Cross-polymerized

The copolymerization between two different monomers can be described using only four reactions, two homo-polymerizations and two cross-polymerization additions. Through appropriate arrangements, equations that allow copolymer composition to be determined from the monomer feed ratio are developed. 

Interpolymerization of two different alkenes is termed cross polymerization or, more usually, copolymerization. 

To promote the cross polymerization of olefins the concentration of the more reactive isobutene is kept low by recycling a stream of hydrocarbon-acid emulsion having a low iso-... 

The pyrolysis of poly[(germylene)diacetylenes] 35 under argon was studied112. At relatively low temperatures (150-250 °C) cross polymerization through the triple bonds was observed and further heating to temperatures up to 1200 °C provided crystalline... 

Photo-oxidation of citronellol in polystyrene beads [120]. A sample of 3.0 g of polystyrene beads (commercial, cross-polymerized with 1% of divinylbenzene) was treated with a solution of 2 mg of tetraphenylporphyrin and 780 mg (5 mmol) of citronellol in 20 mL of ethyl acetate in a petri-dish (30 cm diameter). After 2h in a ventilated hood, the solvent has evaporated and the petri-dish was covered with a glass plate and irradiated for 5 h with a 150 W halogen lamp. The solid support was then washed with 3 x 20 mL of ethanol, the combined ethanol fractions were rota-evaporated and 900 mg of the hydroperoxide mixture (96%) was isolated as a slightly yellow oil. The hydroperoxides were quantitatively reduced to the corresponding allylic alcohols by treatment with sodium sulfite. One of these products is used in the industrial synthesis of rose oxide. 

Since the criss-cross cycloaddition reaction is a sequence of two [3 + 2] cycloaddition steps, the reaction of hexafluoroacetone azine with a,a>-diolefins offers access to a new class of trifluoromethyl-substituted heterocyclic macromolecules. Polymers with interesting structures and properties become available by criss-cross polymerization (88MI3 89MI2 90MI2). 

Recent developments in the cross-polymerization of the organic components used in bicontinuous microemulsions ensure the successful formation of transparent nanostruc-tured materials. Current research into using polymerizable bicontinuous microemulsions as a one-pot process for producing functional membranes and inorganic/polymer nanocomposites is highlighted with examples. 

This type of cross-polymerization of all of the organic components (hke MMA, HEMA and a polymerizable surfactant) in a bicontinuous microemulsion is an important area of recent development in microemulsion polymerization, which can be used to produce nanostructures of transparent polymer solids. The polymerization can be readily initiated using either redox or photo-initiators. The gel formation usually occurred within 20 minutes. The use of this novel type of microemulsion polymerization for preparing transparent inorganic-polymer nanocomposites in the form of films or sheets is emerging and exciting. However, very little pubhshed information about this type of nanocomposite is available, as will be described in the following sections. 

The structure analyses of two special types of dlacetylene "monomers," dlyne dimers and polydiyne macromonomers, are reviewed and preliminary results on the conversion and chromic behavior of one specific system, poly(l,8-nonadlyne) (F18N) are presented. Structure analyses of these materials before and after solid state polymerization allows a qualitative understanding of the dlacetylene polymerization. Cross-polymerized P18N has been shown to display solvatochromlc and thermochromlc behavior, even though this material Is Insoluble and Infusible. Examination of Initial optical spectroscopic data of the chromic behavior as a function of conversion, as well as consideration of the chromic behavior of conventional diacetylenes, leads to a possible explanation of the chromic behavior of crosspolymerlzed P18N. 

Other monomers (for example acrylamide, styrene, vinylpyrrolidone, vinylcar-bazole, vinyl ether, allyl ether, etc.) can be likely studied by carefully selecting other initiating radicals. Cross-polymerization might also be investigated, for example, the addition of TEA-M to vinyl ether since TEA does not react with vinyl ether. The results obtained with this procedure can also be extended to the behavior of different acrylate structures in photopolymerization experiments carried out in bulk. 

