This article was downloaded by: [Memorial University of Newfoundland] On: 04 August 2014, At: 09:48 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Polymer Analysis and Characterization Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gpac20 Synthesis and Characterization of Structurally Modified Polyurethanes Based on Castor Oil and Phosphorus- Containing Polyol for Flame-Retardant Coatings R. H. Patel a , M. D. Shah a & H. B. Patel a a Department of Materials Science , Sardar Patel University , Vallabh Vidyanagar, Gujarat, India Published online: 19 Feb 2011. To cite this article: R. H. Patel , M. D. Shah & H. B. Patel (2011) Synthesis and Characterization of Structurally Modified Polyurethanes Based on Castor Oil and Phosphorus-Containing Polyol for Flame- Retardant Coatings, International Journal of Polymer Analysis and Characterization, 16:2, 107-117, DOI: 10.1080/1023666X.2011.541108 To link to this article: http://dx.doi.org/10.1080/1023666X.2011.541108 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. 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Terms & http://www.tandfonline.com/loi/gpac20 http://www.tandfonline.com/action/showCitFormats?doi=10.1080/1023666X.2011.541108 http://dx.doi.org/10.1080/1023666X.2011.541108 Conditions of access and use can be found at http://www.tandfonline.com/page/terms- and-conditions D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 http://www.tandfonline.com/page/terms-and-conditions http://www.tandfonline.com/page/terms-and-conditions SYNTHESIS AND CHARACTERIZATION OF STRUCTURALLY MODIFIED POLYURETHANES BASED ON CASTOR OIL AND PHOSPHORUS-CONTAINING POLYOL FOR FLAME-RETARDANT COATINGS R. H. Patel, M. D. Shah, and H. B. Patel Department of Materials Science, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India Structural modification of castor oil has been done with tris (m-hydroxy phenyl) phosphate (THPP) using the ester exchange process. The resultant compound was a phosphorus- based polyol that was reacted with different diisocyanates like TDI, IPDI, HMDI, and MDI to form a series of flame-retardant polyurethanes. These polyurethanes have been characterized by various chemical and instrumental analysis techniques. Thermal and flame-retardant properties of these polyurethanes were determined in film form. Coating formulations were prepared and applied on mild steel panels. Various mechanical proper- ties, hardness, and chemical resistance properties were determined. These data were com- pared with the coatings prepared by mechanical blends of polyurethanes based on THPP and castor oil. The overall properties of polyurethanes obtained using ester-exchanged product are better than those of the blends. Keywords: Cast films; Coatings; Ester exchange reaction; Flame-retardant; Polyurethane; Properties INTRODUCTION Urethane polymers of castor oil are used in many commercial applications like coatings, foams, adhesives, cast elastomers, sealants, and encapsulants.[1,2] But their use is restricted to non-burning applications. To make these polyurethanes flame retardant, phosphorus or halogen groups are introduced in the polymer either extrin- sically or intrinsically.[3–5] As extrinsic-type flame retardants are not suitable for many applications, in the present work, attempts were made to prepare intrinsic-type flame-retardant polyurethanes by the use of phosphorus moiety. Two methods were followed. In the first method, a phosphorus-based polyol (EERP) was synthesized by reacting castor oil and tris (m-hydroxy phenyl) phosphate (THPP) using the ester exchange process. This polyol was then allowed to react with various diisocyanates Submitted 20 October 2010; accepted 14 November 2010. The financial assistance from University Grants Commission (UGC), New Delhi, India is gratefully acknowledged. Appreciation is expressed to Sophisticated Instrumentation Center for Applied Research and Testing (SICART), Charutar Vidya Mandal, and Vallabh Vidyanagar for the analysis of the samples. Correspondence: R. H. Patel, Department of Materials Science, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India. E-mail:
