Block copolymer, defined

Fig. 7. Data of Parsonage et al. [77] on the adsorption of a series of block copolymers of polystyrene-poly-2-vinylpyridine. The ordinate is the measured surface density ( d 2) reduced by the density required for the nonadsorbing chains to overlap the abscissa is the solvent-enhanced size asymmetry of the block copolymer defined under Eq. 26. The form of this plot is that suggested by Eq. 28...

Copolymers may be described as alternating copolymers, block copolymers or graft copolymers. The molecular architecture of copolymers may, however, be more complicated than represented in Fig. 8.1. Homopolymers can be linear, star or branched (Fig. 8.2), giving rise to so-called star block copolymers defined by the number of arms (n). 

The differences in the IR and Raman spectra of random copolymers, block copolymers, and polymer mixtures, A and B , will be covered in a moment. It should be appreciated that it is difficult to distinguish between polymer mixtures of the form A - - B and block copolymers defined as A -B from either IR or Raman spectra, because the chemical bonding between species A and B is only one of many bonds within a polymer chain. Column chromatographic separation followed by IR or Raman spectral identification or a GPC-IR method [16] is needed to determine whether a sample is a block copolymer or a mixture. In the case of a random copolymer in which component B is very small, B is mixed into the A A chain sequence in the form -A -B-A ,-. While the IR and Raman spectra of the A sequences may stay essentially the same as the A homopolymer, the spectra of B in an... 

In a dilute solution in a common good solvent for both blocks, the interactions between. different copolymers may be studied using the same direct renormalization procedures as the interactions between two homopolymers A and B equivalent to the two blocks.As for blends, in the asymptotic limit of infinite molecular masses, the chemical difference between the two blocks is irrelevant and the dimensionless virial coefficient gc between block copolymers defined by Eq. (10) is equal to the same value g as for homopolymers. The interactions which may provoke the formation of mesophases are here again due to the corrections to the scaling behavior ... 

Stockmayer and Kennedy (1975) constructed generalized plots showing how the block length ratio 6 and terminal relaxation times Tj and Tjg of the respective constituent components may affect the reduced zero-shear viscosity F of a block copolymer, defined by... 

Rubbery materials are defined by ASTM (D1566) as those which will have less than 50% permanent set after one minute when recovering from a strain of 100% applied for one minute. Of the many rubbery materials available, block copolymers are by far the most common used in hot melts. 

In a somewhat wider sense, one can define amphiphiles as molecules in which chemically very different units are linked together. For example, the structures formed by A B block copolymers in demixed A and/or B homopolymer melts and their phase behavior are very similar to those of classical amphiphiles in water and/or oil [13,14]. Copolymers are used not only to disperse immiscible homopolymer phases in one another, but also to create new, mesoscopically structured materials with unusual and interesting properties [15]. 

The block copolymer produced by Bamford s metal carbonyl/halide-terminated polymers photoinitiating systems are, therefore, more versatile than those based on anionic polymerization, since a wide range of monomers may be incorporated into the block. Although the mean block length is controllable through the parameters that normally determine the mean kinetic chain length in a free radical polymerization, the molecular weight distributions are, of course, much broader than with ionic polymerization and the polymers are, therefore, less well defined,... 

The multifunctional initiators may be di- and tri-, azo- or peroxy-compounds of defined structure (c.g. 20256) or they may be polymeric azo- or peroxy-compounds where the radical generating functions may be present as side chains 57 or as part of the polymer backbone."58"261 Thus, amphiphilic block copolymers were synthesized using the polymeric initiator 21 formed from the reaction between an a,to-diol and AIBN (Scheme 7.22).26 Some further examples of multifunctional initiators were mentioned in Section 3.3.3.2. It is also possible to produce less well-defined multifunctional initiators containing peroxide functionality from a polymer substrate by autoxidalion or by ozonolysis.-0... 

Polyester block copolymers can be defined as (AB) -type alternating multiblock copolymers composed of flexible aliphatic polyester or polyether blocks (A-type blocks) and rigid high-melting aromatic-aliphatic polyester blocks IB-type blocks) (Formula 2.2). 

Ion coupling of anionic and cationic living polymers is an interesting procedure for the synthesis of a well-defined block copolymer. Attempted coupling of the polystyrene anion with the poly-THF cation initiated by triethyloxonium tetrafluoro-borate yielded a block copolymer mixed with homopolymers394. The block ef-... 

Block copolymers containing polysiloxane segments are of great interest as polymeric surfactants and elastomers. Polycondensation and polyaddition reactions of functionally ended prepolymers are usually employed to prepare well-defined block copolymers. The living polystyrene anion reacts with a,co-dichloropoly(dimethyl-siloxane) to form multiblock copolymers398. ... 

The synthesis of well defined block copolymers exhibiting controlled molecular weight, low compositional heterogeneity and narrow molecular weight distribution is a major success of anionic polymerization techniques 6,7,14-111,112,113). Blocks of unlike chemical nature have a general tendency to undergo microphase separation, thereby producing mesomorphic phases. Block copolymers therefore exhibit unique properties, that prompted numerous studies and applications (e.g. thermoplastic elastomers). 

ROMP is without doubt the most important incarnation of olefin metathesis in polymer chemistry [98]. Preconditions enabling this process involve a strained cyclic olefinic monomer and a suitable initiator. The driving force in ROMP is the release of ring strain, rendering the last step in the catalytic cycle irreversible (Scheme 3.6). The synthesis of well-defined polymers of complex architectures such as multi-functionaUsed block-copolymers is enabled by living polymerisation, one of the main benefits of ROMP [92, 98]. 

An important polymer modification reaction is the grafting to or from a polymer backbone by some chemical method to produce a branched structure Q). The characterization of the products of these reactions is often somewhat less well defined than block copolymers (2) due to the complexity of the mixture of products formed. It is therefore useful to prepare and characterize more well defined branched systems as models for the less well defined copolymers. The macromonomer method (3 ) allows for the preparation of more well defined copolymers than previously available. 

Very well defined block copolymers of styrene, p-methyl styrene, p-tert-butyl styrene and PSX were prepared, as judged by GPC, with molecular weights of over 100,000 g/mole. 

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