Process for preparation of copolymers from polyesters and aliphatic polyformals

DETAILED DESCRIPTION We claim: 1.
A process for preparing a copolymer having an inherent viscosity of at least 0.
4 measured at 25.
degree.
C.
using 0.
50 gram of polymer per 100 ml.
of a solvent composed of 60 volumes of phenol and 40 volumes of tetrachloroethane comprising contacting within a temperature range of about 220 to about 280.
degree.
C.
A.
a polyester comprised of 1.
a dicarboxylic acid which is at least 80 mole percent terephthalic acid, and 2.
a diol which is at least 80 mole percent 1,4-butanediol, and B.
based on the weight of the copolymer, from 10 to 60 weight percent of a polyformal having an inherent viscosity of at least 0.
05 measured at 25.
degree.
C.
using 0.
50 gram of polymer per 100 ml.
of a solvent composed of 60 volumes of phenol and 40 volumes of tetrachloroethane corresponding to the structure H--O--R--O--CH.
sub.
2 --O--R--OH wherein R is ##SPC5## a linear aliphatic divalent radical having 2 to 10 carbon atoms, or --R'--O--.
sub.
n R'-- where R' is a linear aliphatic divalent radical having 2 to 4 carbon atoms and n is an integer from 1 to 10.
2.
The process of claim 1 wherein the polyester is poly(tetramethylene terephalate).
3.
The process of claim 2 wherein the temperature range is 240.
degree.
-275.
degree.
C.
4.
The process of claim 3 wherein R is --CH.
sub.
2 CH.
sub.
2 CH.
sub.
2 CH.
sub.
2 CH.
sub.
2 CH.
sub.
2 --.
5.
A process for preparing a copolymer having an inherent viscosity of at least 0.
8 measured at 25.
degree.
C.
using 0.
50 gram of polymer per 100 ml.
of a solvent composed of 60 volumes of phenol and 40 volumes of tetrachloroethane comprising contacting within a temperature range of about 250.
degree.
to 255.
degree.
C.
, within a pressure range of about 0.
01 to 1.
0 mm Hg and for a time within the range of about 1 to 3 hours A.
poly(tetramethylene terephthalate) having an inherent viscosity of at least 0.
5 measured at 25.
degree.
C.
using 0.
50 gram of polymer per 100 ml.
of a solvent composed of 60 volumes of phenol and 40 volumes of tetrachloroethane, and B.
based on the weight of the copolymer, from 30 to 45 weight percent of 1,6-hexanediol polyformal having an inherent viscosity of at least 0