Polymer monofunctional

Chains with uttdesired functionality from termination by combination or disproportionation cannot be totally avoided. Tn attempts to prepare a monofunctional polymer, any termination by combination will give rise to a difunctional impurity. Similarly, when a difunctional polymer is required, termination by disproportionation will yield a monofunctional impurity. The amount of termination by radical-radical reactions can be minimized by using the lowest practical rate of initiation (and of polymerization). Computer modeling has been used as a means of predicting the sources of chain ends during polymerization and examining their dependence on reaction conditions (Section 7.5.612 0 J The main limitations on accuracy are the precision of rate constants which characterize the polymerization. 

Chain compositional heterogeneity is of particular relevance to functional copolymers which find widespread use in the coalings and adhesives industries.13,240,246 In these applications, the functional copolymer and a crosslinking agent are applied together and are cured to form a network polymer. The functional copolymers are based on functional monomers with reactive groups (e.g. OH), it is desirable that all copolymer molecules have a functionality of at least two. Nonfunctional polymer will not be incorporated and could plasticize the network or be exuded from the polymer. Monofunctional polymers are not involved in crosslink formation and will produce dangling ends. 

If R = R (bifunctional polymers), reaction (119) does not affect the functionality but leads to the broadening of the molecular weight distribution, which is occurring anyway, due to the reversibility of propagation. Thus, several bifunctional polymers of 1,3-dioxolane were prepared and used, for example, to form the networks containing degradable and hydrolyzable polyacetal blocks (cf., Section IV.B). Reaction (119), however, may effectively prohibit the preparation of monofunctional polymers, e.g., macromonomers. Indeed, two recent attempts to prepare macromonomers by cationic polymerization of cyclic acetals led to nearly statistical... 

Several monofunctional polymers of tetrahydrofuran-containing polymerizable groups at one chain end (macromonomers) were prepared using the approach outlined in Eqs. (180) and (181). Polymerizable groups were introduced with initiators, e.g. ... 

Monofunctional polymers of A -t-butylaziridine containing polymerizable group (macromonomers) were prepared by initiation of the polymerization with methyltriflate and termination with methacrylic acid [168]. 

The difference between PEO being functionalised at one chain end with a hydrophobic sticker and its counterpart containing the hydrophobic units at both chain ends was examined with oil-in-water (o/w) droplet microemulsions [22-24]. Cetyl pyridiniumchlo-ride/octanol or alkylphenol ethoxylate were used as surfactant. The monofunctional polymers were only capable to decorate the oil droplets whereas the difunctional polymers could also bridge them. Experiments were carried out as a function of the droplet volume... 

Modeling Linear and Nonlinear Homo- and Copolymerizations Assuming Monofunctional Polymer Molecules and Using the PKRCM... 

Figure 12.1 Polymerization scheme for nonlinear copolymerization with crosshnking under PKRCM and monofunctional polymer molecules.

Fig. 14 Predicted phase diagram for a mixture of a telechelic polymer bearing two acceptor end groups and a monofunctional polymer containing only one complementary end group. Reprinted, with permission of John Wiley Sons, Inc., from [91], Copyright 2007...

The solution absorption maximum depends strongly on the bulk and placement of substituents. Studies on 3,4-difunctional polythiophenes explored the extremes of steric interactions, indicating increasing bulk for H < CH3 < 0C H2 + 2 < C >iH2 +2 [110], For monofunctional polymers, the importance of coupling regiospecificity was recognized early [98, 111],... 

At this stage, we realize that we can study monofunctional polymers (/ = 1) and telechelic polymers (/ = 2) (and also their mixtures) from the unified point of view described above. Important examples of the monofunctional case are amphiphilic diblock... 

A wide range of functional thiols, eg, mercaptoethanol (OHCH2CH2SH) and thioglycolic acid (OH(CO)CH2SH), have been used to produce monofunctional polymers (165,209,210). 

Almost quantitative carboxyl formation is observed if the polymer is converted to an intermediate Grignard (171) compound. The CO2 is added rapidly, accompanied by a significant increase in viscosity of the monofunctional polymers and gelling of the bifunctional polymers. Yields depend on the reaction rates and on stirring efficiency. Alternatively, a anhydride can be used as termination agent (reaction 41). 

Harris, N.J., Veronese, F.M., et al., 1999, Multiarmed, monofunctional, polymer for coupling to molecules and surfaces. US Patent Trademark Office, USA. 

The effect of coupling a monofunctional polymer chain with a tetrafunctional metal halide on the MWD of a solution SBR is shown schematically in Fig. 6. For the case of non-quantitative coupling, as shown here, the components of the resulting bimodal MWD consist of... 

When chain transfer occurs during a difvinctional polymerization monofunctional polymers result which have at one end a perfluoropropyl ether group. 

The dlfunctlonal molecules can be expected to grow to no more than DP 200 (53i000 Mn) but this material would be contaminated with a substantial fraction of lower DP monofunctional polymer. 

Intermolecular chain transfer to polymer is well documented in the cationic polymerization of cyclic acetals. In the polymerization of TOX, as will be discussed in Section 4.10.3, chain transfer to polymer is essential for the preparation of thermally stable polyacetal. Intermolecular chain transfer to polymer is detrimental to the synthesis of monofunctional polymers such as macromonomers because segment exchange (scrambling) leads to disproportionation and formation of products having two, one, and none of the functional groups (Scheme 21). " Intermolecular chain transfer to polymer prohibits also the synthesis of block copolymers by sequential polymerization of two cyclic acetals. Addition of DXP to a solution of living polyDXL resulted in further polymerization but the copolymer formed had a nearly statistical distribution of units." ... 

The chain extension of polymers occurred through a disulfide bond formation. When monofunctional polymer obtained by BEDC was used, the molecular weight of the polymer obtained after the chain extension reaction increased about two times compared with the starting polymer. However, with the increase of chain extension reactions of bifunctional polymers obtained by XEDC, the molecular weight increased about three to five times. Similar results were obtained for chain extension reactions by a chelate bond formation. 

In all arm-first methods a living monofunctional polymer of known length and low polymolecularity serves as a precursor. Subsequently, the active sites located at chain end can be used in one of two different ways ... 

Sometimes, polyesterificaion of a monomer (Pj) is carried out in the presence of monofunctional compounds such as cetyl alcohol, ethyl benzoate, or ethyl terephthalate. Let us denote these by MF]. As the polymerization is carried out, the monomer molecules grow in size to give P . Large-chain monofunctional polymers MF are formed when P and MFj interact. The overall polymerization can be expressed as follows ... 

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