Synthesis,Characterization and Therm al Properties of a Novel Phos2 phorus2Containing Copolyesters B ased on22carboxyethyl(phenylphos2 phinic)AcidHaiming Liu,1Rui Wang,2Xi Xu,1Xiao Kai Sun,2Xiaohui Zhou2 1Depart ment of Polymer Science and Materials,State Key Laboratory of Polymer Materials Engineering,Sichuan U niversity,Chengdu610064,China;2Depart ment of Materials Science and Engineering,Beijing Instit ute of Clot hing Technology,Beijing100029,ChinaAbstract:A novel reactive p ho sp horus2containing monomer,22carboxyet hyl(p henylp hosp hinic)acid (CEPPA)and corresponding p hosp horus2containing copolyesters were synt hesized and characterized by F TIR,1H NMR spect ra.The copolyester,which contains0.6wt%p hosp horus,can reach a lim2 iting oxygen index(LO I)value of29.4%.The t hermal p roperties of p hosp horus2containing flame re2 tardant copolyesters were investigated by differential scanning calorimeter(DSC),t hermogravimetry (T G)under air and nitrogen.DSC shows t hat t he glass2t ransition temperat ures(T g),t he melting point s(T m)and t he melting crystallizatio n temperat ures(T mc)of copolyesters decrease wit h increas2 ing p ho sp horus content,Meanwhile t he cold crystallization temperat ures(T cc)increase wit h increas2 ing p ho sp horus content.T GA shows t hat t he initial deco mposition temperat ures(T id)decrease and t he maximum2rate decomposition temperat ures(T max)increase at air and nit rogen at mo sp here,while char yields increase,wit h t he increase of p hosp horus content.The residues of copolyesters after T GA testing were st udied by Fourier transform infrared spectro scop y to better understand t he mechanism of flame retardancy,which show t hat t he charred residue is mainly composed of Ar2P group containing species.K ey w ords:flame retardant;synt hesis;p ho sp horus2containing copolyesters;t hermal properties Document code:A Article ID:100124381(2008)Suppl220420207IntroductionPolyester resin materials are widely used in a wide range of applications such as flooring,surface coatings,vehicle body panels and appliance housings due to having good mechanical and optical p roperties, resistance to fatigue,resistance to creep f ract ure and wear aspect s.1-3However,t he poor flame retardancy of polyester resins limit s t heir usage in which specific fire retardant properties are required.PET resins can be imparted flame retardance eit her by adding flame retardant s or by incorporating reactive flame retard2 ant s.Incorporating a chemically reactive p hosp horus2 containing monomer into t he polymer chain is one of t he most efficient met hods of imp roving t he flame re2 tardancy of polyesters,which impart s polyesters good flame retardancy,t hermal stabilities,and sim2 ultaneously can minimize negative impact upon p hysi2 cal and mechanical p roperties of t he polymer.4-7 Recently,t he researches mainly focus on t he re2 active p hosp horus2containing flame retardant.The mo st important met hod of synt hesis of flame retard2 ant polyesters is t he esterification of diols wit h p hos2 p horus2containing diacid such as22carboxyl et hyl (p henyl)p ho sp hinic acid(CEPPA).324,8211CEPPA containing carboxylic and p hosp hinic acid f unctional2 ities is a biof unctional copolymerizable p ho sp horus mo nomer disclosed by U.S.patent12,13,and can be copolymerized wit h et hylene glycol(EG)and terep h2 t halate(TPA)to form flame retardant poly(et hlene terep ht halate)and renders t he resulting copolyesters and fibers good fire resistance p roperties and t hermal stabilities.024 材料工程/2009年增刊2(SAMPE China2009) In t his work,we have synt hesised a p hosp horus2 containing flame retardant,namely22Carbo xyl et hyl (p henyl)p ho sp hinic acid(CEPPA),which after2 wards was int roduced into esterificatio n and polycon2 densatio n system to obtain polyesters wit h enhanced content of p ho sp horus and of aryl group s in t he st ruct ure.The incorporation of a bulky pendant group containing p ho sp horus into t he polyesters is expected to introduce new interesting properties such as high LOI value,enhanced t hermal stability,flame resistance and flexibility.The performances of t he corresponding copolyesters,such as t hermal p roper2 ties and flame retardancy,were st udied by t he con2 ventional met hods:DSC,T GA and LO I,respective2 ly.1 ExperimentalMaterialsDichlorop henyl p hosp hine(DCPP)and acrylic acids were p urchased f ro m Sinop harm Chemical Rea2 gent Beijing Co.,Lt d.