Copolyesters and molded articles comprising the same

A copolyester consisting essentially of terephthalic acid units, ethylene glycol units, and

• i) 0.5 to 7 mole %, based on the total moles of constituent units of said copolyester, of at least one group of bifunctional compound units (a.sub.2) selected from the group consisting of:
• a) diol units (I) of the following formula:
• ##STR13## wherein A is --CH.sub.2 CH.sub.2 -- or --CH(CH.sub.3)CH.sub.2 --, B is a divalent hydrocarbon group, a carbonyl group, a sulfonyl group, an oxygen atom or a bond, R.sup.1 and R.sup.2 are each, independently, an inert substituent, j and k are each independently an integer of 0 to 8, and s and t are each, independently, an integer of 0 to 4;
• and
• b) diol units (II) of the following formula:
• ##STR14## wherein A is --CH.sub.2 CH.sub.2 -- or --CH(CH.sub.3)CH.sub.2 --, R.sup.3 is an inert substituent, m and n are each, independently, an integer of 0 to 8, and u is an integer of 0 to 4;
• ii) 0.005 to 1 mole %, based on the total moles of constituent units of said copolyester, of multifunctional compound units (b.sub.1) derived from at least one multifunctional compound having at least 3 carboxyl groups, hydroxyl groups, and/or ester-forming groups thereof;
• and
• iii) monofunctional compound units (c) derived from at least one monofunctional compound selected from the group consisting of monocarboxylic acids, monohydric alcohols, and ester-forming derivatives thereof, in an amount satisfying the following formula (.alpha.):
• {2.times. (p-2).times.b.sub.1 }.gtoreq.c.gtoreq.{0.1.times.(p-2).times.b.sub.1 } (.alpha.)
• wherein:
• b.sub.1 =content (mole %) of units (b.sub.1)
• c=content (mole %) of units (c)
• p=average number of functional groups of said multifunctional compound deriving units (b.sub.1).

A copolyester consisting essentially of terephthalic acid units, ethylene glycol units, and

• i) 0.5 to 7 mole %, based on the total moles of constituent units of said copolyester, of at least one group of bifunctional compound units (a.sub.2) selected from the group consisting of:
• a) diol units (I) of the following formula:
• ##STR15## wherein A is --CH.sub.2 CH.sub.2 -- or --CH(CH.sub.3)CH.sub.2 --, B is a divalent hydrocarbon group, a carbonyl group, a sulfonyl group, an oxygen atom or a bond, R.sup.1 and R.sup.2 are each, independently, an inert substituent, j and k are each independently an integer of 0 to 8, and s and t are each, independently, an integer of 0 to 4;
• and
• b) diol units (II) of the following formula:
• ##STR16## wherein A is --CH.sub.2 CH.sub.2 -- or --CH(CH.sub.3)CH.sub.2 --, R.sup.3 is an inert substituent, m and n are each, independently, an integer of 0 to 8, and u is an integer of 0 to 4;
• and
• ii) 0.005 to 0.5 mole %, based on the total moles of constituent units of said copolyester, of multifunctional compound units (b.sub.2) derived from at least one multifunctional compound having at least 3 carboxyl groups, hydroxyl groups, and/or ester-forming groups thereof, at least one of said groups being carboxyl group or ester-forming group thereof;
• wherein said copolymer has an intrinsic viscosity of 1.0 to 1.4 dl/g.

A copolyester consisting essentially of terephthalic acid units, ethylene glycol units, and

• i) 0.5 to 7 mole %, based on the total moles of constituent units of said copolyester, of at least one group of bifunctional compound units (a.sub.2) selected from the group consisting of:
• a) diol units (I) of the following formula:
• ##STR17## wherein A is --CH.sub.2 CH.sub.2 -- or --CH(CH.sub.3)CH.sub.2 --, B is a divalent hydrocarbon group, a carbonyl group, a sulfonyl group, an oxygen atom or a bond, R.sup.1 and R.sup.2 are each, independently, an inert substituent, j and k are each independently an integer of 0 to 8, and s and t are each, independently, an integer of 0 to 4;
• and
• b) diol units (II) of the following formula:
• ##STR18## wherein A is --CH.sub.2 CH.sub.2 -- or --CH(CH.sub.3)CH.sub.2, R.sup.3 is an inert substituent, m and n are each, independently, an integer of 0 to 8, and u is an integer of 0 to 4;
• and
• ii) 0.005 to 0.5 mole %, based on the total moles of constituent units of said copolyester, of multifunctional compound units (b.sub.3) derived from at least one aliphatic or alicyclic multifunctional compound having at least 3 hydroxyl groups and/or ester-forming groups thereof;
• wherein said copolyester has an intrinsic viscosity of 0.8 to 1.5 dl/g.

A copolyester consisting essentially of terephthalic acid units, ethylene glycol units, and

• i) 0.5 to 7 mole %, based on the moles of total constituent units of said copolyester, of at least one group of bifunctional compound units (a.sub.3) selected from the group consisting of units from a condensed ring type aromatic dicarboxylic acid and units from a ring assembly type aromatic dicarboxylic acid;
• ii) 0.005 to 1 mole %, based on the moles of total constituent units of said copolyester, of multifunctional compound units (b.sub.1) derived from at least one multifunctional compound having at least 3 carboxyl groups, hydroxyl groups, and/or ester-forming groups thereof;
• and
• iii) monofunctional compound units (c) from at least one monofunctional compound selected from the group consisting of monocarboxylic acids, monohydric alcohols, and ester-forming derivatives thereof, in an amount satisfying the following formula (.alpha.):
• {20.times.(p-2).times.b.sub.1 }.gtoreq.c.gtoreq.{0.1.times.(p-2).times.b.sub.1 } (.alpha.)
• wherein:
• b.sub.1 =content (mole %) of units (b.sub.1)
• c=content (mole %) of units (c)
• p=average number of functional groups of said multifunctional compound deriving units (b.sub.1).