Polyurethanes as polymerizable dyes for hydrophobic polyester fabric

Article abstract of DOI:10.1007/s11164-012-0532-y

The present invention is to provide a novel benzothiazole-type polymerizable dye containing a urethane bond. A series of monomeric dyes have been prepared by diazotization of various 2-aminobenzothiiazole and coupled with Resorcinol. The polymeric dyes have been prepared by polycondensation of monomeric dyes with hexamethylene diisocyanate (HMDI), and they are characterized by molecular weight, non-aqueous conductometric titration, thermogravimetry analysis, IR, visible spectroscopy, and elemental analysis. The monomeric dyes have also been characterized by elemental analysis and IR spectra. The purity of all the dyes have been checked by thin layer chromatography, and their dyeing performance on nylon and polyester was assessed. The dyeing on polyester fiber had yellow, orange and pink shades with moderate to good light and wash fastness. Polymerizations of monomeric dyes with HMDI on dyed polyester have also been carried out. Color and dyeability of the polymeric dyes have been discussed by comparing them with their corresponding monomeric dyes. The percentage dye bath exhaustion and fixation on fiber have been found to be from good to very good. The dyeing of monomeric dyes showed very good color fastness properties, and their corresponding polymeric dyes showed excellent fastness to light, washing, perspiration, solvent resistance, and sublimation. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0532-y

Res Chem Intermed (2012) 38:2137–2148
DOI 10.1007/s11164-012-0532-y
Polyurethanes as polymerizable dyes for hydrophobic
polyester fabric
•
Medha Joshi Smita Jauhari K. R. Desai
•
Received: 28 June 2011 / Accepted: 6 March 2012 / Published online: 15 March 2012
Ó Springer Science+Business Media B.V. 2012
Abstract The present invention is to provide a novel benzothiazole-type poly-
merizable dye containing a urethane bond. A series of monomeric dyes have been
prepared by diazotization of various 2-aminobenzothiiazole and coupled with Res-
orcinol. The polymeric dyes have been prepared by polycondensation of monomeric
dyes with hexamethylene diisocyanate (HMDI), and they are characterized by
molecular weight, non-aqueous conductometric titration, thermogravimetry analysis,
IR, visible spectroscopy, and elemental analysis. The monomeric dyes have also
been characterized by elemental analysis and IR spectra. The purity of all the dyes
have been checked by thin layer chromatography, and their dyeing performance on
nylon and polyester was assessed. The dyeing on polyester fiber had yellow, orange
and pink shades with moderate to good light and wash fastness. Polymerizations of
monomeric dyes with HMDI on dyed polyester have also been carried out. Color and
dyeability of the polymeric dyes have been discussed by comparing them with their
corresponding monomeric dyes. The percentage dye bath exhaustion and fixation on
fiber have been found to be from good to very good. The dyeing of monomeric dyes
showed very good color fastness properties, and their corresponding polymeric dyes
showed excellent fastness to light, washing, perspiration, solvent resistance, and
sublimation.
Keywords 2-Aminobenzothiazole Á Disperse dyes Á Hexamethylene diisocyanate
(HMDI) Á Number average molecular weight Á Thermogravimetry Á Polyester
M. Joshi Á S. Jauhari (&)
Department of Applied Chemistry, Sardar Vallabhbhai National Institute of Technology,
Surat 395007, Gujarat, India
e-mail: jauharismita@rediffmail.com
K. R. Desai
Department of Pharmaceutical Chemistry, Maliba College, Bardoli, Gujarat, India
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M. Joshi et al.
Introduction
There are few reports apart from some patents [1, 2] on the use of azophenol dyes as
polymerizable dyes. However, Harbak et al. [3] have carried out much work on
polymerizable dyes containing vinylic groups. Kuhn [4] disclosed the first example
of polyoxyalkylene polymeric colorants that fulfills acquired performance require-
ments, such as total removal of fugative tints, and does not influence the final shade
of the fabric in 1964. These large, highly water-soluble molecules could not
penetrate the surface of fabrics and could readily wash away during normal aqueous
dyeing and finishing. The motivation for the development of this exciting new class
of materials is to overcome the deficiencies of both dyes and pigments in specific
applications.
Polymeric colorants offer the advantage of allowing a range of physical
properties such as solubility, absorption, migration, and viscosity that are
tunable. They do not sublimate, are nonabrasive, and generally have low toxicity.
