Patent Publication Number: US-2019169337-A1

Title: Endcapped fluoropolymers for coating applications and processes of producing same

Description:
CROSS REFERENCE 
     The present application claims the priority benefit of U.S. provisional application 62/593,447, filed Dec. 1, 2017, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to novel fluoropolymers having excellent adhesion to substrates and excellent resistance to weathering and corrosion, as well as other advantageous properties, and coating compositions formed from such polymers having high solids content, and to processes of producing such fluoropolymers and coating compositions. 
     BACKGROUND OF THE INVENTION 
     Volatile organic compounds (VOCs) are volatile compounds of carbon that are subject to regulation by various government authorities, and for the purposes of the present invention the term is used consistent with proposed regulations established by the United States Environmental Protection Agency (EPA). More specifically, these proposed regulations establish that a compound of carbon is a VOC if it has a vapor pressure of less than about 0.1 millimeters of mercury at 20° C. 
     A variety of chemicals are within the definition of VOC, and some of these chemicals have short- and long-term adverse health effects when released into the atmosphere. Accordingly, many countries have regulations governing the release of such compounds into the earth&#39;s atmosphere. One relatively large source of release of such compounds into the environment has been from the solvents that are used in coating products such as, paints, varnishes, waxes, adhesives, inks and the like. Many cleaning, disinfecting, cosmetic, degreasing, and hobby products also contain VOCs as solvents or carriers. One method to reduce or eliminate the release of such compounds into the atmosphere is to capture and prevent release of the solvent as it evaporates from the coating composition. Such methods can involve, for example, the installation of a mechanism to capture the vapors and to process such vapors in an incinerator. However, as will be appreciated to those skilled in the art, a substantial capital cost and/or processing cost is incurred as a result of such operations, and such operations can sometimes add detrimentally to the time required to complete such coating operations. 
     In order to reduce and control the VOC emission into the earth&#39;s atmosphere, more and more countries have started to regulate VOC emissions. Such regulations include, in various countries, charging a VOC tax upon release of such compounds. Accordingly, there are many incentives to reduce the release of VOCs into the atmosphere. 
     As a result, new coating compositions have been developed which are low in VOC emissions. For example, in WO 2016/040525, a low VOC and high solid fluoropolymer for coating applications is disclosed. Specifically, WO 2016/040525 discloses a coating composition comprising: a carrier comprising VOC compounds; and one or more fluorocopolymers (herein referred to as “FPVE polymers”) formed by copolymerization of (1) first monomer selected from the group consisting of hydrofluoroalkenes, (2) second monomer comprising vinyl ester(s), and (3) third monomer comprising vinyl ether(s), wherein at least a portion of said vinyl ether monomer is a hydroxyl group-containing vinyl ether, wherein the fluorocopolymer comprises at least about 70% by weight of said coating composition and the VOC portion of said carrier is not greater than about 30% by weight of said coating composition. 
     SUMMARY OF THE INVENTION 
     Upon analyzing the structure of the FPVE polymers via nuclear magnetic resonance spectroscopy, the present inventors discovered that the end groups of the FPVE polymers included carboxylic acid groups. In addition, some HF was found in the FPVE resin. Because a carboxylic acid group is not particularly thermally stable, the present inventors sought to replace the carboxylic acid end groups with another, more thermally stable, end group. During the copolymerization of the FPVE polymers, the end group should be a CH 2 * radical group or a CFH* radical group. Thus, addition of a radical transfer agent should serve to endcap the end groups of the FPVE polymer, and the resulting endgroups should preferably be ether groups and/or alkyl groups. Both ether groups and alkyl groups are much more thermally stable than carboxylic acid groups, and thus will result in a more thermally stable, endcapped fluorocopolymer. This endcapping is accomplished by, at the end of copolymerization of the FPVE polymers, reacting a radical transfer agent, preferably methanol, with the fluorocopolymer, preferably at an increased temperature from the copolymerization temperature, to produce an endcapped fluorocopolymer, preferably containing ether end groups. 
     As used herein, the phrase “radical transfer agent” means a reagent capable of reacting with a CH 2 * radical group or a CFH* radical group. Radical transfer agents include alcohols (which will form ether end groups), amines (which will form amine end groups) and hydrogen (which will form alkyl end groups). Preferably, the radical transfer agent is an alcohol, such as, for example, methanol, ethanol or isopropanol, and the endcapped fluorocopolymer contains ether end groups. More preferably, the radical transfer agent is methanol, and the endcapped fluorocopolymer contains ether end groups. 
     As used herein, the term “copolymer” means polymers having two or more different repeating units, and the term “fluorocopolymer” means copolymers in which at least one of the repeating units is based on a monomer that is a hydrofluoroolefin. The term “terpolymer” means polymers having three or more different repeating units, and the term “terfluorocopolymer” means terpolymers in which at least one of the repeating units is based on a monomer that is a hydrofluoroolefin. The term “tetrapolymer” is intended to include oligomers and copolymers having four or more different repeating units, and the term “tetrafluorocopolymer” means tetrapolymers in which at least one of the repeating units is based on a monomer that is a hydrofluoroolefin. Thus, a tetrapolymer derived from monomers A, B, C and D has repeating units (-A-), (-B-), (-C-) and (-D-), and a tetrafluorocopolymer derived from monomers A, B, C and D has repeating units (-A-), (-B-), (-C-) and (-D-), wherein at least one of these is a hydrofluoroolefin. 
     The repeating units according to the present invention can be arranged in any form, including as alternating copolymers, as periodic copolymers, statistical copolymers, block copolymers and graft copolymers. 
     One aspect of the present invention provides a process for producing endcapped fluorocopolymers, the process including the steps of:
         (a) forming a fluorocopolymer by copolymerization of (1) one or more hydrofluoroolefin monomer(s) selected from the group consisting of hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes, hydrofluoropentenes and combinations of these, and preferably selected from 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, with said 1,3,3,3-tetrafluoropropene preferably comprising, consisting essentially of or consisting of trans-1,3,3,3-tetrafluoropropene, and combinations of these, (2) one or more vinyl ester monomer(s), and (3) one or more vinyl ether monomer(s), wherein at least a portion of said vinyl ether monomer is a hydroxyl group-containing vinyl ether monomer; and   (b) at the end of copolymerization, reacting a radical transfer agent, preferably methanol, with the fluorocopolymer, preferably at an increased temperature from the copolymerization temperature, to produce an endcapped fluorocopolymer, preferably containing ether end groups.       

     According to preferred aspects, the endcapped fluorocopolymers as described in the previous paragraph have a number average molecular weight of greater than about 10,000, preferably greater than about 12,000, and preferably in other embodiments greater than about 15,000, as measured according to the procedure described herein. 
     One aspect of the present invention provides endcapped fluorocopolymers formed by the following process: forming a fluorocopolymer by copolymerization of
         (1) one or more hydrofluoroolefin monomer(s) selected from the group consisting of hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes, hydrofluoropentenes and combinations of these, and preferably selected from 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, with said 1,3,3,3-tetrafluoropropene preferably comprising, consisting essentially of or consisting of trans-1,3,3,3-tetrafluoropropene, and combinations of these;   (2) one or more vinyl ester monomer(s); and   (3) one or more vinyl ether monomer(s), wherein at least a portion of said vinyl ether monomer is a hydroxyl group-containing vinyl ether monomer; and   at the end of copolymerization, reacting a radical transfer agent, preferably methanol, with the fluorocopolymer, preferably at an increased temperature from the copolymerization temperature, to produce an endcapped fluorocopolymer, preferably containing ether end groups.       

