Multiblock copolymer

Property Physical units Copolymers Multiblock copolymers Triblock copolymers... 

In this article, block copolymers prepared by controlled polymerization methods only are considered, primarily di- and triblock copolymers. Multiblock copolymers such as poly(urethanes) and poly(urethane-ureas) prepared by condensation polymerization are not discussed (see Polyurethanes (PUR)). Although these materials do exhibit microphase separation, it is only short range in spatial extent due to the high polydispersity of the pol5uners. 

ABA block copolymer ABC block copolymer Multiblock copolymer Stereoblock copolymer... 

Sometimes, copolymers with many, but short blocks, are named segmented copolymers (multiblock copolymers). Segmented copolymers contain phase domains of microscopic or smaller size. The domains constituted principally of single types of stmctural unit. Typically, a segmented copolymer comprises hard-and soft-segment phase domains. 

The syntheses of PLA copolymers have been widely studied, but most efforts have been focused on random, diblock, and triblock copolymers by the ring-open polymerization of lactide that not only affects the properties of copolymers by phase separation but also causes a rather higher cost of production for the lactide as a monomer. However, growing interests have been recently given to a new class of PLA copolymers multi-block copolymers. Compared to the diblock or triblock copolymers, multiblock copolymer has more and shorter blocks and PLA segments, which alternate in the polymer chain. Consequently, it is possible to get some special properties such as better miscibility between the two components and lower crstallinity. Thus the degradability of the copolymer is expected to be enhanced. Multi-block copolymers can be synthesized by direct polycondensation, coupling reaction or chain-extension reaction of prepolymers. 

For architectures consisting of more than two flexible blocks, but still involving only two kinds of chemically different blocks (e.g., selected comb copolymers, multiblock copolymers, star copolymers, etc.), the phase behavior will be similar, albeit different in detail. For the more complex architectures involving either rigid blocks (hairy rods, rod-coils [54]) or more than two chemically different blocks (triblock copolymers [67-69]), the situation becomes much more complex. 

Living polymerizations afford a variety of options to control polymer size, dispersity, composition, and shape (architecture), as well as allowing specific and defined placement of useful chemical functionalities within these macromolecules. Common strategies for attaching chemical functionalities include the use of functional initiators and post-polymerization reactions. In addition, the absence of chain termination allows access to complex polymeric architectures, which may include block copolymers, multiblock polymers, star polymers, and bottlebrush copolymers. 

The variety of the nanostructures could become even richer and more complex in multiblock copolymers, multiblock multicomponent (e.g. terpolymers) or in nonlinear (e.g. miktoarm stars) (Lodge, 2003) chimeras, approaching that found in nature. Therefore, the synthesis of well defined complex chimeras adds another dimension to the suprastructural hierarchy of the block copolymers with potential biomedical applications (Deming, 2007). 

Mullite fibers Multhiomyan Multiblock copolymers Multi chip modules... 

Table 6. Trade Names of Multiblock Thermoplastic Elastomers Based on Polyurethane/Elastomer, Polyether/Elastomer, and Polyamide/Elastomer Block Copolymers...

Multiblock Copolymers. Replacement of conventional vulcanized mbber is the main appHcation for the polar polyurethane, polyester, and polyamide block copolymers. Like styrenic block copolymers, they can be molded or extmded using equipment designed for processing thermoplastics. Melt temperatures during processing are between 175 and 225°C, and predrying is requited scrap is reusable. They are mostiy used as essentially pure materials, although some work on blends with various thermoplastics such as plasticized and unplasticized PVC and also ABS and polycarbonate (14,18,67—69) has been reported. Plasticizers intended for use with PVC have also been blended with polyester block copolymers (67). 

