Polymerization Synthetic Polymers In Dentistry
PolymerizationSynthetic polymersin dentistryPavel Bradnabradna@vus.czInstitute of clinical and experimentalstomatology2012Poliklinika VFN, Karlovo namesti 321
Dental materials Metallic materials – denture frameworks,supraconstructions, implants, amalgams,orthodontic brackets, wires Inorganic materials - cements, ceramics,gypsum products, investment materials Organic (polymer-based) materials20122
Typical polymer-based materials usedin dentistry Dentures (bases, artificial teeth,relining materials) Filling materials (composites, cements,adhesives) Obturation materials (endodoncy) Impression materials Equipment (spatulas, measures, etc)20123
What is the lecture about? Terms and definitions Structure of polymer chains Polymerization reactions Methyl methacrylate polymers Typical dimethacrylate resins20124
DefinitionPolymer – a chemical compound consistingof giant molecules „MACROMOLECULES“formed by union of many „POLY“ smallrepeating units „MER“mono“MER“ molecules2012POLY“MER“ chain, macromoleculepolymerizationcovalent bond5
Note:In stomatology:Polymers sometimes appointed as resinsbut:Some monomers – (dimethacrylates) arefrequently appointed also as resins,e.g. resin composites20126
What controls polymer properties?1. Chemical composition of polymersmonomer, its structure and compositionVinyl monomersCH2 CHRExamples:Stucture of vinyl polymers-CH2-CHnRR H – polyethylene hydrophobic, semicrystalinepolymersR OH – poly(vinyl alcohol), hydrophilic water solublepolymer with gelling properties20127
CH2 CH-CH2-CHnRR COOH – acrylic acidRR COOH – polyacrylic acidWater solubleCH3CH3CH2 CCH2 CRRR COOH – methacrylic acidR COOCH3 – methyl methacrylateLess water soluble20128
If one or more monomers are linkedtogether:One monomer - HOMOPOLYMERsTwo or three monomers - COPOLYMERs20129
2. Topology of polymer chains-A-A-A-A-A-A-A-Linear polymersNonlinear (branched) polymersPolymer (linear) backboneBranches201210
Cross-linked polymer (polymer networks)A-A-A-A-AA-A-A-AA-A-A-A-A-A-A-A- A-A-A-A-A-A-A-AA-A-A-A-A-AA-A-A-A- A-A-A-A-A-A-Cross-links (permanentconections between chainsrestricting motion ofchainsrigidity)Temporary cross-linksentaglements201211
3. Monomer distribution in copolymersA-B-A-B-B-B-A-statistical -A-A-A-A-A-blockgraft/branched-B-B-B-B-B201212
Cross-links strongly affect mechanicalproperties and thermal behaviour of polymersLinear or branched polymers - flow when heated, canbe easily reshaped upon heating - thermoplasticpolymers(usually soluble in organic solvents)Cross-linked polymers - they can not be reshaped onheating, do not melt, but decompose on heating thermosetting polymers20122011(insolublein organic liquids)13
Glass transitition orsoftening temperature TgTemperature at which rigidity of a polymer decreasesRange of TgRigidGlassy stateLiquidPlastic2012RigidityRubbery stateHigh degree ofcross-linkingLow degree ofcross-linkingLinearMelting range0oC30oCTemperature14
4. Polymer molecular weightSimple compounds –composed of identicalmoleculesM - molecular weightaverageMolecules of polymer –strongly differ (vary by manymonomer units)2012Polymers are characterized bymolecular weight/polymerizationdegree average15
Synthetic polymersPrepared via polymerization reactions: Chain-growth (addition) polymerizationusually free radical polymerization ofmonomers with double bonds Step-growth polymerization (e.g.polycondenzation) of bifunctional monomersfrequently with release of low molecularcompounds (analogous reaction to low molecularweight compounds)201216
Types of chain-growthpolymerizations: Free radical polymerization – activecentre is a free radical (with an unpairedelectron). Cationic polymerization – active centresbear positive charge. Anionic polymerization – active centresbear negative charge.201217
Free radical polymerizationCharacteristics Starts from an active center (e.g free radical)only these molecules are capable to react π-bond of monomer is converted to σ-bond inthe polymer Monomer molecules add sequentially to the endof a growing chain Is very fast and exothermic Produces high molecular weight polymers Free-monomers are present201218
