Preparation and Characterization of Waterborne Hyperbranched

Ind. Eng. Chem. Res. 2010, 49, 4517–4527

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Preparation and Characterization of Waterborne Hyperbranched Polyurethane-Urea and Their Hybrid Coatings Pion Florian,‡ Kishore K. Jena,† Shaik Allauddin,† Ramanuj Narayan,† and K. V. S. N. Raju*,† Organic Coatings and Polymers DiVision, Indian Institute of Chemical Technology, Hyderabad-500 607, India, and Chemistry Department of Rennes, 1 UniVersity, 35000 France

A series of novel waterborne hyperbranched polyurethane-urea (WHBPU) were prepared with different chain extenders (diamine, diol, and siloxane) by a systematic reaction process. Initially, the hyperbranched polyester polyol was prepared by reacting polytetramethyleneglycol (PTMG)-1000 with 2,2-bis(hydroxymethyl) propionic acid (DMPA) in a molar ratio of 1:14 (3rd generation) at 160 °C by one pot synthesis. This was reacted with an adduct of isophorone diisocyanate (IPDI) and DMPA with NCO:OH mole ratio of 1.6:1. Then 50% of free NCO in these prepolymers was reacted with three different chain extenders (diol, diamine and APTES). This reaction mixture was neutralized with triethyl amine and another 50% of free NCO was chain extended with isophorone diamine during water dispersion. The obtained polyester was characterized with Fourier transform-infrared spectroscopy (FT-IR), 1H and 13C NMR, respectively. The properties of WHBPU and their hybrid coatings were studied by FT-IR, 1H NMR, thermogravimetric analyzer (TGA), dynamic mechanical, and thermal analyzer (DMTA), and the contact angle measurement. TGA and DMTA results confirmed that these coatings have good thermal and mechanical properties. The onset degradation temperature of the WHBPU without APTES starts in between 200 and 250 °C, whereas the APTES chain extended WHBPU starts at 250 °C. Tg of WHBPU without APTES varies between 106 and 126 °C, while 129 °C for APTES chain extended WHBPU. The conditions for the reproducible preparation of suitable products have been found and optimized. They enable the tuning of their properties according to the intended use. The aim of the prepared WHBPU films is long-term use as thermal and mechanical resistant systems. Along with these property APTES crosslinked system, the hydrophobic silica-rich surface is likely to be inhibited the hybrid films upon exposure to an aqueous environment. 1. Introduction The everlasting thirst for high performance materials has given birth to intensive research on the development of new and novel hybrid materials. These are gaining importance over the past decade due to its high thermal stability, mechanical properties, and abrasion resistance. In order to realize the best properties from the matrix and reinforcement, it is essential that processing methodology should be innovatively designed.1 To develop new materials with desired properties, the synergistic combination of polymers and inorganic sol-gel precursors via a sol-gel process has recently attracted great attention in the field of material science.2-9 These new hybrid materials could have a controllable combination of polymers giving flexibility and toughness and inorganic part giving hardness, durability, and thermal stability. Basically, the research mainly focused on inorganic modification of organic polymers in composite materials.10,11 During the last decades, the main aim of the paint industry is to provide eco-friendly products (due to environmental restrictions and customer expectations) without affecting the properties or increasing cost. In this way, four new technologies have emerged in paint technology to reduce VOC amount (volatile organic compounds), that is, waterborne coating, * To whom correspondence should be addressed. Phone: 91-4027193208. Fax: +91-40-27193991. E-mail: [email protected] or [email protected]. ‡ Chemistry Department of Rennes. † Indian Institute of Chemical Technology.

UV-curable coating, high solids coating, and powder coating.12 One of the most recently investigated polymers with complex architecture is the dendrimers13 or hyperbranched polymers bearing a number of functional groups at the periphery that could be used selectively for obtaining the desired properties.14-20 For instance, the poor thermal and mechanical properties of conventional polyurethanes can be overcome by introducing a number of cross-linking points through the use of hyperbranched polymers. The use of hyperbranched polymers as precursors with a compact architecture instead of linear polyether or polyester polyols results in HB polyurethanes with excellent material properties.21 We report three types of hyperbranched polyurethaneurea dispersions (WHBPU) preparation and study the effect of different chain extenders on the performance of waterborne hyperbranched polyurethane-urea and their hybrid coatings. 2. Experimental Section 2.1. Materials. Polytetramethylene glycol (PTMG-1000), 2,2-bis (hydroxymethyl) propionic acid (DMPA), Isophorone diisocyanate (IPDI), Dibutyltindilaurate (DBTL), 1,3-propanediol, and 3-aminopropyltriethoxysilane (APTES) were procured from Aldrich Chemicals (Milwaukee, WI). Titanium tetraisopropoxide (TTIP), 4,4′-diamino-diphenyl sulfone, and 1,4-dioxane were purchased from Fluka Chemical Corp (Ronkonkoma, NY). Spectroscopic grade tetrahydrofuran

