Reactive Polymers - American Chemical Society

Chapter 9

Reactive Polymers Water-Soluble Vinyl-Terminated Oligomeric Poly(β-alanine 1

Sun-Yi Huang and M. M. Fisher

Downloaded by UNIV LAVAL on July 11, 2014 | http://pubs.acs.org Publication Date: December 13, 1993 | doi: 10.1021/bk-1994-0548.ch009

Stamford Laboratory, Cytec Industries, 1937 West Main Street, Stamford, CT 06904-0060

Low molecular weight water soluble vinyl terminated oligomeric poly (beta-alanine) was synthesized using organolithium initiators. Vinyl terminated poly (beta-alanine) consists of N-2-carboxyamidoethylacrylamide and oligomers which were fully characterized by analytical methods. The results show that one vinyl terminated group per chain was produced. Reaction time and temperature were the main variables used to control the N-2-carboxyamidoethylacrylamide content, molecular weight, and molecular weight distribution. N-2-carboxyamidoethylacrylamide was homopolymerized in aqueous medium by redox initiation. Poly (N-2-carboxyamidoethylacrylamide) was converted to a Mannich derivative and was quaternized. This new cationic water soluble polymer is an effective organic flocculant for bentonite clarification.

Block and graft copolymers represent an important class of materials which are achieving ever increasing commercial success. Examples are Shell's Kraton, Phillips' Salprene, DuPont's Hytrel, B. F. Goodrich's Estines and Cyanamid's XT polymers. The field of block and graft copolymers has been extensively reviewed in a number of recent monographs (1-3). A significant development in the area of graft copolymer synthesis is the concept of copolymerizing conventional monomers with vinyl terminated prepolymers (4-6). The principal advantage of this approach is the avoidance of a homopolymer which is always obtained when conventional free radical grafting techniques are used. The potential application of vinyl terminated prepolymers, in a number of areas of commercial significance to industries has served as the basis for the development of a novel graft copolymer useful as paper additives, flocculants, fibers, and thermoplastic elastomers. The general purpose was to improve the properties of these materials by incorporating graft segments capable of strong side chain internations. It was 1Current address: American Plastic Council, 1275 Κ Street, NW, Washington, DC 20005 NOTE: This chapter is Part III in a series of articles. 0097-6156/94/0548-0114$06.00/0 © 1994 American Chemical Society

In Macro-ion Characterization; Schmitz, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

9. HUANG & FISHER

115

Reactive Polymers

envisioned that a macroraonomer with desired properties could be synthesized through the base initiated hydrogen transfer polymerization of acrylamide (7): Β

Θ

+ nCH = CH

•

2

C H ^ C H - C - N H

C=0

- (CHJ-CHJ-C-NH-) _jH n

Ο

(I)

Ο

I


NH

2

In 1954, a patent by Matlack (7), and papers by Breslow, et al. (8,9) described the anionic polymerization of acrylamide to high molecular weight poly (beta-alanine). Breslow, et al. suggested two possible mechanisms for the base initiated polymerization of acrylamide. One is a proton abstraction from the amide group by the base in reaction (Π).

ο Β

Θ

+ Oi^CH—

Id:—NHj

ο •

(Π)

CH^CNH + BH

The second is the Michael addition of the initiator to the carbon carbon double bond of acrylamide in reaction (ΠΙ).

ο Β

Θ

+ CH^CH-C-N^

ο •

B-CH2-CH-CNH2

B-CHj -a^CNH

(ΠΙ)

0

They concluded that the predominant initiation reaction is (Π) because a solid material from a reaction mixture of potassium tert-butoxide and acrylamide was a dimer or an oligomer containing a vinyl group. Ogata (10) concluded that nucleophilic addition to the vinyl group must be the initiation step for the polymerization of acrylamide using sodium methoxide by infrared spectroscopy. Tani, et al. (77) studied the products of the reaction of acrylamide with sodium methoxide and sodium tert-butoxide. They found that the tert-butoxide anion abstracts a proton from amide groups and adds to the carbon-carbon double bond, but the methoxide anion only adds to the carbon-carbon double bond. Trossarelli, et al. (72) found that the amounts of tert-butanol in the reaction products agreed with those calculatedfromthe quantity of sodium tert-butoxide employed. Leoni, et al. (75) isolated dimeric and trimeric products from alkyl lithium initiated polymerization of acrylamide. Both groups supported the initiation mechanism in equation (II). Kobayashi, et al. (14) observed that acrylamide was readily polymerized to poly (beta-alanine) by sodium cellulosate and sodium polyvinyl alcohol initiators. No block and graft copolymers were found. However, the reaction led to carbamoylethylation of the polymer backbones which supported the



