versión On-line ISSN 0717-9707
J. Chil. Chem. Soc. v.49 n.2 Concepción jun. 2004
J. Chil. Chem. Soc., 49, N 2 (2004), pags.:133-136
SYNTHESIS AND CHARACTERIZATION OF MACROMONOMERS FROM 2-ALKYL-2-OXAZOLINES
Bernabé L. Rivas*, S.Amalia Pooley, Griselda Fuentes.
Polymer Department, Faculty of Chemistry, University of Concepción, Concepción, Chile.
Macromonomers from 2-oxazoline derivates were synthesized by using 2,2'-iminediethanol and 1-(2-hydroxyethyl) piperazine as terminating agents. The macromonomers are soluble in water and in common organic solvents like chloroform, methanol, and tetrahydrofuran. They were characterized by FT-IR, 1H-NMR , and 13C-NMR spectroscopies. The molecular weight and molecular weight distribution by gel permeation chromatography were determined.
Since Milkovich reported the concept of macromonomer [1-2], many papers have been published on the synthesis and applications of macromonomers [3-18]. Radical polymerization of macromonomer is one of the most widely studied areas.
Macromolecular monomers are polymer species fitted at the end chain with a polymerizable unsaturation. The molecular weight of macromonomers generally range from 1000 (or even less) to 10000 g mol-1 (or slightly more) .
A considerable amount of works has been done in universities and in industrial laboratories to synthesize a large number of macromonomers, differing in the type of repeating monomer and end-group, have so far been prepared, thereby offering the possibility to construct an enormous number of branched polymers in variety of architectures, combinations, and composition. The interest devoted to these species arises from the fact that they are useful intermediates in polymer synthesis [15-16]. The most obvious example is the synthesis of graft copolymers by means of free radical copolymerization of macromonomers with an unsatured comonomer. For this purpose, the macromonomer method is well known as one of the most useful methods among the several methods because the number and length of branch segments of graft copolymer can be controlled. The success in synthesis of well-defined graft copolymers depends upon well-controlled macromonomer.
Actually, the great motivation for research in the field of macromonomers has been the easy access to graft copolymers, which have many potential applications as coating, adhesives, compatibilizer, emulsifiers, moisture retention agents, biomaterials, etc. [17-18]
The aim of this paper is related with the synthesis of macromonomers containing functional groups with potential capability to bind metal ions.EXPERIMENTAL
2-alkyl-2-oxazoline, 2-methyl-2-oxazoline (MOX) and 2-ethyl-2-oxazoline (EtOX) (Aldrich, Milwaukee, USA) were purified by distillation over potassium hydroxide. The 2,2'-iminediethanol and 1-(2-hydroxyethyl) piperazine (Aldrich, Milwaukee, USA) were purified by distillation. Acetonitrile (Merck, Stuttgart, Germany) was distilled from CaH2. Ethyl ether (Merck, Stuttgart, Germany) was dried over calcium chloride and distilled before use. All operations were carried out under nitrogen.
Synthesis of macromonomers
The macromonomers were prepared by living polymerization technique. 4-bromide-1-butene, as the initiator was used. Terminating agents 2,2'-iminediethanol and 1-(2-hydroxyethyl) piperazine were employed.
A pressure resistant pyrex glass tube with nitrogen inlet is charged with a solution of 47 mmol of MeOX and EtOX in 10 mL of acetonitrile. A mixture of 1.33 g (9.85 mmol) of 4-bromide-1-butene as initiator in 5 mL of acetonitrile was added. The reaction was kept at 70°C for 48 h. After cooling at room temperature, a solution of the terminating agent 2,2'-iminediethanol or 1-(2-hydroxyethyl) piperazine was added and the mixture was stirred overnight. The mixture was heated at 70°C for 3 h, followed by treatment with an ion-exchange resin (Amberlyst-21). The solvent was eliminated under vacuum. Then 20 mL of diethylether were added and the mixture was stirred for 24 h. The product was dried until constant weight. Yield: 49-59%
The FT-IR spectra were recorded on a Magna Nicolet 550 spectrophotometer. The 1H-NMR and 13C-NMR were recorded in CDCl3 using a Bruker Multinuclear AM 250 spectrophotometer. The macromonomers were analyzed by gel permeation chromatography (GPC) by using a Perkin Elmer Series 200 with a differential refractive index (DRI) detector and PL-aqua gel-OH columns.RESULTS AND DISCUSSION
The macromonomers were synthesized from alkyl oxazoline derivates according to the following schemes:
a)_a-(3-butenyl)-w-[N,N-bis(2-hydroxyethyl)amino]-poly(N -acylethylenamine) M1 and M3 (see scheme I)
b)a-(3-butenyl)-w-[N-(2-hydroxyethyl)piperazinyl]-poly(N -acylethylenamine) M2 and M4 (see scheme II).
Synthesis of Macromonomers
The macromonomers were synthesized by ionic polymerization. The general experimental conditions are summarized in the table I.
The yield of the macromonomers ranged between 49% and 59 % (see table I). Its were relatively low due to to probably the steric hindrance.
The polymerization of 2-alkyl-2-oxazoline was carried out in acetonitrile at 70°C by using 4-bromide-1-butene as initiator. The living propagating species were reacted with a transfer agent (see Schemes I and II).
