Modern Materials: Polymers and Biomaterialscourses.chem.psu.edu/chem112/Summer/Lecture...

Modern Materials:Polymers and Biomaterials

Chapter 12

Supplementary Reading on Polymers

h // h d / h / i l / l h lhttp://courses.chem.psu.edu/chem112/materials/polymers.html

MJ Bojan CHEM 112 Polymers and BioMaterials 1

Polymers:Polymers: High molecular weight materials formed from many small molecules called monomers

Examples of polymers: plastics DNA proteins rubberExamples of polymers: plastics, DNA, proteins, rubber

How can we understand this important group of molecules?p g p

Structure affects function


Most polymers are formed via one of these types of reaction

Polymer Synthesis

of reaction.

1. Addition polymersMonomer containing a double bond polymerizes via addition reactionPolyethylene, PolystyreneRubber cross‐linking

2. Ring openingCyclic monomer opens to form a linear chain(e.g. polymerization of sulfur)

d l3. Condensation polymerspolymers form via condensation reaction, a small molecule(H2O, HCl, CO2) is eliminated in the reaction

CHEM 112 Polymers and BioMaterials

Silicone polymers, Polyurethanes, Nylon, Proteins

MJ Bojan 3

Synthesis of ADDITION POLYMERS: Synthesis of ADDITION POLYMERS: Double bond opens up, two electrons are used to form two new C‐C single bonds

connecting monomers.

C C

H H

C C

H H

C C

H Hethylene monomers C C

H H

C C

H H

C C

H H

monomers

C C C C C C

H

*

H H H H H

*polyethylene

C C C C C C

H

*

H H H H H

*


Synthesis of ADDITION POLYMERS: Synthesis of ADDITION POLYMERS: By modifying the monomer a variety of polymers can be

made.

H H

H H

CCCH2 CH2

nethylene polyethylene(gladwrap)

F F

CC

F FCF2 CF2

n H Cl

CC

H HCH2 CH

nCl

H HCH2 C

tetrafluoroethylene Teflon,TFalCl

CC

H CH3CH2 C

CH3

vinyl chloride polyvinyl chloride(PVC)

H

CC 2 CH

n

t

H C

CC C

nC

O

OCH3

O OCH3

methyl methacrylate MMA l MMA (Pl i l )


stryrene polystyrene(Styrofoam) methyl methacrylate MMA polyMMA (Plexiglass)

Rubber is an example of a naturally occurring addition polymeraddition polymer.

Problem


Ring Opening Polymerization: a cyclic monomer opens to form a linear chainform a linear chain

Condensation Polymerization: Two molecules join to form l l l b l f ll l l ha larger molecule by elimination of a small molecule such

as water


Ethers, Esters, and Amides are formed via d i icondensation reactions:

alcohol + alcohol → ether + water

R−O−H + H−O−R’ → R−O−R’ + H2O

carboxylic acid + alcohol → ester + watercarboxylic acid + alcohol → ester + water

+ H−O−R’ → + H2OCO

R OHCO

R OR'

carboxylic acid + amine → amide + water

R OH

O+ → + H2O

CO

R OH

N HR

H CO

R NHR'


Polyesters and polyamides are formed via condensation reactions.condensation reactions.

Each monomer has two functional groupstwo functional groups.

OO

C(CH2)4

CN (CH2)6 N

H

H

Nylon 6,6 (polyamide)


There are several classifications or types of Polymers. There are several classifications or types of Polymers.

Plastic: materials that can be formed into shapes.p

Thermoplastic: materials that can be shaped more than once.

Thermosetting plastic: material that can only be shaped once.

Elastomer: material that is elastic in some way. If a moderate amount of deforming force is added, the elastomer will return to its original h U f l f fibshape. Useful for fibers.


Properties of Polymers depend on their structure an bonding

Properties depend on:

1) Structure orientation of chains

bonding.

