Polydiene copolymers

G Holden, NR Legge. Thermoplastic elastomers based on polystyrene-polydiene copolymers. In NR Legge, G Holden, HE Schroeder, eds. Thermoplastic Elastomers. New York Hanser, 1987, pp 47-65. 

Micellization of polydiene copolymers was examined by Petrak and co-workers [ 165] in the case of PEO-PI-PEO for the development of controlled drug release systems. This interest in biomedical applications was also the starting point for extensive studies on micellar systems obtained with PEO-poly(amino acid) [166, 167], PEO-polyesters block copolymers [168, 169] and PEO-poly (ethylacrylate) [170]. PEO-poly(methylidene malonate), also designated by PEO-PMM 212, of the following structure were developed in our group ... 

The dependence of domain dimensions on temperature appears to be small from the few studies that have been made. From studies of polystyrene-fc/ocfc-polydiene copolymers swollen with non-selective solvents, Shibayama et al show that in the equilibrium regime the dimensions decrease slightly with an increase in temperature (as expected from theory), whilst in the non-equilibrium regions the dimensions increase slightly with an increase in temperature, being governed by the coefficient of thermal expansion. 

A number of workers have attempted to study the phase-boundary region for the microdomain-homogeneous-state transition which is expected to occur with polystyrene/polydiene copolymers on heating to relatively high temperatures (> 150 °C). Distinct transitions have been observed by some workers, " but not others, and the picture is far from clear. There is undoubtedly a need for much more work in this area, particularly on systems which exhibit transition behaviour at somewhat lower temperatures, so that problems associated with thermally induced chemical changes do not arise. 

Less extensive studies have been carried out on poly(oxyethylene)/polydiene copolymers which exemplify systems in which the second component is rubbery. ... 

The method described above was applied to the synthesis of star block copolymers (Figure 4), in which each branch was a polystyrene-Z)-polydiene copolymer. Under selected conditions of composition, branch length, and concentration, they exhibit bicontinuous mesomorphic phases referred to as double-diamond structures [29], which had never been observed before. 

Legge, N.R., Holden, G. and Schroeder, H.E., Thermoplastic elastomers based on polystyrene-polydiene block copolymers. Thermoplastic Elastomers, Hanser Publishers, New York, 1987. 

The low temperature ene reactions of 4-substituted-l,2,4-triazoline-3,5-diones (RTD) were used to modify polydiene surfaces. Hydrophilic surfaces (contact angles with water of 30-50°) were obtained on polybutadiene, poly-isoprene and styrene-butadiene copolymers by first treating the polymer at room temperature with RTD (R=Ph,... 

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

Elastomeric Polydiene ABA Triblock Copolymers with Crystalline End Blocks... 

ABA triblock copolymers of the styrene-diene type are well known, and owe their unique properties to their heterophase morphology. This arises from the incompatibility between the polystyrene A blocks and the polydiene B blocks, leading to the formation of a dispersion of very small polystyrene domains within the polydiene matrix. This type of elastic network, held together by the polystyrene "junctions", results in thermoplastic elastomer properties. 

Chemical modification of polydienes - The studies of CAMERON et al.lOb-Dyf may considered quite representative of recent trends in this very rich field( 0). Addition in solution of aryl or alkylsulfenyl chlorides accross the double bond is selective and may be quantitative furthermore it is regioselec-tive and yields block copolymers for partial modification (R=H or CH3) ... 

In addition to the triblock thermoplastic elastomers, other useful copolymers of styrene with a diene are produced commerically by living anionic polymerization. These include di-and multiblock copolymers, random copolymers, and tapered block copolymers. A tapered (gradient) copolymer has a variation in composition along the polymer chain. For example, S-S/D-D is a tapered block polymer that tapers from a polystyrene block to a styrene-diene random copolymer to polydiene block. (Tapered polymers need not have pure blocks at their ends. One can have a continuously tapered composition from styrene to diene by... 

In general, block copolymers are heterogeneous (multiphase) polymer systems, because the different blocks from which they are built are incompatible with each other, as for example, in diene/styrene-block copolymers. This incompatibility, however, does not lead to a complete phase separation because the polystyrene segments can aggregate with each other to form hard domains that hold the polydiene segments together. As a result, block copolymers often combine the properties of the relevant homopolymers. This holds in particular for block copolymers of two monomers A and B. 

The third possibility to prepare graft copolymers is termed grafting onto . This means that a growing chain B attacks the polymer backbone A with formation of a long branch. This attack can be a chain-transfer reaction or a copolymerization with unsaturated groups, for example, in polydienes. These reactions play an important role in the preparation of high impact polystyrene (see... 

The compositional and two-phase morphological relationships of "A-B" blocks, the "A-B-A" and starblocks have been studied intensively. It has been demonstrated that there is a substantial difference between random copolymers and block polymers, and this difference is based solely on the architectural arrangement of the monomeric units. One of the most important differences is that one Tg is observed in the random copolymer, which is related to the overall composition of the polymer. The block polymer has been shown to have two Tg s - one for polystyrene and one for the polydiene segment, and that these Tg s are not affected by the composition of the block copolymer. Since we can now synthesize large quantities of these pure block polymers, more detailed physical studies can be carried out. The two Tg s observed in... 

These results indicate that if polydienes and similar polymers can be prepared quantitatively with tertiary amine terminal groups, then they can be combined with other halogen functional polymers using established techniques to create interesting new block copolymer systems. For example, consider the reaction between telechelic pyridine terminated polybutadiene and monofunctional bromine terminated polystyrene (equation 4) -the latter has been prepared in 95% yield. >it The product would be an ABA... 

One of the most important discoveries relating to synthesis and physical behavior was made by Dr. Milkovich while at the Shell Development Co. He and his colleagues showed that triblock copolymers containing polystyrene-polydiene-polystyrene blocks in appropriate sizes could behave as a physically cross-linked but linear thermoplastic elastomer. Thus Dr. Milkovich was involved with two very crucial discoveries in this field. Interestingly, he received his M. S. degree at Syracuse with Professor Szwarc and his Ph.D. at Akron with Professor Morton. I was pleased that Dr. Milkovich accepted my invitation to be a plenary speaker at the symposium, along with Professors Szwarc and Morton. 

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