In-Situ Polymerization Processing

Park et al. (60) studied dispersion characteristics of MWCNT-PMMA composites synthesized by in-situ bulk polymerization using AIBN as free radical initiator. In their method, CNTs in varying amounts such as 0.001, 0.01 and 0.1 wt% with respect to MMA were first dispersed in MMA monomer by ultrasonication before polymerization. Experimental evidence such as molecular weight of free PMMA prepared via in-situ polymerization with and without CNTs, diameter of pristine MWCNT and diameter of MWCNT in composite, FTIR and SEM studies confirmed the role of AIBN and MWCNT in polymerization. The induced radicals on MWCNT by AIBN were found to trigger grafting of PMMA on to CNT surface. Solvent cast film of the composite was transparent and showed a better nanoscopic dispersion without aggregates compared to the cast film prepared from direct mixing of MWCNT and PMMA. 

Shang et al. (61) used microemulsion polymerization to synthesize MWCNT-PMMA composites for gas sensor applications. Better dispersion, enhanced electrical conductivity and better sensor response was observed for in-situ fabricated composites compared to composites prepared by solution mixing. Ma et al. (62) performed in-situ polymerization of MWCNT-PMMA composites in the presence of an AC electric field to study dispersion and alignment of MWCNT in PMMA matrix induced by the electric field. Experimental evidences from in-situ optical microscopy, Raman spectroscopy, SEM and electrical conductivity showed that both dispersion and alignment qualities were significantly enhanced for oxidized MWCNT compared to pristine MWCNT. 

Coagulation method can be used to fabricate SWCNT-PMMA composites with uniform dispersion (15,22,63,64). First a well-dispersed 

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Y. F. Huang, C. W. Lin, Facile synthesis and morphology control of graphene oxide/polyaniline nanocomposites via in-situ polymerization process, Polymer, vol. 53, pp. 2574-2582, 2012. 

In this section, we consider the different synthesis routes that have been employed to incorporate polymers into LDH with emphasis on the in situ polymerization process, an approach which gives rise to well-defined nanocomposites. 

As can easily be understood, the in situ polymerization process is favored when distances between monomers in the interlamellar space are close to the monomeric repeat distance displayed by the polymer. Such a compatibility of distances was first demonstrated for the polymerization of aniline in V2O5 and FeOCl hosts with an exact matching between NH functions for PANl and the (1-30) crystallographic direction for V2O5 or the (201) direction for FeOCl [63]. 

HIPS resin with both a high gloss and a high impact strength have been produced using a special in situ polymerization process. A bimodal distribution of the elastomer particles and particular size range and morphology type is maintained (8). 

FIGURE 11.13 A schematic illustration of the in situ polymerization process with clay as example. 

It is desirable to directly prepare PP with a desirable terminal functional group, such as Cl, OH, and NH2. In other words, the ideal reaction is a one-pot in situ polymerization process, and no chain-end functionalization would be needed after the polymerization reaction. Three functional St-X molecules were investigated (83), including p-chlorostyrene (St-Cl), silane-protected p-vinylphenol (St-OSi), and silane-protected... 

The monomers have much better solubility and permeability than polymers. The interaction and homogeneity are expected to be better in the resulted composite. The coexisting inorganic moieties can act as nuclei, thus the formed insoluble polymer chains are deposited on them. In addition, the cross-linked polymers cannot be dissolved in solvent, so their composites should be prepared through this in situ polymerization process. The composites of epoxy, polydimethylsiloxane (PDMS), and polymer gels have been prepared via this method to improve mechanical and electrical properties (Sun et al., 2013b). 

Figure 35-10. Notched bar impact strengths, as a function of the mass fraction of the poly(butadiene) component in blends from cis-BR and PS made by the latex process, L, melt-mixing process, M, and the in situ polymerization process, P. (After J. A. Manson and L. H. Sperling.)...

Besides using an in situ polymerization of pyrrole to form an electrically conductive textile, other researchers have adopted a two-step process. The major advantage of the two-step process is that it can be easily adapted into a continuous process for industrial applications. However, the structure of the polypyrrole may be different to that obtained from the in situ polymerization process. Several variations to the a two-step process include first immersing the textile support in a solution containing the oxidant and desired dopant anion and then exposing the impregnated textile to either pyrrole vapor [87-89] or pyrrole dissolved in an aliphatic solvent [90] to initiate the polymerization reaction. Alternately, the textile support may be first exposed to pyrrole vapor and then immersed into an aqueous solution containing the oxidant and desired dopant anion [91]. 

Also, processes involving the in-situ formation of a titania-based polymeric gel in the presence of PCL lead to PCL-Ti02 nanohybrids. Unlike in other systems, the inorganic component is in this case generated in-situ in the presence of the polymeric component [83]. Combinations of sol-gel and in-situ polymerization processes have also been reported. Thus, polybenzoxazine-Ti02 nanohybrid systems were prepared from titanium /so-propoxide and bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl)isopropane [182]. 

Scheme 7.2 In-situ polymerization process for WPU/CNT nanocomposites. Reproduced from Ref [16] with permission.

An in-depth discussion on the major in-situ polymerization processes is provided in Chapter 4. In addition, encapsulation using the mini emulsion process is discussed in Chapter 2, and interfacial polycondensations processes are described in Chapter 5. 

Figure 4.3 shows the schematic of in situ polymerization process. During the in situ polymerization process, nanoparticles such as CNTs and layered silicates are first dispersed in a liquid monomer. The polymerization reaction is initiated either by heat or radiation, by the diffusion of a suitable initiator, or by an organic initiator or by catalyst fixed on the surface of nanoparticles. Upon the completion of polymerization, polymer molecules are either... 

The nylon-clay nanocomposites were prepared by in situ polymerization in the presence of organically modified, with aminolauric acid, montmorillonite. The reaction between nylon monomer and modified montmorillonite rendered nylon chains end-tethered though aminolauric acid to the silicate surface leading to exfoliated silicates (61). However, not all polymer nanocomposite systems could be produced via in situ polymerization processes because of the chemical sensitivity of polymerization catalysts. Direct melt blending of hydrophilic polymers with montmorillonite in its pristine state or polymers with surfactant-intercalated montmorillonite was found to be possible to deliver polymer intercalated or exfoliated nanocomposites (62,63). 

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