EXPERIMENTAL AND MODELLING INVESTIGATION OF A NOVEL TETRAFUNCTIONAL INITIATOR IN FREE RADICAL POLYMERIZATION. by Matthew Justin Scorah

Transcription

1 EXPEIMENTAL AND MODELLING INVESTIGATION OF A NOVEL TETAFUNCTIONAL INITIATO IN FEE ADICAL POLYMEIZATION by Matthew Justi Scorah A thesis preseted to the Uiversity of Waterloo i fulfillmet of the thesis requiremet for the degree of Doctor of Philosophy i Chemical Egieerig Waterloo, Otario, Caada 5 Matthew Justi Scorah 5

2 I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, icludig ay required fial revisios, as accepted by my examiers. I uderstad that my thesis may be made electroically available to the public. ii

3 Abstract A experimetal ad modellig ivestigatio of a tetrafuctioal iitiator desiged for free radical polymerizatios is preseted. Multifuctioal iitiators are believed to provide two advatages over traditioal moofuctioal iitiators. With a higher umber of fuctioal sites per molecule, they are able to icrease polymer productio while simultaeously maitaiig or icreasig polymer molecular weight. Examiatio of the literature idicates the majority of academic ad idustrial published studies have ivestigated difuctioal iitiators with most focusig o styree. I this thesis, a tetrafuctioal iitiator, JWEB5, was systematically ivestigated for a variety of moomer systems i order to develop a better uderstadig of the behaviour of multifuctioal iitiators i free radical polymerizatios. A kietic study comparig the tetrafuctioal iitiator to a moofuctioal couterpart, TBEC, demostrated that the impact of a multifuctioal iitiator is depedet upo moomer type. egardless of the homo- or copolymer system examied, it was observed that the tetrafuctioal iitiator could produce higher rates of polymerizatio due to the greater umber of labile groups per iitiator molecule. However, the ifluece of the tetrafuctioal iitiator o the polymer molecular weight was dictated by the polymerizatio characteristics of the system i questio. I the case of styree, the tetrafuctioal iitiator maitaied similar molecular weights compared to the moofuctioal iitiator while for methyl methacrylate (MMA), switchig from a mooto a tetrafuctioal iitiator actually decreased the polymer molecular weight. Other moomers such as butyl acrylate ad viyl acetate ad copolymers of MMA ad styree or α-methyl styree were examied to study the effect of iitiator fuctioality i free radical polymerizatios. Subsequet to the kietic ivestigatio, polystyree ad poly(methyl methacrylate) samples produced with the tetrafuctioal iitiator were characterized i detail i order to examie the effects of iitiator fuctioality o polymer properties. Samples geerated with the moofuctioal iitiator were used for compariso purposes. Chromatographic iii

4 ad dilute solutio methods were able to detect sigificat levels of brachig i the polystyree sample produced with JWEB5, while poly(methyl methacrylate) samples showed o evidece of brachig. heological tests ivolvig a combiatio of oscillatory ad creep shear measuremets were completed i order to detect differeces betwee samples. The presece of brachig usig rheological techiques was clearly observed for both polystyree ad poly(methyl methacrylate) samples produced with the tetrafuctioal iitiator. I order to explai the experimetal results observed i the kietic ad polymer properties studies, a reactio mechaism for polymerizatios iitiated with a tetrafuctioal iitiator was proposed ad used i the developmet of a mathematical model. eactios ivolvig the fate/efficiecy of fuctioal groups are properly accouted for, while i the past this had bee igored by modellig work i the literature. Based o model predictios, di-radical cocetratios were estimated to be several orders of magitude smaller tha moo-radical cocetratios ad their cotributio i the reactio mechaism was foud to be egligible. Modellig results also demostrated that the cocetratio ad chai legth of various polymer structures (i.e., liear, star or coupled stars) deped upo moomer type ad reactio coditios. iv

5 Ackowledgmets I am idebted to my supervisor, Professor Alexader Pelidis, for his ivaluable guidace, support ad isight i both my academic work ad life i geeral. I cosider myself fortuate to have had the chace to lear from such a excellet metor. I would also like to express my gratitude to my co-supervisor, Professor amdhae Dhib, for his support ad ecouragemet durig the course of my research. May thaks are exteded to Professor Neil McMaus, for sharig his seemigly uedig wealth of laboratory ad chemistry kowledge ad Professor Costas Tzogaakis, for his helpful discussios o polymer rheology. I would like to ackowledge the assistace of ATOFINA Chemicals, specifically Dr. Jerry Wicher ad Dr. Leo Kasehage, for supplyig samples of the iitiators used i this study ad their patiece i aswerig my questios. My thaks go out to eato Cosetio, for his help ruig the experimets with butyl acrylate. My sicere gratitude goes out to those frieds I have made durig the course of my studies i Waterloo, may thaks to Bria Barclay, Jeifer Che, Luke Colema, Luigi D Agillo, Deborah Sarzotti ad William ipmeester, for makig life i graduate school much more ejoyable. I am extremely grateful for the support of my family, particularly my brother, Ed, for his geerosity, support ad friedship. I would ever have fiished grad school without his help. Lastly, I would like to thak my fiacée, Dr. Julie Smith, for her patiece, love ad friedship. I still have o clue how you maage to put up with me. v

6 TABLE OF CONTENTS Abstract... iii Ackowledgmets... v List of Figures... ix List of Tables... xv Abbreviatios... xvi Symbols... xvii CHAPTE 1 - INTODUCTION... 1 CHAPTE - BACKGOUND AND LITEATUE EVIEW Free adical Polymerizatio Multifuctioal Iitiators Brachig i Polymers Brached Polymer Properties Detectio of Log-Chai Brachig efereces CHAPTE 3 - EXPEIMENTAL METHODS Iitiator Selectio eaget Purificatio Polymer Sythesis Polymer Characterizatio Size Exclusio Chromatography H-Nuclear Magetic esoace Differetial Scaig Calorimetry (DSC) Soxhlet Extractio heological characterizatio efereces CHAPTE 4 - POLYMEIZATION OF METHYL METHACYLATE Itroductio Experimetal eagets Purificatio Polymer Sythesis Characterizatio Experimetal Desig esults ad Discussio Temperature Iitiator Cocetratio Iitiator Fuctioality Detectio of Brachig vi

