Abstract:
Copolymers or terpolymers of carbon dioxide and at least one epoxide are found to be useful in formulations for adhesive compositions. Polarity due to the carbonate group and non-polarity due to the alkylene groups in the resulting polyalkylene carbonates makes it possible to adhere a large number of different surfaces such as steel, aluminum, fluoropolymers, and polyesters to themselves or to each other.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to the use of polyalkylene carbonates in hot melt adhesive applications. 
     Polyalkylene carbonates have both the very polar carbonate grouping in the polymer backbone and the non-polar alkylene groups. The combination of these two groupings make the polycarbonates very useful in adhesive compositions. 
     BRIEF SUMMARY OF THE INVENTION 
     Polyalkylene carbonates are produced by copolymerization of carbon dioxide with one or more epoxides. It has been discovered that these polymers possess unique properties in various adhesive applications due to the presence of polar groups in the backbone. The polar/non-polar balance can be easily adjusted to the desired level for any specific application by using different epoxides in different ratios. These polymers also have good adhesion to surfaces to which adhesion is difficult. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The polyalkylene carbonate polymers are prepared by reacting a mixture of one or more epoxides in a solvent such as methylene chloride or hexane under a pressure for 100 to 700 psig of carbon dioxide using a zinc carboxylate catalyst for up to 40 hours at 25° to 110° C. in accordance with the polymerizations described in either Soga et al, Polymer J. 16, 407 (1981) or Inoue, Makromol. Chem., Rapid Commun. 1, 775 (1980), both of which are hereby incorporated in their entirety herein. Thus, Soga et al teach copolymerization of propylene oxide and carbon dioxide by heating at 60° C. for 40 hours using zinc carboxylate catalysts supported on such materials as silicon dioxide, magnesium oxide and aluminum oxide. Inoue used catalysts prepared by the reaction of zinc oxide with aromatic dicarboxylic acids to polymerize propylene oxide in carbon dioxide at 35° C. for 40 hours. 
     Examples of the better known epoxides used in the copolymers and terpolymers of the invention are ethylene oxide, propylene oxide, 1-butene oxide, 2-butene oxide, 1-hexene oxide, cyclopentene oxide, cyclohexene oxide, cycloheptene oxide, styrene oxide, epichlorohydrin, and bis-phenol-A-diglycidyl ether. Mixtures of these epoxides can also be utilized to prepare adhesive compositions. 
     Hot melt adhesive compositions usually are formulated with several other ingredients besides the main adhesive. Thus, the formulation may consist of the main adhesive, a rubbery additive, and a low molecular weight plasticizer. The rubbery additive may be a styrene/butadiene rubber, or more particularly, a styrene/butadiene/styrene triblock rubber. The plasticizers may be selected on the basis of compatibility with the main adhesive. In the case of the instant invention, since the main adhesive is a polyalkylene carbonate, the plasticizer may be preferably the monomeric carbonate such as propylene carbonate or ethylene carbonate. A suitable weight percent ratio of polycarbonate: rubber: plasticizer is 46:46:8. 
    
    
     The following examples are meant to further illustrate, but not to limit, the invention. All parts and percentages are by weight unless otherwise designated. 
     EXAMPLE I 
     To a five gallon stainless steel reactor were added 1373 g of cyclohexene oxide, 369 g of propylene oxide, 4971 g of methylene chloride, and carbon dioxide and the mixture was polymerized according to the method described by Soga et al. Following precipitation and drying of the product, 1506 g of the desired terpolymer were obtained. Nuclear magnetic resonance (NMR), and infrared spectroscopies showed that the product was at least 99% pure as the desired terpolymer between the two epoxides and carbon dioxide. The molar ratio between the epoxides and carbon dioxide was 1:1. 
     EXAMPLE II 
     To a 500 ml stainless steel autoclave were added 30 g of propylene oxide, 90 g of methylene chloride, and carbon dioxide and the mixture was polymerized according to the method described by Inoue. The product was precipitated by the addition of methanol. After drying, 23.1 g of polymer were obtained. The polymer was at least 99% pure polypropylene carbonate as determined by NMR and infrared spectroscopies. 
     Replacement of the propylene oxide with cyclohexene oxide, cyclopentene oxide, and cis-2-butene oxide respectively, gave the appropriate polyalkylene carbonate. 
     EXAMPLE III 
     To illustrate the use of the polyalkylene carbonates as adhesives, a series of specimens were prepared and tested using ASTM Method D1002 as follows: 
     A. Comparative formulation (Not this Invention). 
     230 g of polyvinyl alcohol, 230 g of styrene/butadiene rubber, and 40 g of propylene carbonate were mixed in a Brabender mixer. The mixture was placed between two mild steel plates, 1&#34;×2&#34;× 1  /32&#34;, and pressed hot to effect adhesion. After the plates were cooled and aged for 72 hours, the break strength was determined. Whether the failure of the adhesive bond was cohesive or not was determined by visual examination of the broken specimen. The results of the tests are shown in Table I below. 
     B. The formulation of A was repreated except that the polyvinyl alcohol was replaced by polypropylene carbonate obtained from Example II. 
     C. The formulation of A was repeated except that the polyvinyl alcohol was replaced by polypropylene carbonate/cyclohexene carbonate obtained from Example I. 
     D. The formulation of C was repeated except that the mild steel specimens were replaced with specimens covered with a fluoropolymer. 
     E. The formulation of D was repeated except that the specimens were covered with polyethylene terephthalate. 
     
                       TABLE I______________________________________Sample     Break Strength, psi                    Failure______________________________________A          468           non-cohesiveB          752           non-cohesiveC          1326          cohesiveD          1050          cohesiveE          890           cohesive______________________________________