Simultaneous polymerization

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

The simultaneous polymerization and sol-gel reaction often brings complexity to the overall reaction. Moreover, it is difficult to control the molecular weight of the sample. Recently, Patel et al. [51] have synthesized the rubber grade acrylic copolymers and terpolymers-/n situ silica hybrid nanocomposites using this technique. 

Block copolymer synthesis from living polymerization is typically carried out in batch or semi-batch processes. In the simplest case, one monomer is added, and polymerization is carried out to complete conversion, then the process is repeated with a second monomer. In batch copolymerizations, simultaneous polymerization of two or more monomers is often complicated by the different reactivities of the two monomers. This preferential monomer consumption can create a composition drift during chain growth and therefore a tapered copolymer composition. 

In a very similar way, hydroxy functionalized ATRP initiators such as 2,2,2-tribromoethanol can be used for the simultaneous polymerization of eCL and MMA (Scheme 25) [83]. Purposely, the ROP of eCL is promoted by Al(OfPr)3 added in catalytic amount so that the rapid alcohol-alkoxide exchange reaction (see Sect. 2.4) activates all the hydroxyl functions. In order to avoid initiation by the isopropoxy groups of Al(0/Pr)3. The in-situ formed zPrOH is removed by distillation of the zPrOH/toluene azeotrope. On the other hand, the ATRP of MMA is catalyzed by NiBr2(PPh3)3. The two aforementioned one-step methods provide block copolymers with controlled composition and molecular weights, but with a slightly broad MWD (PDI=1.5-2). 

The term statistical copolymer is proposed here to embrace a large proportion of those copolymers that are prepared by simultaneous polymerization of two or more monomers in admixture. Such copolymers are often described in the literature as random copolymers , but this is almost always an improper use of the term random and such practice should be abandoned. 

For most step polymerizations, for example, in the synthesis of polyl hexamethylene adipa-mide) or polyethylene terephthalate), two reactants or monomers are used in the process, and the polymer obtained contains two different kinds of structures in the chain. This is not the case for chain polymerizations, where only one monomer need be used to produce a polymer. However, chain polymerizations can be carried out with mixtures of two monomers to form polymeric products wiht two different structures in the polymer chain. This type of chain polymerization process in which two monomers are simultaneously polymerized is termed a copolymerization, and the product is a copolymer. It is important to stress that the copolymer is not an alloy of two homopolymers hut contains units of both monomers incorporated into each copolymer molecule. The process can be depicted as... 

This chapter is concerned primarily with the simultaneous polymerization of two monomers to produce statistical and alternating copolymers. The different monomers compete with each other to add to propagating centers, which can be radical or ionic. Graft and block copolymers are not synthesized by the simultaneous and competititive polymerization of two monomers. Each monomer undergoes polymerization alone. A sequence of separate, noncompetitive polymerizations is used to incorporate the different monomers into one polymer chain. The synthesis of block and graft copolymers and variations thereof (e.g., star, comb) are described in Secs. 3-15b-4, 3-15b-5, 5-4, and 9-9. 

Terpolymerization, the simultaneous polymerization of three monomers, has become increasingly important from the commercial viewpoint. The improvements that are obtained by copolymerizing styrene with acrylonitrile or butadiene have been mentioned previously. The radical terpolymerization of styrene with acrylonitrile and butadiene increases even further the degree of variation in properties that can be built into the final product. Many other commercial uses of terpolymerization exist. In most of these the terpolymer has two of the monomers present in major amounts to obtain the gross properties desired, with the third monomer in a minor amount for modification of a special property. Thus the ethylene-propylene elastomers are terpolymerized with minor amounts of a diene in order to allow the product to be subsquently crosslinked. 

The low temperature ( 140°C) anionic ring opening polymerization is further complicated by the crystallinity in nylon 6. Magill [66] has reported that the temperature for maximum crystallization rate in nylon 6 is about 140-145°C. The nucleation rate is low above 145°C, whereas viscous effects hinder crystal growth below this temperature. As a result, at about 140-145°C, heterogeneous reaction conditions can be encountered (as we have seen in our studies) if there is simultaneous polymerization of caprolactam and crystallization of the nylon 6 formed. 

Copolymerization, of course, involves the simultaneous polymerization of a mixture of two (or more) monomers. 

Additionally, an NCA may simultaneously polymerize by more than one mechanism. The active monomer mechanism provides polymers whose molecular weight is not dependent on initiator concentration, and high molecular weight polymers are readily obtained. The normal or carbamate mechanism should provide one polymer molecule per initiator molecule and the initiator is incorporated into the polymer. 

