*Polypropylene - Polymerization and Characterization of Mechanical and Thermal Properties*

#### **Figure 1.**

*Key milestones of the commercialization of polypropylene. Adapted from Ref. [1-4].*

methacrylate and studied the blending behavior between the resulting copolymers

*Synthesis of PP comb polymers (reprinted with permission from Ref. [20]. Copyright 2012 American Chemical*

*Synthesis of three-arm PP star polymer by click chemistry (reprinted with permission from Ref. [14]. Copyright*

*Introductory Chapter: Polypropylene - Synthesis and Functionalization*

*DOI: http://dx.doi.org/10.5772/intechopen.92067*

functionalized PP and prepared PP three-arm star polymer (**Figure 4**) [14] and PPb-polycaprolactone (PP-b-PCL) block copolymers [15]. By terminating the coordination polymerization of iPP with (p-vinylphenyl)chlorosilane, iPP star polymers with 3–8 different numbers of arms were prepared in an H2O/toluene emulsion

Using stereoselective insertion polymerization catalyst, Coates synthesized a group of block copolymers containing iPP as the rigid block and regioirregular polypropylene (rPP) as the elastic block. The mechanical characterization of the iPP-rPP-iPP-rPP-iPP pentablock copolymer indicated a strain at break of 2400% and a maximum true tensile stress of 250 MPa [17]. In collaboration with Bates and LaPointe, the group synthesized a polyethylene-b-iPP-b-polyethylene-b-iPP tetrablock copolymer and evaluated the blending behavior of the tetrablock copolymer with PE/iPP. By "welding" polyethylene (PE) and iPP, together with the tetrablock copolymer, previously impossible due to the immiscibility, the blend was transformed from a brittle glass into a tough plastic, paving a possibility to recycle

Long-chain branching in polymers has shown interesting rheological behaviors [19]. Using norbornene-terminated syndiotactic PP as a macromonomer, Coates

with PS/PP or PMMA/PP blend [13]. The same group prepared azide end-

the world's two most-produced polymer materials [18].

system [16].

**3**

**Figure 5.**

*Society).*

**Figure 4.**

*2010 American Chemical Society).*

#### **Figure 2.**

*Distribution of polymer demand worldwide in 2016 by volume. Adapted from Ref. [5].*

#### **Figure 3.**

*Living and iso-selective propylene polymerization (reprinted with permission from Ref. [8]. Copyright 2017 American Chemical Society).*

resulting polymer could be purified into narrow distributed copolymers with hexane-heptane fractionation. Dong et al. used a brominated isotactic PP with styrene termination as a macroinitiator to copolymerize styrene or methyl

*Introductory Chapter: Polypropylene - Synthesis and Functionalization DOI: http://dx.doi.org/10.5772/intechopen.92067*

#### **Figure 4.**

*Synthesis of three-arm PP star polymer by click chemistry (reprinted with permission from Ref. [14]. Copyright 2010 American Chemical Society).*

#### **Figure 5.**

*Synthesis of PP comb polymers (reprinted with permission from Ref. [20]. Copyright 2012 American Chemical Society).*

methacrylate and studied the blending behavior between the resulting copolymers with PS/PP or PMMA/PP blend [13]. The same group prepared azide endfunctionalized PP and prepared PP three-arm star polymer (**Figure 4**) [14] and PPb-polycaprolactone (PP-b-PCL) block copolymers [15]. By terminating the coordination polymerization of iPP with (p-vinylphenyl)chlorosilane, iPP star polymers with 3–8 different numbers of arms were prepared in an H2O/toluene emulsion system [16].

Using stereoselective insertion polymerization catalyst, Coates synthesized a group of block copolymers containing iPP as the rigid block and regioirregular polypropylene (rPP) as the elastic block. The mechanical characterization of the iPP-rPP-iPP-rPP-iPP pentablock copolymer indicated a strain at break of 2400% and a maximum true tensile stress of 250 MPa [17]. In collaboration with Bates and LaPointe, the group synthesized a polyethylene-b-iPP-b-polyethylene-b-iPP tetrablock copolymer and evaluated the blending behavior of the tetrablock copolymer with PE/iPP. By "welding" polyethylene (PE) and iPP, together with the tetrablock copolymer, previously impossible due to the immiscibility, the blend was transformed from a brittle glass into a tough plastic, paving a possibility to recycle the world's two most-produced polymer materials [18].

