re~ul optim sa~,ion so ~s to pro~uce ~ residu~l ~ree acrylamide ~on~ent of belo~ Ool~ prefer~bly below 0.05~ and most preferab~y 5 below 0~03~. ~ethods curren~ly used for making poly~er for pota~le water txea~ment ~Qy be utillsed.
Alternatively the polym~r may be ~ynthesl~ed and mA~ then b~ su~jected to washing or o~her purific~tio~, as discussed above, so as to red~ce the monomer content.
The inven~ion is of partlcula~ value when applied t~
catiOhic polymers ~eca~se it is well known tha~ they tend to suffer siynifican~ reduc~ion ln visco~i~y durlng m~ny o~ ~heir co~ven~ional uses, ~or inStAnCe downhole acidising, fr~cturing or ~ompletion fluids, and the inven~ivn provides a signi~lc~ m~ciall~ and ~oxi~olo~i~ally ef~tive solution to this pro~lem.
Th~ inhibitor ca~ ~e pres~I~t througho~t the ~ormation o the polymer if it has ~ suffici~n~ly low reactivity xate tha~ it will no~ p~r~icipate i~ or interfere ~ith the polymeri~a~ion ~eaction. ~enerally, however, it is a~ded a~ter the pol~eris~ti~n is completed, If the polymer is present as a fluid solu~ion or ~mulsion or disper~ion ~for insta~ce a reverse phase .` di~persion or emul~ivn) the inhibitor c~n conveniently be incorp~rated into thi~ fluid ~ompositlon merely by ~` stirring.
A par~i~ularily preferred method oS blending the inhibitor with a water ~oluble or ~a~er s~ell~ pol~mer ~omprise~ providing ~he poly~er as a dispersion o~
particJ.es in an non-aqueou~ liquid (for instance ~y disper.s~ng chopped gel into oil or, preferably, r~verse phase polymeri~ation) and then ~ixiny the inhibitor int~
~hs disper~ion, the inhibi~or and ~he non~aqueo~s liquld be~ng selecte~ ~ch th~t ~he inhibi~or is p~e~rently sol~ble in ~he particle~, Pre~erably the particle~ in . ~ :
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the dispexsion are aubs~n~i~lly dry before ~he inhi~l~o~
is a~ded. For in~ance a disper~.ion ~ay ~e m~de by reverse phase polymerisa~ion follow~ ~y azeo~ro~lng, ~nd inhibitor (generally dissolved in wat~r) ~ay then ~e mixed into the dispersion~
~ the polymer is provided ~s a ~olid gel, or i~stance ~s beads or co~inu~ed gel p~rticle~, the inhibitor ox other, (~enerally ~s ~n aqueou~ solution) m~y ~e imbi~ed into the par~icles either be~ore they ~e dried or after dryihg ~in which e~ent ~ ~uxther drying ~tep maybe ~ecessary).
The inhibi~or may servç ~ prevent or reduce viscosity under SUbS~ntiBlly any condi~ions during which such degradation is lik~ly ~o ocGur ~ Qg upon he~ting, expo~ure ~o ultr~ violet radiation or daylight, dilution waters or othe liquors that cont~in i~puri~ies ~eg ferrous iron) th~t cauSe ViScosi~y degradation, or prolonged stor~e. ~he inhi~itor ma~ serv~ to preYen~ or reduce viscosity degrada~ion in any type o~ composition eg 2 dry prod~c~ such as beaa or commi~uted gel, a rev~rse ph~se dispersion, or a sol~ion, ~or in~tance floacu~ant solution ~e~ween inltial ~ake~p and u~e ~ a f~occulant.
The co~positions of ~he i~v~nt~n aan be ~sed ~ox A
~5 wide varle~y of purposes, depending on ~he p~rticuar polymer. For instance such uses can be sele~ted fro~
vlsocification, ~nh~nced oil recovery, ~locculatio~, paper making, soil i~pro~ers, wallpaper and oth~
adhesives, water shut-o~ f and ~oil ~t.~hll~ation ~nd grou~ing, a~sorbents and sofo~th.
It is of par~icul~r value when ~he polymer is ~0 be .subjec~ed ~ heatin~ hot and/or chemically ~ggxesslve conditions, ~g ~ floccula~ for Bayer pro~s~ liquors.
The p~lym~r can b~ use4 ~n varlou~ downh~le 3~ environmentg. F~r ~nstance the p~lymer may be a high ;

