Polystyrene, living polymer initiator

This relation was verified experimentally7 49 and it was shown that the degree of polymerization in a system containing "living polymers is independent of concentrations of initiator or monomer and of temperature. Furthermore, if all the growing centers were formed in a time much shorter than the time of polymerization, a Poisson molecular weight distribution would be obtained. Indeed, by using this technique samples of polystyrene were obtained for which MjMn = 1.04. 

Ion coupling of anionic and cationic living polymers is an interesting procedure for the synthesis of a well-defined block copolymer. Attempted coupling of the polystyrene anion with the poly-THF cation initiated by triethyloxonium tetrafluoro-borate yielded a block copolymer mixed with homopolymers394. The block ef-... 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Anionic polymerisation of hydrocarbon monomers is initiated by lithium butyl to produce a living polymer the association number of which in solution is required to elucidate the kinetics. When the living polymer (for example polystyryl lithium) is terminated, the polystyrene can be isolated and a solution then made to determine its molecular weight, M. If the living polymer is associated in solution, the ratio of its... 

The polydispersity of polymers prepared in this way is usually very low for example, a value MJM of 1.05 was found for a sample of poly(a-methylsty-rene). Living polymers can also be used for the preparation of block copolymers after the consumption of the first monomer, a second anionically polymerizable monomer is added which then grows onto both ends of the initially formed block. By termination of the living polymer with electrophilic compounds the polymer chains can be provided with specific end groups for example, living polystyrene reacts with carbon dioxide to give polystyrene with carboxylic end groups. 

Preparation of the Living" Polystyrene. 18 g of the living polymer was prepared by standard anionic polymerization using n-butyl lithium. The reaction was carried out by the dropwise addition of 20 ml of styrene to 5 ml of the initiator solution in 150 ml of neat THF at -78°C. The styrene drip was adjusted to take approximately 30 min for completion and then the reaction was allowed to stir for two hours before the grafting reaction with mesylated lignin was carried out. The number average molecular weight of the polystyrene, as determined by HPSEC, was 9500 with polydispersity of 1.2. 

The first block (polybutadiene or polystyrene) is prepared by anionic polymerization, under high vacuum, in THF dilute solution (less than 5%), at low temperature (—70 °C) with cumylpotassium as initiator. Then, the living polymer is transformated into a hydroxylated polymer (PV—OH) by addition of ethylene oxide under vacuum, or into a carboxylated polymer (PV-COOH) by addition of carbon dioxide under vacuum. 

The living ends of a suitable polymer may initiate polymerization of another monomer, and thus lead to the synthesis of block polymers free of homopolymers. For sample, one prepares living polystyrene then adds pure methyl methacrylate to its solution and produces in this way a block polymer of styrene and methyl methacrylate (22). Actually, it is possible to produce living polymers with two active ends which can form a block polymer containing three segments—ABA. 

The most important advantage of our technique is the possibility of a direct determination of the absolute rate constants of copolymerization (7). If the living polymer is a poly-A, and a monomer B is the second component of the reacting mixture, then the initial rate determined in our system gives the absolute rate constant the rate constant of the addition of monomer B to the polymer possessing unit A at its end. The rate constants for addition of a-methylstyrene to living polystyrene and styrene to living poly (a-methylstyrene) were determined... 

A half-rufhenocene complex, Ru(indenyl)Cl(PPh3)2 was similarly used for polymerization of MMA in conjunction wifh an MMA-dimer-type initiator, H(MMA)2C1 (Scheme 6.181) [233]. Addition of Al(Oi-Pr)3 accelerated the polymerization rate to afford similar living polymers (M /M = 1.1). The behavior of the Ru-Ind complex was similar in the polymerization of styrene. Polystyrene with narrow MWD (M /Mn= 1.1) was obtained by use of a suitable radical initiator -Me2C(CO2Et)Br. 

Cationic condensation polymerizations of Cl3P=NSiMe3 and PhCl2P=NSiMe3 in the solvents benzene, toluene and dioxane, and initiated by PCI5, appear to be reproducible and result in polymers with a low polydispers-ity. Diblock and triblock polyphosphazene-polystyrene copolymers have been synthesized by quenching the living polymer (135) by a polystyrene phos-... 

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 ability of living polymers to resume growth with the addition of fresh monomer provides an excellent opportunity for the preparation of block copolymers. For example, if a living polymer with one active end from monomer A can initiate the polymerization of monomer B, then an A-AB-B type copolymer can be obtained (e.g., styrene-isoprene copolymer). If, however, both ends of polymer A are active, a copolymer of the type B-BA-AB-B results. Examples are the thermoplastic rubbers polysty-rene-polyisoprene-polystyrene and poly(ethylene oxide)-polystyrene-poly(ethylene oxide). In principle, for fixed amounts of two monomers that are capable of mutual formation of living polymers, a series of polymers with constant composition and molecular weight but of desired structural pattern can be produced by varying the fraction and order of addition of each monomer. 

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