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3.5ThermodynamicsofPolymerization
3.5.1GeneralConceptofThermodynamics3.5.2EnthalpiesofPolymerization3.5.3CeilingTemperatureofPolymer-ization.3.5ThermodynamicsofPolymeri13.5ThermodynamicsofPolymerizationWhethermonomerscanpolymerize,boththermodynamicandkineticfeasibilitiesshouldbetakenintoconsideration.Fromthethermodynamicviewpointtoanalysisthetendencyofpolymerizationordepolymerization.3.5ThermodynamicsofPolymer2Whenpolymerizationisfavorablefromthethermodynamicviewpoint,thenkineticfactorsaretakenintoconsideration.Theenthalpiesofpolymerizationandtheceilingtemperaturearediscussedinthermodynamics..Whenpolymerizationisfavorab3
3.5.1GeneralConceptofThermodynamics
Freeenergycanbeusedtojudgewhetherpolymerizationisfavored.Topolymerization,monomersaretheinitialstate(m),andpolymersarethefinalstate(p).When,monomerspolymerswhen,monomerspolymersWhen,monomerspolymers.
3.5.1GeneralConceptof4Therelationshipbetweenfreeenergyandenthalpy,andentropyis.Therelationshipbetweenfree5△S----Thenegative△Sforpolymerizationarisesfromthedecreasedrandomnessforthepolymerrelativetothemonomer.The△Svaluesfallinthenarrowrangeof-105~-125J/mol·K,andpolymerizationtemperaturefromroomtemperatureto100℃,Soisabout+30~42kJ/mol。.△S----Thenegative△Sforpoly6
Enthalpyvaluesforpolymersarelow,whilethoseformonomersarehigh.Whentheabsolutevalueof△Hisgreaterthan,polymerizationcantakeplace.Thegreater
△Hvalueis,themorepossiblethepolymerizationtakeplace..Enthalpyvaluesforpolyme73.5.2
EnthalpiesofPolymerizationMeasuringmethod:directcalorimetric,heatsofcombustion,thermodynamicequilibriummeasurements.Standardheatofformationalsocanbeusedtoevaluate
.3.5.2EnthalpiesofPolymeriza8Thedifferencesofthesubstituentsonmonomerswillaffectthebondenergy,andtheenthalpiesaredifferent.Theheatofpolymerizationisthedifferencebetweenthebondenergyoftwosinglebondandthatofonedoublebond..Thedifferencesofthesubstit9EffectofStructureFactors
-H=35---163kJ/molThestericeffectofthesubstituentswilldecreasetheenthalpy.Conjugativeeffectdecreasesit,too.
Substituentswithhighelectronegativitywillincreaseit.
Theeffectsofhydrogenbondandsolvationiscomparativelysmall..EffectofStructureFactors10
Thestericeffectofthesubstituentswilldecreasetheenthalpy.
CH2=CH2CH2=C(CH3)2CH2=O
95.051.554.4kJ/mol
CH3CH3CH3CH2=CCH2=CCH=OCOOCH3C6H5
56.5350.0kJ/mol.
Thestericeffectofthes11Conjugativeeffectdecreasestheenthalpyofpolymerization
CH2=CHCH2=CHCH2=C(CH3)C6H5CH=CH2CH=CH2
69.972.874.5kJ/mol
CH2=CHCH2=CHCH3CNCOORCH2=C
72.478.735C6H5.Conjugativeeffectdecreasest12Substituentswithhighelectronegativitywillincreasetheenthalpy.
CH2=CHCH2=CHCH2=CF2CF2=CF2ClNO2
95.890.8129.2154.8kJ/mol
.Substituentswithhighelectro13Itisbecausethatsubstituentswithhighelectronegativitywillgreatlyenhancethebondenergy.Forexample,thebondenergyofC-Csinglebondinhexafluoroethaneis520kJ/mol,whichis350kJ/molhigherthanthatinethane..Itisbecausethatsubstituent14TheeffectsofhydrogenbondandsolvationCH3CH2=CHCH2=CCOOHCOOH
66.942.3kJ/molCH3CH2=CHCH2=CCONH2CONH2
60.235.1kJ/mol.Theeffectsofhydrogenbonda153.5.3
CeilingTemperatureofPolymerizationwhen,,polymerizationcantakeplace
.3.5.3CeilingTemperatureof16Withtemperaturerising,thevalueofapproachestoandreaches,atthispoint,andpolymerizationanddepolymerizationgettoabalance.Thetemperatureofthisbalanceiscalledpolymerizationceilingtemperature(Te)..Withtemperaturerising,theva17ForexampleInthepresencesodiumnaphthaleneorlithiumalkyl,α-methylstyrenecanpolymerizeinbenzenesolution.Whenthetemperatureiselevatedto+40℃andthenloweredto-70℃repeatedly,Theviscosityofthereactingsystemrisesandfallsrepeatedly,whichmeanspolymerizationanddepolymerizationproceedsinareversiblemanner.