7 4.4 Coclusios efereces CHAPTE 5 - COPOLYMEIZATION OF METHYL METHACYLATE/ STYENE AND METHYL METHACYLATE/α-METHYL STYENE Itroductio Experimetal eaget Purificatio Polymer Sythesis Polymer Characterizatio Experimetal Desig esults ad Discussio Styree-Methyl Methacrylate Copolymer Methyl Methacrylate ad α-methyl Styree Copolymer Coclusios efereces CHAPTE 6 - POLYMEIZATION OF BUTYL ACYLATE AND VINYL ACETATE Itroductio Experimetal eaget Purificatio Polymer Sythesis Polymer Characterizatio Experimetal Desig esults ad Discussio Butyl Acrylate Viyl Acetate Coclusios efereces CHAPTE 7 - DETECTION OF BANCHING IN POLYSTYENE AND POLY(METHYL METHACYLATE) Itroductio Experimetal Methods Materials Characterizatio esults ad Discussio SEC ThFFF DSC heology Coclusios vii

8 7.5 efereces CHAPTE 8 - MATHEMATICAL MODELLING OF TETAFUNCTIONAL INITIATOS Itroductio Model Developmet Polymerizatio Mechaism Mathematical Modellig Modellig esults Determiatio of Model Parameters Validatio of Model Validatio of Model Assumptios Case Studies Coclusios efereces... 4 CHAPTE 9 - CONTIBUTIONS TO ESEACH AND ECOMMENDATIONS APPENDIX A BENCH-MAKING OF DIFUNCTIONAL INITIATOS APPENDIX B TEMPEATUE POGAMMING WITH DIFUNCTIONAL INITIATOS APPENDIX C TETAFUNCTIONAL MODEL DEVELOPMENT... 7 viii

9 LIST OF FIGUES Figure.1. Various polymer molecular architectures: (a) star; (b) comb; (c) H- shaped; (d) pom-pom; (e) dedrimer; (f) radomly brached (cotais triad tetrafuctioal brach poits with braches o braches)...1 Figure.. Theoretical ad experimetal g values as a fuctio of star fuctioality. Data poits are take from Table Figure.3. adius of gyratio as a fuctio of molecular weight for moodisperse polystyree stars. Data from ref. (63, 67). Parameters for liear polystyree from ref. (6)...17 Figure.4. Itrisic viscosity as a fuctio of weight-average molecular weight for brached polystyrees. Data take from refs. (93, 94)....1 Figure.5. Zero-shear viscosity at 169.5ºC as a fuctio of weight-average molecular weight for polystyree melts: ope ad closed circles ad squares, liear; triagles, H-polymers. Data from ref. (94) Figure C-NM spectrum of polyethylee sample measured at 1ºC usig deuterium o-dichlorobezee ad 1,,4-trichlorobezee as solvets. Take from ref. (4)...37 Figure.7. Itrisic viscosity, radius of gyratio ad cotractio factors as a fuctio of molecular weight for polystyree (SEC at 3ºC with 1. ml/mi of tetrahydrofura). ef. (57)...43 Figure.8. Zero-shear viscosity as a fuctio of the umber of braches per chai for polyethylee of a costat molecular weight, based o the model of Jaze ad Colby (61) Figure.9. Zero-shear viscosity as a fuctio of weight-average molecular weight for various polyethylee samples at 19ºC: circles, fairly arrow MWD (M w /M ~ -6) liear samples; crosses, broad to very broad MWD (M w /M ~ 6.6-3) brached samples but with arrow rheological polydispersity (E ~ ); squares, broad MWD (M w /M ~ 6.-14) brached samples with large rheological polydispersity (E ~ 6.-14). Data from ref. (175) Figure.1. Loss agle as a fuctio of frequecy at 15ºC obtaied for highdesity, metallocee catalyzed polyethylee samples of icreasig logchai brachig. Take from ref. (65)....5 Figure.11. Loss agle as a fuctio of the reduced modulus (ratio of complex modulus ad plateau modulus) for polystyree samples. Take from ref. (68)...5 Figure 3.1. Decompositio of tetrafuctioal iitiator, JWEB5...7 Figure 3.. Decompositio of moofuctioal iitiator, TBEC....7 Figure 3.3. Diagram represetig the separatio of low ad high molecular weight polymer molecules Figure 3.4. Soxhlet extractio apparatus...76 Figure 3.5. Examples of the storage modulus for three liear polymers. A is moodisperse with a low molecular weight. B is moodisperse with a high molecular weight. C is polydisperse with a high molecular weight. Take from ref. (5)...79 ix