116

MACRO-ION CHARACTERIZATION

initiation mechanism of equation (Π). Moore, et al. (15,16) found that in-situ polymerization of acrylamide initiated by poly (phenylene terephthalamide) anion in solution in vacuo at 80-115°C gave molecular composites of a poly (betaalanine)-graft copolymer and poly (beta-alanine) homopolymer. The result supported the reactions (Π) and (ΙΠ). It is very difficult to draw conclusions based on the conflicting evidencereviewedabove. Initiation of the hydrogen transfer polymerization of acrylamide appears to be dependent on the nature of the bases. Many other factors such as reaction temperature and medium are also expected to influence the reaction. It was also found that the basicity of the initiator and steric effects influence the mode of initiation and the ultimate degree of unsaturation of the poly (beta-alanine) (17). Tarvin (18) successfully copolymerized a high vinyl content of poly (beta-alanine) with acrylonitrile and methyl methacrylate. The terpolymers have wet fusion points at 175°C. In this paper, we have focused on the synthesis and characterization of low molecular weight vinyl terminated poly (beta-alanine) (VTN-3). To obtain a better understanding of the polymerization process, acrylamide was converted to the low molecular weight VTN-3 and N-2-carboxyamidoethylacrylamide (AMD dimer) in various solvents and the rate of formation was measured. We report and discuss the molecular weight determination obtained by gel-permeation chromatographic separation of oligomer and AMD dimer, vapor phase osmometry, NMR, and bromine-bromate titration for unsaturation. AMD dimer was successfully isolated from oligomeric mixtures. Homopolymerization of this monomer produced a high molecular weight water soluble polymer using an aqueous redox system. The preparation of Mannich derivatives and subsequent quaternization with dimethylsulfate was investigated for the cationic derivatives of poly (acrylamide dimer) covering a wide range of molecular weight. This new cationic water soluble polymer has been studied as an effective organic flocculant for bentonite water clarification.

Experimental VTN-3 Oligomer Preparation. Ten g of sublimed acrylamide and 100 ml of pdioxane distilled from CaH are placed in a 250 ml, 4-neck, round-bottom flask equipped with a stirrer, N inlet, thermometer, condenser, and rubber septum. The mixture is stirred in a N atmosphere at ambient temperature for 30 mins. until all of the acrylamide is dissolved. The acrylamide solution is thermostated at 25°C, vigorously stirred, and 4.3 ml (1.58 M) of η-butyl lithium solution slowly added through the rubber septum by a syringe. Thereactionbetween acrylamide and nbutyl lithium is exothermic and the addition is carried out slowly over a few mins. to maintain at 25°C. After 24 hrs. 1 ml of water is added to terminate the reaction. The white dispersed solid is separated from p-dioxane by centrifugation. The solid phase is dried under vacuum at 60°C for 24 hrs. The yield is 9 g of oligomer. 2

2

2

Synthesis of Acrylamide Dimer [N-2-Carboxyamidoethylamide]. AMD dimer was obtained in 75% yield by triple ultrafiltration of a crude VTN-3 reaction mixture prepared in p-dioxane at ambient temperature. A 2-3% aqueous solution