[email protected] International Journal of Polymer Anal. Charact., 16: 107–117, 2011 Copyright # Taylor & Francis Group, LLC ISSN: 1023-666X print=1563-5341 online DOI: 10.1080/1023666X.2011.541108 107 D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 to form a series of structurally modified castor oil–based polyurethanes (EERPPUs). In second method, by the mixing of castor oil–based polyurethane (COPU) and THPP-based polyurethanes (THPPPUs) in different proportions, mechanical blends were prepared. The monomer and the polyurethanes were characterized using vari- ous chemical and instrumental analysis techniques. Thermal and flame-retardant properties of the cast films of the neat polymer and their blends were determined. Various coating formulations were prepared from the polyurethanes based on ester-exchanged polyol and the mechanical blends of COPU and THPPPUs and applied on mild steel panels. Mechanical, physical, and chemical resistance proper- ties of these panels were determined. EXPERIMENTAL SECTION Materials The reagents resorcinol (RC), phosphorus oxychloride (POCl3), toluene diiso- cyanate (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HMDI), and methylene diphenyl diisocyanate (MDI) were obtained from Aldrich and were used without further purification. Castor oil (CO) was obtained from the local market having the hydroxyl value of 153. Solvents methyl ethyl ketone (MEK), xylene (XL), and methanol (MeOH) were used after distillation. Synthesis of Polyol The polyol (EERP) was synthesized by ester exchange reaction[6,7] of castor oil with tris-(m-hydroxy phenyl) phosphate (THPP).[8] In this process, castor oil and THPP were mixed in equimolar proportion in a reaction flask equipped with a ther- mometer, reflux condenser, and overhead stirrer. The mixture was refluxed for 4 h at 140�–150�C followed by heating for 6 h at 170�–180�C to get the crude product, which was vacuum distilled to obtain pure polyol. This polyol contains the moiety of ricinoleic acid, which can be incorporated into a polyurethane chain by reacting with various diisocyanates. Synthesis of Polyurethanes Polyurethanes were synthesized by reacting the novel polyol (EERP) with vari- ous diisocyanates such as TDI, IPDI, HMDI, and MDI. To synthesize the poly- urethane (EERPPU-1), EERP and solvent MEK were charged in a three-necked flask equipped with a dropping funnel, reflux condenser, and mechanical stirrer. TDI was added in a dropwise manner over a period of 1.5 h with constant stirring at 60�C. Heating was continued for a further 2 h to complete the reaction. In this reaction, the ratio of EERP and TDI was used as an equivalent ratio of 1:2 to get an isocyanate (NCO)-terminated polyurethane. After vacuum distillation, pure product was obtained that has ricinoleic moiety in the structure. Other polyurethanes EERPPU-2, EERPPU-3, and EERPPU-4 were also synthesized by reacting the EERP with the diisocyanates such as isophorone 108 R. H. PATEL ET AL. D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 diisocyanate, hexamethylene diisocyanate, and methylene diphenyl diisocyanate respectively (Figure 1) according to the reaction conditions given in Table I. In an another investigation, different polyurethanes were prepared by reacting castor oil with TDI (COPU) (Figure 2)[8] and THPP with diisocyanates such as TDI, Figure 1. Reaction scheme used for the synthesis of polyurethanes (EERPPUs). Table I. Reaction conditions and physical properties of polyurethanes prepared by ester-exchanged product System Reaction conditions Intrinsic viscosity g dL=gm Number average molecular weight Mn Weight average molecular weight Mw Elemental analysis % Temp. �C Time h C H N EERPPU-1 60 3.5 0.92 4571 7907 68.11 (68.32) 7.34 (7.59) 4.39 (4.83) EERPPU-2 60 4.0 0.86 4873 9016 69.33 (68.94) 8.61 (8.78) 4.17 (4.47) EERPPU-3 60 4.5 0.81 3812 7612 65.09 (65.73) 8.22 (8.76) 4.89 (5.11) EERPPU-4 60 3.5 0.95 4953 9330 70.17 (70.51) 7.05 (7.31) 4.12 (4.45) Calculated values are listed in parentheses. POLYURETHANES FOR FLAME-RETARDANT COATINGS 109 D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 IPDI, HMDI, and MDI (THPPPU-1 to THPPPU-4) (Figure 2).