CA1134099A - Dialkyl substituted aldehydes as a chain transfer agent for vinyl chloride polymerization - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to an improved process for preparing vinyl chloride homopolymers and copolymers via emul-sion, suspension or solution polymerization. In the process, a substituted aldehyde, e.g. 2-ethyl hexanal is used as a chain transfer agent.

Description

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This invention relate~ t~ a vinyl chlorid~ polymeri-~ati.on process, and particularly ~o a proce5s for preparing vinyl chlor~de pG~merS (PVC) of moderate ~olecular weight and ~aving desirable process~ng and molding properties.
~ process for preparing vlnyl chloride polymers using chain ~ransfer agen~s to con~rol the molecular wPigh~ has been proposed wherein compositions were suggested as chain transfer agents ~ and these chain transfer agents include aro~atic h~dro-caxbsns, e.g.9 cumene; aldehydes such as acetaldehyde; ke~ones 0 5uch as acetoneS mercapatans ~uch as lauryl m~rcap~an~ chlori~
nated h~drocrabons9 e.g. carbo~ ~e~rachloride~ chloro~orm~
propyle~e chlor~de~ me~ylchlorofo~m, and ~richloro~t~yle~e.
Th~ latter ls de~med to be the i~dustry ~andar~.
Alpha~be~a unsaturated aldeh~des ~uch as methacrol~in3 crotonalde~yde and ci~ral have bee~ proposed ~o "short stop't a ~yl chloride polymeri~ation w~en from a~out 0,1 to 1% by we~ght o the ~ldehyde is incorporated ~nto the pol~meriæati~n medium. Alpha~al~y~alpha, beta unsaturatecl keto~es such as 4-ethoxy-3-me~hyl-3-butene-2-o~e. or m~thylisoprope~yl Icet~ne ~0 ha~e also bee~ proposed as effective as shDrtstopping a~en~s for v~yl chlorid~ polymeriza~
~ he use of variou~ aldehydQs such a~ fl~rmald~hyde, ace~aldehyd~, propylaldehyde, n-butyraldehyde, iso bu~yraldehyde a~d iso-valeraldehyde as a componen~ for a catalys 6 rstem in the p~lymerization t> vi~yl iaonomers has been proposed. The part~sular catalys~ sy~'cem compriLses hydro~en peroæideg, sul~ur dioxide, and the aldehyde~
~ ~s also k~lown that ~sobutyral and high molecular wei~h~ nvtl-substituted aldehydes are ef~ective as ch~n tran~-30 ~r agents i~ the polymerizaSiorl of ~ yl chloride~ ~ut, the~ealdehsrdes tend 'co l~a~e a residue in the res~ which is ~1-odorous or tend to deerease ~cher~l s~ability.

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Thl5 il1S7ent~0n rela~es t~ an i~proved proce~ for ~he polymeri~a~ on of vi~yl chloride wherein vinyl chlorlde monomer or vinyl chl~r~de monon~r and a~ least one other monomes: co~
polymeri~able therewi~h~ is poly~neriæed in the pr~sence of a free radical initiator and a cha~n transfer a~sen~. The imp~ove-ment in the proce~s resides ~ the use Df an aldehyde which is at least dialkyl substltuted. The aldehyde is r~presented by the formula:

