POLYESTER First condensation polymer studied by Carothers in 1930

Mainly of 2 typesa) Saturated: used in synthetic fibers, films and molding applicationb) Unsaturated: used as laminating resin and glass-reinforced plastic

product

Special Polyesters- Polyethylene terephthalate- Polybutylene terephthalate- Polyarylates- Poly(Dihydroxymethylcyclohexyl terephthalate)

Various Techniques to produce Polyester :1. Self Condensation of ω-hydroxy acids

OH-R-COOH + OH-R-COOH etc.

ORCOORCOO

2. Condensation of polyhydroxy compounds with polybasic acids, e.g. a glycol with dicarboxylic acid

HO-R-OH + HOOC-R’-COOH + HO-R-OH

OROOCR’COORO + H2O

3. Ester Exchange:

R’OOC-R-COOR’ + HO-R”-OH

OOC-R’-COO-R”OO + R’OH

4. Ring Opening of Lactone e.g. ϵ-caprolactone with dihydroxy or trihydroxy initiator

RCOO

R O

C

O

5. Alcoholysis of acid chloride of a di-carboxylic acid with polyhydroxy alcohol:

ClOC-R-COCl + HO-R’-OH

OC-R-COOR’O + HCl

COMMON PROPERTIES IN POLYESTER

Chemical Weakness: susceptible to hydrolysis, ammonolysis and ester exchange leads to chain scission

Electrical Insulation at high frequency: Polarity of ester group adversely affect the high frequency electrical insulation properties

Proton acceptor ester group: allows interaction with other grouping either an inter- or an intra molecular nature.

Increases Flexibility and inter chain attraction

UNSATURATED POLYESTER LAMINATING RESINS

Polyester laminating resin are a) Viscous b) Pale yellow coloredc) Low degree of polymerization(~8 to 10)d) Produced from a glycol and di acid e) provide site of cross-linking

SELECTION OF RAW MATERIAL

C

HOOC

C

H H

COOH

C

HOOC

C

H COOH

H

HC CH

C CO

O O

Maleic Acid-used in conventional general

purpose resins

Fumaric Acid -preferred b/s of less corrosiveness, resins have greater heat resistance,

light coloured product

Maleic Anhydide

1. Di-acids:

2. Diols:

H3CHC CH2

OH OH

HO-CH2-CH2-O-CH2CH2-OH

1,2-Propylene Glycol

Diethylene Glycol

- Most important glycol- Give resin with less crystallinity- More compatible with styrene- More use of glycols higher in homologous series

gives product with more flexibility and greater water resistance

- They are sometime preferred when the product with

i. greater water absorption ii. inferior electrical properties

Are required.

3. Saturated Acid:

Function: to space out the double bond and thus reduces the cross link density

C

C

O

O

O

COOH

COOHPhthalic Anhydride

Provides an inflexible link and maintains rigidity- low price, and cheaper resins formed- Detrimental effect – reduces heat

resistance of laminates- Cystalline solid and Tm=131ᵒC.

Isophthalic acid (Tm=347ᵒC) Provides higher H.D.T. , Flexural

moduli, and better craze resistance also useful in preparation of resilient

gel coats provides better water and alkali

resistance as compared to phthalic anhydride.

HOOC-(CH2)4-COOHAdipic Acid:

When flexible resin is requires Used in gel coats

4. Diluents:

Styrene Low Price Compatibility Low viscosity Ease of use

MMA is sometime use in conjunction with Styrene for translucent sheeting

Vinyl toluene and diallyl phthalate is occasionally employed

H2C CH

OTHER SPECIAL MATERIALS FOR HEAT RESISTANCE RESIN:

HC

HCCH

HC

CH2

CH

CH

OC

CO

O

Nadic Anhydride

N N

N OH2C C

HCH2O

H2CC

HH2C

O

H2C

CH

CH2

Triallyl Cyanurate

POLYMERIZATION

Glycol + Diacids+ Saturated Acide.g. Propylene Glycol + Maleic Anhydride + Phthalic Acid

150-200 C at 6-12 hrs.⁰N2 , Xylene,

HC

HC

OC

CO

O

Maleic Anhydride

+H2CHO C

H

CH3

OH

Propylene Glycol

HC

HC COOH

C

O

OH2C C

H

CH3

OH

Polymer Formation

E.g.