10 Figure 3.6. Typical storage ad loss modulus curves for a moodisperse high molecular weight polymer. Take from ref. (5)...79 Figure 4.1. Moomer coversio as a fuctio of time for the polymerizatio of MMA with JWEB5 at T 1 (11 C) ad T (1 C)...86 Figure 4.. Molecular weight averages as a fuctio of coversio for the polymerizatio of MMA with JWEB5 at T 1 (11 C) ad T (1 C) Figure 4.3. Polydispersity as a fuctio of coversio for the polymerizatio of MMA with JWEB5 at T 1 (11 C) ad T (1 C)...88 Figure 4.4. Moomer coversio as a fuctio of time for the polymerizatio of MMA with JWEB5 at C 1 (1 x 1-3 M ) ad C (5 x 1-4 M)....9 Figure 4.5. Molecular weight averages as a fuctio of coversio for the polymerizatio of MMA with JWEB5 at C 1 (1 x 1-3 M ) ad C (5 x 1-4 M)...91 Figure 4.6. Polydispersity as a fuctio of coversio for the polymerizatio of MMA with JWEB5 at C 1 (1 x 1-3 M ) ad C (5 x 1-4 M) Figure 4.7. Moomer coversio as a fuctio of time for the polymerizatio of MMA: comparig Tetra to Moo at T (1ºC) ad C (5 x 1-4 M)...9 Figure 4.8. Moomer coversio as a fuctio of time for the polymerizatio of MMA at T 1 (11ºC): comparig Tetra at C (5 x 1-4 M), Moo at C (5 x 1-4 M) ad Moo at 4C ( x 1-3 M)...94 Figure 4.9. Weight-average molecular weights as a fuctio of coversio for the polymerizatio of MMA at T 1 (11ºC): comparig Tetra at C (5 x 1-4 M), Moo at C (5 x 1-4 M) ad Moo at 4C ( x 1-3 M) Figure 4.1. SEC chromatograms for polymer produced with Tetra at T 1 (11ºC) ad C (5 x 1-4 M) Figure SEC chromatograms for polymer produced with Moo at T 1 (11ºC) ad 4C ( x 1-3 M) Figure 4.1. adius of gyratio as a fuctio of molecular weight for PMMA samples from rus Tetra, T 1 (11ºC), C (5 x 1-4 M) ad Moo, T 1 (11ºC), 4C ( x 1-3 M) with similar weight-average molecular weights...11 Figure Chromatograms depictig the effect that the liear fractio i a polymer has o the detectio of brachig by SEC-MALLS...1 Figure 5.1. Moomer coversio as a fuctio of time for the bulk polymerizatio of styree at 11ºC (C =.4 M, 4C =.16 M) Figure 5.. Weight-average molecular weight as a fuctio of coversio for the bulk polymerizatio of styree at 11ºC (C =.4 M, 4C =.16 M) Figure 5.3. Polydispersity as a fuctio of coversio for the bulk polymerizatio of styree at 11ºC (C =.4 M, 4C =.16 M) Figure 5.4. SEC chromatograms for polymer samples from experimet S-TC (from SEC1) Figure 5.5. SEC chromatograms for polymer samples from experimet S-MC (from SEC1) Figure 5.6. Moomer coversio as a fuctio of time for the bulk polymerizatio of MMA at 11ºC (C =.4 M, 4C =.16 M) Figure 5.7. Weight-average molecular weight as a fuctio of coversio for the bulk polymerizatio of MMA at 11ºC (C =.4 M, 4C =.16 M) x

11 Figure 5.8. Effect of mode of termiatio o degree of polymerizatio Figure 5.9. Moomer coversio as a fuctio of time for the bulk copolymerizatio of styree ad MMA at 11ºC (C =.4 M, 4C =.16 M) Figure 5.1. Weight-average molecular weight as a fuctio of coversio for the bulk copolymerizatio of styree ad MMA at 11ºC (C =.4 M, 4C =.16 M) Figure Copolymer compositio as a fuctio of coversio for the bulk copolymerizatio of styree ad MMA at 11ºC (C =.4 M, 4C =.16 M) Figure 5.1. adius of gyratio ad correspodig brachig factor as a fuctio of molecular weight: (a) polystyree; (b) poly(methyl methacrylate); (c) styree-methyl methacrylate copolymer; (d) g values for PS, PMMA ad copolymer samples produced with the tetrafuctioal iitiator...1 Figure Itrisic viscosity ad correspodig brachig factor as a fuctio of molecular weight: (a) polystyree; (b) poly(methyl methacrylate); (c) styree-methyl methacrylate copolymer; (d) g values for PS, PMMA ad copolymer samples produced with the tetrafuctioal iitiator...15 Figure Weight-average molecular weight as a fuctio of coversio for the bulk polymerizatio of styree at 1ºC (all samples are >99% coversio) Figure SEC chromatograms for polymer samples from experimet S-TC1 (from SEC)...18 Figure Weight-average molecular weight as a fuctio of coversio for the bulk polymerizatio of MMA at 1ºC (all samples are >99% coversio)...19 Figure Moomer coversio as a fuctio of time for the bulk copolymerizatio of α-methyl styree ad MMA at 11ºC (C =.4 M, 4C =.16 M) Figure Weight-average molecular weight as a fuctio of coversio for the bulk copolymerizatio of α-methyl styree ad MMA at 11ºC (C =.4 M, 4C =.16 M) Figure Itrisic viscosity cotractio factor as a fuctio of molecular weight for polymer produced with the tetrafuctioal iitiator...13 Figure 6.1. Moomer coversio as a fuctio of time for the bulk polymerizatio of butyl acrylate at 8ºC Figure 6.. Gel fractio as a fuctio of coversio for butyl acrylate experimets with o chai trasfer aget Figure 6.3. Weight average molecular weight of soluble material extracted from poly(butyl acrylate) samples Figure 6.4. Molecular weight averages as a fuctio of coversio for the bulk polymerizatio of butyl acrylate with [CTA] =.5 wt.% Figure 6.5. Molecular weight averages as a fuctio of coversio for the bulk polymerizatio of butyl acrylate with [CTA] =.5 wt.% Figure 6.6. Polydispersity idex as a fuctio of coversio for the bulk polymerizatio of butyl acrylate at 8ºC (SEC1) Figure 6.7. Coversio as a fuctio of time for the bulk polymerizatio of viyl acetate at 1ºC xi

12 Figure 6.8. Weight average molecular weight as a fuctio of coversio for the bulk polymerizatio of viyl acetate at 1ºC. Isert: weight average molecular weight for less tha 6% coversio Figure 7.1. Plots of radius of gyratio, itrisic viscosity ad their respective brachig factors as a fuctio of molecular weight for polystyree samples (circles PS-M; triagles PS-T) Figure 7.. Plots of radius of gyratio, itrisic viscosity ad their respective brachig factors as a fuctio of molecular weight for poly(methyl methacrylate) samples (circles PMMA-M; triagles PMMA-T) Figure 7.3. Number of log-chai braches per molecule as a fuctio of molecular weight for PS-T. The subscript umber deotes the type of brachig (tri- or tetrafuctioal) while the subscript w idicates a weight average Figure 7.4. Number of log-chai braches per molecule as a fuctio of molecular weight for PS-T ad PS-M samples. The subscript umber deotes the type of brachig (tri- or tetrafuctioal) while the subscript w idicates a weight average Figure 7.5. Maxwell elemet Figure 7.6. Logarithm of horizotal shift factors as a fuctio of temperature for polystyree ad poly(methyl methacrylate) samples Figure % Joit probability cotour regios for WLF parameters estimated from polystyree data Figure % Joit probability cotour regios for WLF parameters estimated from poly(methyl methacrylate) data...17 Figure 7.9. Logarithm of horizotal shift factors as a fuctio of iverse temperature for polystyree ad poly(methyl methacrylate) samples Figure 7.1. Storage ad loss moduli master curves at ºC for polystyree samples Figure Storage ad loss moduli master curves at 5ºC for poly(methyl methacrylate) samples Figure 7.1. Shear compliace as a fuctio of time for sample PS-M at varyig shear stress ad ºC Figure Shear creep compliace versus time for polystyree samples at ºC ad poly(methyl methacrylate) samples at 5ºC Figure Complex compliace as a fuctio of frequecy for polystyree samples at ºC ad poly(methyl methacrylate) samples at 5ºC. Data poits are master curves obtaied from dyamic experimets while lies were geerated by coverted creep data Figure Storage ad loss modulus master curves geerated by combiig dyamic ad creep data for polystyree at ºC ad poly(methyl methacrylate) at 5ºC Figure Cole-Cole plot for polystyree ad poly(methyl methacrylate) samples Figure educed Va Gurp-Palme plot for polystyree ad poly(methyl methacrylate) samples xii