3 C ~ _

- 2 where~n:
Rl i5 hydrogen, lower alkyl with the alk~l pl~rtion having from 1 to 6 carbon atoms and cycl~hexyl;
R2 is a lower alkyl groùp with the alkyl portion hav~ng from 1 ~o 6 carbc~n atoms and ¢yclohexyl; ~nd R3 ~s ethyl, propyl3 butyl, and cyclohexyl.
In a preferred em~odiment, the aldehyde is ~ ethyl hexanal .
Adva~tages o:E this invent:ion i2~clude:
ths ab~ y t~ con~rl~l the molecular ueight ~f poly-v~nyl chlor~d~ hom~polym~rs and cop~lymers at reduced po~ym~rl-~ation te~perature and ye~ form a polymer hav~g desirable pro-c~ss~g characteristics;
the abili~y to form a polymer ha~ing enhanced thermal stab~lity as compared to polymers formed in the presence o chlorina~ed chain transfer agents or non-subs~i~u~ed aldehydes, the abili~y tv produce a poly~er possibly suita~le for ~ood use because i~ does no~ contain the residue of a 30 possible carcinogenlc chain ~ransfer agen~;
the ablli~y to afec~ and control molecular w~igh~
with a snkall pr~portion of chain trans~er agent; and l the abilit~ to produce a pol~mer which is s~bstan-tially free of ~bjectlonable aldehyd~ odor as is ound in those cases wherein isobutyraldehyde is employed as the chaln trans-~er agent.
I~ accor~ance with the present invention, polyvinyl chloride homopolymers and polyvinyl chloride copolymers and l~terpolymers are prepared in the p~esence of select ehain transfer agentsO The vinyl monomer suitable for use in tke process o~ this invention are those polymerizable with vinyl chloride under pol~merization condltions and include~ for ex-ample, yinyl acetate, ethylene, acrylic monomers~ e.g., l~we.r alkyl (Cl to C6) esters of acrylic and metha~rylic a~ acry-lamide, N-me~hylolacrylamide, acrylic acid, glycidal acrylates9 etc. In preferred practice, the polymers ar~ ~inyl chl~ride homopolym2rs or interpolymers of,vinyl chloride, vinyl acetate, and ethylene and those containing small amounts or less than 10~ acrylamide.
. The vinyL chloride polymer is prepared by co~ventional polymeri~ation techniques which includle a~ue~us emulsion and suspension free radical ~nit;ated p~lyme~i~a~ion a~d sol~e~t ~r solution polym~rlzation. General~y, emulsion polymerization is used and a typical polymer r~cipe compr~se~ water in a propor-tio~ of from about 100 t~ abou~ 300 weight parts per 100 parts monom~r ~phm); conventional suspending a~ents su~h as gelat~j hydro~ym~thyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose~ talc, clay~ a~d polyvinyl alcohol in a proportion o from about 0.05 to 0~5 phm9 chaîn transfer agents in a propor-tion of fro~ ~ o 5% and ree radical initiators such as benzylperoxide, diacetyl peroxide, azo-bis-isobutyronitrile, diisopropyl peroxy dicarbonate9 t-butylperoxy p;valate, aml~D~-ium persulEate, and azo bis~alpha, gamma-dimethyl valeronitrile) in a proportion~o~ from about O.OOS t~ about 5, and generally 11 ~ 40~!9 r~m 0.01 to 1 ph~.
The advantageous ~eature o this lnvention resides in ~he use o an al~cyl substituted aldehyde represented by the or~ula:
Rl O

R~
whaxein:
Rl is hydrogen, lower alkyl havin~ from Cl to C~
carbon atoms, and cyclohexyl;
~ 2 is a lower alkyl group having from 1 ~o 6 carbDn atom~ and cyclo~exyl; a~d R3 is ethyl~ prnpyl, butyl, and cyclo~exyl.
The chain transfex agent generally is comb~ned Ln a proportion of from about 0.1 to 5Z, and preferably 0.5 to about 2% by weig~ of the monomer or efec~.vely reducing ~he mole-`
cular weight o~ the vinyl chloride. It: can be used i~ ~reater quantities or as a solvent in solution po~meriæation w~ere low ~lecular weight polymers are desired, On the other hand, the ~hermal ~tabilit~ of ~he polymer is ~ch ~rea~er ~han is ob~a~ned with the con~entional chain transfer agents~ e.~. ~he chlorinated -chain tra~sfer agents.
The present chai~ tra~sfer agents ha~e ad~a~ageous ~e~tures o~er other chaln ~ransfer agents. They do n~t p~ly merize ~nto the backbone of the vin~l chloride ~om~pDlymer or copolymer as do for e~ample substituted ol~fins such as iso-butylene or propyl~ne. Therefore~ they pro~ide similar p~lymer characteristics to trichlorQethylene ~nd ~hu~ equipme~t sui~ed or n speci~ic i~herent v~scosity can readily be ad~pted ~o the polymers producQd by thls p~ocess. By virtue of the ~act that the chain ~ransfer age~ts are at least disubstit~ted~ less ac71 .!
functionalit~ is ~ntroduced lnto ~he homopolymer~ ~h~n ls the o~

case with nonsubstituted aldehydes, e~g. acetaldehyde and there-fore the thermal stability of the resul~ing homopolyrZler or co~
polymar is enhanced. Another fac~or wi~h respec:t ~o ~he present chaln transfer agents is ~hat ~chey are not suspect o~ ~arcino-genicity as compared to many of ~he chlorinated chain ~anser agents and therefore probably can be used in packaging food products . Another feature is that the chain trans fer agent and particularly 2-ethyl hexanal does not impart an ob~ectio~able odor lnto the polymer as does isobu~:yr21dehyde which is an ex-10 ample o a dialkyl s~l~sti'cuted cha~ transer agen~.
~ he follow~n~ exampLes are provided to illustrate pre-ferred embodiments o~ the invention and are not itltended to restrict the scope thereof. All parts are parts by wei~ht un~
le~s otherwise stated, and all temper~tures axe in C.

