Polyesters, carboxylated

Recent advances have seen both Tighe(87) and Lenz(90)developing procedures for carboxylated polyesters. Tighe has evaluated biologically produced polymers.(88) American Cyanamid Company continues to modify poly(glycolic acid) by copolymerizing ethylene oxide.(89)... 

Carboxylated Polyester Additives for Improving the Adhesion of Coatings... 

Carboxylated polyesters were prepared by extending hydroxyl-terminated polyester segments with dianhydrides. Carboxylated polyesters which were soluble in common lacquer solvents were effective in improving the adhesion of coatings on a variety of substrates when 1-10% was blended with cellulose acetate butyrate, poly(vinyl chloride), poly(methyl methacrylate), polystyrene, bisphenol polycarbonates, and other soluble polymers. 

Incorporation of carboxyl groups in vinyl polymers (J) and polyolefins (1, 7) improves the adhesion of these polymers to various materials. However, many of these carboxylated polymers, particularly the carboxylated polyolefins, have limited solubility in volatile, lacquer-type solvents such as butyl acetate or methyl ethyl ketone and thus are limited in their ability to improve the adhesion of coatings applied from solvents. Carboxylated polyesters that are soluble in these solvents can be prepared. We were therefore interested in determining the effects of structure and carboxyl content on the adhesion of coatings of various classes of polymers blended with carboxylated polyesters. 

Preparation of Carboxylated Polyesters. Hydroxyl-terminated polyester segments were prepared by conventional procedures and extended with an equimolar amount of dianhydride (2). To avoid the possibility of crosslintdng the polymer, reaction1 with the dianhydride was carried out at 175 °C. Depending upon the size of the reaction mixture, about 1 to 3 hours were required for all of the dianhydride to react and for a medium-to-high melt viscosity to be obtained. Inherent viscosities were 0.3 to 0.4. 

The specimens were coated with a blend of the carboxylated polyester and second polymer in a solvent (10% solids), which, when possible, consisted of a conventional lacquer solvent (74.2% toluene, 7.4% butyl alcohol, 7.4% Solvesso 100 solvent, 3.7% ethyl acetate, 3.7% butyl acetate, and 3.6 Cellosolve acetate). If the second polymer was not soluble (polysulfone, polycarbonates, PPO), chloroform was used. The coatings were dried for 1 hour at room temperature and then for 2 hours in an oven at 115°C. The coating thickness was about 0.5 mil. 

The carboxylated polyesters were prepared by a two-step process (1) preparation of a hydroxyl-terminated polyester segment and (2) reaction with a dianhydride to extend the polyester and introduce carboxyl groups. When the dianhydride is pyromellitic (II), the equation is as follows ... 

The carboxylated polyesters based on examples 9-14 in Table I were soluble in butyl acetate and methyl ethyl ketone, but it was necessary to add up to 10% of an alcohol (methyl or butyl) to toluene to give solubility. Some of these carboxylated polyesters were also soluble in plasticizers. Carboxylated T50I(NPG) and T50H(NPG) (3000-molecu-lar weight segments extended with PMDA) were soluble in dibutyl phthalate but not in dioctyl phthalate. The similar H( NPG) carboxylated polyester was soluble in both dibutyl and dioctyl phthalates, but it was inferior to the above two polymers in promoting adhesion. 

All the coated samples listed in the tables were heated in an oven for 2 hours at 115 °C to ensure the removal of all solvent. Drying at room temperature, however, was sufficient for many of the coatings to pass the cellophane tape test. The cellulose acetate butyrate blends with 1% of each of the four carboxylated polyesters in Table II, for instance, passed the adhesion test on steel after the coatings had dried at 23 °C for only 0.5 hour, and the blends with 1% of the polyesters having acid numbers of 39-126 passed the adhesion test on aluminum. 

Metal specimens coated with the various blends were immersed in water in an accelerated test to determine the effect of high humidity. Cellulose acetate butyrate blends containing carboxylated polyesters prepared with hexahydroterephthalic acid [H(NPG), T50H(NPG)] were particularly susceptible to moisture and failed the adhesion test after immersion for only 0.5 hour similar blends containing T50I(NPG) extended with dianhydride Via or with PMDA passed the adhesion test after immersion for 16 hours. When coatings on cold-rolled steel of cellulose acetate butyrate (EAB-381-0.5) blends containing 1% of each of the... 

T50I(NPG)/PMDA was of particular interest because of its adhesive characteristics, oxidative stability, and polymer cost. Table III shows the improvement in adhesion obtained when various substrates were coated with blends containing this polyester (acid number 39). As indicated in the table, the ease of obtaining adhesion on the different substrates decreased approximately in the following order brass > steel > copper > chrome-coated steel > aluminum > nylon 66 > poly (ethylene terephthalate). In spite of the wide differences in structure and polarity of the various polymers, the carboxylated polyester significantly improved the adhesion of the coatings. 

The presence of a plasticizer in addition to the carboxylated polyester adversely affected the adhesion of some of the polymers—e.g., cellulose acetate butyrate and poly (vinyl chloride) plastisols. 

Oxidative Stability of Carboxylated Polyesters. The polyesters which were extended with dianhydrides are those in Table I which were soluble in the lacquer solvents. Of these, theoretical considerations indicate that T50I(NPG) should be the most oxidatively and thermally stable because it is the only one with a completely aromatic acid component (terephthalic and isophthalic), and the glycol component has the stable neopentyl structure. When K-l polycarbonate films containing 5% of this polyester extended with PMDA were heated in a forced-air oven at 200°C, the film life (time to brittleness when creased) was not lowered appreciably (compared with a control containing no carboxylated polyester). The incorporation of 5% of the similar carboxylated T50H(NPG)... 

Similar ACECs (Scheme 47) were prepared in a different way [28]. The carboxylic polyesters were prepared by polycondensation of 4-cyclohexene-1,2-di-carboxylic acid anhydride with a glycol. Then the glycidylation of COOH groups with ECH followed by ep oxidation of cyclohexene rings with PA A was carried out. Depending on the COOH groups content in the intermediate polyester, various glycidyl/epoxycyclohexane ratios can be obtained. 

Anisic acid, a-carboxyl, polyester with ethylene glycol —, —, polyester with 1,6-hexanediol... 

Poly((3-malic acid) is the most simple carboxylated polyester [47-49]. It is prepared by ring opening polymerization of the mono-benzyl ester (3-lactone of malic acid and subsequent debenzylation. It has been explored as drug carrier. Reaction of itaconic anhydride with PCL with hydroxy terminals results in polyesters with carboxylic and C=C double bond functional terminals, suitable for further reactions to form networks and gels, (5) and (6) [50,51]. 

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