10.1021/ie900840g  2010 American Chemical Society Published on Web 04/13/2010

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Ind. Eng. Chem. Res., Vol. 49, No. 10, 2010

Scheme 1. Preparation of HPB-OH 3rd Generation

(THF) and sulfur free toluene from S.D. Fine Chemicals (Mumbai, India) were used as received. 2.2. Synthesis of Hyperbranched Polyester (HBP-OH). Hyperbranched polyester polyol (3rd generation) was synthesized by melt polycondensation technique. The required amounts of PTMG and 14 equivalents of DMPA (Scheme 1) were charged into four necked round bottomed flask (R.B), which was placed over a heating mantle equipped with thermometer, mechanical stirrer, nitrogen inlet and dean-stark apparatus. Then it was slowly heated and maintained between 160-190 °C with continuous nitrogen flow. The reaction was continued until the acid value reached below 10. The percentage of esterification of the polyester was calculated by NMR and was about 91%. 2.3. Synthesis of DMPA and IPDI Adduct. The adduct was prepared by reacting the DMPA and IPDI (NCO:OH mol ratio of 2:1) at 50 °C with constant flow of nitrogen. The change of NCO value during the reaction was determined by di-nbutylamine titration method to find out the end point. 2.4. Synthesis of Waterborne Hyperbranched Polyurethane-Urea (WHBPU). The NCO-terminated hyperbranched polyurethane (HBPU) prepolymers were prepared by reacting the HBP-OH with DMPA/IPDI adduct at 60 °C until the required NCO value achieved. The NCO:OH mole ratio of polyester and adduct was 1.6:1.The reaction was carried out by the using of 1,4-dioxane solvent. The 50% of free NCO in these prepolymers was reacted with three different chain extenders like 1,3 propanediol; 4,4′-diamino-diphenyl sulfone and APTES.22,23 This reaction mixture was neutralized with triethyl amine and another 50% of free NCO was chain extended with isophorone diamine during water dispersion under vigorous stirring. The resulting product was a WHBPU with a solid content of about 30%. These dispersions were casted on Teflon sheet and kept at room temperature and humidity. These samples were named as WHBPU-IP-100%; WHBPU-DIO-50%; WHBPU-DIA-50%; and WHBPU-AP-50%. In WHBPU-IP-100% the free NCO was chain extended with isophorone diamine. Where DIO stands for diol chain extender, DIA for sulfone diamine and AP represents for APTES cross-linker. Scheme 2 shows the steps involved in the synthesis of waterborne hyperbranched polyurethane-urea with different chain extenders. Table 1 shows the various reactants used to prepare hyperbranched polyesters, hyperbranched polyurethane-urea, and