EXA~E 1 Sevexal polyvinyl chloride hom~polymer samples ~7ere prepared by conYentional polymeriza~ion ~echnique ~n a 1-1/2 liter stirred ~eactor. In the polymer~zation process, the con-tents, e.g. vinyl chloride monomer (YCM~, water~ suspendingagent, chain transfer agent t~TA) and free radical i~tiator were charged to the reactor and heated t~ a temperature o 65~. Polymerization was conti~ued until a 15 pound pressure drop occurred or when the pressure drop rom the ~ppropria~e initial pre~sure of ~55 psig to about 140 pslg~ When polym~r ization ~as complete, the conten~s were cooled and ~he rea~tor ~ented. The polym~r suspension was 11tered and the ca~e dried i~ an ~ven.
Table 1 bel~ pr~vides detail of various rec~pes em-ployed ~nd ~he mel~ flow and inheren~ vlscoslty ~f the resper~tive recipes.

3~l3 r~
o~
r~r~ oo c ~r~ Ln ~
G~ ¦ O 1` i~
o o ~ ~ ~ o n o\o o. o~ ~o X ~ O O ~ 5~ O O
.

r~ . ~ ~
oo l r~ r~ 3 c ~r~o o\ ~ co o o ~ n ~ x o o o\o n Ln o o . . , a~ ~ n ~ oo o~ ~r o o ~ C ~ ~~ ~o 1~ r~ ~ o ~ ~ . r~
. r~ ~ ~ ~ r~ o~o r~ r~ ~ .c ~ Ln Ln r~ I o o ~o Ln ~ X oo ~ o\
O o . , a) ~ ~n a~ ~o ~ ~ o o ~ C n ~ V 1~ ~t ~ o h b4 ~ ~ ~ ro o\
ror~ ~ ~ ~ Ln ~o ~o l o ,~ a~ Ln al ~ CO
O O ~D n o ~ C~ q o\o~ Ln ~ ~
~o ~ o o ~ ~ n--~ ~D oo Ln ~ o h ~
0~
~n ¦r~ r~ c r~ n o o~o Lno ~ ~ o 0\o 0 ~ ~O
U~ o o . . U~ ~ o n ~
V ~ o o ~ ~ n o c~ . . r~
u~ . . r~ ~ o\
~ b~ Ln a~
~ ~ 1 o o~o Ln U~ ~ o~ o\o o Ln t~ o o ~ ~ Ln o ~o ~\o~ oo ~ ~ ~ ~o oo ~ ~ o o ~
~1 . . ,_~ h I t~~1 o\ rl Jb~r~ O
_~ ~ 1o o ~o ~ ;~ 0\o Ln N Ln ~ O O . . ~ ~ Ln ~t ~ ¢
z ~o ~o o ~ - ~ ~o oo ~ ~ o ~ o ~h, C
h O r~
O C tLI
r~ O\o C~ O~oLn .~ I a ~ 1 o o ~o ~ ) Ln ~ ~o ~ n ~
o O h ~ o cn ~o h I O
~O ~O E~ o r~ ~ ~1 o o oo O
.~ ~ ~ I
b~ r~ O\o O O E--,~ I OIr~ a) ~ d' ~ r~ ~ 0\o ~ u~
~O ~ C I O ~ r~ ~ I~ C '' ~0 ~) O O Z ~0 co ':1 0 0 ~1 ~ j ,~ 0\o , ~ o 3a.) '-- ~ ~ L
L') ~ ~ 4 ~S h E~ ~ 3 X O J~
' X o ~ ~
t-d h O h ~ L) C--~ ~ F40 h p~ ~ c) ~: .~ ~- r~ E;E~ ~~ '' ~ ~ ~ ~ a~ C
a~ ~ ~ ~c E~ ~ c ."
~ ~ ~ ~ C ,1 C ~ I I
E~ Lrl ~ o o ~ O C.. ~ .
O ~ Cd E3 .rl h ~
C ~ ~ L~ H

~J - 6 -The above table shows that conversions with 2-eth~71 hexanal were well wi~:hin the conv~rs~on range of con~xol ~rich-loroethylene and isobutyraldehyde CrA. On a weig~t lbas~s~ the isobutraldehyde was more e~fect~Te than the 2-ethyl hexanal ~hich was more effective tha~ the control tr-Lchloroethylene in achieving a specific ~nherent viscosit~r. The 2-ethyl hexanal appeared to be about 50~O more effective (co~pare runs 3 and 8) than trichloroethylene. ~n ~he other ha~d~ the resins contain-ing isobut~raldehyde had an ob~ec~ionable odor.