13 Figure elaxatio spectra for polystyree ad poly(methyl methacrylate) samples Figure Viscosity versus shear rate for polystyree ad poly(methyl methacrylate) samples. Parameters for the Cross-Carreau model are give i Table 7.4 for sample Figure 7.. educed viscosity as a fuctio of shear rate for polystyree ad poly(methyl methacrylate) samples Figure 8.1. Molecular structure of tetrafuctioal iitiator, JWEB5...3 Figure 8.. Coversio as a fuctio of time for the bulk polymerizatio of styree iitiated with TBEC at varyig cocetratios ad reactio temperatures...19 Figure 8.3. Molecular weight as a fuctio of coversio for the bulk polymerizatio of styree iitiated with TEBC at varyig cocetratios ad reactio temperatures.... Figure 8.4. Molecular weight as a fuctio of coversio for the bulk polymerizatio of styree iitiated with TEBC at varyig cocetratios ad reactio temperatures (Figure 8.3 cotiued)....1 Figure 8.5. Coversio as a fuctio of time for the bulk polymerizatio of styree iitiated with JWEB5 at varyig cocetratios ad reactio temperatures... Figure 8.6. Molecular weight as a fuctio of coversio for the bulk polymerizatio of styree iitiated with JWEB5 at varyig cocetratios ad reactio temperatures....3 Figure 8.7. Coversio as a fuctio of time for the bulk polymerizatio of MMA iitiated with TBEC at varyig cocetratios ad reactio temperatures....4 Figure 8.8. Molecular weight as a fuctio of coversio for the bulk polymerizatio of MMA iitiated with TBEC at varyig cocetratios ad 11ºC...5 Figure 8.9. Molecular weight as a fuctio of coversio for the bulk polymerizatio of MMA iitiated with TBEC at varyig cocetratios ad 1ºC...6 Figure 8.1. Coversio as a fuctio of time for the bulk polymerizatio of MMA iitiated with JWEB5 at varyig cocetratios ad reactio temperatures...7 Figure Molecular weight as a fuctio of coversio for the bulk polymerizatio of MMA iitiated with JWEB5 at varyig cocetratios ad reactio temperatures....8 Figure 8.1. Moo- ad di-radical cocetratios as a fuctio of coversio for the bulk polymerizatio of styree (11ºC, 4. mmol/l of JWEB5)....3 Figure Moo-radical cocetratios of liear, star (1 core) ad coupled star ( cores) chais as a fuctio of coversio for the bulk polymerizatio of styree (11ºC, 4. mmol/l of JWEB5)...31 Figure Cocetratio of liear, star (1 core) ad coupled ( cores) star polymer species for the bulk polymerizatio of styree (11ºC, 4. mmol/l of JWEB5)....3 xiii

14 Figure Cocetratio of polymer species with varyig umber of fuctioal groups as a fuctio of time for the bulk polymerizatio of styree (11ºC, 4. mol/l of JWEB5)...34 Figure Number- ad weight-average molecular weight for the bulk polymerizatio of styree (11ºC, 1 mmol/l of JWEB5) Figure (a) Mole fractio of various polymer species. (b) Weight-average chai legth. Idetical coditios as reported i Figure For combiatio data: solid lie liear, lie ad ope circles 1 core, lie ad grey circles cores. For disproportioatio data: dashed lie liear, lie ad diamods 1 core, liear ad grey diamods cores Figure Weight-average molecular weight as a fuctio of coversio for icreasig trasfer to moomer i the bulk polymerizatio of styree (11ºC, 1 mmol/l of JWEB5)...39 Figure Mole fractio ad chai legth of star ad coupled star polymer chais for icreasig trasfer to moomer i the bulk polymerizatio of styree (11ºC, 1 mmol/l of JWEB5). Solid lie.1 mol/(l mi), lie ad circles 1 mol/(l mi), dashed lie 1 mol/(l mi), lie ad triagles 5 mol/(l mi)...39 xiv

15 LIST OF TABLES Table.1. Theoretical equatios for mea-square radius cotractio factor (g) for several brached structures Table.. Experimetal g values for star polymers i theta ad good solvets...16 Table.3. Values of ε for polyethylee... Table 4.1. Effect of temperature o the rate of polymerizatio of MMA with JWEB Table 5.1. Styree-methyl methacrylate experimet coditios Table 5.. α-methyl styree-methyl methacrylate experimet coditios Table 5.3. Power law coefficiets for radius of gyratio-molecular weight relatioship ad Kuh-Mark-Houwik-Sakurada coefficiets...13 Table 6.1. Butyl acrylate ad viyl acetate experimet coditios Table 7.1. Molecular weight characterizatio of polystyree ad poly(methyl methacrylate) samples Table 7.. Material properties for polystyree ad poly(methyl methacrylate) samples Table 7.3. Model parameters for horizotal shift factors Table 7.4. Cross-Carreau model parameters Table 8.1. Database etries for styree, methyl methacrylate ad their polymers Table 8.. Database etries for TBEC ad JWEB Table 8.3. Estimated parameters for moofuctioal ad tetrafuctioal models xv

