Shape linear copolymers

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

The criterion of stability (R) is the constant limit value of the emulsified volume percentage at 20°C (32, 32.). It appears that 7/3 water toluene emulsions are more efficiently stabilized by star-shaped block copolymers whereas linear block copolymers give better results for 3/7 water toluene emulsions the stability of the l/l water toluene emulsions seems to be insensitive to the molecular architecture of PTBS/PO block copolymers. 

ROP can also be used to generate star-shaped block copolymers in a combinatorial manner.Meier et al7 employed a five-arm star-shaped PEG compound as a macroinitiator for the ROP of 8-caprolactone monomer. Using this strategy, the PEG compound formed the core of the star while the outer shell was comprised of polyesters. Polymerizations were performed on a Ghemspeed ASW2000 by mixing monomer and initiator at different ratios and heating to 130 °C. Polymerizations were demonstrated to be reproducible by the low variation in measured MW values in iterative experiments. Moreover, a linear relationship was observed between MWs (calculated by both GPC and NMR) and different [M]/[I]... 

It was also shown that functional zinc alkoxides are also effective initiators for the ring-opening polymerization of -caprolactone imder very mild conditions via a polymerization mechanism described for aluminum alkoxides (345). Tin octoate, Sn(0(0)CCH(C2H5)C4H9)2, is another type of initiator to synthesize telechelics based on PCL. In particular, when it is used in conjunction with hydroxyl functional compounds or prepolymers, telechelics, linear and star-shaped block copolymers, or networks can be obtained via corresponding alkyl octoate formation (346-354). More recently, novel end-chain and mid-chain telechelics functionalized with photoactive groups of PCL were synthesized (355). 

Figure21 Generalized phase diagram including morphologies found in polystyrene-block-poly(Z-L-lysine), linear block copolymers, O bottle-brush shaped block copolymers, and schematic presentation of the undulated lamellar morphology. (Reprinted from H. Schlaad, H. Kukula, B. Smarsly, M. Antonietti, and T. Pakula. Polymer 43 5321,2002. Copyright [2002], with permission from Elsevier Science.)...

The viscosity of the graft copolymers were measured in benzene (for comparison with the original PEGME segments) and water. The viscosities of the linear and star shape graft copolymers, as expected, increase as the number of branches increase and also as the size of the branches increases, Table 1. 

Fig. 1.12. Linear (a) and comb-shaped (b) copolymers containing rigid and flexible chain fragments c) method of arrangement of rigid and flexible fragments in the lattice in the Floiy roach.

Feldthusen J, Bela I and Mueller A H E (1998) Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates by combination of living cationic and anionic polymerizations, Macromolecules 31 578-585. 

Li, M., Jahed, N.M., Min, K., Matyjaszewski, K. Preparation of linear and star-shaped block copolymers by ATRP using simultaneous reverse and normal initiation process in bulk and miniemulsion. Macromolecules 37(7), 2434-2441 (2004)... 

Two types of well defined branched polymers are acessible anionically star-shaped polymers and comb-like polymers87 88). Such macromolecules are used to investigate the effect of branching on the properties, 4n solution as well as in the the bulk. Starshaped macromolecules contain a known number of identical chains which are linked at one end to a central nodule. The size of the latter should be small with respect to the overall molecular dimensions. Comb-like polymers comprise a linear backbone of given length fitted with a known number of randomly distributed branches of well defined size. They are similar to graft copolymers, except that backbone and branches are of identical chemical nature and do not exhibit repulsions. 

The morphology of the ABA-type linear block copolymers is strongly influenced by the volume fraction of the two components. For example, in PS-EB-PS-type block copolymer as the volume fraction of PS is increased, the shape of the dispersed PS phase changes from spherical (comprising body-centered cubic spheres of PS dispersed in continuous soft phase) to cylindrical form (hexagonal packed cylinders of PS) [10,133,134]. When the volume fraction of the two phases... 

The paper is organized in the following way In Section 2, the principles of quasi-elastic neutron scattering are introduced, and the method of NSE is shortly outlined. Section 3 deals with the polymer dynamics in dense environments, addressing in particular the influence and origin of entanglements. In Section 4, polymer networks are treated. Section 5 reports on the dynamics of linear homo- and block copolymers, of cyclic and star-shaped polymers in dilute and semi-dilute solutions, respectively. Finally, Section 6 summarizes the conclusions and gives an outlook. 

Abstract This review highlights recent (2000-2004) advances and developments regarding the synthesis of block copolymers with both linear [AB diblocks, ABA and ABC triblocks, ABCD tetrablocks, (AB)n multiblocks etc.] and non-linear structures (star-block, graft, miktoarm star, H-shaped, dendrimer-like and cyclic copolymers). Attention is given only to those synthetic methodologies which lead to well-defined and well-characterized macromolecules. 

In analogy to linear-block copolymers different cases can be distinguished when blending asymmetric miktoarm (PS-PI)n-PS and H-shaped (PS-PI)3-PS-(PI-PS)3 copolymers with homopolymer PS [122]. If the latter s molecular weight is lower than the respective PS block, a transition from the L structure to hexagonally packed cylinders without observation of an intervening cubic morphology is observed in the case of the (PS-PI)n-PS types. If the H-shaped (PS-PI)3-PS-(PI-PS)3 star-block copolymer is blended with 30% to... 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

ABA triblock copolymers, sometimes referred to as dumbbell shaped copolymers when B is a linear macromolecule. 

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