The molecular weight of the resulting macromonomers varied between 1500 and 5020 g mol-1 with a molecular weight distribution varying between 1.0 and 1.1. These were determined by size exclusion chromatography (see table II). These values indicate a narrow distribution of the length of the chains. This is a characteristic of the ionic polymerization.
All the macromonomers were characterized by FT-IR, 1H-NMR, and 13C-NMR spectroscopies.
The FT-IR spectra analysis shows the following typical absorption signals:
M1: 3432cm-1 (s,OH); 1632cm-1 (s, C=O), 1427cm-1 (=CH2)
The 1H-NMR spectra of the isolated product in CDCl3 show the following absorption signals:
For macromonomer M1 the signals a, and c, at d = 2.0-2.25 ppm are assigned to methyl protons adjacent to carbonyl group and methylene protons adjacent to vinyl group. Signals h at 2.31-2.77 ppm are assigned to methylene protons linked to nitrogene of amino group. Signals b, f, g, and i at d =3.0-3.7 ppm are assigned to methylene protons linked to nitrogen of amide group of the main chain and methylene protons adjacent to hydroxy group. Signals at d = 5.03-5.82 ppm (ABX) are assigned to vinyl group (see figure 1).
For the macromonomer M2 the signals a and c at d = 1.99-2.20 ppm are assigned to methyl protons adjacent to carbonyl group and methylene protons adjacent to vinyl group. Signals h, i, and j at d = 2.31-2.72 ppm are assigned to methylene protons of piperazine and methylene protons linked to nitrogen of piperazine. Signals b, f, g, and k are assigned to methylene group linked to nitrogen of the main chain (NCH2CH2) and methylene group of adjacent to hydroxy group at d = 3.45-3.7 ppm. Signals d and e at d = 5.03-5.82 ppm (ABX) are assigned to vinyl group (See figure 2).
For the macromonomer M3 the signal a at d = 1.10-1.21 is assigned to methyl group. Signals b and d at d = 2.20-2.27 ppm are assigned to methylene protons adjacent to carbonyl group and methylene protons adjacent to vinyl group. Signal i at d = 2.53-2.73 ppm is assigned to methylene protons linked to nitrogen of amine group of the main chain, methylene protons adjacent to nitrogen of amine group. Signals c, g, h and j at d = 2.98-3.80 ppm are assigned to methylene group linked to nitrogen of the main chain (NCH2CH2) and methylene group adjacent to hydroxy group. Signals at d = 4.84-5.83 ppm (ABX) are assigned to vinyl group (see figure 3).
For the macromonomer M4 the signal a at d = 1.12-1.20 ppm is assigned to methyl protons. Signals b, d, i, j, and k at d =2.31-2.72 are assigned to methylene protons adjacent to carbonyl group, methylene protons adjacent to vinyl group, methylene protons of piperazine and methylene protons linked to nitrogen of piperazine. Signals c, g, h and l at d = 3.49-3.67 ppm are assigned to methylene group linked to nitrogen of the amide group of the main chain and methylene group adjacent to hydroxy group. Signals e and f at d = 5.05-5.84 ppm (ABX) are assigned to vinyl group (see figure 4).
The 13C-NMR spectrum shows the following absorption signals corroborating the expected macromonomer structures. The assignment of the absorption signals was carried out as follows (in ppm):
For M1: at d = 20.82 ppm (carbon a), at d = 33.95 (carbon c), at 44.80 (carbon f), at d = 46.43 (carbon g), at d = 54.02 (carbon b), at d = 55.62 (carbon h), at d = 57.90 (carbon i), at v = 117.63 , 135.94 (vinyl terminal carbons), and at d = 170.45, 171.034 (carbonyl carbons).
For M2 at d = 10.21 (carbon a), at d = 21.12 (carbon b), at d = 35.33 (carbon d), at d = 45.23 (carbon g), at d = 46.80, 52.53, 55.92 (carbons c, h and i), at d = 57.90 (carbon j), at d = 62.04 (carbon k) at d = 119.01 and 135.24 (vinyl terminal carbons), and at d = 170.66, 171.29 (carbonyl carbons).For M3 at d = 25.56, 26.78 (carbons a and b, respectively), at d = 43.25 (carbon g), at d = 45.11 (carbon h), at d = 53.58 (carbon c), at d = 55.78 (carbon i), at d = 58.79 ppm (carbon j), at d = 119.53 (carbon f), at d = 134.06 (carbon e), at d = 170.45, 171.034 (carbonyl carbons).
For M4 at d = 25. 24, 25.77 (carbons a and b, respectively) at d = 43.12 (carbon g), at d = 44.77 (carbon h), at d = 51.84, 52.09 (carbons c, i and j), at d = 56.59 (carbon k), at d = 61.09 (carbon l), at d = 116.20 (carbon f), at d = 134.59 (carbon e), at d = 172.45, 173.65 (carbonyl carbons).
In conclusion the four macromonomers from 2-alkyl-2-oxazoline were completely soluble in water. The molecular weight and polydispersity were determined. It demonstrated a tendency to a narrow distribution of the length of the polymer chains. That is in good agreement with the expected values for a living system.
The authors thank to FONDECYT (Grant No 8990011). Griselda Fuentes thank to CONICYT the Ph D. fellowship.
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(Received: November 19, 2003 Accepted: December 16, 2003)