16 ABBEVIATIONS α-ms ATP DSC EPM FFF GPC IC JC KMHS LALLS LCB LDPE LS MALLS MMA MW MWD NMP NM PDI PS PMMA AFT ALLS I SANS SAXS SEC TGIC TTS ThFFF Visc UV WLF α-methyl styree Atom trasfer radical polymerizatio Differetial scaig calorimetry Ethylee propylee copolymer Field-flow fractioatio Gel permeatio chromatography Iteractio chromatography Joit cofidece regio Kuh-Mark-Houwik-Sakurada equatio Low-agle laser light scatterig Log-chai brachig Low-desity polyethylee Light scatterig Multi-agle laser light scatterig Methyl methacrylate Molecular weight Molecular weight distributio Nitroxide-mediated polymerizatio Nuclear magetic resoace Polydispersity idex Polystyree Poly(methyl methacrylate) eversible additio-fragmetatio chai trasfer polymerizatio ight-agle laser light scatterig efractive idex detector Small-agle eutro scatterig Small-agle X-ray scatterig Size exclusio chromatography Temperature-gradiet iteractio chromatography Time-temperature superpositio Thermal field-flow fractioatio Viscometer Ultra-violet light detector Williams-Ladel-Ferry equatio xvi

17 SYMBOLS α β γ δ ε η η [η] θ ν ρ σ τ τ * ω Kuh-Mark-Houwik-Sakurada parameter Expoet for A -M power law Shear rate Loss agle Expoet relatig g ad g' Zero-shear viscosity Complex viscosity Itrisic viscosity Theta coditio Expoet for g -M power law Desity Shear stress elaxatio time Characteristic shear stress of Cross-Carreau model Frequecy A Secod virial coefficiet a Cross-Carreau model parameter a T Frequecy shift factors b T Modulus shift factors d/dc Specific refractive idex icremet E a Activatio eergy f Brach poit fuctioality f Iitiator efficiecy Gº N Plateau modulus G' Storage modulus G'' Loss modulus G * Complex modulus G red educed modulus g Mea-square radius cotractio factor g' Itrisic viscosity cotractio factor H elaxatio modulus h Hydrodyamic radius cotractio factor J Shear compliace J * Complex compliace J e º Zero-shear or steady-state recovery compliace K A Pre-expoetial costat for A -M power law K g Pre-expoetial costat for g -M power law K [ η ] Kuh-Mark-Houwik-Sakurada parameter k d Fuctioal group decompositio rate costat k p Propagatio rate costat Termiatio rate costat k t xvii

18 k tc k td M M a M c M e M M w M z g h p T T g V V f Termiatio by combiatio rate costat Termiatio by disproportioatio rate costat Molecular weight Arm molecular weight Critical molecular weight Molecular weight betwee etaglemets Number-average molecular weight Weight-average molecular weight z-average molecular weight ate idex of viscosity power-law model Ideal gas law costat adius of gyratio Hydrodyamic radius ate of polymerizatio Temperature Glass trasitio temperature Volume Free volume xviii

19 CHAPTE 1 - INTODUCTION The focus of this work has bee to explore the use of multifuctioal iitiators i free radical polymerizatio. This has bee completed through experimetal ad modellig studies of a ovel tetrafuctioal peroxide iitiator with the followig objectives i mid: 1. Study the kietics of a tetrafuctioal iitiator ad compare to a appropriate moofuctioal couterpart.. Examie the effects of usig a multifuctioal iitiator o polymer properties. 3. Model the behaviour of tetrafuctioal iitiators i free radical polymerizatio. I Chapter, a brief review of the ature of free radical polymerizatio is give followed by advaces i multifuctioal iitiators ad their applicatio. A iheret property of iitiators with fuctioalities greater tha two is the ability to itroduce brachig ito the fial polymer product. As such, a detailed discussio of brached polymers, their properties ad the detectio of brachig i polymers is preseted. The experimetal techiques used to study the polymerizatio kietics of the tetrafuctioal iitiator ad its moofuctioal couterpart are described i Chapter 3. The methods employed i characterizig the polymer samples are also discussed i detail with relevat backgroud iformatio provided. The first of several experimetal studies is preseted i Chapter 4. Previous work foud i the literature o the use of multifuctioal iitiators, the majority of which are difuctioal, has cetered o the polymerizatio of styree. I this chapter, the tetrafuctioal iitiator is employed i a kietic study of the bulk polymerizatio of methyl methacrylate (MMA). The performace of the tetrafuctioal iitiator is evaluated based o rates of polymerizatio, molecular weights ad evidece of brachig for a rage of coversios ad uder differet operatig coditios. These results are 1

20 the compared to experimets where a appropriate moofuctioal couterpart is ru uder idetical coditios. The behavior of the tetrafuctioal iitiator i the polymerizatio of MMA was observed to be ulike that of styree. I Chapter 5, the experimetal kietic study is exteded to systems of two moomers. The homopolymerizatios of methyl methacrylate ad styree ad the copolymerizatios of MMA/styree ad MMA/α-methyl styree were ivestigated. A similar procedure for evaluatig the tetrafuctioal iitiator s behaviour was performed where coversio ad molecular weight results are compared to idetical rus completed with the moofuctioal iitiator. Dilute solutio properties such as the radius of gyratio ad itrisic viscosity were utilized i the detectio of brachig. Chapter 6 provides the fial segmet of the kietic study where the homopolymerizatios of butyl acrylate ad viyl acetate iitiated with the tetrafuctioal iitiator were explored. The polymerizatio of both moomers is characterized by sigificat trasfer reactios. As such, they were chose i order to examie the behaviour of a multifuctioal iitiator whe trasfer reactios to both moomer ad polymer domiate. The impact of a chai trasfer aget o a multifuctioal iitiator was also ivestigated. I Chapter 7, the characterizatio of polystyree ad poly(methyl methacrylate) samples produced by both the moo- ad tetra-fuctioal iitiators is preseted. Size exclusio chromatography setups equipped with a light scatterig detector ad viscometer were used to detect evidece of brachig i the polymer samples. heological characterizatio was performed by dyamic ad creep tests. As see with previous studies o polymer brachig, rheological methods are far more sesitive to the presece of brached chais, ad differeces detected i the rheological characterizatio are ot see by dilute solutio methods. A mathematical model for free radical polymerizatio iitiated with a tetrafuctioal iitiator is developed ad discussed i Chapter 8. The model is able to accurately predict the experimetal data collected for the tetrafuctioal iitiator. The validity of two major