     According to preferred aspects, the present invention provides endcapped fluorocopolymers as described in the previous paragraph, wherein the polymer has a number average molecular weight of greater than about 10,000, preferably greater than about 12,000, and preferably in other embodiments greater than about 15,000, as measured according to the procedure described herein. 
     One aspect of the present invention provides methods of reducing the release of volatile organic compounds (VOCs) into the earth&#39;s atmosphere during coating operations of the type that permit the escape of VOCs into the earth&#39;s atmosphere. In preferred embodiments, the methods according to this aspect include the steps of:
         (a) providing a substrate to be coated;   (b) providing a coating composition which is formed by steps comprising:
           (i) providing one or more fluorocopolymers by copolymerization of (1) one or more hydrofluoroolefin monomer(s) selected from the group consisting of hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes, hydrofluoropentenes and combinations of these, and preferably selected from 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, with said 1,3,3,3-tetrafluoropropene preferably comprising, consisting essentially of or consisting of trans-1,3,3,3-tetrafluoropropene, and combinations of these, (2) one or more vinyl ester monomer(s), and (3) one or more vinyl ether monomer(s), wherein at least a portion of said vinyl ether monomer is a hydroxyl group-containing vinyl ether monomer, and at the end of copolymerization, reacting a radical transfer agent, preferably methanol, with the one or more fluorocopolymers, preferably at an increased temperature from the copolymerization temperature, to produce one or more endcapped fluorocopolymers, preferably containing ether end groups, wherein the endcapped fluorocopolymer preferably has a number average molecular weight of greater than about 10,000, preferably greater than about 12,000, and certain other embodiments greater than about 15,000, as measured according the procedure as described herein; and   (ii) providing a carrier for said one or more endcapped fluorocopolymers, said carrier comprising one or more VOC compounds; and   (iii) combining said one or more endcapped fluorocopolymers with said carrier to produce a polymeric composition comprising not greater than about 30% by weight of said carrier, preferably with a solids content of at least about 70% by weight;   
           (c) coating the substrate with said coating composition; and   (d) forming a protective polymeric layer on said substrate by allowing at least a substantial portion of said VOCs in said carrier to evaporate into the earth&#39;s atmosphere, whereby said protective coating is formed.       

     Another aspect of the present invention provides methods for obtaining a VOC tax credit as a result of reducing the release of volatile organic compounds (VOCs) into the earth&#39;s atmosphere compared to a baseline coating operation of the type that permits the escape of VOCs into the earth&#39;s atmosphere. In preferred embodiments, methods according to this aspect include the steps of:
         (a) establishing a baseline release of VOCs from an existing operation which involves coating of a substrate with an existing coating composition;   (b) providing a reduced VOC coating composition formed by steps comprising:
           (i) providing one or more fluorocopolymers by copolymerization of (1) one or more hydrofluoroolefin monomer(s) selected from the group consisting of hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes, hydrofluoropentenes and combinations of these, and preferably selected from 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, with said 1,3,3,3-tetrafluoropropene preferably comprising, consisting essentially of or consisting of trans-1,3,3,3-tetrafluoropropene, and combinations of these, (2) one or more vinyl ester monomer(s), and (3) one or more vinyl ether monomer(s), wherein at least a portion of said vinyl ether monomer is a hydroxyl group-containing vinyl ether monomer, and at the end of copolymerization, reacting a radical transfer agent, preferably methanol, with the one or more fluorocopolymers, preferably at an increased temperature from the copolymerization temperature, to produce one or more endcapped fluorocopolymers, preferably containing ether end groups, wherein the endcapped fluorocopolymer preferably has a number average molecular weight of greater than about 10,000, preferably greater than about 12,000 and certain other embodiments greater than about 15,000, as measured according to the procedure as described herein; and   (ii) providing a carrier for said one or more endcapped fluorocopolymers, said carrier comprising one or more VOC compounds; and   (iii) combining said one or more endcapped fluorocopolymers with said carrier to produce a polymeric composition comprising not greater than about 30% by weight of said carrier, preferably with a solids content of at least about 70% by weight;   
           (c) coating the substrate with said reduced VOC coating composition; and   (d) forming a protective polymeric layer on said substrate by allowing at least a substantial portion of said VOCs in said carrier to evaporate into the earth&#39;s atmosphere, whereby said protective coating is formed and whereby the VOCs released using said reduced VOC coating compositions is reduced compared to said baseline release of VOC; and   (e) submitting to an appropriate governmental agency a claim for tax credit based at least in part on said reduction in VOCs released from said coating operation.       

     According to certain preferred embodiments, the endcapped fluorocopolymer coating composition formed by step (b) (as described above) of this invention has a solid content of from about 70% to about 90% by weight, and even more preferably in certain embodiments from about 75% to about 85% by weight. In preferred embodiments, the endcapped fluorocopolymer coating composition formed by step (b) of this invention has a solid content of greater than about 75%. 
     According to preferred embodiments, the endcapped fluorocopolymer coating composition formed by step (b) of this invention has a VOC content of less than about 450 g/l, more preferably less than about 400 g/l, and even more preferably less than about 350 g/l. 
     According to preferred embodiments, the endcapped fluorocopolymer coating composition formed by step (b) of this invention has a VOC content of from about 450 g/l to about 100 g/l, more preferably from about 400 g/l to about 200 g/l, and even more preferably from about 350 g/l to about 250 g/l. 
     As used herein, the term “hydrofluoroolefins” means compounds consisting of carbon, hydrogen and fluorine and having at least one carbon-carbon double bond. Hydrofluoroolefins include, but are not necessarily limited to, hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes and hydrofluoropentenes, and the like. Preferred hydrofluoroolefins used to form the coating composition of step (b) comprise one or more tetrafluoropropenes. The tetrafluoropropene(s) used in step (b) preferably comprise 1,3,3,3-tetrafluoropropene (HFO-1234ze) and/or 2,3,3,3-tetrafluoropropene (HFO-1234yf), with said 1,3,3,3-tetrafluoropropene preferably comprising, consisting essentially of or consisting of trans-1,3,3,3-tetrafluoropropene. 
     In preferred embodiments, the fluorocopolymer of step (b) is formed by solution copolymerization of the monomers represented by (1), (2) and (3) of step (b)(i) (as described above). In preferred embodiments, step (b)(i) comprises solution copolymerizing:
         (1) from about 40 mol % to about 60 mol %, and even more preferably from about 45 mol % to about 55 mol %, and even more preferably about 50 mol % of hydrofluoroolefin monomer(s), preferably selected from the group consisting of hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes and hydrofluoropentenes, more preferably from the group consisting of HFO-1234ze, HFO-1234yf and combinations of these, and even more preferably HFO-1234ze, with said HFO-1234ze preferably comprising, consisting essentially of or consisting of trans-HFO-1234ze;   (2) from about 5 mol % to 45 mol % of vinyl ester or vinyl ether or both of them, more preferably from about 10 mol % to about 40 mol %, and even more preferably from about 20 mol % to about 40 mol %, represented by formula CH 2 ═CR 1 —O(C═O) X R 2  and CH 2 ═CR 3 —OR 4 , respectively, wherein x is 1 and wherein R 1  and R 3  are independently either hydrogen or a methyl group, preferably hydrogen, and wherein R 2  and R 4  are independently selected from the group consisting of an unsubstituted straight-chain, branched-chain or alicyclic alkyl group having 1 to 12 carbon atoms, preferably from 2 to 8 carbon atoms; and   (3) from about 3 mol % to about 30 mol % of hydroxyalkyl vinyl ether, more preferably from about 3 mol % to about 20 mol %, and even more preferably from about 3 mol % to about 10 mol % represented by formula CH 2 ═CR 3 —O—R 5 —OH, where R 3  is as defined above, preferably hydrogen, and R 5  is selected from the group consisting of a C2 to C12 unsubstituted straight-chain, branched-chain or alicyclic alkyl group, more preferably an unsubstituted straight chain alkyl group having from 3 to 5 carbons, preferably 4 carbons, wherein the mol % are based on the total of the monomers in the copolymer formation step.       

