End capping Technology

We can do end capping of both –OH groups and –COOH Groups:

-OH Group end capping

For –OH groups of MEG can be end capped by using the following chemicals.

1) Napthalinic acid2) Benzoic acid3) Stearic Acid4) Or any mono carboxylic

Acid compound

_COOH group end capping…

COOH groups can end capped by using the following

Ethylene or propylene carbonate phenylene-bis-oxazoline (2, 2'-1, 3-

phenylene-bis(2-oxazoline) Dicyclohexyl carbodiimide Sodium methoxide or sodium methylate Alkylacetylacetonate ( Ex. Methyl

acetylacetonate) N-Benzoyl-E-Caprolactam 1-morpholino-1-cyclohexene 1-methyl imidazole Monocyclic imino ether compound Epoxy compounds

Polyester end capping

-OH group end capping will be used for the stopping polymerization at required IV.Why because, in polycondensation reaction ethylene glycol end group only react to increase the MW (not –COOH groups)

Even though we end cap –COOH group, polymerization will continue through the ethylene glycol endgroups.If we end cap both side of -OH group, there is no chance to undergo further polymerization. –OH end capped polymer can add at any stage of reaction because it was already blocked both side –OH groups; it won’t react farther; it will work as a plasticizer and nucleating agent.

After PC, there are very few –COOH end groups (<35 meg/ton).

It may create hydrolytic degradation or oxidative degradation. For avoiding such degradation generally –cooh groups will be end capped.

even if we added _COOH end capped polymer at the end of EI or PC again it will react through ethylene glycol end group and increase the IV. It won’t work as a nucleating agent.

After Esterification, the following polymer chains are in reactor

1) Both side Hydroxyl group terminated oligomers (min 90%)2) One side Hydroxyl group terminated and other side –COOH terminated oligomer (max 10%)3) Both side –COOH terminated oligomer (very few, not more than 1%)

Esterification was carried out @ 240 to 250 deg C under vacuum.

The above condition -COOH groups of PTA react with MEG to form BHET, but under vacuum –COOH cannot react with –OH group of MEG. (under vacuum MEG will be removed very quickly so that MEG has no time to react with –COOH groups)

At the end polycondenzation:

The resin contains

1) Both side Hydroxyl group terminated polymer chain (more than 95%)2) One side Hydroxyl group terminated and other side –COOH terminated polymer chain (very few,

less than 3%)

Polycondenzation was carried out @ 280 to 290 deg C under very fine vacuum

In polycondenzation reaction, polymerization was happed as follows

Hydroxyl group terminated polymer chains can only involved in the polycondenzation reaction and give MEG as by product. –COOH terminated polymer chain cannot more reactive in polycondenzation reaction