Reaction products polymerization-blocking

A number of BMI resias based on this chemistry became commercially available through Rhc ne Poulenc for appHcation ia priated circuit boards and mol ding compounds and Rhc ne Poulenc recognized the potential of bismaleimides as building blocks for temperature-resistant thermoset systems. The basic chemistry, however, was not new, because the Michael addition reaction had been employed by Du Pont to obtain elastomeric reaction products from bismaleimides and Hquid polymeric organic diamines (15). 

The fullerene C o was used as the Unking agent for the synthesis of (PCHD-fc-PS)6 and (PS-fc-PCHD)6 star-block copolymers [154], The polymers were then aromatized with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, DDQ, in 1,2-dichlorobenzene to yield the corresponding copolymers containing poly(l,4-phenylene) blocks. In order to achieve high 1,4-isomer contents and to avoid termination reactions, the polymerization of CHD was conducted in toluene at 10 °C without the presence of any additive to yield products with low molecular weights. Coupling of the PCHD-fo-PSLi to C60... 

Reaction Injection Molding. RIM uses the anionic polymerization of nylon-6 to carry out polymerization in the mold. A commercial process involves the production of block copolymers of nylon-6 and a polyether by mixing molten caprolactam, catalyst, and polyether prepolymer, and reacting in a mold (27,28). 

This reaction has the characteristics of a dead end polymerization, and the conversion of monomeric MMA to polymer can be controlled via the azo content of the polystyrene and the reaction temperature. The separation of the reaction products into homopolymer and block copolymer was achieved by selective solvent extraction thus, cyclohexane was used to dissolve the homopolystyrene, acetonitrile the homo-poly-MMA and the copolymer was completely soluble in benzene. The compositition of the crude product as a function of the ratio of MMA/prepolymer is shown in Fig. 4.5 58> ... 

Fig. 4.5. Composition of the Product O, block copolymer, , homo PMMA, A, A homo polystyrene reaction temp. O, , A 85 °C,. , A 75 °C (a) obtained by solution polymerization, (b) obtained by precipitation polymerization.

The color change and the sensitivity of conversion to order of addition of monomers and peroxide indicate that in order to obtain an AFR polymer the polar monomers must first be complexed or allowed to react with the active or living end of the anionic polymer chain, or otherwise solvate it before the polymer chain is attacked by the peroxide. Success or failure of the subsequent free radical block polymerization depends on the nature of the complex or reaction product formed. The resultant species are no longer active for propylene polymerization. The necessity of complex formation has also been observed by Milovskaya and coworkers (4). They have shown that vinyl chloride, a weak complexing agent, can be polymerized effectively with triethylaluminum peroxide only when it is present with a more active complexing compound such as an ester or an ether. 

More evidence In favor of polymer chain growth on both sides of a metalloporphyrln plane was obtained In the copolymerization of propylene oxide and phthallc anhydride. The catalyst was the combination of EtPh3PBr and TPPAl-(-0-CHMe-CH2-)-Cl (TPPAlPPO), which can be obtained by the polymerization of propylene oxide with TPPAICI (Equation 1). If the copolymerization proceeds on both sides of a metalloporphyrln plane, a block copolymer, polyetherpolyester. Is expected to be formed on one side, and a polyester Is expected on the other side. In fact, GPC of the reaction product (Figure 8) showed two narrow peaks and clearly Indicated the formation of polymers with different chain lengths. Thus, this reaction provides the first example of a catalytic reaction occurring on both sides of a metalloporphyrln pleme. 

Adhesives which are meant to cure at temperatures of 120 or 171°C require curatives which are latent at room temperature, but react quickly at the cure temperatures. Dicyanodiamide [461-58-5], (TH INI is one such latent curative for epoxy resins. It is insoluble in the epoxy at room temperature but rapidly solubilizes at elevated temperatures. Other latent curatives for 171°C are complexes of imidazoles with transition metals, complexes of Lewis acids (eg, boron trifluoride and amines), and diaminodiphenylsulfone, which is also used as a curing agent in high performance composites. For materials which cure at lower temperatures (120°C), these curing agents can be made more soluble by alkylation of dicyanodiamide. Other materials providing latency at room temperature but rapid cure at 120°C are the blocked isocyanates, such as the reaction products of toluene diisocyanate and amines. At 120°C the blocked isocyanate decomposes to regenerate the isocyanate and liberate an amine which can initiate polymerization of the epoxy resin. Materials such as Monuron can also be used to accelerate the cure of dicyanodiamide so that it takes place at 120°C. 

