FR2555995A1 - PROCESS FOR THE PRODUCTION OF LOW MOLECULAR WEIGHT ACRYLAMIDE POLYMERS - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR THE PRODUCTION OF ACRYLAMIDE POLYMERS OF LOW MOLECULAR WEIGHT. THE LOW MOLECULAR WEIGHT ACRYLAMIDE HOMOPOLYMERS AND COPOLYMERS ARE PREPARED BY REVERSE EMULSION POLYMERIZATION OF ACRYLAMIDE IN THE PRESENCE OF A CHAIN TRANSFER AGENT CHOSEN BETWEEN ERYTHORBIC ACID, ASCORAMENYTIN ACID AND HUDITROBIC ACID, BUTYL. THE PROCESS OF THE INVENTION PROVIDES A LOW MOLECULAR WEIGHT POLYACRYLAMIDE WHICH CAN BE USED WITHOUT DANGER IN CONTACT WITH FOOD PRODUCTS.

Description

255599S

i

  The present invention relates to a method for

  production of water-soluble, low molecular weight acrylamide polymers and copolymers by

  polymerization in inverse emulsion or in solution in use

  reading a chain transfer agent. The solution or emulsion polymerization of acrylamide is a process

  Already known. The prior art teaches the use of

  aliphatic cools such as isopropyl alcohol, ethanol

  nol and methanol as chain transfer agents

  for the solution polymerization of acrylamide.

  Other techniques utilize various sulfur compounds or organic sulfur compounds as the heat transfer agents, such as thioglycol, thioglycolic acid, and the like.

  and n-dodecylmercaptan (United States of America patents)

  that N 4 196 272 and N 4 245 072). Another technique,

  used for the solution polymerization of acrylamide

  of, involves initiators of oxidation-reduction in

  which bisulfite ion plays the role of a transfer agent

of chain.

  U.S. Patent No. 4,307,215 teaches the use of formic acid and alkali metal formates as chain transfer agents, using inverse emulsion polymerization conditions.

  All the compounds of the prior art have

  disadvantages that make them, at best, difficult to use in industry. For example, they

  are not effective and require high concentrations of

  the chain transfer agent to obtain the

  desired molecular weight, or they have

  strong and pungent odors that are frequently

  final polymer, which severely limits market opportunities; some are corrosive or toxic, others produce a retarding effect

  accentuated on the polymerisation of acrylamide, by

  therefore reducing productivity.

  No teaching of the present invention has been found in the prior art. The present invention

  eliminates the problems of the prior art.

  The present invention is directed to a process for producing a polymer or copolymer comprising

  the inverse aqueous emulsion polymerization of a representative

  comprising the group consisting of (i) acrylamide, (ii)

  thacrylamide and (iii) a mixture of 10 to 90% of (i) or (ii) and a monomer selected from the group consisting of acrylic acid, methacrylic acid, methacrylate

  N, N-dimethylaminoethyl, sodium acrylate, iso-

  propylacrylamide and acrolein, in the presence of at least one surfactant, of at least one free radical initiator and a chain transfer agent for limiting the molecular weight and consequently for the effect thereof. the viscosity ? of the oliftion of polymer or copolymer, said agent

  chain transfer being selected from the group consisting of

  erythorbic acid and its alkali metal salts,

  ascorbic acid and its alkali metal salts,

  and butylated hydroxytoluene.

  The chain transfer agents used in the practice of the present invention are

  well-known compounds, most of which have been used

  me additives in the food and beverage industry.

  They are easy to obtain, their handling is safe and they do not show the toxicity or the hygienic risks associated with the compounds of the prior art. This is particularly important since polymers

  The resultants are used in various cosmetic formulations.

  ticks and also as additives in the food industry.

  drawn. By using emulsion polymerization techniques, the present invention overcomes the problems

  high viscosity and poor heat transfer.

  As a result, the ratio of water to monomer can be

  kept very low, thus raising the amount of polymer

  It is produced in a given reaction batch.

  A high temperature of polymerization is not

  not necessary in the implementation of this

  vention. The degree of branching of the polymer would thus be

  reduced by improving the quality of the product.

  As a result of the high cost of energy, the lower temperature of polymerization would also improve the economy.

from production.

