**6. Waterborne PUD based on polycarbonate diols (PCD)**

The polyols used in PUD synthesis are of polyether-, polyester-, polycaprolactone- and polycarbonate- origin. The use of individual types of polyol chains and their functionalities depend on the purpose of the potential use, e.g.; PUD made from polyesters can have slightly elevated strength and oil resistance compared to polyether-based PUD and have been largely used in PU paints as they exhibit outstanding resistance to light and aging. Polyether polyols are susceptible to light and oxygen when hot, however, they improve water dispersion, and impart chain flexibility (Gunduz & Kisakurek, 2004). The use of PCD in PUD, as compared to other polyols, imparts better hydrolysis resistance, improved ageing and oil resistance, excellent elastomeric properties even at low temperature, improved mechanical properties, good weathering and fungi resistance (Garcia et al., 2010). PCD used as the soft segment component in PUD synthesis are usually obtained from dimethylcarbonate or ethylene carbonate and a linear aliphatic diol (Foy et al., 2009). The properties of PUD are related to their chemical structure (Cakić et al., 2009; Athawale & Kulkarni, 2010) and are mainly determined by the interactions between the hard and soft segments, and the interactions between the ionic groups (Garcia et al., 2011). The properties of PUD are strongly influenced by composition and ionic content, an important target in an investigation of the role of the composition (Lee at al., 2004, 2006).

### **6.1. Experimental**

94 Polyurethane

PUD (synthesized from glycolized oligoester PET/PG (1:2), Fig. 4b) synthesized from depolymerised oligoesters with lower molar ratio of PET repeating unit to glycol in glycolysis reaction showed lower thermal stability in the initial stage of degradation may be due to the presence of greater amount of aromaticity in polyester backbone which makes the PU chains susceptible to scission and relieves the structure crowing (Athawale & Kulkarni, 2010). In later stage (above 300 oC), it showed enhanced thermal stability. It has also been proved that two or three peaks of first decomposition were well correlated with the higher value of polydispersity of GPC results (1.65), for oligoester polyols PET/PG (1:2) compared to the values of polydispersity (1.20), for oligoester polyols PET/PG(1:10). Curve marked as 2, in Figures 4b, 4d and 4f, which shifted third decomposition step temperature to the higher values, shows that glycolized oligoester obtained with higher molar ratio of PET/glycol of

Because of the presence of oligoester polyols wich lower molecular weight in glycolysis reaction and a diamine were used in the synthesis of PUD, two kinds of hard segments are formed, urethane and urea. It has been estabilished that the urethanes have lower thermal resistance than urea and therefore the first decomposition process at about 190 - 250 oC and the second at about 270 – 290 oC of PUD should correspond to the urethane and urea hard segments, respectively. The decomposition temperature of the soft segment is observed at 400-430 oC. The decomposition temperature for investigated samples are listed in Table 1.

decomposition

*T*1on (oC) *T*1max (oC) *T*2 (oC) *T*3 (oC)

247.0 270.7 349.7 400.3

Third decomposition

Sample First decomposition Second

PET/TEG (1:2) - 288.0 335.1 401.9 PET/PEG400 (1:2) 248.6 - 316.5 403.4 PET/PG (1:10) 251.7 288.1 327.0 411.3 PET/TEG (1:10) - 277.6 379.6 416.4 PET/PEG400 (1:10) - - 305.4 422.4

The degradation profile of PUD was dependent on mole ratios of PET to glycol in

The samples based on PET/glycol, at molar ratio of 1:10, had better thermal stability than samples based on PET/glycol, at molar ratio of 1:2. The higher values of temperature for third decomposition stage, for samples with molar ratio of 1:10, probably is due to the

1:10 have better thermal stability of obtained PUD.

PET/PG (1:2) 190.2

**Table 1.** Temperature of decomposition of PUD

increased length of glycol in glycolyzed oligoester polyol.

glycolyzed products.

Water-based PUD derived from IPDI, with different molar ratio PCD to DMPA, were prepared by the modified dispersing process. The ionic group content in PU-ionomer structure was varied by changing the amount of the internal emulsifier, DMPA (4.5, 7.5 and 10 wt% to the prepolymer weight).

Three waterborne PUD were prepared using NCO/OH = 1.5 by method in which the dispersing procedure was modified (Lee et al., 2006). In the modified procedure only the dispersing stage was varied compared to the standard procedure. The prepolymer solution was mixed with a small amount of deionized water for dispersion of polymer in water. Solvent was added for reducing the viscosity, if necessary.