1) Structure, orientation of chains

2) Identity of side groups

3) Chain length3) Chain length

4) Degree of cross‐linking


Degree of crystallinity is the amount of ordering in a polymer

Polymer chains tend to be flexible and easily entangled or folded; tend to be disordered

− hard to crystallize; often amorphousCrystallinity affects

− hard to crystallize; often amorphous physical properties:crystalline polymers are stiffer, harder, morestiffer, harder, more

dense

Crystallinity affects optical properties:1) Amorphous polymers are transparent (glasslike)2) Partly crystalline and partly glassy polymers are translucent) y y p y g y p y

Side chains


There are ways to Increase order or crystallinity in a polymer

Interactions between chains of a polymer lend elements of order to the structure of

polymers.

Stretching (or extruding) the polymer chains as they form can increase the amount of order, leading to a greater degree of crystallinity in the polymer.y y p y

MJ Bojan CHEM 112 Polymers and BioMaterials

Average molecular mass affects degree of crystallinitycrystallinity.

low and high density polyethylene

LDPE: average molecular mass of 104 amu

Sodium polyacrylate:HDPE: average molecular mass of 106 amu

C C

O- -O

OO

CH2

CHCH2

CHCH2

C C

better known as…


Polymer properties can be modified by crosslinking polymer chains togethercrosslinking polymer chains together.

• Crosslinking: covalent bonds between chains: increases stiffness, strengthstrengthExamples: rubber, Silicone

• Metal ions can serve as cross‐linking agentsMetal ions can serve as cross linking agentsExample: Sodium alginate

• Intermolecular forces can hold polymer chains together:Intermolecular forces can hold polymer chains together:a) LDF’s hold chains in nonpolar polymers together:

Polyethylene, polypropyleneb) Dipole dipole forces: PVCb) Dipole‐dipole forces: PVCc) H‐bonding PVA

plays an important role in biological polymersDNA ProteinsDNA, Proteins,


Cross linking with covalent bonds formed between chains make the polymer stiffer; more crystalline

Example: Vulcanization of Rubber• Natural rubber is too soft and chemically reactive to make a useful material.

B l i i th bb ( li ki th h i ith lf ) f l• By vulcanizing the rubber (crosslinking the chains with sulfur) useful materials are made.

S8

Isoprene

8

heat

(monomer) Natural rubber(gummy)

Cross‐linked rubber(tough elastomer)


Silicones represent a different kind of polymer: based on silicon rather than carbonbased on silicon rather than carbon.

Silicones are chains of alternating silicon and oxygen atoms with organic substituents on the siliconorganic substituents on the silicon.

Monomer: R2SiCl2silicon compound with organic groups (R) attached.

Formed via Condensation reaction

E lExample:

dichlorodimethylsilane [(CH3)2SiCl2] with water (H2O).

The silicone formed is dimethylsiloxaneThe silicone formed is dimethylsiloxane.


By changing the R group, the properties of the polymer are changedchanged.

Properties of SiliconesNontoxic, stable (unreactive)

Properties depend on:1) R‐group Nontoxic, stable (unreactive)

flame resistanthydrocarbon substituents act to

repel water.

1) R group2) Chain length3) Degree of cross‐linking

– No crosslinks: liquid silicone oils repel water.Silicones are either rubbers or oils

depending on the chain length and degree of cross‐linking.

No crosslinks: liquid silicone oilshigh T lubricants, hot oil baths

– Few cross links; silicone rubber

Uses:Lubricants

g g– Few cross links; silicone rubbercaulking material

More cross links: silicone resins LubricantsCar polishGaskets, sealantsWaterproofing (organic groups form

– More cross links: silicone resinscoatings and adhesives

All li k SiO t barrier)


– All cross links: SiO2 = quartz

Metal ions can serve as cross‐linking agents

Gummy worms: polymer of Sodium alginateGummy worms: polymer of Sodium alginate

Alginate is a polysaccharide found in seaweed: (It’s edible!)

Used to thicken food (like milkshakes)Used to thicken food (like milkshakes)

To make gummy worms:

add crosslinker: CaCl2add crosslinker: CaCl2

Ca+2 ions hold chains together.