  An emulsion is generally obtained

  persant a phase in the form of very small droplets (ie the dispersed phase) in another phase

  (ie the continuous phase) in the presence of a surfac-

  suitable tif. The most common emulsion form is an oil-in-water emulsion in which the oil constitutes the dispersed phase and water constitutes the continuous phase. Another form of emulsion is the water-in-oil type emulsion in which water constitutes the dispersed phase. This emulsion is also sometimes called

  inverse emulsion. The term emulsion used in the pre-

  This invention only refers to emulsions of the type

  water-in-oil unless otherwise specified.

  As is well known, surfactants can

  to be classified according to the EHL system, that is to say

  "hydrophilic-lipophilic balance". In general, to prepare

  For water-in-oil emulsions, the surfactants used should be oil-soluble and should have an EHL range of about 1 to 12, preferably about 4 to 6. The desired range of EHL can be also

  be obtained using mixtures of surfactants com-

  taking ionic and nonionic surfactants. Surprising

  Suitable facets include sorbitan fatty acid esters, fatty acid monoglycerides and diglycerides, polyoxyethylenesorbitol esters, polyethylenesorbitan fatty acid esters, and

polyoxyethylated alcohols.

  The total concentration of surfactants used may vary from about 0.5 to 20.0 parts by weight

  per 100 parts by weight of the oily phase, preferably

  from about 2.0 to 15.0 parts by weight of the oily phase. Acrylamide is generally polymerized in an inert atmosphere (eg N 2 or GO 2) at a pH of about 3 to 8. When the pH is greater than about 9, the amide groups can be hydrolyzed and when the pH is below about 2.5, an imidation often

  place, resulting in the formation of an inert cross-linked polymer

  luble in the water. Thus, the preferred pH range in the practice of the present invention is between

about 3 and 8.

  The ratio of the aqueous phase to the oil phase

  is crucial in the implementation of the present

  the invention for stability and performance. In

  general, the ratio of the aqueous phase to the oil phase

  should be about 1: 5 and especially about 1: 2. A ratio of the aqueous phase to the oily phase of 1: 1 or

  even 2: 1 can be used as long as the emulsion

  sultante is stable. Since the monomer is

  under in the aqueous phase, it is better to maintain the

  concentration of the oily phase as low as possible

  to increase the polymer yield in a given batch.

  The polymerization temperature should generally

  be in the range of about 20 to about C and especially in the range of about 25 to about

60 C.

  The free radical initiators used in the practice of this invention are the well known organic peroxides and azo initiators. As examples, suitable initiators include the following: tert-butyl peroctoate, peroctoate

  tert-amyl, tert-butyl peroxypivalate, peroxynival

  tert-amylate late, t-butyl peroxvypivalate, tert-butyl neohexancarate, xyn :. Tert-amylate, peroxynodeodecanoyl, tert-amyl neodecanoate, dibenzoyl peptylate,

  diacetyl peroxide, dilauro-peroxide, peroxidic acid

  di (2-ethylhexyl) carbonate, di-peroxydicarbonate

  (phenoxyethyl), 1,1-di (tert-butylperoxy) cyclohexane,

  1,1-di (tert-butylperoxy) 3,3,5-trimethylcyclohexane, 2,5-

  dimethyl-2,5-di (2-ethylhexanoylperoxy) hexane, 2,5-dimethyl-2,5di (benzoylperoxy) hexane, di-tert-butyl peroxide,

  di (tert-butyldiperoxy) azelate, tert-butyl peroxide

  cumyl, azobisisobutyronitrile, 2,2'-azobis (2,4-dimethyl-

  valeronitrile), 2-tert-butylazo-2-cyano-4-methoxy-4-

  methylpentane, 2-tert-butylazo-2-cyano-4-methylpentane,

  2-tert-butylazo-2-cyanopropane, 2-tert-butylazo-2-

  cyanobutane, 1-tert-butylazo-1-cyanocyclohexane, hydro-

  tert-butyl peroxide and cumene hydroperoxide.

  Water-soluble initiators of free radicals such as potassium persulfate, ammonium persulfate and hydrogen peroxide can also be used. One can also use a mixture of two or

  more than two initiators of free radicals. The concentration

  The initiator ratio should range from about 0.005 to about 5.0 parts by weight per 100 parts by weight of the monomer, preferably from about 0.05 to about 2.5 parts by weight per 100 parts by weight. weight

of monomer.

