IE53470B1 - Linear basic polymers,their preparation and use - Google Patents

Abstract

1. A linear basic polymer consisting of 90 to 10 mole % of units of the formula see diagramm : EP0071050,P10,F3 and from 10 to 90 mole % of units of the formula see diagramm : EP0071050,P10,F4 and having a Fikentscher K value of from 10 to 200 (measured in 0.5% strength aqueous sodium chloride solution at 25 degrees C).

Description

German Laid-Open Application DOS 1,720,737 discloses a process for the preparation of basic polymer.s in which poly-N-vinyl-N-methyIcarboxylic acid amides are subjected to acid hydrolysis at elevated temperature to give basic polymers with secondary amino groups.

It is true that hydrolysis of the formyl compounds proceeds sufficiently rapidly at from 100 to 110°C, but, as described in Example 2, stoichiometric amounts of hydrochloric acid at about 100° C result in a degree of hydrolysis of only 62 mole X. As described in Example 1, 2.6 moles of hydrochlo-ic acid per mole of formyl group equivalent at from 108 to 109 °C are required to achieve a degree of hydrolysis of 93 mole X. The polymers are thereby in some cases modified to an undesirable extent.

German Laid-Open Application DOS 1,692,854 discloses the addition of polymers of N-vinyl-N-methylcarboxylic acid amides to stock as drainage assistants to improve the drainage rate in papermaking. However, the effectiveness of these drainage assistants is still in need of improvement.

U.S. Patent 4,217,214 discloses the use of polyvinylamine hydrochloride having a molecular weight of not less than 3 x 10$ as a flocculant for particles suspended in watery and for the treatment of waste water and sludge. As stated in the patent, polyvinylamine hydrochloride is prepared by reacting acetaldehyde with acetamide to give ethylidene-bis-acetamide, splitting this product into N-vinylacetamide and acetamide by means of heat, polymerizing the N-vinylaeetamide and hydrolyzing the poly-N-vinylacetamide. Although polyvinylamine hydrochloride is a good flocculant, its effectiveness in the treatment of sludge is still in need of improvement.

Xt is an object of the present invention to provide linear basic polymers which contain, as the characteristic component, copolymerized units of the formula -CH--CHI NH2 and which are better than conventional basic polymers when used as retention agents, drainage assistants and flocculants in papermaking.,or for flocculating sludge.

We have found that this object is achieved, according to the invention, with linear basic polymers which contain from 90 to 10 mole X of units of the formula -CH--CH4 « NH2 and from 10 to 90 mole X of units of the formula -ch2-chNH-CHO and have a Fikentscher K value of from 10 to 200 (measured in 0.5X strength aqueous sodium chloride solution at °C).

The preparation of the compound of the formula CH2=CH-NH-CH0 (N-vinyIformamide) was first disclosed in German Published Application DAS 1,224,304. Homopolymerization of N-vinyIformamide has not yet been disclosed.

He have found that N-vinylformamide can be polymerized using free radical polymerization initiators, eg. peroxides, hydroperoxides, redox catalysts, or azo compounds which dissociate into free radicals, preferably those azo compounds described for this purpose in German LaidOpen Application DOS 1,495,692. The polymerization is carried out in a solvent or diluent at from 30 to-140° C. The molecular weight of the polymers varies, depending on the polymerization conditions, and is characterized in the text which follows by means of the Fikentscher K value. The K value can vary within wide limits, for example from 10 to 200. Polymers having a high K value, eg. above 80, are preferably prepared by polymerizing N-vinylformaaide in water. Polymers having a lower K value, eg. below 80, are obtained by carrying out the polymerization in the presence of known regulators or in a solvent which regulates the polymerization, eg. an alcohol, such as methanol, ethanol or n- or iso-propanol, or acetone or methyl ethyl ketone. Examples of other polymerization regulators are hydroxylaramonium salts, chlorinated hydrocarbons and thio compounds, eg. dodecyImercaptan. Polymers having a lower K value can be prepared by, for example, polymerizing N-vinylformamide in isopropanol using an isopropanol-soluble polymerization initiator based on an azo compound. 2,2'-Azo-bis-(isobutyronitrile) is an example of a particularly suitable azo compound for the polymerization in isopropanol. High molecular weight polymers of N-vinylformamide are prepared using watersoluble azo compounds, etj. 2,2'-azo-bis-C2-amidinoprop53470 ane) hydrochloride or 4,4'-a20-bis-(4’-cyano-pentanoic acid), the reaction being'. carried out in aqueous solution. As well as by solution polymerization in water, a watersoluble solvent or a mixture of water and a water-soluble solvent, the polymerization can also be carried out as a water-in-oil emulsion polymerization in a water-immiscible solvent. The reverse suspension polymerization can also be used for the preparation of finely divided polymers. If an aqueous medium is used, the pH during polymerization is from 4 to 9, preferably from 5 to 7. In the case of solution polymerization, polymer solutions having a solids content of from 5 to 50Z by weight, preferably from 3 to 30Z by weight, are predominantly prepared.