HC

HC COOH

C

O

O CH

H2C OH

HC

HC

C

O

O

C

O

O

Propylene Glycol

Phthalic Anhydride

O CO

CH

HC C

O

O

CH3

CH

H2C OH

CH3

HC

H2C OH

CH3

CHH2C O

CH3

C

O

C

O

O CHH2C O

CH3

POLYESTER

CROSS-LINKING

At Room Temp(Cold Curing)

- BPO used as initiator

At elevated temperature

MEKP or cyclohexanone cobalt as a Accelerator

ROOH + Co2+ OH− + RO▪ + Co3+

ROOH + Co3+ ROO + H+ + Co2+

O O C

CH3

C2H5

OOH

C

CH3

C2H5

OOH

Methyl-Ethyl Keto Peroxide

O O

OOH OOH

Cyclohexanone peroxide

C

O

C

O

O O

Benzoyl Peroxide

Cross-linking by styrene and BPO as initiator

PROPERTIES

High chemical resistance Good insulation properties (low frequency) Thermally stable(~200⁰C) UV resistance Flame retardant

POLYESTER-GLASS-FIBER LAMINATES

APPLICATIONS Other applications include such - diverse items as chemical storage vessels,- chemical plant components,- swimming pools, - stacking chairs, - trays, - and sports equipment.

POLY(ETHYLENE TEREPHTHALATE) (PET)

PREPARATION Bulk condensation of monomers Terephthalic Acid or di-methyl

terephthalate, Ethylene glycol

HOOC COOH

Terephthalic Acid

H2C

H2C OHHO

Ethylene Gylcol

+

C

O

C

O

OH2C

H2C O

n

- H₂O

COMMERCIAL ROUTES Dimethyl terephthalate (DMT) is reacted with excess ethylene glycol

(mole ratio 1:2.1–2.2) at 150ᵒC. The output of the process is bis(hydroxyethyl) terephthalate (BHET).

The pre-polymerization step (250–280ᵒC, 2–3 kPa) follows in which BHET is polymerized to a degree of poymerization (DP) of up to 30.

The next step is the polycondensation process where the DP is further increased to 100 by heating under vacuum, the process conditions being 280–290ᵒC and 50–100 Pa.

Up to this stage, PET (poly ethylene terephthalate )is suitable for applications that do not require high molecular weight or high intrinsic viscosity [η], such as fibers and sheets.

Solid-state polymerization is used to further increase the DP to 150. The operating conditions are 200–240ᵒC at 100 kPa and 5–25 h.

Ester exchange and Polycondensation

PROPERTIES Virgin PET is produced at different specifications

because different applications require different properties.

Examples of intrinsic viscosity [η] for different applications are

a) recording tape 0.60, b) carbonated drink bottles 0.73–0.81, and c) industrial tire cord 0.85 dl gˉ 1.

PET granules can be processed in many ways depending on application and final product requirements.

SYNTHETIC FIBERPET is widely used in synthetic fibers designed to simulate wool cotton, or rayon, depending on the processing conditions. - They have good wash-and-wear properties - resistance to wrinkling. In the

Production of fiber: the molten polymer is extruded through spinnerets and rapidly cooled in air.The filaments thus formed are, however, largely amorphous and weak. They are therefore drawn at a temperature (80ᵒC) above Tg and finally heated at 190ᵒC under tension, whereby maximum molecular orientation, crystallinity, and dimensional stability are achieved.

The melting point of highly crystalline PET is 271ᵒC. Crystalline PET has - good resistance to water - Resistance to dilute mineral acids but is degraded by concentrated nitric and sulfuric acids. - It is soluble at normal temperatures only in proton donors which are capable of interaction

with the ester group, such as chlorinated and fluorinated acetic acids, phenols, and anhydrous hydrofluoric acid.