Step-growth polymerizationCharacteristics Proceeds by conventional functional group reactions(condensation, addition) Needs at least 2 functional groups per reactant Any monomer molecule has the „same“ probabilityto react After an elementary reaction – ability to grow remains Polymers are formed more slowly than by free radicalpolymerization Polymers are generally of lower molecular weight Dimers, trimers or oligomers are present (instead of free2012 monomers)201119
Stages of free radical polymerization1. Initiation/induction – process starts- Primary radical formationIn - InInitiatorT, hνIn. In. (activation)Free radicals– Addition of primary radical on the doublebond of monomerIn. MIn-M.201220
2. Propagation - the addition of monomer tothe active center (free radical) to generatea new active centerIn-M. MIn-M-M.In-M-M. MIn-M-M-M.In-M-M-M. yMIn-M-M-M-. My.3. Termination – the growing chain is stopped- Radical coupling/recombination (most common). .M -InIn-M2012xyIn-Mx-My-In21
- Chain transfer – An atom is transferredto the growing chain, terminating the chain growthand starting a new chain.1. Original chain terminates-M-M-M. XB-M-M-M-XChain transfer agent B.new active radical2. New chain growth startsB. MBM.monomernew chain201222
Special cases of chain transfer reactions:A retarder is a substance that reacts with a.growing chain forming less reactive radical Band thus making polymerization rate „slow“An inhibitor is a substance that reacts with anactive radical to form stable compoundsunable addition to monomer - completely stops“inhibits” polymerization.201223
Examples of step-growth polymerizationPolycondensationSetting reaction of C-silicone impression materials .OSiOO .OSi OOO SiSiOO SiO O .OHO Si OOHO-4CH3OH .OSi .O Si(OCH3) 4O .OHO SiOHOO .OSi .O OO2012 24
PolyadditionSetting reaction of A-silicone impression materialsVinyl terminated siloxane oligomerAddition of -H on vinyl double bondMethylhydro-dimethylsiloxane – a cross-linking agent201225
Methyl methacrylate (MMA) polymersMost frequently used group of polymers inprosthetic dentistryBased on MMA monomerR H – methacrylic acid OCH3C CCH2ROCH3 CH3-CH2-OHmethyl methacrylate (MMA)- hydroxy ethyl methacrylate(HEMA)Why? Because these materials can be easily adopted toindividual purposes (fillings, prostheses), polymerizationis fast and they are well accepted by the human body201226
Properties of MMA Colorless liquid Immisible with water but with organicsolvents Melting point-48oC Boiling point100.3oC Density0.945 g/mL Heat of polymerization 54.3 kJ/mol(!! exothermic reaction !!) Irritant !! Flamable !!CH3CH2 CC OOCH3201227
Properties of poly(methyl methacrylate) - PMMA Transparency and high clarity Low absorption of visible and UV light (to 250 nm) Compression strength 90 – 100 MPa Very rigid - elastic modulus above 2.4 GPa Water sorption up to app. 1.0 wt % Temperature resistance Tg 120 – 125oC Soluble in organic solvents (MMA, aceton, toluene etc)Density 1.19 g/cm3 (causes polymerization contraction/shrinkage app. 22 vol %)201228
Application of PMMA in dentistryHow to overcome polymerizationshrinkage ?2012
First applications for dentures via compressionmoulding of molten PMMA powder (too expensiveand complicated) 1936 – Kulzer: powder/liquid systemPowder – PMMA prepolymer with residuals of DBPLiquid – MMA monomer and additives- When mixed together a workable - plasticmass (dough) is formed and polymerized inindividualy fabricated mould- Decreased polymerisation shrinkage (app. 6vol%)atpowder/liquidratio3-2,6/1201230
PMMA prepolymer beadsPrepared by suspension polymerization2012Average particle size 0.005-0.100 mmAcrylics and Other Synthetic Resins Used in Dentistry31
Polymerization scheme of MMAmonomers Initiation– Thermal decomposition of dibenzoyl peroxide(DBP)OheatO2O.(2 phenyl. CO2)OOCH3CH3. CH CO CH2-C2OC OO.C OOOCH3CH3201232
Thermal decomposition of peroxidesC concentration of peroxidek kinetic constantt timeEffect of temperatureThe temperature dependence of kinetic constant is given by an Arhenius law:with : k(T) kinetic constant at temperature T (K)Ea Activation energyR Gas constantT Temperature in KThe higher temperature – the higher concentration of20122011radicals and higher polymerizatin rate33
