Star Shaped Polymers

The synthesis of various multi-arm star polymers has long been of growing practical and theoretical interest to a variety of industries. Star polymers have shown to be useful as surfactants, lubricants, rheology modifiers, and viscosity modifiers. Actually, star polymers are considered as viscosity modifiers and oil additives (15). 

Star polymers may be synthesized in several ways. The arm-first method joins preformed arms together using a linking agent, and the core-first method utilizes a multifunctional initiator to grow the 

The synthesis of A2B miktoarm star polymers has been discussed and exemplified using PIB as a component. The synthesis involves a quasi living cationic polymerization of isobutylene from a monofunctional cationic initiator. This initiator also contains a blocked hydroxyl group. Eventually, the blocked hydroxyl group of the initiator is deblocked, and functionalized with a branching agent. This activated reagent is then used for an atom transfer radical polymerization process of /erf-butyl acrylate (18). 

The synthesis of higher order comb or star polymers with more than 20 PIB arms emanating from a core of condensed siloxanes, preferably cyclosiloxanes has been described (15). 

The stars are characterized by a combination of two symbols, the first of which indicates the number-average molecular weight (M ) of the arms, and the second the number of arms (N ). For example, 9K-4.4 designates a star having at average 4.4 PIB arms, each arm of M =9 k Dalton. 

In this family of Ceo-polymers, two to twelve long and flexible polymer chains are covalently linked to a fullerene unit with topologies similar to that of sea-stars. Such polymers have also been called flagellenes, in the first example reported in 1992, since its shape resembles that of flagellated-unicellular protozoa [43]. 

This field has been mainly explored by the group of Mathis (Chapter 5), who have developed several syntheses of a number of flagellanes and studied their chemical and physical properties [44]. 

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More recent examples include end-functionalized multiarmed poly(vinyl ether) (44), MVE/styrene block copolymers (45), and star-shaped polymers (46—48). With this remarkable control over polymer architecture, the growth of future commercial appHcations seems entirely likely. 

The linear diblocks are then coupled by a polyfunctional coupling agent such as epoxidised linseed oil to give a star-shaped polymer. As already mentioned, commercial materials of this type have a tetramodal distribution. 

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 synthesis of tailor-made star-shaped polymers can be performed in several ways by means of a plurifunctional organometallic initiator, or by reacting a living precursor polymer with a plurifunctional reagent, to build the centra] body, or by block copolymerization involving a diunsaturated monomer (Scheme 3). 

The purpose of this review is to show how anionic polymerization techniques have successfully contributed to the synthesis of a great variety of tailor-made polymer species Homopolymers of controlled molecular weight, co-functional polymers including macromonomers, cyclic macromolecules, star-shaped polymers and model networks, block copolymers and graft copolymers. 

The results show that the C5o-Pst star-shaped polymer L-B hlms are hrmly fixed on the surface of the substrate, even after the surface was scanned for many times. The topography, high density, order and preferred orientation of the hlms are dominating factors in friction. The C5o-Pst him could play a signihcant role in microtribological applications. 

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. 

Fig. 47a, b. Structure and dynamics of star-shaped polymers with different functionalities, a Kratky plot of the static structure factor (S(Q, 0) Q2 vs. Q Rg. b Q(Q)/Q3 vs. Q Rg, as derived from Eqs (94) and (123), assuming Rouse dynamics... 

When the various results obtained by combined elastic and quasielastic neutron scattering measurements on star shaped polymers in dilute solutions... 

Star-shaped polymer molecules with long branches not only increase the viscosity in the molten state and the steady-state compliance, but the star polymers also decrease the rate of stress relaxation (and creep) compared to a linear polymer (169). The decrease in creep and relaxation rate of star-shaped molecules can be due to extra entanglements because of the many long branches, or the effect can be due to the suppression of reptation of the branches. Linear polymers can reptate, but the bulky center of the star and the different directions of the branch chains from the center make reptation difficult. 

Moreover, star shaped polymers, which have p branches of known length connected by one of their ends to a central nodule are also of interest. The size of the nodule should be kept small with respect to the whole star molecule. The methods developed to synthesize these tailor made polymers have been reviewed recently. ... 

The star-shaped polymers were prepared by the addition of the DVB solution to the "living polydienyllithium hexane solution. Prior to the addition of divinylbenzene (DVB), a portion of the linear polymer solution was isolated via the sidearm, which enabled the arm molecular weight to be determined. 

The alteration in solution viscosities brought about by the conversion of the allyllic-lithium active center to the alkoxy-lithium species is in accord with the general trend 148,1491 observed for star-shaped polymers in concentrated solution. It must be noted though that viscosity measurements cannot generally be used to detect differ-... 

Daoud, M. and J. P. Cotton. 1982. Star shaped polymers a model for the conformation and its concentration dependence . Phys.43 531-538. 

Hyper-branched polymers are prepared in a single-step polymerization from ABX monomers. Thus, a perfectly branched structure is present in dendrimers, whereas irregular branching is present in hyper-branched polymers. Aluminum alkoxide-based initiators or tin-based catalysts have been successfully used for the preparation of, hyper-branched [160-162, 166-168], dendrimer-like star polymers [160], and star-shaped polymers. The first and second generations of the benzyl ester of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) are effective initiators for the ROP of lactones (e-CL) in the presence of Sn(Oct)2. The... 

Star-shaped polymers can be prepared by using a multifunctional initiator, e.g., pentaerythritol and a catalyst which initiates ROP of the selected monomer. A second approach is to use telechelic prepolymers that are linked together after polymerization. 

ADMET is a step growth polymerization in which all double bonds present can react in secondary metathesis events. However, olefin metathesis can be performed in a very selective manner by correct choice of the olefinic partner, and thus, the ADMET of a,co-dienes containing two different olefins (one of which has low homodimerization tendency) can lead to a head-to-tail ADMET polymerization. In this regard, terminal double bonds have been classified as Type I olefins (fast homodimerization) and acrylates as Type II (unlikely homodimerization), and it has been shown that CM reactions between Types I and II olefins take place with high CM selectivity [142], This has been applied in the ADMET of a monomer derived from 10-undecenol containing an acrylate and a terminal double bond (undec-10-en-l-yl acrylate) [143]. Thus, the ADMET of undec-10-en-l-yl acrylate in the presence of 0.5 mol% of C5 at 40°C provided a polymer with 97% of CM selectivity. The high selectivity of this reaction was used for the synthesis of block copolymers and star-shaped polymers using mono- and multifunctional acrylates as selective chain stoppers. 

Dendrimers with their multiple end-standing functional groups are ideally suited for the construction of star-shaped polymers. Indeed, the end-standing functional groups can be used as initiators for polymerization ( grafting from method) or as functional groups for grafting onto . They can also be used as redistribution centers in equilibrium polymerization. 

Of particular interest is the substance containing silicon and titanium atoms in the chain, which is a star-shaped polymer, oligotetrakis(methylphenylsiloxanohydroxy)titanium. 

D]/[V] in the star-shape polymer estimated by H NMR of the star-shape polymer estimated by SEC in toluene d - of the star-shape polymer estimated by SEC in toluene... 

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