Slow monomer addition

Silylated diamines, 156, 187-188 Silylated monomers, 72 Silylation, distillation and, 338 6NT6 alternating polyesteramide, synthesizing, 189-190 6,6 -linked polymers, 480 Size exclusion chromatography (SEC) analyses, 90, 490 Slabstock foam, 233-234 Slow monomer addition, 57 Small-angle neutron scattering (SANS), 282... 

DB degree of branching /initiator functionality y [Mo]/[AB ]q Semi-batch = slow monomer addition. 

A challenging goal in this field, particularly from the synthetic point of view, is the development of general AB polymerization methods that achieve control over DB and narrow MWDs. Experimental results and theoretical studies mentioned above suggest that the SCV(C)P from surfaces, which are functionahzed with monolayers of initiators, permit a controlled polymerization, resulting structural characteristics (molecular weight averages, DB) of hyperbranched polymers. In particular, it is expected that the use of polyfunctional initiators with a different number of initiator functionahty, copolymerization, and slow monomer addition techniques lead to control the molecular parameters. 

Herzig and Deubzer also reported the slow monomer addition process in the formation of hyperbranched poly(carbosiloxanes)188. In this report, they added vinyltris(dimethyl-siloxyjsilane (9) (previously reported by Rubinsztajn181) to various cores (16, 17 and 18). A dependence of polymer molecular weight on overall amount of monomer added was established by viscosity measurements. In addition, the formation of small cyclic compounds was reported and quantified. 

As a typical example, Frey etal. [16, 27] described the anionic polymerization of glycidol, which was considered also as a latent AB2 (= ABB ) monomer (Scheme 24.3). The polymerization proved to be very versatile and led to hb polymers with a rather narrow molar mass distribution (Mu,/M = 1.1-1.4) due to a chain growth-hke character of the reaction when only partial deprotonation to the initiating alkoxide (initiating site, triol in Scheme 24.3) was performed. This led to a more or less simultaneous growth of all chain ends, and allowed control of both the molar mass and polydispersity. By use of the trifunctional initiator (core molecule) and slow monomer addition, cychzation was suppressed such that the molar mass and polydispersity could be controlled. 

Several approaches to enhance the D B of hb polymers, including a slow monomer addition procedure without or with the use of core molecules of type By [60, 62,... 

The DB of branching can be modified by special synthetic approaches, as demonstrated by the NMR quantification of subunits. Copolymerization - for example, the addition of bifunctional monomers AB - resulted in an increase in linear units and, therefore, in a decrease of the DB [109-112]. An enhancement of DB was realized, for example, by employing a slow monomer addition technique [113], the polymerization of prefabricated dendron macromonomers [56, 114], and by a stepwise addition of the monomer mixture for the (A2 + B3) approach [92]. Whereas dendritic and terminal units are essential for a dendritic structure, in the case of hb polymers the content of the linear units can vary greatly. To date, few examples of AB2 hb polymerizations have been reported were the linear unit is a chemically labile structure that either breaks down to the initial educts, or reacts immediately with a further terminal unit to form the stabile dendritic unit. Thus, a hb polymer containing only T and D units is formed, with 100% DB [35,115-119]. 

A strong dependence of the molar mass distribution on DP was also found for hb polymers obtained by SCVP, with Mw/Mn DP [126]. The broad molar mass distribution may be influenced by the different reactivities of the functional groups of the monomers, using the method of slow monomer addition [57, 62, 127, 128] or by adding a multifunctional core molecule [63, 127]. In A2 + B3 systems, both the polydispersity and the development of the molar mass are very sensitive to the amount of the added A2 monomer and to the formation of cycles [129,130]. 

Yan and Muller developed a systematic definition for the SGVP, also showing that slow monomer addition procedures can lead to an elevated DB of 0.66. The definition and determination of the terminal (T), linear (L), and dendritic (D) units after reaction of a A2 + By is more complicated and has been the focus of several studies. " The NMR analysis of these structures is not trivial, and... 

A highly activated AB2-monomer is 3,5-bis(trimethylsiloxy) benzoyl chloride (3-3) that leads to a high DB of 60% in a bulk polycondensation, as the once-reacted monomer is activated for the second condensation step the DB was increased to 64% by slow monomer addition to trimethylolpropane (2-(hydroxymethyl)-2-ethylpropane-f,3-diol) (TMP) as a core molecule. As mentioned above, 2,2-bis(hydroxymethyl) propanoic add (bisMPA) (3-6) is a major monomer for aliphatic hb polyesters (Boltom) but shows cydization and other side reactions (e.g., etherification) during polycondensation. A comparable easy-to-handle monomer is bis(4-hydroxyphenyl) pentanoic acid that can be easily polycondensed in the melt or solution, leading to polyesters with a DB of 50% and with only a low tendency for side reartions. Smet et al. presented highly branched copolyesters by a combination of AB2-polycondensa-tion and the ROP of -caprolactone. ... 

NHS)-ester of lysine dihydrochloride in the presence of a polyfiinctional core, using the slow monomer addition strategy. A self-evident method for preparing hh poly(lysine) by direct self-condensation was reported more recendy by Klok and co-workers. ... 

Bharathi, P. and Moore, J.S. (2000) Controlled synthesis of hyperbranched polymers by slow monomer addition to a core. Macromolecules, 33,3212-3218. 

To favor AMM over ACEM, a slow monomer addition process is beneficial as the instantaneous concentration of monomer is kept low. In the ideal case where the ACEM is totally suppressed, the molar mass of the final polymer is controlled by the initial [ROH]/[monomer] ratio and a linear relationship is observed between and [ROH]/[monomer]. However, exclusive AMM is rarely observed. 

Despite these important advances, the controlled preparation of branched polyglycidols with MWs exceeding 6000 has remained a challenge until very recendy. A facile two-step approach via low-MW polyglyddol macroinitiators was developed by Frey et al. Tbe polyfunctionality of tbe macroinitiators affords higher concentrations of alkoxide active sites even at elevated degrees of polymerization. Thus, hyperbranched polyglyddols of MWs up to 24 000 were obtained under slow monomer addition conditions. 

Chen et al. [137] employed microwave irradiation for the preparation of amine-or anhydride-terminated hb-PIs. A BB 2-type triamine monomer, namely 2,4,6-tris (4-aminophenyl)pyridine (TAPP) (1-16, Scheme 9a), was synthesized under microwave irradiation to prepare a series of amine- and anhydride-terminated triphenylpyridine-containing hb-PIs by A2 + BB 2 polymerization. Several commercially available aromatic dianhydrides, namely pyromellitic dianhydride (PMDA, 1-23, Scheme 9b), BTDA, and ODPA, were used as A2 type monomers to react with the BB 2 type aromatic triamine (TAPP). The addition of dianhydride to triamine with a monomer molar ratio of 1 1 yielded the amine-terminated polymer, whereas the reverse monomer addition order with a molar ratio of 2 1 gave the anhydride-terminated polymer. Slow monomer addition was used to avoid any high local concentration. The authors kept the total solid content below 0.08 mol/L for the amine-terminated polymer and 0.06 mol/L for the anhydride-terminated polymer to prevent insoluble gels. During the whole polymerization, continuous microwave irradiation was employed to enhance the reactivity and... 

Even if the AM mechanism operates in a cationic polymerization of oxiranes in the presence of hydroxyl groups, it does not eliminate the possible contribution of a conventional active chain end (ACE) mechanism (active center oxonium ion located at the macromolecular chain end). In order for an AM-type propagation to prevail, the instantaneous concentration of monomer should be kept as low as possible (e.g. via continuous slow monomer addition). 

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