In situ bulk polymerization

The in situ bulk polymerization of vinyl monomers in PET and the graft polymerization of vinyl monomers to PET are potential useful tools for the chemical modification of this polymer. The distinction between in situ polymerization and graft polymerization is a relatively minor one, and from a practical point of view may be of no significance. In graft polymerization, the newly formed polymer is covalently bonded to a site on the host polymer (PET), while the in situ bulk polymerization of a vinyl monomer results in a polymer that is physically entraped in the PET. The vinyl polymerization in the PET is usually carried out in the presence of the swelling solvent, thereby maintaining the swollen PET structure during polymerization. The swollen structure allows the monomer to diffuse in sufficient quantities to react at the active centers that have been produced by chemical initiation (with AIBM) before termination takes place. 

FIGURE 11.20 TGA curves and the CCA curves for pure polystyrene and three PS/clay nanocomposites obtained with in situ bulk polymerization, VB16 and OH16 are two ammonium-modified MMT and P16 is phosphonium-modified MMT. (From Zhu, J. et al., Chem. Mater., 13, 3774, 2001. With permission.)... 

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. 

Parketal. 2003 (60) MWCNT CVD IIjin Nanotec Co., Korea Purified In situ Bulk Polymerization CNT Loading levels 0.001 to 0.1 wt% Film SEM studies showed good wetting, uniform dispersion and strong interfacial adhesion between CNT and matrix ... 

Hu Y, Zhou S, Wu L (2009) Surface mechanical properties of transparent poly(methyl methacrylate)/zirconia nanocomposites prepared by in situ bulk polymerization. Polymer 50(15) 3609-3616... 

In this method, semiconductor nanoparticles are dispersed directly in monomeric solution prior to a polymerization process. Guan et al. [242] used this method for synthesis of transparent polymer nanocomposites with high ZnS nanophase contents using a one-pot route via in-situ bulk polymerization. Uniform distribution of ZnS nanoparticles in the polymer matrix was observed due to covalent bonding between ZnS nanoparticles and the polymer matrix. This uniform distribution improved the thermal stability and mechanical properties of the nanocomposite. The nanocomposites also exhibited good transparency and adjustable refractive index due to controlled structore and ZnS content. 

High impact polystyrene (HIPS) is a blend of PS that has been polymerized in the presence of polybutadiene. This leads to PS chains with grafted polybutadiene, as well as some free PS and PB, and the resultant polymer blend has improved impact strength. HIPS/MMT nanocomposites were formed though in-situ bulk polymerization in the presence of polybutadiene [86]. Intercalated nanocomposites with improved thermal stabihty were formed although the dispersion was different in the PS matrix phase compared to the rubber phase. 

Park S J, Cho M S, Lim ST, Choi H J and Jhon M S (2003) Synthesis and dispersion characteristics of multi-walled carbon nanotube composites with poly(methyl methacrylate) prepared by in situ bulk polymerization, Macromol Rapid Commun 24 1070-1073. 

Hatui G, Bhattacharya P, Sahoo S, Dhibar S, Das CK (2014) Combined effect of expanded graphite and multiwall carbon nanotubes on the thermo mechanical, morphological as well as electrical conductivity of in situ bulk polymerized polystyrene composites. Compos A Appl Sci Manuf 56 181-191... 

PMMA modified by inorganic nanoparticles such as Ti02, ZnS Mn, CdSe, CdSe/ZnS, ZnO, and CNTs has led to enhanced optical [16], thermal [149], and electrical properties, as compared to pure polymer. For example, Althues et al. [16] reported an efficient method for generation of completely transparent and strongly luminescent ZnS Mn/PMMA nanocomposites. They used in-situ bulk polymerization of transparent dispersions containing ZnS Mn nanoparticles in a mixture of MMA and AA the effective diameter of nanoparticles in the monomer dispersion was 22 nm. Two factors were responsible for the stability of the ZnS Mn/monomer dispersion, i.e., coordination of AA, which modified the surface of the nanoparticles and led to hydrophobization, and adsorption of ions leading to a surface charge... 