     According to preferred embodiments, the endcapped fluorocopolymer coating composition formed by step (b) of this invention has a VOC content of from about 450 g/l to about 100 g/l, more preferably from about 400 g/l to about 200 g/l, and even more preferably from about 350 g/l to about 250 g/l. 
     Hydrofluoroolefins include but are not necessarily limited to hydrofluoroethylene, hydrofluoropropene, hydrofluorobutene and hydrofluoropentene, and the like. According to certain preferred embodiments, the hydrofluoroolefin used to form the coating composition of step (b) comprises 1,3,3,3-tetrafluoropropene (HFO-1234ze) and/or 2,3,3,3-tetrafluoropropene (HFO-1234yf), with said HFO-1234ze preferably comprising, consisting essentially of or consisting of trans-HFO-1234ze. 
     In preferred embodiments, the fluorocopolymer of step (b)(i) is formed by copolymerization, and preferably solution copolymerization, of the monomers represented by (1), (2) and (3) as follows:
         (1) from about 40 mol % to about 60 mol %, and even more preferably from about 45 mol % to about 55 mol %, and even more preferably about 50 mol % of hydrofluoroolefin monomers, preferably selected from the group consisting of hydrofluoroethylenes, hydrofluoropropenes, hydrofluorobutenes and hydrofluoropentenes, preferably from the group consisting of HFO-1234ze, HFO-1234yf and combinations of these, and even more preferably HFO-1234ze with said HFO-1234ze preferably comprising, consisting essentially of or consisting of trans-HFO-1234ze;   (2A) from about 10 mol % to about 40 mol % of vinyl ester, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %, represented by formula CH 2 ═CR 1 —O(C═O) X R 2 , wherein x is 1 and wherein R 1  is either hydrogen or a methyl group, and wherein R 2  is selected from the group consisting of an unsubstituted straight-chain, branched-chain or alicyclic alkyl group having 1 to 12 carbon atoms;   (2B) from about 10 mol % to about 40 mol % of vinyl ether, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %, represented by formula CH 2 ═CR 3 —OR 4 , wherein R 3  is independently either hydrogen or a methyl group and wherein R 4  is independently selected from the group consisting of an unsubstituted straight-chain, branched-chain or alicyclic alkyl group having 1 to 12 carbon atoms; and   (3) from about 3 mol % to about 30 mol % of hydroxyalkyl vinyl ether, more preferably from about 3 mol % to about 20 mol %, and even more preferably from about 3 mol % to about 10 mol %, represented by formula CH 2 ═CR 3 —O—R 5 —OH, where R 3  is as defined above, preferably hydrogen, and R 5  is selected from the group consisting of a C2 to C12 unsubstituted straight-chain, branched-chain or alicyclic alkyl group, wherein the mol % are based on the total of the monomers in the copolymer formation step.       

     In preferred embodiments, the endcapped fluorocopolymer coating composition formed by step (b) of the present invention has a solids content of from about 70% to about 90% by weight, more preferably in certain embodiments of from about 75% to about 85% by weight, and at the same time has a VOC content of from about 450 g/l to about 100 g/l, more preferably from about 400 g/l to about 200 g/l, and even more preferably from about 300 g/l to about 200 g/l. 
     According to a preferred embodiment of the present invention, the copolymer formation step (b)(i) comprises providing one or more fluorocopolymers by copolymerization of:
         (1) first monomer(s) consisting essentially of HFO-1234ze and/or HFO-1234yf, wherein the HFO-1234ze is preferably trans-HFO-1234ze, preferably in an amount of from about 5 mol % to about 60 mol %, and more preferably from about 10 mol % to about 55 mol %,   (2) second monomer(s) comprising:
           A) vinyl ester monomer(s), preferably in an amount of from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %, represented by formula CH 2 ═CR 1 —O(C═O) X R 2 , wherein x is 1 and wherein R 1  is either hydrogen or a methyl group, and wherein R 2  is selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain alkyl group having 5 to 12 carbon atoms, wherein said alkyl group includes at least one tertiary or quaternary carbon atom, and   B) vinyl ether monomer(s), preferably in amounts of from about 5 mol % to about 45 mol % of vinyl ether, more preferably from about 10 mol % to about 40 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %, represented by formula CH 2 ═CR 3 —OR 4  respectively, wherein R 3  is independently either hydrogen or a methyl group and wherein R 4  is independently selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain alkyl group having 1 to 5 carbon atoms; and   
           (3) third monomer(s) selected from hydroxyl group-containing vinyl ether monomer(s), preferably in an amount of from about 3 mol % to about 60 mol % of hydroxy vinyl ether monomer, preferably in an amount of from about 3 mol % to about 30 mol %, more preferably from about 3 mol % to about 20 mol %, and even more preferably from about 3 mol % to about 10 mol %, represented by formula CH 2 ═C—R 5 —OH, where R 5  is selected from the group consisting of a C2 to C6 substituted or unsubstituted straight-chain or branched-chain alkyl group, wherein the mol % are based on the total of the monomers in the copolymer formation step.       