[8] These COPU and THPPPUs were mixed in different proportions (see Table III) using a mechan- ical blending process. The resultant polyblends also contain ricinoleic moiety. Figure 2. Reaction scheme used for the synthesis of (A) COPU and (B) THPPPUs.[10] 110 R. H. PATEL ET AL. D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 Characterization The number of hydroxyl groups of THPP and EERP was determined by hydroxyl group estimation.[9] THPP contains 2.9 hydroxyl groups and EERP con- tains 2.6 hydroxyl groups per mole of sample. The percentage of free NCO groups[9] in polyurethanes are in the range of 1.8% to 2.4%. Purity of the monomers and poly- mers was confirmed by thin layer chromatography (TLC). Reaction conditions and percentage yield of the polyurethanes are given in Table I. Intrinsic viscosity of the polyurethanes was measured using an Ubbelohde suspended level viscometer in xylene; the values are between 0.81 and 0.95 dL=gm. Elemental analysis of the polyurethanes was carried out in a PerkinElmer model 2400 series II elemental ana- lyzer. Molecular weight of the polyurethanes was determined by the gel permeation chromatographic (GPC) technique using a PerkinElmer Series 200 GPC system. A PerkinElmer Spectrum GX FT-IR spectrophotometer was used to record the infra- red spectra of the EERP and polyurethanes. Characterization of the mechanical blends have been reported elsewhere in the literature.[8,10] Preparation of the Films Thermal and flame-retardant properties of the polyurethanes in the form of film (Table II) were determined. For this purpose, the films were cast using the following method. Table II. Thermal and flame-retardant properties of polyurethane films % Weight loss from TGA in air (�C) System 10% 30% 70% IPDT �C Activation energy Ea k.J mole�1 Char yield at 500�C % LOI % UL 94 EERPPU-1 225 270 325 355 55.08 10.09 29 V0 EERPPU-2 265 310 370 372 61.19 8.56 27 V1 EERPPU-3 225 275 355 359 54.29 8.03 26 V1 EERPPU-4 270 320 390 379 62.36 11.41 30 V0 Table III. Flame-retardant properties of mechanical blends based on COPU and THPPPUs System Proportion LOI % UL 94 COPU:THPPPU-1 50:50 36 V0 60:40 35 V0 70:30 33 V0 COPU:THPPPU-2 50:50 35 V0 60:40 33 V0 70:30 31 V0 COPU:THPPPU-3 50:50 30 V0 60:40 29 V0 70:30 28 V0 COPU:THPPPU-4 50:50 37 V0 60:40 35 V0 70:30 33 V0 POLYURETHANES FOR FLAME-RETARDANT COATINGS 111 D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 A Teflon sheet of 2.5mm thickness was punched to the required size (0.2� 5� 9 cm). This sheet was placed on a triangular leveling plate and leveled by moving the rotating screw of this plate. A required amount of polyurethanes was mixed with MEK solvent and poured on the prepared site of the sheet. The assembly was kept for 4 h at room temperature for complete setting. The assembly was then kept inside a preheated oven at 50�C for 24 h for complete setting. After cooling, the films were removed from the mold and used for the measurement of the properties mentioned in the next part. Testing of the Films Thicknesses of the films were in the range of 1.91 to 2.11mm as measured with the help of micrometer screw gauge. Shore A hardness of the films was measured using a TSE hardness testing machine. These values are 80, 75, 72, and 83 respect- ively for EERPPU-1, EERPPU-2, EERPPU-3, and EERPPU-4 films. Thermal analysis was also carried out using a thermogravimetric analyzer, a PerkinElmer Pyris-1 TGA, at a