PropagationCH3.O-CH2-COCH3 n(CH2 C)C OO (CH2-CC OOO)nC OOOCH3.CH2- CC OOCH3CH3CH3CH3CH3 Chain terminationCH3R1-H2C-CCH3. .C OOC CH2-R2C OOCH3CH3CH3R1- H2C -CCH3CC OOCH2-R2C OOCH3CH3201234
Chain transfer to Phenolic inhibitors-MX – CH2-CH2. HO--OH-MX – CH2-CH3 HO-hydroquinone (HQ)HOOCH3-OStable hydroquinoneradicals will notpropagate - stoppolymerization reactionmethoxy phenol (hydroquinonemono methyl ether) phenol(butylated hydroxytoluene - BHT)Sterically hindered phenols – less efficient but reducedcolor change after polymerization - Synergetic mixtures20122011HQ MEHQ35
Note1. Eugenol phenol(inhibits polymerisation)4-Allyl-2-metoxyfenolZinc oxide-eugenol cements-may negatively affector stop setting of composite materials2. Oxygen inhibitionMx I. O2MxIOOHStable hydroperoxidOxygen-inhibited layer on thecomposite/adhesive surfaces201236
Why polymer inhibitors are added?Usually 0.01 – 0.005 wt %1. To extend monomer shelf-life byrestricting spontaneous polymerization2. To decrease sensitivity of monomers to ambientlight3. To prolonge the working time201237
PMMA is often modified for dentalapplication by: Cross-linking(effect of a molecular weight increase)- improves hardness and stiffness- improves wear and solvent resistance but increasebrittleness- increases thermal resistance (polymers are easilyfinished - grinded and polished withoutmelting)- increases crazing resistance (small cracks originating atthe teeth-denture margin)201238
Copolymerization (with acrylic andmethacrylic monomers, PVC, PVAc,butadiene) disturbs regular intermolecularorder of a homopolymer– decreases softening temperature- improves fatique and impact resistance- increase dissolution rate in MMA Blending of various MMA polymers– increase rate of dissolution in MMA- decreases softening temperature201239
Glass transitition temperature (softening) ofvarious methacrylic polymersrigidMethacrylatePolymer TgoCCH3CH2 Cmethyl125ethyl65n-propyl38CH3 (ethyl,n-butyl33propyl, butyl)C OOSoft, fasterdissolution201240
Plasticizing –- to reduce stiffness, hardness and softeningtemperature- to prepare flexible polymers (acrylic reliningmaterials – combinations of MMA homo orcopolymers with plasticizers)Plasticizershigh-boiling compounds swell polymers (phatalates –dibutyl/dioctyl phtalates) – leachable potentiallyharmfull201241
Classification of methacrylate polymersaccording to initiation reactions(activation)– Heat activated (heat cured/heat curing)resins (prosthetic polymers)- Chemically activated (self cured/curing,cold curing, autopolymerizing, fast curing)resins (prosthetic polymers, restorativecomposites, resin cements, and adhesives)- Light activated (LC/UV cured) resins(restorative composites, resin cements and2012adhesives)42
Heat activated resins(denture base resins, resins for artificial acrylicteeth, crown and bridge polymers)Composition:powder: PMMA prepolymer with dibenzoyl peroxide (up to0.5 - 0.6 wt %)liquid: MMA, cross-linking agent (app. 1- 6 wt %),inhibitors, additives (plasticizers), regulatorsVolume mixing ratio (powder/liquid): 3-2.5/1.0201243
Chemically activated resins(denture reparations, relining materials,orthodontic appliences, pouring resins)Composition:powder: PMMA prepolymer or copolymer (fine particlesize), dibenzoyl peroxideliquid: MMA, crosslinking agents, inhibitors, acclerators(1-4 wt %), UV absorbersAcclerators1. Tercial aromatic amine2. Barbituric acid derivatives combined with aliphatic amine (lower colorchange) and Cu cations3. Sodium p-toluene-sulfinate (for systems containing methacrylic acid),2012Cu cations44
Scheme of DBP decomposition accelerated by terc. amineH3C-NCH3 O OCH3CH3-N. O-. CH3Free radicalN,N-dimethyl-p-toluidine (DMPT); N,N-di(hydroxyethyl)-p-toluidineCompared to heat activated resins: Lower molecular weight Higher amount of free monomer 3-5 wt %, heatactivated app. up to 1 % Lesscolor stability due to oxidation of aromatic amine2012201145accelerators