     As used herein, unless otherwise specifically indicated, reference to mol % is to the mol % of monomers used in the formation of the fluorocopolymer of the present invention, based on the total of the monomers. 
     In certain embodiments of the process, the copolymer and endcapped copolymer as formed by step (b) of the invention have a number average molecular weight as measured by gel phase chromatography (“GPC”) according to the method described in Skoog, D. A., Principles of Instrumental Analysis, 6th ed.; Thompson Brooks/Cole: Belmont, Calif., 2006, Chapter 28, which is incorporated herein by reference, of from about 5000 to 50,000, more preferably from about 12,000 to about 20,000 and in certain embodiments a weight average molecular weight preferably from about 5000 to about 30,000, and more preferably from about 20,000 to about 30,000. The values described herein for molecular weight are based on measurements that use an Agilent-PL gel chromatography column (5 um MIXED-C 300*7.5 mm). The mobile phase is tetrahydrofuran (THF) at a flow rate of 1 ml/minute and a temperature of 35° C. A refractive index detector is used. The unit is calibrated with polystyrene narrow standard available from Agilent. 
     In certain embodiments, the coating composition formed by step (b) has a VOC content of less than about 450 g/l, more preferably less than about 400 g/l, and even more preferably less than about 300 g/l. The values described herein for VOC are based on measurements made according to ASTM D1644, which covers the standard test method for the determination of the weight percent volatile content of solvent-borne and water-borne coatings. The procedure for calculating the Volatile Organic Compound (VOC) content of a liquid coating is to obtain a sample of the liquid coating to be tested and then weighing the coating in an aluminum foil dish to obtain the weight to the nearest 0.1 mg, which is designated in the following calculations as (W1). Add to the aluminum foil dish 3±1 ml of toluene solvent to form the coating specimen. The specimen is then draw into the syringe and the filled syringe is placed on the scale and the scale is tarred. The cap is removed from the syringe and the specimen is dispensed from the syringe into the dish to the target specimen weight (0.3±0.1 g if the expected result is =&lt;40% volatile and 0.5±0.1 g if the expected result is &gt;40% volatile. The specimen is spread out in the dish to cover the bottom of the dish completely with as uniform of a thickness as possible. Obtain and record the weight of the specimen to the nearest 0.1 mg, which is designated as the Specimen Weight (SA) in the following calculations. The foil dish containing the specimens is then heated in the forced draft oven for 60 min at 110° C. Each dish is removed from the oven, placed immediately in a desiccator, cooled to ambient temperature, weighed to the nearest 0.1 mg, and this weight is recorded, and is indicated as W2 in the following calculations. 
     To calculate the VOC, V, in the liquid coating, the following equations are used: 
         VA= 1000* DA* ( W 2 −W 1)/ SA    
     where: 
     VA=% volatiles (first determination), 
     W1=weight of dish, 
     W2=weight of dish plus specimen, 
     SA=specimen weight, 
     DA=specimen specific gravity, and 
     VB=% volatiles (duplicate determination; calculate in same manner as VA). 
     As used herein, the term “substrate” refers to any device or article, or part of a device or article, to be coated. 
     As used herein, the term “carrier” is intended to refer to a component of a composition that serves to solvate, disperse and/or emulsify a monomeric or polymeric component of a composition. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a nuclear magnetic resonance (NMR) spectrum for carboxylic acid in an endcapped fluorocopolymer, and in the same fluorocopolymer without the endcapping. 
         FIG. 2  shows an NMR spectrum for HF in an endcapped fluorocopolymer, and in the same fluorocopolymer without the endcapping. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As described above, preferred aspects of the present invention involve coating methods that provide reduced VOC emissions while at the same time providing effective and efficient protective coatings on substrates. As those skilled in the art will appreciate, the quality of a protective coating applied to a substrate can be measured by a variety of coating properties that, depending on the particular application, are important for achieving a commercially successful coating on a given substrate. These properties include but are not limited to: (1) viscosity, (2) color retention, (3) substrate adhesion and (4) thermal stability. 
     Viscosity as used herein is measured according the ASTM Standard Test Method for Measuring Solution Viscosity of Polymers with Differential Viscometer, Designation D5225-14. According to this method as used herein, the viscometer used is a Brookfield viscometer (DV-II+Pro) using spindles S18/S31 using torque values from between 40% and 80% at room temperatures of about 23±2° C. If a solvent is used for the measurements, it is butyl acetate. 
     According to certain preferred embodiments, the coating compositions formed according to the present methods exhibit: (1) a solid concentration of at least about 70% by weight; (2) a viscosity, as measured by the ASTM Standard Test Method for Measuring Solution Viscosity of Polymers with Differential Viscometer, Designation D5225-14, of not greater than about 1700 mPa-s at about 23±2° C.; (3) a color change after about 1000 hours, of not greater than 2.0, more preferably not greater than about 1.5, and even more preferably not greater than about 1.2, as measured in comparison to the initial color, each as measured by ASTM D 7251, QUV-A; and (4) a VOC content of not greater than about 450 g/l, more preferably not greater than about 400 g/l, and even more preferably not greater than about 350 g/l. 
     The QUV-A is measured as indicated above according to ASTM D 7251, which is QUV Accelerated Weathering Tester Operating Procedure by which accelerated testing is performed in an accelerated testing cabinet sold under the trade mark QUV® manufactured by Q-Lab Corporation of Cleveland, Ohio. Two lamps are used in this testing cabinet: “A” lamps (UVA-340) have a normal output of 0.69 W/m 2  @340 nm m and a maximum output of 1.38 W/m 2  @340 nm m; and “B” lamps (UVB-313) have a normal output of 0.67 W/m 2  @310 nm m and a maximum output of 1.23 W/m 2  @310 nm m. As used herein, the designation QUV-A refers to tests using the A lamps and QUV-B refers to tests using the B lamps. The procedure is accomplished using the following steps:
         1. Measure the initial gloss of the coating film three times and obtain the average of the measurements, which is designated in the following calculations as “A.”   2. Place the test plate containing the coating in the panel holder in the cabinet and power the cabinet on.   3. Set the PROGRAM button in the control panel and select the desired program operation.   4. Engage the RUN button to start test.   5. Record down the exposure time indicated on the led panel.   6. Stop the machine after the indicated hours, remove the test plate, and measure the gloss three times to get an average result for the indicated exposure time, and record this value as “B” for use in the calculation below.   7. Determine Gloss retention using the formula: Gloss Retention=B/A       

     Monomers 
     Hydrofluoroolefins 
     The hydrofluoroolefin monomers according to the methods of the present invention can include in certain preferred embodiments hydrofluoroethylene monomer, that is, compounds having the formula CX 1 X 2 ═CX 3 X 4 ; wherein X 1 , X 2 , X 3 , X 4  are each independently selected from H or F or Cl atom, but at least one of them is a hydrogen atom. Examples of hydrofluoroethylene monomers include, among others: 
     CH 2 ═CHF, 
     CHF═CHF, 
     CH 2 ═CF 2 , and 
     CHF═CF 2 . 
     The hydrofluoroolefin monomers according to certain preferred aspects of the methods of the present invention include, and preferably consists essentially of or consist of hydrofluoropropenes having the formula CX 5 X 6 ═CX 7 CX 8 X 9 X 10 ; wherein X 5 , X 6 , X 7 , X 8 , X 9  and X 10  are independently selected from H or F or Cl atom, but at least one of them is a hydrogen atom and another is a fluorine atom. Examples of hydrofluoropropene monomers include, among others: 
     CH 2 ═CFCF 3  (HFO-1234yf), 
     trans-CHF═CHCF 3  (trans-HFO-1234ze), 
     CHCl═CFCF 3  and 
     CH 2 ═CHCF 3 . 
     In preferred embodiments, the hydrofluoroolefin comprises, consists essentially of or consists of HFO-1234yf and/or HFO-1234ze. In preferred embodiments, the hydrofluoroolefin comprises, consists essentially of or consists of HFO-1234ze, with said HFO-1234ze preferably comprising, consisting essentially of or consisting of trans-HFO-1234ze. 
     The hydrofluoroolefin monomers according to certain preferred aspects of the methods of the present invention include hydrofluorobutene according to the following formula: CX 11 X 12 ═CX 13 CX 14 X 15 CX 16 X 17 X 18 ; wherein X 11 , X 12 , X 13 , X 14 , X 15 , X 16   ,  X 17  and X 18  are independently selected from H or F or Cl atom, but at least one of them is a hydrogen atom and at least one is a fluorine atom. Examples of hydrofluorobutene include, among others, CF 3 CH═CHCF 3 . 
     Vinyl Esters 
     The copolymers in accordance with the present invention preferably are also formed from vinyl ester monomer units, preferably in amounts of from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %. In preferred embodiments, the vinyl ester monomer(s) are represented by the formula CH 2 ═CR 1 —O(C═O) X R 2 , wherein x is 1 and wherein R 1  is either hydrogen or a methyl group, and wherein R 2  is selected from the group consisting of a substituted or unsubstituted, preferably unsubstituted, straight-chain or branched-chain, preferably branched chain, alkyl group having 5 to 12 carbon atoms, more preferably having from 5 to 10 carbon atoms, and even more preferably 8 to 10 carbon atoms. In preferred embodiments, the alkyl group includes at least one tertiary or quaternary carbon atom. In highly preferred embodiments, the vinyl ester includes at least one quaternary carbon according to the following formula: 
     
