Optical quality polycarbonates with reduced static charge and method for making same

DETAILED DESCRIPTION OF THE INVENTION Polycarbonate resins are prepared in a melt process by the reaction of a diaryl carbonate and a dihydric phenol in the presence of a basic catalyst.
Commonly, the diaryl carbonate is diphenyl carbonate and the dihydric alcohol is bisphenol A, and these reactants will be used for exemplary purposes throughout the present application.
Many alternative materials have been proposed for use in preparing polycarbonates, however, and the utilization of such alternative materials is intended to be within the scope of the present invention.
When diphenyl carbonate reacts with bisphenol A, it produces a growing polymer having a reactive hydroxyl group which is available for the continued growth of the polymer chain.
When an alternative reaction occurs which results in the incorporation of a moiety without this reactive hydroxyl group, the ability of the chain to continue the chain extension is terminated.
Chains with terminal groups of this type are said to be endcapped.
A variety of endcapping reagents have been disclosed in the art, including those described in U.
S.
Pat.
Nos.
4,774,315, 5,028,690, 5,043,203, 5,644,017 and 5,668,202 which are incorporated herein by reference.
In general such endcapping reagents are utilized when producing polycarbonates by interfacial processes, rather than melt processes because they can introduce complications to the recovery of various product and recycle streams.
In melt processes, therefore, endcapping generally results from the reaction of the extending polymer with free phenol, which is released as a by-product of the polymerization reaction.
The endcapping level of a polycarbonate resin can be expressed a percentage value, by determining the number of chains which are terminated with a reactive hydroxyl group (uncapped) and then taking the remainder of the chain ends as being capped.
Such a determination can be made using spectroscopic measurements.
The level of endcapping (E/C%) is then given by the formula: E/C%=(capped chain ends/total chain ends) X 100 Normal melt processing reaction conditions produce polycarbonate resin products with an endcap level in the range of 80-85%