Copolymer synthetic procedures

The oxocarbenium perchlorate C(CH20CH2CH2C0+C104 )4 was employed as a tetrafunctional initiator for the synthesis of PTHF 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHF-fc-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-fr-PS-fc-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

An example for the synthesis of poly(2,6-dimethyl-l,4-phenylene oxide) - aromatic poly(ether-sulfone) - poly(2,6-dimethyl-1,4-pheny-lene oxide) ABA triblock copolymer is presented in Scheme 6. Quantitative etherification of the two polymer chain ends has been accomplished under mild reaction conditions detailed elsewhere(11). Figure 4 presents the 200 MHz Ir-NMR spectra of the co-(2,6-dimethyl-phenol) poly(2,6-dimethyl-l,4-phenylene oxide), of the 01, w-di(chloroally) aromatic polyether sulfone and of the obtained ABA triblock copolymers as convincing evidence for the quantitative reaction of the parent pol3rmers chain ends. Additional evidence for the very clean synthetic procedure comes from the gel permeation chromatograms of the two starting oligomers and of the obtained ABA triblock copolymer presented in Figure 5. 

Interest in new solid polymer electrolytes has driven some research groups to investigate other materials containing proton conducting moieties aside from sulfonic acid. Polymers and copolymers from monomers containing phosphonic-based proton conductors have been reported. Phosphonic and/or phosphinic acid containing polymers have not been well studied because of the rather limited synthetic procedures available for their preparation, compared with sulfonic acid derivatives. Miyatake and Hay... 

Scheme 12 Schematic representation of the synthetic procedure that was applied for the preparation of three triblock copolymers with the same first and second blocks...

The synthetic procedure of PE-fo-PCL using hydroxyl terminated polyethylene was reported [39]. Terminally hydroxylated polyethylene was prepared during a metallocene-catalyzed polymerization using controlled chain transfer reaction with alkylaluminum compounds. PE-fo-PCL block copolymer was synthesized from terminally hydroxylated PE and e-caprolactone (e-CL) using Sn(Oct)2 as a catalyst for ring opening polymerization. 

Figure 3. Synthetic procedure for the ferrocene-ethylene oxide-siloxane branch copolymers H and I.

The chlorosilane method was adopted for the synthesis of miktoarm stars of the type B(A-b-B)2 where A is PI and B is PS [27]. The synthetic procedure was similar to that used for the preparation of A2B stars except that two of the arms are diblock copolymers, as shown in Scheme 9. Extensive characterization data were given to confirm the synthesis of well defined copolymers. 

The synthetic procedure for the synthesis of the inverse starblock copolymers is given in Scheme 25. Diblock arms (I) having the living end at the PS chain end were prepared by anionic polymerization with sequential addition of monomers. In order to accelerate the crossover reaction from the PILi to the PSLi chain end a small quantity of THF was added prior the addition of styrene. The living diblock (I) solution was added dropwise to a stoichiometric amount of SiCl4 until two arms are linked to the silane. This step was monitored by SEC and is similar to a titration process. The end point of the titration was determined by the appearance of a small quantity ( 1%) of trimer in the SEC trace. The diblock (I) was selected over the diblock (II) due to the increased steric hindrance of the styryl anion over the isoprenyl anion, which makes easier the control of the incorporation of only two arms into the silane. 

N-Benzyl and iV-alkoxy pyridinium salts are suitable thermal and photochemical initiators for cationic polymerization, respectively. Attractive features of these salts are the concept of latency, easy synthetic procedures, their chemical stability and ease of handling owing to their low hygroscopicity. Besides their use as initiators, the applications of these salts in polymer synthesis are of interest. As shown in this article, a wide range of block and graft copolymer built from monomers with different chemical natures are accessible through their latency. 

In the following we would like to describe the synthesis of graft copolymers with silicone backbone based on polymeric initiators. These graft copolymers might find application as compatibilizers and, furthermore, the synthetic procedure allows broad combination possibilities. 