Long-chain branching in polymers has shown interesting rheological behaviors [19]. Using norbornene-terminated syndiotactic PP as a macromonomer, Coates

resulting polymer could be purified into narrow distributed copolymers with hexane-heptane fractionation. Dong et al. used a brominated isotactic PP with styrene termination as a macroinitiator to copolymerize styrene or methyl

*Living and iso-selective propylene polymerization (reprinted with permission from Ref. [8]. Copyright 2017*

*Key milestones of the commercialization of polypropylene. Adapted from Ref. [1-4].*

*Polypropylene - Polymerization and Characterization of Mechanical and Thermal Properties*

*Distribution of polymer demand worldwide in 2016 by volume. Adapted from Ref. [5].*

**Figure 1.**

**Figure 2.**

**Figure 3.**

**2**

*American Chemical Society).*

synthesized a group of well-defined s-PP bottlebrush polymers with a molecular weight from 46 kDa to 172 kDa using Grubbs' metathesis catalyst (**Figure 5**) [20]. A decrease in both melting and crystallization temperature was observed and attributed to the constraints on the rigid backbone. Further research by Bates and Hillmyer revealed a scaling transition that depends on the length of the backbone [21]. Hazer evaluated the surface property and mechanical property of a group of graft copolymer containing polypropylene as the backbone and polyethylene glycol (PEG) as the side chain [22]. With 15% of PEG, the graft copolymer demonstrated ultimate stress of 22 MPa and elongation at break of 670%. Bielawski developed a direct C▬H azidation method to introduce azide functionalities into commercially available PP [23] and prepared PP-g-PEG using click chemistry. Tasdelen used a similar approach and synthesized PP-g-PCL copolymers [24].

"Reactive" polyolefin approach, adding functional monomer units into the polyolefin chain, has emerged as a powerful tool to chemically functionalize polyolefins [25]. Pan copolymerized p-(3-butenyl)styrene and propylene with (pyridylamido)Hf/[Ph3C][B(C6F5)4]/Al<sup>i</sup> Bu3 catalytic system, which selectively copolymerize α-olefin over styrene [26]. The pendant styrenic vinyl groups in the resulting polymer were quantitatively converted into carboxylic acid groups with thiol-ene addition. The same group further extended this methodology to prepare amino-containing iPP, which exhibited high thermal stability and melting temperature [27]. Chung synthesized a group of hydroxyl-functionalized PP using silaneprotected 10-undecen-1-ol as a comonomer and converted the hydroxyl pendant group into butylated hydroxytoluene (BHT) derivatives (**Figure 6**) [28]. The resulting BHT-functionalized PP demonstrated improved thermal stability and higher dielectric constant. With two methylene group spacers between BHT and ester linkage, the materials displayed superior thermal stability at 190°C compared with general and capacitor grade PP [29].

Polypropylene is one of the most important plastics in our daily life. However, the materials itself also caused a significant amount of plastic pollution. As much exciting progress has been achieved recently to introduce functionalities and improve both mechanical and thermal stabilities, the research community should also emphasize on developing approaches to recycle PP and PE from the processed product.

**Author details**

South China Advanced Institute for Soft Matter Science and Technology,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

South China University of Technology, Guangzhou, P.R. China

*Introductory Chapter: Polypropylene - Synthesis and Functionalization*

*DOI: http://dx.doi.org/10.5772/intechopen.92067*

\*Address all correspondence to: wwang41@vols.utk.edu

provided the original work is properly cited.

Weiyu Wang

**5**

*Synthesis of BHT-functionalized PP (reprinted with permission from Ref. [28]. Copyright 2015 American Chemical Society).*

*Introductory Chapter: Polypropylene - Synthesis and Functionalization DOI: http://dx.doi.org/10.5772/intechopen.92067*