Poly-d-aminoethylenes) are prepared from the polymerization product by solvolysis in the presence of acids or bases at from 20 to 200°C, preferably from.40 to 180°C and particularly preferably from 70 to 90°C,.the formyl group being split off. From about 0.05 to 1.5 equivalents (for the purposes of this invention, one equivalent is 1 gram equivalent) of an acid, eg. hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric acid, are required per formyl group equivalent in the poly-N-vinylformamide. The pH in the case of acid hydrolysis is from 5 to 0, preferably from 3 to 0, and can be established by .addition of a carboxylic acid, eg. formic acid, acetic acid -or propionic acid, a sulfonic acid, eg. benzenesulfonic acid or toluenesulfonic acid, or an inorganic acid, eg. hydrochloric acid, sulfuric acid, phosphoric acid or hydrobromic acid.

The hydrolysis proceeds substantially more rapidly than that of N-methyl-N-vinylformamide polymers and can therefore be carried out under milder conditions, ie. at lower temperatures and without an excess of acid. < Solvolysis of the formyl groups in the poly-Nvinylformamide can also be carried out in an alkaline medium, for example at a pH of from 9 to 14. This pH is preferably established by addition of sodium hydroxide solution or potassium hydroxide solution, but it is also possible to use ammonia, an amine or an alkaline earth metal base, eg. calcium hydroxide, from 0.05 to 1.5, preferably from 0.4 to 1.0, equivalents of a base are used for the alkaline hydrolysis.

The formyl group can be split off in various solvents, eg. in water, an alcohol, ammonia or an amine, or a mixture of, for example, water and an alcohol, or an aqueous solution of ammonia and/or an amine. In some cases, it may be advantageous to carry out the solvolysis in an inert diluent, eg. in dioxane or an aliphatic or aromatic hydrocarbon. Poly-(1-aminoethylenes) are obtained in all cases. In the case of hydrolysis, the formyl group is split off from the poly-N-viny Iformamide by an acid or base in water, and formic acid or a salt of formic acid is obtained as a by-product. In the case of solvo25 lysis in an alcohol, also in the presence of an acid or base, a formic acid ester is obtained as a by-product, while formamide or a substituted formamide is obtained if the solvolysis is carried out in ammonia or an amine.

Particularly suitable alcohols for the solvolysis are low-boiling alcohols, eg. methanol, ethanol, isopropanol, n-propanol, n-butanol and isobutanol.

The solvolysis by-products can be removed from the system either during or after solvolysis. Thus, for example, if alcohol is used as the solvent, it is possible to remove the resulting formic acid ester azeotropically from the reaction mixture, in which case an entraining agent may be necessary. The hydrolysis by-product (formic acid) can also be removed from the system during or after hydrolysis. Preferably, the polyvinylformamide is hydrolyzed with sodium hydroxide solution or hydrochloric acid at from 70 to 90°C in aqueous solution. The K value of the hydrolyzed polymer corresponds to that of the non-hydrolyzed N-vinylformamide homopolymer.

The polyvinylforaamides are thereby partially hydrolyzed, so that from 10 to 90X, preferably from 20 to 90X, of the formyl groups are split off. In this manner, polymers are obtained which contain from 90 to 10 mole X of units of the formula -CHg-CHNHg and from 10 to 90 mole X of units of the formula -CHg-CHNH-CHO in random distribution and which can be defined, for example, by the following formula: 3 4 7D 0.2 to 0.9.

The hydrolysis depends on the reaction conditions, and can be carried out under atmospheric, reduced or superatmospheric pressure. Aqueous or alcoholic solutions are obtained, from which the polymer can be isolated after the low molecular weight constituents have been separated off. However, the aqueous or alcoholic solutions obtained during solvolysis can also be used directly as retention agents, drainage assistants and flocculants in papermaking or as flocculants for sludge. These polymers have an excellent action which is superior to that of conventional commercial products, eg. polyethyleneimines, or polyamidoamines modified with ethyleneimine. In the case of hydrolysis with bases, polymers with free amino groups are obtained, while hydrolysis with acids gives the corresponding polymer salts, from which, however, polymers having free amino groups can likewise be obtained after addition of a base, eg. sodium hydroxide solution or potassium hydroxide solution.