hyperbranched polyurethane-urea/silica hybrid along with their equivalent ratios. 2.5. Preparation of Films. The films were prepared by casting formulations on tin foil using applicator. The supported films were kept at 75 °C inside the oven for two hours to evaporate the residual solvent slowly and then these films were kept at room temperature and humidity condition for 10 days. All the hybrid films were tack free within four hours but film characterization was done after 10 days curing. The cured films were amalgamated and used for different characterization. 2.6. Instrumental Characterization. The 1H and 13C NMR spectra of the hyperbranched polyesters were recorded on Varian VXR-Unity 200 MHz and Bruker UXNMR 300 MHz spectrometers in dimethyl sulfoxide-d6 (DMSO-d6) with Me4Si (TMS) as internal standard. For infrared analysis of HBP-OH and chain extended samples were prepared by casting the formulation onto a clean KBr pellet. These samples were put into an oven at 60 °C for 1 h to completely remove the solvent before recording the FTIR spectra. Infrared data was obtained with the Thermo Nicolet Nexus 670 spectrophotometer between 4000 and 400 cm-1 with a resolution of 4 cm-1. TGA Q-500 was used to study the thermal decomposition profile of WHBPU samples under nonisothermal conditions at a constant rate of 10 °C/min in inert nitrogen atmosphere (flow rate: 30 mL min-1) from 25 to 500 °C. The storage modulus (E′), cross-link density and glass transition temperature (Tg) were measured by using DMTA IV instrument in tensile mode at a frequency of 1 Hz and with a heating rate of 3 °C/min by scanning the films periodically from -20 to 200 °C in nitrogen atmosphere. E’ and E′′ characterize the elastic and viscous component of a material under deformation, E’ is a measure of mechanical energy stored under load.22,23 Differential scanning calorimeter (DSC) analyses performed with Mettler Toledo DSC 821e thermal system; Zurich, Switzerland. Contact angle measurements were done to determine the hydrophilic and hydrophobic nature of the films using contact angle measuring instrument (KRUSS, GmbH, Hamburg) by sessile drop method which involves placing a drop of water using a micro syringe on the dry films and then measuring the contact angle between the solid liquid interfaces. 3. Results and Discussion 3.1. GPC Analysis. The molecular weight and polydispersity of polyester sample were analyzed by GPC (Shimadzu LC 10ATVP series, Japan) with a refractive index detector using polystyrene standards. The GPC values of hyperbranched polyester generally are given lower molecular weight than the estimated values due to higher branched nature. 3.2. NMR Analysis. The 1H NMR of HBP-OH’s is shown in Figure 1(a). The peaks are from 0.645 to 1.308 ppm corresponding to the CH3 (Terminal, Linear, and Dendritic), from 1.290 to 1.786 ppm corresponding to the CH2 belonging to the core, from 3.869 to 4.332 ppm due to the CH2 attached to the alcohol function and the oxygen of core molecule, from 3.869 to 4.332 ppm showing the CH2 attached to the ester group and the peak comprise between 4.418 and 4.98 ppm represents the terminal and linear alcohol groups. Figure 1(b) shows the 13 C NMR of HBP-OH with different characteristics peaks. The peaks are at 17 ppm corresponding to the methyl groups of DMPA, from 45-51 ppm corresponding to quaternary carbons (qc) and methylene groups and carbonyl groups resonated at: 62-68 and 171-175 ppm. In WHBPU-IP-100%, two new peaks are visible at 6.9 ppm and 6.648-6.673 ppm due to the formation of urethane and


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Scheme 2. Idealized Structure of WHBPU

Table 1. Monomer Used for Preparation of WHBPU at OH: NCO Equiv.Wt.Ratio of 1:1.6 with Different Chain Extenders polyester

Mw(theor)

Mw(GPC)

Mn(GPC)

PDI ) Mw/Mn

HBP-OH PTMG- 1000+DMPA (third generation)

2624

2382

1751

1.36

HBP-OH:NCO (IPDI+DMPA) OH:NCO ) 1:1.6

sample code

chain extenders mole percentage of free NCO

WHBPU-IP-100 WHBPU-DIA-50 WHBPU-DIO-50 WHBPU-AP-50

100% 50% 50% 50%

urea as shown in Figure 1(c). In the case of WHBPU-DIA50%, the same peaks are observed; the only difference was the aromatic protons coming from the diamine at 7.682-7.704 ppm shown in Figure 1(d). In the case of WHBPU-DIO50% the urea peak at 6.85 ppm and urethane peak is observed at 7.482 ppm shown in Figure 1(e). For the WHBPU-AP50% extended by APTES, both urea and urethane peaks are observed at 6.298 and 7.52 ppm (Figure 1(f)).24,31

methods and data reported in the Table 2. Figure 2 shows the magnified methyl region of the 1H NMR, quaternary carbon and CdO zone of the 13C NMR.

The degree of branching of hyperbranched polyester was calculated from 1H and 13C NMR by Frechet and Frey

HBP-OH NMR 1H: Scheme 3 [Structure (a)] δ ) 0.645-1.308 (H3+H5); δ ) 1.290-1.786 (H1); δ ) 2.5 (DMSO); δ )

ByFrechet:DBFrechet ) [D + T/D + L + T]

(1)

or Frey:DBFrey ) [2D/2D + L]

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Figure 1. (a) 1H NMR and (b) 13C NMR spectra of hyperbranched polyester (HBP) in DMSO-d6+CDCl3, (c) 1H NMR spectrum of WHBPU-IP-100% in DMSO-d6+CDCl3, (d) 1H NMR spectrum of WHBPU-DIA-50% in DMSO-d6+CDCl3, (e) 1H NMR spectrum of WHBPU-DIO-50% in DMSO-d6+CDCl3 and (f) 1H NMR spectrum of WHBPU-AP-50% in DMSO-d6+CDCl3. Table 2. Degree of Branching of the Synthesized Hyperbranched Polyester sample name