The range of products possible by combining polymer chemistry and color
chemistry is virtually inexhaustible. New examples frequently occur in the
chemical literature of research, which are associated with the various applica-
tions of polymeric colorants [5–17]. Polymeric colorants are finding applications
in a wide variety of technologies. Their applications are dependent on their
higher molar mass. In the broad sense, the term macromolecular colorants are
defined as a group of intermediate or high molar mass compounds that may
also be thought of being intrinsically or structurally colored polymers, i.e.,
possessing inherent properties [18], self-colored polymers [19], polymeric dyes
[20], and polymeric pigments [21]. Each of these terms is somewhat limited in
its application. A monomeric dye is a polymerizable dye that contains a
polymerizable group, normally through an ethylenic type double bond in the
dye molecule. Polymeric dyes may be defined through their application as
polymers and dyes that possess suitably inherent properties. They are soluble in
the medium in which they are applied or in the substrate with which they form a
composite. Polymeric dyes are useful polymers or oligomers due to their
tinctorial strength [22].
The present communication refers to the synthesis, characterization, and dyeing
performance on polyester of various monomeric and polymeric dyes. Polymeriza-
tion of monomeric dyes on dyed polyester was also carried out, and dyeing
properties were compared with those of polymeric dyes.
Experimental
Materials and methods
All the chemicals used were of analytical grade. Various 2-aminobenzothiazoles
have been prepared by the methods reported in the literature [23]. The C, H, N, S
contents have been estimated by Thermofinigen-1101 Flash elemental analyzer
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Polyurethanes as polymerizable dyes for hydrophobic polyester fabric
2139
(Italy). The sulfur content has been determined by the Carius method [24]. IR
spectra of all the polymers have been scanned in KBr pellets on a Perkin Elemer
257 spectrophotometer. The visible spectra were recorded on a Carl Zeiss UV/
Vis Specord spectrophotometer. Number average molecular weights (Mn) of PUs
have been estimated by non-aqueous conductometric titration. The titration has
been carried out in formic acid against perchloric acid as titrant. A digital
conductometer (Toshniwal, India) was used for this purpose. Values of the
number average molecular weight (Mn) of all polymer samples have been
calculated by the method reported in the literature [25]. Thermogravimetric
analysis for polymers was carried out on a DuPont thermobalance in air at a
heating rate of 10 K min-1. The fastness to light, sublimation, perspiration, and
organic solvents was assessed in accordance with BS: 1,006–1,978. The rubbing
fastness test was carried out using a crock meter (Atlas) in accordance with
AATCC-1961. The wash fastness test was carried out in accordance with IS:
765–1,979. The details of various fastness tests are mentioned in the literature
[26]. The percentage dyebath exhaustion and fixation of the dyes on fabric were
also calculated according to the standard method described in the literature [27].
Synthesis of monomeric dyes 4a–h
The synthesis of the monomeric dye 4a–h comprises of two steps.
(a) Diazotization of 2-aminobenzothiazole derivatives 1a–h.
Dry sodium nitrite (0.02 mol) was added by stirring to cold concentrated sulfuric
acid (1.2 mL) at such a rate that brown fumes were not produed. After addition,
the mixture was warmed gradually on a water bath to between 60 and 65 °C,
when all the sodium nitrite went into the solution. The solution was then cooled
to 3 °C and a mixture (20 mL) of acetic acid–propionic acid (17:3) was added
dropwise. The resulting nitrosylsulfuric was then cooled to 0 °C and the finely
ground compound 1a–h (0.02 mol) was added portionwise and vigorous stirring
was continued at 0–3 °C for 2 h. The excess nitrous acid (giving a positive test
on starch-iodide paper) was decomposed with urea. The clear diazonium salt
solution 2a–h thus obtained was used immediately in the coupling reaction
(Scheme. 1).
(b) Coupling of diazonium salt solution 2a–h with Resorcinol 3.
The Resorcinol 3 (0.02 mol) was dissolved in 10 mL acetic acid and cooled at
0 °C. Freshly prepared diazonium salt solution 2a–h was added dropwise to this
well-stirred solution over a period of 2 h, keeping the temperature below 5 °C. The
reaction mixture was stirred for 45 min at 0–3 °C, maintaining the pH at 4–5 by the
help of 10 % sodium acetate solution. The reaction mass was then diluted with
100 mL water, filtered, washed, and dried in an oven at 50 °C. The dye 4a–h thus
obtained was recrystallized from a minimum amount of DMF. The same procedure
was repeated for the preparation of the dyes 4b–h using Resorcinol 3. The synthetic
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M. Joshi et al.