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mol~cula~ weight anionic poly~er ~o~ enhan~ed oil recovery. ~owever, the inven~ior.s is o~ partic~l~r value in hot ag~ressive downhole envixonm~n~s, as described ln PCT applicati~n GB/90/ filed ~oday ~y th~ same ap~ ant and inventor. 'rhu~ it may be a high molecular weight anior.1c polymer, ~generally cro~link~ble) ~or do~nhole fracturing uses, a high molecula~ w~ight ~nionic or cationic polymer fox downhole acidlsing, a medium to h~gh molecular weig~t catl~nic polymer for downh~le 10 c:omp1etion ~luids, or a mediu~n moleaular weight anlonic polymer a~ a fl~id loss additi~e in drilling fluid~.
llhe polymer may be one tnat i ~o ~e reaoted, at its pendent g~oups, at ele~ated tempe~ature after it~
forma~ion and the inhib.itor minimises degrad~tion durlng 15 xeaction. ~or in~t~nce polya~rylamide can 13~ hydroly~ed by heating in aqueous ~13cali and degrad~tion durlng the hydrolysis can be minimi~;ed in ~he invention~
The polymer may bs expo~e~ fo~ pxolonged p~ri~ds to ~; an ~lec:~rolyk~, for inst~r.ce as in a textile prin~ing 20 past:e. The polym.er may ~e expos~ for long perlod5 ~o ult~aviol~t r~dio~ion, for inst~nce a ~n agricult~lral polymer for enchan~ment o~ soil stru~ure. ~he polymer may ~e ~xposed to high ~emp~ratures ~02 a short pe~iod, for instance it m~ be zl w~ll paper prepa~te adhesive and 25 mc>lecular weight degradatiorl during hot smbvssing or foamins sta~es o~ the wallpaper can ~e minimise~ by the p~esen~e of the inhibi~or o the inven~ion.
~ he amount of inhibi~or that ha~ to be added will ~e found by trial and experiment~ I~ us~ally at l~ast 0.0~
30 and ~enerally a~ le.as~ 0.1~. since the inhibitor may tend to dilute ~h~ ~ctivity of the polynler it is generally pre~erred that the amount should be below ~0%, pre~ra~ly below 10~ and mos~ pre~erably below 5~ by `- weiS~ht of ~he polymer.

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~ o~ever, wh~rl a dilution eff~ct d~e~ not crea~e ~
problem or is ev~n deslra~ for instan~e when ~he inhibitor is a poly~er, or d~ring s~oxage ~orms o~
polimer, ~h~t complemen~s the properties o the polymer that is to be stabilised) ~he~ l~rger a~o~nts may ~e used, e.g. up to 50% by weight.
Some of th~ disco~eri~ on wh~ch th~ ~irs~ aspect of the i~ven~ion are based are ~ppl~cable ~lso ~o ot~er ccmpo~iti~ns~ for instar.ce to composition~ ~hexe ~he mo~om~rs from which the polymer i~ made ~re free of ~meth)~cryl~mide and/or ~o polyacryla~.ide~ th~ ~re contamin~t~d wi~h up to, for ins~nce, 0.5% ox even 1% by weight fr~e (meth)acrylamid~ monomer. ~he invention there~oxe includes also other z.~pec~s whi~h are applicable to such polymers, as well as t~ ~he polymer~ 5 de~ined in the first aspect ~f ~he inYention.
A se~o~ asp~ct of the invention resid~ in ef~ective w~ys of .incorpora~ing ~he inhibi~or wi~h th~
polymer that is ~o be ~tabilisçd. In JP-A-60tZ106$7 and FR-A-2604444 the inhibitor is a~d~d to a ~olutio~ of the polymer, bu~ this renders ~he inhi~i~ion technique inapplicabl~ to 501~ing the problem of s~o~age ~t~bility o~ dry polymers or susperl~ion poly~er~, and ~hese axe the ~orms in which such poly~er~ are most usually supplied co~m~rcially. ~e ~ave surp~isingly ~ound tha~ the i~.hibitor can be added ~o the polymer ~hile in the for~
of ~ ~el, a powder or a dispersion in wa~er immisci~le liq~id. ~ui~able methods ar~ d~cri~ed a~ve.
The only p~oposals in the litera~ure for the use of monomer~ of ~he type dis~ussad aboYe I~P 60~10~57 and FR
Z604444) relate to the st~bilisatio~ o~ a~rylamide polymers. In a thixd a~pec~ o~ the inven~lon, we have surp~isin~y fo~nd that it i~ possible to ~tabllige, in a ~imila~ manner, polymers made ~rom monomers that are.
3S entirely ~ree of ~rneth) ~Frylamide. ~hus, it i~ now .

