Modified polyester polymers

Details Modified polyester polymers Modified polyester polymers

1995-01-12

1999-08-17

Acquah, Samuel A.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

528272, 528274, 528285, 528286, 528308, 5283086, 2643281, 26432814, 26432818, 26433111, C08G 6316

Patent

active

059395168

DESCRIPTION:

BRIEF SUMMARY
This invention relates to modified polyethylene terephthalate polymers and copolymers, to a method of making such polymers and copolymers, in particular which enables an improved manufacturing process, to the use of such polymers in the manufacture of bottles and bottle preforms, particularly as made by and in injection blow moulding processes, and to carbonated soft drinks and mineral water bottles and preforms for such bottles made using such polymers.
Polyethylene terephthalate (PET) is made by the condensation polymerisation of a terephthalate material with an ethylene glycol material, with the net elimination of a low molecular weight hydroxylic species. The simplest chemistry is the direct polyesterification reaction between terephthalic acid and ethylene glycol with the elimination of water. Other routes, differing in the detail of the chemistry include those starting from dimethyl terephthalate and ethylene glycol, with the elimination of methanol initially and subsequently ethylene glycol and water or from low molecular weight oligomers compositionally approximating to bis(2-hydroxyethyl) terephthalate with the elimination of ethylene glycol and water. Bis(2-hydroxyethyl) terephthalate is nominally the diester of one mole of terephthalic acid with two moles of ethylene glycol. The material typically used in PET manufacture is made by esterifying terephthalic acid and ethylene glycol at a molar ratio of about 1:1.05 to 1:1.7, typically 1:1.15 to 1:3--and removing from about 1.5 to 2 molar parts of water. This yields a mixture of compounds believed to include mono-esters the true bis(2-hydroxy-ethyl) terephthalate diester and low molecular weight oligomers. The mean degree of polymerisation (here referring to the number of ethylene terephthalate residues in the oligomer) of the mixture is typically from 2.5 to 5. This oligomer is commonly referred to as bis(2-hydroxyethyl) terephthalate as if it were a true monomer or simply using the term `monomer`.
Although water may be nominally absent, in fact, it will usually be present as residual moisture in the starting materials or as generated by reactions. Current techniques for the manufacture of high molecular weight polyethylene terephthalate polymers e.g. for use in the manufacture of carbonated drinks (CSD) bottles, carbonated or still mineral water bottles, or highly oriented film products, use a polymerisation method which includes an initial melt phase polymerisation, which usually generates an intermediate polymer, followed by solid phase polymerisation, with the removal of ethylene glycol (mainly) and water (trace). The intermediate polymer is typically mainly glycol ended and has a degree of polymerisation of about 100.
Such two step processes are used because melt phase polymerisation is ultimately diffusion limited and this reduces the rate of removal of the low molecular weight hydroxylic product and thus the molecular weight (usually expressed as polymer viscosity) obtainable, in practice, in the melt. The desired higher molecular weights can be obtained by melt phase polymerisation using extended reaction times, which is economically unattractive, or by using relatively higher reaction temperatures. However, at such high reaction temperatures, side reactions yielding acetaldehyde or other undesirable materials take place more readily and the contaminant products are undesirable, particularly in products intended for food contact applications such as bottles for carbonated drinks. The use of solid phase polymerisation enables the further reaction to be carried out at lower temperatures thus reducing the extent of undesired side reactions.
At the end of melt phase polymerisation, the intermediate polymer is extruded and cut into pellets. As the cooling rates in extrusion are fairly high, the solid pellet product is typically amorphous. The solid phase polymerisation step includes the conversion of the polymer into a crystalline form and continues the polymerisation until the desired, somewhat higher, molecular weight is reached. The rate of

REFERENCES:
patent: 4219527 (1980-08-01), Edelman et al.
patent: 4234708 (1980-11-01), Edelman et al.
patent: 5239045 (1993-08-01), Hirahara et al.

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