Synthesis of Monomeric Dyes 4a-h
0-5 °C
N
N
S
+ -
N Cl
NH2
N
NaNO2/HCl
S
R
R
2a-h
1a-h
Coupling with
HO
OH
3
HO
OH
S
N
N
N
R
4a-h
Where,
R
=
6- Cl, 6- OCH3, 4- CH3, 6- NO2, 6-F, H, 6- OC2H5, 6-Br
Scheme 1 Synthetic scheme of monomeric dyes 4a–h
scheme is shown in Scheme. 1. The characterization data for dyes 4a–h are given in
Table 1.
Synthesis of polymeric dyes 5a–h
The synthesis of the polymeric dyes 5a–h was carried out by polycondensation
reaction of the monomeric dyes 4a–h with the Hexamethylene diisocyanate
(HMDI). A typical synthesis was described below. The synthetic scheme is shown
in Scheme 2. The characterization data for polymeric dye 5a–h are given in
Table 2.
To an ice-cooled solution of monomeric dye 4a–h (0.01 mol) in dry tetrahy-
drofuran (50 mL), a solution of HMDI (0.01 mol) in 50 mL dry tetrahydrofuran was
added gradually with constant stirring. The colloidal suspension that formed
immediately was then stirred at room temperature for an hour. The resultant
suspension was refluxed for 2 h. The resulting solid product was then filtered off
and air-dried (95 % yields).
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Polyurethanes as polymerizable dyes for hydrophobic polyester fabric
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M. Joshi et al.
Synthesis of Polymeric Dyes 5a-h
HO
OH
OCN - (CH2)6 - NCO
N
+
N
N
S
R
Hexamethylene Diisocyanate
4a-h
(1) DMF, 0
°C, 1hr
(2) Reflux, 2hr
-------------------
-------------------
n
COO NH (CH2)6 NH
COO
N
N
N
S
R
5a-h
Where,
R
=
6- Cl, 6- OCH3, 4- CH3, 6- NO2, 6-F, H, 6- OC2H5, 6-Br
Scheme 2 Synthetic scheme of polymeric dyes 5a–h
Dyeing method
Dyeing method for monomeric dyes
Dyeing at 130–135 °C temperature and high pressure (24–30 psi) is a convenient
method for dyeing polyester fabric in the laboratory. A laboratory model glycerin-
bath high-temperature beaker dyeing machine was used. A paste of finely powder
dye (40 mg) was prepared with dispersing agent Dodamol (80 mg); wetting agent
Tween-80 (5 mg) and water (1 mL) in a ball mill for 10 min. To this paste, water
(99 mL) was added with stirring and the pH was adjusted to 4.5–5 using acetic acid.
This dye suspension (100 mL) was added to a beaker provided with a lid and a
screw cap. Before closing the lid and tightening the metal cap over the beaker, a
wetted pattern of polyester fabric was rolled into the beaker. The beaker was then
placed vertically on the rotatory carrier inside the tank and the clamp plate was
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Polyurethanes as polymerizable dyes for hydrophobic polyester fabric
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M. Joshi et al.
firmly tightened. The rotatory carrier was then allowed to rotate in the glycerin bath,
the temperature of which was raised to 135 °C (for polyester fabric) at the rate of
2 °C min-1. The dyeing was continued for 1 h, under pressure. After cooling for
1 h, the beaker was removed from the bath and washed with water. The pattern was
thoroughly washed with hot water at 50 °C and then with cold water, and finally
dried at room temperature.
Dyeing method for polymeric dyes
Polycondensation of monomeric dyes on dyed polyester After dyeing, the dyed
fabrics were rinsed with water, squeezed and introduced into n-hexane (100 mL)
containing diisocyanate (0.5 mL 37–40 % w\v) and stirred at room temperature for
half an hour. The fabrics were washed with water and treated with detergent (0.2 %
v\v) in water at 80 °C for 30 min. After washing with water, the fabrics were dried.