       
         
         
             
             
         
       
     
     where each of R 7  and R 8  are alkyl groups, preferably branched alkyl groups, that together contain from 5 to about 8, more preferably from 6 to 7, carbon atoms. 
     Examples of vinyl ester monomers that are preferred according to certain preferred embodiments include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl capronate, vinyl laurate, VEOVA-9 (vinyl versatate ester formed from a C9 carbocylic acid, produced by Momentive), VEOVA-10 (vinyl versatate ester formed from a C10 carbocyclic acid, produced by Momentive) and vinyl cyclohexanecarboxylate. Each of VEOVA-9 and VEOVA-10 contain at least one quaternary carbon according to Formula A above. According to preferred embodiments, the vinyl ester comprises vinyl versatate ester having from 11 to 12 carbon atoms in the molecule, preferably with at least one quaternary carbon according to Formula A above. Particularly preferred vinyl esters include VEOVA-9 and VEOVA-10. 
     Vinyl Ethers 
     The copolymers in accordance with the present invention preferably are also formed from vinyl ether monomer units, preferably in amounts of from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %. In preferred embodiments, the vinyl ether monomer(s) are represented by the formula CH 2 ═CR 3 —OR 4 , wherein R 3  is independently either hydrogen or a methyl group and wherein R 4  is selected from the group consisting of a substituted or unsubstituted, preferably unsubstituted, straight-chain or branched-chain, preferably straight chain, alkyl group having 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms. Examples of vinyl ether monomers that are preferred according to certain preferred embodiments include alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, hexyl vinyl ether, octyl vinyl ether, decyl vinyl ether and lauryl vinyl ether. Vinyl ethers including an alicyclic group can also be used, for example, cyclobutyl vinyl ether, cyclopentyl vinyl ether and cyclohexyl vinyl ether. According to preferred embodiments, the vinyl ether comprises, consists essentially of, or consists of ethyl vinyl ether. 
     Preferably, in those embodiments in which vinyl ether and vinyl ester monomers are both present, the amount of vinyl ether and vinyl ester monomers together comprise from about 25 mol % to about 45 mol % of the total monomers. In such preferred embodiments comprising both the vinyl ether and the vinyl ester, the vinyl ether is preferably present in an amount of from about 10 mol % to 20 mol %, and the vinyl ester is preferably present in an amount of from about 10 mol % to 20 mol %. 
     Hydroxy Vinyl Ethers 
     The copolymers in accordance with the present invention preferably are also formed from hydroxyl vinyl ether monomer units, preferably in amounts of from about 3 mol % to about 60 mol % of hydroxy vinyl ether monomer, preferably in an amount of from about 3 mol % to about 30 mol %, more preferably from about 3 mol % to about 20 mol %, and even more preferably from about 3 mol % to about 10 mol %. In preferred embodiments, the hydroxyl vinyl ether monomer(s) are represented by the formula CH 2 ═CR 3 —O—R 5 —OH, where R 3  is as defined above, preferably hydrogen, and where R 5  is selected from the group consisting of a C2 to C6 substituted or unsubstituted, preferably unsubstituted, straight-chain or branched-chain, prefeethrably straight chain, alkyl group. Examples of preferred hydroxyalkyl vinyl ether monomers include hydroxyl-ethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxypentyl vinyl ether and hydroxyhexyl vinyl ether. In certain embodiments, the copolymer is formed from about 5 mol % to about 20 mol % of hydroxyalkyl vinyl ether monomers, based on the total weight of the monomer. 
     In preferred embodiments, the comonomers according to the fluorocopolymer formation step (b)(i) (as described above) comprise, and preferably consist essentially of:
         (1) first monomer consisting essentially of HFO-1234ze, preferably in an amount of from about 40 mol % to about 60 mol %, and even more preferably from about 45 mol % to about 55 mol %, and even more preferably about 50 mol %,   (2) second monomer(s) comprising:
           A) vinyl ester monomer represented by formula CH 2 ═CR 1 —O(C═O) X R 2  wherein x is 1 and wherein R 1  is either hydrogen or a methyl group, preferably hydrogen, and wherein R 2  is a substituted or unsubstituted branched or straight-chain alkyl group having 6 to 8 carbon atoms, preferably an unsubstituted branched-chain alkyl group having 6 to 8 carbon atoms, wherein said alkyl group preferably includes at least one tertiary or quaternary carbon atom, wherein said vinyl ester monomer is present in an amount of from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %; and   B) vinyl ether monomer(s), represented by formula CH 2 ═CR 3 —OR 4  respectively, wherein R 3  is independently either hydrogen or a methyl group, preferably hydrogen, and wherein R 4  is selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain, preferably straight chain, alkyl group having 1 to 3 carbon atoms, preferably 2 carbon atoms, said vinyl ether monomer(s) preferably being present in amounts of from about 10 mol % to about 40 mol %, more preferably from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %; and   
           (3) third monomer(s) consisting of hydroxyalkyl vinyl ether represented by formula CH 2 ═CR 3 —O—R 5 —OH, where R 3  is methyl or hydrogen, preferably hydrogen, and R 5  is selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain C3 to C5 alkyl, preferably C4, unsubstituted straight-chain alkyl group, wherein the amount of said third monomer is preferably present in an amount of from about 3 mol % to about 30 mol %.       