The breakthrough in peptide chemistry, which opened up applications in biochemistry and molecular biology, was the development of solid phase synthesis by Merrifield in 1963. This formed the basis of automated synthetic procedures in which the nascent peptide chain was covalently linked to a solid support such as a styrene-divinylbenzene copolymer the complex isolation and purification procedures needed to separate reactants and products at the end of each reaction cycle, which characterised previous solution methods of peptide synthesis, were replaced by a simple washing step. With modern automated methods of peptide synthesis, the time for an Fmoc reaction cycle has been reduced to 20 min, so that a 50-residue peptide can be synthesised in a day (Chan and White 2000). 

Poly(vinyl alcohol) is typically obtained by alcoholysis of poly(vinyl esters), for example from polyfvinyl acetate) and methanol in the presence of NaOH. The process can be completed or only partially conducted. In this latter case a copolymer (alcohol/ester) is obtained. Other synthetic procedures are used, most of them also based on the hydrolysis of poly(vinyl esters). Poly(vinyl alcohol) is typically used in the atactic form, but isotactic or syndiotactic poly(vinyl alcohols) also are known. 

The functionalization of spherical silica particles and silicon wafers with PVFA-co-PVAm has been carried out using various synthetic procedures with VFA as the key monomer. The simplest approach used to produce PVFA-co-PVAm/ silica hybrid materials is adsorption of PVFA-co-PVAm on the inorganic component from aqueous solution. Depending on the copolymer composition about 0.02 to 0.1 g PVFA-co-PVAm per gram silica is immobilized. The increase of the PVAm content of the co-polymer leads to a significant increase in the amount of adsorbed PVFA-co-PVAm. 

A new star—block copolymer architecture, the inverse star—block copolymer, was recently reported.87 These polymers are stars having four polystyrene-/risoprene) copolymers as arms. Two of these arms are connected to the star center by the polystyrene block, whereas the other two are connected through the polyisoprene block. The synthetic procedure is given in Scheme 32. The living diblocks (I) were prepared by anionic polymerization and sequential addition of monomers. A small quantity of THF was used to accelerate the initiation of the polymerization of styrene. The living diblock copolymer (I) was slowly added to a solution of SiCL. The reaction was monitored by SEC on samples with-... 

In contrast to the rod-coil diblock copolymer consisting of perfectly monodisperse rods, the liquid crystalline morphologies of rod-coil diblock copolymer containing polydisperse rods seem to be studied in less detail. In certain cases, the polydisperse nature of the rod-segments could hinder self-assembly into regularly ordered supramolecular structures. However, due to relatively simple synthetic procedures, liquid crystalline polymer can be of benefit for new materials with controlled internal dimensions ranging from the nanometer to macroscopic scale. 

In contrast to conventional and commercially available block copolymers, block copolymers that carry electronically active blocks are relatively rare and the synthesis is challenging, since multi-step organic synthetic procedures have to be combined with one or more polymerization techniques. Further difficulties arise from the limited solubilities and the limited amount of material available from one batch, making the preparation of such materials tedious and time-consuming. 

Arborescent graft copolymers having a highly branched PS core and a PEO shell were prepared by a combination of anionic polymerization, grafting onto and from techniques [278]. The synthetic procedure is described in the following scheme (Scheme 107). 

This volume continues in the same format as the first edition with updates on the syntheses of various types of polymers, including olefin-sulfur dioxide copolymers, polythioesters, sulfide polymers, polyisocyanates, polyoxyalkyihydroxy compounds, polyvinyl carbazole, polyvinyl acetate, polyallyl esters, polyvinyl fluoride, and miscellaneous polymer preparations. The book should be useful to academic and industrial chemists who desire typical synthetic procedures for preparing the polymers described herein. In addition to reviewing the latest journals, we survey the patent literature and give numerous additional references. 

However, the synthetic procedures leading to the above copolymers do not guarantee the achievement of the same microstructure. The as-obtained sequence distributions are probably unstable because the presence of transesterification reactions leads to highly complicated solid state behavior, which typically depends on the thermal history and processing conditions of the sample. Definite relations between the phase behavior, the molar mass, and the molar mass distribution are not easily available because... 

Scheme 10.9 Synthetic procedure of amphiphilic core-shell cylindrical brushes with PS-b-PAA diblock copolymer side chains [100]. (Reproduced with permission of the American Chemical Society.)...

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