(Beijing,China)wit h a p uri2 ty of97%and used wit hout f urt her p urification.Te2 rep ht halic acid(TPA),et hylene glycol(EG),and Sb2O3were supplied by Sinopec Tianjin Pet rochemi2 cal Co.,Lt d.(Tianjin,China).All ot her materials were commercially available.Synthesis of22carboxyethyl(phenylphosphinic)acid (CEPPA)22carboxyet hyl(p henylp ho sp hinic)acid(CEP2 PA)was synt hesized according to t he reported litera2 t ures.12,13Dichlorop henylp hosp hine,200.0g(1.12mol) was placed in a reactor under a nit rogen p urge, stirred and warmed to70℃.At temperat ure,drop2 wise addition of acrylic acid92.6g(1.29mol),was started and t he temperat ure was maintained at802 85℃.When t he addition was complete,t he mixt ure was maintained briefly at80285℃.and t hen heated f urt her to1252130℃.The mixt ure was maintained at 1252130°C for one hour and t hen cooled to ambient temperat ure.The desired22carbo xyet hyl(p henyl) p hosp hinic acid can be obtained after hydrolysis of t he above mixt ure which are composed of t he cyclic anhydride of CEPPA acid and t he mixed anhydride of acrylic acid wit h32chlorocarboxyet hyl(p henylp hos2 p hinic)acid.The synt hetic route is shown in Figure1.Fig11 The synt hetic route of CEPPASynthesis of phosphorus2containing copolyesters TPA,EG,CEPPA,and Sb2O3were int roduced in a15002ml four2necked round2bottomed flask e2 quipped wit h a t hermometer and a mechanical stirrer. The mixt ure was heated in nitrogen at mosp here to 235℃under a p ressure of0.3M Pa until t he conver2 sion of t his esterification is at96%.Then t he esteri2 fication product s were t ransferred to a1.0L reactor equipped wit h a nit rogen inlet,a condenser,and a mechanical stirrer.The reactor was fitted to a vacu2 um system and evacuated to remove all oxygen.The reactor was t hen heated to2802285℃under a p res2 sure of less t han50Pa and maintained for223h to give t he p ho sp horus2containing copolyesters.Finally t he heat and vacuum were removed and t he resulting polymer melt s were ext ruded at t he N2pressure and cooled wit h water.Thus copolyesters containing dif2 ferent amount of CEPPA were synt hesized.CharacterizationThe st ruct ure of CEPPA was determined by F T2 IR,1H NMR spect ra,which were performed on a Nicolet F TIR670inf rared spect rop hotometer(Nico2 let,U SA)and a Bruker500(5002M Hz)NMR spec2 t rometer(Fallanden,Switzerland)wit h DMSO2d as a solvent,respectively.The struct ure of p ho sp horus2 containing copolyesters was recorded by using a Nicolet F TIR670inf rared spectrop hotometer.The t hermal behavior of t he copolyesters sam2 ples was recorded using a DSC6200(Seiko Instru2 ment s Inc.,J apan).Indium was used as a standard for temperat ure calibration and t he analysis was made under a co nstant st ream of nit rogen(50ml/min). The weight s of DSC specimens are about5mg.They were heated to300℃,kept at t his temperat ure for10 min to eliminate any previous t hermal history,and124 Synthesis,Characterization and Thermal Properties of a Novel Phosphorus2containing Copolyesters Based on…t hen immediately cooled to room temperat ure.After t he t hermal t reat ment ,t hey were heated at 20℃/min to obtain t he melting endot herm and t he crystal 2lization exot herm f rom 25℃to 300℃and t hen were cooled at -20℃/min f rom 300℃to 50℃to obtain t he cooling crystallization exot herm.The t hermogravimet ric analysis (T GA )was per 2formed wit h a WC T 22D Thermal Analyzer (Beijing ,China )at a heating rate of 20°C /min under air at 2mo sp here and a nit rogen at a flow rate of 50ml/min ,and t he temperat ure ranged f rom room temperat ure to 800℃.Continuous