introduction to polymer AND acrylic resin

lecture given 3/2/2026

what are the parts of the material properties pyramid?

properties, processing, composition, structure

what kinds of things are made of polymers?

plastics, rubber, elastomer, fiber, foam, composite, adhesive, glue, paint

a polymer has a molecular weight of over…

5000

what was the first use of polymer in dentistry, and what is the most recent advancement?

1901- study on polymethylmethacrylate denture

2023- first 3DP high ceramic filled composite

methane

CH4

ethane

CH3CH3

butane

CH3CH2CH2CH3

hexane

C3(CH2)8CH3

addition

R* + C=C → R-C-C*

condensation

a-R-a + b-R’-b → a-R-R’-b + a-b

a-b is usually an acid or water

what is the structure of a polymer?

chain

primary level of a polymer

configuration (sequence)

secondary level of polymer structure

conformation- a helix and b sheets

tertiary level of polymer structure

3D structure with multiple polymers

linear polymer chain structure

like spaghetti, linear structure with no networking

crosslinked polymer chain structure

like a net, has crosslinked chains

no melting point

amorphous polymers

have molecular chains arranged randomly with no long term order

they soften rather than melt suddenly

polystyrene

crystalline polymers

have a regular order or pattern of molecular arrangement

have a sharp melting point

HDPE is semi-crystalline

the glass transition appears to be a…

second order transition as the heat capacity and thermal expansion coefficient of the polymer undergo finite changes

the glass transition temperature depends on…

the rate of measurement

t/f we have a complete theoretical understanding of glass transition

false

a

glassy state

b

rubbery state or viscoelastic state

c

melt state

d

brittle

e

tough/soft

f

melt

Tg ___ Tm

<

in crystallizable polymer, Tg and Tm have a ____ correlation

rough

a melting temperature range is observed in all ________ polymers

semicrystalline

stronger intermolecular forces result in a(n) ______ in tm

increase

rigid chains have much higher…

tm

plastic working temperature ___ Tg

rubber working temperature ___ Tg

<, >

copolymer

polymer chain made by 2 or more monomers

linear homopolymer

base unit = repeating unit

statistical copolymer

base unit =/= repeating unit

alternating copolymer

2 base units = repearting unit

what type of copolymer are dental materials usually made of?

statistical copolymer

t/f polymer is typically a mixture of different sized molecules

true

Mn

number average molecular weight

Mw

weight average molecular weight

Mn < ____ < Mw < ___

Mv, Mz

polydispersity index (PDI)

Mw/Mn

threshold molecular weight value

TMWV- lowest molecular weight where the desired property value is achieved

the higher the molecular weight…

higher Tm, crystallinity, Tg, density, viscosity, wear resistance, strength

lower solubility

materials with higher PDI for same average Mn…

wider Tg range, lower surface hardness, lower Tm or soft point (Tg), lower tensile/tear/impact strength, lower brittleness, lower aging resistant, lower viscosity, higher creep

radical addition polymerization

R-C-C-R’ → R-C* + *C-R’ or R-C- + +C-R’ or R-C+ + -C-R’

R-C* + C=C → R-C-C-C*

R-C-C-C* + C=C → R-C-C-C-C-C*

what are the mechanisms of free radical polymerization?

induction (activation, initiation), propagation, termination chain transferring

induction

activation- fast, R-R’ → R. + R.’

initiation- slow, R. + MH → R-H + M.

propagation

fast, produces heat

termination

M. + M. → M-M

chain transferring

M. + M’H → M’. + MH

activation

free radicals can be generated by activation of radical producing molecules, ie initiator, using heat, redox reaction, and light

heat

commonly employed initiator is benzoyl peroxide (BPO) which is activated rapidly between 50-100C to release 2 free radicals per BPO molecule

redox chemical reaction

consists of 2 reactants, when mixed undergo reaction

eg tertiary amine (the activator) and benzoyl peroxide (the initiator)

visible light or ultraviolet light

camphorquinone (CQ) and an organic amine (dimethylaminoethyl-methacrylate) generate free radicals when irradiated by light in the blue or violet region

light is a wavelength of about 470mn is needed

initiation

free radicals formed by initiator open double or triple carbon bonds in the monomer

new free radicals with monomer structure form

slow reaction

propagation stage

rapid addition of monomer molecules to free radical- free electrons shifted to end of chain

the resulting free radical monomer complex acts as a new free radical center which is approached by another monomer to form a dimer, which also becomes a free radical

very fast reaction, exothermal

chain transfer stage

the active free radical of a growing chain is transferred to another molecule and a new free radical for further growth is created termination occurs in the latter

termination stage

reaction terminates when insufficient free radicals exist, reaction also may be stopped by any material that will react with free radical

