Macromonomers amphiphilic

By ROMP of norbornenyl-(PS-b-PEO) macromonomers, amphiphilic spheres with hydrophilic or hydrophobic outer layer have been synthesized. Scheme 5. The peculiar topology of these polymacromonomers makes them particularly suitable for applications such as unamolecular micelles or associative thickeners. 

A novel approach to RAFT emulsion polymerization has recently been reported.461529 In a first step, a water-soluble monomer (AA) was polymerized in the aqueous phase to a low degree of polymerization to form a macro RAFT agent. A hydrophobic monomer (BA) was then added under controlled feed to give amphiphilic oligomers that form micelles. These constitute a RAFT-containing seed. Continued controlled feed of hydrophobic monomer may be used to continue the emulsion polymerization. The process appears directly analogous to the self-stabilizing lattices approach previously used in macromonomer RAFT polymerization (Section 9.5.2). Both processes allow emulsion polymerization without added surfactant. 

Novel thermally responsive polymeric nanoparticles that show high colloidal stability were prepared by Laukkanen et al. via emulsion polymerisation of VCL in the presence of the amphiphilic macromonomer cw-methoxy polyethylene oxide undecyl a-methacrylate (MAC11EO42) (Fig. 15) [177,178,182]. The macromonomer itself proved to be highly sur-... 

Fig. 16 The thermal response of different polymeric structures based on PVCL and the amphiphilic macromonomer MAC11EO42. Left Shrinking of the grafted PVCL microgel. Right Heat-induced aggregation of the graft copolymer and formation of a mesoglobule [181]...

Laukkanen A (2005) Thermally responsive polymers based on N-vinylcaprolactam and an amphiphilic macromonomer. Academic Dissertation. Yliopistopaino, University of Helsinki, http //ethesis.helsinki.fi/julkaisut/mat/kemia/vk/laukkanen... 

In this review we summarize and discuss the amphiphilic properties of polyoxyethylene (PEO) macromonomers and PEO graft copolymer molecules, the aggregation of amphiphilic PEO macromonomers into micelles, the effect of organized aggregation of macromonomers on the polymerization process, and the kinetics of radical polymerization and copolymerization of PEO macromonomer in disperse (dispersion, emulsion, miniemulsion, microemulsion, etc.) systems [1-5]. 

Macromonomers afford a powerful means of designing a vast variety of well-defined graft copolymers. These species are particularly useful in the field of polymer blends as compatibilizers and/or stabilizers (surfactants). When macromonomer itself is an amphiphilic polymer, then its polymerization in water usually occurs rapidly as a result of organization into micelles. In copolymerizations, important factors for macromonomer reactivity are the thermodynamic repulsion or incompatibility between the macromonomer and the trunk polymer and its partitioning between the continuous phase and the polymer particles [4,5]. 

Kinetics of Radical Polymerization of Conventional Monomer and Amphiphilic Macromonomers in Disperse Systems... 

Thus the use amphiphilic macromonomers is another method to achieve the particle formation and their subsequent stabilization. Macromonomers can be pre-reacted to form graft copolymers, which are be introduced into the reaction medium afterwards. Macromonomers can also be copolymerized with classical monomers in situ to form graft copolymers. This is a simple and flexible method for producing monodisperse micron-sized polymer particles. Macromonomers can produce ion-free acrylic lattices with superior stability and film forming properties compared to conventional charge stabilized lattices. These non-con-... 

Kawaguchi et al. [12] have modified Paine s model for the dispersion copolymerization of amphiphilic PEO macromonomers. The authors have modeled the variation of the particle size and its distribution with reaction conditions. For example, the expressions for the critical conversion (x Xthe particle radius (r), and the surface area (S) occupied by a PEO chain are as follows ... 

Lacroix-Desmazes and Guyot [13] applied Paine s model to the dispersion copolymerization of amphiphilic macromonomers and re-discussed this model in terms of possible incorporation of a new parameter - the chain transfer parameter (Css the chain transfer constant for transfer to solvent-alcohol). The relations for the rate of dead chains (kj) and chain length (CL) are as follows ... 