9. HUANG & FISHER

Reactive Polymers

117


of the initialreactionproduct was pressurized through an Amicon Model 402 stirred ultrafiltration cell equipped with a UM-5 membrane. The filtrate purity was 98-100% of AMD dimer. An alternative procedure for obtaining pure dimer in 40% yield was to heat the same crude VTN-3 product in p-dioxane to reflux. The slurry was quickly filtered to separate the insoluble oligomer. The dimer recrystallized from the filtrate on cooling. Homopolymerization of AMD Dimer. Polymerization of AMD dimer was carried out in a 250 ml 3-neck flask containing 4 g of AMD dimer and 96 g deionized water at pH=6.0. The initiation temperature was 40°C. Sodium metabisulfite concentration was varied between 38-5000 ppm based on monomer while the ammonium persulfate concentration was 1500-30000 ppm based on monomer. The polymerization was complete in six hrs. In some runs, 4,4'-azobis (4-cyanovaleric acid) was used as the initiator. Mannich and Quaterization on Poly(acrylamide dimer). The preparation of Mannich derivatives of poly (acrylamide dimer) using formaldehyde and dimethylamine and subsequent quaternization with dimethyl sulfate were carried out as follows: A solution of freeze-dried polymer, 0.5 g in 10.22 g of water was prepared. 0.91 g of 35% (CH ) NH solution was added followed by 0.48 g of 44% HCHO solution. The reaction was carried out at ambient temperature at pH=ll for 6 hrs. and then 0.89 g of (CH ) S0 was slowly added. After 12 hrs. the Mannich quaternary polymer solution was analyzed (79) and cationic equivalent (CEQ) was found to be 5.14 meq/g. The degree of substitution is defined as [CEQ/3.08 - l]xl00% where 3.08 is the theoretical CEQ of 100% quaternization. A 67% quaternization was achieved. The quaternary polymer was dialyzed for 2 days in Spectrapor membrane (m.wt. cut off 2,000) and freezedried. The CEQ on the dialyzed product was 2.15. 3 2

3 2

4

Kinetic Measurement. Aliquots of the reaction mixture were removed at various times and analyzed for the residual AMD monomer using a Hewlett Packard 7620 Research Gas Chromatograph. The column was packed with 8'x20 mm 20% Carbowax 20M WA-N-DMCS 60/80 mesh and helium was used as the carrier gas. Characterization. Number average molecular weights were determined by a Knaner Dampf-Druck vapor phase osmometer. GPC analyses were performed using a Perkin-Elmer M601 equipped with 10, 10, 10, 10 À styragel columns. Columns were standarized by purified standard VTN-3 samples, Mw = 141, 13,800, 19,200, 20,200, 28,200; InMi = a + bVi, where a = 1.545.10, and b = 36.2. Samples concentrations were 0.1 - 0.5% by weight in hexafluoroisopropanol (0.01 M KO AC). GPC analyses were also performed using Sephadex G-10 and G-25. G-10 and G-25 were packed with cross-linked polysaccharide swollen in 0.1M NaN0 solution. 6

5

4

3

8

3

Flocculation of Bentonite Suspensions. Bentonite flocculation results for the cationic poly (AMD dimer) samples and commercial cationic polyamine and poly (diallydimethylammonium chloride) were compared. The standard practice (20)


118

MACRO-ION CHARACTERIZATION

was followed where the dosage, in ppm, of real polymer required to reduce the slurry transmittance to 20% of the initial value, T^, was used as a measure of the relative flocculation efficiency.


Results and Discussion Synthesis of VTN-3 Oligomer. The high temperature polymerization of acrylamide in pyridine using t-butyl lithium initiator was discussed (17) and it is the preferred method for preparing water soluble poly (beta-alanine) in the 10,000 -20,000 molecular weight range. The polymer was shown to contain an average of one vinyl group per chain. A synthetic route to obtain lower molecular weight poly (beta-alanine) in 141 - 1,000 molecular weight range was desired in order to have available a wide range of macromonomer for copolymerization studies. A process using p-dioxane as the solvent, alkyl lithium initiators and a reaction temperature of ~25°C was developed. The major reaction product is an oligomer which corresponds to the structure of CH =CHCONH(CH CH CONH) H, where η = 1 - 10. Reaction conditions and product characteristics are summarized in (Table I). Since the degree of polymerization under these conditions is low, NMR, VPO, and unsaturation determination could be used for detailed structural analysis. In particular, integrated NMR spectra were used to determine number average molecular weights. These valuesreportedin column 11 of Table I are 2

2

2

n

in good agreement with Mn values calculated from the degree of unsaturation and VPO data (± 10-15%). In contrast to high temperature polymerizations where only t-butyl lithium gave high degree of vinyl termination, all alkyl lithium compounds examined in this series of experiments produced high yields of vinyl terminated oligomer. Apparently proton abstractionfromthe amide group is favored at low temperature even for unhindered alkyl lithiums. These oligomers are highly water soluble and soluble in DMSO. They are partially soluble in absolute alcohol, methanol but insoluble in non-polar organic solvents. DSC analysis indicated decomposition above 210°C rather than true melting. The proposed mechanism of acrylamide polymerization with organolithium compounds is as follows:

Rli + CH = C H - C N H 2

(Γθ θ CH2 = CHCNHU

2

/

»

Low Temperature Polymerization

R-CH CHCNH 2

θ Li

free CH = CHCNHLi 2

R~CH CHCNH 2

R=η-butyl, s-butyl, t-butyl, vinyl

Φ Li

2

High Temperature Polymerization


HUANG & FISHER

Reactive Polymers

INITIATION. ΡΘ CH = ŒCNHLi +

θί?

