polymerization synthetic polymers used in dentistry

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  • 1

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    PolymerizationSynthetic polymers used in

    dentistry

    Pavel Bradna

    Institute of Dental Research

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    Dental materials Inorganic - gypsum products,

    investment materials, cements,ceramics

    Metals denture frameworks,supraconstructions, implants, amalgams,orthodontic brackets, wires

    Organic (polymer-based) materials

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Typical applications of polymers indentistry

    Impression materials Obturation materials (endodoncy) Equipment (spatulas, measures, etc)

    Dentures (bases, artificial teeth,relining materials)

    Filling materials (composites, cements,adhesives)

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    What is the lecture about?

    Terms and definitions Structure of polymer chains Polymers in dentistry Polymerization Methyl methacrylate polymers Typical dimethacrylate resins

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Definition

    Polymer a chemical compound consistingof giant molecules MACROMOLECULESformed by union of many POLY smallrepeating units mers

    MONOMER molecules POLYMER chain, macromolecule

    polymerization covalent bond

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    1. Chemical composition of polymers

    type of monomer, its structure

    What controls polymer properties?

    CH2=CH

    RVinyl polymers

    R = H : polyethylene hydrophobic,semicrystalline polymers

    R = OH : poly(vinyl alcohol), hydrophilic watersoluble polymer with gelling properties

    Examples:

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Linear polymers A-A-A-A-A-A-A- Nonlinear (branched) polymers

    Branches

    Polymer (linear)backbone

    2. Topology of polymer chains

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    A-B-B-A- A-B-A-B-B-A-A-B- A-B-A-B-B-A-A-B-

    A-B-A-B-B-A- A-B-B-A- A-B-A-B-B-A-

    Cross-linked polymer (polymer networks)

    Cross-links (permanentconnections between

    chains restricting motionof chains rigidity)

    Temporary cross-linksentanglements

    A-A-B-A-B-

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Homopolymers (one type of monomer - A) A-A-A-A-A-A-A- linear/branched Copolymers (2-3 comonomers) A-B-A-B-B-B-A- statistical (random)

    A-A-A-B-B-B-B-A-A- block A-B-A-B-A-B-A- alternating -A-A-A-A-A- graft/branched -B-B-B-B-B

    3. Monomer distribution in copolymer chains

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    Simple compounds composed of identicalmolecules

    4. Polymer molecular weight

    Molecules of polymer strongly differ (vary by manymonomer units)

    Polymers are characterized bymolecular weight/polymerization

    degree average

    -numberaverage

    -weightaverage

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Number average, Mn

    Mn= Mi ni/ni=Mixi

    Definitions of molecular weight averages

    Mw= Mi (ni Mi)/ni Mi =Mi (mi/mtotal)=Mi wi

    xi states for molefraction of molecules with Mi

    Weight average, Mw

    Polymerization degree

    wi states for weight fraction of molecules with Mi

    Pw= Mw/MoMo states for molecular weight of repeating unit

    Polydispersity Mw/ Mn

    -numberaverage

    -weightaverage

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    5. Supramolecular structure (molecular organization)

    Amorphous polymers coiled irregular(random) shape of polymer chains

    Semicrystalline polymers domains withregular (crystalline) structures acting asspecial type of cross-links

    Amorphous domains

    Crystallites

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    C

    C

    C

    C

    C

    C

    C

    C

    Van-der-Waalsinteractions

    NH

    (CH2)5

    C O

    NH

    NH

    C O

    C O

    C O

    NH

    (CH2)5

    H-bridges

    Typical for polyamides, polyethylene, polypropylene etc.

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    Influence of cross-links on physicalproperties of polymers

    Cross-linked polymers - they cannot be reshapedon heating, do not melt, but decompose onheating, insoluble in organic liquids(thermosetting polymers).

