Polymerization process

1. A process comprising the step of melt-mixing a semi-aromatic polyamide (A) having a melting point on second heating of 295° C. or less comprising terephthalamide repeat units and a polyamide oligomer (B) having a melting point on second heating at least 10° C. greater than the melting point on second heating of semi-aromatic polyamide (A), said polyamide oligomer (B) comprising terephthalamide repeat units and having an amine end group concentration of less than 2000 me q/Kg and an inherent viscosity of at least 0.10 measured according to ISO 307:2007, at a temperature which is greater than the melting point on first heating of both semi-aromatic polyamide (A) and polyamide oligomer (B) for a time period sufficient to produce semi-aromatic polyamide (C) having a melting point on second heating which is greater than or equal to 300° C., wherein said melting points on first and second heating are determined according to ASTM D3418:2015.

2. The process of claim 1 wherein semi-aromatic polyamide (A) comprises repeat units derived from:

(a) at least one dicarboxylic acid comprising:

(i) greater than 20 to about 100 mole percent terephthalic acid;

(ii) from 0 to about 80 mole percent dicarboxylic acid selected from isophthalic acid and aliphatic diacids comprising 4 to 20 carbon atoms; and

(b) at least one aliphatic diamine having 4 to 20 carbon atoms; and optionally

(c) an aliphatic lactam or an aliphatic amino carboxylic acid with 6 to 20 carbon atoms.

3. The process of claim 1 wherein polyamide oligomer (B) comprises the same terephthalamide repeat units of semi-aromatic polyamide (A).

4. The process of claim 1 wherein the semi-aromatic polyamide (A) is selected from the group consisting of: PA6T/6I, PA6T/610, PA6T/66, PA 6T/612, PA10T/1010, PA10T/101, PA 10T/11, PAST/510, PA6T/DT, PA4T/410, PA6T/9T, PA9T/10T, PAST/5I, PA6T/6I/6, and PA6T/6I/66.

5. The process of claim 1 in which the melt-mixing takes place in an extruder.

6. The process of claim 5 wherein the extruder is a twin-screw extruder.

7. The process of claim 1 wherein polyamide oligomer (B) has an amine end group concentration of less than or equal to 1000 meq/Kg and an IV of at least 0.15.

8. The process of claim 1 wherein the time period is less than 3 minutes.

9. The process of claim 1 wherein the time period is less than 1 minute.

10. The process of claim 1 wherein the weight percent of semi-aromatic polyamide (A) ranges from 60 to 90 and polyamide oligomer (B) ranges from 10 to 40 weight percent based on the weight percent of A and B.

11. The process of claim 1 wherein semi-aromatic polyamide (C) comprises at least 5 mole percent higher terephthalamide content than semi-aromatic polyamide (A).

12. The process of claim 1 wherein semi-aromatic polyamide (C) has an excess of amine end groups.

13. The process of claim 1 wherein semi-aromatic polyamide (C) has an excess of acid end groups.

14. The process of claim 1 wherein the melt-mixing temperature is between 425° C. and 250° C.

15. The process of claim 1 wherein the time period sufficient to produce semi-aromatic polyamide (C) ranges from about 15 seconds to 4 minutes.

16. The process of claim 1 wherein the melt-mixing temperature ranges from about 305° C. to 400° C.

17. The process of claim 1 wherein polyamide oligomer (B) comprises at least 10 mole percent higher content of terephthalamide repeat units than semi-aromatic polyamide (A), based on the total molar content of dicarboxylic acid repeat units in semi-aromatic polyamide (A).

18. The process of claim 17 wherein the terephthalamide repeat units are hexamethylene terephthalamide repeat units.