Into a 250 ml glass reaction kettle, equipped with a mechanical stirrer containing a torque meter, a thermometer, a condenser for reflux and nitrogen gas inlet, was added 60 g (0.03 mol) of PCD (dried under vacuum at 120 oC); and 4, 8 or 12 g (0.03, 0.06 or 0.09 mol) of DMPA dispersed in 30 ml DMF. The reaction mixture was heated at 70 oC for 0.5 h to obtain a homogeneous mixture. This step is important for the resulting equal uniform distribution of hydrophilic monomer, DMPA, on PU backbone. After that 20, 32 or 40 g (0.09, 0.15 or 0.18 mol) of IPDI and DBTDL (0.03 wt. % of the total solid) were added to the homogenized mixture and stirred at 80 oC for 2.5 h. Dibutyl amine back titration method was used for the determination of the reaction time necessary to obtain completely NCO-terminated prepolymer. Then the mixture was cooled down to 60 oC and carboxylic groups (DMPA equiv) were neutralized with TEA dissolved in NMP (2 wt % of the total reaction mass) by stirring the reaction mixture at 60 ° C for 1h.

Subsequently, the prepolymer solution was mixed with 0.3 ml of deionised water for dispersion step-by-step. Stirring was increased during the addition of water, and the mixture was diluted with NMP. Waterborne PUD was obtained by drop-wise addition of water to the mixture in order to obtain PUD with solid content of about 30% at 30 oC for 1h. The chain extension was carried out with solution of 0.9 or 1.8 g (0.015 or 0.03 mol) of EDA in 2 ml of deionised water at 35 oC for 1h. The mixture was heated to 80 oC under vacuum in order to remove NMP and to obtain PUD with solid content of about 30%.

Thermal Analysis of Polyurethane Dispersions Based on Different Polyols 97

The decrease in DMPA content produces a decrease in the hard segment content of PU ionomers. The resistance to thermal degradation of PU ionomer increased by decreasing the

**Figure 5.** TGA curves (a) and DTA curves (b) of cured films of PUD based on PCD with 4.5% DMPA

The wide application of PUD makes necessary better understanding of the chemistry-structure relationship that improves the thermal stability as this is important prerequisite to obtain tailor-made products for high performance applications. In this work, the investigation on thermal degradation of PUD with well-defined architectures indicated that diol types and DMPA content had great influence on thermal stability. PUD with lower DMPA content has shown enhanced thermal stability. The degradation profiles of PU aqueous dispersions were influenced by the type of chain extender, length of the hard segment and type of catalysts. The TG curves showed that the length of the hard segment had a strong influence on the thermal profile of the samples as a whole. The possibility for using glycolysis products of waste PET in PUD manufacturing was confirmed. The effects of glycol type and the different mole ratios of PET to glycol on thermal properties of PUD have been described. The degradation profile of the dispersions was dependent on mole ratios of PET to glycol in glycolyzed products. The samples based on (PET/glycol molar ratio 1:10) have shown enhanced thermal properties,

which can be ascribed to increased length of glycol in glycolyzed oligoester polyol.

DMPA content due to the lower hard segment content.

(1), 7.5% DMPA (2), 10% DMPA (3).

**7. Conclusions** 

**Author details** 

Ivan S. Ristić

Suzana M. Cakić and OliveraZ. Ristić

*University of Niš, Faculty of Technology, Leskovac, Serbia* 

*University of Novi Sad, Faculty of Technology, Novi Sad, Serbia* 

The thermal stability of PU was determined by TG. The DTG thermogram of cured films of PUD based on PCD showed several degradation steps (Fig.5b). Detailed analysis of the thermogram is represented in Table 2. The decrease in the DMPA content produces a slight increase in the decomposition temperature (Fig.5a). However, the degradation mechanism was very complex due to the different stability of the hard and soft segments.

The removal of residual water due to incomplete drying of PU was produced at around 130 oC. The DTA thermogram of the used aliphatic PCD shows the main degradation at 350 oC and other less important at 265 oC (Garcia, 2010, 2011). Because this diol and EDA were used in the synthesis of PU, two kinds of groups in hard segments have been formed, i.e., urethane and urea ones. The decomposition temperature of PUD is mostly influenced by the chemical structure of the component having the lowest bond energy (Coutinho et al., 2003; Cakic et al.,2009). The urethane bond has lower thermal resistance than the urea bond and thus the first decomposition process at about 280 oC corresponds to the beginning of the urethane part of hard segment degradation and second at about 300 oC to the degradation of the urea part of hard segment. The degradation in PU at 264–268 oC is characteristic of the polyol. The degradation of soft segment (mainly composed of polyol) is produced at 329–338 oC. The soft and hard segments content were quantified from the weight loss at above mentioned temperatures (265 oC from PCD degradation, 280 oC and 300 oC correspond to the urethane and urea hard segment degradation, and 330 oC from degradation of soft segment).

