Monomer Syntheses

According to Pham et al [17] (table 2) the substituent (R) affects the yield of the synthesis. 

TABLE 2. Effect of the substituents on the yield of the Grignard reaction. 

Another convenient way to synthesize this kind of monomer is to brominate 3-methylthiophene and then use Grignard coupling [18]  

It is also possible to synthesize alkylthiophene via 3-lithiumthiophene, which is prepared by lithation of 3-bromothiophene  

This reaction can be carried out at -70 C to prevent exchange of 3-thienyllithium into 2-thienyllithium [19]. Further reaction with suitable halogenated alkanes gives the desired alkylthiophene. 

Several alternative routes have been suggested, which in some cases are especially useful to prepare alkyl derivatives of EDOT with substitution at the dioxane ring. The most important of these alternative pathways appears to be the acid catalyzed transetherification of 3,4-dimethoxythiophen (or other lower alkoxythiophenes) with vicinal diols. - ° The Williamson ether synthesis can lead to low yields particularly in the case of long chain 1,2-dibromoalkanes due to the competing elimination reactions instead of nucleophilic substitution, resulting in a-olefins or a-acetylenes. Although 

Synthesis of EDOT from oxalic acid ester and thio-diacetic add ester. 

Mitsunobu reaction for the synthesis of EDOT derivatives. (Adapted from D. Caras-Quintero and P. Bauerle, 2002, Chem Commun 22 2690-2691.) 

The exchange of the furan-oxygen in 2,5-dimethoxy-3,4-ethylendioxytet-rahydrofuran by sulfur using NaSH and the elimination of two moles of methanol demonstrate another alternative route to EDOT, as described in a patent application.  

In the past years we have synthesized a variety of compoimds with oxadiazole and thiadia-zole moieties [7]  

The rod-like thiadiazole derivative 3 is liquid crystalline and shows a smectic as well as a nematic LC phase with the following phase behaviour c 103 Sa 180 n 203 i. An acrylate monomer was prepared by hydroboration of the terminal double bond and subsequent esterification with acryloyl chloride and then polymerized. The resulting polymer 5 exhibits a mesophase which has not yet been identified. 

Unfortunately the clearing point of the polymer is at 246 °C, where the material starts to decompose. Therefore orientation in an electric field was not possible. 

In contrast to the thiadiazole the oxadiazole 4 is neither liquid crystalline as monomer nor as polymer. The reason for the lack of mesogenic properties is that the substitution of the sulphur by oxygen introduces a bend into the molecule which prevents the formation of a LC phase. 

Additionally the oxadiazole monomer 14 was synthesized, in which the ester group is replaced by a biphenyl unit. By this it is possible to investigate the influence of the ester function on the photoconductive properties of the liquid crystalline compoimds. 

An interesting alternative in using diols, but starting from 3,4-dihydroxythiophene-2,5-dicarboxylic acid diethyl ester (the same intermediate as used in the Gogte pathway above), was developed independently by the groups of Reynolds [25] and Bauerle [26], who utilized the Mitsunobu reaction with azodicarboxylic acid ester-phosphane as the etherification agent. 

A completely distinct synthesis of the thiophene heterocycle has been published starting with 2,3-dimethoxybutadiene and SCI2 [28], In the last step of this EDOT synthesis, a transetherification reaction as mentioned above is necessary, using ethylene glycol. 

Exchanging the furan-O in 2,5-dimethoxy-3,4-ethylendioxytetrahydrofuran for sulfur with NaSH and eliminating 2 mol of methanol is another alternative pathway to EDOT, described in a patent [29]. 

All characteristic last steps in the synthesis of EDOT, i.e. the ring closure to the dioxane structure, are also sufficient for the formation of the analogous seven-membered rings (1,3-dioxepanes), the 3,4-propylenedioxythiophenes (ProDOTs) Williamson ether synthesis [13], transetherification [30] and Mitsunobu reaction [25]. The analogous basic five-membered ring compound 3,4-methylenedioxythiophene (MDOT, a 1,3-dioxolane derivative) is also accessible by Williamson ether synthesis using bro-mochloromethane [31]. 

Oxetanes are generally prepared by cyclization of the corresponding a.y-disubstituted compounds7)  

If difunctional substrates with suitable R groups are unvailable, the corresponding 3,3-disubstituted oxetanes may be prepared by an exchange reaction by the use of cation solvating media, e.g. glycols 7). 

Examples of 3,3-disubstituted oxetanes obtained by these methods are listed in Table 5.1. More information on the synthesis of oxetanes, including those substituted in 2 and 4 positions, can be found in Ref. 8). 

As the polymerization proceeds, the amount of P O. decreases to the optimal final concentration of 83% [52]. PBO is a lyotropic polymer meaning that is displays liquid crystalline behavior which is dependent upon the concentration in solution [53]. The two stage method of adjusting the PjO. concentration allows the production of PBO at high polymer concentrations. 

