Transparent random copolymers

Transparent random copolymer PP types and nucleated transparent PP are gaiifeg increasing importance in various application areas. For the coloration of such PP types, highly transparent pigment grades have been developed, which maintain the transparency of the pol)mier and provide all advantages of pigments in the coloration. 

This daia indicates that the random copolymer has greater transparency but inferior low temperature impact strength. 

Metallocene catalysts produce random copolymers [29-31] with different property profiles (Table 14). These data show that random copolymers have higher stiffness and higher transparency at certain melting point levels. A very low content of extractables in low-melting... 

The most widely used rigid copolymer of styrene is the random copolymer of styrene (70%)-acrylonitrile (30%) (SAN), which has randomly placed repeating units. This transparent copolymer is more ductile and has a higher... 

Random copolymers of styrene and butadiene with high proportions of styrene are amorphous and transparent. These copolymers contain the following repeating units ... 

Addition of DPP to growing MPP at 60° C produced still another type of copolymer. Solvent-cast films of this material are transparent. The copolymer does not crystallize on heating, forms stable solutions in m-xylene, and has a single glass transition, at 190°C. The thermal behavior is similar to that of a random copolymer, but the NMR spectrum (Figure 7) is more nearly that expected of a block copolymer. The methyl proton peak is rather sharp with the chemical shift expected for... 

The large availability of nucleating agents based on sorbitol enables the fabrication of clear PP products, with transparencies between 89 (homopolymer) and 96% (metallocen random copolymers). 

Over 40 % of the PP produced in Europe is used to make films. Random copolymers with ethylene are superior with regard to toughness, transparency, shrink characteristics and sealability. These films exhibit low stiffness, strength and hardness. The thickness of these films lies between 12 and 125 pm. 

Uniform random copolymers generally display a single-phase morphology. The ordered sequence distribution (see Figure 1) is too short to induce microphase separation in amorphous systems. For example, a transparent impact polystyrene is obtainable by the order sequence distribution of butadiene between styrene segments (9). 

The phenomenon appears to be similar to the so-called miscibility window in some blends with random copolymers [ten Brinke et al., 1983]. Microphase separation and the evolution of the multiblock copolymer phase in the form of smallsized particles (up to 100 nm in diameter) is the physical basis of their transparency. Thus, these transparent blends are considered micro-heterogeneous systems [Papkov et al., 1998]. Detailed theoretical and experimental investigations are required to understand details of this phenomenon [Sikora and Karasz, 1993]. 

Partially aromatic, melt processable, polyamides are produced as random copolymers, which do not crystallize and are therefore transparent, but are still capable of high-temperature use because of their high Tg values. Several commercial polymers of this type that have glass-like clarity, high softening point, and oil and solvent resistance have been developed. For example, Trogamid T (Dynamit Nobel) contains repeat units of... 

As shown in Scheme 2.27, POEVE and PNIPAM have similar structures with both hydrophilic and hydrophobic parts in each monomer unit. Quite recently, our group examined another possibility for thermosensitive phase separation random copolymers of hydrophilic and hydrophobic monomers.Although random copolymers have been investigated previously, the achieved phase separation was broad, with hysteresis and low turbidity. By living cationic polymerization in the presence of added bases, our group successfully prepared random copolymers of IBVE and HOVE, both of which are typical hydrophobic and hydrophilic monomers, and which are not thermosensitive themselves. At low temperature, the polymers were soluble in water, but when the temperature was increased to a critical point, the transparent solution became opaque. The phase separation was quite sensitive (Scheme 2.27(a)) and the temperature of phase separation was governed by the monomer feed ratio. 

On the other hand, the clear/transparent samples show a single glass transition temperature, but because they are block copolymers, their values are different from those of the respective random copolymers [40]. 

Polyolefin blends comprised 25-95 wt% of a crystalline random copolymer, EPRl (of propylene with ethylene and/or an alpha-olefin), and 5-75 wt% of a mixture consisting of PE and EPR2. The density of EPRl was about equal that of the mixture. The blends had good transparency and impact resistance even at low temperatures and were used to manufacture food containers, medical, packaging films, etc. 

Random copolymer resins are produced by mixing the polypropylene monomer at the first stages of polymerization with ethylene or with another comonomer such as butene. With the low level incorporation of comonomer, the resulting resin exhibits somewhat lower stiffness, a lower melting point, and reduced hardness compared with the PP homopolymer. However, it features better transparency, lower blush resistance, and slightly improved impact resistance at 0°C. 

Applications for PP inside refrigeration equipment are as yet limited. High-impact copolymers have made some inroads, but an interesting development is the use of high-clarity random copolymers. Boxes and trays require a degree of transparency and new PP random copolymers offer an alternative to the appliance producer. 

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