  Acrylamide or methacrylamide is poly-

  In the practice of the present invention, the present invention is directed to producing nonionic homopolymers of low molecular weight. However, it is also possible to

  copolymerize with one or more comonomers. Comoros

  suitable denomers include, for example, the acid

  acrylic, methacrylic acid, N, N methacrylate

  dimethylaminoethyl, sodium acrylate, isopropyl

  acrylamide and acrolein. As is well known to those skilled in the art, comonomers can be chosen

  to produce cationic or anionic polyelectrolytes

  c. During the copolymerization, the concentration of acrylamide (or methacrylamide) is about 10 to% and preferably about 10 to 75% total monomer,

in weight.

  Chain transfer compounds, by definition

  nition, are used to limit the growth of

  polymer chain and therefore the molecular weight.

  Under theoretical conditions, these compounds should have no effect on the rate of polymerization. They are used in a concentration range of about 0.001 to 5.0 parts by weight per 100 parts by weight of monomer, preferably from about 0.01 to 2.5 parts by weight.

  weight per 100 parts by weight of the monomer.

  The following compounds are transfer agents

  Effective Chain Factors of the Present Invention:

  Erythorbic acid and its alkali metal salts

  such as sodium erythorbate, ascorbic acid and its alkali metal salts, vitamins such as

  niacin, vitamin E and riboflavin, and hydroxy-

Bityl toluene (BHT).

  20. From the point of view of the supply facilities

  and cost, the chain transfer agents that

  the implementation of the present invention is

  are sodium erythorbate, erythorbic acid and hydroxy-butene-butylated. These compounds have been classified as antioxidants suitable for use in the food industry, for example according to FDA regulations (see Kirk-Othmer Encyclopedia of Chemical Technology, Volume 3, 3rd edition, page 140, Table 2). In addition, they do not have a particular tolerance level, which

  indicates that they can be safely used for any purpose

  concentration as additives for food products.

  Therefore, the chain transfer compounds that

  in accordance with the invention may be used

  alone or in combination with each other to produce a low molecular weight acrylamide polymer that can be safely used for applications

in contact with food.

Examples

  Definitions of Materials Used in WHO Examples - Odorless Mineral Essence, sold under the Trade Mark Shell Sol-71 by Shell Oil Co. Span 80 - Sorbitan Monooleate from ICI Americas, Inc. EA - Erythorbic Acid Pfizer Inc. NaEA Sodium Erythorbate from Pfizer Inc. Acrylamide Monomer, Grade "Reactive

  Fisher "of Fisher Scientific.

  A 50% aqueous solution of monomeric acrylamide inhibited with about 25 ppm copper (Cu ++) of the firm

Dow Chemicals.

  Water tridistilled Queen City Pure Water (Buffalo, N1.Y.). Before use, this water was boiled and allowed to cool while purging

  nitrogen. Until the moment of use, it is

was under an atmosphere of nitrogen.

  Lupersol 223M75-di-peroxydicarbonate

  (Ethylhexyl), marketed by Pennwalt Corp.'s Lucidol Divo.

  Versenex Q 80 - diethylenetriamine acid

  penta-acetic acid, a chelating agent from Dow Chemicalse Vazo 0 64 Azo-bis-isobutyronitrile

DuPont firm.

  Vazo W 52 - 2,2'-azo-bis (2,4-dimethylvalo)

nitrile) from DuPont.

  BiT - butylated hydroxytoluene 5 296-di-tertiary

  *,} tyl-p-cresol 26-di-tert-butyl-4-methylphenol from Aldrich Chemical Co., Inc.

Riboflavin - Vitamin B2 from Roche.

  Vitamin Dne E - α-Tocopheryl Acetate of _, t I t. r} -d r '3-. Lonz-G = formic acidic acetic acid - certified A.CoS. of the irme

Fisher Sientic Company.

  Acrylamide Monomer, "99% + Gold Quality Label for Electrophoresis" from Aldrich Chemical Company, Inc.

  K2D208 - Potassium persulfate "Baker Ana-

  lyzed Reagent "from J.T. Baker Chemical Co.

