Process for the production of polyvinylidene fluoride copolymers

A process for preparing a copolymer, comprising the steps of:

• a) Charging to a reactor an initial charge comprising water, surfactant, a fluorinated monomer M1 and adding vinylidene fluoride to the reactor until the operating pressure is reached;
• b) Initiating the polymerization by adding an initiator;
• c) Continuously feeding vinylidene fluoride and optionally the initiator until all the vinylidene fluoride has been added to the reactor to form the copolymer;
• d) Removing the copolymer from the reactor;
• e) Optionally drying the copolymer to form a powder;
• wherein the weight content of said fluorinated monomer M1 introduced in the reactor throughout the process is lower than 11 wt % based on the total weight of vinylidene fluoride and said fluorinated monomer M1 introduced in the reactor throughout the process;
• and wherein the whole amount of said fluorinated monomer M1 used in the process is added to the reactor prior to step b).

A copolymer comprising recurring units derived from vinylidene fluoride and recurring units derived from a fluorinated monomer M1;

• said copolymer having a melting temperature Tm defined by the relationship:
• (154.45−1.9472*x)−3<Tm (° C.)<(154.45−1.9472*x)+3
• wherein x is the weight content of said fluorinated monomer M1 expressed as percent based on the total weight of said copolymer;
• the melting temperature being measured by DSC according to the ASTM E794-06 (2018) standard test method;
• wherein the fluorinated monomer M1 is hexafluoropropene and wherein the weight content of hexafluoropropene based on the total weight of said copolymer is greater than 17 wt %.