Park et al. [144] conducted a study in which PMMA/MWCNT nanocomposites were prepared via both in-situ bulk polymerization and suspension polymerization, using the radical initiator 2,2-azobis(isobutyronitrile) (AIBN). The electrical and electrorheological (ER) properties of the nanocomposites were investigated. The conductivity of pure PMMA and MWCNT/PMMA nanocomposites were measured, and it was shown that the conductivity of MWCNT/PMMA composites rapidly increased when MWCNTs were added to the PMMA matrix, i.e., 3.192 x 10 , 2.163 X 10 2, and 1.693 x 10 Scm for 1.5, 5 and 10wt% of MWCNT in the composites, respectively. The conductivity of insulating PMMA was about 1 X 10 2Scm [144]. 

The thermally stable reactive surfactant imidazolium salts (Cn, Cie, and Cig) were used to modify montmorillonite (Table 3.3) to prepare PS nanocomposites via in situ bulk polymerization [49-53]. In spite of the long alkyl chains in the compounds, the basal spacing of modified MMT was small. Nonetheless, the nanocomposites exhibited a... 

Styryltropylium (a carbo-cation) was used to modify clay for producing PS nanocomposites by in situ emulsion polymerization (Table 3.4) [60]. The resulting nanocomposites exhibited a mixture of intercalated and exfoliated structures. The nanocomposites exhibited improved thermal stability and fire retardancy. Halloysite nanotubes (HNT) are a kind of aluminosilicate clay with a hollow nanotubular structure (about 20-50 nm in diameter and several hundred nanometers in length) [61]. HNT was modified with y-methacryloxypropyltrimethoxysilane to produce a nanoclay (Table 3.4). HNT/PS nanocomposites were prepared by in situ bulk polymerization. The thermal stability of the HNT/PS nanocomposites was better than that of the pure polystyrene. 

Z. Tang, D. Lu, J. Guo, and Z. Su, Thermal stabilities of vermiculites/polystyrene (VMTs/PS) nanocomposites via in-situ bulk polymerization. Materials Letters, 62 (2008), 4223-5. 

G. A. Wang, C. C. Wang, and C. Y. Chen, The disorderly exfoliated LDHs/PMMA nanocomposite synthesized by in situ bulk polymerization. Polymer, 46 (2005), 5065-lA. 

Spontaneous, in situ bulk polymerization of styrene-MA in the presence of branched polyethylene,polypropylene, polystyrene, poly(vinyl chloride), poly(ethylene-co-... 

Zeng and Lee (2001) prepared PMMA/clay nanocomposites via in-situ bulk polymerization. The compatibility of the initiator and monomer with the clay surface was found to profoundly affect the clay dispersion. Furthermore, by using a nanoclay (MHABS) that was modified by a surfactant containing a polymerizable group (the chemical structure is shown in the top right of Figure 1.2), exfoliated PMMA/clay nanocomposites with excellent clay dispersion were synthesized. 

Poly(methyl methacrylate) (PMMA) was also used in MMT nanocomposite foam preparation (Fu and Naguib, 2006 Weickmann et al, 2010). Organomodified MMT was used in its preparation by in situ bulk polymerization and batch foaming process with N2. The MMT acted as a heterogeneous nucleation agent in polymer matrix that reduced cell size and increased cell density. Moreover, MMT addition decreased dielectric constant and slightly increased the thermal conductivity as well as the mechanical strength due to the well-dispersed clay mineral platelets (Yeh et al., 2009). 

In most cases, in situ suspension polymerization is carried out with nanoparticles dispersed in monomers. The surface modification of nanoparticles is usually required in order to achieve a good dispersion. Since the mechanism of in situ suspension polymerization is similar to that of in situ bulk polymerization, the surface modification used in bulk polymerization, including ion-exchange reaction, surfactant and coupling agent, polymer grafting and acid treatment can also be applied here. 

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