     Copolymer Formation Methods 
     It will be appreciated by those skilled in the art, based on the teachings contained herein, that copolymers of the present invention may be formed to achieve the preferred characteristics described herein using a variety of techniques, and all such techniques are within the scope of the present invention. 
     In preferred embodiments, the fluorocopolymer is preferably produced in a polymerization system that utilizes a carrier for the monomer/polymer during and/or after formation. According to one preferred embodiment the carrier acts as a solvent and/or dispersant for the monomer and/or polymer, and such operations include dispersion, emulsion and solution polymerization. Examples of carriers in such systems, including preferably solvents for solution polymerization, include: esters, such as methyl acetate, ethyl acetate, propyl acetate and butyl acetate; ketones, such as acetone, methyl ethyl acetone and cyclohexanone; aliphatic hydrocarbons, such as hexane, cyclohexane, octane, nonane, decane, undecane, dodecane and mineral spirits; aromatic hydrocarbons, such as benzene, toluene, xylene, naphthalene, and solvent napthta; alcohols, such as methanol, ethanol, tert-butanol, iso-propanol, ethylene glycol monoalkyl ethers; cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and dioxane; fluorinated solvents, such as HCFC-225 and HCFC-141b; dimethyl sulfoxide; and the mixtures thereof. 
     It is contemplated that the temperature conditions used in the polymerization process and in the reaction of the fluorocopolymer with the radical transfer agent of the present invention can be varied according to the particular equipment and applications involved and all such temperatures are within the scope of the present invention. Preferably, the polymerization is conducted at a temperature in a range of from about 30° C. to about 150° C., more preferably from about 40° C. to about 100° C., and even more preferably from about 50° C. to about 70° C., depending on factors such as the polymerization initiation source and type of the polymerization medium. Preferably, the reaction of the fluorocopolymer with the radical transfer agent is conducted at an increased temperature from the polymerization temperature, and in a range of from about 90° C. to about 150° C., more preferably from about 120° C. to about 140° C., even more preferably from about 125° C. to about 135° C., and even more preferably at about 130° C. 
     It is also contemplated that the reaction times employed in the polymerization process and in the reaction of the fluorocopolymer with the radical transfer agent of the present invention can be varied according to the particular equipment and applications involved and all such reaction times are within the scope of the present invention. Preferably, the reaction time of the fluorocopolymer with the radical transfer agent is for a period of time in a range of from about 2 hours to about 6 hours, more preferably from about 3 hours to about 5 hours, and even more preferably, for about 4 hours. In a particularly preferred embodiment, the reaction of the fluorocopolymer with the radical transfer agent is conducted at a temperature of about 130° C. for about 4 hours. 
     In certain preferred embodiments, it is preferred that the solution polymerization is conducted under conditions under which the total amount of the solvent used in the copolymerization process, based on the weight of the solvent and monomer in the solution, is from about 10 wt % to about 40 wt %, more preferably in amounts of from about 10 wt % to about 30 wt %, and more preferably in certain embodiments in an amount of from about 15% to about 25%. In certain of such embodiments, the solvent used in the solution copolymerization process comprises, preferably consists essentially of, and more preferably in certain embodiments consists of C2-C5 alkyl acetate, and even more preferably butyl acetate. 
     In certain preferred embodiments, it is preferred that the reaction of the fluorocopolymer with the radical transfer agent is conducted under conditions under which the amount of the radical transfer agent to be reacted with the fluorocopolymer is in the range of from about 8 wt % to about 10 wt % of the fluorocopolymer. 
     In preferred embodiments, the copolymer as formed in accordance with the preferred methods described herein are prepared by copolymerizing those monomers under conditions effective to achieve a copolymer having a number average molecular weight of 5000 to 50,000, or in some embodiments 5000 to 10,000 as measured by gel phase chromatography (“GPC”) according to the method described in Skoog, D. A., Principles of Instrumental Analysis, 6th ed.; Thompson Brooks/Cole: Belmont, Calif., 2006, Chapter 28, which is incorporated herein by reference. In certain embodiments, the copolymer has a number average molecular weight that is greater than about 10,000, and even more preferably from 10,000 to about 14,000. According to certain preferred embodiments, the copolymer has a molecular weight distribution of 2 to 10, more preferably 2.5 to 8, and most preferably 3 to 6. Applicants have found that in certain embodiments the use of copolymers having a molecular weight less than 5000 produces weatherability and chemical resistance of the protective coating that is less than is desired for some applications, and that when the polymers have a molecular weight of more than 50,000, coating compositions having viscosities that may negatively impact the spreading or coating properties of the coating compositions and hence difficulties in the coating operations result. 
     In preferred embodiments, the formation of endcapped fluorocopolymer coating compositions comprises, and preferably consists essentially of:
         (i) providing one or more fluorocopolymers by copolymerization of
           (1) first monomer consisting essentially of HFO-1234ze, with said HFO-1234ze preferably comprising, consisting essentially of or consisting of trans-HFO-1234ze, preferably in an amount of from about 20 mol % to about 30 mol %, and even more preferably from about 22 mol % to about 27.5 mol %, and even more preferably about 25 mol %,   (2) second monomers comprising:
               A) vinyl ester monomer represented by formula CH 2 ═CR 1 —O(C═O) X R 2  wherein x is 1 and wherein R 1  is either hydrogen or a methyl group, preferably hydrogen, and wherein R 2  is an unsubstituted branched-chain alkyl group having 6 to 8 carbon atoms, wherein said alkyl group preferably includes at least one tertiary or quaternary carbon atom, wherein said vinyl ester monomer is present in an amount of from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %; and   B) vinyl ether monomer(s), represented by formula CH 2 ═CR 3 —O—R 4 , wherein R 3  is either hydrogen or a methyl group, preferably hydrogen, and wherein R 4  is selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain, preferably straight chain, alkyl group having 1 to 3 carbon atoms, preferably 2 carbon atoms, said vinyl ether monomer(s) preferably being present in amounts of from about 10 mol % to about 40 mol %, more preferably from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %; and   
               (3) third monomer(s) consisting of hydroxyalkyl vinyl ether represented by the formula CH 2 ═CR 3 —O—R 5 —OH, where R 3  is methyl or hydrogen, preferably hydrogen, and R 5  is selected from the group consisting of a C3 to C5, preferably C4, unsubstituted straight-chain alkyl group, wherein the amount of said third monomer is preferably from about 3 mol % to about 30 mol %; and   
           (ii) at the end of copolymerization, reacting a radical transfer agent, preferably methanol, with the one or more fluorocopolymers, preferably at an increased temperature from the copolymerization temperature, to produce one or more endcapped fluorocopolymers, preferably containing ether end groups; and   (iii) providing a carrier for said one or more endcapped fluorocopolymers, said carrier comprising one or more VOC compounds and preferably selected from aromatic hydrocarbons such as xylene and toluene; alcohols such as n-butanol; esters such as butyl acetate; ketones such as methyl isobutyl ketone, and glycol ethers such as ethyl cellusolve, with C2-C5 alkyl acetate being preferred, and even more preferably comprising, consisting essentially of, or consisting of butyl acetate; and   (iv) combining said one or more endcapped fluorocopolymers with said carrier to produce a polymeric composition comprising not greater than about 30% by weight of said carrier, preferably with a solids content of at least about 70% by weight. According to preferred embodiments, the endcapped fluorocopolymer composition of the present invention, and in particular the endcapped fluorocopolymer formed as described in the preceding sentence, has a polymer number average molecular weight as measured by gel phase chromatography (“GPC”) according to the method described in Skoog, D. A., Principles of Instrumental Analysis, 6th ed.; Thompson Brooks/Cole: Belmont, Calif., 2006, Chapter 28, which is incorporated herein by reference, of from about 5000 to 50,000, more preferably from about 7000 to about 15000, and has a solids content of from about 70% to about 90% by weight, and even more preferably from about 70% to about 85% by weight, and preferably a VOC content of less than about 400 g/l, more preferably from about 400 g/l to about 100 g/l, and even more preferably from about 350 g/l to about 200 g/l. It is also preferred in such embodiments as described in the present application in general, and in this paragraph in particular, that the coating compositions of the present invention have a viscosity at 25° C. of less than about 1900 mPa-s, more preferably less than about 1800 mPa-s and even more preferably of less than about 1700 mPa-s as measured by Ford Cup at least at one of 12 revolutions per minutes (r/m), 30 r/m and 60 r/m, and preferably at all three speeds, preferably as measured according to ASTM D1200-10 (2014) or ASTM D2196 as appropriate.       