FILM FORM PET is also used in film form (Melinex, Mylar) and as a molding material. The manufacture of PET film

closely resembles the manufacture of fiber. Production of filma) The film is produced by quenching extruded sheet to the amorphous state and then reheating and stretching the sheet approximately threefold in the axial and transverse directions at 80–100ᵒC. To stabilize the biaxially oriented film, it is annealed under restraint at 180–210ᵒC. b) This operation increases the crystallinity of PET film and reduces its tendency to shrink on heating. The strength of PET in its oriented from is outstanding. Application of biaxially oriented PET film are in - capacitors, - For magnetic tape. - Due to its high strength and dimensional stability - of the polyester film use in x-ray and

photographic film - to a number of graphic art and drafting applications. - The film is also used in food packaging, including boil-in-bag food pouches. - Metallized polyester films have many uses as a decorative material.

BOTTLE MANUFACTURING In the late 1970s a) Beverages bottles: Producing carbonated beverages PET bottles by blow molding has gained prominence (particularly in the United States) because PET has low permeability to carbon dioxide. b) Bottles for various purposes: The process has been extended, particularly in Europe, to produce bottles for other purposes, such as fruit juice concentrates and sauces, wide-necked jars for coffee, and other materials.

c) Material for microwave: Because of its excellent thermal stability, PET is also used material for microwave and conventional ovens.

COPOLYMER OF PET PET copolymer, such as isphthalic acid modified PET, rather than homopolymer

PET. PET bottles are normally made from copolymer PET because of its - lower crystallinity, - improved ductitlity,- better process ability, and - better clarity.

POLY(BUTYLENE TEREPHTHALATE) (PBT)

PREPARATION :

HO (CH2)4 OH

Butan-1,4-diolH3COOC COOCH3

Dimethyl-terephthalate

+

C

O

C

O

OH2C O

4

PBT

- CH3OH

PROPERTIES Thermal Properties- B/s of the longer sequence of methylene groups in polymeric chains leads to both more flexibility and less polarity than PET. - This leads to lower values for Tm (about 224ᵒC) and Tg (22–43ᵒC).- The low Tg facilitates rapid crystallization when cooling in the mold, and this

allows short injection-molding cycles and high injection speeds. Other Propertieso dimensional stability, o particularly in water, and its resistance to hydrocarbon oils without showing

stress cracking.o high mechanical strengtho excellent electrical propertieso relatively low heat-deflection temperature 130ᵒF (54ᵒC) at 264 psi (1.8 MPa). o The low water absorption of PBT—less than 0.1% after 24-h immersion—is

outstanding.

o Both dimensional stability and electrical properties are retained under conditions of high humidity.

o The lubricity of the resin results in outstanding wear resistance.

APPLICATION pump housings, impellers, bearing bushings, gear wheels, automotive exterior and under-the-hood parts, and electrical parts such as connectors and fuse cases.

Aromatic Polyester- Homopolymer- Co-polyester

AROMATIC POLYESTERHistory: In the 1960s the Carborundum Company introduced the homopolymer of p-hydroxybenzoic acid under the trade name Ekonol. It is used in plasma coating.

Production by the self-ester exchange of the phenyl ester of p-hydroxybenzoic acid.

HO C O C6H5

O

-C6H5OHO C

O n

Phenyl ester of p-hydroxybenzoic acid Homopolymer of p-hydroxybenzoic acid

PROPERTIES: Average mol. wt. 8000–12,000 Da. insoluble in dilute acids and bases and all solvents up to their

boiling points. Tm=500ᵒC and is difficult to fabricate. It can be shaped only by hammering (like a metal), by impact

molding and by pressure sintering (420ᵒC at 35 MPa). The difficulty in fabrication has severely limited the wider

application of these polymers. Available as a finely divided powder in several grades, based

on particle size. The average particle size ranges from 35 to 80 μm.