The emulsifier provides sites for the particle nucleation and stabilizes growing or the final polymer particles. Even though conventional emulsifiers (anionic, cationic, and nonionic) are commonly used in emulsion polymerization, other non-conventional ones are also used they include reactive emulsifiers and amphiphilic macromonomers. Reactive emulsifiers and macromonomers, which are surface active emulsifiers with an unsaturated group, are chemically bound to the surface of polymer particles. This strongly reduces the critical amount of emulsifier needed for stabilization of polymer particles, desorption of emulsifier from particles, formation of distinct emulsifier domains during film formation, and water sensitivity of the latex film. 

In the case of more water-soluble monomers and (amphiphilic) macromonomers, the Smith-Ewart [16] expression does not satisfactorily describe the particle nucleation. The HUFT [9,10] theory, however, satisfactorily describes the polymerization behavior or the particle nucleation of such unsaturated hydrophilic and amphiphilic monomers. The HUFT approach implies that primary particles are formed in the aqueous phase by precipitation of oligomer radicals above a critical chain length. The basic principals of the HUFT theory is that formation of primary particles will take place up to a point where the rate of formation of radicals in the aqueous phase is equal to the rate of disappearance of radicals by capture of radicals by particles already formed. Stabilization of primary particles in emulsifier-free emulsion polymerization may be achieved if the monomer (or macromonomer) contains surface active groups. Besides, the charged radical fragments of initiator increases the colloidal stability of the polymer particles. 

Thus in the emulsifier-free emulsion copolymerization the emulsifier (graft copolymer, etc.) is formed by copolymerization of hydrophobic with hydrophilic monomers in the aqueous phase. The ffee-emulsifier emulsion polymerization and copolymerization of hydrophilic (amphiphilic) macromonomer and hydro-phobic comonomer (such as styrene) proceeds by the homogeneous nucleation mechanism (see Scheme 1). Here the primary particles are formed by precipitation of oligomer radicals above a certain critical chain length. Such primary particles are colloidally unstable, undergoing coagulation with other primary polymer particles or, later, with premature polymer particles and polymerize very slowly. 

The polymerizability of R-(EO)n-VB macromonomers has its maximum (Rp) around n=15-20 [51]. This finding was related to the micelle formation which is expected to be unfavored for either too long or too short chain length of PEO. The macromonomers and their polymacromonomers with very short R are soluble in water and therefore they lose their amphiphilic nature. The parameters of R and n of macromonomer (R-(EO)n-VB) were found to correlate with the formation of micelles and their structure. In the aqueous phase the scattering intensity increased with the concentration of macromonomer above the CMC. The critical micellar concentration in water was found to be in the range from 3.3 xl0 5to 7.1xl0 5 mol dm-3 for several R-(EO)n-VB macromonomers. 

Short chain amphiphiles can be incorporated into the backbone of the polymer chains. The resulting graft macromolecules are able to form both intrachain and interchain aggregates. Polymeric surfactants assemble into a variety of intrachain micelles. These polymeric surfactants and/or amphiphilic polymacromonomers can also form mixed aggregates which incorporate free monomeric (macromonomer with a very small hydrophobic group) surfactants. 

The incorporation yields of the stabilizers are always very limited, but the highest value is obtained for the PEO-MA macromonomer, and the lowest for the amphiphilic compound (surfmer) with the longest hydrophobic sequence ca. 0.5% ... 

A series of amphiphilic diblock macromonomers were successfully used as steric stabilizers in the emulsion polymerization styrene [98]. Copolymerization led to the formation of polymer latexes of high colloidal stability. These... 

When the macromonomer is an amphiphilic polymer, its polymerization in the polar media is unusually rapid as a result of its organization into micelles. Under such conditions, the unsaturated groups are concentrated in the micelle they mostly form the hydrophobic core of aggregates (micelles). During the polymerization, the non-polymerizing micelles and/or the monomer saturated continuous phase act as a monomer reservoir. 

Such hydrophilic macromonomers (DPn=7-9) were radically homopolymer-ized and copolymerized with styrene [78] using AIBN as an initiator at 60 °C in deuterated DMSO in order to follow the kinetics directly by NMR analysis. The macromonomer was found to be less reactive than styrene (rM=0.9 for the macromonomer and rs=1.3 for styrene). Polymerization led to amphiphilic graft copolymers with a polystyrene backbone and poly(vinyl alcohol) branches. The hydrophilic macromonomer was also used in emulsion polymerization and copolymerized onto seed polystyrene particles in order to incorporate it at the interface. 

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