chemical shift

(D) (L) (T) DBFrechet DBFrey

1.0 HBP-OH CH3 (1H, 1.0-1.35 ppm) 1.0 Cq (13C, 46.5-51.5 ppm) CdO (13C, 171.5-175 ppm) 1.0

2.1 1.6 1.6 0.4 1.5 0.2

55.3 46.7 44.4

48.8 55.6 57.1

3.12-3.554 (H4+H8); δ ) 3.556-3.754 (H1′); δ ) 3.869-4.332 (H2); δ ) 4.418-4.98 (H6+H7).22 13C NMR: Scheme 3 [Structure (b)] δ ) 16.87 (C5+C9); δ ) 26.09-29.40 (C2); δ ) 39.43 (DMSO); δ ) 40-50 (C4+C10); δ ) 61.10-65.05 (C6+C7); δ ) 70.80 (C1); δ ) 77.312 (CDCl3)); δ ) 173-178 (C3+C10).25-28 WHBPU-IP-100%. Scheme 3 [Structure (c)] NMR 1H (ppm): δ ) 0.766-1.266 (H3+H12+H13+H14+H17+TEA(CH3)); δ ) 1.519-1.629 (H1+H8+H9+H11); δ ) 2.276-2.302 (H2O); δ ) 2.493-2.555 (DMSO); δ ) 2.754-2.879 (H7+TEA(CH2)); δ ) 2.941-3.081 (H19); δ ) 3.216-3.760 (H1′+H10); δ )

3.929-3.992 (H2+H4+H5+H16); δ ) 6.648-6.673 (H20+H21+ H22+H23); δ ) 6.967-6.997 (H6+H15); δ ) 9.737 (H18).29-31 WHBPU-DIA-50%. Scheme 3 [Structure (d)] NMR 1H: δ ) 0.988-1.120 (H3+H11+H12+H13+H16+TEA (CH3)); δ ) 1.7741.947 (H1+H7+H8+H10); δ ) 2.491-2.645 (DMSO); δ ) 2.961-3.244 (H6+TEA(CH2); δ ) 3.508-3.784 (H2+H4+ H1′+H9+H15); δ ) 6.587-6.657 (H18+H19+H29+H30); δ ) 6.850-6.90 (H5+H14); δ ) 7.682-7.704 (H20+H21+H22+ H23+H24+H25+H26+H27); δ ) 9.837 (H17). WHBPU-DIO-50%. Scheme 3 [Structure (e)] NMR 1H: δ ) 0.907-1.120 (H3+H12+H13+H14+H17+H23+TEA (CH3)); δ ) 1.554-1.646 (H1+H8+H9+H11+H21); δ ) 2.502-2.641(DMSO); δ ) 2.946-3.247 (TEA (CH2)); δ ) 3.439-3.854 (H2+H4+ H5+H1′+H7+H10+H19+H24); δ ) 6.848-6.855 (H6+H15+H20); δ ) 6.714-6.755 (urea NH); δ ) 10.036 (H18). WHBPU-AP-50%. Scheme 3 [Structure (f)] NMR 1H: δ ) 0.4-0.6 (H23); δ ) 0.864-1.209 (H3+H12+H13+H14+H17+TEA (CH3)); δ ) 1.514-1.613 (H1+H8+H9+H11+H22); δ ) 2.506-


Figure 2. Peaks corresponding to the dendritic, linear and terminal (a) Carbonyl (b) quaternary carbon from the 13C NMR and (c) methyl zone from 1H NMR of hyperbranched polyester (HBP-OH) in DMSO-d6+CDCl3.

2.664 (DMSO); δ ) 2.770-3.116 (TEA (CH2)); δ ) 3.307-3.762 (H2+H4+H1′+H5+H10+H16); δ ) 3.917-3.997 (H4+H7); δ ) 4.379-4.486(H25); δ ) 6.438-6.532 (H19+H20); δ ) 6.972-6.992 (H6+H15); 9.235 (H18). 3.3. FTIR Analysis. Figure 3 (a) shows FTIR spectra of the HBP-OH in the zone 400-4000 cm-1. The broad peak at 3425 cm-1 is attributed to the OsH stretching absorbance and the CdO strong band at 1754 cm-1 from the ester linkages. The broad complex band of the hydroxyl (OsH) vibration region at about 3425 cm-1 is attributed to the combined effect of the differently associated hydroxyl groups, that is, hydrogen bonding between sOH and sOH or between sOH and sCdO group of more electronegative ester function.32 The FTIR spectra of WHBPU-IP-100%; WHBPU-DIO-50%; WHBPU-DIA-50%; and WHBPU-AP-50%, respectively, are shown in Figure 3(b). This figure shows that most of the organic functional group peaks of these samples coincide. The FTIR spectra are mainly characterized by bands at 3150-3600 cm-1 (NsH stretching vibrations), 2800-3000 cm-1 (CsH asymmetric and symmetric stretching vibrations), 1600-1800 cm-1 (CdO stretching vibrations), 1564 cm-1 (amide II, δN-H+ν C-N), 1310-1350 cm-1 (amide III, δN-H+ν C-N) 1240 cm-1 (OsCdO of ester), 1126 cm-1 (CsOsCdO of ester, CsOsC of PTMG), respectively. The presence of amide group in the films suggests the formation of urethane and urea functions. The hydrogen bonded NsH peaks vibrate at 3200-3500 cm-1 and the free NsH peaks at 3500-3600 cm-1.33-35 The very strong band of CsOsC stretching vibration of ether group in thin films appeared at 1126 cm-1. The NsH and CdO stretching zones are the major part of these samples in the FTIR spectra. This is because of the formation of hydrogen bond in different