The linear basic polymers according to the invention are used to accelerate drainage of the wet fiber web and to increase the retention of fines and fillers by cellulose fibers during papermaking. Faster drainage of the stock on the papermaking machine enables the speed of the machine and hence production to be increased. 'Moreover, these compounds permit better sheet formation and reduce the water content of the still moist paper, so that less energy is required for drying the sheet than when conventional drainage and retention agents are used.

Improved retention during papermaking saves raw materials, enables cheaper fillers to be used instead of more expensive fibers, reduces the circulation of water through the paper mill and, as a result of better and more uniform fixing of fines and fillers, improves the printability of the paper. It a.lso. means that less material passes into the effluent.

From 0.005 to 0.5% by weight, preferably from 0.01 to 0.1% by weight, based on the dry fiber, of the poly-d-aminoethylenes) obtained in the solvolysis of poly-N-vinyIformamides is added to the stock before sheet formation for papermaking. Particularly advantageous effects are obtained with basic polymers having a K value above 80.

The polymers according to the invention are also used for the treatment of sludge from municipal or industrial water treatment plants. Polymers having a K value of more than 80 but not more than 200 are preferably . used here. The sludge is composed of those substances which have settled at the bottom of the treatment facilities during clarification of the effluent, and has a solids content of about from 2 to 8% by weight. By adding the polymers used according . to the invention to the sLudge, especially to sludge from municipal sewage plants, it is possible to obtain a residue which can easily be filtered or centrifuged and has a high solids content of up to about 30% by weight. The flocculant is used in an amount of from 100 to 350 g/cm of sludge. The flocculant employed must be distributed well in the sludge, for example in a mixing drum. Flocculation starts virtually immediately after addition of the flocculant,’ and an increase in the- particle size of the solids to be flocculated can be observed. The water is separated off from the residue using a conventional apparatus, eg. a perforated belt press or centrifuge, and the residue can then be dumped or* burned· The K value of the polymers was measured in 0.5% strength aqueous sodium chloride solution at 25 °C by the method of H. Fikentscher, Cellulosechemie 13 <1932), 58 to 64 and 71 to 74; K .= k.-103, 1. Preparation of the polymers EXAMPLE 1.1 g ¢1,125 mmoles) of vinylformamide were dissolved in 385 g of water in a flask provided with a stirrer, a thermometer and an apparatus for working’ under nitrogen.... 1.3 g ¢4.8 mmoles) of 2,2'-azo-bis-<2-amid25 inopropane) hydrochloride were added, the oxygen was removed by passing in nitrogen and the reaction mixture was heated to 60 °C in the course of half an hour and kept at this temperature for 5 hours. The conversion was then 99.3%. 534 70 450 g of 102 strength sodium hydroxide solution (1,125 mmoles) uere then added to the resulting viscous polymer solution, uhich had a K value of 81, and the mixture uas heated at 80 °C for 5 hours, to give a polymer in uhich all the formyl groups had been split off (degree of hydrolysis = 902). A total of 916 g of an aqueous polymer solution having a Brookfield viscosity, measured at 25°C, of 140 mPa.s uere obtained.

EXAMPLE 1.2 g of N-vinyIformamide uere dissolved in 385 g of uater in the apparatus described in Example 1.1? and uere polymerized to a conversion of 98.12 in the course of 5 hours at 55 °C by addition of 0.65 g of 2,2'-azo-?bis-" (2-amidinopropane) hydrochloride. The resulting polymer, uhich had a K value of 95, uas heated at 80° C uith 23 g of 362 strength hydrochloric acid (227 mmoles) for 3 hours to give 489 g of a polymer solution in uhich 202 of the formyl groups had been split off from the polymer. The Brookfield viscosity of the solution, measured at 25°C, uas 16,000 mPa.s.