21 model assumptios is assessed. Case studies are preseted ivestigatig the effect of termiatio ad trasfer reactios. The model is foud to be a useful tool i uderstadig the behaviour of multifuctioal iitiators i various moomer systems. 3

22 CHAPTE - BACKGOUND AND LITEATUE EVIEW.1 Free adical Polymerizatio Free radical polymerizatios are characterized by a series of reactios that occur at ay time durig the reactio. The chemical reactios ca be grouped ito the followig four categories: iitiatio, propagatio, termiatio, ad chai trasfer reactios. Iitiatio The polymerizatio of a moomer begis with the geeratio of radicals from the decompositio of a iitiator molecule. These radicals are the able to add oe moomer uit ad form primary radicals. Equatio.1 ad. demostrate the mechaism for the geeratio of primary radicals. kd I (.1) i k + M p 1 1 i (.) I the above equatios, I is a iitiator molecule, uit ad 1 a primary radical. i a iitiator radical, M a moomer Propagatio With the geeratio of primary radicals, the drivig reactio ivolved i a polymerizatio may proceed, amely propagatio. This step ivolves the sequetial additio of moomer uits to a radical chai. k p + M + 1 (.3) I Equatio.3, is a radical chai with moomers uits. 4

23 Termiatio The termiatio of radicals ca occur by two processes: combiatio ad disproportioatio. The former ivolves two radical chais reactig together to form oe dead polymer chai (Equatio.4), while the latter produces two dead polymer chais (Equatio.5). + P (.4) ktc m + m ktd + m P + P (.5) m P is a dead polymer molecule of chai legth. Chai Trasfer eactios Depedig o the ature of the reactio mixture, radical chais may react with other molecules ad trasfer the active radical site. Equatio.6 provides the geeral mechaism for trasfer reactios where Z ca be ay species i the reactio mixture such as moomer, solvet, impurities, chai trasfer aget or polymer. k fz + Z P + Z (.6). Multifuctioal Iitiators Multifuctioal iitiators are believed to provide two advatages over traditioal moofuctioal iitiators. Firstly, research has show that they aid i icreasig polymer productio (1-7). It is kow from free radical polymerizatio theory that the molecular weight is iversely proportioal to the rate of polymerizatio. As such, with the use of a moofuctioal iitiator it is ot possible to simultaeously obtai high rates ad high molecular weights for bulk or solutio processes. Multifuctioal iitiators are see as a alterative to this problem. It has bee show that iitiators cotaiig two or more fuctioal groups ca geerate high rates of polymerizatio while producig polymer of similar or higher molecular weight whe compared to a moofuctioal iitiator. Such a effect has bee attributed to the sequetial decompositio of the fuctioal groups, thus allowig repeated iitiatio, propagatio ad termiatio of the same molecule. 5

24 The secod advatage of multifuctioal iitiators is their ability to itroduce brachig ito the fial polymer product. Whe three or more labile groups are cotaied withi a sigle molecule, the resultig polymer chai will have a structure resemblig a star. Star polymers are the simplest class of brached structures ad as such, they have received a great deal of iterest (8, 9). The itroductio of brachig is see as advatageous from the polymer processig viewpoit, especially i polymer stretchig operatios where brachig has bee foud to improve such properties as melt stregth (1, 11). Multifuctioal iitiators is a area of research that has grow rapidly i the last few decades with the majority of studies dealig with cotrolled/livig polymerizatios such as atom trasfer radical polymerizatio (ATP)(1), reversible additio-fragmetatio chai trasfer polymerizatio (AFT)(13), itroxide-mediated polymerizatio (NMP)(14), aioic polymerizatio (15) ad catioic polymerizatio (16). I compariso, there are relatively few studies that ivestigated the use of multifuctioal iitiators i free radical polymerizatios. Ad those that have researched this area typically deal with difuctioal iitiators for the polymerizatio of styree. Iterest i the use of multifuctioal iitiators for free radical polymerizatio bega over three decades ago. Prisyazhyuk ad Ivachev produced fudametal work o uderstadig the mechaism of polymerizatio with difuctioal iitiators (1). The authors examied the kietics of several diperoxides havig labile fuctioal groups of differig thermal stability i the polymerizatio of styree. Work was also completed o the use of usymmetrical difuctioal iitiators to produce block copolymers. Polymerizatio was first carried out i styree at a lower temperature to form polystyree macroiitiators. These macroiitiators were the used i the polymerizatio of methyl methacrylate (MMA) at a higher temperature to form block copolymers. Nearly a decade later, Ivachev (1979) reviewed the curret state of free radical polymerizatio iitiatio, summarizig most of the past work o difuctioal iitiators (17). Aother sigificat review came from Simioescu et al. (1986) who compiled a extesive list of work ivolvig the sythesis, decompositio ad use of difuctioal ad multifuctioal free 6

25 radical polymerizatio iitiators (18). Although some of the sythesis ad decompositio studies dealt with iitiators with a fuctioality greater tha two, very little work was completed o the use of these iitiators i actual polymerizatios. Similar to earlier work, recet studies o multifuctioal iitiators are cocered more with difuctioal molecules. The group of Choi ad coworkers have writte umerous papers startig with the employmet of symmetrical difuctioal iitiators i the polymerizatio of styree ad developig a kietic model of this system (3, 19). The group advaced to experimetal ad modelig work for usymmetrical difuctioal iitiators (, 1), the to combiatios of iitiators () ad fially, modified their batch model for a tubular reactor (3). Villalobos et al. (1991) foud that previous models usig difuctioal iitiatio had serious limitatios for the predictio of molecular weights ad molecular weight distributios at high coversio. They modified ad exteded curret models i the literature makig comparisos to their experimetal work (4). Similarly, Gozález et al. (1996) adapted a model to allow for the use of mixtures of moo- ad difuctioal iitiators ad compared their results to experimetal data (5). Esteoz et al. (1996) evaluated several difuctioal iitiators for the sythesis of highimpact polystyree ad attempted to predict their experimetal behaviour (4). More recetly, Cavi et al. () completed a thorough kietic ad modelig ivestigatio of,5-dimethyl-,5-bis(-ethyl hexaoyl peroxy)hexae i the polymerizatio of styree (6). By combiig ad adaptig various models foud i the literature, the group was able to accurately predict coversio data but molecular weights up to oly 7% coversio. Dhib et al. () compiled a extesive review of the work to date o difuctioal iitiators ad icorporated the results ito a computer simulatio/database package (5). All of these studies have show, either through experimetal or modelig results, the ability of difuctioal iitiators over their moofuctioal couterparts to reduce batch times while maitaiig or icreasig the polymer molecular weight. As for iitiators of fuctioality higher tha two, a limited amout of work has bee doe i free radical polymerizatio. Meceloglu et al. (199) reported o the sythesis of three tetrafuctioal iitiators based o the reactio of tetrakis(dimethylamio)titaium 7