records of sample temperat ure ,sample weight ,and it s first derivative were taken.The limiting oxygen index (LOI )values were measured on a J F 23oxygen index meter (Jiangning ,China )according to ASTM D2863,wit h sheet di 2mensions of 100mm ×6.5mm ×3mm.To investigate t he mechanism of flame retardan 2cy ,t he st ruct ure of chars of t he p hosp horus 2co ntai 2ning copolyesters after T GA test at air at mosp here was recorded by using a Nicolet F TIR 670infrared spect rop hotometer.2 R esults and discussionSynthesis and characterization of CEPPACEPPA was synt hesized t hrough t he reaction of DCPP and acrylic acid ,and sequent hydrolysis ac 2cording to Figure 1.The st ruct ure of CEPPA was determined by F TIR ,1H NMR spect ra.Figure 2shows t he F TIR spect rum of CEPPA.The st rong band in t he 330022500cm -1range is as 2signed to p ho sp horus acid and carboxylic acids O —H st retching ,which indicates t he formation of P —O H and C —O H.The stretching band observed near1731.13cm -1is att ributed to t he carboxylic acid C =O stretching.In addition ,t he peaks at 1225.90,1419.59and 943cm -1are assigned to carboxylic acid characteristic C —O st retching and in 2plane and out 2of 2plane O —H bending bands ,respectively.Simultaneously ,t he peak observed at about 2907.52cm -1belongs to t he absorption of —CH 2.The peaks at 1143.6and 1122.36cm -1are att ributed to P =O absorption.The peaks at 1050and 968cm -1can be assigned to p ho sp horus acid in 2plane and out 2of 2plane P —O H st retching.14However ,no charac 2teristic absorption peak for P —Cl is observed at a 2round 3002600cm -1,which demonst rates t hat ,t he reactio n of CEPPA proceeded completely.Figure 3shows t he 1H NMR spect rum of CEP 2PA.The peak at about 11.56pp m should be assignedto t he active 2O H (e )of CEPPA (carboxylic acids ).And t he multiplet between 7.48and 7.73pp m corre 2sponds to t he p henyl ring p rotons (a ).The peak at about 2.49pp m is assigned to t he solvent DMSO 2d6(f ).The multiplet between 2.26and 2.30,between 1.96and 2.02pp m can be assigned to t he C H 2p ro 2tons (c ,d )respectively.3,4Above characterizations confirm t hat t he target p roduct CEPPA was synt hesized successfully.Synthesis and characterization of phosphorus 2contai 2ning copolyestersFigure 4shows t he F TIR spect rum of t he p hos 2p horus 2containing copolyester.The absorption of —CH 2is observed at about 2977160cm -1.Thepeaksat1716136and1249.22cm -1are assigned to C =O and C —O ab 2sorption ,respectively.The peaks at 116148and1100.49cm -1are att ributed to t he vibration f rom P224 材料工程/2009年增刊2(SAMPE China 2009) =O gro up and t he peak at 1020.52cm -1can be as 2signed to P —O —C absorption.Meanwhile ,t he st rong band in t he 330022500cm -1range assigned to p hosp horus acid and carbox 2ylic acids O —H st retching disappears.In addition ,t he absorption of p ho sp horus acid in 2plane and out 2of 2plane P —O H st retching observed at 1050and 968cm 21,respectively disappears ,which indicates t he re 2action of CEPPA and EG ,t he formation of p ho s 2p horus acid ester and Carboxylic acidester.Figure 4 F TIR spectrum of PET 2co 2CEPPATable 1 Phosphorus Content ,Phosphorus Comonomer Molar Fraction ,and Thermal Propertiesof Various Phosphorus 2Containing PolyestersSample code P /wt %CEPPA/mol %T g /℃T cc /℃T m /℃T mc /℃PET00079.07134.33255.24200.49PET030.311.1877.75135.77249.72184.36PET060.622.3775.84151.93245.00181.18PET090.923.1875.18160.80241.65169.78PET12 1.226.7772.20163.17236.94160.38PET15 1.529.5171.51164.38230.12152.95PET181.831.6870.68165.85228.43149.90Differential scanning calorimetry (DSC)analysisDifferential Scanning Calorimet ry (DSC )is use 2f ul in t he determination of relationship s between p roperties and molecular st ruct ures.Samples were heated f rom 25to 300℃in nit rogen at mosp here at a flow rate of 50ml/min and a heating rate of 20℃/min ,and t hen were cooled f rom 300to 25℃at a flow rate of 50ml/min and a heating rate of 220℃/min.As shown in Figure 5,6and Table I ,t he glass 2t ran 2sition temperat