EXAMPLE 1.3 g of N-vinylformamide were dissolved in 385 g of uater in the apparatus described in Example 1.1,0.65 g of the azo compound described in Example 1.1 uas added, as a polymerization ini Ha. tor, and the mixture uas heated to 55 °C in the course of 1 hour. -Polymerization was carried out at 55°C in the course of 5 hours . After the polymerization, the reaction mi xture uas heated for another half an hour at 60 °C to complete the conversion. which was then 100%. The resulting polymer, which had a K value of 120, was then hydrolyzed with 68.5 g of 36% strength hydrochloric acid (676 mmoles) at 90 °C for 2 hours to give 534.5 g of an aqueous polymer solution having a Brookfield viscosity, measured at 25eC, of 10,500 mPa.s. 60% of the formyl groups of the polymer employed in the hydrolysis had been split off.

EXAMPLE 1.4 1,410.8 g of N-vinyIformamide were dissolved in 7,888.4 g of water in a flask provided with a stirrer, a thermometer and an apparatus for working under nitrogen. 8.07 g of 2,2’-azo-bis-(2-amidinopropane) hydrochloride were added, the oxygen was removed by passing in nitrogen and the reaction mixture was heated to 50°C in the course of 1.4 hours and kept at this temperature for 7 hours. The conversion was then 99.6%.

The resulting viscous polymer solution (K value of the homopolymer: 120) was then heated at a temperature of 90° C with 1,715.4 g of concentrated hydrochloric acid 20 for 4 hours to give a polymer containing 10 mole % of N-vinyIformamide and 90 mole % of N-vinylamine as copolymerized units (90% of the formamide groups in the polymer had been hydrolyzed and the K value was 120).

EXAMPLE 1.5 1,410.8 g of N-vinylformamide were polymerized in 7,888.4 ml of water at 50 °C usi.ng 2,2'-azo-bis-(2amidinopropane) hydrochloride as the polymerization initiator, in the apparatus described in Example 1.4. The polymerization had ended after 7 hours and the conversion 34 7 0 was 99.6X. 1,143.6 g of concentrated hydrochloric acid were added to the viscous polymer solution (K value of the polymer: 120) and the reaction mixture was heated to 90 °C for 4 hours to give a polymer containing 40 mole X of N-vinylformamide and 60 mole X of aminoethylene as copolymerized units (60X of the N-formyl groups had been hydrolyzed, K value: 120).

EXANPLE 1.6 (Comparative) Polydimethyl-aminoethyl methacrylate hydrochloride having a K value of 160 was used as a prior art flocculant, 2a. Use of the polymers as retention agents, drainage assistants and flocculants The following polymers were used: Polymer I: A commercially available high molecular weight polyethylene imine Polymer II: A polyamidoamine obtained from adipic acid and diethylenetriamine, onto which ethyleneimine had been grafted and which had been crosslinked with polyethylene glycol dichlorohydrin ether containing 9 ethylene oxide units, cf. Example 3 of German Patent 2,434,816.

Polymer III: The polymer according to Example 1.3 Polymer IV: The polymer according to Example 1.2 Polymer V: The polymer according to Example 1.1 Polymer VI: The polymer according to Example 1.3, but polymerized only up to a. K value of 102'and with 82% - of the .formyl groups removed by hydrolysis with hydrochloric acid.

Polymer VII; A polymer obtained from N-methyl-N-vinylformamide, which had a K value of 106 and had been hydrolyzed to the extent of 75X with hydrochloric acid (prepared according to Example 2 of German Laid-Open Application DOS 1,692,854).

EXAMPLE 2.1 Various amounts of the polymers to be tested were added to 1 I of ligneous, kaolin-containing newsprint stock having a consistency of 2 g/l and a pH of 7.8, and a Schopper-Riegler apparatus was used to determine the SR freeness and the drainage time, ie. the time taken for 700 ml of back water to run out of the apparatus. The polymers used and the results achieved therewith are shown in Table 1.

TABLE 1 Freeness (SR) and drainage time (sec) with a polymer addition of 0.02% 0.06% 0.1% 0.02% 0.06% 0.1% no addition 64 99.2 25 Polymer I (comparative) 57 45 . 40 75.2 47.4 39.4 Polymer II (comparative) 54 40 36 67'. 2 39.6 32.5 30 Polymer III (according to the invention) 46 33 30 51.0 28.8 24.8 3 4 7 0 EXAMPLE 2.2 The drainage-accelerating effect of polymer V was tested by the procedure described in Exanple 2.1. Polymer II was used for comparison with the prior art. The results are shown in Table 2.