can occur from chain transfer

addition polymerization reaction is terminated by: direct coupling of 2 free radical chain ends, exchange of hydrogen atom from one growing chain to another

this relates to the oxygen inhibited layer- terminated early because of oxygen

photo polymerization

the use of light source (light energy) in the preparation of polymers

photoinitiator

UV- irgacure 2959— 3D print, post curing

blue visible light: CQ, lucirin (TPO), PPD,

content- 05.-1% initiator in most commercial dental composite

shade issue- CQ is a yellowish compound

t/f european commission is banning TPO use

true

inhibitors

used to completely stop the conversion of monomer to polymer produced by accidental initiation during storage

phenols, quinones, or hydroxyquinones, or even molecular oxygen are employed to inhibit the polymerization

butylated hydroxytoluene is often used in dental composite

inhibitor effect

used in 3DP to prevent undesired polymerization of resin fluid

oxygen permeable sheet in carbon 3D

thermoplastic polymer has _____ structure

linear chain

polymer network density

a mechanical property

material property changes in resin polymerization

exothermal reaction

temperature increase

material property changes in resin polymerization

light absorption change

low translucent, shade change

material property changes in resin polymerization

volume shrinkage

shrinkage stress

material property changes in resin polymerization

viscosity increase

determine working time

material property changes in resin polymerization

modulus increase…

hardness and strength increase

what is the working time (s, minimum) and setting time (min, maximum) of restorative materials, self cure?

90, 5

what is the working time (s, minimum) and setting time (min, maximum) of restorative materials, dual cure?

90, 10

what is the working time (s, minimum) and setting time (min, maximum) of luting materials, self ans dual cure?

60, 10

what is the working time (s, minimum) of light cure materials?

none because you control the light

degree of conversion

the fraction of monomer’s functional group has been reacted in polymerization

auto acceleration effect / gel effect / trommsforff-norrish effect

a dangerous reaction behavior that can occur in free radical polymn system- high temp

a broadening of the molecular weight distribution (MWD) simultaneously occurs

pre-made CAD/CAM polymer/Composite

higher defree of conversion from pre-polymerization (done by manufacturing)

need to form a shape for final use by milling

not a ceramic even though there is a ceramic content (as filler)

what is this?

chain growth

what is this?

step growth

what type of materials go through step growth?

impression material

what type of materials go through chain growth?

adhesive cement, composite material

what type of growth is the blue line?

chain growth

what type of growth is the black line?

living chain growth

what type of growth is the red line?

step growth

what are examples of step growth polymerization?

polycarbonate chemistry, polyurethane chemistry, epoxy chemistry (endo materials)

what happens during silicone polymer condensation?

alcohol releases from the reaction mixture and contributes to the contraction/shrinkage of the impression

what happens during additive silicone setting reaction, and what is an example of additive silicone?

polyaddition- step growth polymerization

not polycondensation, no small molecules released, not free radical shrinkage, less shrinkage

PVS

photopolymer

a polymer that can be selectively cross-linked by radiation (UV, blue light)

normally composted by large molecular weight oligomer or monomers

from soluble to insoluble polymer, or the opposite way

used for 3D printing, electric circuit print, lithography, plate printing

vat polymerization

what post processing of 3D printed material is necessary?

cleaning/washing- remove adhered monomer resin

trimming- clean off the extra support structures

post curing- increase the degree of conversion

creep of polymer materials

the long term deformation of a polymer under a sustained or intermittent load at stresses below the yield point

may be partially or fully recovered with extended time

time dependent!

what is this?

creep compliance in stress strain curves

what do plasticizers do?

separate polymer chains

lower Tg, E, H, and increase toughness

polymer early stage degradation

polymer long chain may break down while the material is in the same dimension but deteriorate property

may release small molecules

higher water absorption

when engineering polymer, what is the goal?

improved mechanical and thermal properties, improved resistance to degradation, improved chemical resistance

polyaryletherketon (PAEK)

commercialized for industry in 1980s

high performance thermoplastic polymers

use for dental implants, framework, restoration

polyaryletheretherketone (PEEK) is one form

what are characteristics of PEEK?

elastic modulus 3.8 GPa, similar to bone

may be processed via injection molding, 3DP

can be used in metal free RPD

radiolucent- reduce artifact in CT

cannot be repaired, must be made once, bonding issue

what are acrylic polymer uses in dentistry?

denture bases and artificial teeth, denture liners and tissue conditioners, composite restorative and pit/fissure sealant, custom tray for impressions, temporary restoratives, mouth guards, maxillofacial prosthesis, veneers, cements and adhesives

what are acrylic acids made of?

acrylic acid (propenoic acid) and methacrylic acid