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possi~le to stabili~e polymexs in which 100~ G~ ~he mono~ers are ~nionic ox ca~ionic. ~uit~ble anionic and cationic mono~ers a~e thos~ ted ~bove ~or in~orporation in the acryl~mide polymer~ ~f ~he ~irst ~spect o~ inv~ntion. Copolymer~ of them with o~her non-ionic monomers, ~or in~tance ~inyl acet~mide, N-viny~-N-~ethyl ~ce~amide, N,N-dimethylasry1~mide ~r vinyl pyrrolidone can ~e used.
Preferably the polymers ~re ormed fro~ ~onomers 10 selected ~xo~ A~.PS or, preferably, dialkylaminoalkyl methacryl~te or dialkyla~inoalkyl ~meth)acryla~ides whe~e the cent~21 alkylene ~roup contains at lea~t 2 carbon ato~s, as diseussed a~ove~
~;As indi~ated above, prefer~ed results are achieved whe~ th~ sta~ilising mono~er is ~llylic, either an :allylic monom~r or a poly~ex made ~xom monomer co~prisiny allylic monomer, and ~cordlng ~o a ~ourth aspe~ o~ the invention any of the polymers di~cu~sed ~bnv~ a~e st~bilised by ~he use, a~ inhibi~or, o~ an allylio ~onomer or polymer, pre~erably ~admac~
In a fifth aspect o4' the invention, any of .the polymers discussed above are s~abillsed by the addition of a polymer that in~l udes et~ylenic un~atur~ion, ~or inst~nce, the allylic polymers or othex ethylenically un~tura~ed polymers ~nentionec~l above.
~ n the ~eco~d a~d ~hird aspect~ of ~he invention~, the inhl~iting ethylenically unsaturated ~onomer i~
pr~ferably one ~ ~hose dis~ussed above ~or use in the ~`.fir~t aspect of ~he invention bu~ ~an~ al~ernativsly, be other mono~e~s such ~s acrylamide itself, acrylonitril~
:or acrylic aeid. The produ~t~ of th2se second t~ f~he aspect~ of ~he invention ~y otherwise be ormul~ted u~ing ~he ~me m~terial~, ~nd for the ~am~ purpo~es ~
a~ discussed ~bove ~ox the ~r8t a~peat o ~he in~en~ion.

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Blank ~admac ~iscosity % Vis~ Y
ICP) ~etained (~P) ~ ined Initial 113 - ~6 .
l ho~r . 10 150c 11~ 1~2.7~ 104 120.9 hours @
1~0c ~6 76,1~ 98,5 114.5 4 hours ~
150c 6~ 58O4~ ~ g7.7%

1~ Hours @ 150c47.S 42.0~ 86.5 100.6 .

: When the proca3s o~ example~ s repeak~d u~ing the co-pol3~er of 60 p~rts sod~m ~mp~, 32.5 part~ by weight acryl~mide a~d 7.5 p~r~s by wei~h~ ~od~um a~ryla~e, ~he addition of lO00 ppm dadmac again ~ave a dramatic improvement in viscosi~y xetenti~n.
~xa~pl~e 3 .
30 TQ demons~rate the potential bene~it of various hibitoxs on polymers made fr~ ethylenically . unsa~urated monome~s and which ~ not cont~minat~d with any ac~ylamide at all, a laboratory tes~ wa8 d~veloped observ~ng the vlRco~ity ~hanges ~ro~ itially mAk~ng up `35 a 1% sol~tion o~ ~he pol~mer in lS~ ~gueou~ hydrochlor~c '.`~
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acid follo~ed by storing it ~r one hour at 200~C. ~he polymer for this laboratory test was ~ homopolymer of dimethyl aminoe~hyl (meth~ ~cryla~e (dmaema) gu~ternlsed with ~e~hyl ~hloride. ~he pro~ess was conduc~ed for each S inhibi~or at a in~ibitor dosage o~ lOOppm ~nd ~t inhibitor dosage of 500ppm~ Th~ polymer ~ which no in~ibitor ~ad been Added u~erwent 63.5~ vi~co~ity degradation during the test. ~hus any value hi~her than thi~ is am improv~me~t. ~he values in ~he presence of the variou~ sta~ilisers are shown in ~ble 1 below.
Vi~osity was measured as in ~xampl~ 2.

