Chain extenders are used for used for improving the melt-strength for EBM grade PET and also used in PCR PET flakes moulding to minimize the IV drop. SSP accelerators are used to reduce the SSP time by increasing IV fast Hope the document may help for Polyester R&D chemist

1. 25.05.2015
CHAIN EXTENDERS
Chainextenders(orcouplingagents) canserve to reversethe MW damagecaused by hydrolysisof
polyestersor can modify therheology of the polymerto increaseits melt strength.
Pyromelliticdianhydride (PMDA)
The mostcommon chain extendersarethe dianhydrides (alsoknownastetracarboxylicdianhydrides).
The most commonof these ispyromelliticdianhydride(PMDA).The lattercanbe usedinsynergistic
combinationswithhinderedphenolicaromaticphosphatessuchasIRGANOX1425 manufacturedby
CibaGeigyThe hinderedphenolicaromaticphosphateisusedatlevelsof 0.1–2.5 wt%.The hindered
phenolicaromaticphosphate isanadvantageousco-synergistsince itservesbothasa solid-state-
polymerizationcatalyst andaheatstabilizertoprotectthe PET fromoxidationduringsolid-state
polymerization.
Anotherhighlyeffectchainextenderistrimelliticanhydride (TMA) whichgivesrise tobranchingof the
PET structure.
Figure 14.1 Reactionof pyromelliticdianhydride (PMDA) chainextenderwithPETendgroups(hydroxyl
and carboxylicacidgroups) togive chainextensionandbranchingof PET

2. PMDA isan effective chainextensionadditive forthermoplasticpolyesterssuchasPET andPBT. It is
suitable forthe followingapplications:
 Enhancementof the intrinsicviscosityof PETand PBT
 Reactive extrusionof PETand PBT
 Melt strengthenhancement of PETand PBT for the productionof blownpolyesterfoams
 As a meltviscosityandmelt-strength-enhancingadditive formodifyingPETforfilmblowingand
extrusion blowmoulding applications
 Tensile strengthenhancementof PETandPBT for strappingapplicationswithoutthe needfor
solid-state polycondensation
 Upgradingof recycledPETflake toresinsuitable forbottlingapplications(>0.80dL/g)
 As an additive toreduce the time necessaryforsolid-phase polymerizationof PETandPBT
resins
 To increase the elongational viscosityof PETandPBT resinsbyfacilitatingextendedand
branchedarchitectures
One of the maincommercial usesof PMDA is to improve the meltstrength
PHENYLENEBISOXAZOLINE
Both 1,3-phenylenebisoxazoline (1,3-PBO)and1,4-phenylenebisoxazoline (1,4-PBO) are effectivechain
extenders
PBO isa veryreactive compoundtowardsPETcontainingcarboxyl endgroupsbutnothydroxyl end
groups. PBO alsoacts as a carboxyl groupscavengerandindoingso increasesthe hydrolyticstabilityof
the resultantPET.

3. SSP ACCELERATOR
Solid-state polycondensationof PETis bothtime-consumingandenergy-intensive.Recently,additives
have beendevelopedtoaccelerate thisprocess SuchadditivesenablePETwitha veryhighIV to be
producedat reducedresidence timesinthe solid-state reactor,withenhancedoutputsandata reduced
cost. Suchadditivesacceleratethe IV enhancementof PETat low cost. One suchSSP acceleratoris
Irgamod1425 whichwhenusedinPET at levelsof between0.1–0.5 wt%givesanSSP accelerationof
approximately50%
Effectof a commercial solid-statingaccelerator(Irgamod1425) on the rate of intrinsicviscosity
enhancementof PET
Irgamod1425 alsocontributes to reduced yellowingofthe PET resin

4. Nucleating agents for PET
Quickcoolingof the PET meltresultsinthe formationof small spherulitesbutthe crystallinity,however,
remainslowbecause the polymerispractically‘frozen’initsamorphousstate.Slow coolingof the PET,
on the otherhand,leadsto a highdegree of crystallinity;however,the spherulitesgrow toa large size at
whichoptimummechanical propertiesare notattained.Inaddition,anunevenspherulitesize
distributionresults.Achievingahighdegree of crystallinityandsmall spherulitesinPETsimultaneously
requiresthe use of nucleatingagentsandcrystallizationpromoters.
NucleatingagentsinPETserve twomainfunctions,asfollows:
• To induce asmall and regularcrystalline structure.
• To suppresslarge crystal growthwhichcauses brittleness.
Additional functionsof the nucleatingsysteminclude the following:
• To decrease demouldingtime (i.e.decrease cycle time forthe part).
• To allowthe material tocrystallize atauniformrate in the mouldwhichtendstoresultinlower
moulded-instresses.
The nucleatingsystemforcommercial PETinjectionmouldingcompoundsisthustypicallybasedona
three-componentpackage comprisingthe following:
(i) sodiumstearate (chemical nucleatingagent)
(ii) sodiumionomer(melt-miscible nucleatingagent)
(iii) poly(etherester) (plasticizertofacilitate chainfolding)
Dr. K MuniswamyReddy