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magnitude within the hard-hard segment and hard-soft segment. FTIR was used to study the effect of chain extenders on the phase morphology of the waterborne hyperbranched polyurethane-urea. Scheme 4 shows the hydrogen bonding interaction present between different groups of the coatings. Two major spectrum regions of interest in this work were, the NsH stretching vibration at 3000-3800 cm-1 and the carbonyl stretching vibration at 1600-1800 cm-1. The extent and strength of hydrogen bonding in both hard-hard and hard-soft segments was studied by deconvulation of NsH and CdO zones of infrared absorption of the two spectral regions by different chain extenders.36-40 Besides these bands, hybrid also has the characteristic absorption peaks at 1100 and 800 cm-1 due to the asymmetric and symmetric vibration modes of SisOsSi and confirms that the siloxane group was introduced into the PU backbone. A detailed analysis of the structure of the synthesized samples through FTIR spectroscopy was presented in earlier publication.41-43 Figure 4 (a) shows the 1600-1800 cm-1 region is assigned to free carbonyl and hydrogen bonded carbonyl absorption of the urethane/urea groups in the WHBPU samples. These samples can form medium to strong hydrogen bonding has its carbonyl peak, whereas, the urea compound can form very strong, bidentate hydrogen bonding shows a peak maximum at 1631 cm-1, much lower than that of the ester or urethane.41 Peak deconvulation of WHBPU samples have confirmed the bands assigned to the free CdO in urethane group is centered at approximately 1720-1740 cm-1, whereas those assigned to the free CdO in urea group is centered at approximately 1650-1710 cm-1.44,45 The representative deconvulation spectrum of WHBPU-DIA-50% and WHBPU-DIO50% is shown in Figures 4(b) and (c). Figure 4 (d) shows the 3000-3800 cm-1 region assigned to free NsH and hydrogen bonded NsH absorption of the urethane/urea groups in the WHBPU samples. Figures 4(e) and (f) show the deconvoluted curve of the N-H stretching zone of WHBPU-DIO-50% and WHBPU-DIA-50%. In each spectrum, the NsH stretching vibration exhibits a strong absorption peak centered at around 3200-3500 cm-1 arising from the hydrogen bonded NH, whereas the free NH stretching vibration appears at ca. 3500-3580 cm-1. Interestingly, another peak observed at ca. 3200-3275 cm-1 corresponds to the NsHsO (type-2) of ether hydrogen bonding. This result might be due to the phase-mixed state between hard and soft segment via hydrogen bonding in the polymers.46-48 The band of hydrogen bonding (type-1) between NsH and carbonyls at 3400-3450 cm-1 was shifted to lower wavenumber with the increasing of urea groups. Because band position is related to the strength of the H-bonded NsH band, then the shift to lower frequency with increasing urea concentration indicated a decrease in the bond strength of the NsH bond. This shows that a polar chain extender, for example, 4,4′-diamino-diphenyl sulfone selectively enhances hard segment cohesion due to its polarity and therefore produces more hydrogen bonding characteristics. The peak contribution of type 1 and type 2 hydrogen bonding structure in WHBPU-DIA-50% and WHBPU-DIO50% suggests that the amount of phase mixing is higher in WHBPU-DIO-50% compared to the amount of phase separation. In the case of WHBPU-DIA-50% both phase mixing and phase separation is observed but phase separation is more observed in WHBPU-DIA-50% as compared to WHBPUDIO-50%. 3.4. XRD Analysis. The XRD analysis has been performed in powder X-ray diffraction after grinding the films. Figure 5 shows

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Scheme 3. Panels (a) and (b) Illustrate the Proton and Carbon Position of Hyperbranched Polyester (HBP) (c) Proton Position of WHBPU-IP-100% Sample, (d) Proton Position of WHBPU-DIA-50% Sample, (e) Proton Position of WHBPU-DIO-50% Sample and (f) Proton Position of WHBPU-AP-50% Sample

the XRD curves of WHBPU-IP-100%; WHBPU-DIO-50%; WHBPU-DIA-50%; and WHBPU-AP-50% samples. All diffractogrammes contain a broad peak around 18° (2θ angle), which suggests that the diffraction is mostly by an amorphous polymer region. The higher broad peak is obtained in the WHBPU-DIO50% sample, but the broad peak around 18° whose intensities get decreased in the case of diamine and siloxane chain extender. On the comparison of WHBPU-DIO-50% extender and WHBPU-IP100%, the peak intensities of the diamine were lower than diol.

