Polystyrene difunctional

Polystyrene-polytetrahydrofuran block copolymers121122 are an interesting case of coupling between functional polymers The mutual deactivation of living anionic polystyrene and living cationic polyoxolane occurs quantitatively to yield polystyrene-polyoxolane block copolymers. Since either of the initial polymer species can be mono- or difunctional, diblock, triblock or multiblock copolymers can be obtained. 

To complete this previous work, it was interesting to study in detail the reaction between AIBN and a living anionic polystyrene, for monofunctional polystyrene I Me as well as for difunctional polystyrene M t Me . 

A bimolecular process was reported by two independent groups, i.e., Hocker [19] and Rempp [20] in 1980. Macrocyclic polymers have been successfully prepared by the coupling reaction of a two-ended living polystyryl anion with a difunctional electrophile such as a, a -dibromo-p-xylcnc under high dilution to yield cyclic and linear mixtures. The cyclic polymer was isolated by a fractional precipitation. This bimolecular end-to-end reaction process has been used for synthesizing cyclic polystyrene by many researchers [21-25]. 

Polymeric supports can also be used with advantage to form monofunctional moieties from difunctional (Hies. Leznoff has used this principal in the synthesis of sex attractants on polymer supports (67). Starting from a sheap symmetrical diol he blocked one hydroxyl group by the polymer. Functionalization of cross-linked polymers is mostly performed by chloromethylation (65). A very promising method to introduce functional groups into crosslinked styrene-divinylbenzene copolymers is the direct lithiation with butyllithium in presence of N,N,N, N -tetramethyl-ethylenediamine (TMEDA) (69, 70). Metalation of linear polystyrene with butyl-lithium/TMEDA showed no exchange of benzylic hydrogen and a ratio of attack at m/p-position of 2 1 (71). In the model reaction of cumene with amylsodium, a kinetic control of the reaction path is established. After 3h of treatment with amyl-sodiuni, cumene is metalated 42% in a-, 39% m-, and 19% p-position. After 20h the mixture equilibrates to affort 100% of the thermodynamically more stable a-prod-uct (72). 

The simplest case of a polymer molecule which can undergo either cyclization or chain extension is that in which the groups are situated at each end of the polymer chain (which can react together). An example of this type of polymer is a,hydroxy-terminated polystyrene which reacts with a difunctional isocyanate, and our first studies were carried out with this reaction system. Obviously, the chain extension reaction leads to an increased specific viscosity, and cyclization leads to the reverse. 

Besides the use of micromolecular multiinitiators, block copolymers can be obtained from macromolecular initiators. In a first step, a polymeric initiator is generally synthesized by reacting a mono- or difunctional polymer with a functional initiator. Various macromolecular initiators were prepared in this way including quite different sequences polystyrene [13, 18, 19, 25, 26], poly(dimethylsiloxane) [27], polymethylmethacrylate) [13,15,28], polyvinylacetate [28], polyvinylchloride [29, 30], polyesters [30], polycarbonate [31,32], polybutadiene [13, 25, 33], polyamide [34], polyethylene glycol) [35] or polyaromatic [36], An excellent review of the synthesis and uses of such macroinitiators was written by Nuyken and Voit [37]. Thus, only few typical examples are going to be mentioned below. 

The inverse relationship between rate and MW traditionally presents a problem for the economic production of high MW polystyrene products owing to their slow production rates. The production rate of high MW products is generally increased by the use of peroxides. The addition of a simple monofunctional peroxide such as tert-butyl perbenzoate results in about a 15 % production rate increase over the use of auto-initiation. The use of difunctional peresters [2] and perketals [3] results in >30% rate increases over auto-initiation. However, these... 

By selecting the sulphide group SY, various difunctional PMMAs and polystyrenes were prepared. The end-functionality determined by H NMR scattered from 0.8 to 1.4.I25b... 

A structure resembling that of the dumbbell polymers was made by Frechet et al. In this case the connector is linked with polyether dendritic groups [272, 273]. The synthetic approach involved the preparation of a difunctional polystyrene chain in THF using potassium naphthalenide as initiator. The living polymer was end-capped with 1,1-diphenylethylene (DPE) to reduce its nucle-ophilicity and avoid side reactions with benzylic halomethyl groups. Addition of the fourth generation dendrimer [G-4] -Br led to the final product (Scheme 100). 

The discovery of living cationic polymerization has provided methods and technology for the synthesis of useful block copolymers, especially those based on elastomeric polyisobutylene (Kennedy and Puskas, 2004). It is noteworthy that isobutylene can only be polymerized by a cationic mechanism. One of the most useful thermoplastic elastomers prepared by cationic polymerization is the polystyrene-f -polyisobutylene-(>-polystyrene (SIBS) triblock copolymer. This polymer imbibed with anti-inflammatory dmgs was one of the first polymers used to coat metal stents as a treatment for blocked arteries (Sipos et al., 2005). The SIBS polymers possess an oxidatively stable, elastomeric polyisobutylene center block and exhibit the critical enabling properties for this application including processing, vascular compatibility, and biostability (Faust, 2012). As illustrated below, SIBS polymers can be prepared by sequential monomer addition using a difunctional initiator with titanium tetrachloride in a mixed solvent (methylene chloride/methylcyclohexane) at low temperature (-70 to -90°C) in the presence of a proton trap (2,6-dt-f-butylpyridine). To prevent formation of coupled products formed by intermolecular alkylation, the polymerization is terminated prior to complete consumption of styrene. These SIBS polymers exhibit tensile properties essentially the same as those of... 

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