In general, when reacting two monomers in a polymerization reaction, different products may be formed, depending on the reactivity ratios of the monomers and the reaction conditions (see Fig. 10). Therefore, in order to describe the reaction products fully it is necessary to analyze the copolymer (MMD, CH) and to determine the amount of homopolymers which may have been formed as unwanted by-products. For a block copolymer it would be of... 

Polymerization is an addition reaction of a basic building-block that remains chemically unchanged, except for the absence of the double bond, after the reaction. Condensation polymerization is a substitution reaction. Two groups of reactive compounds of the same or different types react with one another. Low molecular secondary products such as water, ammonia, hydrogen chloride, alcohols, etc. are produced in the reaction. 

When lactones copolymerize with cyclic ethers, such as j -ptopiolactone with tetrahydrofiiran, in the early steps of the reaction the cyclic ethers polymerize almost exclusively. This is due to the greater basicity of the ethers. When the concentration of the cyclic ethers depletes to the equilibrium value, their consumption decreases markedly. Polymerizations of the lactams com-mence. The products are block copolymer. 

Further, when another cyclosiloxane is added to this reaction system, polymerization resumes to produce block poly(organosiloxanes) of the ABBA type. Because the B sections are identical, we may treat the product as a triblock copolymer. For example, when hexaphenylcyclotrisiloxane is added to the product of reaction (6.25), the reaction may be represented as follows ... 

Combination of anionic polymerization and post polymerization reactions has been used for the synthesis of poly(acrylic acid-b-N,N-diethylacrylamide) (PAA-PDEA) copolymers [9]. Initially the synthesis of a precursor poly(tert-butylacrylate-b- N,N-diethylacrylamide) (PtBMA-PDEAAm) block copolymer was realized via sequential anionic polymerization of the tert-butyl acrylate and diethylacrylamide monomers. However, an amount of PtBMA homopolymer was detected in the crude reaction product. In order to remove the vast majority of the homopolymer, the authors proposed the precipitation of the crude product in hexane, where the homopolymer is highly soluble, in contrast to the block copolymer. The piuified block copolymer was subjected to deprotection of the tert-butyl group in acidic media, leading to the desirable DHBC. The final block copolymer showed pH and thermosensitive solution aggregation. 

The synthesis of a well defined poly(vinyl alcohol)-b-poly(aciylic acid) (PVA-PAA) DHBC has been recently reported in the literature [32] by a two step synthetic scheme. First the synthesis of a poly(acrylonitrile) (PAN) block was realized via cobalt-mediated radical polymerization, using a poly(vinyl acetate) (PVAc) macroinitiator, followed by hydrolysis of both blocks. The polymerization was performed in DMF, a very good solvent for PAN, and at low temperature, where block copolymers with low polydispersity were obtained. The polymerization procedure led to well defined macromolecules with relatively high molecular weights. The obtained copolymers were transformed to the desired DHBCs by hydrolysis, using large excess of potassium hydroxide in a water/ethanol mixture. The successful completion of the hydrolysis reaction was monitored by NMR and IR spectroscopy. An additional macroscopical indication of the DHBC formation was the aqueous solubility of the reaction product. 

Polymerization involves the reaction of the monomer building blocks into polymers. The polymerization reaction types involve addition reactions and condensation reactions. Addition reactions typically involve the use of ethene to form polyethene and polyethylene. Condensation reactions typically involve different reaction products reacting to form a heteropolymer and a small molecular by-product. The reaction of 1,6-diaminoethane and hexanedioic acid to form nylon and water is a classic example. Polymers made from one monomer type are termed homopolymers, and those formed with two different monomers are referred to as copolymers. 

Another interesting feature of the SB 12 catalyst is its low deactivation rate (figure 14). This results in a nearly constant reaction rate allowing easy polymerization control and production of block copolyaer by multiple step polymerization. 

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