  Lupersol Q 256 - 2,5-dimethyl-2,5-di-t 2

  ethylhexanoylperoxy] hexane, marketed by Lucidol

Div. from Pennwalt Corporation.

  Lupersol C 331-80B-1,1-di- [tert-butyl-

  peroxy] cyclohexane, marketed by Lucidol Div. from Pennwalt Corp.

  DS-606 4- (tert-butylperoxycarbonyl) -3-hexyl-

  6- (7- (tert-butylperoxycarbonyl) heptyl) cyclohexene,

  marketed by the Lucidol Div. from Pennwalt Corp.

  Lupersol 0 TA-54M75-tertiary peroxypivalate

  amyl, marketed by Lucidol Div. from Pennwalt Cor-

poration.

REFERENCE METHOD

  Formulation: Parts by weight Acrylamide 50 Tridistilled water 50

OMS 200

  Span w 80 Initiator 0.05 or according to the required amount Chain transfer agent Procedure Using a triple flail scale (Ohaus), 50 g of solid acrylamide monomer were weighed and then dissolved with stirring ( at room temperature) in 50 g of tridistilled water. In the same manner, 20 g of Span 80 were weighed and dissolved in 200 g of WHO. These two solutions were then mixed in a blender

  eLrin- -n high-speed stainless steel for approxi-

  3 mm rins to form a water-in-oil emulsion.

  The solution was then transferred to a 1 liter (jacketed) reactor equipped with a stirrer, condenser, thermometer and purge line. 'nitrogen. The actual bowl of the reactor was immersed in a thermostated bath (+ 0.1 C) and preset to the

  desired reaction temperature (e.g. 35 C). The emulsified

  The stirring was purged with nitrogen for about half an hour before addition of the initiator. The desired amount of initiator was weighed into small tared glass cups using a

  Mettler analytical balance (+ 0.0001 g). The small coupel-

  was placed in a 10 ml glass beaker to which

  about 5 ml of acetone was added. This solution has

  subsequently added to the emulsion with stirring. The beaker

  with the small cup was rinsed again with some

  milliliters (2-5 ml) of acetone and the contents were added back to the reactor. At this point, the electric timer has been triggered to indicate the beginning of the polymerization. When a chain transfer agent was used, it was weighed and transferred to the reactor in the same way. Only the choice of the solvent varies according to the transfer agent that is used, for example water for EA,

  WHO for BHT, a water-methanol mixture for riboflavin

  born. However, the initiator must always be the last

component added to the reactor.

  At predetermined time intervals, emulsion samples were taken from the reactor

  using a hypodermic syringe and a needle.

  After weighing, the emulsion was precipitated in acetone

  or in methanol with stirring. The syringe and the

  guille were weighed again to obtain the weight of

the emulsion sample.

  The precipitated polymer was filtered through pre-weighed filter paper and dried under vacuum at about 50 C to constant weight (usually

  about 12 hours). The solids content is obtained

  from which the percentages can be calculated

of transformation.

  For the polymerization of aqueous acrylamide solution (from Dow Chemicals), the monomer is first treated with 0.2 parts by weight of Versenex (chelating agent) per 100 parts by weight of monomer, to eliminate the inhibitor (copper). The rest of the procedure is the same as for mono acrylamide

solid mother described above.

  Solution viscosity measurement of the polymer: The dry polymer was first ground in

  a Micro-Mill device (Model No. 502 from the firm Techni-

  lab Instruments) for about 3 minutes. Then 4.00 g of the polymer was mixed with 24 ml of methanol with stirring in a 250 ml beaker. After total wetting

  of the polymer, 198 ml of tridis-

  and continued stirring for a further 5 minutes to obtain a 1.8% aqueous solution of polymer which

  it has been used for viscosity measurements.

  A Brookfield RVF viscometer equipped with a

  pin 4 and set to speed 4 (rpm) was used

  for solution viscosity measurements at 25 ° C.

  The REFERENCE METHOD has been used in

  all examples, unless otherwise specified.

Example 1

  This example illustrates the use of EA and NaEA as chain transfer agents with types

  different types of free radical initiators, as

  the results of Table I.

  EA acid was used at the concentration -

  0.1 g per 100 g of acrylamide monomer and NaEA salt

  at the concentration of 0.2 g per 100 g of monomer.