Ρ =010^

Φ

2

ρ

Ρ • CH = CHCNHCH CHCNH 2

2

2

0

CR, = CHCNIOI CH CNHLi 2

2

PROPAGATION = CHCNHO^O^CNHU +CH = CHCNH Downloaded by UNIV LAVAL on July 11, 2014 | http://pubs.acs.org Publication Date: December 13, 1993 | doi: 10.1021/bk-1994-0548.ch009

2

2

Ρ

Ρ

Ρθ θ ' CT^CNH Li

CH = CHCNHCH CH CNH ^ 2

2

2

TERMINATOR

Ρ Θ© Œ = CHCNHCH CH CNHU 2

2

2

Ρ + CH =CHCNH 2

2

Œ = CHCNHCH CH CNH 1 m p-dioxane 2

Œ

2

2

2

2

Ρ

2

Ρ 2

DMFoi *

2

d

m

s

q

Pee

Ρ

CH = ŒCNHŒ CH CNH 2

2

= ŒCNHLi

Ρ θ θ Ρ Œ = CHCNHCH CH CNHU + Œ =CHCNH 2

2

C H ^ C N I i ^ + CH = CHCNHIi

2

2

CHAIN TRANSFER

CH = ŒCNHCH CH CNH' 2

2

^

2

V

CH CH CNHLi + 2

2

= ŒCNHCH CH CNH -^^ C H ^ C N I ^ 2

2

CH = CHCNH — 2

2

+ CH = CHCNHI 2



20.1

25.2

n-Butyl

sec-Butyl L i

t-Butyl L i

t-Butyl L i

t-Butyl L i

Vinyl L i

118-2

118-1

119-1

119-3

119-2

117-C

—

—

289

286

260

c

b

24 83

490 430

25

117-B Vinyl L i 25.2 24 0.039 25 90 " Inherent viscosities were measured for 1% polymer in IN aqueous NaCl. Unsaturation was determined by bromine-bromate titration. Mn was determined by vapor phase osmometry.

256

231

256

234 430

270

290

270

—

0.046

C

NMR

Mn

Rby

b

Mn by

Unsaturation

0.032

0.039

0.040

ηΐΓύΥ

0.030

85

79

24 40

90

75

24 22

75

Conver sion (%)

24

Time (hr)

276

25

25

25

25

25

Temp. (°C)

252

25.5

20.4

20.9

21.3

Initiator

Sample No.

Monomer Initiator (mole/mole)

Table I. Synthesis of Vinyl Terminated Poly (beta-alanine) Oligomer


88

—

91

—

112

113

106

Unsaturation %


9.