CH3CH3nCH2=C-[-CH2-C-]n-.ForexampleInthepresence18Inmostcasespolymerizationtakeplaceatlowtemperature.Athightemperaturemoremonomersaredepolymerized.Withinawiderangeoftemperature,monomersandpolymersareinabalancestateandthereseemstobeaseriesofceilingtemperatures,soceilingtemperaturesTehasrelationtomonomerconcentration..Inmostcasespolymerizationt19PropagationanddepolymerizationarereversiblereactionsPropagationanddepolymerizationrateequationAtbalancestateDPisverygreat
.Propagationanddepolymerizati20Inthermodynamics
investigationastandardstateshouldbechosen.Forsolidandliquidthestandardstateisdefinedaspuresubstance,at1atmandwhosedegreeofactivityequals1,thermodynamicfunctionsatstandardstateismarkedwitha“0”atitstoprightcorner.Inthermodynamicsinvestigatio21Atnonstandardstate
Atbalance
BalancetemperatureTeisdefinedasthebalancetemperaturewhen[M]e=1mol/L.AtnonstandardstateAtbalanc22CeilingtemperatureTe-----BalancemonomerconcentrationThereisacorrespondingbalancemonomerconcentrationatacertainceilingtemperatureTe..Ifthebalancemonomerconcentrationisverylowthepolymerizationmaybelookonasaverythoroughprocess..CeilingtemperatureTe-----Bal23At25℃,forvinylacetate[M]e=1.4×10-11mol/L,forSt2×10-8,forMMA2.86×l0-5,forα-methylSt[M]e=2.6mol/L,At130℃,forMMA[M]e=0.5mol/L,.At25℃,forvinylacetate.24
thermodynamic
analysisandkinetics
deed
PolymerizationceilingtemperaturecanbeestimatedbythedataofandAtacertaintemperature,andarenotquitedifferent.Andonecanbeasubstituteforanothersometimes..thermodynamicanalysisandki25Whethersomemonomercanpolymerizeshouldbejudgedbyboththermodynamicandkineticanalysiskineticanalysisisnousewhendynamicanalysisresultisnopolymerizationfeasibility.Whethersomemonomercanpolym26Ifpolymerizationcantakeplacefromthethermodynamicviewpoint,appropriateinitiatorsarethensearchedtosolvetherateofpolymerizationproblem..Ifpolymerizationcantakepla27Takepropyleneforexample,theheatofpolymerizationofpropyleneis85.8kJ/mol.Thus,thepolymerizationcantakeplace,however,thepolymerizationtakesplaceonlyafterthecomplexationinitiationsystembeenfound..Takepropyleneforexample,th283.5ThermodynamicsofPolymerization
3.5.1GeneralConceptofThermodynamics3.5.2EnthalpiesofPolymerization3.5.3CeilingTemperatureofPolymer-ization.3.5ThermodynamicsofPolymeri293.5ThermodynamicsofPolymerizationWhethermonomerscanpolymerize,boththermodynamicandkineticfeasibilitiesshouldbetakenintoconsideration.Fromthethermodynamicviewpointtoanalysisthetendencyofpolymerizationordepolymerization.3.5ThermodynamicsofPolymer30Whenpolymerizationisfavorablefromthethermodynamicviewpoint,thenkineticfactorsaretakenintoconsideration.Theenthalpiesofpolymerizationandtheceilingtemperaturearediscussedinthermodynamics..Whenpolymerizationisfavorab31
3.5.1GeneralConceptofThermodynamics
Freeenergycanbeusedtojudgewhetherpolymerizationisfavored.Topolymerization,monomersaretheinitialstate(m),andpolymersarethefinalstate(p).When,monomerspolymerswhen,monomerspolymersWhen,monomerspolymers.