Light activated resins(light cured denture base materials, compositematerials, adhesives, light cured glassionomer cements)Composition (usually one component):1. Dimethacrylate resin, light initiating systemcamphorquinone (CQ) - amine, inhibitorsLight468 nmCQ2012amineamineH.Free radicals are. from aminesformedHCQ2. Filler particles46
Typical dimethacrylate monomers (resins)Main applications: composite resins, adhesives, crosslinkers1. BIS-GMA yl]propane (Bowen monomer, 1955)2012higher molecular weight – less polymerizationshrinkage, high boiling point, no odor47
Capable of Hbridge formationhigh viscosityMeth.Composition of this spacer controlsrefractive index of the monomerwhich plays a key role in thecomposite s optical propertiesMeth.Increased molecular mass - less polymerizationshrinkage app. 5-6 vol %201248
2. Urethane dimethacrylate (UDMA) dimethacrylate)Also of high viscosity3. Triethylene glycoldimethacrylate TEGDMA (low viscositydiluent)n 1 ethylene glycoldimethacrylate (EGDMA)4. 1,6 hexane dioldimethacrylate201249
Examples of monomers used in dentaladhesives2-hydroxyethyl methacrylate4-acryloxyethyl trimelitic acid anhydride20124-methacryloxyethyl trimelitic acidanhydride/acid50
Dipentaerythritol penta rogenphosphatePolymers and monomers for GICMaleic acidPolyacrylic acid with pendantmethacrylate groupsItaconic acid201251
Other polymersAlternatives to acrylic denture basepolymersThermoplastic semicrystaline polymers/injectionmolding at high temperaturesPolyacetal, POMHO2C-(CH2)4-CO2H H2N-(CH2)6-NH2 adipic acidhexamethylene diamine [CO(CH2)4CO-NH(CH2)6NH]n polyamideNylon 66201252
Summary1. Polymers, characterization, properties (molecular structure)2. Chain-growth polymerization (free radical); step-growth(polycondenzation and polyaddition)3. Phases of free radical polymerization4. Properties of MMA, polymerization of PMMA5. Inhibitors6. Characteristics of heat, chemical and light activation systems7. Dimethacrylate resins used in composite materials8. Other monomers and polymers in dentistry201253
Literature: Craig RG., Powers JM., Wataha JC: DentalMaterials, Properties and Manipulation, Mosby Powers JM., Sakagushi RL: Craig s RestorativeDental Materials, Mosby Gladwin M., Bagby M.: Clinical Aspects of DentalMaterials, Theory, Practice and Cases, LippincottWilliams/Williams Anusavice KJ.: Phillips Science of DentalMaterials, SaundersActual edditions of these text books201254
Typical polymer-based materials used in dentistry Dentures (bases, artificial teeth, relining materials) Filling materials (composites, cements, adhesives) Obturation materials (endodoncy) Equipment (spatulas, measures, etc) Impression materials
Polymers Nitinol Memory Wire Amazon 14.95 Polymers Silly Putty Amazon 9.95 Polymers Plastic cups Kroger 6.54 Polymers Plastic spoons Kroger 3.69 Polymers Measuring spoons Kroger 5.45 Polymers Isopropyl alcohol Kroger 8.70 Polymers Dry Ice 21.63lbs Kroger 29.55 .
after polymerization. For example, after Nylon 6,6 forms, the leftover product was water. Step-growth polymerization often requires two different monomers to form one polymer. Step-growth polymerization occurs when monomers start to join together. Any monomer can star forming chains, so the molecular weight is low.
1600 Bellwood Road Richmond, VA 23237, U.S.A. TEL 1-804-271-7677 USA. 01 Introduction/What is Radical Polymerization? 01 Radical polymerization is initiated by the formation of free radicals. Free radicals are formed by thermac energy, light, or radioactivity. Radical polymerization
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Water soluble polymers cover a wide range of highly varied families of products of natural or synthetic origin,and have numerous uses. Among these families, synthetic polymers, and more particularly coagulants and flocculants,are . 12. water. IV-7- 2 Influence of the polymers 15.
Classification of polymers based on their structure can be of three types: (i) Linear polymers: These polymers are similar in structure to a long straight chain which identical links connected to each other. The monomers in these are linked together to form a long chain. These polymers have high melting points and are of higher density.
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