26 with either, -azoisobutyroitrile, tetracyaoethylee or isophoroe diisocyaate (6). Very little polymerizatio iformatio was reported. Cera et al. () reported a kietic study showig that the use of difuctioal ad trifuctioal cyclic iitiators would allow for high rates of polymerizatio while producig high molecular weight polymer (7). Holziger ad Kickelbick () are aother group that has used multifuctioal iitiators i free radical polymerizatio (7). Their work examied the sythesis of various iitiators for thermal or photoiduced free radical polymerizatio from modified cubic spherosilicate cages. The data showed that polymer with a broad polydispersity was beig produced which the authors attributed to the formatio of various molecular architectures. Kwo et al. (3) sythesized a ovel tetrafuctioal photoiiferter for the productio of star polystyree by radical polymerizatio (8). The resultig polymer was foud to have a broad molecular weight distributio (.5) with roughly 3 out of the 4 arms retaiig their fuctioal groups. As such, this star polystyree was used as a polymeric photoiiferter for further polymerizatio of styree..3 Brachig i Polymers Brached polymers are defied as macromolecules cotaiig poits where three or more log chais are attached together. I other words, a brached polymer is characterized by more tha two chai eds. These macromolecules lie i betwee the two extremes of liear polymers ad polymer etworks; however, they are more related to liear polymers. Brachig ca be deliberately or iadvertetly itroduced ito a polymer either i the polymerizatio or extrusio process. Durig polymerizatio of may moomers, a variety of side reactios such as trasfer to polymer ca occur iadvertetly leadig to brach poits. Brachig ca also be itroduced deliberately durig polymerizatio with the choice of the proper iitiator or the additio of a polyfuctioal moomer or aget. I extrusio, brachig may be caused by thermal degradatio, radiatio or chemical meas. The determiatio of log-chai brachig (LCB) both qualitatively ad quatitatively has bee the focus of polymer researchers for over sevety years. The reaso for such a iterest ca be attributed to the fact that the occurrece of eve a small amout of brachig ca cosiderably ifluece the properties of a polymer. LCB is kow to ifluece several solutio ad melt properties varyig 8

27 from itrisic viscosity to swell durig blow moldig. As may commercially produced polymers cotai sigificat amouts of brached material, the detectio of LCB is of tremedous practical importace. This sectio deals with the detectio of brachig i polymers ad is divided ito two parts. The first segmet ecompasses the various properties iflueced by brachig while the secod part reviews methods to detect or estimate brachig. Short-chai brachig (e.g., the result from copolymerizatio with a moomer cotaiig side groups or from back-bitig) is ot cosidered i this chapter. The properties ad characterizatio of macromolecular rigs or polymer etworks are also ot withi the scope of this text. The occurrece of brachig was postulated, roughly sevety years ago, by the work of Staudiger ad Schulz i order to explai certai uexpected observatios with polystyree (9). Flory later showed that trasfer reactios durig the free radical polymerizatio of styree could produce log-chai braches (3). Already by the early 195 s, a oteworthy amout of work dealt with the mechaism ad kietics of brachig reactios, the effect of brachig o polymer properties ad the possible determiatio of LCB. I 1953, Stockmayer ad Fixma reviewed the state of dilute solutio properties of brached polymers (31). A short time later, Melville published a accout of liear ad brached polymers discussig the implicatio of brachig ad its possible detectio (3). Sice that era, umerous reviews of brachig have bee compiled. I 1968, Graessley summarized methods for the detectio of brachig based o dilute solutio methods (33). I that same year, Dexheimer ad coworkers compiled a list of studies ot oly icludig the effects of brachig o polymer properties but also the kietics ad mechaism of brachig (34). Small wrote a otable review of log-chai brachig examiig its ifluece o various polymer properties ad the estimatio of LCB (35). The work also icluded a survey of brachig i specific polymers such as polyethylee, poly(viyl acetate), polystyree, poly(methyl methacrylate) ad poly(viyl chloride). More recet reviews iclude work by Burchard (36, 37), ad Mays ad Hadjichristidis (38), who examied the solutio properties of brached macromolecules, ad oovers (39) who provided comprehesive surveys of the literature for brached polymers i 9

28 geeral. eviews o the effect of brachig i the melt state iclude those of Graessley (4) ad Vega ad coworkers (41). Brached polymers ca have various structures depedig upo their sythesis. Figure.1 shows the architecture of some typical model brach structures ad a example of radom brachig. A great deal of research has ivolved the sythesis of model brached polymers (4, 43) with arrow molecular weight distributios (MWD) i order to specifically observe the effect of brachig. These results help to costruct fudametal theories which ca aid i the ivestigatio of radomly brached polymers. (a) (b) (c) (d) (e) (f) Figure.1. Various polymer molecular architectures: (a) star; (b) comb; (c) H-shaped; (d) pom-pom; (e) dedrimer; (f) radomly brached (cotais tri- ad tetrafuctioal brach poits with braches o braches)..3.1 Brached Polymer Properties Dilute Solutio Properties Mea-square radius The size of a macromolecule is oe of its most fudametal properties. Although there are several ways to represet the dimesios of a polymer chai, the mea-square radius is a typical measure of size, give by the followig: 1