    Linear or branched polymers - flow when heated, canbe easily reshaped upon heating - thermoplasticpolymers(usually soluble in organic solvents)

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Glass transition (softening temperature)Temperature Tg

    Rig

    idity

    Temperature at which rigidity of polymer decreases

    Temperature

    Glass

    LiquidPlastic

    Range of Tg

    Linear

    Low degree ofcross-linking

    High degree ofcross-linking

    Rigid

    Rubberystate

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    Polymers used in dentistryNatural polymers

    - polysaccharides (agar and alginates) - poly(isoprene)

    natural rubberCis-poly(1,4-isoprene) - (impression materials)

    guttaperchaTrans-poly(1,4-isoprene) - (obturation points)2-methyl-1,3-butadiene

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Step-growth polymerization of bifunctional monomers, frequently with releaseof low molecular compounds (analogous reactionto low molecular weight compounds)

    Polymers used in dentistrySynthetic polymers

    Prepared via polymerization reactions:

    Addition (chain-growth) polymerizationof monomers with a double bond

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    Addition polymerization

    Starts from an active center (only thesemolecules are capable to react)

    -bond of monomer is converted to -bondin the polymer

    Monomers add sequentially to the end of agrowing chain

    Is very fast and exothermic

    Produces high molecular weight polymers

    Characteristics

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Types of addition polymerizations:

    Free-radical polymerization active centeris a radical (contains unpaired electron) andthe propagating site of reactivity is a carbonradical.

    Cationic polymerization - the active center isan acid, and the propagating site of reactivityis positively charged

    Anionic polymerization - the active center isa nucleophile, and the propagating site ofreactivity is negatively charged

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    Few common polymers prepared via addition polymerization

    Name(s) Formula Monomer Properties

    Polyethylene low density (LDPE) (CH2-CH2)n

    ethylene CH2=CH2

    soft, waxy solid

    Polyethylene high density (HDPE) (CH2-CH2)n

    ethylene CH2=CH2

    rigid, translucent solid

    Polypropylene (PP) different grades [CH2-CH(CH3)]n

    propylene CH2=CHCH3

    atactic: soft, elastic solid isotactic: hard, strong solid

    Poly(vinyl chloride) (PVC) (CH2-CHCl)n

    vinyl chloride CH2=CHCl strong rigid solid

    Polystyrene (PS) [CH2-CH(C6H5)]n

    styrene CH2=CHC6H5

    hard, rigid, clear solid soluble in organic solvents

    Polytetrafluoroethylene (PTFE, Teflon) (CF2-CF2)n

    tetrafluoroethylene CF2=CF2 resistant, smooth solid

    Poly(methyl methacrylate) (PMMA, Lucite, Plexiglas)

    [CH2-C(CH3)CO2CH3]n

    methyl methacrylateCH2=C(CH3)CO2CH3 hard, transparent solid

    cis-Polyisoprene natural rubber

    [CH2-CH=C(CH3)-CH2]n

    isoprene CH2=CH-C(CH3)=CH2

    soft, sticky solid

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Step-growth polymerization

    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

    Combines two different reactants in analternating structure

    Characteristics

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    Polymers are formed more slowly than by additionpolymerization

    Polymers are generally of lower molecular weight

    Types of step-growth polymerization

    Polycondensation

    Polyaddition

    (C) Institute of Medical Biochemistry, 1st Faculty of Medicine, Charles University, and Institute of Dental Research in Prague

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    Formula Type Components Tm Cpolyester

    MylarPhthalic acids Instruments, matrices

    polycarbonate (Bisphenol A)phosgene

    Artificial teeth,Veneering shells,

    Prefabricated crowns,orthodontic brackets

    ~[CO(CH2)4CO-NH(CH2)6NH]n~

    polyamideNylon 66

    HO2C-(CH2)4-CO2H

    H2N-(CH2)6-NH2

    Surgical suture materials

    ~[CO(CH2)5NH]n~polyamide

    Nylon 6Perlon

    Surgical suture materials

    polyamideKevlar

    para HO2C-C6H4-CO2H

    para H2N-C6H4-NH2

    Fibre reinforced splints

    Toluenediisocyanate

    HOCH2CH2OH Die materials

    Few common polymers

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    A. Stages of free radical polymerization

    1. Initiation/induction process starts- Primary radical formation

    In. + In. (activation)

    In. + M

    Addition of primary radical on the double bond of monomer

    T, h

    In-M.

    In - InInitiator Fr

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