This might be due to the formation of more polar urea groups in the structure and formed more inter chain hydrogen bonding between the macromolecular chains which can induce disorganization. 3.5. TGA Analysis. This technique used to measure changes in the mass of a sample as a function of temperature. In TGA, typical weight loss profiles were analyzed by the percent of weight loss at any given temperature, the percent of noncom-


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Figure 3. (a) FTIR spectrum of hyperbranched polyester (HBP-OH) and (b) The FTIR spectra of different WHBPU thin films coated on KBr pellet and recorded at ambient temperature.

busted residue at final temperature, and the onset/endset temperature of various degradation steps. Two-steps decomposition profile is obtained for WHBPU-IP-100%; WHBPU-DIO50%; WHBPU-DIA-50%; and WHBPU-AP-50% coatings, respectively. The results of TGA analysis are summarized in Table 3. Figure 6 shows the TGA profiles of the different chain extended samples. The onset of the first step is around 220 °C and completed around 320 °C correspond to the decomposition of the urethane, urea segment. The percentage of weight loss at 320 °C corresponds to 44.0%, 50.0%, 54.0%, and 59.0% for WHBPU-AP-50%; WHBPU-DIA-50%; WHBPU-IP-100%; and WHBPU-DIO-50%, respectively. The second stage of degradation corresponds to the decomposition of soft segment and polymer attached to the siloxane network, which started at 320 °C and ended at about 450 °C. A comparison of the characteristic thermal decomposition data from Table 3 shows that the stability order follows: WHBPU-DIO-50% < WHBPU-IP-100% < WHBPU-DIA-50% < WHBPU-AP-50%. The T1on and T2on

values of WHBPU-DIO-50%; WHBPU-IP-100%; WHBPUDIA-50%; and WHBPU-AP-50% were 218.61, 349.71; 228.37, 365.22; 242.19, 380.17, and 252.72, 415.76 °C, respectively. These above observed values suggest that, the coatings WHBPU-IP-100% and WHBPU-DIA-50% are more stable than WHBPU-DIO-50%. This phenomenon might be due to the more polar nature of diamine chain extender, which enhances the inter chain association between the macromolecular chains due to the presence of polar sulfone groups and there by is more phase separation. But in case of diol chain extended polymer contains more urethane bonds, whereas WHBPU-IP-100% and WHBPU-DIA-50% formulations have more polar urea functionality. This urea group takes part in more intermolecular chain association as compared to urethane through hydrogen bonds and improved the thermal stability. But in the case of siloxane extended hybrids, WHBPU-AP-50% shows the higher thermal stability as compared to other chain extenders, which might be due to the formation of SisOsSi

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Scheme 4. Hydrogen Bonding Interaction Present in the WHBPU

Figure 5. XRD curves of WHBPU-IP-100%; WHBPU-DIO-50%; WHBPUDIA-50%; and WHBPU-AP-50% samples. Table 3. Thermal Property of Different WHBPU Films sample name

T1on [°C]

T2on [°C]

percentage of weight loss at 320 °C

WHBPU-IP-100% WHBPU-DIA-50% WHBPU-DIO-50% WHBPU-AP-50%

228.37 242.19 218.61 252.72

365.22 380.17 349.71 415.76

54 50 59 44

linkage in the composite and act as barrier for heat and mass transfer in the composite.49-52 The important in the thermal analysis of WHBPU-DIO-50% is observed that at 450-500 °C the polymer completely degrade. This might be due to the structural arrangement at the time of phase mixing and phase separation.

Figure 4. (a) Amide I region of FTIR spectra of different WHBPU films; (b) and (c) curve resolution of four infrared bands in the carbonyl stretching vibration region for WHBPU-DIA-50% and WHBPU-DIO-50%; (d) NsH region of FTIR spectra of different WHBPU films; and (e) and (f) FTIR peak deconvolution of NsH region for WHBPU-DIO-50% and WHBPU-DIA-50%.


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Figure 6. TG profiles of the different chain extended samples.