  The initiators were used at a concentration

  0.1 g per 100 g of monomer, after taking into account

  account of any differences in the titles.

TABLE I

  Polymer time- Viscosity Brook-

  Polymer trance agent Transformation, field of a

  Initiator fert chain sation, min. 1.8% elution at 1.8% polymer at 25 ° C, in mPa.s Euazo @ 55 _ 400 74 14 000 Lu azo 55 _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ __ _ _ _ _ __ _ _ _

EA 360 75 2500

245,100 26,000

Vazo 52 EA 260 100 7900 "

___ _-._.___. _: 300 100 24 500

  Lupersol 245 EA 300 100 4500 GoT: _ _ _ '_ _' '__ _ 300 100 24 500 Lupersol' 256 NaBA 240,100 4500 -9

Polymerization temperature: 35 C.

  Polymerization temperature 35 C.

naJ W

Example 2

  The vitamins listed in Table II have been successfully used as

  chain with various initiators of free radicals.

  The initiators were used at a concentration of 0.1 g per 100 g acrylamide monomer after

  have taken into account any differences in the titles.

  The concentrations of vitamins used, in grams per 100 g of acrylamide monomer, are listed

in Table II.

TABLE II

  Brook-polydispersity trans-concentration agent

* Initiator fert chain agent, Transformation, field of the

  min. 1.8% g / 100 g polymer at 25 ° C., monomer in mpas. Lupersol 5,800 100 2,800,200 Vitamin B2 0.2 g / 100 g of 300 98 1000 (Riboflavin) Lupersol monomer 360 85 19 500 33180B Vitamin E 0.66 g / 100 g 360 57 3000 monomer Niacin 0.1 g / 100 g 360 360 4800 monomer Niacin 0.05 g / 100 g 360 56 4000 monomer Polymerization temperature: 35C -% n ln oo us

Example 3

  The REFERENCE METHOD was used, except that a reaction temperature profile was chosen. DS-606 is a sequential initiator whose peroxide has two initiator groups with different period activities. The profile involved a

  temperature of 35 C for 4.5 hours followed by a rise

  temperature at 45 C with holding at this temperature.

for 1.5 hours.

  EA acid was used at a concentration

  0.1 g per 100 g acrylamide monomer.

  DS-606 was used in a

  concentration of about 0.1 g per 100 g of monomeric acrylamide

  re after taking into account any differences in titles.

  It is known that sequential initiators produce a high molecular weight polymer and this example shows (in Table III) that EA acid is useful to use as a chain transfer agent, with this

  type of initiator of free radicals.

TABLE III

  Polymerization time- Viscosity Brook-

  Transformation agent, field of a polymer

  Initiator fert chain sation, min. % elution at 1.8% of polymer at 25 ° C, _________________ in mPa.s

- 360 100 38 000

DS-606 .....

EA 300 100 2800

ru Ln o tn

Example 4

  BHT is a food grade antioxidant

  silent. Some vitamins, eg ascorbic acid (vitamin C) and α-tocopheryl acetate (vitamin E) are also antioxidants. This example illustrates the use of BHT as a chain transfer agent,

  as shown in Table IV.

  BHT was used at a concentration of

  0.1 g per 100 g of acrylamide monomer.

  The product Lupersol - (331-80B constituting the initiator was used at a concentration of 0.1 g per 100 g of acrylamide monomer, taking into account

any differences in titles.

TABLE IV

Hard Polymer- Viscosity Brook-

  Trans-agent Polymerization time Transformation, field of a Bo-

  Initiator fert chain sation, min. % 1.8% 1.8% polymer elution at 25 ° C, mpas Lupersol - 360 85 19 500

331-80B BHT 360 74 5500

  -300 100 o 27 500 Lupersol o223M75 BHT 360 80 9500

223M75

  Polymerization temperature: 35 Ctn nQ

IVS5995

Example 5

  The experimental method used in this example was as follows: Solid acrylamide was dissolved in tridistilled water until a clear solution was obtained.

  This solution was poured into a glass reactor previously

  heated by either a heating jacket or a water bath at the reaction temperature. The reactor was equipped with a stirrer, a nitrogen purge, a thermometer and a condenser. The stirrer and the nitrogen purge were triggered. After half an hour, the initiator dissolved in about 5 ml of acetone was

  added to the reactor and the stopwatch was started.