     In preferred embodiments, the formation of endcapped fluorocopolymer coating compositions comprises, and preferably consists essentially of:
         (i) providing one or more fluorocopolymers by copolymerization of
           (1) first monomer consisting essentially of HFO-1234ze, with said HFO-1234ze preferably comprising, consisting essentially of or consisting of trans-HFO-1234ze in an amount of from about 40 mol % to about 60 mol %, and even more preferably from about 45 mol % to about 55 mol %, and even more preferably about 50 mol %,   (2) second monomer(s) comprising:
               A) vinyl ester monomer represented by formula CH 2 ═CR 1 —O(C═O) X R 2  wherein x is 1 and wherein R 1  is either hydrogen or a methyl group, preferably hydrogen, and wherein R 2  is an unsubstituted branched-chain alkyl group having 6 to 8 carbon atoms including at least one tertiary carbon atom, wherein said vinyl ester monomer is present in an amount of from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %; and   B) vinyl ether monomer(s), represented by formula CH 2 ═CR 3 —O—R 4 , wherein R 3  is either hydrogen or a methyl group, preferably hydrogen, and wherein R 4  is selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain, preferably straight chain, alkyl group having 1 to 3 carbon atoms, preferably 2 carbon atoms, said vinyl ether monomer(s) preferably being present in amounts of from about 10 mol % to about 40 mol %, more preferably from about 5 mol % to about 45 mol %, more preferably from about 10 mol % to about 30 mol %, and even more preferably from about 10 mol % to about 20 mol %; and   
               (3) third monomer(s) consisting of hydroxyalkyl vinyl ether represented by the formula CH 2 ═CR 3 —O—R 5 —OH, where R 3  is either hydrogen or a methyl group and R 5  is selected from the group consisting of a substituted or unsubstituted straight-chain or branched-chain C3 to C5 alkyl, preferably C4, unsubstituted straight-chain alkyl group, wherein the amount of said third monomer is preferably from about 3 mol % to about 30 mol %; and   
           (ii) at the end of copolymerization, reacting a radical transfer agent, preferably methanol, with the one or more fluorocopolymers, preferably at an increased temperature from the copolymerization temperature, to produce one or more endcapped fluorocopolymers, preferably containing ether end groups; and   (iii) providing a carrier for said one or more endcapped fluorocopolymers, said carrier comprising one or more VOC compounds selected from aromatic hydrocarbons such as xylene and toluene; alcohols such as n-butanol; esters such as butyl acetate; ketones such as methyl isobutyl ketone, and glycol ethers such as ethyl cellusolve, with C2-C5 alkyl acetate being preferred, and even more preferably comprising, consisting essentially of, or consisting of butyl acetate; and   (iv) combining said one or more endcapped fluorocopolymers with said carrier to produce a polymeric composition comprising not greater than about 30% by weight of said carrier, preferably with a solids content of at least about 70% by weight.       

     Coating Composition Formation Methods 
     The endcapped copolymers as formed in accordance with the procedures described herein may then be used to form various coating compositions that have the substantial advantages described above. For example, various solvents can be used for the preparation of solution-type paints or coatings by adding those solvents to the endcapped fluorocopolymer of the present invention formed as described herein. In certain embodiments, preferred solvents for formation of the coating composition include aromatic hydrocarbons such as xylene and toluene; alcohols such as n-butanol; esters such as butyl acetate; ketones such as methyl isobutyl ketone, and glycol ethers such as ethyl cellusolve and various commercial thinners. 
     In certain embodiments, the coating composition of the present invention has a solid content of from about 70% to about 90% by weight based on the total weight of the coating composition, and more preferably in certain embodiments from about 75% to about 85% by weight of solids. In certain preferred embodiments, the solids comprise and preferably consist essentially of the endcapped copolymers of the present invention and/or cross-linked copolymers formed using the endcapped copolymers of the present invention. Although it is contemplated that those skilled in the art will be able to form coatings using the present compositions according to any one of known methods, in preferred embodiments the coating is formed by brushing, rolling, air spraying, airless spraying, flow coating, roller coating, spin coating, and the like, and any combination of these may be used. Furthermore, the coating can be applied on various substrates. The coating film can be formed directly on a substrate or via a primer or if necessary, via an undercoating layer. Although all thicknesses are within the scope of the present invention, in preferred embodiments the outermost cured coating film layer has a layer thickness of from about 20 to about 30 μm. 
     EXAMPLES 
     The present invention is further illustrated by the following non-limiting examples. 
     Example 1 
     Endcapped Fluorocopolymer Preparation 
     A solution polymerization operation is carried out by charging into a 1000 ml stainless steel autoclave equipped with a stirrer the components as indicated in the following Table 1: 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                   
                   
                   
                 Monomer, 
               
               
                 COMPONENT 
                 Weight, 
                 Wt % of 
                 Monomer 
                 mol % of 
               
            
           
           
               
               
               
               
               
               
            
               
                 TYPE 
                 NAME 
                 grams 
                 solution 
                 Moles 
                 polymer 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Solvent 
                 butyl acetate 
                 61.6 
                 10.1 
                   
                   
               
               
                 First Monomer 
                 trans-1,3,3,3- 
                 253 
                 41.6 
                 2.22 
                 50 
               
               
                 (HFO) 
                 tetrafluoropropene 
               
               
                   
                 (trans-HFO-1234ze) 
               
               
                 Second 
                 VEOVA-10 
                 157.4 
                 25.8 
                 0.8 
                 18 
               
               
                 Monomer 
               
               
                 (vinyl ester) 
               
               
                 Second 
                 ethyl vinyl ether 
                 57.6 
                 9.5 
                 0.8 
                 18 
               
               
                 Monomer 
               
               
                 (vinyl ether) 
               
               
                 Third 
                 hydroxybutylvinyl 
                 72.2 
                 11.9 
                 0.62 
                 14 
               
               
                 Monomer 
                 ether 
               
               
                 (alkylhydroxy 
               
               
                 ether) 
               
               
                 Initiator 
                 tert-Butyl 
                 6.5 
                 1.1 
               
               
                   
                 peroxypivalate 
               
               
                   
               
            
           
         
       
     