heating rate of 10�C=min in air atmosphere. Flame retardancy of the films was determined by limiting oxygen index (LOI) value (ASTM D2863) and UL 94, vertical burning test method (ASTM D3801). In UL 94 test method for the sample to achieve a V-0 rating it must self-extinguish within 10 s and there should not be any sign of dripping of the burning polymer. If the sample continu- ously burns or if it drips polymer, a V-1 or V-2 rating is given. All these data are reproduced in Tables II and III. Preparation of Coatings Various coating formulations were prepared from polyurethane systems and the blends by adding methyl ethyl ketone solvent. These formulations were applied on mild steel (m.s.) test panels using a film applicator. Care was taken during coating to obtain uniform film thickness of about 100 mm. The coated materials were then kept in an open place at room temperature for a specific time period (Tables IV and V) for complete setting. Certain important physical parameters like pot life of the formulations and drying properties of the coatings such as surface drying, tack-free drying, and hard drying were determined and are given in these tables. Table IV. Coating performance of polyurethanes (EERPPUs) Drying properties System Pot life at room temperature min Surface drying min Tack-free drying min Hard drying min EERPPU-1 180 30 150 250 EERPPU-2 210 35 180 270 EERPPU-3 210 40 180 270 EERPPU-4 180 30 120 230 112 R. H. PATEL ET AL. D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 Characterization of Coatings Once the coating panels were prepared, the next step was the determination of properties. Various properties like hardness, impact resistance, flexibility, and adhesion were determined by standard methods. The chemical resistance properties of the coatings were determined by the immersion test method where the test panels were immersed in different solutions of chemical reagents such as 10% sodium chlor- ide, 10% hydrochloric acid, and 10% sodium hydroxide. The uncoated part of the test panels was sealed with paraffin wax. The panels were then dipped in these solu- tions in a closed glass chamber for seven days. Visual observations of these panels were done in terms of change in color, softening and blistering of films, and partial and complete removal of the films from the test panels. RESULTS AND DISCUSSION Microanalysis data for carbon, hydrogen, and nitrogen were in general agree- ment with the calculated values given in Table I. The structure of the polyurethanes can be confirmed from GPC data. Number-average molecular weight and weight-average molecular weight are given in Table I. The IR spectrum of EERP shows a broad absorption band at 3417 cm�1 due to OH stretching frequency. The strong band at 1739 cm�1 clearly indicates the C¼O stretching frequency of the ester group in polyol. The bands at 1058 cm�1 and 1172 cm�1 are due to, respectively, P-O-C and P¼O stretching frequency. The bands at 1619 cm�1 and 1463 cm�1 are attributed to C¼C stretching frequency in the aliphatic chain and aromatic ring respectively. IR spectra of polyurethanes (EERPPU-1 to EERPPU-4) show broad bands around 3315–3388 cm�1 due to >N�H bond. The bands around 1541–1551 cm�1 and 1600–1635 cm�1 confirm the presence of –NHCOO– groups. The absorption bands around 2263–2275 cm�1 show the presence of terminal NCO groups in Table V. Coating performance of mechanical blends Drying properties System Proportion Pot life at room temperature min Surface drying min Tack-free drying min Hard drying min COPU:THPPPU-1 50:50 110 30 155 225 60:40 115 35 160 230 70:30 120 35 165 232 COPU:THPPPU-2 50:50 90 25 130 240 60:40 95 30 135 245 70:30 100 30 140 255 COPU:THPPPU-3 50:50 130 40 170 260 60:40 135 40 175 263 70:30 140 45 180 270 COPU:THPPPU-4 50:50 95 25 130 235 60:40 100 30 140 238 70:30 110 30 145 240 POLYURETHANES FOR FLAME-RETARDANT COATINGS 113 