PBO polymerization can proceed to high molecular weights even when there is a 5% excess of TA. The high degree of polymerization that can be obtained with an excess of one monomer can be explained by the low of solubility of TA in PPA. The solubility at 140°C is 0.0006 g TA per 1 g PPA [44]. 

The polymerization kinetics of PBO has been studied by several researchers, but it is difficult to draw a unanimous conclusion from these researches due to complexity of the reaction system involving an isotropic-nematic phase transition [55-57]. The polymerization rate for PBO was found to decrease sharply 

---

Frcc-Radical Reactions. Eree-radical reactions of maleic anhydride are important in polymeri2ations and monomer synthesis. Nucleophilic radicals such as the one from cyclohexane [110-82-7] serve as hydrogen donors that add to maleic anhydride at the double bond to form cyclohexylsuccinic anhydride [5962-96-9] (20) (63). 

Ammonium sulfate is also recovered as a by-product in large amounts during the coking of coal, nickel refining, and organic monomer synthesis, particularly during production of caprolactam (qv). About four metric tons of ammonium sulfate are produced per ton of caprolactam which is an intermediate in the production of nylon. 

Luck, R.M. and Sadhir, R.K., Shrinkage in conventional monomers during polymerization. In Sadhir, R.K. and Luck, R.M. (Eds.), Expanding Monomers, Synthesis. Characterization and Applications. CRC Press, Boca Raton, FL, 1992, p. 5. 

Synthesis Solid-phase. Polymerization of N-protected a-amino acids (Fmoc or Boc). Solid-phase sub-monomer synthesis... 

The monomer synthesis and cyclopolymerization were carried out following the procedure of Butler et al. (21). The resulting polyimide was shown to possess primarily pyrrolidine rings as indicated by infrared spectroscopy (21). Initially, the reduction was carried out with LiAlH in tetrahydrofuran. 

We first discuss the materials research which includes monomer synthesis, growth of monomer crystalline structures and polymerization in the solid state, yielding the requisite polymer structures. Next, the nonlinear optical experimental research is discussed which includes a novel experimental technique to measure x (w). Linear and nonlinear optical data obtained for the polydiacetylene films is subsequently presented. Detailed theoretical analysis relating the data to x (< >) and subsequently to its molecular basis will be discussed in a later publication. 

Linear and nonlinear optical properties of a class of polydiacetylenes that can be grown as large area and controlled thickness thin films have been investigated. This involved an integrated research effort including monomer synthesis, thin film growth and new measurement techniques. 

The authors would like to thank Dr. Nick Economou of Lincoln Laboratory for fabricating the Silicon gratings, and Jacque Georger, Joe Gormley and Mike Rooney for expert technical assistance. Guidance in monomer synthesis and many fruitful discussions with Michael Rubner and Daniel Sandman of our laboratory are gratefully acknowledged. 

Monomer Synthesis. 4-Allyloxystyrene was prepared by the Wittig reaction of 4-allyloxybenzaldehyde and methyltriphenylphosphonium bromide, under basic conditions. The allyloxybenzaldehyde was prepared, in turn, by the alkylation of 4-hydroxybenzaldehyde with allyl bromide. This method, which provides high purity monomer in high overall yield, is outlined in Scheme 1 and has been previously described (2). Alternatively, the monomer may be prepared by the direct alkylation of p-vinylphenol with allyl bromide (8,9), although this method is less convenient due to the difficulties in synthesizing and storing the highly reactive vinyl phenol (10). 

Silicone membranes, flow through, 15 722— 723. See also Membrane processes Silicone monomers, synthesis of,... 

The second and third steps in the monomer synthesis involve the replacement of bromine with an acetylene protected by an acetone adduct, followed by cleavage of the adduct. These steps will be discussed in more depth later as they are the same for systems containing only monomer or a monomer/oligomer mixture. 

Cyanate ester monomers must be stored under dry conditions, because water can react with cyanate ester resins and deliver carbamates as undesired side products (Scheme 2) [186]. Even when the carbamates are only formed in the presence of a catalyst, this catalytic effect can be caused by traces remaining from the monomer synthesis. The formation of carbamates is critical, as they can decompose to amines and CO2. While the amine easily reacts with another cyanate ester, the CO2 can act as a blowing agent and hence leads to uncontrolled porosity during the processing. 

FIGURE 17.1 Monomer synthesis chemical flow diagram based on methane feedstock. 

In summary, monomer synthesis from basic, readily available inexpensive feedstocks based on fossil fuels is both an art and a science developed over the last half century or so. 

Monomer synthesis is both an art and science developed by great and ongoing research efforts allowing the inexpensive and safe availability of the starting materials upon which the polymer industry is based. Commercial monomer synthesis is based on both the availability of inexpensive materials and an interconnectiveness between products and synthetic by-products that are essential to the synthesis of other essential materials. 

---