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Poly(siloxane)s, Poly(silazane)s and Poly(carbosiloxane)s
Published in Narendra Pal Singh Chauhan, Functionalized Polymers, 2021
Claire E. Martin, Giovanni Fardella, Ricardo Perez, Joseph W. Krumpfer
End-capping is an important aspect of introducing functionality to the polymer chain ends. For example, the use of chlorodimethylsilane, ( CH3)2SiHCl , terminates the polymer chain with a hydridosilane, a functional group important in hydrosilylation reactions. Indeed, we will see this is one of the primary methods for preparing surfactants. Additionally, other monomers used to modify both chain ends, such as 3-aminopropyldimethylmethoxysilane, (NH2CH2CH2) (CH3)2Si(OCH3) , dimethylvinylchlorosilane, (CH3)2CH2CHSiCl , or glycidoxysilanes, are important crosslinking agents for polyurethanes, hydrosilylation networks, and epoxies, respectively. We note that this is a thermodynamic control over the molecular weight through affecting the equilibration process, which occurs late in the polymerization.
Telechelic Polymers by Ring-Opening Polymerization
Published in Eric J. Goethals, Telechelic Polymers: Synthesis and Applications, 2018
End-group functionalities can be introduced in polymer chains by initiation, by end-capping, or by transfer. To obtain functional end-groups at both chain ends, a combination of two methods or a subsequent reaction (e.g., chain coupling) may be necessary.
Combinatorial Polymer and Lipidoid Libraries for Nanomedicine
Published in Vladimir Torchilin, Mansoor M Amiji, Handbook of Materials for Nanomedicine, 2011
Jordan J. Green, Robert Langer, Daniel G. Anderson
The end-capping group can significantly change the effectiveness of the base polymer, either making an ineffective polymer highly effective or nullifying the effectiveness of an effective polymer depending on the end-capping molecule. Initial in vitro transfections in COS-7 fibroblasts and HepG2 hepatocytes showed that transfection efficacy can be improved over two orders of magnitude in both cell lines by single carbon differences to the length of the capping molecule (C32-103, capped with 1,2 diaminopropane >> C32-102, capped with ethylenediamine, see Fig. 7.5(a)).60 Whereas C32-102 reduces gene delivery compared to unmodified C32, C32-103 enhances efficacy. Optimization of end-group was also found to be dependent on base polymer composition. For example, the ethylene glycol diamine end-capping groups 121 and 122 enhanced gene delivery when end-capped to D60 polymer, but decreased gene delivery when end-capped to C32 polymer. The possible improvement to non-effective gene delivery polymers was dramatic. C20, which has only a slight difference in structure than C32, but is two orders of magnitude less effective than C32 for gene delivery,48 can be improved to have significant gene delivery activity by just modifying the ends of the polymer.
Advances in self-crosslinking of acrylic emulsion: what we know and what we would like to know
Published in Journal of Dispersion Science and Technology, 2019
Sumit Parvate, Prakash Mahanwar
Silane-modified polymers are prepared by using three mechanisms: (i) Copolymerization: Here copolymerization takes place by incorporating polymerizable (e. g. vinylsilane or methacryloxy) organofunctional groups into the chain during the production of the polymer. (ii) Endcapping: Here covalent bond is formed by reaction between silane’s organofunctional group and the terminal functional group of the polymer backbone chain. (iii) Radical grafting: Unsaturations in silanes, such as vinylsilane, methacryloxysilanes forms a bond with polymer chains by radical grafting reaction. These polymers can form stable siloxane bonds (-Si-O-Si-) after the crosslinking of the remaining Si-alkoxy group. Due to their dual reactivity, organosilanes acts like bridges between inorganic or organic substrates ultimately improves adhesion. Steps of self- crosslinking reactions of silanes have been illustrated in Figure 11.