According to Table 2, the decrease in DMPA content produced a slight increase in the decomposition temperature and a decrease in the weight loss for the decomposition of urethane and urea hard segments, which can be ascribed to a decrease in the amount of hard segment. The decomposition temperature of the soft segments is produced at 329–338 oC and the weight loss increase by decreasing DMPA content 20.9 and 23.5 to 6.2wt.% in PU ionomers.


**Table 2.** Temperature of decomposition and weight loss of PUD (obtained by TG measurements)

The decrease in DMPA content produces a decrease in the hard segment content of PU ionomers. The resistance to thermal degradation of PU ionomer increased by decreasing the DMPA content due to the lower hard segment content.

**Figure 5.** TGA curves (a) and DTA curves (b) of cured films of PUD based on PCD with 4.5% DMPA (1), 7.5% DMPA (2), 10% DMPA (3).

## **7. Conclusions**

96 Polyurethane

ionomers.

Sample PUD

Subsequently, the prepolymer solution was mixed with 0.3 ml of deionised water for dispersion step-by-step. Stirring was increased during the addition of water, and the mixture was diluted with NMP. Waterborne PUD was obtained by drop-wise addition of water to the mixture in order to obtain PUD with solid content of about 30% at 30 oC for 1h. The chain extension was carried out with solution of 0.9 or 1.8 g (0.015 or 0.03 mol) of EDA in 2 ml of deionised water at 35 oC for 1h. The mixture was heated to 80 oC under vacuum in

The thermal stability of PU was determined by TG. The DTG thermogram of cured films of PUD based on PCD showed several degradation steps (Fig.5b). Detailed analysis of the thermogram is represented in Table 2. The decrease in the DMPA content produces a slight increase in the decomposition temperature (Fig.5a). However, the degradation mechanism

The removal of residual water due to incomplete drying of PU was produced at around 130 oC. The DTA thermogram of the used aliphatic PCD shows the main degradation at 350 oC and other less important at 265 oC (Garcia, 2010, 2011). Because this diol and EDA were used in the synthesis of PU, two kinds of groups in hard segments have been formed, i.e., urethane and urea ones. The decomposition temperature of PUD is mostly influenced by the chemical structure of the component having the lowest bond energy (Coutinho et al., 2003; Cakic et al.,2009). The urethane bond has lower thermal resistance than the urea bond and thus the first decomposition process at about 280 oC corresponds to the beginning of the urethane part of hard segment degradation and second at about 300 oC to the degradation of the urea part of hard segment. The degradation in PU at 264–268 oC is characteristic of the polyol. The degradation of soft segment (mainly composed of polyol) is produced at 329–338 oC. The soft and hard segments content were quantified from the weight loss at above mentioned temperatures (265 oC from PCD degradation, 280 oC and 300 oC correspond to the urethane

order to remove NMP and to obtain PUD with solid content of about 30%.

was very complex due to the different stability of the hard and soft segments.

and urea hard segment degradation, and 330 oC from degradation of soft segment).

T (oC) Weight loss

According to Table 2, the decrease in DMPA content produced a slight increase in the decomposition temperature and a decrease in the weight loss for the decomposition of urethane and urea hard segments, which can be ascribed to a decrease in the amount of hard segment. The decomposition temperature of the soft segments is produced at 329–338 oC and the weight loss increase by decreasing DMPA content 20.9 and 23.5 to 6.2wt.% in PU

(wt%) T (oC) Weight loss

4.5%DMPA 129.8 1.1 268; 329 10.1; 20.9 282; 301 23.5; 45.4 7.5%DMPA 137.3 1.0 264; 338 3.8; 23.5 290; 304 17.5; 53.7 10%DMPA 128.8 0.9 267; 331 10.5; 6.2 280; 301 22.9; 59.3

**Table 2.** Temperature of decomposition and weight loss of PUD (obtained by TG measurements)

Residual water Soft segment Hard segment

(wt%) T (oC) Weight

loss (wt%)

The wide application of PUD makes necessary better understanding of the chemistry-structure relationship that improves the thermal stability as this is important prerequisite to obtain tailor-made products for high performance applications. In this work, the investigation on thermal degradation of PUD with well-defined architectures indicated that diol types and DMPA content had great influence on thermal stability. PUD with lower DMPA content has shown enhanced thermal stability. The degradation profiles of PU aqueous dispersions were influenced by the type of chain extender, length of the hard segment and type of catalysts. The TG curves showed that the length of the hard segment had a strong influence on the thermal profile of the samples as a whole. The possibility for using glycolysis products of waste PET in PUD manufacturing was confirmed. The effects of glycol type and the different mole ratios of PET to glycol on thermal properties of PUD have been described. The degradation profile of the dispersions was dependent on mole ratios of PET to glycol in glycolyzed products. The samples based on (PET/glycol molar ratio 1:10) have shown enhanced thermal properties, which can be ascribed to increased length of glycol in glycolyzed oligoester polyol.