ures (T g )and t he melting point s (T m )of copolyesters decrease wit h increasing p ho sp horus content.This is because incorporation of CEPPA dis 2rupt s t he original struct ure and makes t he resulting copolymer chain more flexible.Meanwhile t he cold crystallization temperat ures (T cc )increase and t he melting crystallization temperat ures (T mc )decrease wit h increasing p hosp horus content ,respectively ,in 2dicating difficulty in crystallization wit h increased CEPPA concent ration.3,16In addition ,t he addition of CEPPA in PET greatly affect s t he crystallization and st ruct ure.Fig 2ure 5,6shows t hat t he T m and T mc of t he copolyes 2ters decrease wit h t he increasing content of CEPPA.And t he T cc value increases wit h t he increasing con 2324 Synthesis ,Characterization and Thermal Properties of a Novel Phosphorus 2containing Copolyesters Based on …tent of CEPPA.While t he content of p hosp horus va 2ries f rom 0wt %to 1.8wt %,t he T mc and T m value of copolyesters varies from 200.49℃to 149.90℃and f rom 255.24℃to 228.43℃,respectively.And t hecontent of p ho sp horus varies from 0wt %to 1.8wt %,t he T cc value of copolyesters varied from 134.33℃to 165.85℃.Table 2 Decomposition Temperature ,Residual Char ,and LOI Values of Phosphorus 2Containing CopolyestersSample code Air at mosphereT id /℃T max /℃Char yield at 700℃/wt %N 2at mosphereT id /℃T max /℃Char yield at 700℃/wt %LOI PET0418.2445.38/575.21 1.37415.79453.279.2023.3PET03412.2448.80/570.39 1.40415.55454.0411.426.9PET06411.8449.11/575.52 1.44414.72454.2014.729.4PET09411.8450.97/576.30 1.90414.50455.2915.130.4PET12410.4451.13/581.43 2.10414.07459.5315.531.5PET15409.3451.60/583.76 2.82413.86461.2316.733.7PET18402.3453.15/574.603.41412.16461.3917.735.9Therm al decomposition behaviors of phosphorus 2con 2taining copolyestersThe effect of CEPPA on t he t hermal stability of t he copolyesters was st udied by means of t hermo 2gravimet ric experiment s carried out at a heating rate of 20℃/min under air and nit rogen at mosp here.Figure 7,8show t he mass lo ss and mass lo ss rate curves obtained from T GA experiment s in air and nit rogen ,Table II gives t he initial decompo sitiontemperat ures (T id ),t he maximum decompo sition rate temperat ures (T max )and t he residues of samples at 700℃.As can be seen in Figure 7,8and table II ,t he p ure PET and t heir copolyesters have similar t hermal stabilities.And t he initial decompo sition temperat ures (T id )of t he copolyesters decrease wit h increasing p ho sp horus content under nit rogen and air at mo sp heres ,which is att ributed to t he poorer stabil 2ity of O =P —O t han —C —C —bond.17,18424 材料工程/2009年增刊2(SAMPE China 2009) Furt hermore,Figure7shows two stage decom2 position patterns.The first is similar to t heir t hermal degradatio n in nit rogen(Figure8),located f rom a2 bout3002520℃.The second is not found in t heir degradatio n in nit rogen at mo sp here,which is owing to a f urt her oxidative degradation of carbonaceous residue located from5202650℃.The maximum2rate degradation temperat ures of t he first stage increase wit h increasing p hosp horus content under nit rogen and air at mo sp heres.Howev2 er,t he maximum2rate degradation temperat ures of second stage under air at mosp here slightly changes wit h increasing p ho sp horus content.This behaviour may be att ributed to p ho sp horus2containing group s t hat decompo se at earlier stages and forms a p ho s2 p horous2rich char layer.The t hick layer prevent s f urt her decompo sition of t he copolyesters by raising t he maximum2rate degradation temperat ure of second stage and leads to a high char yield.On t he ot her hand,t he char yield of copolyesters increase wit h increasing p hosp horus content under ni2 t rogen and air at mosp here.Simultaneously,t he a2 mount of char formed f ro m t he samples depends on t he amount of CEPPA,and correlates well wit h t he LOI values of t he copolyesters.This is because p ho s2 p horus2containing copolyesters are easy to form p ho s2 p horic acid