To justify the synthetic efforts for the synthesis of concave reagents, the gain in selectivity must be combined with an easy recovery. Usually, polymer fixation allows easy recycling, and therefore, the concave pyridine la has been attached to a Merrifield resin (27, see Fig. 8a).Indeed, the polymeric material 27 was able to catalyze the alcohol addition to diphenylketene comparably to the soluble concave pyridine la. but complications may exist due to swelling of the resin and substrate depletion deep within the polymer. Therefore, soluble polymers loaded with the concave pyridine I a have also been synthesized. However, this material behaved unreproducibly, especially because side reactions led to cross-polymerized insoluble material. Furthermore, due to reptation (leakage through membrane), an easy separation of product and catalyst would not be possible by ultrafiltration. 

A Before cross-polymerization, B PDA networks. C Ligjit insensitive model. 

Amorphous PDAs. The cast films of 1 were heated between two quartz panes (1 x T, 1 mm thick) at above their melting points, upon which thermal cross polymerization of DA groups took place and orange to red brown tran arent materials were obtained. It seems that simultaneous irradiation with UV light (fi om a medium pressure Hg lanq)) he s the thermal polymerization. Some of the polymers 2 only undergo thermal polymerization in the amorphous state (7P). 

F ure 1. UV-Visible absoiption spectra of some cross-polymerized DA-contaming polyesters. 

A Copolymer before cross-polymerization. B Copolymer irradiated with electron beam (50 Mrads) at 20 C. C Copolymer irradiated at 60 C (Liquid crystalline state) with UV lig t. D Copolymer heated at 100 C (molten state). E Potyester 1 (x=3, y=7) irradiated with UV fight. 

Amorphous PDAs. Yu et al.(2i) prepared poly(hexa-2,4-diynylene terephthalate), which is not photosensitive, but does polymerize by heating at 150 C. A value of 3.2 X 10 ° esu (determined the degenerate four wave mixing technique at 532 nm) has been reported for this material The polymers 3 and 4 (Chart 4) are not photosensitive, but underwent cross-polymerization when heated at 180°C (in the molten state) for 2.5 hours with simultaneous UV irradiation, giving red transparent materials. The x values for these materials were found to be 1.9 - 3.5 x 10 ° esu for polymers 3 and 2.7 -2.9 x 10 esu for polymers 4. Absorption spectra of one of the polymers 4 are shown in Figure 3. The films have an absorption maximum at 400 nm and a trough at 340-350 nm, but absorption tails down towards 700 nm due to their amorphous nature. 

We have been discussing the mechanism of polymerization of a single monomer (homopolymer). However, when two or more monomers polymerize in situ, the chains obtained differ in composition and location of each mer. These are controlled by the ratios between the tendency to homopoly-merize and to cross-polymerize ti and rj. (Details will follow.)... 

Scheme 6.39. A representation of acid-catalyzed cross polymerization of 2-methylpropene [wobutylene, (CH3)2C=CH2] with a trace of 2-methyl-l,3-butadiene [isoprene, CH2=C(CH3)-CH=CH2] followed by cross-linking chains with sulfur (part of the process of Vulcanization).

The foregoing relations and those that follow should apply to the networks of higher functionality formed by cross polymerization as well as to those with =4 formed by cross-linking pairs of units. 

Fig. 1. Percent gel and distribution of cross-link density between sol and gel versus the log of the total cross-link density for the cross polymerization of primary chains having a most probable distribution. Two curves representing networks with junction functionalities of 4 (solid) and 24 (dashed) are shown with arrows pointing to the left. In each case M 358,000. The other solid lines represent the gelation behavior of a tetrafunctional system and have arrows pointing to the right.

If r = r, the structure is strictly alternating since each monomer wants only to add the other. If r r =l, the structure is random, since P and Q chains have an equal probability of adding either monomer. If and are both greater than unity, a block copolymer results, since cross polymerization is unlikely. Equation 16.151 describes the instantaneous copolymer composition. If the monomers are not consumed at the same rate, there will be significant compositional drift over the course of the polymerization. 

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