29 s = N i= 1 r i N (.7) where the polymer molecule is cosidered to be comprised of N small elemets of idetical mass ad r i is the distace of the i th uit from the polymer molecule s cetre of gravity. The use of agled brackets deotes that the summatio is averaged over all possible coformatios that the polymer chai ca assume. The term radius of gyratio is widely used whe referrig to a polymer molecule s size ad is simply the square root of the mea-square radius: 1 g = s (.8) Theoretical calculatios for the mea-square radius of gyratio usually assume that a polymer molecule ca be a represeted by a radom flight chai made up of N freely joited uits. Discrepacies betwee the model ad actual chais arise for two reasos, kow as short ad log rage effects. The short rage effects are due to uits ot beig completely free to rotate but havig bod restrictios, while log rage effects occur because itersectios of uits are impossible. Short rage effects are addressed by dividig the polymer chai ito loger segmets of several bods so that each uit ca be cosidered to be freely joited. If log rage effects, also kow as volume exclusio, are abset, the chais obey the radom flight model ad take a uperturbed state. I this case, the mea-square radius is represeted by s (the subscript deotes a uperturbed value). From the work of Flory (44), log rage effects are oexistet at the θ poit (particular temperature, T θ, for a specific solvet) ad s = s (.9) θ Compared to a liear chai of the same umber of uits, a brached chai is more compact. As a result, the impact of brachig o the size of a polymer chai is to 11

30 decrease the mea-square radius as brachig icreases. To assess the decrease i size due to brachig, the mea-square radius of a brached polymer is compared to the size of a liear aalog of idetical molecular weight. Quatitatively, this was defied by Zimm ad Stockmayer (45) with the followig brachig or cotractio factor: s = (.1) br g g = br s g l l M M The subscript M idicates that both the brached (br) ad liear (l) chais have idetical molecular weights. Because brached polymers are more compact ad have smaller dimesios, g will always be less tha uity with smaller values beig a idicatio of a higher amout of brachig. Theoretical equatios for the calculatio of cotractio factors for various types of brachig have bee developed ad are give i Table.1. Although ot a complete list of the results i the literature, Table.1 does summarize the earlier work which provided expressios for more commo types of brachig. Other groups who derived idetical equatios or equatios for other types of brachig structures iclude Orofio (46, 47), Kurata ad Fukatsu (48), Forsma (49), Burchard (36), Nakamura ad coworkers (5), ad oovers (51). The equatios for g give i Table.1 are based o the radom flight model where chais are assumed to be i a uperturbed state. If Equatio.9 is assumed to hold, these equatios ca be compared to experimetal values of g θ, where the mea-square radius for both liear ad brached chais is measured at the θ poit. Values of s ca be obtaied experimetally from radiatio or eutro scatterig experimets. By measurig the agular depedece of the itesity of scattered radiatio betwee the particles ad the probig radiatio, the particle size ca be determied. Well developed techiques for determiig a particle s size iclude light scatterig (LS), small-agle X-ray scatterig (SAXS), ad small-agle eutro scatterig (SANS) (5). The theory of light scatterig from macromolecular solutios is provided i the works of Debye ad Zimm (53-55) ad is reviewed ad applied to brached polymers by Burchard 1

31 (36). Light scatterig experimets provide a z-average estimate of the radius of gyratio ( g(z) ). For samples with a arrow molecular weight distributio, this does ot provide a problem ad g = g(z). However, whe samples with a broad molecular weight distributio are aalyzed, the icrease i polydispersity (M w /M ) has a substatial effect ad g(z) will icrease. This icrease i the z-average radius of gyratio is sigificat eough that it will couterbalace the decrease i size due to brachig. As a result, the g(z) for a polydisperse brached polymer may seem idetical to that of a polydisperse liear sample. Therefore some fractioatio method must be used i order to obtai moodisperse fractios where the cotractio factor ca be calculated. Further discussio cocerig the determiatio of g for polydisperse samples will be provided i the sectio for detectig LCB. Values of experimetally determied cotractio factors for stars of varyig fuctioality are provided i Table. ad plotted i Figure.. The theoretical equatios for stars with moodisperse ad polydisperse arms i a uperturbed state are also show. The experimetal results are for stars with arrow molecular weight distributios. Studies have foud that g θ values for stars with less tha roughly 1 arms are predicted quite well by Equatio.1. However, at higher fuctioalities, g θ is observed to be greater tha the theoretical values. Deviatios betwee the two values have bee attributed to various factors icludig a greater umber of segmet-segmet iteractios (56) ad a higher desity of segmets ear the core (57, 58). The discrepacy has also bee observed with other types of brachig structures such as combs ad radom brachig (59). The radius of gyratio ca be related to a molecular weight by a equatio of the followig form: ν g = K M (.11) g where K ad ν are costats. The expoet ca vary betwee.33 for hard spheres to g 1 for a rigid rod. I the case of liear chais, a expoet of.5 refers to a uperturbed 13

32 state while i good solvets, ν is closer to.6. A excellet summary of g -M data i the literature by Fetters ad coworkers provides estimates for these parameters i both θ ad good solvets for a umber of liear polymers (6). The parameters i Equatio.11 are ot oly iflueced by the experimetal coditios (solvet, temperature) but are also affected by the polymer s structure. For moodisperse stars it has bee foud that icreasig the umber of arms decreases K while ν remais idetical to that of the g liear polymer (see Figure.3). However, for radomly brached polymers it has bee foud that ν is closer to.5 ad i some cases much lower. Such low values of this expoet might be cosidered a idicatio of the brached polymer beig i a uperturbed state; however, this is ot the case. A explaatio as to why ν is so small for radomly brached polymers has bee foud usig fractal behaviour ad a overview is give by Burchard (37). Table.1. Theoretical equatios for mea-square radius cotractio factor (g) for several brached structures. Brachig type Theoretical brachig factor ef. egular stars moodisperse arms 3 f g = (.1) (45) polydisperse arms Stars with ureacted fuctioal groups f 6 f g = (.13) (45) ( f + 1)( f + ) 3 f g z = (.14) (37) f ( + 1) moodisperse arms 1+ 3( f 1) α = ( + ( f 1) α ) polydisperse arms 1+ ( f 1) α = 4 ( + ( f 1) α ) 1 3 = λ λ ( 1 λ) + λ( 1 λ) + ( 1 λ) 3 Symmetrical combs g (.15) (61) g (.16) (61) g + 1 (.17) (6) 14