**1. Introduction**

124 Polycrystalline Materials – Theoretical and Practical Aspects

http://www.sciencenews.org/view/generic/id/57618/title/Building\_a\_cheaper\_

Witze, A. (2010). Building a cheaper catalyst*. Science News* Web Edition.

catalyst

Isotactic polypropylene (iPP) is one of the most important thermoplastic polymers owing to its low manufacturing cost and versatile properties. Moreover, iPP exhibits a very interesting polymorphic behavior (Awaya, 1988; Busse et al., 2000; Lotz et al., 1996; Vagar, 1992). At least five modifications: monoclinic α form, trigonal β form, orthorhombic γ form, δ and smectic phase have been reported. The α form is the best known and most stable in commercial grades of iPP being found in most melt crystallized specimens, especially those being added α Nucleating agents (NA) (Labour et al., 1999; Vagar, 1986). The β form is metastable thermodynamically and is obtained under some special conditions such as a high degree of supercooling, temperature gradient, shear-induced crystallization or addition of βnucleating agents (Fillon et al., 1993; Ismail & Al-Raheil, 1998). The γ form occurs in lowmolecular-weight iPP or under high pressure and the mesomorphic form results from quenching (Meille et al., 1990; Lotz et al., 1986). Different crystalline form of iPP leads different properties like optical and mechanical properties.

NA as one of the additives presents a role of increasing the nucleation density of polymer greatly and enhancing the nucleation rate dramatically so as to have a great impact on the mechanical properties of polymer (Kristiansen et al., 2003; Romankiewicz et al., 2004; Tenma & Yamaguchi, 2007). So far, two kinds of NAs, α phase and β phase NAs discriminated by the form of iPP they induce have been widely put into use in modifying iPP. The α phase NA can improve the stiffness and optical properties of iPP while decrease its toughness (Gui et al., 2003; Zhang G.P. et al., 2003; Zhang Y.F. & Xin, 2006). The β phase NA will induce βiPP during crystallization, which can improve toughness and heat distortion temperature of iPP while decrease its stiffness (Tordjeman et al., 2001; Zhao et al., 2008). Thereby, it is well expected to balance the iPP's stiffness and toughness. Xin's research group firstly proposed the idea of compounding α/β NAs. However, whether compounding α, β NAs will enhance stiffness and toughness simultaneously or not and what influence will α/β compounded NAs take on the crystallization kinetics, crystallization morphologies, and mechanical proprieties of iPP call our eye.

Controlled Crystallization of Isotactic Polypropylene

Phosphate/Amide

Sorbitol/Amide

Wang, 2009; Zhang & Xin, 2007)

compounded NA, 3988/DCHT (Zhao & Xin, 2010).

was in accordance with the other two α/β compounded NAs.

iPP

NA40/NABW

iPP

DMDBS/TMB-5

Table 1. Isothermal crystallization kinetics parameters of pure iPP and nucleated iPP (Bai &

Based on α/βCompounded Nucleating Agents: From Theory to Practice 127

the study on the non-isothermal crystallization kinetics of iPP nucleated by Sorbitol/Amide

Except for Amide NA, Carboxylate NA is proved to be another highly effective β NA for iPP. Xu gave us the picture of non-isothermal crystallization kinetics of iPP nucleated by Phosphate/Carboxylate compounded NA, NA40/H-Ba (Xu, 2010). From the point view of crystallization temperature, the addition of NA40/H-Ba enhanced the crystallization rate of iPP. Judging from the Avrami exponent, the spherulite of iPP grew in the way of threedimensional during non-isothermal crystallization with the presence of NA40/H-Ba, which

Compounded NAs TC/℃ t1/2/s n *n*

123 42 2.70

125 66 2.58 127 108 2.84 129 197 3.10 131 428 3.04

133 24 2.76

135 47 2.61 137 78 2.77 149 141 2.99 141 252 2.72

124 180 2.44

126 306 2.43 128 516 2.6 130 840 2.63 132 1356 2.58

134 30 2.65

136 54 2.90 138 102 3.00 140 204 3.30 2.85

2.77

2.54

2.96

In this work, three kinds of well studied α/β compounded NAs, Phosphate/Amide, Sorbitol/Amide, and Phosphate/Carboxylate were selected to review. This short review aims to present some conclusions of α/β compounded NAs and to lay the foundation for compounding α and β NAs afterwards.