~ Viscosi~y Retained ; Degradation I~hibito~ 10~ ppm 500 ppm BIank 63.S~ 63.5%
Dadmac 69~3~ ~3.3%
Atmac 75.6% 7~.8 Allyl sulp~onate 65.5% 71.
20 Vinyl Sulpho~ate 7~o6~
Maleic Anhydri~e 76.3~ 71l~%
Amps (Sodium Salt) 43,23 3~.~%
4~aema 73.6% 7~.6 Ap~ac 74.9~ 91.4~
2S Acryli~ Acid 79.~ 75.Zg .~ Aarylamide 79,8~ 86.0%
Acrylic Pr~-P~lymer 67.0% 65.9 ~hi~ is a pre-polymer according ~o the Example of . 30 E~ropea~ Application ~9301075.

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Claims (12)

1. A polymeric composition comprising a blend of a polymer of (meth)acrylamide, free (meth)acrylamide monomer and viscosity degradation-viscosity degradation inhibitor, characterised in that the amount of free (meth)acrylamide monomer is below 0.1% by weight of the polymer and the LD50 of the inhibitor is above 400 and the inhibitor is an ethylenically unsaturated monomer.

2. A composition according to claim 1 in which the inhibitor is selected from ethylenically unsaturated cationic monomers, allylic monomers, maleic acid or anhydride, fumaric acid or anhydride, vinyl sulphonate, and styrene phosphonate.

3. A composition according to claim 1 in which the inhibitor is an allylic monomer.

4. A composition according to claim 1 in which the inhibitor is diallyl dimethylammonium chloride.

5. A composition according to any preceding claim in which the polymer of acrylamide has intrinsic viscosity above 4 dl/g and is selected from acrylamide homopolymer and copolymers of acrylamide with anionic or cationic ethylenically unsaturated groups.

6. A composition according to any of claims 1 to 4 in which the acrylamide polymer has intrinsic viscosity above 4 dl/g and is a copolymer with a monomer selected from dialkylaminoalkylmethacrylate, dialkylaminoalkyl-(meth)acrylamide where the central alkylene groups contains at least 2 carbon atoms, and 2-acrylamido-2-methylpropanesulphonate.

7. A composition according to any of claims 1 to 4 in which the acrylamide polymer is a copolymer of acrylamide with dimethyl or diethyl aminoethylmethacrylate or dimethyl or diethyl aminopropyl(meth)acrylamide.

8. A method of making a composition that comprises a blend of a viscosity-degradation inhibitor and a polymer formed by polymerisation of a water soluble ethylenically unsaturated monomer or monomer blend, characterised in that the inhibitor is an ethylenically unsaturated monomer and is added to the polymer either by imbibing an aqueous solution of the inhibitor into solid gel particles of the polymer before or after drying, or by mixing an aqueous solution of the inhibiotr into a dispersion of the polymer in particulate form in a non-aqueous liquid.

9. A polymeric composition comprising a blend of a viscosity-degradation inhibitor and a polymer formed from water soluble ethylenically unsaturated monomer or monomer blend, characterised in that the inhibitor is an allylic monomer.

10. A polymeric composition comprising a blend of viscosity degradation inhibitor and a polymer formed from water soluble ethylenically unsaturated monomer or monomer blend characterised in that the inhibitor is an ethylenically unsaturated monomer and the polymer is formed from monomers that consist essentially only of ethylenically unsaturated cationic or anionic monomers.

11. A composition according to any of claims 8, 9 and 10 in which the inhibitor is dially dimethylammonium chloride.

12. A composition according to any of claims 8 to 11 in which the polymer is formed of monomers that comprise dialkylaminoalkylmethyacrylates and dialkylaminoalkyl-(meth)acrylamides wherein the central alkylene group contains at least 2 carbon atoms.