BLEND WITH OTHER POWDERSA. Blend with metals: metals, such as bronze, aluminum, and nickel-

chrome.Applications: - flame-spray compounds. - Plasma sprayed coatings -thermally stable, self-lubricating, and wear

and corrosion resistant.- abradable seals for jet aircraft engine parts.

B. Blended up to 25% with PTFE. Such blends have good temperature and wear resistance and are self-lubricating. Applications include seals, bearings, and rotors.

COPOLYMERIC AROMATIC POLYESTERS

E.g. Polyarylates, are copolyester of terephthalic acid, isophthalic acid and bisphenol A in the ratio of 1:1:2.

COOHHOOC CHO OH

CH3

CH3

COOHHOOC

Terephthalic Acid(1)

Isophthalic Acid(1)

Bisphenol A(2)

O CCH3

CH3

O CO

CO

O C O CO

C

O

CH3

CH3 n

Polyarylates

PROPERTIES Two isomeric acid (Isophthalic and Terephthalic acid) leads to an

irregular chain which inhibits crystallization.

Due to this, it is processed at much lower temperatures than would be possible with a crystalline homopolymer. Nevertheless the high aromatic content of these polyesters ensures a high Tg (~90ᵒC).

The polymer is self-extinguishing - limiting oxygen index of 34- a self-ignition temperature of 545ᵒC- HDT under load (1.8 MPa) is about 175ᵒC

OPTICAL AND MECHANICAL PROPERTIES

good optical properties - luminous light transmission 84–88%- 1–2% haze- refractive index 1.61

high impact strength between that PC and Psulfone exceptionally high level of recovery after deformation (important in

applications such as clips and snap fasteners) good toughness at both elevated and low temperatures with very little notch sensitivity, and high abrasion resistance which is

superior to that of polycarbonates.

WEATHERABILITY AND FLAMMABILITY

Polyarylates weatherability and flammability (high oxygen index, low flame spread) are inherent and are achieved without additives.

The weatherability properties therefore do not deteriorate significantly with time. (Tests show that over 5000 h of accelerated weathering results in virtually no change in performance with respect to luminous light transmittance, haze, gloss, yellowness, and impact.)

Having no flame-retardant additives, the combustion products of polyarylate are only carbon dioxide, carbonmonoxide, and water, with no formation of toxic gas.

LIQUID CRYSTALLINE POLYMER Different approach: polymers with good melt processability coupled

with high softening point

trade names Vectra (Celanese) and Xydar (Dartco Manufacturing)

the retention of liquid crystalline order in the melt gives lower melt viscosities than would otherwise be achieved.

Heat distortion temperatures are also in the high range of 180–240ᵒC . LCPs have thus heralded a new era of readily molded engineering and electrical parts for high temperature use.

WHOLLY AROMATIC COPOLYESTER

Introduced in late 1984 by Dartco manufacturing under the trade name Xydar.

Xydar injection molded resin is based on terephthalic acid, p,p’-dihydroxybiphenyl, and p-hydroxybenzoic acid.

PROPERTIES OF POLYESTER OF THIS CLASS

Melt Viscosity- Long rigid chains undergo parallel ordering in melt resulting in a) low melt viscosity b) good injection-molding characteristics at high Tm i.e. 400-430ᵒC.

Mechanical Strength - The melt solidifies to form highly packed fibrous chains in molded parts which gives

exceptionally physical propertiesa) Tensile modulus = 2.4×106 psi. (16500 MPa) at room temperature = 1.2×106 psi. (8300 MPa) at 300ᵒC.b) Tensile strength = 138 MPa and Compressive strength = 41 MPa

Thermal Properties:- Thermal oxidative stability outstanding- Decomposition temperature under N2 =560-570ᵒC.

- Inherently flame retardant- Oxygen index= 42- Smoke generation is extremely low

Chemical Properties- Extremely inert substance- i.e. resistance towards acids, solvents, boiling solvent and

hydrocarbon.- but attacked by concentrated acids and boiling caustic- Can withstand with high level of UV irradiation- Transparent to microwave.