Random copolymer, defined

Concerning EO/PO random copolymers, defining the composition in all the possible situations is necessary to know the reactivity of both primary and secondary hydroxyls with EO and PO, as already mentioned. 

A living cationic polymeriza tion of isobutylene and copolymeriza tion of isobutylene and isoprene has been demonstrated (22,23). Living copolymerizations, which proceed in the absence of chain transfer and termination reactions, yield the random copolymer with narrow mol wt distribution and well-defined stmcture, and possibly at a higher polymerization temperature than the current commercial process. The isobutylene—isoprene copolymers are prepared by using cumyl acetate BCl complex in CH Cl or CH2CI2 at —30 C. The copolymer contains 1 8 mol % trans 1,4-isoprene... 

The same procedure can be employed to make well defined comb-like polymers Living polystyrene can be grafted onto a partially chloromethylated polystyrene89 146), or onto a random copolymer of styrene and methyl methacrylate containing less than 10% of the latter monomer I48). 

The purpose of this study was to prepare a series of random copolymers of NIPAAM with predictable and well defined temperatures of precipitation covering the range of 0 to 45 C, as well as some that precipitate above 55 C under the conditions of high salt used in DNA hybridization assays. The N-substituted acrylfiunides offer the greatest chemical similarity to NIPAAM and therefore should copolymerize randomly with the latter ( ). Thus, copolymers of NIPAAM with AAM, NMAAM, NEAAM, NNBAAM and NTBAAM were prepared at selected monomer ratios and their aqueous solution behavior was evaluated. 

The beads comprise an uncrosshnked propylene random copolymer having a melting point of at least 140C, as a base resin. The time required to attenuate an air pressure within the foamed beads applied by a pressurising treatment with air from 1.2 to 0.8 kgf/sq.cm.(G) under atmospheric pressure at 23C is at least 80 minutes and the CNl value of the foamed beads, which is defined by a given equation, is smaller than 3.80. 

Well-defined diblock (P—R) and triblock (P R — P) copolymers consisting of the polypropylene block (P) and the ethylene-propylene random copolymer block (R) were prepared by adding ethylene monomer during the living coordination polymerization of propylene with the soluble V(acac)3/Al(C2H5)2Cl/anisole catalyst U1). 

Polymers that contain more than one type of monomeric repeat unit are called copolymers. By copolymerizing two or more monomers in varying ratios and arrangements, polymeric products with an almost limitless variety of properties can be obtained. As shown in Eq. (20), there are four basic types of copolymers as defined by the distribution of comonomers A and B, for example. Although the properties of a random copolymer are intermediate between those of the two homopolymers, block and graft copolymers exhibit the properties of both homopolymers. The properties of an alternating copolymer are usually unique. 

While the reinforcement effect at low areal density is still poorly understood due to the occurrence of this 2D phase separation, at high coverage, the problem can be reduced to the replacement of a narrow interface by two wider ones. The width aI of an interface between polymers A and B is given by Eq. (3), where Xa-b Is the interaction parameter between monomers A and B. The question is then to define a reasonable value of the interaction parameter between the random copolymer and the two polymers on either side of the interface. In the simplest case, where we are considering a A r-B random copolymer at the interface between homopolymers A and B, these equivalent interaction parameters can be written as ... 

The radical nature of nitroxide-mediated processes also allows novel types of block copolymers to be prepared in which copolymers, not homopolymer, are employed as one of the blocks. One of the simplest examples incorporate random copolymers124 and the novelty of these structures is based on the inability to prepare random copolymers by living anionic or cationic procedures. This is in direct contrast to the facile synthesis of well-defined random copolymers by nitroxide-mediated systems. While similar in concept, random block copolymers are more like traditional block copolymers than random copolymers in that there are two discrete blocks, the main difference being one or more of these blocks is composed of a random copolymer segment. For example, homopolystyrene starting blocks can be used to initiate the copolymerization of styrene and 4-vi-nylpyridine to give a block copolymer consisting of a polystyrene block and a random copolymer of styrene and 4-vinylpyridine as the second block.166... 

Block copolymers were defined above, and it was noted that there was a tendency for blocks to form when both of the reactivity ratios, r and r2, were greater than unity. This approach results in a random copolymer with extended blocks of Mj and M2 rather than a pure block copolymer with well-defined block length and composition. More precise control can be achieved through living polymerization, since on exhaustion of the first monomer added, Mj,... 

There have been several other well-defined random copolymers based on styrene derivatives prepared with trimethylsilylstyrene [123], p-acetoxystyrene [124], p-methoxymethylstyrene, and p-acetoxymethylstyrene [125]. The resulting copolymers served as precursors to functional materials with Si, phenol, or hydroxybenzyl moieties, or for subsequent crosslinking or grafting processes. 

This polymer was synthesized via NMRP (Nitroxide Mediated Radical Polymerization) (Benoit et al. 1999) by sequential polymerization of 2VP and a mixture of NIPAAm and DMIAAm. Using the macroinitiator method, the preparation of well-defined linear block copolymers consisting of a homo polymer block P2VP (pH-sensitive) and a random copolymer block of PNlPAAm (temperamre sensitive) with DMIAAm (photo crosslinker) was possible. 

The success of the living-radical polymerization field will be defined on the basis of the commercialization of any of these processes [48], It is believed that the strength of the living-radical polymerization systems lies in their ability to make polymers of novel architecture, for example, block copolymers. However, very little work has been done to look at the properties of materials prepared by these processes. It remains to be seen whether block copolymers, prepared by living-radical polymerization processes, have any performance advantages over random copolymers prepared by conventional free-radical polymerization. 

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