The polyetherimide—polysdoxane multiblock copolymers are relatively hard (about 70 on the Shore D scale). Their main appHcation is flame-resistant wire and cable covering (24), where they combine very low flammabiUty with a low level of toxic products in the smoke. This unusual and vital combination of properties justifies their relatively high price, about 37/kg, at a specific gravity of about 1.2. 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

Decomposition in the presence of styrene at 60°C or with a tertiary amine in the presence of methyl methacrylate gives the corresponding ABA active block copolymer or ABBA active block copolymer, respectively. When both active block copolymers are used as polymeric initiators in another vinyl polymerization, an ABCBA type multiblock copolymer is obtained [34]. 

Polyaddition reactions based on isocyanate-terminated poly(ethylene glycol)s and subsequent block copolymerization with styrene monomer were utilized for the impregnation of wood [54]. Hazer [55] prepared block copolymers containing poly(ethylene adipate) and po-ly(peroxy carbamate) by an addition of the respective isocyanate-terminated prepolymers to polyazoesters. By both bulk and solution polymerization and subsequent thermal polymerization in the presence of a vinyl monomer, multiblock copolymers could be formed. 

Segmented or multiblock copolymers can be made by combining a functionally terminated oligomer or prepolymer with at least two monomers. To form a... 

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). 

Mucor miehei, 84 Multiblock copolymers, 7-8, 26 Multichip modules, dielectrics for, 270-271 Mylar, 21... 

Further improvements were made by carboxylating the polystyrene anion, leading to quantitative yields39S 396. Multiblock copolymers of molecular weight 500,000 consisting of sixty segments of poly-THF and polystyrene were prepared397. The effect of the molar feed ratio of the two components is shown in Fig. 7. 

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. ... 

Somewhat limited work has been reported over the last decade. There are several reports on the synthesis and physical and structural characterization of styrene-dimethylsiloxane 141 144) and methylmethacrylate-dimethylsiloxane145> diblock, triblock and multiblock copolymers. Several reports are also available on the thermal223), solution 224,2251 and surface196 2261 characterization of various styrene-dimethyl-siloxane block copolymers synthesized by anionic techniques. 

Polydimethylsiloxane based multiblock copolymer systems containing 1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene polycarbonate units and phenolphthalein polycarbonate units were synthesized and evaluated231 . Both copolymer systems showed good phase separation, increased rubbery character and improved processa-... 

Tough, transparent, heat and flame resistant, multiblock (bisphenol fluorenone carbonate) (BPF)-dimethylsiloxane copolymers have been synthesized by interfacial polycondensation of phosgene with various mixtures of BPF end-capped siloxane oligomers and free BPF or its monosodium salt 232). Siloxane content of the copolymers were varied between 7 and 27%. Presence of two Tg s, one below —100 °C and the other as high as 275 °C, showed the formation of two-phase morphologies. 

Poly(arylester)-polysiloxane multiblock copolymers have also been synthesized by the interfacial polymerization of aminopropyl terminated polysiloxane oligomers with bisphenol-A and a mixture of isophthaloyl and terephthaloyl chlorides117, 193-1951 as illustrated in Reaction Scheme XV. In these reactions the poly(arylester) blocks are formed in situ during the copolymerization, so the control of their block sizes is not very precise. It is also important to note that since aminopropyl terminated siloxane oligomers are employed, the linkages which connect the arylester and siloxane blocks are amide linkages. 

Multiblock polyethylene-polydimethylsiloxane copolymers were obtained by the reaction of silane terminated PDMS and hydroxyl terminated polyethylene oligomers in the presence of stannous octoate as the catalyst 254). The reactions were conducted in refluxing xylene for 24 hours. PDMS block size was kept constant at 3,200 g/mole, whereas polyethylene segment molecular weights were varied between 1,200 and 6,500 g/mole. Thermal analysis and dynamic mechanical studies of the copolymers showed the formation of two-phase structures with crystalline polyethylene segments. 

Using these macroinitiators PDMS-polystyrene and PDMS-poly(methyl methacrylate) multiblock copolymers were synthesized 305). Due to the backbone Structure of these macroinitiators and their thermolysis mechanisms, the copolymers obtained... 

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