Result and discussion
A weak amine, such as compound 1a–h, required the use of nitrosylsulfuric acid,
and it was diazotized satisfactorily at 0 °C by adding to nitrosylsulfuric acid in an
acetic acid–propionic acid mixture. The resulting diazonium salt solution 2a–h was
generally used within a few hours since this decomposed on standing, even when
cold. Coupling was usually accompanied by some evidence of decomposition;
however, by careful addition of the diazonium salt solution 2a–h at 0–3 °C to a
solution of the coupler in acetic acid, a 68–84 % yield of the dye was usually
obtained. To complete coupling, particularly for reactions using nitrosylsulfuric acid
in the diazotization, the pH of the reaction mixture was eventually adjusted to
approximately 4–5. Thus, an appropriate amount of 10 % sodium acetate solution
was slowly added below 3 °C. The purified dyes were all found to have satisfactory
elemental analyses. All the dyes required purification to eliminate contaminants
arising from diazo decomposition and/or the coupling components used. The purity
of the dyes was checked by thin layer chromatography (TLC) using ethyl acetate–
benzene (1:4) as the solvent system. When adsorbed onto silica chromatography
plates, each dye produced a single color spot. All the recrystallized dyes exhibited
well-defined melting points characteristic of pure compounds.
The IR spectra of the dyes reveal that the band appearing at 1,573 cm-1 is due to
the stretching vibration of the C=C, which is conjugated with C=O. The
unsaturation is also indicated by the C–H stretching vibrations, which appear at
3,320–3,330 and 720–740 cm-1 (out-of-plane deformation vibrations). The band at
623 cm-1 is an out-of-plane-deformation vibration characteristic of CH=CH. The
band appearing at 625–675 cm-1 can be attributed to an in-plane deformation
vibration of the C=O. The bands at 1,336 cm-1 are due to a stretching vibration of
C–N–C, the first being asymmetrical and the second symmetrical. The band of the
skeletal C–C bond appears at 1,573 cm-1, and the band at 1,620 cm-1 is due to –
N=N– stretching vibration. The strong characteristics band at 620–630 cm-1 is due
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Polyurethanes as polymerizable dyes for hydrophobic polyester fabric
2145
to –S–H stretching vibration and that at 1,123 cm-1 is due to –C–N stretching. The
band around 1,450–1,480 cm-1 is due to an ester group.
Thermogravimetric investigations were carried out for the polymeric dyes in the
range 25–650 °C, at a heating rate of 10 °C min-1 in air atmosphere. Typical TGA
curves for the selected polymeric dyes 5b, 5f, 5g, and 5h are shown in Fig. 1. All
the polymeric dyes have good thermal stability and degrade in a single step.
All the dyes were applied at 2 % depth on polyester fabric. No problem was
encountered in preparing satisfactory dispersions when the monomeric dyes were
milling with the dispersing agent. Then, the polymerization was carried out on these
polyester fabrics dyed with monomeric dyes with the HMDI. All the fastness
properties shown in Tables 3 and 4 are interrelated, since all depend, among other
things, on the rate of diffusion of dye in the fabric. This rate is a function of the
geometry of the dye molecule and depends on both the slimness of the molecule,
i.e., the magnitude of its smallest cross-section, and the molecular weight. Rate of
dyeing and wash fastness are the most important of this type of diffusion-related
properties and may be considered to be directly related. The concentration of the
dye in the fabric appeared to be the most influential factor in the fastness of the
dyes. For example, the variation of light fastness of dye with their concentration in
the substrate is partly a function of their particle size. In any system where particles
are formed from a liquid phase, they appear in a random range of sizes. Moreover,
their average size increases with concentration. This concept will be met only in dye
systems that are molecularly dispersed, but it is also likely to occur with polymer
dyes are dispersed in a medium. The polymeric dyes have larger molecular size and
they were slightly less soluble in polyester fabric compared to the monomeric dyes,
slightly restricting the depth of dyeing. The wash fastness rating of the polyester
dyeing was primarily influenced by the depth of the shade. The lighter shade of the
polyester dyeing means that staining was low, which did not lose color. Thus, the
lighter shade restricted the occurrence of any staining. Monomeric dyes were much
more soluble in polyester, which suggests that the higher solubility of these dyes
allows greater depths to be achieved.
Fig. 1 Thermogravimetric analysis curves of polymeric dyes
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M. Joshi et al.
