Main-chain copolymers

Absolute configuration of the chiral centers in the isotactic copolymer main chain can be determined by comparing the CD spectrum of the copolymer that is a polyketone with that of (S)-3-methylpentan-2-one [126]. A recent model study has confirmed this assignment, showing that the copolymer with ( -configuration in the main chain exhibits plus optical rotation in (CF3)2CHOH and minus in CHC13 [128-130], The study has also revealed that the enantiose-lectivity for the propene insertion is at least 95% ee. 

Block Type The preparation of molecular brushes with block copolymer backbones has been reported [39, 58, 90, 110-112]. These examples are mostly brush-coil block copolymers, in which one block is a cylindrical brush while the other is composed of a Hnear polymer chain. As an example, comonomers of octadecyl methacrylate (ODMA) and TMS-HEMA were polymerized sequentially via ATRP to afford a PODMA-b-P(TMS-HEMA) (PODMA = poly(octadecyl methacrylate)) diblock copolymer main chain. The poly(HEMA-TMS) block was converted into PBIEM polyinitiator, which was used for the polymerization of nBA this formed a PnBA block brush with a PODMA coil at the end of the main chain [28]. Owing to the crystalline nature of the PODMA segments, the self-assembly of the brush-coil block molecular bmshes was observed using AFM. This type of material gives rise to a new class of supersoft thermoplastic elastomers [95,113]. 

In conclusion, the mechano-chemical act of chemical bonds splitting on the ternary copolymer main chains stays on the basis of the mechanical resistance decay in the case of MELANA fibres supposed to sonic fatigue. The generated mechano-radicals initiate o chain of reactions that in time affects the supramolecular-morpho-logical structure, reflected by the decrease of mechanical properties [830-951]. 

The term "acetal resins" commonly denotes the family of homopolymers and copolymers whose main chains are completely or essentially composed of repeating oxymethylene units (—CH2—O—). The polymers are derived chiefly from formaldehyde or methanal [50-00-00] either directly or through its cychc trimer, trioxane or 1,3,5-trioxacyclohexane [110-88-3]. 

Peifluoioalkoxy (PFA) fluoiocaibon lesins aie designed to meet industry s needs in chemical, electrical, and mechanical appHcations. These melt processible copolymers contain a fluorocarbon backbone in the main chain and randomly distributed perfluorinated ether side chains ... 

In 1975, the synthesis of the first main-chain thermotropic polymers, three polyesters of 4,4 -dihydroxy-a,a -dimethylbenzalazine with 6, 8, and 10 methylene groups in the aHphatic chain, was reported (2). Shortly thereafter, at the Tennessee Eastman Co. thermotropic polyesters were synthesized by the acidolysis of poly(ethylene terephthalate) by/ -acetoxybenzoic acid (3). Copolymer compositions that contained 40—70 mol % of the oxybenzoyl unit formed anisotropic, turbid melts which were easily oriented. 

The polyamides are soluble in high strength sulfuric acid or in mixtures of hexamethylphosphoramide, /V, /V- dim ethyl acetam i de and LiCl. In the latter, compHcated relationships exist between solvent composition and the temperature at which the Hquid crystal phase forms. The polyamide solutions show an abmpt decrease in viscosity which is characteristic of mesophase formation when a critical volume fraction of polymer ( ) is exceeded. The viscosity may decrease, however, in the Hquid crystal phase if the molecular ordering allows the rod-shaped entities to gHde past one another more easily despite the higher concentration. The Hquid crystal phase is optically anisotropic and the texture is nematic. The nematic texture can be transformed to a chiral nematic texture by adding chiral species as a dopant or incorporating a chiral unit in the main chain as a copolymer (30). 

Properties have been determined for a series of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and poly [3,3-bis(methoxymethyl)oxetane]- (9-tetrahydrofuran. The block copolymers had properties suggestive of a thermoplastic elastomer (308). POX was a good main chain for a weU-developed smectic Hquid crystalline state when cyano- or fluorine-substituted biphenyls were used as mesogenic groups attached through a four-methylene spacer (309,310). Other side-chain Hquid crystalline polyoxetanes were observed with a spacer-separated azo moiety (311) and with laterally attached mesogenic groups (312). 

This combination of monomers is unique in that the two are very different chemically, and in thek character in a polymer. Polybutadiene homopolymer has a low glass-transition temperature, remaining mbbery as low as —85° C, and is a very nonpolar substance with Htde resistance to hydrocarbon fluids such as oil or gasoline. Polyacrylonitrile, on the other hand, has a glass temperature of about 110°C, and is very polar and resistant to hydrocarbon fluids (see Acrylonitrile polymers). As a result, copolymerization of the two monomers at different ratios provides a wide choice of combinations of properties. In addition to providing the mbbery nature to the copolymer, butadiene also provides residual unsaturation, both in the main chain in the case of 1,4, or in a side chain in the case of 1,2 polymerization. This residual unsaturation is useful as a cure site for vulcanization by sulfur or by peroxides, but is also a weak point for chemical attack, such as oxidation, especially at elevated temperatures. As a result, all commercial NBR products contain small amounts ( 0.5-2.5%) of antioxidant to protect the polymer during its manufacture, storage, and use. 

A graft copolymer is a polymer that is comprised of molecules with one or more species of blocks connected as side chains to the backbone, having constitutional or configurational features different from those in the main chain. The simplest case of a graft copolymer can be represented as follows ... 

In detail, the structure of a macroinitiator with active sites in the main chain is classified into two types that derive different types of block copolymers, as shown in Fig. 1. 

A block copolymer composed of liquid crystalline polymer (LCP) segments or that composed of segments having an LCP unit in their main chain or side chain was synthesized [67,68]. The latter showed partial compatibility and second-phase separation even when in a melt liquid crystalline state. 

Systematic studies67) to determine the properties of solutions of the obtained graft copolymers showed that graft copolymers containing stiff main chains (PAA,... 

Incorporation of flexible siloxane spacers into side chain or main chain liquid crystalline polymers have been shown to drastically reduce the transition temperatures 255,267,271,272,277) anc[ aiso increase the response time of the resultant systems to the applied thermal, optical or electrical fields 350-353>. In addition, siloxanes also provided elastomeric properties and improved the processibility (solution or melt) of the resulting liquid crystalline copolymers. 

In one of their notable examples, the hydroboration polymerization of low molecular weight allyl-telechelic polyisobutylene with tripylborane (trip = 2,4,6-triisopropylphenyl) was found to yield air-stable organoboron segmented block copolymers. These boron main-chain polymers (8) (Fig. 8), unlike the general ones, were stable to air. The stability was due to the steric hindrance of the bulky tripyl groups preventing oxygen attack of the borons.28... 

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