~A~EL~ 2 A polyvinyl chloride-polyvinyl aceta~e cop~lymer was prepared in the same manner as the homopolymer of Ex~mple 1 e~cept tha~ ~he recipe contained 600 grams water, 0.18 grams of a sodium salt of ethylenedlamine tetracetic ac~d, 0.18 grams sodlum bicarbonate, 0.45 grams polyvinyl pyrrolidone, 311 g~ams vinyl chloride monomer, 0.25 grams azo-bis-~dimethyl) valeroni-~rile) and 1.% 2-ethyl hexanal. The polymeriæation was e~ected for 5.5 hours at a temperature o 73C'. The inheren~ visc~s~ty 20 of th~ ~e5ulting polymer obtained was 0.~03 and the yield was 78.4X. The p~r~icle size distribution of the resulting polymer showed the predomi~ant porti~n being between 60 and 100 m~sh.

~XAMPI~ 3 The procedure of Example 1 was rep~ated except that 400g VCM9 80~g water, O.lg NaHC03, 0.208g carboxymethyl cellu~
lose, 0.67 ml t-butyl peroxypivalate (75% in odorles~ mineral spirits) and 3g 2 ethyl buty~aldehyde were reacted at 65C for 3.5 hr. The resulting polymer had a melt fl~w of 14 and an 30 inherent viscosity ~.58B. Very li~tle to no odor was observed, and the polymer had compar~ble thermal s~ability to 2~ethyl hexanal.

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Three different polyvinyl chlorlde homopolymers pre-pare~ in accordance with the procedure of Example 1, exrept for ~he substitution o var~ous chain transfer agents and amount of chain transfer agent in the polymer, w~re evaluated for thermal stability. The resins A, B and C had the following composition:

~esin. A B C D
CTA 2EH TCE 2E~ ~cetaldehyde 10 ~t ~ rz CTA 0.25 0.70 0.40 1%
IV 0.691 0.669 0.662 0.692 1,1 1.2 1.2 ~ n a first series o tests, varlous comparlson resins in the neat state, were heated to a temperature of 370~F in a plate press for about 20 seconds and then examined ~or color development. ~sins A and C w~ich con~ain 2-ethyl hexanal as a chain transfer agent9 had a pale yellow tn pink color. ~es;n B, which contained the t~ichloroethylene chain tr~ns~er agent~
2~ had a light pink color thus sh~wl~g that it dlscclored sl~g~tly more than the sther two resins preparad with 2-e hyl hexanal.
Res~n D had an orangish cast.
I~ a secon~ serles of te~ts, identical quantities of resins B~C were compounded with various acrylic resin process-~ng aids, lubrica~ts, stabiliæ~xs and dyes. These compounds were pas~ed ~hrough a two roll mlll having a space between ~he rolls to g~e a sheet of approximatel~ 36 mil~ in ~hickness.
Each resin was milled for about 60 minu~es and speclmens wi~h-drawn at two minute interva~s. The thermal stabili~y o~ th~
30 resins was measu~ed ~n terms oE the time it ~ook or the res~n to become neutral gray-clear i~ color, and then ~o yellow and brown. ~esins B and C, respectively, without prehea~, required 36 and 46 mlnutes, respectively, to become neutral-gr~y. With a resin preheat of 30 minutes at 130C., resin B required only 22 minutes to beeome neutral-gray, whereas resin C required 46 minutes, This test shows that molding co~pounds prepared with the vinyl chloride homopolymer polymerize~ in the presence of 2-ethyl hexanal had greater thermal stab-Llity than the vinyl chloride homopolymer polymerized in the presence of trichloro-ethylene.

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Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a process for suspension polymerizing vinyl chloride monomer and monomers copolymerizable therewith in the presence of water, suspending agent, chain transfer agent, and free radical initiator to form a polymer con-taining at least 50% by weight vinyl chloride, the improve-ment for obtaining desirable polymer melt rheology which comprises using as a chain transfer agent from 0.1 to 5% by weight of 2-ethyl hexanal by weight of the total monomers.

2. The process of claim 1, wherein said 2-ethyl hexanal is present in a proportion of 0.5 to 2% and said polymer is polyvinyl chloride homopolymer.