Control over reverse addition fragmentation transfer polymerization processes
A procedure for improved temperature control in controlled radical polymerization processes is disclosed. The procedure is directed at controlling the concentration of the persistent radical in ATRP and NMP polymerizations procedures and the concentration of radicals in a RAFT polymerization process by feeding a reducing agent or radical precursor continuously or intermittently to the reaction medium through one of more ports.
1. A method of mitigating uncontrolled exothermic reactions in a RAFT polymerization process, comprising:
i) generating an activated RAFT agent by adding a free-radical initiator at a controlled rate of addition to a RAFT polymerization mixture comprising a RAFT agent and at least a first free-radically polymerizable compound; and
ii) mitigating the uncontrolled exothermic reactions during the RAFT polymerization process by adding further amounts of the free-radical initiator at a controlled rate of addition to generate or regenerate activated RAFT agents.
2. The process of claim 1 , wherein the controlled rate of addition further controls:
i) instantaneous concentrations of radicals in the RAFT polymerization process;
ii) the rate of polymerization of the RAFT polymerization process; or
iii) the temperature of the RAFT polymerization process.
3. The process of claim 1 , wherein the free-radical initiator is added at polymerization conditions at which the free-radical initiator has an activation-dependent t 1/2 value of between 30 sec. and 30 min.
4. The process of claim 3 , wherein the controlled rate of addition is adjusted to maintain the polymerization conditions at which the free-radical initiator has an activation-dependent t 1/2 value of between 30 sec. and 30 min.
5. The process of claim 1 , wherein the controlled rate of addition:
a) controls propagation of polymeric chains formed in the RAFT polymerization mixture;
b) maintains the RAFT polymerization mixture at a targeted rate of polymerization;
c) maintains the RAFT polymerization mixture at a targeted polymerization temperature;
d) allows conversion of the at least first free-radically polymerizable compound to exceed 80% conversion; or
e) combinations thereof.
6. The process of claim 5 , wherein the controlled rate of addition is adjusted continuously or intermittently to maintain the targeted rate of polymerization or the targeted polymerization temperature.
7. The process of claim 6 , wherein the targeted polymerization temperature is in the range of between 25° C. and the temperature at which the t ½ conversion rate is at least 30 sec.
8. The process of claim 6 , wherein the targeted polymerization temperature is in the range of between 25° C. and the temperature at which the t ½ conversion rate is 30 sec or less.
9. The process of claim 1 , wherein the controlled rate of addition comprises continuous, intermittent, adjustable, or combinations thereof.
10. The process of claim 1 , wherein the free radical initiator is 2,2′-azobis(2-methylpropionitrile) (AIBN); a peroxide; a peroxy acid; tert-butyl peracetate; 1,1-bis(tert-butylperoxy)-3,3,5-(dibutylphthalate)trimethylcyclohexane; 2,2′-azobis(4-methoxy-2.4-dimethyl valeronitrile) (V-70); 2,2′-azobis(2,4-dimethylvaleronitrile) (V-65); dimethyl 2,2′-azobis(2-methylpropionate) (V-601); 2,2′-azobis(2-methylbutyronitrile) (V-59); 1,1′-azobis(cyclohexane-1-carbonitrile) (V-40); or 2,2′-azobis[N-(2-propenyl)-2-methylpropionamide] (VF-096).
11. The process of claim 1 , wherein the at least first free-radically polymerizable compound is an unsaturated monomer.
12. The process of claim 11 , wherein the unsaturated monomer is a hydrophilic unsaturated monomer.
13. The process of claim 11 , wherein the unsaturated monomer is a hydrophobic unsaturated monomer.
14. The process of claim 1 , wherein the RAFT agent is one or more dithioesters.
15. The process of claim 1 , wherein the polymerization process is conducted in a bulk polymerization process; is performed in the presence of a solvent; is conducted from solid surfaces; or is conducted in a biphasic polymerization process, an emulsion polymerization process, a mini-emulsion polymerization process, a microemulsion polymerization process, a reverse emulsion polymerization process, or a suspension polymerization process.
16. The process of claim 1 , wherein the resulting polymer is a linear polymer or copolymer, a branched polymer or copolymer, a block copolymer, a brush polymer or copolymer, a star polymer or copolymer, or a star macromolecule.
17. The process of claim 1 , wherein the process further comprises:
a) adding one or more further amounts of the at least first free-radically polymerizable compound;
b) polymerizing at least a second free-radically polymerizable compound at a second polymerizing temperature;
c) polymerizing a plurality of free-radically polymerizable compounds at a corresponding plurality of polymerizing temperatures;
d) cross-linking the polymerization mixture at a cross-linking temperature; or
e) combinations thereof.
18. The process of claim 17 , wherein the temperature of the polymerization mixture is adjusted to the at least second polymerizing temperature using a heating or cooling source or adjusting the controlled addition rate of a second free-radical initiator.
19. The process of claim 1 , wherein the polymerization process is conducted in an industrial scale system.
20. The process of claim 1 , wherein the uncontrolled exothermic reactions are mitigated in intensity, duration, or frequency during the RAFT polymerization process.