Ordered copolymers

Isolated chitins are highly ordered copolymers of 2-acetamido-2-deoxy-/3-D-glucose and 2-amino-2-deoxy-j6-D-glucose. The occurrence of the latter is explained by the fact that in vivo chitin is covalently finked to proteins via the nitrogen atom of approximately one repeating unit out of ten, therefore upon isolation a degree of deacetylation close to 0.10 is found. Chito-biose, 0-(2-amino-2-deoxy-j6-D-glucopyranosyl)-(l 4)-2-amino-2-deoxy-... 

ABS Three-component copolymer of acrylonitrile, butadiene, and styrene, alloy Rubber-toughened materials in which the matrix can be a mixture of polymer tyrpes. alternation copolymer Ordered copolymer in which every other building is a different mer. azeotropic copolymer Copolymer in which the feet and composition of the copolymer are the same, blends Mixtures of different polymers on a molecular level may exist in one or two phases, block copolymer Copolymer that contains long sequences or runs of one mer or both mers. 

Homopolymers of polybutadiene can consist of three basic isomeric forms (czs-1,4, trans-1,4, and 1,2 vinyl), and these can be present in different sequential order. Copolymers may obtain a variety of co-monomers, such as styrene, acrylonitrile, etc. Depending on their distribution in the chain, random copolymers or block copolymers of different types and perfection can be produced. There are many synthetic elastomers based on butadiene available commercially. 

If all these challenges are met, and comparable progress can be made with the furanosides, there will still be the challenge of the synthesis of regularly ordered copolymers, and cts-linked, rather than trans-linked, polysaccharides. The field can still use the good offices of green-eyed magicians in white overalls. ... 

Many combinations of diacids—diamines and amino acids are recognized as isomorphic pairs (184), for example, adipic acid and terephthalic acid or 6-aminohexanoic acid and 4-aminocyclohexylacetic acid. In the type AABB copolymers the effect is dependent on the structure of the other comonomer forming the polyamide that is, adipic and terephthalic acids form an isomorphic pair with any of the linear, aliphatic C-6—C-12 diamines but not with -xylylenediamine (185). It is also possible to form nonrandom combinations of two polymers, eg, physical mixtures or blends (Fig. 10), block copolymers, and strictly alternating (187—188) or sequentially ordered copolymers (189), which show a variation in properties with composition differing from those of the random copolymer. Such combinations require care in their preparation and processing to maintain their nonrandom structure, because transamidation introduces significant randomization in a short time above the melting point. 

An example of a one-dimensional superlattice structure is structure 1, which is an ordered copolymer. The skeleton is formed by silicon and germanium atoms. A unit cell is three times larger than that of a homopolymer. The band structure of this ordered copolymer changes to the zone-folded profile, which may result in a characteristic absorption spectrum. 

However, for the copolyesters consisting of more or less lienar costructural units, the values for the ordered copolymers appear to be slightly higher. Examples are given below(21,44) ... 

Polymer F is the ordered copolymer produced by the reaction of the diamine below and terephthaloyl chloride H2N 3 CONHNHCO CONHNHCO NH ... 

These more orderly copolymers are known as block copolymers. This is not possible with straightforward free radical-initiated polymerization, but requires special techniques which are beyond the scope of this book. An A-B block has molecules with a chain of type A monomer units joined at one end to a chain of type B units. A-B-A blocks have only type A chains at the ends of the molecules. A-B-A block copolymers can be used as associative thickeners (Chapter 10). 

Another way of preparing the ordered copolymer consists of using the masked-disilene method. If the monomer (masked disilene) is designed in such a manner that one of the silicon atoms has two methyl groups and the other silicon has two -hexyl substituents, it would be expected that the polymer obtained from it should have a stereo regular arrangement. This has been accomplished and in the Si NMR of this polymer two distinct... 

The interest at this point is to analyze the melting temperature-composition and melting temperature-block length relations of some typical ordered copolymers. Although the primary concern is the equilibrium condition, it can be anticipated, from the above discussion, that there could very well be complications in achieving this state. For an ideal, ordered copolymer of sufficient block length the parameter p will approach unity. Therefore, should be invariant with composition. This ex-... 

Hydrogenated poly(butadiene), an ethylene-butene random copolymer, is often used as die crystallizing block, in di- and triblock copolymers. In this context the copolymer is commonly referred to as polyethylene. This nomenclature can be misleading since it carries the connotation that hydrogenated poly(butadiene) behaves as a homopolymer with respect to crystallization. In fact, it behaves as a typical random copolymer that is located within the structure of an ordered copolymer. 

It can be envisaged that in the fibrous proteins where the amino acid residues that crystallize (comparable to the A units) are arranged in one block, those that do not crystallize are present in another. The two differing blocks would then alternate along the chain. This arrangement would be formally equivalent to that of an ordered copolymer. It is also possible to have a random sequence distribution between the crystalUzable and noncrystalUzable units. Distinction between these possibilities involves structural determinations, thermodynamic studies, and an assessment of physical and mechanical properties. 

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