TABLE 2 freeness (SR) and drainage time (sec) with a polymer addition of 0.06% 0.1% 0.06% 0.1% no addition 66 107.5 Polymer II • (comparative) 50 41 .56.8 41.4 Polymer V 47 38 51.0 36.3 EXAMPLE 2.3 Various 'amounts of the polymers shown in Table 3 were added to 1 I of stock comprising 80% of bleached sulfite pulp and 20X of kaolin and having an alum content of 0.5% and a pH of 6 , and sheets of paper were then produced with the aid of a Rapid-KBthen sheet-forming apparatus. The weight per unit area of the sheets of paper and their filler content, which was determined by ashing, are criteria for the effectiveness of the polymer. The higher the weight, per unit area end the fi I ler content of the sheets of paper, the...more effective the retention agent.

TABLE 3 Height per unit area (g/cm ) and ash content (%) 0.02% with a 0.04% polymer 0.06% addition of 0.02% 0.04% 0.06% no addition 58.0 4^2 Polymer I (comparative) 61.3 62.1 62.6 7.7 9.1 9.7 10 Polymer II (comparative) 62.3 64.1 64.5 9.6 11.7 12.0 Polymer III 67.6 69.9 70.8 12.0 14.7 14.7 EXAMPLE 2.4 The filter retention was determined as described in Example 2.3, using a stock comprising 80% of bleached sulfite pulp and 20% of kaolin and having an alum content of 1.5% and a pH of 4.8. The effectiveness of polymer IV was compared with the conventional retention agents I and II, and the results are summarized in Table 4.

TABLE 4 Ash content with a 0.02% polymer 0.04% addition 0.06% of no addition 3.7 Polymer I (comparative) 5.8 6.3 7.0 Polymer II (comparative) 8.8 9.5 9.9 Polymer IV 10.9 11.9 12.6 EXAMPLE 2 .5 To determine the flocculating effect and purification effect on waste water of the polymers accord30 ing to the invention, various amount's of the poLymers shown in Table 5 were added to a stock rich in fines and containing, per liter, 1 g of sulfite pulp and 0'.25 g of kaolin. The suspension was stirred and allowed to 3 4 7 0 settle, and the transparency of the supernatant purified water was in each case determined photometrically. The results are summarized in Table 5.

TABLE 5 Transparency (%) with a polymer addition of 0.02% 0.04% no addition 19.0 Polymer I (comparative) 42.0 60.8 Polymer II (comparative) 41.9 52.1 Polymer III 57.5 77.8 EXAMPLE 2.6 Various amounts of the polymers to be tested were added to 1 I of a ligneous, kaolin-containing news- print stock having a consistency of 2 g/l and a pH of 7.8, and a Schopper-Riegler apparatus was used to deter- mine the SR freeness and I the drainage time. ie. the time taken for 700 ml of back water to run out of the apparatus. The polymers .used and the results achieved therewith are shown in Table 6. TABLE 6 Freeness (SR) and drainage time (sec) with a polymer addition of 0.02% 0.06% 0.1% 0.02% 0.06% 0.1% no addition 62 99.3 61 101.0 Polymer II 51 38 34 68.0 40.1 34.0 (comparative) 51 39 34 68.2 40.2 34.0 Polymer VII 50 50 . 50 66.8 64.6 66.0 (comparative) 50 49 50 66.5 63.8 67.0 Polymer VI 49 34 31 61.4 33.4 29.3 49 . 33 31 62.0 32.3 29.5 3 4 70 The effectiveness of the polymer VI used according to the invention has been improved, compared with that of the closest prior art (Polymer VII), in a manner which could not be predicted.

EXAMPLE 2.7 The filler retention was determined on a stock comprising 80% of bleached sulfite pulp and 20% of kaolin and having an alum content of 0.5% and a pH of 6.0. Various amounts of the polymers shown in Table 7 were added to 1 I of this stock,and sheets of paper were then produced with the aid of a Rapid-KBthen sheet-forming apparatus. The filler content of the sheets of paper, which was determined by ashing, is a criterion of the effectiveness of the polymer as a retention agent.