3.5.1GeneralConceptof32Therelationshipbetweenfreeenergyandenthalpy,andentropyis.Therelationshipbetweenfree33△S----Thenegative△Sforpolymerizationarisesfromthedecreasedrandomnessforthepolymerrelativetothemonomer.The△Svaluesfallinthenarrowrangeof-105~-125J/mol·K,andpolymerizationtemperaturefromroomtemperatureto100℃,Soisabout+30~42kJ/mol。.△S----Thenegative△Sforpoly34
Enthalpyvaluesforpolymersarelow,whilethoseformonomersarehigh.Whentheabsolutevalueof△Hisgreaterthan,polymerizationcantakeplace.Thegreater
△Hvalueis,themorepossiblethepolymerizationtakeplace..Enthalpyvaluesforpolyme353.5.2
EnthalpiesofPolymerizationMeasuringmethod:directcalorimetric,heatsofcombustion,thermodynamicequilibriummeasurements.Standardheatofformationalsocanbeusedtoevaluate
.3.5.2EnthalpiesofPolymeriza36Thedifferencesofthesubstituentsonmonomerswillaffectthebondenergy,andtheenthalpiesaredifferent.Theheatofpolymerizationisthedifferencebetweenthebondenergyoftwosinglebondandthatofonedoublebond..Thedifferencesofthesubstit37EffectofStructureFactors
-H=35---163kJ/molThestericeffectofthesubstituentswilldecreasetheenthalpy.Conjugativeeffectdecreasesit,too.
Substituentswithhighelectronegativitywillincreaseit.
Theeffectsofhydrogenbondandsolvationiscomparativelysmall..EffectofStructureFactors38
Thestericeffectofthesubstituentswilldecreasetheenthalpy.
CH2=CH2CH2=C(CH3)2CH2=O
95.051.554.4kJ/mol
CH3CH3CH3CH2=CCH2=CCH=OCOOCH3C6H5
56.5350.0kJ/mol.
Thestericeffectofthes39Conjugativeeffectdecreasestheenthalpyofpolymerization
CH2=CHCH2=CHCH2=C(CH3)C6H5CH=CH2CH=CH2
69.972.874.5kJ/mol
CH2=CHCH2=CHCH3CNCOORCH2=C
72.478.735C6H5.Conjugativeeffectdecreasest40Substituentswithhighelectronegativitywillincreasetheenthalpy.
CH2=CHCH2=CHCH2=CF2CF2=CF2ClNO2
95.890.8129.2154.8kJ/mol
.Substituentswithhighelectro41Itisbecausethatsubstituentswithhighelectronegativitywillgreatlyenhancethebondenergy.Forexample,thebondenergyofC-Csinglebondinhexafluoroethaneis520kJ/mol,whichis350kJ/molhigherthanthatinethane..Itisbecausethatsubstituent42TheeffectsofhydrogenbondandsolvationCH3CH2=CHCH2=CCOOHCOOH
66.942.3kJ/molCH3CH2=CHCH2=CCONH2CONH2
60.235.1kJ/mol.Theeffectsofhydrogenbonda433.5.3
CeilingTemperatureofPolymerizationwhen,,polymerizationcantakeplace
.3.5.3CeilingTemperatureof44Withtemperaturerising,thevalueofapproachestoandreaches,atthispoint,andpolymerizationanddepolymerizationgettoabalance.Thetemperatureofthisbalanceiscalledpolymerizationceilingtemperature(Te)..Withtemperaturerising,theva45ForexampleInthepresencesodiumnaphthaleneorlithiumalkyl,α-methylstyrenecanpolymerizeinbenzenesolution.Whenthetemperatureiselevatedto+40℃andthenloweredto-70℃repeatedly,Theviscosityofthereactingsystemrisesandfallsrepeatedly,whichmeanspolymerizationanddepolymerizationproceedsinareversiblemanner.
CH3CH3nCH2=C-[-CH2-C-]n-.ForexampleInthepresence46Inmostcasespolymerizationtakeplaceatlowtemperature.Athightemperaturemoremonomersaredepolymerized.Withinawiderangeoftemperature,monomersandpolymersareinabalancestateandthereseemstobeaseriesofceilingtemperatures,soceilingtemperaturesTehasrelationtomonomerconcentration..Inmostcasespolymerizationt47PropagationanddepolymerizationarereversiblereactionsPropagationanddepolymerizationrateequationAtbalancestateDPisverygreat
.Propagationanddepolymerizati48Inthermodynamics
investigationastandardstateshouldbechosen.Forsolidandliquidthestandardstateisdefinedaspuresubstance,at1atmandwhosedegreeofactivityequals1,thermodynamicfunctionsatstandardstateismarkedwitha“0”atitstoprightcorner.Inthermodynamicsinvestigatio49Atnonstandardstate
Atbalance
BalancetemperatureTeisdefinedasthebalancetemperaturewhen[M]e=1mol/L.
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