     The butyl acetate, the ethyl vinyl ether monomer, the vinyl ester monomer (VEOVA-10), the hydroxybutyl vinyl ether, the initiator and 10 grams of zinc oxide were charged into the vessel. The mixture was solidified with liquid nitrogen, and deaerated to remove the dissolved air. Then, the trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234ze) was added to the mixture in the autoclave, and the mixture was then gradually heated to about 57° C. The mixture was then stirred (at about 300 rpm) for about 0.5 hours to carry-out solution copolymerization of the monomers. 
     Then, at the end of copolymerization, 50 grams of methanol (as a radical transfer agent) was added into the autoclave to react with the fluorocopolymer. In order to increase the yield of the endcapping reaction, the temperature of the mixture was increased from about 57° C. to about 130° C. after addition of the methanol. The mixture was then stirred (at about 300 rpm) for about 4 hours to carry out the endcapping reaction and produce an endcapped fluorocopolymer. 
     After the autoclave was cooled to room temperature, any unreacted monomers were purged and then the autoclave was opened and a vacuum was applied to the autoclave for a sufficient period of time to remove sufficient excess solvent to achieve a solid content (copolymer content) in the autoclave of about 68% by weight. The endcapped fluorocopolymer had a weight of 763 grams, and a yield of 97%. The endcapped fluorocopolymer (without solvent) was tested and found to have: a number average molecular weight in the range of about 10,000 to 12,000; a hydroxyl value of about 65 mg KOH/g; and a fluorine content in the range of about 29 to 32 wt %. After post-treatment (filtering the zinc oxide and concentrating to a solid content of about 70%), the resulting endcapped fluorocopolymer plus solvent combination was in the form of a clear solution having a solid, that is, copolymer, content of about 70%. 
     NMR testing ( 1 H NMR) was performed on the endcapped fluorocopolymer, and the results were compared to the same fluorocopolymer without the endcapping (i.e., comparing the same fluorocopolymer before and after endcapping). The NMR results show that the endcapped fluorocopolymer has much less carboxylic acid (see  FIG. 1 ) and HF (see  FIG. 2 ) than that of the same fluorocopolymer without the endcapping. As such, the thermal stability of the endcapped fluorocopolymer should be greatly improved in comparison to the same fluorocopolymer without the endcapping. 
     In addition, thermal stability testing was performed using the endcapped fluorocopolymer as follows. The polymer sample (polymer plus solvent combination having a 70% solid content) was heated in an oven at 80° C. During the heating, any color change to yellow was observed, and the pH value of the polymer sample was tested. If the color became yellow and/or the pH value went below 1.0 (indicative of HF being generated), then the test was stopped and the time was recorded. In most cases, these two phenomena occurred at the same time. If the sample&#39;s color was yellow to begin the test, then only the time to reach a pH value below 1.0 was recorded. The results of this testing for seven different polymer samples are shown below in Table 2, wherein Batch 1 is a non-endcapped FPVE polymer, and Batches 2-7 are endcapped FPVE polymers wherein methanol was used as the radical transfer agent. In Table 2, a longer recorded time is indicative of a better thermal stability of the sample, and a better and more complete endcapping reaction for that particular Batch. 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Batch No.: 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 reaction temperature 
                 n/a (no 
                 110 
                 130 
                 150 
                 130 
                 130 
                 130 
               
               
                 (° C.) (with radical 
                 endcapping) 
               
               
                 transfer agent) 
               
               
                 reaction time (hours) 
                 n/a 
                 4 
                 3 
                 4 
                 4 
                 5 
                 6 
               
               
                 thermal durability 
                 only a few 
                 &lt;1 
                 7 
                 20 
                 15 
                 20 
                 30 
               
               
                 (days @ 80° C.) 
                 hours 
               
               
                 color (before 
                 colorless 
                 colorless 
                 colorless 
                 yellow 
                 colorless 
                 A little 
                 yellow 
               
               
                 thermal stability 
                   
                   
                   
                   
                   
                 yellow 
               
               
                 test) 
               
               
                   
               
            
           
         
       
     
     As seen in Table 2, the best thermal stability was obtained by Batch 5, which started as a colorless solution and had a thermal durability of 15 days. In Batch 5, the reaction of the fluorocopolymer with methanol was conducted at a temperature of 130° C. for 4 hours. As shown by Batch 3 and Batch 5, the endcapped fluorocopolymer produced by the reaction of the fluorocopolymer with methanol at a temperature of 130° C. for 3 hours (i.e., Batch 3) or 4 hours (i.e., Batch 5) did not change color or generate HF gas after treatment at 80° C. for at least 168 hours (7 days). In contrast, typical FPVE polymers will begin yellowing and generating HF gas after treatment at 80° C. for four (4) hours. Thus, these results show that the endcapping of the fluorocopolymer as described herein leads to a significant improvement in the thermal stability of the resulting endcapped fluorocopolymer. 
     Example 2 
     Coating Composition Preparation 
     A coating composition was also prepared using the endcapped fluorocopolymer from Example 1 above. The coating composition was prepared from the following components: 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                   
                   
                 Weight 
                   
               
               
                 Component 
                 Name 
                 (g) 
                 Supplier 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Fluorocopolymer 
                 endcapped 
                 58.6 
                   
               
               
                   
                 fluorocopolymer from 
               
               
                   
                 Example 1 above, 70% 
               
               
                   
                 solid content 
               
               
                 Pigment 
                 carbon black FW200 
                 2.5 
                 Orion Engineered 
               
               
                   
                   
                   
                 Carbons 
               
               
                 Pigment 
                 R-960 titanium dioxide 
                 15.6 
                 DuPont ™ 
               
               
                   
                   
                   
                 Ti-Pure ® 
               
               
                 Dispersant 
                 SOLSPERSE-32500 
                 3 
                 Lubrizol Corp. 
               
               
                 Solvent 
                 butyl acetate 
                 20.3 
               
               
                 Curing agent 
                 Desmodur N 3900 (NCO 
                 12.4 
                 Covestro 
               
               
                   
                 19.6%) 
               
               
                   
               
            
           
         
       
     
     The coating composition was prepared as follows. A pigment paste mixture was made by mixing the fluorocopolymer, the pigments and the dispersant in a high-speed dispersion machine with glass beads to disperse the mixture and reduce the size of the pigment. The mixture was dispersed for about 3 hours at 3000 RPM, until the fineness of the composition was less than about 20 μm. The mixture was then filtered to remove the glass beads. 
     Next, the solvent was added to the pigment paste mixture, and the resulting mixture was well mixed by the high-speed dispersion machine for about 30 minutes at 1500 RPM. Then, the curing agent was added to the mixture, and the resulting mixture was again well mixed by the high-speed dispersion machine for about 30 minutes at 1500 RPM, thus forming the coating composition. 
     In order to form the coating film, conventional methods such as a brush, a roller, an air spray, an airless spray, a flow coater, a roll coater, a spin coater, and the like may be utilized, and the coating can be applied on various substrates. In addition, the coating film can be formed directly on a substrate or on a primer layer, or if necessary on an undercoating layer. In the present case, the coating film was applied to a substrate and the outermost cured coating film layer had a layer thickness of about 20-30 μm. 
     After coating was complete, the coated substrate was kept at room temperature (about 20-25° C.) for about one week to ensure that the outermost coating film layer was completely cured.