Table 3 Dyeing and fastness properties of monomeric dyes on polyester
Dyes no. Shade on
polyester
Light Wash
fastness fastness
Perspiration fastness Sublimation Rubbing fastness
fastness
Acid
Alkaline
Dry
Wet
4a
4b
4c
4d
4e
4f
Pink
4
4–5
5
4–5
4–5
5–4
4–5
4–5
4–5
5
4–5
5–4
4–5
4–5
5–4
4–5
5–4
5–4
5
4–5
4
4–5
4–5
4–5
4
Yellow
4–5
5
Light yellow 4–5
4–5
5–6
5–6
4–5
6
4–5
5
4
Light pink
Orange
3–4
4–5
4
4
4–5
5
4–5
4–5
5
4–5
4–5
5
Light orange
Bright pink
4g
4h
5
5
Light yellow 4–5
5–6
5
5
4–5
5
Table 4 Dyeing and fastness properties of polymeric dyes on polyester
Dyes no. Shade on
polyester
Light Wash
fastness fastness
Perspiration fastness Sublimation Rubbing fastness
fastness
Acid
Alkaline
Dry
Wet
5a
5b
5c
5d
5e
5f
Dark pink
4–5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5–4
5
5
Dark yellow 5–6
Dark yellow 5–6
5–6
5
4
5
5
5
5–4
5
Dark pink
4–5
5–6
5–6
5
5
5–4
5
Dark orange 5–6
Dark orange 5–6
5–4
5–4
5
5
5
5
5g
5h
Pink
6
5
5
5
5
Yellow
5
5
5
5
All the fastness properties of fabric containing the monomeric dyes (Table 3)
range from good to excellent, while dyed fabric with corresponding polymeric dyes
(Table 4) shows excellent fastness properties. Table 5 indicates the results of the
bleeding test. The dyed fabric with the polymeric dyes has excellent fastness to
water, very good to excellent fastness to ethanol, toluene, and n-butanol–xylene
(1:9), and good to very good fastness to cellosolve solvent. It can be suggested that
the polymeric dyes may react with polyester fabric and are easily soluble under
the dyeing condition. Thus, polymeric dyes applied to polyester fabric are more
resistant to removal by solvent extraction.
Absorption maxima of dyes recorded in DMF solution and concentrated sulfuric
acid are shown in Tables 1 and 2. The logarithm of molar extinction coefficient (log
e) of the dyes range from 3.11 to 4.71, indicating high intensity of absorption. The
introduction of electron-donating or electron-attracting groups at suitable positions
on the coupler ring affects the absorption characteristics of the dyes. Table 1 shows
that the exhaustion and fixation of the monomeric dyes on polyester fabric are
higher than those of their corresponding polymeric dyes (Table 2). The polymeric
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Polyurethanes as polymerizable dyes for hydrophobic polyester fabric
2147
Table 5 Bleeding properties of polymeric dyes 5a–h
Dye no.
Water
Ethanol
Toluene
n-Butanol–xylene (1:9)
Cellosolve
5a
5b
5c
5d
5e
5f
5
5
5
5
5
5
5
5
4–5
5–4
5–4
5–4
5–4
5–4
5–4
5–4
5
5–4
5–4
5–4
5–4
5–4
5–4
5
4–5
5–4
5–4
5
5–4
5–4
5–4
5
4–5
4–5
5–4
5–4
4–5
5–4
5–4
5g
5h
5–4
dyes have larger molecular size and tend to have more interactions with the fabric.
Polyester fabric is crystalline and hydrophobic in structure. Consequently, diffusion
of the polymeric dye within the fabric proceeds slowly under the given dyeing
conditions, thereby affecting the exhaustion value. The polymeric dyes exhaust
smoothly onto the fabric when applied from a stable dispersion under dyeing
conditions and provide satisfactory color shade with slightly lower depths. The
substantivity of the dye, which determines its tendency to partition in favor of
the fabric, depends on factors such as molecular size, geometry, and (in particular)
the polarity of the molecule. During the dyeing process, the fabric is in the glasslike
state below about 80 °C and inaccessible to aqueous solutions of dye. When the
glass-to-rubber transition temperature is reached, the fabric immediately becomes
readily dyeable.
Conclusion
Good yields of all the monomeric and polymeric dyes were obtained. These dyes
provide a narrow range of color shades, and excellent affinity and intensity of
color. The utilization of these dyes was possible because of certain essential dye
properties, such as fast leveling on fabric, excellent fastness to light, wet treatment
and sublimation, and very good to excellent thermal and chemical resistance. From
the above studies, it is clear that increasing the molecular size of the dye molecule
via polymerization has led to improvements of the fastness properties. The polymeric
dyes on polyester fabric have a relatively low depth shade with excellent fastness and
staining ratings.
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