Figure 7. DMTA profiles of WHBPU-DIA-50%, WHBPU-DIO-50%, and WHBPU-AP-50% coatings (a) tan δ curves (b) storage modulus curves. Table 4. E′, Tg, υe, and Tanδ of WHBPU Films sample name WHBPU-DIA-50% WHBPU-DIO-50% WHBPU-AP-50% a

a

Tg1 [°C] 61.76 67.45

a

Tg2 [°C] 126.63 106.32 129.82

b

Tg1[°C] 59.61 64.87

b

Tg2 [°C] 125.83 104.19 127.08

tanδ (Tg2)

E’ (at Tg + 5 °C) [Pa]

ν (at Tg + 5 °C) [mol°cm-3]

0.812 0.768 0.898

1.05 × 108 0.78 × 108 1.18 × 108

1.04 × 10-2 0.813 × 10-2 1.16 × 10-2

a

Tg from DMTA. b From DSC.

3.6. DMTA Analysis. It is an important tool to measure the glass transition temperature (Tg), cross-link density as well as the change in loss and storage modulus (E′′ and E′) with respect to temperature. The tensile storage modulus (E′) was measured the stiffness and cross-link density of the materials. The E’ and tan δ vs temperature curves of WHBPU-urea based system with different chain extenders are shown in Figure 7. The soft and hard segment Tg′s are reported in Table 4, suggest that the soft segment Tg1 of the WHBPU-DIA-50% decreased and hard segment Tg2 is increased, when a comparison is made with WHBPU-DIO-50%. This observation might be due to the polar nature of sulfone diamine, which selectively enhances the hard segment cohesion and results in a better phase separation, where as diol chain extended film shows more phase mixing characteristics.20,21 Furthermore, the presence of siloxane groups in WHBPU-AP-50% coating increases the

Tg and stiffness of the polymer. The E’ and cross-link density values at Tg+5 °C of WHBPU-AP-50%, WHBPU-DIA-50%, and WHBPU-DIO-50% were 1.18 × 108 Pa, 1.16 × 10-2 mol/cm3; 1.05× 108 Pa, 1.04 × 10-2 mol/cm3 and 0.78 × 108 Pa, 0.813 × 10-2 mol/cm3, respectively. At Tg+5 °C not much difference of E’ is observed between WHBPUDIO-50%, WHBPU-DIA-50%, and WHBPU-AP-50% samples, but significant difference is observed in the glassy state. The increase of Tg and storage modulus are in the order: WHBPUAP-50% > WHBPU-DIA-50% > WHBPU-DIO-50%. These phenomenons might be due to the siloxane network in the hybrid coatings, which increase the restriction of molecular motion of the polymers in two reasons one is the strong hydrogen bonding interaction between polymer and silanol and second one is the formation of SisOsSi groups.53,46 The flexibility of soft segment in the DIO-50% is observed

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4. Conclusions

Figure 8. DSC curves of WHBPU-DIA-50%, WHBPU-DIO-50%, and WHBPU-AP-50% coatings. Table 5. Contact Angle of WHBPU Films sample name

contact angle after 20 days curing (degree)

contact angle after 40 days curing (degree)

WHBPU-IP-100% WHBPU-DIA-50% WHBPU-DIO-50% WHBPU-AP-50%

48 51 47 63

48 52 46 71

due to more homogeneous arrangement of the structure after phase mixing. 3.7. DSC Analysis. Glass transition temperature (Tg) measurements were made using DSC with heating rate 10 °C/min in N2 atmosphere and temperature range -50 to 200 °C. DSC curves of coatings are shown in Figure 8. DSC showed that Tg1 for WHBPU-DIA-50% is 59.61 °C which is a low value in comparison with the value of WHBPU-DIO-50% (Tg1 ) 64.87 °C). This could be due to the phase mixing which increase the value Tg1 through inter- and intramolecular interactions. The observation on the Tg2 shows that the WHBPU-DIO-50% had a Tg of 104.19 °C which is very low value in comparison with WHBPU-DIA-50%. This is probably due to lack of phase separation. The formed hybrid network on WHBPU-AP-50% has Tg2 of 127.08 °C. This increase of Tg2 might be due to the increase of the cross-link density. Both networks showed only a single Tg and thus, no phase separation. This above DSC analysis shows the same behavior like DMTA analysis. We did not observe Tg1 in case of WHBPU-AP-50% sample in the DSC analysis. In DSC analysis of all the samples show a broad endothermic peak in between 200 and 250 °C. This indicates that all the samples are semicrystalline in nature. 3.8. Contact Angle. The contact angle data of WHBPU-DIO50%, WHBPU-DIA-50%, and WHBPU-AP-50% films are reported in Table 5. The data shows that the hydrophilic behavior is improved more in the case of diol chain extender. This is due to the presence of more phase mixing behavior. But in the case of WHBPU-DIA-50% and WHBPU-AP-50% coatings, the contact angle increases as compared to WHBPUDIO-50%. The hydrophobic nature is increased in diamine and APTES chain extenders which might be due to more phase separated structure and inorganic phase. The phase mixing and phase separation of the different samples are analyzed in the FTIR section. After curing 40 days all samples show small change in contact angle but in the case of WHBPU-AP-50% shows 10 degree increase in contact angle, which may be due to formation of SisOsSi linkages after condensation of silanol groups.