D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 polyurethanes. The bands around 1028–1076 cm�1 and 1199–1249 cm�1 are due to P-O-C and P¼O stretching frequencies respectively. Thermal Analysis The thermogravimetric analysis technique was used to determine the thermal stability of cured polyurethane films. The TGA curves of polyurethanes are pre- sented in Figure 3. The percentage weight loss, i.e., 10%, 30%, and 70%, of all the polyurethanes are listed in Table II. The integral procedure decomposition tempera- ture (IPDT) values were calculated from the respective thermograms using Doyle’s method[11] and are listed in Table II. From the thermograms, it can be seen that IPDI (EERPPU-2) and MDI (EERPPU-4) based systems are more stable than TDI (EERPPU-1) and HMDI (EERPPU-3) based systems. All these phosphorus-based polyurethane degradation mechanisms follow the condensed phase retardation.[12] IPDI (EERPPU-2) and MDI (EERPPU-4) based polyurethanes start to degrade rapidly after 10% degradation. while a sharp degradation can be observed for TDI (EERPPU-1) and HMDI (EERPPU-3) based systems after 30% weight loss. In these processes, protective char layers are formed on the surface, which helps in the retar- dation of fire. For all polyurethanes, notable char values in the range of 8.03 to 11.41% were observed. Activation energy (Ea) values for all polyurethanes were determined by Broido’s method[13] and are listed in Table II. Flame-Retardant Properties of Polyurethanes and Blends The flame-retardant behavior of polyurethane films was determined by LOI and UL 94 methods. These data are listed in Tables II and III. TDI (LOI 29%) (EERPPU-1) and MDI (LOI 30%) (EERPPU-4) based polyurethanes offer higher Figure 3. TG thermograms at 10�C=min for the polyurethanes (EERPPU-1 to EERPPU-4). 114 R. H. PATEL ET AL. D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 flame retardancy than IPDI (LOI 27%) (EERPPU-2) and HMDI (LOI 26%) (EERPPU-3) based polyurethanes. The same trend was observed for the UL 94 test where TDI (EERPPU-1) and MDI (EERPPU-4) based systems show a V-0 rating and IPDI (EERPPU-2) and HMDI (EERPPU-3) based systems show a V-1 rating. These data are comparable with the char values, where TDI (EERPPU-1) and MDI (EERPPU-4) based polyurethanes have higher char values of 10.09% and 11.41% respectively than those of the IPDI (EERPPU-2) and HMDI (EERPPU-3) based polyurethanes.[3] Castor oil based polyurethane (COPU) is flammable in nature because of the absence of phosphorus moiety in the structure. To make it flame retardant, poly- urethanes based on THPP (THPPPUs) were incorporated in different proportions by a mechanical blending process. Table III shows that LOI value is increased in all systems with increase in the proportion of THPPPU. All the blends show a V-0 rating. Mechanical, Hardness, and Chemical-Resistance Properties of Polyurethanes and Blends The strength of adhesion to the coated panels and flexibility[14] of the polyur- ethanes and blends were determined respectively by crosshatch and mandrel bend test methods (ASTM D3359 and ASTM D522 standards). The results show that the test panels have 100% adhesion in all systems and the panels also pass 14-inch mandrel flexibility. Scratch hardness and pencil hardness of coated panels[15,16] were measured respectively according to ASTM D2197 and ASTM D3363 testing methods. TDI (EERPPU-1) and MDI (EERPPU-4) based polyurethane systems have higher scratch resistance than IPDI (EERPPU-2) and HMDI (EERPPU-3) based systems due to their aromatic nature. The pencil hardness of all coated materials also follows the same trend. The results of scratch hardness and pencil hardness of coated materi- als are listed in Table VI. Scratch hardness properties of the blends are in the range of 1100–1800 g, as listed in Table VII, which are much lower than those of the poly- urethanes (EERPPUs) (Table VI). Pencil hardness properties