Polymers with Pendant Functional Groups

POLYMERS WITH PENDANT FUNCTIONAL GROUPS A. General Methodology and Scope 

The simplest examples of so-called functional or functionalized polymers are perhaps those with pendant functional groups. The introduction of pendant functional groups to synthetic polymers, in general, may be achieved by two methods (1) polymerization of monomers with pendant functional groups and (2) chemical transformation of the pendant groups in preformed polymers. Both of them involve advantages and disadvantages, and most of the currently available polymers of this type are pro- 

In such syntheses, therefore, one deals with a hybrid process of methods 1 and 2, discussed above. 

Pendant-Functionalized Polymers by Living Cationic Polymerization 

Vinyl Ethers with Polar Functional Groups 

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This technique is based on the use of a linear polymer with pendant functional groups that can be activated to initiate the polymerization of a second monomer. Based on this definition, the linear precursor polymer can be considered as a multifunctional macromolecular initiator. The importance of the grafting from technique by cationic polymerization of the second monomer increased considerably with the advent of living cationic polymerization. The advantage is the virtual absence of homopolymer formation via chain transfer to monomer. 

At this point, some alternative methods are worthy of mention for the synthesis of polydepsipeptides. The copolymerization of lactones and amino acid carboxy-anhydrides using stannous octanoate as catalyst affords random polydepsipeptides, and is an attractive way to prepare polymers with pendant functional groups [42]. In addition, the ROP of amino acid N-carboxyanhydrides and lactic acid anhydrosulfite affords polymers the structure of which may be either random or blocky-like , depending on the catalyst/initiator system used [43, 44). 

Another important role of the pendant-functionalized vinyl ethers is that they can be precursors of initiators for living cationic polymerization of other vinyl ether and styrene derivatives, from which polymers with terminal functional groups can be prepared (see Section IV). 

Hybrid versions of silicone-thermoplastic semi-IPNs have been developed (19). A hybrid interpenetrating network is one in which the cross-linked network is formed by the reaction of two polymers with structurally distinct backbones. Hydride-functionalized siloxanes can be reacted with organic polymers with pendant unsaturated groups such as polybutadienes (5) in the presence of platinum catalysts. Compared with the polysiloxane semi-IPNs discussed earlier, the hydride IPNs tend to maintain mechanical and morphologically derived properties, whereas properties associated with siloxanes are diminished. The probable importance of this technology is in cost-effective ways to induce thermoset characteristics in thermoplastic elastomers. 

Yokoe M., Aoi M., Okada M., Biodegradable polymers based on renewable resources. IX. Synthesis and biodegradation behavior of polycarbonates based on l,4 3,6-dianhydrohexitols and tartaric acid derivatives with pendant functional groups, /. Polym. Set Part A Polym. Chem., 43, 2005, 3909-3919. 

Aziridinyl)ethyl methacrylate n, A vinyl monomer that combines a reactive vinyl group with an aziridinyl functional group. It can be polymerized alone or with other vinyl monomers to yield polymers with pendant aziridinyl groups that promote adhesion of coatings to the polymer. Odian GC (2004) Principles of polymerization. John Wiley and Sons Inc., New York. 

PBI-based polymer electrolytes with pendant functional groups were proposed by Gieselman and Reynolds [133, 134], by producing N-substituted PBI with sulfonates, which could be traced back to Sansone s work [130]. In the following years, more efforts were devoted to prepare sulfonated PBI membranes by reacting PBIs with sodium (4-bromomethyl)benzenesulfonate [135, 136], arylsulfonates, or alkylsulfonates [137]. The introduction of benzylsulfonic, arylsulfonic, or alkylsulfonic acids was found to create proton conductivity in the presence of water. Using A-substitution, the sulfonation degree of the membranes could be accurately controlled [133]. 

The bonding to preformed polymer requires macromolecules with pendant functional groups capable of reaction with herbicides or their derivatives. The nature of the bond can vary with different rates of cleavage... 

Fig. 2I, Olelin functionalization of acrylic polymers through reaction with pendant hydroxyl groups.

However, certain additives can decrease the rate of thermal decomposition [28]. These additives include cyclic sulfates, sulfones, sultones, aliphatic and aromatic anhydrides, and polymers with pendant carboxylic acid functional groups. Most of these materials are latent acids, which decompose on heating in the presence of moisture to form a strong acid, as shown for cyclic sulfate, 9, in Eq. 5. 

Other commercially relevant monomers have also been modeled in this study, including acrylates, styrene, and vinyl chloride.55 Symmetrical a,dienes substituted with the appropriate pendant functional group are polymerized via ADMET and utilized to model ethylene-styrene, ethylene-vinyl chloride, and ethylene-methyl acrylate copolymers. Since these models have perfect microstructure repeat units, they are a useful tool to study the effects of the functionality on the physical properties of these industrially important materials. The polymers produced have molecular weights in the range of 20,000-60,000, well within the range necessary to possess similar properties to commercial high-molecular-weight material. 

Accordingly, the synthesis of novel cinnamate polymers with high functionality and performance is very important from the viewpoint of both polymer chemistry and practical use. Recently, we have reported the synthesis of polymers with pendant photosensitive moieties such as cinnamic ester and suitable photosensitizer groups by radical copolymerizations of 2-(cinnamoyloxy) ethyl methacrylate with photosensitizer monomers (9), by copolymerizations of chloromethylated styrene with the photosensitizer monomers followed by the reactions of the copolymers with salts of... 

The effective complexation of CD was also used for the preparation of side-chain polyrotaxanes [96-102], All of these side-chain systems are based on Method 4 or Method 5 (Figure 9) and were reported by Ritter and coworkers. For Method 4, the CD was threaded on to a small molecule bearing a functional group Y and with one end blocked, i.e., a hemirotaxane. The reaction of Y with X, a pendant functional group in a preformed polymer, gives thermally stable... 

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