End capping of polyester oligomers. which may used as plasticizer for PVC, used as nucleating agent in Polyester synthesis etc..

1. End capping Technology
We can do endcappingof both –OH groupsand –COOH Groups:
-OH Group endcapping
For –OH groups of MEG can be
endcappedby usingthe
followingchemicals.
1) Napthalinicacid
2) Benzoicacid
3) StearicAcid
4) Or any monocarboxylic
Acidcompound
_COOH group end capping…
COOH groups can end capped by usingthe
following
 Ethylene or propylene carbonate
 phenylene-bis-oxazoline (2,2'-1, 3-
phenylene-bis(2-oxazoline)
 Dicyclohexyl carbodiimide
 Sodium methoxide or sodiummethylate
 Alkylacetylacetonate( Ex. Methyl
acetylacetonate)
 N-Benzoyl-E-Caprolactam
 1-morpholino-1-cyclohexene
 1-methyl imidazole
 Monocyclic imino ether compound
 Epoxy compounds
Polyesterendcapping
-OH groupendcappingwill be usedforthe
stoppingpolymerizationatrequiredIV.
Why because,inpolycondensationreaction
ethylene glycol endgrouponlyreacttoincrease
the MW (not–COOH groups)
Eventhoughwe endcap –COOH group,
polymerization will continue throughthe
ethylene glycol endgroups.
If we endcap bothside of -OHgroup,there is
no chance to undergo furtherpolymerization. –
OH endcappedpolymercanadd at any stage of
reactionbecause itwasalreadyblockedboth
side –OH groups;it won’treact farther;it will
workas a plasticizerandnucleatingagent.
AfterPC,there are veryfew –COOH
endgroups(<35 meg/ton).
It may create hydrolyticdegradation
or oxidative degradation.For
avoidingsuchdegradationgenerally –
cooh groupswill be endcapped.
evenif we added_COOH endcapped
polymeratthe endof EI or PC againit
will reactthroughethyleneglycol end
groupand increase the IV. It won’t
workas a nucleatingagent.

3. AfterEsterification,the followingpolymerchainsare inreactor
1) Both side Hydroxyl groupterminatedoligomers(min90%)
2) One side Hydroxyl groupterminatedandotherside –COOHterminatedoligomer(max 10%)
3) Both side –COOHterminatedoligomer(veryfew,notmore than1%)
Esterificationwascarriedout@ 240 to 250 deg C undervacuum.
The above condition -COOHgroupsof PTA react withMEG to form BHET, but undervacuum –COOH
cannot react with –OH groupof MEG. (undervacuumMEG will be removedveryquicklysothat MEG
has no time toreact with –COOH groups)
At the endpolycondenzation:
The resincontains
1) Both side Hydroxyl groupterminatedpolymerchain(more than95%)
2) One side Hydroxyl groupterminatedandotherside –COOHterminatedpolymerchain(veryfew,
lessthan3%)
Polycondenzationwascarriedout@280 to 290 degC underveryfine vacuum
In polycondenzationreaction,polymerizationwashappedasfollows
Hydroxyl groupterminatedpolymerchainscanonlyinvolvedinthe polycondenzationreactionandgive
MEG as by product. –COOH terminatedpolymerchaincannotmore reactive inpolycondenzation
reaction