TABLE 7 Ash content with a 0.02% polymer addition of 0.04% 0.06% no addition 3.7 20 Polymer II (comparative) 9.3 10.6 11.5 Polymer VII (comparative) 10.0 9.8 9.9 Polymer VI 9.6 12.1 13.1 2b. Use of the polymers as flocculants for sludge 0.1% strength aqueous solutions of the polymers 25 according to Examples 1.4, 1.5 and 1.6 were prepared and were tested as flocculants for sewage sludge. The following test methods were used: a) Determination of the flocculation number and filtration rate 500 ml of sewage sludge were treated with defined 4 7 0 amounts of a 0.12 strength aqueous flocculant solution in a 1 I measuring cylinder. Flocculation occurred during mixing. The contents of the measuring cylinder were then emptied into a BUchner funnel and filtered. The flocculation uas evaluated visually uith the aid of the filter, no visible flocculation = flocculation number 1 slight flocculation = flocculation number 2 average flocculation = flocculation number 3 good flocculation, sufficient for practical purposes = flocculation number 4 very good, optimum flocculation = flocculation number 5 The amounts of filtrate after 30,.60, 90 and 120 seconds uere also measured. b) Flocculation activity In this test, the amount of flocculant which must be added to sludge to achieve optimum flocculation (flocculation number = 5) uas determined, also in a 1 I measuring cylinder.

EXAMPLE 3 The flocculation activity of the polymers according to Examples 1.4 and 1.5 uas determined, in comparison uith that of the polymer according to 1.6, on digested sludge from a municipal purification plant by the method described above under b). The amount of the polymer according to Example 1.4 required for optimum flocculation was 200 mg/l of sludge, that of the polymer according to Example 1.5 was 150 mg/l, while 250 mg of the polymer according to Example 1.6 had to be used per I of sludge.

The polymers according to Examples 1.4 and 1.5 are substantially more effective than the prior art polymer.

EXAMPLE 4 The flocculation number and filtration rate of 5 the polymers according to Examples 1.4 and 1.5, in comparison with the polymer according to Example 1.6, were determined on digested sludge from a municipal purification plant by the method described under a): Polymer according to Example Amount added mg/l of sludge Floccula- tion number Amount of filtrate in ml after 30 60 90 120 seconds 1.4 100 3-4 1.4 150 4-5 15 1.4 200 5 310 360 370 375 1.5 50 3-4 • 1.5 100 4 1.5 150 5 325 370 380 390 Comparative 1.6 150 3 1.6 200 4 1.6 250 5 230 325 350 370

Claims (10)

1. A process for the preparation of a linear basic polymer containing, as characteristic components, from 90 to 10 mole % of copolymerized units of the formula -CHg-CHnh 2 and from 10 to 90 mole % of copolymerized units of the 5 formula -ch 2 -chNH-CHO and having a Fikentscher K value of from 10 to 200 (measured in 0.5% by weight strength aqueous chloride solution at 25°C), wherein the compound of the formula CH 2 =CH-NH-CHO (N-vinyl10 formamide) is polymerized to a polyvinylformamide in the presence of a free radical polymerization initiator, and the resulting polymer is solvolyzed at from 20 to 200°C in the presence of an acid or base, from 10 to 90% of the formyl groups being split off from the N-vinylformamide homo15 polymer.

2. A process as claimed in claim 1, wherein vinylformamide is polymerized in aqueous solution using a polymerization initiator based on a water-soluble azo compound, and the polymer thus prepared is solvolyzed in an alcohol 20 or water.

3. A process as claimed in claim 1 or 2, wherein from 0.05 to 1.5 equivalents of a mineral acid are used per formyl group equivalent of the polyvinylformamide obtained during polymerization. 25

4. A process as claimed in claim 3, wherein from 0.4 to 1 equivalent of a mineral acid is used per formyl group equivalent of the polyvinylformamide obtained during polymerization. 5347 0

5. A process as claimed in claim 1, wherein from 0.4 to 1 equivalent of a base is used per formyl group equivalent of the polyvinylformaraide.

6. A process for the preparation of a linear basic 5 polymer carried out substantially as described in any of the foregoing Examples 1.1, 1.2 or 1.3.

7. A linear polymer when prepared by a process as claimed in any of claims 1 to 6.

8. A linear basic polymer containing from 90 to 10 10 mole % of units of the formula -ch 2 -chnh 2 and from 10 to 90 mole % of units of the formula -ch 2 -chNH-CHO and having a Fikentscher K value of from 10 to 200 (measured in 0.5% by weight strength aqueous sodium chloride solution at 25°C). 15

9. A linear basic polymer as claimed in claim 7 or 8 having a Fikentscher K value of more than 80 but not more than 200 (measured in 0.5% by weight strength aqueous sodium chloride solution at 25°C).

10. The use of a linear basic polymer as claimed in 20 any of claims 7 to 9 as a retention agent, drainage assistant or flocculent in papermaking or for flocculating sludge.