A series of WHBPU dispersions were prepared by reacting 50% free NCO with diol, diamine, and APTES and followed by neutralization and regular chain extension using isophorone diamine and water under vigorous stirring. One of the chain extender, APTES is used to prepare organic-inorganic hybrid WHBPU through the sol-gel approach. The chemical interactions between polyester, polyurethane and chain extenders were confirmed by NMR and FTIR spectroscopy. The molecular arrangement structure was studied using X-ray diffraction analysis. The inorganic precursor (APTES), which helps in the formation of thermally stable SisOsSi linkages during sol-gel process, led to significant improvement in the thermal properties of the resulting hybrid. The value obtained from dynamic mechanical analysis and DSC showed the increased glass transition temperatures in the resulting hybrid systems compared with that of diol and diamine system. WHBPU dispersions developed in this study offer good balance between thermomechanical and mechanical properties. In this study we obtained more Tg, cross-link density and onset thermal degradation temperature of WHBPU dispersions compared with the other published work. The synthesis approach of our work was totally different than other waterborne polyurethane.54,55 In the study, WHBPU dispersions with no free NCO group in prepolymers would be friendly to environment. Therefore, it is believed that such dispersions would be hopeful for making novel coatings for some special purposes. Acknowledgment K.K.J. thanks the Council of Scientific and Industrial Research (CSIR, New Delhi, India) for awarding the research fellowship. Literature Cited (1) Chiang, P. C.; Whang, W. T.; Tsai, M. H.; Wu, S. C. Physical and Mechanical Properties of Polyimide/Titania Hybrid Films. Thin Solid Films 2004, 447, 359. (2) Birnie, D. P.; Bendzko, N. 1H and 13C NMR Observation of the Reaction of Acetic Acid with Titanium Isopropoxide. J. Mater. Chem. Phys. 1999, 59, 26. (3) Lippert, J. L.; Melpolder, S. M.; Kelts, L. M. Raman Spectroscopic Determination of the pH Dependence of Intermediates in Sol-Gel Silicate Formation. J. Non-Cryst. Solids. 1988, 104, 139. (4) Gonzalez-Oliver, C. J. R.; James, P. F.; Rawson, H. Silica and SilicaTitania Glasses Prepared by the Sol-Gel Process. J. Non-Cryst. Solids. 1982, 48, 129. (5) Mendez-Vivar, J.; Mendoza-Serna, R.; Bosch, P.; Lara, V. H. Influence of Isoeugenol As a. Chelating Agent on the Structure of Si-Ti Polymeric Systems Obtained from Alkoxides. J. Non-Cryst. Solids. 1999, 248, 147. (6) Karthikeyan, A.; Almeida, R. M. Crystallization of SiO2-TiO2 Glassy Films Studied by Atomic Force Microscopy. J. Non-Cryst. Solids. 2000, 274, 169. (7) Habsuda, J.; Simon, G. P.; Cheng, Y. B.; Hewitt, D. G.; Diggins, D. R.; Toh, H.; Cser, F. Sol-Gel Derived Composites from Poly(silicic acid) and 2-hydroxyethylmethacrylate: Thermal, Physical and Morphological Properties. Polymer 2002, 43, 4627. (8) Zhou, W.; Dong, J. H.; Qin, K. Y.; Wei, Y. Preparation and properties of poly (styrene-co- maleic anhydride)/silica Hybrid Materials by the in situ Sol-Gel Process. J. Polym. Sci., Part A-1: Polym. Chem. 1998, 36, 1607. (9) Lu, S.; Melo, M. M.; Zhao, J.; Pearce, E. M.; Kwei, T. K. OrganicInorganic Polymeric Hybrids Involving Novel Poly(hydroxymethylsiloxane). Macromolecules 1995, 28, 4908. (10) Iwamoto, T.; Morita, K.; Mackenzie, J. D. Liquid State 29Si NMR Study on the Sol-Gel Reaction Mechanisms of Ormosils. J. Non- Cryst. Solids. 1993, 159, 65.

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ReceiVed for reView May 22, 2009 ReVised manuscript receiVed March 18, 2010 Accepted March 30, 2010 IE900840G

Preparation and Characterization of Waterborne Hyperbranched

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