H U A N G

& F I S H E R

121

Reactive Polymers

Effect of Temperature on the Conversion of Acrylamide to AMD Dimer and Oligomer. For organolithium initiated oligomerization of acrylamide in pdioxane, the relative yield of dimer and oligomer was found to depend strongly on the reaction temperature. Results are shown in (Table Π). A large amount of acrylamide dimer is produced in the early stages of the polymerization especially when the lowest polymerization temperatures were used. Therefore, pure dimer is isolated essentiallyfreefromoligomer contamination. The concentration of dimer linearly decreasedfrom80% to 20% as the polymerization temperature was increased from 16°C to 50°C. Correspondingly, the concentration of oligomer linearly increased from 15% to 70%. The overall conversion was -90%. The reason that dimer can readily be isolated is that acrylamide dimer has a very low solubility in p-dioxane (13). The formation of oligomer occurs predominantly after dimer has precipitated. The molecular weight distribution of oligomer was also found to depend on reaction temperature. Mw/Mn increases as the reaction temperature increases. For reaction temperatures between 15°C and 25°C, Mw/Mn is about 2 - 3 in an agreement with a step-growth mechanism. However, when the reaction temperature is the range of 30 - 50°C, Mw/Mn > 3 which may indicate chain branching is occurring. The formation of acrylamide dimer was also shown to depend on the nature of the solvent. DMF or DMSO are solvents for AMD dimer and oligomerization past the dimer stage occurs readily as shown in (Figure 1). (Figures 2 and 3) are typical GPC curves of VTN-3. Solvent Effect. Both the rate of reaction and formation of oligomers strongly depend on solvent Comparable reactions were carried out in DMSO, DMF, and p-dioxane. t-Butyl Li was used as the initiator under identical reaction conditions in three different solvents. (Figure 4) shows that 80% of the acrylamide monomer has disappeared in 30 minutes in DMSO. In the same experiment, 65% of the monomer has disappeared in DMF. Only 50% of the monomer is converted to oligomer in p-dioxane. After -1 hour of reaction time, acrylamide dimer starts to precipitate in p-dioxane but remains in solution in DMF and DMSO. A homogeneous phase is obtained throughout the reaction in DMF and DMSO solvents and a heterogeneous phase in p-dioxane. Poly (acrylamide dimer). Homopolyraerization of acrylamide dimer produced a relatively low molecular weight polymer. Since higher molecular weights were desired for paper additives and water treating applications, an effort was made to upgrade the yield and molecular weight of this polymer. Initiator types, initiator concentration, temperature, and the reaction time were varied for a series of acrylamide dimer polymerizations in aqueous medium, and the results are summaried in (Table ΠΙ). Initiator levels of -15,000 ppm persulfate and 35-75 ppm of metabisulfite resulted in high conversion and acceptable viscosity. Yields dropped off rapidly below 15,000 ppm persulfate and high conversion but low viscosities were obtained when the metabisulfite concentration was increased in contrast to acrylamide. Acrylamide (sample no. 101-4) could be polymerized to a very high molecular weight polymer under similar conditions. This bulk viscosity is about the weight-average molecular weight of greater than 10 of polyacrylamide (27). 6



35

6-7

85 90 85

24 24

85

24

24

83

83

24 83

85

24

15

36

52

71

13

17

51

57

13

33

55

50

57

80

A M Dimer Content (%)

0

w

21,000

72

49

38

14

22,000

66

3,750

32

5,970

5,600

11,000

2,600

6,200

28

4,100

3,600

2,900

M.

5,880

14,000

11,000

7,910

M

29,400

76

52

37

1

28

18

Oligomer Content (%)

a

0.06

0.05

0.03

0.08

3.51

— — — —

0.06 3.96

0.08

4.49

0.05

0.06

3.39

2.64

0.03

2.99

0.04

—

—

2.38

0.04

2.73

r|inh 0.02

w

—

w

M /M

d

d

c

b

0.07 21 69 24 6-8 90 45 " Reaction conditions: 1). 20g acrylamide, 200 ml p-dioxane, 8.8 ml (1.58M) n-BuLi. 2). 20g acrylamide, 200 ml p-dioxane, 9.5 ml (1.5M) s-BuLi. 3). 20g acrylamide, 200 ml p-dioxane, 6.3 ml (2.30M) t-BuLi. Acrylamide dimer and oligomer contents calculated from G P C data. Oligomer molecular weight distribution was calculated from integrated GPC chromatograms. Inherent viscosities were determined for 1% polymer in I N N a C l aqueous solution.

25

6-6

16

50

6-2

n-BuLi

35

6-4

6-5

18

15

6-1

n-BuLi

90

24

41

5-3

6-3

85

24

31

5-2

92

24

20

50

2

5-4

85

24

20

98

16

5-5

n-BuLi

58-1

Conv. (%)

15

10

Initiator

Time (hrs.)

5-1

Temp. °C

Sample No.

Table II. The effect of Temperature on the Acrylamide Dimer Content and the Molecular Weight


9.

HUANG & FISHER

Reactive Polymers

123


Oligomer

Elution Volume (ml)

Figure 1. G P C chromatogram of vinyl terminated poly (beta-alanine) oligomer prepared in D M F and D M S O . A . 20 g acrylamide, 200 m l D M F , 6.4 m l t - B u L i (1.8 M ) . B . 20 g acrylamide, 200 m l D M S O , 6.4 m l t-Buli (1.8 M ) . C . acrylamide dimer.

AMD Dimer

60

Reactive Polymers - American Chemical Society

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