Propylene oxide cured copolymers

High-resoIution proton and silicon NMR has been used to study structure formation in solution mixtures of ethylene oxide/propylene oxide triblock copolymers and methyl silsesquioxane. These mixtures are precursors to ultra low dielectric constant filim used in the fabrication of integrated circuits. The solution NMR results show that micelle formation is suppressed during solvent casting and curing of the films, and that miscibility is enhanced by the interactions of both the ethylene oxide and propylene oxide blocks of the triblock copolymer with the methyl silsesquioxane matrix. 

Proton NMR in solution has been used to study composite formation in mixtures of ethylene oxide/propylene oxide triblock copolymers and methyl silsesquioxane. The porous films for low constant applications are prepared (Figure 1) by mixing the polymers and methyl silsesquioxane in butanol followed by spin casting (5). The film is then heated to 120°C to condense the methyl silsesquioxane into a relatively rigid network. After the matrix has been cured, a high temperature treatment (> 400 °C) is used to remove the polymer and obtain the final porous film. 

The ethylene oxide/propylene oxide triblock copolymers were chosen to maintain miscibility as the composite cures. To achieve this, it is necessary to have favorable interactions between the polymer and the matrix, even as the matrix becomes more hydrophobic. We have explored the intermolecular interactions between the matrix and the polymer using two-dimensional (2D) exchange NMR (7) on the neat mixture, and Figure 6 shows the 2D exchange... 

The polyols used are of three types polyether, polyester, and polybutadiene. The polyether diols range from 400 to about 10,000 g/mol. The most common polyethers are based on ethylene oxide, propylene oxide, and tetrahydrofuran or their copolymers. The ether link provides low temperature flexibility and low viscosity. Ethylene oxide is the most hydrophilic and thus can increase the rate of ingress of water and consequently the cure rate. However, it will crystallize slowly above about 600 g/mol. Propylene oxide is hydrophobic due to hindered access to the ether link, but still provides high permeability to small molecules like water. Tetrahydrofuran is between these two in hydrophobicity, but somewhat more expensive. Propylene oxide based diols are the most common. 

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Table IV. Properties of Cured Copolymers of Propylene Oxide and...

In these studies we have used solution NMR to study structure formation and the intermolecular interactions between the polymer and the matrix during the cure that affect the miscibility. The triblock copolymers form micelles in aqueous solution with the propylene oxide block at the center and the ethylene oxide block at the exterior (6), and micelle formation can be monitored via the proton linewidths. The NMR studies show that the triblock copolymers do not form micelles in the butanol solutions used for solution casting films of the low-k dielectrics, or in neat mixtures of the triblock copolymers with the methyl silsesquioxane. The methyl silsesquioxane starting material contains a... 

Solid -state NMR methods were used to characterise the heterogeneous dynamics, miscibility, and microdomain structure in nanostructured thermoset blends of epoxy resin (ER) and amphiphilic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymers (PEO-PPO-PEO). NMR experiments show that there is a distinct dynamic difference between the block copolymer (both PEO and PPO) and cured-ER matrix indicating the presence of phase separation, which also confirms the existence of the interphase region including a considerable amount of immobilised PEO and mobilised partially cured ER. An improved method based on spin-diffusion experiments enabled a quantitative determination of the interphase thickness. ... 

Propylene oxide rubbers (PO rubbers) These materials were first announced in 1963 (Gruber et ai, 1963 1964) and are copolymers of propylene oxide with a cure-site monomer (usually allyl glycidyl ether used to a proportion of about 10% of the total monomer). Their structures may be represented by ... 

Parel elastomer, a copolymer of propylene oxide and allyl glycidyl ether, has a combination of properties that make it very useful in many rubber applications. It can be vulcanized with a conventional mixture of sulfur and accelerators. The cured elastomer has a low glass transition temperature (approximately -55 to -60 C.), and the excellent dynamic properties of natural rubber. It can be made very stable to high temperature oxidative degradation, and is better than neoprene in this respect, when NBC is added as a stabilizer. 

A large variety of addition copolymers and terpolymers, prepared from hydroxyalkyl acrylates and/or methacrylates have been treated with MA to prepare polymers with pendent maleate residues.An addition polymer prepared from ethyl acrylate-hydroxypropyl methacrylate-styrene was treated sequentially with MA and propylene oxide.Blends of these polymers with vinyl monomers were cured with peroxides to obtain films with physical properties better than regular cured unsaturated polyesters. In another example, a styrene-butyl acrylate-hydroxyethyl methacrylate terpoly-mer was treated with MA to obtain a molding resin.When blended with styrene and cured with peroxides, the molding exhibited low shrink (less than 5%) and Rockwell hardness (M scale) 55. The same chemistry and technology have been explored for preparing radiation-curable coatings. " ... 

It is evident that reactions of unsaturated polymers with bisnitrile oxides lead to cross-linking. Such a procedure has been patented for curing poly(butadiene), butadiene-styrene copolymer, as well as some unsaturated polyethers and polyesters (512-514). Bisnitrile oxides are usually generated in the presence of unsaturated polymers by dehydrochlorination of hydroximoyl chlorides. Cross-linking of ethylene-propylene-diene co-polymers with stable bisnitrile oxides has been studied (515, 516). The rate of the process has been shown to reduce in record with the sequence 2-chloroterephthalonitrile oxide > terephthalonitrile oxide > 2,5-dimethylterephthalonitrile oxide > 2,3,5,6-tetramethylterephthalo-nitrile oxide > anthracene-9,10-dicarbonitrile oxide (515). 

Until they are vulcanized, elastic, amorphous ethylene-olefinic copolymers have very little possible utility except as components of caulks or sealants. However, grafting MA on the copolymers, using peroxide initiators, and compounding the modified materials with zinc oxide provides improved rubbers. A typical recipe would consist of 100 parts ethylene-propylene copolymer, 20 parts zinc oxide, 7 parts MA, and 2 parts BPO. Curing is carried out at 160°C for 30-45 min. Previously grafted copolymers, containing 2-5 MA residues, can also be cured with N-phenyl-B-naphthylamine initiator, steric acid modifier, and zinc oxide crosslinker. 

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