of polyurethanes are better than those of the blends. A tabular impact tester was used to determine impact resistance[15] of coated polymeric materials according to ASTM D2794. An indenter of 500 g was dropped on a coated panel from a certain height until the film cracked. Impact resistance Table VI. Mechanical and hardness properties of polyurethane coatings System Adhesion (crosshatch) Flexibility 1=400 bending mandrel Scratch hardness g Pencil hardnessa Impact resistance lb. in. EERPPU-1 Pb P 2350 3H 250 EERPPU-2 P P 2250 3H 300 EERPPU-3 P P 2100 2H 350 EERPPU-4 P P 2400 3H 200 a6H> 5H> 4H> 3H> 2H> 1H>H> 1HB> 2HB> 3HB> 4HB> 5HB> 6HB. bP¼ passes the 1=400 mandrel and crosshatch adhesion test. POLYURETHANES FOR FLAME-RETARDANT COATINGS 115 D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 properties of IPDI (EERPPU-2) and HMDI (EERPPU-3) based systems are higher than those of TDI (EERPPU-1) and MDI (EERPPU-4) based systems due to the presence of flexible moiety in the polyurethanes (Table VI). Impact resistance of the blends is better than that of the polyurethanes because of the presence of large flexible ricinoleic moiety of castor oil (Table VII). Visual observations of the immersion test show that polyurethane-coated test panels have better chemical resistance than the blends. All the films remain unchanged in sodium chloride solution. A slight discoloration and softening occur for the blends. Not a single film of the blends was removed from the test panels. Polyurethanes remain unaffected in all these solutions, and no blistering was observed for polyurethanes and the blends. CONCLUSIONS Ester exchange polyol-based polyurethanes (EERPPUs) have better overall properties, especially superior scratch hardness, while the mechanical blends have higher impact resistance properties. Chemical resistance properties of the polyur- ethanes and the blends are comparable. From the present study, it can be concluded that the polyurethanes (EERPPUs) can be used in flame-retardant coatings where the maximum requirement is of scratch hardness properties, and when impact resist- ance properties are preferred, blends can be used. REFERENCES 1. Chattopadhyay, D. K., and K. V. S. N. Raju. 2007. Structural engineering of poly- urethane coatings for high performance applications. Prog. Polym. Sci. 32: 352–418. 2. Park, H. S., H. J. You, H. J. Jo, I. W. Shim, H. S. Hahm, S. K. Kim, and Y. G. Kim. 2006. Preparation of modified polyesters containing triphosphorous and their applications to PU flame-retardant coatings. J. Coat. Technol. Res. 3: 53–60. Table VII. Mechanical and hardness properties of mechanical blends System Proportion Adhesion (crosshatch) Flexibility 1=400 bending mandrel Scratch hardness g Pencil hardnessa Impact resistance lb. in. COPU:THPPPU-1 50:50 Pb P 1800 1H 350 60:40 P P 1600 H 350 70:30 P P 1500 H 350 COPU:THPPPU-2 50:50 P P 1600 H 350 60:40 P P 1500 H 350 70:30 P P 1400 H 350 COPU:THPPPU-3 50:50 P P 1300 1HB 400 60:40 P P 1200 1HB 400 70:30 P P 1100 2HB 400 COPU:THPPPU-4 50:50 P P 1700 1H 350 60:40 P P 1600 H 350 70:30 P P 1500 H 350 a6H> 5H> 4H> 3H> 2H> 1H>H> 1HB> 2HB> 3HB> 4HB> 5HB> 6HB. bP¼ passes the 1=400 mandrel and crosshatch adhesion test. 116 R. H. PATEL ET AL. D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4 3. Patel, R. H., H. B. Patel, and M. D. Shah. 2009. Synthesis, characterization, and proper- ties of flame-retardant polyurethanes. Int. J. Polym. Anal. Charact. 14: 563–565. 4. Spirckel, M., N. Regnier, B. Mortaigne, B. Yousset, and C. Bunel. 2002. Thermal degra- dation and fire performance of new phosphate polyurethanes. Polym. Degradation Stab. 78: 211–218. 5. Kemmlein, S., O. Hahn, and O. Jann. 2003. 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Ch. 16, p. 611. POLYURETHANES FOR FLAME-RETARDANT COATINGS 117 D ow nl oa de d by [ M em or ia l U ni ve rs ity o f N ew fo un dl an d] a t 0 9: 48 0 4 A ug us t 2 01 4