  The small beaker used to dissolve the initiator was rinsed with 3 to 5 ml of acetone and this rinsing acetone was added to the reactor. The formulation used is as follows: g of acrylamide monomer 500 g of tridistilled water

  1.0 part (per 100 parts of Poriamre) of initia-

  1.0 part (per 100 parts of monaer)

cat transfer agent).

  When the chain transfer agent was used, it was added to the aqueous monomer solution

before the addition of the initiator.

  Molecular weight was determined by dilution viscometry using a viscometer

  Cannon Ubbelhode dilution tube 75-immersed in a bath-

  marries thermostatically (+ 0.1 C); The value M was determined using the Mark-Houwink equation [n] = KMe v o

  K = 6, -80 x 10-4 dl / g, a = 0.66 and [n] represents the visco-

  intrinsic property for polyacrylamide in water at 30 C.

  This example demonstrates, as Table V shows, that EA acid can successfully lower the

  molecular weight of the polymer prepared polyacrylamide

  solution, without significantly delaying the polymerization rate.

BOARD.

  Trans Agent Reaction Time Transformation, Average in Vis-

  Anitideutren minutes cosity of the weight initiator fert of molecular chain to molecular Mà C in water ______________ ____________________ tridistilled peroxypivalate 60 82 966 100 of tertl.oamyl Lupersol ... TA-54M75l @EA 80 89 75 700 o

TA-54M75

  ..., .. DTD: Polymerization temperature: 35 C.

w u1 r in

Example 6

  The following examples have used various

  organic oxides that are soluble in oil. Meadow-

  This example illustrates the utility of EA acid as a chain transfer agent with a water-soluble initiator such as

  as shown in Table VI. The initiator was used

  at a concentration of 0.1 g per 100 g of monomer after correction for the different titles. Doo: uoIUesTlimqlod ap ainqeugdtau I 0%

00 0 0%, 09 The VA

9 (ZSZHX)

  008 OL OOL 09 - - mnsseod ap aejlnszao - Peaum ua '__amouom 9ozgM aia: uIOd o p a 00O / s ue ap%' yg uoTini%. 'uTm auseqo ap lae -os e applTIoTemlaoJsue0theToTesTagm -sue0l op luaeilauseq? ap _ll_naeTTuI -poos aTsoDsTA -Tod ap agmaosp uoT2ezuaouoD-sue2 ap luaBv

IA VIRVIV

Example 7

  In an attempt to understand the effect of EA acid on the reaction, the

  concentration of the initiator at 0.1 g per 100 g of monomer

  re (0.1 pcm) and the concentration was initially

  0.1 to 4.0 g per 100 g of monomer.

  Then two other polymerizations were conducted

  in which the EA concentration was maintained at 0.1 per 100 g of monomer (0.1 pcm) and was

  the initiator concentration of 0.2 to 0.3 pcm.

  The results given in Table VII

  As the initiator concentration rises, the rate of polymerization increases; however,

  the molecular weight of the polymer increases because of the

  reduced concentration in EA with respect to the initiator concentration. Therefore, although EA acid is an effective chain transfer agent, the EA:

can be decisive.

TABLE VII

  REVERSE EMULSION POLYMERIZATION OF ACRYLAMIDE

A 35 C

  Initiator: LUPERSOL 256; Additive: erythorbic acid Initiator Additive Duration Transformation Viscosity at pcm - pcm min. % 25 C, mPa.s

0.1 0.1 360 79 125

0.1 0.25 360 73 125

0.1 1.0 360 59 125

0.1 4.0 360 41 <100

0.2 0.1 240 100 1250

0.3 0.1 120 100 5750

  Viscosity: Brookfield viscosity of an 18% solution ,.

  using pin n 4 at speed n 4.

Example 8

  The REFERENCE METHOD was used, except that the polymerization temperature was C and instead of 50.0 g of solid acrylamide monomer and 50.0 g of tridistilled water were weighed to form the solution. aqueous acrylamide, 100 g of 50% commercial acrylamide solution were weighed into a beaker. This solution as received was inhibited with 25 ppm CuSO 4 and a chelating agent would normally be added prior to formation of an emulsion. However, Versenex '80 Chelate was not used to remove the +2 inhibitor

  Cu + 2 in the reactions listed in Table VIII.