or anhydrides which can cause acid2catal2 ysed char accumulation and tend to inhibit complete oxidation of t he carbon to carbon dioxide,and conse2 quently contributed to increase t he amount of char and t he LO I values of copolyesters.Thus,t he char formation can cause increase in t he amount of residue and a retardation of t he release of volatile f uel,lower t he t hermal co nductivity of t he burning materials, and consequently,reduce t he mass loss of t he poly2 mers.19-21Limited oxygen index(LOI)testTo investigate flame retardancy of p hosp horus2 containing copolyesters,t he limited oxygen index (LO I)values of t he copolyesters wit h different CEP2 PA content s,and t he compositions of p hosp horus2 containing copolyesters and correspo nding LO I values are listed in Table II.The LOI values of copolyesters increase wit h t he increasing content of CEPPA. While t he content of p hosp horus reaches1.8wt%,t he LO I value of copolyester is reached35.8demon2 st rating t hat CEPPA has good flame retardant effect on t he copolyesters.The structure of the residues of copolyesters after TG AtestFigure9 F TIR spectra of residues of PET18after T GAtest at different temperat ures at air at mosphereTo f urt her understand t he oxidative t hermal de2 compo sition of p hosp horus2containing copolyesters, Changes in t he F TIR spectra wit h temperat ure for t he copolyester(PET18)at air at mosp here are inves2 tigated.Figure9displays t he F TIR spectra of resi2 dues after T GA test f rom room temperat ure to 525℃.As shown in F TIR spect ra,at450℃,t he ab2 sorption bands between2500and3700cm-1assigned to O—H group become broadened.The intensities of absorption bands at170021720cm-1and124021250 cm-1which are att ributed to C=O and C—O st retc2 hing,respectively decrease f rom room temperat ure to 450℃.At450℃,The peak at1122.39cm-1(P=O absorption)disappears and t he intensity of t he peak at1099.24cm-1(P=O absorption)decreases,indi2 cating t he gradual degradation of t he group s in t he rage f rom room temperat ure to450℃.22,23Simultaneously,at400℃,new peak assigned to C=C st retch of benzene ring and Ar2P st retch was observed at1600-1550cm-1and about1415cm-1, respectively indicating t he existence of species contai2 ning Ar2P group.The copolyester after t hermal deg2 radation at575℃at air at mosp here shows a typical spect rum of highly carbonized materials.As shown in Figures8,at temperat ure up to575℃,changes in t he peak absorption became evident.The vibration band of C—H group appearing at2980-2960cm-1524 Synthesis,Characterization and Thermal Properties of a Novel Phosphorus2containing Copolyesters Based on…disappear and t he absorption bands between2500and 3700cm-1assigned to O—H group become more broadened.24At525℃,The peaks at1700-1720cm-1and 124021250cm-1att ributed to C=O and C-O st retc2 hing,respectively and t he peaks at1122.39and 1099.24cm-1assigned to P=O absorption respec2 tively,decrease nearly entirely.The intensity of t he broadened peaks at160021610cm-1and1415cm-1 greatly increase,which show t he residue is mainly composed of Ar2P group and p hosp hate.A similar suggestion was reported by Wei Liu.253 ConclusionsCEPPA can be copolymerized wit h TPA and EG in t he conventio nal melt polymerizatio n p rocess used for PET.The copoyester,which contains0.6% p hosp horus,can reach a limiting oxygen index(LO I) value of29.4%.Incorporation of CEPPA into PET increases t he cold crystallization temperat ure and re2 duces t he glass2transition temperat ures,t he melting point s,t he heating crystallization temperat ures of t he resulting copolymers.Meanwhile,t he t hermal stabilities of p hosp2containing copolyesters de2 crease,while char yields increase wit h increasing p hosp horus content.F TIR spectra of residues of t he copolyester show t hat t he charred residue is mainly composed of Ar2P group containing species.References[1] Tachita Vlad2Bubulac;Corneliu Hamciuc;Oana Petreus.HighPerform.Polym.2006,18,255.[2] P. 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