Intermolecular forces can hold polymer chains together:

linear chain polymer

Polyvinylalcohol (PVA) is an Addition Polymer

catalyst CH2 CH2

vinyl alcohol

polymer

x = 103 ‐ 104heat

CH CH

OH OHx

vinyl alcoholpoly(vinyl alcohol)

Add a cross‐linker: borax B4O72−(forms H‐bonding crosslink)

+ B 4O72−

viscoelasticMJ Bojan CHEM 112 Polymers and BioMaterials 20

Biological Polymers: Proteins are polyamides.

Th i idThe monomers are amino acids:React via condensation polymerization

H H

N C C

H

H

H O

OH

N C C

H

H

H O

OH

N C C

H

H

H O

OH

+ +

HR

OH HR

OH HR

OH

N C C

H

*

H O

HN C C

H O

*

H

RN C C

R OH

R

ProteinProtein

amide linkage or peptide bondMJ Bojan 21

The sequence of amino acids is the primary structure of the protein.

Secondary structure of proteins:

Alpha helices and beta sheets

Tertiary structure (protein folding) is even more complex. This structure is important in protein activity.p p y


Biological Polymers DNA and RNA are polyesters (of H3PO4).

The monomers are nucleotidesReact via condensation polymerization

( 3 4)

p y

MMonomer; nucleotide

Polymer; polynucleotide


The DNA and RNA strands are held together byH‐ bonds.

Bases are paired


Biomaterials:Biomaterials: are any materials that have biomedical applications.applications.

For example, the materials that are used to fill teeth are biomaterials.

Characteristics of Biomaterials

The biomaterials must be biocompatible:The body’s immune system must not attack th bi t i lthe biomaterial.

Physical requirements:Biomaterials must be created for a specific environment.

Artificial heart valves must open and close 70 to 80 times per minuteArtificial heart valves must open and close 70 to 80 times per minute.

Chemical requirements:

Biomaterials must be of medical grade.g

Polymers are very important biomaterials: beware of fillers, stabilizers, etc.


The different The different types of types of Polymers have bio applications. Polymers have bio applications.

Plastic: materials that can be formed into shapes.

Thermoplastic: materials that can be shaped more than once. (Used as replacements for blood vessels.)

Thermosetting: materials that can only be shaped once (Used in dental devices, and orthopedics such as hip replacements.)

Elastomer: material that is elastic in some way. If a moderate amount of deforming force is added, the elastomer will return to its original shape. Used as catheters, and for covering leads on implanted electronics, like pacemaker.

CHEM 112 Polymers and BioMaterials

, p

MJ Bojan 26

Examples of Biomaterial Applications

Polymers are be used in many biological applications.

Heart Replacement and Repairs:

Polyethylene terephthalate called Dacron™Polyethylene terephthalate, called Dacron™, is often used in the manufacture of artificial heart valves.

Dacron™ is used because tissue will grow through a polyester mesh.

Vascular grafts: A vascular graft is the replacement forg A vascular graft is the replacement for a piece of blood vessel.

Dacron™ is used for large arteries.

C C

F F

**

Polytetrafluoroethylene, is used for smaller vascular grafts.

F F


Artificial Tissue:

Polymers are be used in many biological applications.

• Artificial skin, which is grown in the laboratory, is used to treat patients with extensive skin loss.

• The challenge with growing artificial skin is• The challenge with growing artificial skin is getting the cells to align properly.

• Therefore a scaffold must be used for the cells.• The most successful scaffold is lactic acid‐

glycolic acid copolymer.

Hip Replacements:

• About 200 000 total hip replacements are performed each year• About 200,000 total hip replacements are performed each year.

• A metal ball, a cobalt chromium alloy, is often used in a hip replacement.

• This alloy is attached to a titanium alloy and cemented using a tough thermoset

polymer.

• The acetabulum, which accommodates the femur, is lined with a polyethylene layer


Modern Materials: Polymers and Biomaterialscourses.chem.psu.edu/chem112/Summer/Lecture...

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