  The initiator was added in an amount of 0.1 g / g of monomer, taking into account the title. The EA transfer agent has been added before the initiator

  amount of 0.1 g / 100 g of monomer.

  It should be noted that EA acid reduces

  the molecular weight of the polymer is effectively reduced by

  only slightly faster than the rate of polymerisation-

TABLE VIII

  Polymerization time- Viscosity Brook-

  Transformation agent oyriTransformation, field of a

  Initiator fert chain sation, min. % 1.8% elution at 1.8% polymer at 25 ° C, mpas.

300 97 16 300

Luazo 70

EA 360 99 7300

Ln

  By way of comparison, the acid was evaluated

  as a chain transfer agent using

  the REFERENCE METHOD in this test.

  The initiator was added in an amount of 0.1 g / 100 g of monomer. Formic acid was also added in an amount of 0.1 g / 100 g of monomer, which is the amount normally used when

  erythorbic acid or BHT to reduce the weight of

the molecular of the polymer.

  The aforementioned U.S. Patent No. 4,307,215 teaches the use of formic acid and alkali metal formates as highly effective chain transfer agents for acrylamide. In evaluating formic acid as a chain transfer agent in the present invention, it was found to greatly retard the rate of polymerization as can be seen from Table A, unlike chain transfer agents, ie, EA, BHT, etc., from the

  present invention. This delay in speed is in-

  desirable from the point of view of an industrial process. In addition, formic acid is corrosive and, therefore, requires special handling precautions with respect to the longevity of the equipment and the

operator safety.

  No viscosity value for the polymer prepared using formic acid is indicated on

  table A, since the final percentage of trans-

  formation being very weak, very little polymer could

to be collected.

TABLE A

  Polymerization time- Viscosity Brook-

  Polymer trance agent Transformation, field of a

  Initiator fert chaeta sation, min. % lution at 1.8% of polymer at 250C, mpas Lupersol 256 Formic acid 360 18%

300 300% 24 500

  Polymerization temperature: 35 C l ur

Claims (9)

  1.- Process for preparing a polymer or   of a copolymer, characterized in that it comprises the   lymerization in inverse aqueous emulsion of a representative   selected from the group consisting of (i) acrylamide, (ii) methacrylamide and (iii) a mixture of 10 to 90% of (i) or (ii) and a monomer selected from the group consisting of acrylic acid, methacrylic acid, N, N-dimethylaminoethyl methacrylate, sodium acrylate, isopropylacrylamide and acrolein, in the presence of   of at least one surfactant, at least one initiator of   free agents and a chain transfer agent for   limit the molecular weight and viscosity of the solu-   polymer or copolymer, the chain transfer agent being selected from the group consisting of erythorbic acid and its alkali metal salts, ascorbic acid and its alkali metal salts, vitamins   and butylated hydroxytoluene, or mixtures thereof.   2. The process of claim 1, wherein   in that the chain transfer agent is used in   in an amount ranging from about 0.001 to about 5.0 parts by weight per 100 parts by weight. monomer weight.   3. Process according to claim 2, characterized   in that the chain transfer agent is   erythorbic acid or sodium erythorbate.   4. Process according to claim 2, characterized   characterized in that the inverse aqueous emulsion polymerization is carried out on a water-in-oil type emulsion in which water constitutes the dispersed phase and   the oil constitutes the continuous phase.   5. Process according to claim 2, characterized   in that the surfactant used is at least   a representative is oil soluble and has a   hydrophilic-lipophilic equilibrium range of about 1 to 12.   6. Process according to claim 3,   characterized in that the surfactant of which at least one representative is present is present in an amount of from about 0.5 to about 20.0 parts by weight per 100 parts by weight. weight of the oily phase.   7. The process of claim 4, wherein   characterized in that the ratio of aqueous phase to oil phase is in the range of about 1: 1 to 1: 5.   8. The process of claim 2, wherein   in that the polymerization temperature is   kills in the range of about 20 to about 80 C.   9. The process of claim 2, wherein   terized in that the initiator of free radicals which one   uses at least one representative is present in the middle   in the course of polymerization in an amount of from about 0.005 to about 5.0 parts   weight per 100 parts by weight of monomer.