It is known since a long tune that the simultaneous polymerization of two or more olefinic monomers yields copolymers the properties of which axe different from those of a mixture of the corresponding homopolymers, and in which the monomeric units are present in the same polymeric chain. The physical properties of these copolymers are different depending on the nature of their constituents, their molar composition and their internal structural arrangement. 

We have successfully demonstrated the concept of simultaneous polymerization and poling of photocrosslinkable systems to produce high quality films with large second-order nonlinear optical susceptibilities and low scattering losses. The ability to process these materials under mild conditions may help avoid potential problems encountered in... 

Terpolymer — The product of simultaneous polymerization of three different monomers or of grafting one monomer to the copolymer of two monomers. 

The cyanates are mixed with thermoplastic polymers. They can be also dissolved in a monomer and then a simultaneous polymerization is carried out. So-called SINs (Simultaneous Interpenetrating Networks) are obtained. 

Polystyrene modified dicyanate polymer was obtained by simultaneous polymerization of styrene monomer and BPA/DC. The handling of low viscous dicyanate solution in styrene is more convenient that the processing of crystalline BPA/DC or high-viscous dicyanate prepolymers [52]. A similar patent specification describes the polymerization of a mixture of styrene, BPA/DC and p-isopropenyl cyanate BMI (cf. Sect. 5) was also used [53]. 

Semi-IPNs are obtained by simultaneous polymerization of styrene and polycyclo-trimerization of BPA/DC (Sect. 2) [52, 53], IPNs consisting of two separate networks are formed, if unsaturated monomers with two or more polymerizable double bonds are used. 

In a recent paper Saegusa and his co-workers (64) report that ethylene oxide is converted to dioxane in yields of up to 96% when the monomer is treated with a catalytic amount (generally 2—5 mol %) of a superacid such as trifluoromethanesul-fonic acid, or a derivative of a superacid such as ethylfluorosulfonate, in methylene chloride or nitromethane at temperatures between 10 and 40 °C. The authors propose that dioxane is formed by a simultaneous polymerization and degradation of the formed polymer. Propagation as well as degradation are assumed to occur via the ester species. 

An interpenetrating polymer network (IPN) consisting of an epoxy and an elastomer has been developed by Isayama.29 This is a two-component adhesive-sealant where the components are simultaneously polymerized. It consists of the MS polymer, developed in Japan by Kanegafuchi and commonly used in sealant formulations, with the homopolymerization of DGEBA using a phenol catalyst and a small amount of silane as a graft site to connect the MS polymer and epoxy homopolymer networks. 

Such differences in reactivities would be plausible if during chain growth in the solid phase, polymerization and crystallization were simultaneous. This means that a newly added monomer unit is incorporated into the crystal lattice at the same time that it is attached chemically to the polymer chain. This would imply that the cationic chain ends are directly on the crystal surface (simultaneous polymerization and crystallization as symbolized by Model A in Figure 2). 

The difference in formaldehyde equilibrium concentration between homogeneous and heterogeneous polymerization is large enough to indicate a difference in the physical state of cationic chain ends in the dissolved and in the crystalline polymer. Thus, Model B is ruled out. In the homopolymerization of trioxane and in the heterogeneous copolymerization with small amounts of dioxolane the active centers of chains which have precipitated from the solution predominantly are directly on the crystal surface (Model A). According to Wunderlich (20, 21), this is the first case in addition polymerization where Model A—simultaneous polymerization and crystallization—has been proved experimentally. 

Table 1 summarizes the various attempts carried out in this stndy as well as the final parameters of the condensation, i.e. conditions, nnmber average molar mass M, and cycle content at hnal conversion. In most instances, large contents of small cycles were generated, whereas polymer chains of low molar masses were synthesized. During certain experiments, a donble distribntion of the molar masses was observed (see Table 1), probably due to two types of simultaneous polymerization (vide infra). 

Varying the relative rates of the two reactions in a simultaneous polymerization permits a great variety of synthetic detail. One component... 

Experiments were centered around conditions that would result in simultaneous polymerization or simultaneous gelation of the two components. Reactions off center resulted in one reaction or the other proceeding faster. Thus a range of properties at or near simultaneous gelation could be systematically observed. The range of the initiator concentration was 0.18-0.46% (based on n-butyl acrylate). The epoxy was prereacted from one to eleven hours before the acrylate mix was added. 

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